Dear Loops Friends,
If you are interested, the attached paper shows that coronal loops cannot be explained by thermal nonequilibrium. The results appear to rule out the widespread existence of coronal heating that is both highly concentrated low in the corona and steady or quasi-steady (slowly varying or impulsive with a rapid cadence). Comments are welcomed.
Best wishes, Jim
******************************************************************************** James A. Klimchuk NASA Goddard Space Flight Center Solar Physics Lab, Code 671 Bldg. 21, Rm. 158 Greenbelt, MD 20771 USA
Phone: 1-301-286-9060 Fax: 1-301-286-7194 E-mail: James.A.Klimchuk@nasa.govmailto:James.A.Klimchuk@nasa.gov Home page: http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html
********************************************************************************
Jim,
Amy and I addressed the issues of excess density, flat temperature profiles and large scale height about 10 years ago. Having flows of 30-40 km/sec, as is observed in TRACE and now verified by EIS, solves these problems quite nicely. So there is a viable mechanism other than nanoflares.
Leon
Klimchuk, James A. (GSFC-6710) wrote:
Dear Loops Friends,
If you are interested, the attached paper shows that coronal loops
cannot be explained by thermal nonequilibrium. The results appear to rule out the widespread existence of coronal heating that is both highly concentrated low in the corona and steady or quasi-steady (slowly varying or impulsive with a rapid cadence). Comments are welcomed.
Best wishes,
Jim
James A. Klimchuk
NASA Goddard Space Flight Center
Solar Physics Lab, Code 671
Bldg. 21, Rm. 158
Greenbelt, MD 20771
USA
Phone: 1-301-286-9060
Fax: 1-301-286-7194
E-mail: James.A.Klimchuk@nasa.gov mailto:James.A.Klimchuk@nasa.gov
Home page: http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Leon,
As I recall, your paper with Amy relied on footpoint heating, which does lead to higher apex densities and flatter temperature ratios. The observed densities near 1 MK are so high, however, that the loops become thermodynamically unstable. Also, the high speed EIS flows are typically seen in faint regions and are not associated with the types of loops that Jim is attempting to model.
Harry
On 12/5/09 3:16 PM, "Leon Golub" golub@cfa.harvard.edu wrote:
Jim,
Amy and I addressed the issues of excess density, flat temperature profiles and large scale height about 10 years ago. Having flows of 30-40 km/sec, as is observed in TRACE and now verified by EIS, solves these problems quite nicely. So there is a viable mechanism other than nanoflares.
Leon
Klimchuk, James A. (GSFC-6710) wrote:
Dear Loops Friends,
If you are interested, the attached paper shows that coronal loops
cannot be explained by thermal nonequilibrium. The results appear to rule out the widespread existence of coronal heating that is both highly concentrated low in the corona and steady or quasi-steady (slowly varying or impulsive with a rapid cadence). Comments are welcomed.
Best wishes,
Jim
James A. Klimchuk
NASA Goddard Space Flight Center
Solar Physics Lab, Code 671
Bldg. 21, Rm. 158
Greenbelt, MD 20771
USA
Phone: 1-301-286-9060
Fax: 1-301-286-7194
E-mail: James.A.Klimchuk@nasa.gov mailto:James.A.Klimchuk@nasa.gov
Home page: http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Harry,
The work relied on asymmetric heating which gave rise the flow. The heating input was a generic exponential, adjust to fit the observed intensity in one TRACE channel and the result then also reproduced the other channel without further adjustment.
Leon Sent from my Verizon Wireless BlackBerry
-----Original Message----- From: Harry Warren harry.warren@nrl.navy.mil Date: Mon, 07 Dec 2009 08:19:04 To: A mailing list for scientists involved in the observation and modeling ofsolar loop structuresloops@mithra.physics.montana.edu Subject: Re: [Loops] loops and thermal nonequilibrium
Leon,
As I recall, your paper with Amy relied on footpoint heating, which does lead to higher apex densities and flatter temperature ratios. The observed densities near 1 MK are so high, however, that the loops become thermodynamically unstable. Also, the high speed EIS flows are typically seen in faint regions and are not associated with the types of loops that Jim is attempting to model.
Harry
On 12/5/09 3:16 PM, "Leon Golub" golub@cfa.harvard.edu wrote:
Jim,
Amy and I addressed the issues of excess density, flat temperature profiles and large scale height about 10 years ago. Having flows of 30-40 km/sec, as is observed in TRACE and now verified by EIS, solves these problems quite nicely. So there is a viable mechanism other than nanoflares.
Leon
Klimchuk, James A. (GSFC-6710) wrote:
Dear Loops Friends,
If you are interested, the attached paper shows that coronal loops
cannot be explained by thermal nonequilibrium. The results appear to rule out the widespread existence of coronal heating that is both highly concentrated low in the corona and steady or quasi-steady (slowly varying or impulsive with a rapid cadence). Comments are welcomed.
Best wishes,
Jim
James A. Klimchuk
NASA Goddard Space Flight Center
Solar Physics Lab, Code 671
Bldg. 21, Rm. 158
Greenbelt, MD 20771
USA
Phone: 1-301-286-9060
Fax: 1-301-286-7194
E-mail: James.A.Klimchuk@nasa.gov mailto:James.A.Klimchuk@nasa.gov
Home page: http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Wow, I'm surprised, and pleased, at the interest this paper has generated! Let me first respond to Leon's comment. As Harry said (thanks!), in order to get the extreme excess densities that are observed in most warm loops, the footpoint heating needs to be so concentrated that no equilibrium exists (which strictly speaking is different from an instability). Hence, thermal nonequilibrium. A few years back, Spiros P. and I addressed your suggestion with Amy that asymmetric heating and steady flows might explain the observations. Our modeling showed that the density enhancement was adequate to explain some loops, but the scale height is too small and the filter-ratio temperature profile is far too structured (paper attached). We thus rejected this explanation. Sorry!
Thanks for your comment, Jim
-----Original Message----- From: loops-bounces@solar.physics.montana.edu [mailto:loops- bounces@solar.physics.montana.edu] On Behalf Of Harry Warren Sent: Sunday, December 06, 2009 6:19 PM To: A mailing list for scientists involved in the observation and modeling of solar loop structures Subject: Re: [Loops] loops and thermal nonequilibrium
Leon,
As I recall, your paper with Amy relied on footpoint heating, which does lead to higher apex densities and flatter temperature ratios. The observed densities near 1 MK are so high, however, that the loops become thermodynamically unstable. Also, the high speed EIS flows are typically seen in faint regions and are not associated with the types of loops that Jim is attempting to model.
Harry
On 12/5/09 3:16 PM, "Leon Golub" golub@cfa.harvard.edu wrote:
Jim,
Amy and I addressed the issues of excess density, flat temperature profiles and large scale height about 10 years ago. Having flows of 30-40 km/sec, as is observed in TRACE and now verified by EIS, solves these problems quite nicely. So there is a viable mechanism other than nanoflares.
Leon
Klimchuk, James A. (GSFC-6710) wrote:
Dear Loops Friends,
If you are interested, the attached paper shows that coronal loops
cannot be explained by thermal nonequilibrium. The results appear to rule out the widespread existence of coronal heating that is both highly concentrated low in the corona and steady or quasi-steady (slowly varying or impulsive with a rapid cadence). Comments are welcomed.
Best wishes,
Jim
James A. Klimchuk
NASA Goddard Space Flight Center
Solar Physics Lab, Code 671
Bldg. 21, Rm. 158
Greenbelt, MD 20771
USA
Phone: 1-301-286-9060
Fax: 1-301-286-7194
E-mail: James.A.Klimchuk@nasa.gov
mailto:James.A.Klimchuk@nasa.gov
Home page: http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
-- // --------------------------------------------------------------------- // Harry P. Warren phone : 202-404-1453 // Naval Research Laboratory fax : 202-404-7997 // Code 7673HW email : hwarren@nrl.navy.mil // Washington, DC 20375 www : http://tcrb.nrl.navy.mil/~hwarren // ---------------------------------------------------------------------
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Jim,
We were indeed modelling the long, relatively faint loops seen in the plage regions surrounding sunspots, which are exactly where EIS is seeing the flows. It's been known for a long time (the Palermo people did such modelling 20 years ago) that flows in coronal loops drop the density ("When you start a flow going, the loop disappears.") or alternatively, if you see the loop it means the density is enhanced. I'm not sure why your modelling failed, but we were able to reproduce the scale height quite well. Having the flow (in either direction) extends the emission scale height quite a bit beyond the hydrostatic value.
As you know, the AIA on SDO will have far more extensive temperature coverage than TRACE does. There is a puzzle right now in that EIS sees the flows at higher temperatures than we saw in TRACE. I think that this topic is going to be a major one in the coming years.
Leon
Klimchuk, James A. (GSFC-6710) wrote:
Wow, I'm surprised, and pleased, at the interest this paper has generated! Let me first respond to Leon's comment. As Harry said (thanks!), in order to get the extreme excess densities that are observed in most warm loops, the footpoint heating needs to be so concentrated that no equilibrium exists (which strictly speaking is different from an instability). Hence, thermal nonequilibrium. A few years back, Spiros P. and I addressed your suggestion with Amy that asymmetric heating and steady flows might explain the observations. Our modeling showed that the density enhancement was adequate to explain some loops, but the scale height is too small and the filter-ratio temperature profile is far too structured (paper attached). We thus rejected this explanation. Sorry!
Thanks for your comment, Jim
-----Original Message----- From: loops-bounces@solar.physics.montana.edu [mailto:loops- bounces@solar.physics.montana.edu] On Behalf Of Harry Warren Sent: Sunday, December 06, 2009 6:19 PM To: A mailing list for scientists involved in the observation and modeling of solar loop structures Subject: Re: [Loops] loops and thermal nonequilibrium
Leon,
As I recall, your paper with Amy relied on footpoint heating, which does lead to higher apex densities and flatter temperature ratios. The observed densities near 1 MK are so high, however, that the loops become thermodynamically unstable. Also, the high speed EIS flows are typically seen in faint regions and are not associated with the types of loops that Jim is attempting to model.
Harry
On 12/5/09 3:16 PM, "Leon Golub" golub@cfa.harvard.edu wrote:
Jim,
Amy and I addressed the issues of excess density, flat temperature profiles and large scale height about 10 years ago. Having flows of 30-40 km/sec, as is observed in TRACE and now verified by EIS, solves these problems quite nicely. So there is a viable mechanism other than nanoflares.
Leon
Klimchuk, James A. (GSFC-6710) wrote:
Dear Loops Friends,
If you are interested, the attached paper shows that coronal loops
cannot be explained by thermal nonequilibrium. The results appear to rule out the widespread existence of coronal heating that is both highly concentrated low in the corona and steady or quasi-steady (slowly varying or impulsive with a rapid cadence). Comments are welcomed.
Best wishes,
Jim
James A. Klimchuk
NASA Goddard Space Flight Center
Solar Physics Lab, Code 671
Bldg. 21, Rm. 158
Greenbelt, MD 20771
USA
Phone: 1-301-286-9060
Fax: 1-301-286-7194
E-mail: James.A.Klimchuk@nasa.gov
mailto:James.A.Klimchuk@nasa.gov
Home page: http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
-- // --------------------------------------------------------------------- // Harry P. Warren phone : 202-404-1453 // Naval Research Laboratory fax : 202-404-7997 // Code 7673HW email : hwarren@nrl.navy.mil // Washington, DC 20375 www : http://tcrb.nrl.navy.mil/~hwarren // ---------------------------------------------------------------------
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Dear All,
In a basic model of steady, isothermal hydrodynamic flow (http://adsabs.harvard.edu/abs/2006ApJ...649.1078P), steady flows can only affect hydrostatic scale heights under exceptional conditions. These states have fast flows approaching the sound speed and form a small part of the solution space right next to unphysical regimes with density inversions. If significantly many loops really are of this kind, it would be an interesting problem explaining why. On the other hand, it's clear from rho*V*A why steady flows decrease densities.
Best regards,
Gordon
On Mon, 07 Dec 2009 09:11:07 -0500 Leon Golub golub@head.cfa.harvard.edu wrote:
Jim,
We were indeed modelling the long, relatively faint loops seen in the plage regions surrounding sunspots, which are exactly where EIS is seeing the flows. It's been known for a long time (the Palermo people did such modelling 20 years ago) that flows in coronal loops drop the density ("When you start a flow going, the loop disappears.") or alternatively, if you see the loop it means the density is enhanced. I'm not sure why your modelling failed, but we were able to reproduce the scale height quite well. Having the flow (in either direction) extends the emission scale height quite a bit beyond the hydrostatic value.
As you know, the AIA on SDO will have far more extensive temperature coverage than TRACE does. There is a puzzle right now in that EIS sees the flows at higher temperatures than we saw in TRACE. I think that this topic is going to be a major one in the coming years.
Leon
Klimchuk, James A. (GSFC-6710) wrote:
Wow, I'm surprised, and pleased, at the interest this paper has generated! Let me first respond to Leon's comment. As Harry said (thanks!), in order to get the extreme excess densities that are observed in most warm loops, the footpoint heating needs to be so concentrated that no equilibrium exists (which strictly speaking is different from an instability). Hence, thermal nonequilibrium. A few years back, Spiros P. and I addressed your suggestion with Amy that asymmetric heating and steady flows might explain the observations. Our modeling showed that the density enhancement was adequate to explain some loops, but the scale height is too small and the filter-ratio temperature profile is far too structured (paper attached). We thus rejected this explanation. Sorry!
Thanks for your comment, Jim
-----Original Message----- From: loops-bounces@solar.physics.montana.edu [mailto:loops- bounces@solar.physics.montana.edu] On Behalf Of Harry Warren Sent: Sunday, December 06, 2009 6:19 PM To: A mailing list for scientists involved in the observation and modeling of solar loop structures Subject: Re: [Loops] loops and thermal nonequilibrium
Leon,
As I recall, your paper with Amy relied on footpoint heating, which does lead to higher apex densities and flatter temperature ratios. The observed densities near 1 MK are so high, however, that the loops become thermodynamically unstable. Also, the high speed EIS flows are typically seen in faint regions and are not associated with the types of loops that Jim is attempting to model.
Harry
On 12/5/09 3:16 PM, "Leon Golub" golub@cfa.harvard.edu wrote:
Jim,
Amy and I addressed the issues of excess density, flat temperature profiles and large scale height about 10 years ago. Having flows of 30-40 km/sec, as is observed in TRACE and now verified by EIS, solves these problems quite nicely. So there is a viable mechanism other than nanoflares.
Leon
Klimchuk, James A. (GSFC-6710) wrote:
Dear Loops Friends,
If you are interested, the attached paper shows that
coronal loops cannot be explained by thermal nonequilibrium. The results appear to rule out the widespread existence of coronal heating that is both highly concentrated low in the corona and steady or quasi-steady (slowly varying or impulsive with a rapid cadence). Comments are welcomed.
Best wishes,
Jim
James A. Klimchuk
NASA Goddard Space Flight Center
Solar Physics Lab, Code 671
Bldg. 21, Rm. 158
Greenbelt, MD 20771
USA
Phone: 1-301-286-9060
Fax: 1-301-286-7194
E-mail: James.A.Klimchuk@nasa.gov
mailto:James.A.Klimchuk@nasa.gov
Home page: http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
-- //
// Harry P. Warren phone : 202-404-1453 // Naval Research Laboratory fax : 202-404-7997 // Code 7673HW email : hwarren@nrl.navy.mil // Washington, DC 20375 www : http://tcrb.nrl.navy.mil/~hwarren //
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
-- ______________________________________________________________________________ Leon Golub Smithsonian Astrophysical Observatory 60 Garden Street Cambridge, MA 02138 617 495 7177 FAX 496 7577 lgolub@cfa.harvard.edu ______________________________________________________________________________ _______________________________________________ Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Gordon,
I agree with your comment. In fact, it is fairly easily shown directly from the momentum equation that flows up to the sound speed increase the pressure scale height by at most a factor two, when v~c_s, much less when v<c_s because the flow effect scales as (v/c_s)^2.
A really original solution as to why observed loops can be overdense near their apexes was presented by Craig Deforest in 2007. If the unresolved strands that make up the observed loop increase in cross- section from footpoints to apex an observer would conclude that the loop is overdense and has a scale height much larger than what follows from the loop temperature. In reality there is simply more emitting volume near the apex. Of course one has to explain why strands increase in cross-section, while the loops that they collectively form appear not to, but Craig shows some nice images in his paper that seem to support his suggestion.
There are ways to verify this from observations.
Cheers,
Piet
Gordon Petrie wrote:
Dear All,
In a basic model of steady, isothermal hydrodynamic flow (http://adsabs.harvard.edu/abs/2006ApJ...649.1078P), steady flows can only affect hydrostatic scale heights under exceptional conditions. These states have fast flows approaching the sound speed and form a small part of the solution space right next to unphysical regimes with density inversions. If significantly many loops really are of this kind, it would be an interesting problem explaining why. On the other hand, it's clear from rho*V*A why steady flows decrease densities.
Best regards,
Gordon
On Mon, 07 Dec 2009 09:11:07 -0500 Leon Golub golub@head.cfa.harvard.edu wrote:
Jim,
We were indeed modelling the long, relatively faint loops seen in the plage regions surrounding sunspots, which are exactly where EIS is seeing the flows. It's been known for a long time (the Palermo people did such modelling 20 years ago) that flows in coronal loops drop the density ("When you start a flow going, the loop disappears.") or alternatively, if you see the loop it means the density is enhanced. I'm not sure why your modelling failed, but we were able to reproduce the scale height quite well. Having the flow (in either direction) extends the emission scale height quite a bit beyond the hydrostatic value.
As you know, the AIA on SDO will have far more extensive temperature coverage than TRACE does. There is a puzzle right now in that EIS sees the flows at higher temperatures than we saw in TRACE. I think that this topic is going to be a major one in the coming years.
Leon
Klimchuk, James A. (GSFC-6710) wrote:
Wow, I'm surprised, and pleased, at the interest this paper has generated! Let me first respond to Leon's comment. As Harry said (thanks!), in order to get the extreme excess densities that are observed in most warm loops, the footpoint heating needs to be so concentrated that no equilibrium exists (which strictly speaking is different from an instability). Hence, thermal nonequilibrium. A few years back, Spiros P. and I addressed your suggestion with Amy that asymmetric heating and steady flows might explain the observations. Our modeling showed that the density enhancement was adequate to explain some loops, but the scale height is too small and the filter-ratio temperature profile is far too structured (paper attached). We thus rejected this explanation. Sorry!
Thanks for your comment, Jim
-----Original Message----- From: loops-bounces@solar.physics.montana.edu [mailto:loops- bounces@solar.physics.montana.edu] On Behalf Of Harry Warren Sent: Sunday, December 06, 2009 6:19 PM To: A mailing list for scientists involved in the observation and modeling of solar loop structures Subject: Re: [Loops] loops and thermal nonequilibrium
Leon,
As I recall, your paper with Amy relied on footpoint heating, which does lead to higher apex densities and flatter temperature ratios. The observed densities near 1 MK are so high, however, that the loops become thermodynamically unstable. Also, the high speed EIS flows are typically seen in faint regions and are not associated with the types of loops that Jim is attempting to model.
Harry
On 12/5/09 3:16 PM, "Leon Golub" golub@cfa.harvard.edu wrote:
Jim,
Amy and I addressed the issues of excess density, flat temperature profiles and large scale height about 10 years ago. Having flows of 30-40 km/sec, as is observed in TRACE and now verified by EIS, solves these problems quite nicely. So there is a viable mechanism other than nanoflares.
Leon
Klimchuk, James A. (GSFC-6710) wrote:
Dear Loops Friends,
If you are interested, the attached paper shows that coronal
loops cannot be explained by thermal nonequilibrium. The results appear to rule out the widespread existence of coronal heating that is both highly concentrated low in the corona and steady or quasi-steady (slowly varying or impulsive with a rapid cadence). Comments are welcomed.
Best wishes,
Jim
James A. Klimchuk
NASA Goddard Space Flight Center
Solar Physics Lab, Code 671
Bldg. 21, Rm. 158
Greenbelt, MD 20771
USA
Phone: 1-301-286-9060
Fax: 1-301-286-7194
E-mail: James.A.Klimchuk@nasa.gov
mailto:James.A.Klimchuk@nasa.gov
Home page: http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
-- //
// Harry P. Warren phone : 202-404-1453 // Naval Research Laboratory fax : 202-404-7997 // Code 7673HW email : hwarren@nrl.navy.mil // Washington, DC 20375 www : http://tcrb.nrl.navy.mil/~hwarren //
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
-- ______________________________________________________________________________
Leon Golub Smithsonian Astrophysical Observatory 60 Garden Street Cambridge, MA 02138 617 495 7177 FAX 496 7577 lgolub@cfa.harvard.edu ______________________________________________________________________________
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Hi Piet,
Craig's nifty idea is a possible explanation for the larger-than-hydrostatic scale heights (although as you say, how can the unresolved strands expand faster than the loop), but unfortunately it does NOT explain the excess densities. In fact, it makes the problem worse! We find that warm loops are over dense when we use a filling factor of unity to get the density from the observed EM and loop diameter: n = sqrt(EM/(df)). Taking f<1 makes the loops even more over-dense.
Jim
-----Original Message----- From: loops-bounces@solar.physics.montana.edu [mailto:loops- bounces@solar.physics.montana.edu] On Behalf Of Petrus Martens Sent: Monday, December 07, 2009 12:11 PM To: A mailing list for scientists involved in the observation and modeling of solar loop structures Subject: Re: [Loops] loops and thermal nonequilibrium
Gordon,
I agree with your comment. In fact, it is fairly easily shown
directly from the momentum equation that flows up to the sound speed increase the pressure scale height by at most a factor two, when v~c_s, much less when v<c_s because the flow effect scales as (v/c_s)^2.
A really original solution as to why observed loops can be overdense
near their apexes was presented by Craig Deforest in 2007. If the unresolved strands that make up the observed loop increase in cross- section from footpoints to apex an observer would conclude that the loop is overdense and has a scale height much larger than what follows from the loop temperature. In reality there is simply more emitting volume near the apex. Of course one has to explain why strands increase in cross-section, while the loops that they collectively form appear not to, but Craig shows some nice images in his paper that seem to support his suggestion.
There are ways to verify this from observations. Cheers, Piet
Gordon Petrie wrote:
Dear All,
In a basic model of steady, isothermal hydrodynamic flow (http://adsabs.harvard.edu/abs/2006ApJ...649.1078P), steady flows can only affect hydrostatic scale heights under exceptional conditions. These states have fast flows approaching the sound speed and form a small part of the solution space right next to unphysical regimes with density inversions. If significantly many loops really are of this kind, it would be an interesting problem explaining why. On the other hand, it's clear from rho*V*A why steady flows decrease densities.
Best regards,
Gordon
On Mon, 07 Dec 2009 09:11:07 -0500 Leon Golub golub@head.cfa.harvard.edu wrote:
Jim,
We were indeed modelling the long, relatively faint loops seen in the plage regions surrounding sunspots, which are exactly where EIS is seeing the flows. It's been known for a long time (the Palermo people did such modelling 20 years ago) that flows in coronal loops drop the density ("When you start a flow going, the loop disappears.") or alternatively, if you see the loop it means the density is enhanced. I'm not sure why your modelling failed, but we were able to reproduce the scale height quite well. Having the flow (in either direction) extends the emission scale height quite a bit beyond the hydrostatic value.
As you know, the AIA on SDO will have far more extensive temperature coverage than TRACE does. There is a puzzle right now in that EIS sees the flows at higher temperatures than we saw in TRACE. I think that this topic is going to be a major one in the coming years.
Leon
Klimchuk, James A. (GSFC-6710) wrote:
Wow, I'm surprised, and pleased, at the interest this paper has generated! Let me first respond to Leon's comment. As Harry said (thanks!), in order to get the extreme excess densities that are observed in most warm loops, the footpoint heating needs to be so concentrated that no equilibrium exists (which strictly speaking is different from an instability). Hence, thermal nonequilibrium. A few years back, Spiros P. and I addressed your suggestion with Amy that asymmetric heating and steady flows might explain the observations. Our modeling showed that the density enhancement was adequate to explain some loops, but the scale height is too small and the filter-ratio temperature profile is far too structured (paper attached). We thus rejected this explanation. Sorry!
Thanks for your comment, Jim
-----Original Message----- From: loops-bounces@solar.physics.montana.edu [mailto:loops- bounces@solar.physics.montana.edu] On Behalf Of Harry Warren Sent: Sunday, December 06, 2009 6:19 PM To: A mailing list for scientists involved in the observation and modeling of solar loop structures Subject: Re: [Loops] loops and thermal nonequilibrium
Leon,
As I recall, your paper with Amy relied on footpoint heating, which does lead to higher apex densities and flatter temperature ratios. The observed densities near 1 MK are so high, however, that the loops become thermodynamically unstable. Also, the high speed EIS flows are typically seen in faint regions and are not associated with the types of loops that Jim is attempting to model.
Harry
On 12/5/09 3:16 PM, "Leon Golub" golub@cfa.harvard.edu wrote:
Jim,
Amy and I addressed the issues of excess density, flat temperature profiles and large scale height about 10 years ago. Having flows of 30-40 km/sec, as is observed in TRACE and now verified by EIS, solves these problems quite nicely. So there is a viable mechanism other than nanoflares.
Leon
Klimchuk, James A. (GSFC-6710) wrote: > Dear Loops Friends, > > > > If you are interested, the attached paper shows that coronal > loops > cannot be explained by thermal nonequilibrium. The results appear
to
> rule out the widespread existence of coronal heating that is both > highly > concentrated low in the corona and steady or quasi-steady (slowly > varying or impulsive with a rapid cadence). Comments are
welcomed.
> > > > Best wishes, > > Jim > > > >
> *** > > James A. Klimchuk > > NASA Goddard Space Flight Center > > Solar Physics Lab, Code 671 > > Bldg. 21, Rm. 158 > > Greenbelt, MD 20771 > > USA > > > > Phone: 1-301-286-9060 > > Fax: 1-301-286-7194 > > E-mail: James.A.Klimchuk@nasa.gov
mailto:James.A.Klimchuk@nasa.gov
> Home page:
http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html
> > > >
> *** > > > > > ------------------------------------------------------------------------ > > > _______________________________________________ > Loops mailing list > Loops@solar.physics.montana.edu > https://mithra.physics.montana.edu/mailman/listinfo/loops _______________________________________________ Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
-- //
// Harry P. Warren phone : 202-404-1453 // Naval Research Laboratory fax : 202-404-7997 // Code 7673HW email : hwarren@nrl.navy.mil // Washington, DC 20375 www : http://tcrb.nrl.navy.mil/~hwarren //
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--
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--
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Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Jim,
You're right of course for f=1. I better start catching up with my reading... Quick question beforehand: overdense with respect to what? The scaling law for uniform heating? Or simulations? And overdense by what factor?
Cheers,
Piet
Klimchuk, James A. (GSFC-6710) wrote:
Hi Piet,
Craig's nifty idea is a possible explanation for the larger-than-hydrostatic scale heights (although as you say, how can the unresolved strands expand faster than the loop), but unfortunately it does NOT explain the excess densities. In fact, it makes the problem worse! We find that warm loops are over dense when we use a filling factor of unity to get the density from the observed EM and loop diameter: n = sqrt(EM/(df)). Taking f<1 makes the loops even more over-dense.
Jim
-----Original Message----- From: loops-bounces@solar.physics.montana.edu [mailto:loops- bounces@solar.physics.montana.edu] On Behalf Of Petrus Martens Sent: Monday, December 07, 2009 12:11 PM To: A mailing list for scientists involved in the observation and modeling of solar loop structures Subject: Re: [Loops] loops and thermal nonequilibrium
Gordon,
I agree with your comment. In fact, it is fairly easily shown
directly from the momentum equation that flows up to the sound speed increase the pressure scale height by at most a factor two, when v~c_s, much less when v<c_s because the flow effect scales as (v/c_s)^2.
A really original solution as to why observed loops can be overdense
near their apexes was presented by Craig Deforest in 2007. If the unresolved strands that make up the observed loop increase in cross- section from footpoints to apex an observer would conclude that the loop is overdense and has a scale height much larger than what follows from the loop temperature. In reality there is simply more emitting volume near the apex. Of course one has to explain why strands increase in cross-section, while the loops that they collectively form appear not to, but Craig shows some nice images in his paper that seem to support his suggestion.
There are ways to verify this from observations. Cheers, Piet
Gordon Petrie wrote:
Dear All,
In a basic model of steady, isothermal hydrodynamic flow (http://adsabs.harvard.edu/abs/2006ApJ...649.1078P), steady flows can only affect hydrostatic scale heights under exceptional conditions. These states have fast flows approaching the sound speed and form a small part of the solution space right next to unphysical regimes with density inversions. If significantly many loops really are of this kind, it would be an interesting problem explaining why. On the other hand, it's clear from rho*V*A why steady flows decrease densities.
Best regards,
Gordon
On Mon, 07 Dec 2009 09:11:07 -0500 Leon Golub golub@head.cfa.harvard.edu wrote:
Jim,
We were indeed modelling the long, relatively faint loops seen in the plage regions surrounding sunspots, which are exactly where EIS is seeing the flows. It's been known for a long time (the Palermo people did such modelling 20 years ago) that flows in coronal loops drop the density ("When you start a flow going, the loop disappears.") or alternatively, if you see the loop it means the density is enhanced. I'm not sure why your modelling failed, but we were able to reproduce the scale height quite well. Having the flow (in either direction) extends the emission scale height quite a bit beyond the hydrostatic value.
As you know, the AIA on SDO will have far more extensive temperature coverage than TRACE does. There is a puzzle right now in that EIS sees the flows at higher temperatures than we saw in TRACE. I think that this topic is going to be a major one in the coming years.
Leon
Klimchuk, James A. (GSFC-6710) wrote:
Wow, I'm surprised, and pleased, at the interest this paper has generated! Let me first respond to Leon's comment. As Harry said (thanks!), in order to get the extreme excess densities that are observed in most warm loops, the footpoint heating needs to be so concentrated that no equilibrium exists (which strictly speaking is different from an instability). Hence, thermal nonequilibrium. A few years back, Spiros P. and I addressed your suggestion with Amy that asymmetric heating and steady flows might explain the observations. Our modeling showed that the density enhancement was adequate to explain some loops, but the scale height is too small and the filter-ratio temperature profile is far too structured (paper attached). We thus rejected this explanation. Sorry!
Thanks for your comment, Jim
-----Original Message----- From: loops-bounces@solar.physics.montana.edu [mailto:loops- bounces@solar.physics.montana.edu] On Behalf Of Harry Warren Sent: Sunday, December 06, 2009 6:19 PM To: A mailing list for scientists involved in the observation and modeling of solar loop structures Subject: Re: [Loops] loops and thermal nonequilibrium
Leon,
As I recall, your paper with Amy relied on footpoint heating, which does lead to higher apex densities and flatter temperature ratios. The observed densities near 1 MK are so high, however, that the loops become thermodynamically unstable. Also, the high speed EIS flows are typically seen in faint regions and are not associated with the types of loops that Jim is attempting to model.
Harry
On 12/5/09 3:16 PM, "Leon Golub" golub@cfa.harvard.edu wrote:
> Jim, > > Amy and I addressed the issues of excess density, flat temperature > profiles and large scale height about 10 years ago. Having flows of > 30-40 km/sec, as is observed in TRACE and now verified by EIS, solves > these problems quite nicely. So there is a viable mechanism other than > nanoflares. > > Leon > > > Klimchuk, James A. (GSFC-6710) wrote: >> Dear Loops Friends, >> >> >> >> If you are interested, the attached paper shows that coronal >> loops >> cannot be explained by thermal nonequilibrium. The results appear
to
>> rule out the widespread existence of coronal heating that is both >> highly >> concentrated low in the corona and steady or quasi-steady (slowly >> varying or impulsive with a rapid cadence). Comments are
welcomed.
>> >> >> Best wishes, >> >> Jim >> >> >> >>
>> *** >> >> James A. Klimchuk >> >> NASA Goddard Space Flight Center >> >> Solar Physics Lab, Code 671 >> >> Bldg. 21, Rm. 158 >> >> Greenbelt, MD 20771 >> >> USA >> >> >> >> Phone: 1-301-286-9060 >> >> Fax: 1-301-286-7194 >> >> E-mail: James.A.Klimchuk@nasa.gov mailto:James.A.Klimchuk@nasa.gov >> Home page:
http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html
>> >> >>
>> *** >> >> >> >> >> ------------------------------------------------------------------------ >> >> >> _______________________________________________ >> Loops mailing list >> Loops@solar.physics.montana.edu >> https://mithra.physics.montana.edu/mailman/listinfo/loops > _______________________________________________ > Loops mailing list > Loops@solar.physics.montana.edu
> https://mithra.physics.montana.edu/mailman/listinfo/loops
//
// Harry P. Warren phone : 202-404-1453 // Naval Research Laboratory fax : 202-404-7997 // Code 7673HW email : hwarren@nrl.navy.mil // Washington, DC 20375 www : http://tcrb.nrl.navy.mil/~hwarren //
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--
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--
Piet Martens Tel: 617-496-7769 Center for Astrophysics Fax: 617-496-7577 60 Garden Street, MS 58 Cell: 617-999-0353 Cambridge, MA 02138 pmartens@cfa.harvard.edu
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Piet, Jim,
Jim is of course right that unresolved structure makes the excess density problem worse, though at this point I've lost track of just how bad it really is.
In fact, in that 2007 paper I cited some of the discrepancies between density-sensitive line pair spectral measurements of density, and corresponding EUV measurements using relative photometry - the discrepancies seem to go in the right direction (i.e. that spectral diagnostics yield higher densities than one would expect from simple EUV photometry).
The whole point of the geometric argument I was making then is that large bundles of active region threads expand much more rapidly than the threads themselves, in current EUV images. Assuming that the image threads come from structures that expand at the same rate as the bundle neatly solves the hydrostatic scale height problem. It is not necessary to assume that loop strands are expanding faster than the body of the loop.
Jim and Marcello published a very nice analysis indicating that (at least) they're not being stupid, but IMHO there are still too many uncertainties in instrument performance to know whether loop strands are indeed unresolved and expanding rapidly. I haven't followed up in the literature, because I think higher resolution (maybe from Hi-C) is required to nail down that argument on one side or the other. (I won't expand this note still further by elaborating).
Best, Craig
On Dec 7, 2009, at 11:22 AM, Klimchuk, James A. (GSFC-6710) wrote:
Hi Piet,
Craig's nifty idea is a possible explanation for the larger-than- hydrostatic scale heights (although as you say, how can the unresolved strands expand faster than the loop), but unfortunately it does NOT explain the excess densities. In fact, it makes the problem worse! We find that warm loops are over dense when we use a filling factor of unity to get the density from the observed EM and loop diameter: n = sqrt(EM/(df)). Taking f<1 makes the loops even more over-dense.
Jim
-----Original Message----- From: loops-bounces@solar.physics.montana.edu [mailto:loops- bounces@solar.physics.montana.edu] On Behalf Of Petrus Martens Sent: Monday, December 07, 2009 12:11 PM To: A mailing list for scientists involved in the observation and modeling of solar loop structures Subject: Re: [Loops] loops and thermal nonequilibrium
Gordon,
I agree with your comment. In fact, it is fairly easily shown directly from the momentum equation that flows up to the sound speed increase the pressure scale height by at most a factor two, when v~c_s, much less when v<c_s because the flow effect scales as (v/c_s)^2.
A really original solution as to why observed loops can be overdense near their apexes was presented by Craig Deforest in 2007. If the unresolved strands that make up the observed loop increase in cross- section from footpoints to apex an observer would conclude that the loop is overdense and has a scale height much larger than what follows from the loop temperature. In reality there is simply more emitting volume near the apex. Of course one has to explain why strands increase in cross-section, while the loops that they collectively form appear not to, but Craig shows some nice images in his paper that seem to support his suggestion.
There are ways to verify this from observations.
Cheers,
Piet
Gordon Petrie wrote:
Dear All,
In a basic model of steady, isothermal hydrodynamic flow (http://adsabs.harvard.edu/abs/2006ApJ...649.1078P), steady flows can only affect hydrostatic scale heights under exceptional conditions. These states have fast flows approaching the sound speed and form a small part of the solution space right next to unphysical regimes with density inversions. If significantly many loops really are of this kind, it would be an interesting problem explaining why. On the other hand, it's clear from rho*V*A why steady flows decrease densities.
Best regards,
Gordon
On Mon, 07 Dec 2009 09:11:07 -0500 Leon Golub golub@head.cfa.harvard.edu wrote:
Jim,
We were indeed modelling the long, relatively faint loops seen in the plage regions surrounding sunspots, which are exactly where EIS is seeing the flows. It's been known for a long time (the Palermo people did such modelling 20 years ago) that flows in coronal loops drop the density ("When you start a flow going, the loop disappears.") or alternatively, if you see the loop it means the density is enhanced. I'm not sure why your modelling failed, but we were able to reproduce the scale height quite well. Having the flow (in either direction) extends the emission scale height quite a bit beyond the hydrostatic value.
As you know, the AIA on SDO will have far more extensive temperature coverage than TRACE does. There is a puzzle right now in that EIS sees the flows at higher temperatures than we saw in TRACE. I think that this topic is going to be a major one in the coming years.
Leon
Klimchuk, James A. (GSFC-6710) wrote:
Wow, I'm surprised, and pleased, at the interest this paper has generated! Let me first respond to Leon's comment. As Harry said (thanks!), in order to get the extreme excess densities that are observed in most warm loops, the footpoint heating needs to be so concentrated that no equilibrium exists (which strictly speaking is different from an instability). Hence, thermal nonequilibrium. A few years back, Spiros P. and I addressed your suggestion with Amy that asymmetric heating and steady flows might explain the observations. Our modeling showed that the density enhancement was adequate to explain some loops, but the scale height is too small and the filter-ratio temperature profile is far too structured (paper attached). We thus rejected this explanation. Sorry!
Thanks for your comment, Jim
-----Original Message----- From: loops-bounces@solar.physics.montana.edu [mailto:loops- bounces@solar.physics.montana.edu] On Behalf Of Harry Warren Sent: Sunday, December 06, 2009 6:19 PM To: A mailing list for scientists involved in the observation and modeling of solar loop structures Subject: Re: [Loops] loops and thermal nonequilibrium
Leon,
As I recall, your paper with Amy relied on footpoint heating, which does lead to higher apex densities and flatter temperature ratios. The observed densities near 1 MK are so high, however, that the loops become thermodynamically unstable. Also, the high speed EIS flows are typically seen in faint regions and are not associated with the types of loops that Jim is attempting to model.
Harry
On 12/5/09 3:16 PM, "Leon Golub" golub@cfa.harvard.edu wrote:
> Jim, > > Amy and I addressed the issues of excess density, flat > temperature > profiles and large scale height about 10 years ago. Having > flows of > 30-40 km/sec, as is observed in TRACE and now verified by EIS, > solves > these problems quite nicely. So there is a viable mechanism > other than > nanoflares. > > Leon > > > Klimchuk, James A. (GSFC-6710) wrote: >> Dear Loops Friends, >> >> >> >> If you are interested, the attached paper shows that coronal >> loops >> cannot be explained by thermal nonequilibrium. The results >> appear
to
>> rule out the widespread existence of coronal heating that is >> both >> highly >> concentrated low in the corona and steady or quasi-steady >> (slowly >> varying or impulsive with a rapid cadence). Comments are
welcomed.
>> >> >> >> Best wishes, >> >> Jim >> >> >> >>
>> *** >> >> James A. Klimchuk >> >> NASA Goddard Space Flight Center >> >> Solar Physics Lab, Code 671 >> >> Bldg. 21, Rm. 158 >> >> Greenbelt, MD 20771 >> >> USA >> >> >> >> Phone: 1-301-286-9060 >> >> Fax: 1-301-286-7194 >> >> E-mail: James.A.Klimchuk@nasa.gov mailto:James.A.Klimchuk@nasa.gov >> Home page:
http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html
>> >> >> >>
>> *** >> >> >> >> >> ------------------------------------------------------------------------ >> >> >> _______________________________________________ >> Loops mailing list >> Loops@solar.physics.montana.edu >> https://mithra.physics.montana.edu/mailman/listinfo/loops > _______________________________________________ > Loops mailing list > Loops@solar.physics.montana.edu
> https://mithra.physics.montana.edu/mailman/listinfo/loops
//
// Harry P. Warren phone : 202-404-1453 // Naval Research Laboratory fax : 202-404-7997 // Code 7673HW email : hwarren@nrl.navy.mil // Washington, DC 20375 www : http://tcrb.nrl.navy.mil/~hwarren //
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--
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--
Piet Martens Tel: 617-496-7769 Center for Astrophysics Fax: 617-496-7577 60 Garden Street, MS 58 Cell: 617-999-0353 Cambridge, MA 02138 pmartens@cfa.harvard.edu
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
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Another geometrical point is that the line-of-sight column density increases at loop top if you look at it out-of-plane at all. And then another geometrical effect is that if it is not a planar loop, then that twist can augment the line-of-sight effect. The twist, incidentally, can be present even in a potential field. The "loop top" and "above-the-loop-top" brightenings observed by SXT need to have these considerations.
Hugh
On 7 Dec 2009, at 10:42, Craig DeForest wrote:
Piet, Jim,
Jim is of course right that unresolved structure makes the excess density problem worse, though at this point I've lost track of just how bad it really is.
In fact, in that 2007 paper I cited some of the discrepancies between density-sensitive line pair spectral measurements of density, and corresponding EUV measurements using relative photometry - the discrepancies seem to go in the right direction (i.e. that spectral diagnostics yield higher densities than one would expect from simple EUV photometry).
The whole point of the geometric argument I was making then is that large bundles of active region threads expand much more rapidly than the threads themselves, in current EUV images. Assuming that the image threads come from structures that expand at the same rate as the bundle neatly solves the hydrostatic scale height problem. It is not necessary to assume that loop strands are expanding faster than the body of the loop.
Jim and Marcello published a very nice analysis indicating that (at least) they're not being stupid, but IMHO there are still too many uncertainties in instrument performance to know whether loop strands are indeed unresolved and expanding rapidly. I haven't followed up in the literature, because I think higher resolution (maybe from Hi- C) is required to nail down that argument on one side or the other. (I won't expand this note still further by elaborating).
Best, Craig
On Dec 7, 2009, at 11:22 AM, Klimchuk, James A. (GSFC-6710) wrote:
Hi Piet,
Craig's nifty idea is a possible explanation for the larger-than- hydrostatic scale heights (although as you say, how can the unresolved strands expand faster than the loop), but unfortunately it does NOT explain the excess densities. In fact, it makes the problem worse! We find that warm loops are over dense when we use a filling factor of unity to get the density from the observed EM and loop diameter: n = sqrt(EM/(df)). Taking f<1 makes the loops even more over-dense.
Jim
-----Original Message----- From: loops-bounces@solar.physics.montana.edu [mailto:loops- bounces@solar.physics.montana.edu] On Behalf Of Petrus Martens Sent: Monday, December 07, 2009 12:11 PM To: A mailing list for scientists involved in the observation and modeling of solar loop structures Subject: Re: [Loops] loops and thermal nonequilibrium
Gordon,
I agree with your comment. In fact, it is fairly easily shown directly from the momentum equation that flows up to the sound speed increase the pressure scale height by at most a factor two, when v~c_s, much less when v<c_s because the flow effect scales as (v/c_s)^2.
A really original solution as to why observed loops can be overdense near their apexes was presented by Craig Deforest in 2007. If the unresolved strands that make up the observed loop increase in cross- section from footpoints to apex an observer would conclude that the loop is overdense and has a scale height much larger than what follows from the loop temperature. In reality there is simply more emitting volume near the apex. Of course one has to explain why strands increase in cross-section, while the loops that they collectively form appear not to, but Craig shows some nice images in his paper that seem to support his suggestion.
There are ways to verify this from observations.
Cheers,
Piet
Gordon Petrie wrote:
Dear All,
In a basic model of steady, isothermal hydrodynamic flow (http://adsabs.harvard.edu/abs/2006ApJ...649.1078P), steady flows can only affect hydrostatic scale heights under exceptional conditions. These states have fast flows approaching the sound speed and form a small part of the solution space right next to unphysical regimes with density inversions. If significantly many loops really are of this kind, it would be an interesting problem explaining why. On the other hand, it's clear from rho*V*A why steady flows decrease densities.
Best regards,
Gordon
On Mon, 07 Dec 2009 09:11:07 -0500 Leon Golub golub@head.cfa.harvard.edu wrote:
Jim,
We were indeed modelling the long, relatively faint loops seen in the plage regions surrounding sunspots, which are exactly where EIS is seeing the flows. It's been known for a long time (the Palermo people did such modelling 20 years ago) that flows in coronal loops drop the density ("When you start a flow going, the loop disappears.") or alternatively, if you see the loop it means the density is enhanced. I'm not sure why your modelling failed, but we were able to reproduce the scale height quite well. Having the flow (in either direction) extends the emission scale height quite a bit beyond the hydrostatic value.
As you know, the AIA on SDO will have far more extensive temperature coverage than TRACE does. There is a puzzle right now in that EIS sees the flows at higher temperatures than we saw in TRACE. I think that this topic is going to be a major one in the coming years.
Leon
Klimchuk, James A. (GSFC-6710) wrote:
Wow, I'm surprised, and pleased, at the interest this paper has generated! Let me first respond to Leon's comment. As Harry said (thanks!), in order to get the extreme excess densities that are observed in most warm loops, the footpoint heating needs to be so concentrated that no equilibrium exists (which strictly speaking is different from an instability). Hence, thermal nonequilibrium. A few years back, Spiros P. and I addressed your suggestion with Amy that asymmetric heating and steady flows might explain the observations. Our modeling showed that the density enhancement was adequate to explain some loops, but the scale height is too small and the filter-ratio temperature profile is far too structured (paper attached). We thus rejected this explanation. Sorry!
Thanks for your comment, Jim
> -----Original Message----- > From: loops-bounces@solar.physics.montana.edu [mailto:loops- > bounces@solar.physics.montana.edu] On Behalf Of Harry Warren > Sent: Sunday, December 06, 2009 6:19 PM > To: A mailing list for scientists involved in the observation > and > modeling of > solar loop structures > Subject: Re: [Loops] loops and thermal nonequilibrium > > > Leon, > > As I recall, your paper with Amy relied on footpoint heating, > which > does > lead to higher apex densities and flatter temperature ratios. > The > observed > densities near 1 MK are so high, however, that the loops become > thermodynamically unstable. Also, the high speed EIS flows are > typically > seen in faint regions and are not associated with the types of > loops > that > Jim is attempting to model. > > Harry > > > On 12/5/09 3:16 PM, "Leon Golub" golub@cfa.harvard.edu wrote: > >> Jim, >> >> Amy and I addressed the issues of excess density, flat >> temperature >> profiles and large scale height about 10 years ago. Having >> flows of >> 30-40 km/sec, as is observed in TRACE and now verified by >> EIS, solves >> these problems quite nicely. So there is a viable mechanism >> other than >> nanoflares. >> >> Leon >> >> >> Klimchuk, James A. (GSFC-6710) wrote: >>> Dear Loops Friends, >>> >>> >>> >>> If you are interested, the attached paper shows that coronal >>> loops >>> cannot be explained by thermal nonequilibrium. The results >>> appear
to
>>> rule out the widespread existence of coronal heating that is >>> both >>> highly >>> concentrated low in the corona and steady or quasi-steady >>> (slowly >>> varying or impulsive with a rapid cadence). Comments are
welcomed.
>>> >>> >>> >>> Best wishes, >>> >>> Jim >>> >>> >>> >>> >
> *************** >>> *** >>> >>> James A. Klimchuk >>> >>> NASA Goddard Space Flight Center >>> >>> Solar Physics Lab, Code 671 >>> >>> Bldg. 21, Rm. 158 >>> >>> Greenbelt, MD 20771 >>> >>> USA >>> >>> >>> >>> Phone: 1-301-286-9060 >>> >>> Fax: 1-301-286-7194 >>> >>> E-mail: James.A.Klimchuk@nasa.gov > mailto:James.A.Klimchuk@nasa.gov >>> Home page:
http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html
>>> >>> >>> >>> >
> *************** >>> *** >>> >>> >>> >>> >>> ------------------------------------------------------------------------ >>> >>> >>> _______________________________________________ >>> Loops mailing list >>> Loops@solar.physics.montana.edu >>> https://mithra.physics.montana.edu/mailman/listinfo/loops >> _______________________________________________ >> Loops mailing list >> Loops@solar.physics.montana.edu >> https://mithra.physics.montana.edu/mailman/listinfo/loops > -- > // > --------------------------------------------------------------------- > // Harry P. Warren phone : 202-404-1453 > // Naval Research Laboratory fax : 202-404-7997 > // Code 7673HW email : hwarren@nrl.navy.mil > // Washington, DC 20375 www : > http://tcrb.nrl.navy.mil/~hwarren > // > --------------------------------------------------------------------- > > > > > > _______________________________________________ > Loops mailing list > Loops@solar.physics.montana.edu > https://mithra.physics.montana.edu/mailman/listinfo/loops _______________________________________________ Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
--
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--
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Dear Piet,
If I understand the steady isothermal theory correctly, the scale height can become unbounded wherever the flow approaches the sonic point, v -> c_s, because of a v^2-c_s^2 factor. Beyond a (generally different) critical point, v=sqrt(g_s Z_0) where g_s is the solar surface gravitational acceleration and Z_0 a length scale of the flux tube spatial expansion, mass conservation demands that the density invert.
Best regards,
Gordon
On Mon, 07 Dec 2009 10:11:07 -0700 Petrus Martens pmartens@cfa.harvard.edu wrote:
Gordon,
I agree with your comment. In fact, it is fairly easily shown directly from the momentum equation that flows up to the sound speed increase the pressure scale height by at most a factor two, when v~c_s, much less when v<c_s because the flow effect scales as (v/c_s)^2.
A really original solution as to why observed loops can be overdense near their apexes was presented by Craig Deforest in 2007. If the unresolved strands that make up the observed loop increase in cross- section from footpoints to apex an observer would conclude that the loop is overdense and has a scale height much larger than what follows from the loop temperature. In reality there is simply more emitting volume near the apex. Of course one has to explain why strands increase in cross-section, while the loops that they collectively form appear not to, but Craig shows some nice images in his paper that seem to support his suggestion.
There are ways to verify this from observations.
Cheers,
Piet
Gordon Petrie wrote:
Dear All,
In a basic model of steady, isothermal hydrodynamic flow (http://adsabs.harvard.edu/abs/2006ApJ...649.1078P), steady flows can only affect hydrostatic scale heights under exceptional conditions. These states have fast flows approaching the sound speed and form a small part of the solution space right next to unphysical regimes with density inversions. If significantly many loops really are of this kind, it would be an interesting problem explaining why. On the other hand, it's clear from rho*V*A why steady flows decrease densities.
Best regards,
Gordon
On Mon, 07 Dec 2009 09:11:07 -0500 Leon Golub golub@head.cfa.harvard.edu wrote:
Jim,
We were indeed modelling the long, relatively faint loops seen in the plage regions surrounding sunspots, which are exactly where EIS is seeing the flows. It's been known for a long time (the Palermo people did such modelling 20 years ago) that flows in coronal loops drop the density ("When you start a flow going, the loop disappears.") or alternatively, if you see the loop it means the density is enhanced. I'm not sure why your modelling failed, but we were able to reproduce the scale height quite well. Having the flow (in either direction) extends the emission scale height quite a bit beyond the hydrostatic value.
As you know, the AIA on SDO will have far more extensive temperature coverage than TRACE does. There is a puzzle right now in that EIS sees the flows at higher temperatures than we saw in TRACE. I think that this topic is going to be a major one in the coming years.
Leon
Klimchuk, James A. (GSFC-6710) wrote:
Wow, I'm surprised, and pleased, at the interest this paper has generated! Let me first respond to Leon's comment. As Harry said (thanks!), in order to get the extreme excess densities that are observed in most warm loops, the footpoint heating needs to be so concentrated that no equilibrium exists (which strictly speaking is different from an instability). Hence, thermal nonequilibrium. A few years back, Spiros P. and I addressed your suggestion with Amy that asymmetric heating and steady flows might explain the observations. Our modeling showed that the density enhancement was adequate to explain some loops, but the scale height is too small and the filter-ratio temperature profile is far too structured (paper attached). We thus rejected this explanation. Sorry!
Thanks for your comment, Jim
-----Original Message----- From: loops-bounces@solar.physics.montana.edu [mailto:loops- bounces@solar.physics.montana.edu] On Behalf Of Harry Warren Sent: Sunday, December 06, 2009 6:19 PM To: A mailing list for scientists involved in the observation and modeling of solar loop structures Subject: Re: [Loops] loops and thermal nonequilibrium
Leon,
As I recall, your paper with Amy relied on footpoint heating, which does lead to higher apex densities and flatter temperature ratios. The observed densities near 1 MK are so high, however, that the loops become thermodynamically unstable. Also, the high speed EIS flows are typically seen in faint regions and are not associated with the types of loops that Jim is attempting to model.
Harry
On 12/5/09 3:16 PM, "Leon Golub" golub@cfa.harvard.edu wrote:
Jim,
Amy and I addressed the issues of excess density, flat temperature profiles and large scale height about 10 years ago. Having flows of 30-40 km/sec, as is observed in TRACE and now verified by EIS, solves these problems quite nicely. So there is a viable mechanism other than nanoflares.
Leon
Klimchuk, James A. (GSFC-6710) wrote: > Dear Loops Friends, > > > > If you are interested, the attached paper shows that >coronal loops > cannot be explained by thermal nonequilibrium. The >results appear to > rule out the widespread existence of coronal heating that >is both highly > concentrated low in the corona and steady or quasi-steady >(slowly > varying or impulsive with a rapid cadence). Comments are >welcomed. > > > > Best wishes, > > Jim > > > >
> *** > > James A. Klimchuk > > NASA Goddard Space Flight Center > > Solar Physics Lab, Code 671 > > Bldg. 21, Rm. 158 > > Greenbelt, MD 20771 > > USA > > > > Phone: 1-301-286-9060 > > Fax: 1-301-286-7194 > > E-mail: James.A.Klimchuk@nasa.gov
mailto:James.A.Klimchuk@nasa.gov
> Home page: >http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html > > > >
> *** > > > > > ------------------------------------------------------------------------ > _______________________________________________ > Loops mailing list > Loops@solar.physics.montana.edu > https://mithra.physics.montana.edu/mailman/listinfo/loops _______________________________________________ Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
-- //
// Harry P. Warren phone : 202-404-1453 // Naval Research Laboratory fax : 202-404-7997 // Code 7673HW email : hwarren@nrl.navy.mil // Washington, DC 20375 www : http://tcrb.nrl.navy.mil/~hwarren //
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-- ______________________________________________________________________________ Leon Golub Smithsonian Astrophysical Observatory 60 Garden Street Cambridge, MA 02138 617 495 7177 FAX 496 7577 lgolub@cfa.harvard.edu ______________________________________________________________________________ _______________________________________________ Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
--
Piet Martens Tel: 617-496-7769 Center for Astrophysics Fax: 617-496-7577 60 Garden Street, MS 58 Cell: 617-999-0353 Cambridge, MA 02138 pmartens@cfa.harvard.edu
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Dear Gordon,
I don't disagree with your comment. My thought experiment was a bit different: take an isothermal flux tube expanding as r^2, and with a steady mass conserving flow. Now compare the density at the sonic point in such a Parker wind with the density at the same point if the flux tube were static (same density at the bottom). What I found is a difference of about a factor two.
Obviously the momentum equation shows you that the mass flux term scales as (v/c_s)^2 compared to the pressure gradient term, which was my other point, and hence you can solve in a series expansion around the static solution if the velocities involved are observed to be subsonic.
Cheers,
Piet
Gordon Petrie wrote:
Dear Piet,
If I understand the steady isothermal theory correctly, the scale height can become unbounded wherever the flow approaches the sonic point, v -> c_s, because of a v^2-c_s^2 factor. Beyond a (generally different) critical point, v=sqrt(g_s Z_0) where g_s is the solar surface gravitational acceleration and Z_0 a length scale of the flux tube spatial expansion, mass conservation demands that the density invert.
Best regards,
Gordon
On Mon, 07 Dec 2009 10:11:07 -0700 Petrus Martens pmartens@cfa.harvard.edu wrote:
Gordon,
I agree with your comment. In fact, it is fairly easily shown directly from the momentum equation that flows up to the sound speed increase the pressure scale height by at most a factor two, when v~c_s, much less when v<c_s because the flow effect scales as (v/c_s)^2.
A really original solution as to why observed loops can be overdense near their apexes was presented by Craig Deforest in 2007. If the unresolved strands that make up the observed loop increase in cross- section from footpoints to apex an observer would conclude that the loop is overdense and has a scale height much larger than what follows from the loop temperature. In reality there is simply more emitting volume near the apex. Of course one has to explain why strands increase in cross-section, while the loops that they collectively form appear not to, but Craig shows some nice images in his paper that seem to support his suggestion.
There are ways to verify this from observations.
Cheers,
Piet
Gordon Petrie wrote:
Dear All,
In a basic model of steady, isothermal hydrodynamic flow (http://adsabs.harvard.edu/abs/2006ApJ...649.1078P), steady flows can only affect hydrostatic scale heights under exceptional conditions. These states have fast flows approaching the sound speed and form a small part of the solution space right next to unphysical regimes with density inversions. If significantly many loops really are of this kind, it would be an interesting problem explaining why. On the other hand, it's clear from rho*V*A why steady flows decrease densities.
Best regards,
Gordon
On Mon, 07 Dec 2009 09:11:07 -0500 Leon Golub golub@head.cfa.harvard.edu wrote:
Jim,
We were indeed modelling the long, relatively faint loops seen in the plage regions surrounding sunspots, which are exactly where EIS is seeing the flows. It's been known for a long time (the Palermo people did such modelling 20 years ago) that flows in coronal loops drop the density ("When you start a flow going, the loop disappears.") or alternatively, if you see the loop it means the density is enhanced. I'm not sure why your modelling failed, but we were able to reproduce the scale height quite well. Having the flow (in either direction) extends the emission scale height quite a bit beyond the hydrostatic value.
As you know, the AIA on SDO will have far more extensive temperature coverage than TRACE does. There is a puzzle right now in that EIS sees the flows at higher temperatures than we saw in TRACE. I think that this topic is going to be a major one in the coming years.
Leon
Klimchuk, James A. (GSFC-6710) wrote:
Wow, I'm surprised, and pleased, at the interest this paper has generated! Let me first respond to Leon's comment. As Harry said (thanks!), in order to get the extreme excess densities that are observed in most warm loops, the footpoint heating needs to be so concentrated that no equilibrium exists (which strictly speaking is different from an instability). Hence, thermal nonequilibrium. A few years back, Spiros P. and I addressed your suggestion with Amy that asymmetric heating and steady flows might explain the observations. Our modeling showed that the density enhancement was adequate to explain some loops, but the scale height is too small and the filter-ratio temperature profile is far too structured (paper attached). We thus rejected this explanation. Sorry!
Thanks for your comment, Jim
-----Original Message----- From: loops-bounces@solar.physics.montana.edu [mailto:loops- bounces@solar.physics.montana.edu] On Behalf Of Harry Warren Sent: Sunday, December 06, 2009 6:19 PM To: A mailing list for scientists involved in the observation and modeling of solar loop structures Subject: Re: [Loops] loops and thermal nonequilibrium
Leon,
As I recall, your paper with Amy relied on footpoint heating, which does lead to higher apex densities and flatter temperature ratios. The observed densities near 1 MK are so high, however, that the loops become thermodynamically unstable. Also, the high speed EIS flows are typically seen in faint regions and are not associated with the types of loops that Jim is attempting to model.
Harry
On 12/5/09 3:16 PM, "Leon Golub" golub@cfa.harvard.edu wrote:
> Jim, > > Amy and I addressed the issues of excess density, flat temperature > profiles and large scale height about 10 years ago. Having flows of > 30-40 km/sec, as is observed in TRACE and now verified by EIS, > solves > these problems quite nicely. So there is a viable mechanism other > than > nanoflares. > > Leon > > > Klimchuk, James A. (GSFC-6710) wrote: >> Dear Loops Friends, >> >> >> >> If you are interested, the attached paper shows that coronal >> loops >> cannot be explained by thermal nonequilibrium. The results >> appear to >> rule out the widespread existence of coronal heating that is >> both highly >> concentrated low in the corona and steady or quasi-steady (slowly >> varying or impulsive with a rapid cadence). Comments are welcomed. >> >> >> >> Best wishes, >> >> Jim >> >> >> >>
>> *** >> >> James A. Klimchuk >> >> NASA Goddard Space Flight Center >> >> Solar Physics Lab, Code 671 >> >> Bldg. 21, Rm. 158 >> >> Greenbelt, MD 20771 >> >> USA >> >> >> >> Phone: 1-301-286-9060 >> >> Fax: 1-301-286-7194 >> >> E-mail: James.A.Klimchuk@nasa.gov mailto:James.A.Klimchuk@nasa.gov >> Home page: >> http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html >> >> >> >>
>> *** >> >> >> >> >> ------------------------------------------------------------------------ >> _______________________________________________ >> Loops mailing list >> Loops@solar.physics.montana.edu >> https://mithra.physics.montana.edu/mailman/listinfo/loops > _______________________________________________ > Loops mailing list > Loops@solar.physics.montana.edu
> https://mithra.physics.montana.edu/mailman/listinfo/loops
//
// Harry P. Warren phone : 202-404-1453 // Naval Research Laboratory fax : 202-404-7997 // Code 7673HW email : hwarren@nrl.navy.mil // Washington, DC 20375 www : http://tcrb.nrl.navy.mil/~hwarren //
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-- ______________________________________________________________________________ Leon Golub Smithsonian Astrophysical Observatory 60 Garden Street Cambridge, MA 02138 617 495 7177 FAX 496 7577 lgolub@cfa.harvard.edu ______________________________________________________________________________ _______________________________________________ Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
--
Piet Martens Tel: 617-496-7769 Center for Astrophysics Fax: 617-496-7577 60 Garden Street, MS 58 Cell: 617-999-0353 Cambridge, MA 02138 pmartens@cfa.harvard.edu
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Dear Gordon and Piet,
All I can contribute to this discussion is the observation that the flows are steady and continual, lasting for at least several days if not longer. The individual strands may come and go, but the overall structure of the fan only changes slowly. Meanwhile, the flows go on and on. My measurement (unpublished, sorry to say - long story) is that the flows increase in velocity, reaching up to 140 km/sec by the time they get to heights of ~10^5 km. After that they become too faint to see.
These are very long closed loops, about as near to being open structures as they can be and still be closed. I suspect that the material cools as it flows and it comes down at transition region temperatures. Going up, it's at ~1 MK in TRACE (Fe IX/X and Fe XII), probably hotter as seen in XRT. AIA should be able to see the cooler material (Fe VIII at 131A) and tell us if it's coming down.
So the puzzle in my mind is why we don't see the instabilities that you folks insist should be present. There are, of course, lumps in the flow; if there weren't then we would not be able to tell that anything is moving. But those start at the footpoints and move upward - they are, in fact, what we measure to determine the velocities.
Cheers,
Leon
Gordon Petrie wrote:
Dear Piet,
If I understand the steady isothermal theory correctly, the scale height can become unbounded wherever the flow approaches the sonic point, v -> c_s, because of a v^2-c_s^2 factor. Beyond a (generally different) critical point, v=sqrt(g_s Z_0) where g_s is the solar surface gravitational acceleration and Z_0 a length scale of the flux tube spatial expansion, mass conservation demands that the density invert.
Best regards,
Gordon
On Mon, 07 Dec 2009 10:11:07 -0700 Petrus Martens pmartens@cfa.harvard.edu wrote:
Gordon,
I agree with your comment. In fact, it is fairly easily shown directly from the momentum equation that flows up to the sound speed increase the pressure scale height by at most a factor two, when v~c_s, much less when v<c_s because the flow effect scales as (v/c_s)^2.
A really original solution as to why observed loops can be overdense near their apexes was presented by Craig Deforest in 2007. If the unresolved strands that make up the observed loop increase in cross- section from footpoints to apex an observer would conclude that the loop is overdense and has a scale height much larger than what follows from the loop temperature. In reality there is simply more emitting volume near the apex. Of course one has to explain why strands increase in cross-section, while the loops that they collectively form appear not to, but Craig shows some nice images in his paper that seem to support his suggestion.
There are ways to verify this from observations.
Cheers,
Piet
Gordon Petrie wrote:
Dear All,
In a basic model of steady, isothermal hydrodynamic flow (http://adsabs.harvard.edu/abs/2006ApJ...649.1078P), steady flows can only affect hydrostatic scale heights under exceptional conditions. These states have fast flows approaching the sound speed and form a small part of the solution space right next to unphysical regimes with density inversions. If significantly many loops really are of this kind, it would be an interesting problem explaining why. On the other hand, it's clear from rho*V*A why steady flows decrease densities.
Best regards,
Gordon
On Mon, 07 Dec 2009 09:11:07 -0500 Leon Golub golub@head.cfa.harvard.edu wrote:
Jim,
We were indeed modelling the long, relatively faint loops seen in the plage regions surrounding sunspots, which are exactly where EIS is seeing the flows. It's been known for a long time (the Palermo people did such modelling 20 years ago) that flows in coronal loops drop the density ("When you start a flow going, the loop disappears.") or alternatively, if you see the loop it means the density is enhanced. I'm not sure why your modelling failed, but we were able to reproduce the scale height quite well. Having the flow (in either direction) extends the emission scale height quite a bit beyond the hydrostatic value.
As you know, the AIA on SDO will have far more extensive temperature coverage than TRACE does. There is a puzzle right now in that EIS sees the flows at higher temperatures than we saw in TRACE. I think that this topic is going to be a major one in the coming years.
Leon
Klimchuk, James A. (GSFC-6710) wrote:
Wow, I'm surprised, and pleased, at the interest this paper has generated! Let me first respond to Leon's comment. As Harry said (thanks!), in order to get the extreme excess densities that are observed in most warm loops, the footpoint heating needs to be so concentrated that no equilibrium exists (which strictly speaking is different from an instability). Hence, thermal nonequilibrium. A few years back, Spiros P. and I addressed your suggestion with Amy that asymmetric heating and steady flows might explain the observations. Our modeling showed that the density enhancement was adequate to explain some loops, but the scale height is too small and the filter-ratio temperature profile is far too structured (paper attached). We thus rejected this explanation. Sorry!
Thanks for your comment, Jim
-----Original Message----- From: loops-bounces@solar.physics.montana.edu [mailto:loops- bounces@solar.physics.montana.edu] On Behalf Of Harry Warren Sent: Sunday, December 06, 2009 6:19 PM To: A mailing list for scientists involved in the observation and modeling of solar loop structures Subject: Re: [Loops] loops and thermal nonequilibrium
Leon,
As I recall, your paper with Amy relied on footpoint heating, which does lead to higher apex densities and flatter temperature ratios. The observed densities near 1 MK are so high, however, that the loops become thermodynamically unstable. Also, the high speed EIS flows are typically seen in faint regions and are not associated with the types of loops that Jim is attempting to model.
Harry
On 12/5/09 3:16 PM, "Leon Golub" golub@cfa.harvard.edu wrote:
> Jim, > > Amy and I addressed the issues of excess density, flat temperature > profiles and large scale height about 10 years ago. Having flows of > 30-40 km/sec, as is observed in TRACE and now verified by EIS, > solves > these problems quite nicely. So there is a viable mechanism other > than > nanoflares. > > Leon > > > Klimchuk, James A. (GSFC-6710) wrote: >> Dear Loops Friends, >> >> >> >> If you are interested, the attached paper shows that coronal >> loops >> cannot be explained by thermal nonequilibrium. The results >> appear to >> rule out the widespread existence of coronal heating that is >> both highly >> concentrated low in the corona and steady or quasi-steady (slowly >> varying or impulsive with a rapid cadence). Comments are welcomed. >> >> >> >> Best wishes, >> >> Jim >> >> >> >>
>> *** >> >> James A. Klimchuk >> >> NASA Goddard Space Flight Center >> >> Solar Physics Lab, Code 671 >> >> Bldg. 21, Rm. 158 >> >> Greenbelt, MD 20771 >> >> USA >> >> >> >> Phone: 1-301-286-9060 >> >> Fax: 1-301-286-7194 >> >> E-mail: James.A.Klimchuk@nasa.gov mailto:James.A.Klimchuk@nasa.gov >> Home page: >> http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html >> >> >> >>
>> *** >> >> >> >> >> ------------------------------------------------------------------------ >> _______________________________________________ >> Loops mailing list >> Loops@solar.physics.montana.edu >> https://mithra.physics.montana.edu/mailman/listinfo/loops > _______________________________________________ > Loops mailing list > Loops@solar.physics.montana.edu
> https://mithra.physics.montana.edu/mailman/listinfo/loops
//
// Harry P. Warren phone : 202-404-1453 // Naval Research Laboratory fax : 202-404-7997 // Code 7673HW email : hwarren@nrl.navy.mil // Washington, DC 20375 www : http://tcrb.nrl.navy.mil/~hwarren //
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-- ______________________________________________________________________________ Leon Golub Smithsonian Astrophysical Observatory 60 Garden Street Cambridge, MA 02138 617 495 7177 FAX 496 7577 lgolub@cfa.harvard.edu ______________________________________________________________________________ _______________________________________________ Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
--
Piet Martens Tel: 617-496-7769 Center for Astrophysics Fax: 617-496-7577 60 Garden Street, MS 58 Cell: 617-999-0353 Cambridge, MA 02138 pmartens@cfa.harvard.edu
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
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Dear Leon,
However, those quasi-periodic intensity perturbations (or lumps) along fan-like loops may not be signatures of steady flows but just the acoustic waves (see my recent paper, Wang et al. 2009, 503, L25). So you don't need to worry about any instability caused by flows. In this paper, I reported the first Doppler shift measurements of these moving features with Hinode/EIS, which show the amplitudes of only several km/s in Fe XII, but not tens of km/s as expected if they are episodic flows of 100-120 km/s, also in this case the Doppler shift at the footpoints is less than 7 km/s. Therefore, I wonder the moving blobs seen in XRT are wave features (they are actually periodic with period about 10-12 min), while steady flows seen in EIS near the footpoint of dark regions are not possible detected by imaging observations as you pointed.
Best Regards
Tongjiang
------------------- Tongjiang Wang
NASA GSFC - Code 671 Bldg 21 - RM 177B Greenbelt, MD 20771
Tel. 301-286-6575 Fax. 301-286-1617
On Sat, 19 Dec 2009, Leon Golub wrote:
Dear Gordon and Piet,
All I can contribute to this discussion is the observation that the flows are steady and continual, lasting for at least several days if not longer. The individual strands may come and go, but the overall structure of the fan only changes slowly. Meanwhile, the flows go on and on. My measurement (unpublished, sorry to say - long story) is that the flows increase in velocity, reaching up to 140 km/sec by the time they get to heights of ~10^5 km. After that they become too faint to see.
These are very long closed loops, about as near to being open structures as they can be and still be closed. I suspect that the material cools as it flows and it comes down at transition region temperatures. Going up, it's at ~1 MK in TRACE (Fe IX/X and Fe XII), probably hotter as seen in XRT. AIA should be able to see the cooler material (Fe VIII at 131A) and tell us if it's coming down.
So the puzzle in my mind is why we don't see the instabilities that you folks insist should be present. There are, of course, lumps in the flow; if there weren't then we would not be able to tell that anything is moving. But those start at the footpoints and move upward - they are, in fact, what we measure to determine the velocities.
Cheers,
Leon
Gordon Petrie wrote:
Dear Piet,
If I understand the steady isothermal theory correctly, the scale height can become unbounded wherever the flow approaches the sonic point, v -> c_s, because of a v^2-c_s^2 factor. Beyond a (generally different) critical point, v=sqrt(g_s Z_0) where g_s is the solar surface gravitational acceleration and Z_0 a length scale of the flux tube spatial expansion, mass conservation demands that the density invert.
Best regards,
Gordon
On Mon, 07 Dec 2009 10:11:07 -0700 Petrus Martens pmartens@cfa.harvard.edu wrote:
Gordon,
I agree with your comment. In fact, it is fairly easily shown
directly from the momentum equation that flows up to the sound speed increase the pressure scale height by at most a factor two, when v~c_s, much less when v<c_s because the flow effect scales as (v/c_s)^2.
A really original solution as to why observed loops can be overdense
near their apexes was presented by Craig Deforest in 2007. If the unresolved strands that make up the observed loop increase in cross- section from footpoints to apex an observer would conclude that the loop is overdense and has a scale height much larger than what follows from the loop temperature. In reality there is simply more emitting volume near the apex. Of course one has to explain why strands increase in cross-section, while the loops that they collectively form appear not to, but Craig shows some nice images in his paper that seem to support his suggestion.
There are ways to verify this from observations. Cheers, Piet
Gordon Petrie wrote:
Dear All,
In a basic model of steady, isothermal hydrodynamic flow (http://adsabs.harvard.edu/abs/2006ApJ...649.1078P), steady flows can only affect hydrostatic scale heights under exceptional conditions. These states have fast flows approaching the sound speed and form a small part of the solution space right next to unphysical regimes with density inversions. If significantly many loops really are of this kind, it would be an interesting problem explaining why. On the other hand, it's clear from rho*V*A why steady flows decrease densities.
Best regards,
Gordon
On Mon, 07 Dec 2009 09:11:07 -0500 Leon Golub golub@head.cfa.harvard.edu wrote:
Jim,
We were indeed modelling the long, relatively faint loops seen in the plage regions surrounding sunspots, which are exactly where EIS is seeing the flows. It's been known for a long time (the Palermo people did such modelling 20 years ago) that flows in coronal loops drop the density ("When you start a flow going, the loop disappears.") or alternatively, if you see the loop it means the density is enhanced. I'm not sure why your modelling failed, but we were able to reproduce the scale height quite well. Having the flow (in either direction) extends the emission scale height quite a bit beyond the hydrostatic value.
As you know, the AIA on SDO will have far more extensive temperature coverage than TRACE does. There is a puzzle right now in that EIS sees the flows at higher temperatures than we saw in TRACE. I think that this topic is going to be a major one in the coming years.
Leon
Klimchuk, James A. (GSFC-6710) wrote:
Wow, I'm surprised, and pleased, at the interest this paper has generated! Let me first respond to Leon's comment. As Harry said (thanks!), in order to get the extreme excess densities that are observed in most warm loops, the footpoint heating needs to be so concentrated that no equilibrium exists (which strictly speaking is different from an instability). Hence, thermal nonequilibrium. A few years back, Spiros P. and I addressed your suggestion with Amy that asymmetric heating and steady flows might explain the observations. Our modeling showed that the density enhancement was adequate to explain some loops, but the scale height is too small and the filter-ratio temperature profile is far too structured (paper attached). We thus rejected this explanation. Sorry!
Thanks for your comment, Jim
> -----Original Message----- > From: loops-bounces@solar.physics.montana.edu [mailto:loops- > bounces@solar.physics.montana.edu] On Behalf Of Harry Warren > Sent: Sunday, December 06, 2009 6:19 PM > To: A mailing list for scientists involved in the observation > and modeling of > solar loop structures > Subject: Re: [Loops] loops and thermal nonequilibrium > > > Leon, > > As I recall, your paper with Amy relied on footpoint heating, > which does > lead to higher apex densities and flatter temperature ratios. > The observed > densities near 1 MK are so high, however, that the loops become > thermodynamically unstable. Also, the high speed EIS flows are > typically > seen in faint regions and are not associated with the types of > loops that > Jim is attempting to model. > > Harry > > > On 12/5/09 3:16 PM, "Leon Golub" golub@cfa.harvard.edu wrote: > > > Jim, > > > > Amy and I addressed the issues of excess density, flat > > temperature > > profiles and large scale height about 10 years ago. Having > > flows of > > 30-40 km/sec, as is observed in TRACE and now verified by EIS, > > solves > > these problems quite nicely. So there is a viable mechanism > > other than > > nanoflares. > > > > Leon > > > > > > Klimchuk, James A. (GSFC-6710) wrote: > > > Dear Loops Friends, > > > > > > > > > > > > If you are interested, the attached paper shows that > > > coronal loops > > > cannot be explained by thermal nonequilibrium. The results > > > appear to > > > rule out the widespread existence of coronal heating that is > > > both highly > > > concentrated low in the corona and steady or quasi-steady > > > (slowly > > > varying or impulsive with a rapid cadence). Comments are > > > welcomed. > > > > > > > > > > > > Best wishes, > > > > > > Jim > > > > > > > > > > > > > ************************************************************** > *************** > > > *** > > > > > > James A. Klimchuk > > > > > > NASA Goddard Space Flight Center > > > > > > Solar Physics Lab, Code 671 > > > > > > Bldg. 21, Rm. 158 > > > > > > Greenbelt, MD 20771 > > > > > > USA > > > > > > > > > > > > Phone: 1-301-286-9060 > > > > > > Fax: 1-301-286-7194 > > > > > > E-mail: James.A.Klimchuk@nasa.gov > mailto:James.A.Klimchuk@nasa.gov > > > Home page: > > > http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html > > > > > > > > > > > > > ************************************************************** > *************** > > > *** > > > > > > > > > > > > > > > ------------------------------------------------------------------------ > > > _______________________________________________ > > > Loops mailing list > > > Loops@solar.physics.montana.edu > > > https://mithra.physics.montana.edu/mailman/listinfo/loops > > _______________________________________________ > > Loops mailing list > > Loops@solar.physics.montana.edu > > https://mithra.physics.montana.edu/mailman/listinfo/loops > -- > // > --------------------------------------------------------------------- > // Harry P. Warren phone : 202-404-1453 > // Naval Research Laboratory fax : 202-404-7997 > // Code 7673HW email : hwarren@nrl.navy.mil > // Washington, DC 20375 www : > http://tcrb.nrl.navy.mil/~hwarren > // > --------------------------------------------------------------------- > > > > > > _______________________________________________ > Loops mailing list > Loops@solar.physics.montana.edu > https://mithra.physics.montana.edu/mailman/listinfo/loops _______________________________________________ Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
-- ______________________________________________________________________________ Leon Golub Smithsonian Astrophysical Observatory 60 Garden Street Cambridge, MA 02138 617 495 7177 FAX 496 7577 lgolub@cfa.harvard.edu ______________________________________________________________________________ _______________________________________________ Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
--
Piet Martens Tel: 617-496-7769 Center for Astrophysics Fax: 617-496-7577 60 Garden Street, MS 58 Cell: 617-999-0353 Cambridge, MA 02138 pmartens@cfa.harvard.edu
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Dear Tongjiang,
This is exactly the "argument" I've been having for the past ten years, starting with Nakariakov in 1999. I've been waiting for the Doppler data since then, because where I see flows, other people see waves. I do think that the EIS results are now showing higher velocities of some tens of km/sec, and in TRACE the flows do start out slow at the footpoints, so there's no inconsistency with what you're saying about the speeds. There is a difference in that EIS sees the upflows at somewhat higher temperatures than we do with TRACE, and XRT sees them too, meaning higher T. I'm hoping that AIA will help sort this out.
What I can tell you is that when we see waves in the corona, they are quite clearly periodic and there's no doubt about it. Just look at any movie (with high time cadence) taken above sunspots: it looks like a loudspeaker pulsing away. These fans are different, and if you look closely at your time-distance plots, you'll see the lower portions curving upward, as the flows accelerate on their way up.
Leon
Tongjiang Wang wrote:
Dear Leon,
However, those quasi-periodic intensity perturbations (or lumps) along fan-like loops may not be signatures of steady flows but just the acoustic waves (see my recent paper, Wang et al. 2009, 503, L25). So you don't need to worry about any instability caused by flows. In this paper, I reported the first Doppler shift measurements of these moving features with Hinode/EIS, which show the amplitudes of only several km/s in Fe XII, but not tens of km/s as expected if they are episodic flows of 100-120 km/s, also in this case the Doppler shift at the footpoints is less than 7 km/s. Therefore, I wonder the moving blobs seen in XRT are wave features (they are actually periodic with period about 10-12 min), while steady flows seen in EIS near the footpoint of dark regions are not possible detected by imaging observations as you pointed.
Best Regards
Tongjiang
Tongjiang Wang
NASA GSFC - Code 671 Bldg 21 - RM 177B Greenbelt, MD 20771
Tel. 301-286-6575 Fax. 301-286-1617
On Sat, 19 Dec 2009, Leon Golub wrote:
Dear Gordon and Piet,
All I can contribute to this discussion is the observation that the flows are steady and continual, lasting for at least several days if not longer. The individual strands may come and go, but the overall structure of the fan only changes slowly. Meanwhile, the flows go on and on. My measurement (unpublished, sorry to say - long story) is that the flows increase in velocity, reaching up to 140 km/sec by the time they get to heights of ~10^5 km. After that they become too faint to see.
These are very long closed loops, about as near to being open structures as they can be and still be closed. I suspect that the material cools as it flows and it comes down at transition region temperatures. Going up, it's at ~1 MK in TRACE (Fe IX/X and Fe XII), probably hotter as seen in XRT. AIA should be able to see the cooler material (Fe VIII at 131A) and tell us if it's coming down.
So the puzzle in my mind is why we don't see the instabilities that you folks insist should be present. There are, of course, lumps in the flow; if there weren't then we would not be able to tell that anything is moving. But those start at the footpoints and move upward - they are, in fact, what we measure to determine the velocities.
Cheers,
Leon
Gordon Petrie wrote:
Dear Piet,
If I understand the steady isothermal theory correctly, the scale height can become unbounded wherever the flow approaches the sonic point, v -> c_s, because of a v^2-c_s^2 factor. Beyond a (generally different) critical point, v=sqrt(g_s Z_0) where g_s is the solar surface gravitational acceleration and Z_0 a length scale of the flux tube spatial expansion, mass conservation demands that the density invert.
Best regards,
Gordon
On Mon, 07 Dec 2009 10:11:07 -0700 Petrus Martens pmartens@cfa.harvard.edu wrote:
Gordon,
I agree with your comment. In fact, it is fairly easily shown
directly from the momentum equation that flows up to the sound speed increase the pressure scale height by at most a factor two, when
v~c_s,
much less when v<c_s because the flow effect scales as (v/c_s)^2.
A really original solution as to why observed loops can be
overdense
near their apexes was presented by Craig Deforest in 2007. If the unresolved strands that make up the observed loop increase in cross- section from footpoints to apex an observer would conclude that the loop is overdense and has a scale height much larger than what
follows
from the loop temperature. In reality there is simply more emitting volume near the apex. Of course one has to explain why strands
increase
in cross-section, while the loops that they collectively form
appear not
to, but Craig shows some nice images in his paper that seem to
support
his suggestion.
There are ways to verify this from observations. Cheers, Piet
> Gordon Petrie wrote:
Dear All,
> In a basic model of steady, isothermal hydrodynamic flow >
(http://adsabs.harvard.edu/abs/2006ApJ...649.1078P), steady flows
can > > only affect hydrostatic scale heights under exceptional conditions. > > These states have fast flows approaching the sound speed and form a > > small part of the solution space right next to unphysical regimes with > > density inversions. If significantly many loops really are of this > > kind, it would be an interesting problem explaining why. On the other > > hand, it's clear from rho*V*A why steady flows decrease densities.
> Best regards, > Gordon > On Mon, 07 Dec 2009 09:11:07 -0500
Leon Golub golub@head.cfa.harvard.edu wrote:
Jim, > > > We were indeed modelling the long, relatively faint
loops seen in > > > the plage regions surrounding sunspots, which are exactly where EIS > > > is seeing the flows. It's been known for a long time (the Palermo > > > people did such modelling 20 years ago) that flows in coronal loops > > > drop the density ("When you start a flow going, the loop > > > disappears.") or alternatively, if you see the loop it means the > > > density is enhanced. I'm not sure why your modelling failed, but we > > > were able to reproduce the scale height quite well. Having the flow > > > (in either direction) extends the emission scale height quite a bit > > > beyond the hydrostatic value.
> > > As you know, the AIA on SDO will have far more extensive
temperature > > > coverage than TRACE does. There is a puzzle right now in that EIS > > > sees the flows at higher temperatures than we saw in TRACE. I think > > > that this topic is going to be a major one in the coming years.
> > > Leon > > > > > > Klimchuk, James A. (GSFC-6710) wrote: > Wow, I'm surprised, and pleased, at the interest this paper
has > > > > generated! Let me first respond to Leon's comment. As Harry said > > > > (thanks!), in order to get the extreme excess densities that are > > > > observed in most warm loops, the footpoint heating needs to be so > > > > concentrated that no equilibrium exists (which strictly speaking > > > > is different from an instability). Hence, thermal nonequilibrium. > > > > A few years back, Spiros P. and I addressed your suggestion with > > > > Amy that asymmetric heating and steady flows might explain the > > >
observations. Our modeling showed that the density enhancement was
> adequate to explain some loops, but the scale height is too
small > > > > and the filter-ratio temperature profile is far too structured > > > > (paper attached). We thus rejected this explanation. Sorry!
> > > > > Thanks for your comment, > Jim > > > > > > -----Original Message----- > > From: loops-bounces@solar.physics.montana.edu [mailto:loops- > > bounces@solar.physics.montana.edu] On Behalf Of Harry Warren > > Sent: Sunday, December 06, 2009 6:19 PM > > To: A mailing list for scientists involved in the
observation > > > > > and modeling of
> > solar loop structures > > Subject: Re: [Loops] loops and thermal nonequilibrium > > > > > > > > > > > > Leon, > > > > > > > As I recall, your paper with Amy relied on
footpoint heating, > > > > > which does
> > lead to higher apex densities and flatter temperature
ratios. > > > > > The observed
> > densities near 1 MK are so high, however, that the loops
become
> > thermodynamically unstable. Also, the high speed EIS flows
are > > > > > typically
> > seen in faint regions and are not associated with the
types of > > > > > loops that
> > Jim is attempting to model. > > > > > > > Harry > > > > > > > > > > > > On 12/5/09 3:16 PM, "Leon Golub"
golub@cfa.harvard.edu wrote:
> > > > > > > > Jim, > > > > > > > > > Amy and I addressed the issues of excess
density, flat > > > > > > temperature
> > > profiles and large scale height about 10 years ago.
Having > > > > > > flows of
> > > 30-40 km/sec, as is observed in TRACE and now verified
by EIS, > > > > > > solves
> > > these problems quite nicely. So there is a viable
mechanism > > > > > > other than
> > > nanoflares. > > > > > > > > > Leon > > > > > > > > > > > > > > > Klimchuk, James A. (GSFC-6710)
wrote:
> > > > Dear Loops Friends, > > > > > > > > > > > > > > > > > > > > > > > > > If you
are interested, the attached paper shows that > > > > > > > coronal loops
> > > > cannot be explained by thermal nonequilibrium. The
results > > > > > > > appear to
> > > > rule out the widespread existence of coronal heating
that is > > > > > > > both highly
> > > > concentrated low in the corona and steady or
quasi-steady > > > > > > > (slowly
> > > > varying or impulsive with a rapid cadence). Comments
are > > > > > > > welcomed.
> > > > > > > > > > > > > > > > > > > > > > > > > Best wishes, > > > > > > > > > > > Jim > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
> > *************** > > > > *** > > > > > > > > > > > James A. Klimchuk > > > > > > > > > > > NASA Goddard Space Flight Center > > > > > > > > > > > Solar Physics Lab, Code 671 > > > > > > > > > > > Bldg. 21, Rm. 158 > > > > > > > > > > > Greenbelt, MD 20771 > > > > > > > > > > > USA > > > > > > > > > > > > > > > > > > > > > > > > > Phone:
1-301-286-9060
> > > > > > > > > > > Fax: 1-301-286-7194 > > > > > > > > > > > E-mail: James.A.Klimchuk@nasa.gov > > mailto:James.A.Klimchuk@nasa.gov > > > > Home page: > > > > > > >
http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html
> > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
> > *************** > > > > *** > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
> > > > _______________________________________________ > > > > Loops mailing list > > > > Loops@solar.physics.montana.edu > > > > https://mithra.physics.montana.edu/mailman/listinfo/loops > > > _______________________________________________ > > > Loops mailing list > > > Loops@solar.physics.montana.edu > > > https://mithra.physics.montana.edu/mailman/listinfo/loops > > -- > > > > > // > > > > >
> > // Harry P. Warren phone : 202-404-1453 > > // Naval Research Laboratory fax : 202-404-7997 > > // Code 7673HW email : hwarren@nrl.navy.mil > > // Washington, DC 20375 www : > > > > >
http://tcrb.nrl.navy.mil/~hwarren
> > // > > > > >
> > > > > > > > > > > > > > > > > > > > > > > > > > >
> > Loops mailing list > > Loops@solar.physics.montana.edu > > https://mithra.physics.montana.edu/mailman/listinfo/loops > _______________________________________________ > Loops mailing list > Loops@solar.physics.montana.edu > https://mithra.physics.montana.edu/mailman/listinfo/loops > > > -- > > >
Leon Golub Smithsonian Astrophysical Observatory 60 Garden Street Cambridge, MA 02138 617 495 7177 FAX 496 7577 lgolub@cfa.harvard.edu
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops > _______________________________________________
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
> > -- >
Piet Martens Tel: 617-496-7769 Center for Astrophysics Fax: 617-496-7577 60 Garden Street, MS 58 Cell: 617-999-0353 Cambridge, MA 02138 pmartens@cfa.harvard.edu
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Dear Leon,
I just would like to remind you that the regions showing tens of km/s upflows seen in EIS coronal lines are typically for weak or dark fan structure in TRACE and XRT, while the propagating wave features are often seen in bright fan-like loops (like those shown in my paper, where the brighter part of fan loops show RED-SHFIT!). Indeed there are other EIS observations show bright fan-like loops show redshift while not blue shifts. Moreover, as you mentioned the steady flow is not possibly seen in imaging observations, that means that the moving brobs features correspond to episodic jets or pulsive flows, thus Doppler shift fluctuations of tens of km/s amplitudes are expected for a upflow of 100-120 km/s for fan-like loops with a typical inclination of 50-60 deg (see Marsh et al. 2009 who derived the inclination from STEREO/EUVI obs), but my study did not show this is the case. Finally, in the dark region showing tens of km/s EIS blue shifts, the waves may co-exist with upflows, therefore, the upwards moving blobs are not necessary to be the upflows. I'll try to look for more examples to support my view. Thank you for your discussions.
Best Regards
Tongjiang
On Mon, 21 Dec 2009, Leon Golub wrote:
Dear Tongjiang,
This is exactly the "argument" I've been having for the past ten years, starting with Nakariakov in 1999. I've been waiting for the Doppler data since then, because where I see flows, other people see waves. I do think that the EIS results are now showing higher velocities of some tens of km/sec, and in TRACE the flows do start out slow at the footpoints, so there's no inconsistency with what you're saying about the speeds. There is a difference in that EIS sees the upflows at somewhat higher temperatures than we do with TRACE, and XRT sees them too, meaning higher T. I'm hoping that AIA will help sort this out.
What I can tell you is that when we see waves in the corona, they are quite clearly periodic and there's no doubt about it. Just look at any movie (with high time cadence) taken above sunspots: it looks like a loudspeaker pulsing away. These fans are different, and if you look closely at your time-distance plots, you'll see the lower portions curving upward, as the flows accelerate on their way up.
Leon
Tongjiang Wang wrote:
Dear Leon,
However, those quasi-periodic intensity perturbations (or lumps) along fan-like loops may not be signatures of steady flows but just the acoustic waves (see my recent paper, Wang et al. 2009, 503, L25). So you don't need to worry about any instability caused by flows. In this paper, I reported the first Doppler shift measurements of these moving features with Hinode/EIS, which show the amplitudes of only several km/s in Fe XII, but not tens of km/s as expected if they are episodic flows of 100-120 km/s, also in this case the Doppler shift at the footpoints is less than 7 km/s. Therefore, I wonder the moving blobs seen in XRT are wave features (they are actually periodic with period about 10-12 min), while steady flows seen in EIS near the footpoint of dark regions are not possible detected by imaging observations as you pointed.
Best Regards
Tongjiang
Tongjiang Wang
NASA GSFC - Code 671 Bldg 21 - RM 177B Greenbelt, MD 20771
Tel. 301-286-6575 Fax. 301-286-1617
On Sat, 19 Dec 2009, Leon Golub wrote:
Dear Gordon and Piet,
All I can contribute to this discussion is the observation that the flows are steady and continual, lasting for at least several days if not longer. The individual strands may come and go, but the overall structure of the fan only changes slowly. Meanwhile, the flows go on and on. My measurement (unpublished, sorry to say - long story) is that the flows increase in velocity, reaching up to 140 km/sec by the time they get to heights of ~10^5 km. After that they become too faint to see.
These are very long closed loops, about as near to being open structures as they can be and still be closed. I suspect that the material cools as it flows and it comes down at transition region temperatures. Going up, it's at ~1 MK in TRACE (Fe IX/X and Fe XII), probably hotter as seen in XRT. AIA should be able to see the cooler material (Fe VIII at 131A) and tell us if it's coming down.
So the puzzle in my mind is why we don't see the instabilities that you folks insist should be present. There are, of course, lumps in the flow; if there weren't then we would not be able to tell that anything is moving. But those start at the footpoints and move upward - they are, in fact, what we measure to determine the velocities.
Cheers,
Leon
Gordon Petrie wrote:
Dear Piet,
If I understand the steady isothermal theory correctly, the scale height can become unbounded wherever the flow approaches the sonic point, v -> c_s, because of a v^2-c_s^2 factor. Beyond a (generally different) critical point, v=sqrt(g_s Z_0) where g_s is the solar surface gravitational acceleration and Z_0 a length scale of the flux tube spatial expansion, mass conservation demands that the density invert.
Best regards,
Gordon
On Mon, 07 Dec 2009 10:11:07 -0700 Petrus Martens pmartens@cfa.harvard.edu wrote:
Gordon,
I agree with your comment. In fact, it is fairly easily shown
directly from the momentum equation that flows up to the sound speed increase the pressure scale height by at most a factor two, when
v~c_s,
much less when v<c_s because the flow effect scales as (v/c_s)^2.
A really original solution as to why observed loops can be
overdense
near their apexes was presented by Craig Deforest in 2007. If the unresolved strands that make up the observed loop increase in cross- section from footpoints to apex an observer would conclude that the loop is overdense and has a scale height much larger than what
follows
from the loop temperature. In reality there is simply more emitting volume near the apex. Of course one has to explain why strands
increase
in cross-section, while the loops that they collectively form
appear not
to, but Craig shows some nice images in his paper that seem to
support
his suggestion.
There are ways to verify this from observations. Cheers, Piet
> > Gordon Petrie wrote: Dear All, > > In a basic model of steady, isothermal hydrodynamic flow >
(http://adsabs.harvard.edu/abs/2006ApJ...649.1078P), steady flows
can > > only affect hydrostatic scale heights under exceptional conditions. > > These states have fast flows approaching the sound speed and form a > > small part of the solution space right next to unphysical regimes with > > density inversions. If significantly many loops really are of this > > kind, it would be an interesting problem explaining why. On the other > > hand, it's clear from rho*V*A why steady flows decrease densities.
> > Best regards, > > Gordon > > On Mon, 07 Dec 2009 09:11:07 -0500 Leon Golub golub@head.cfa.harvard.edu wrote: > Jim, > > > > We were indeed modelling the long, relatively faint
loops seen in > > > the plage regions surrounding sunspots, which are exactly where EIS > > > is seeing the flows. It's been known for a long time (the Palermo > > > people did such modelling 20 years ago) that flows in coronal loops > > > drop the density ("When you start a flow going, the loop > > > disappears.") or alternatively, if you see the loop it means the > > > density is enhanced. I'm not sure why your modelling failed, but we > > > were able to reproduce the scale height quite well. Having the flow > > > (in either direction) extends the emission scale height quite a bit > > > beyond the hydrostatic value.
> > > > As you know, the AIA on SDO will have far more extensive
temperature > > > coverage than TRACE does. There is a puzzle right now in that EIS > > > sees the flows at higher temperatures than we saw in TRACE. I think > > > that this topic is going to be a major one in the coming years.
> > > > Leon > > > > > > > Klimchuk, James A. (GSFC-6710) wrote: > > Wow, I'm surprised, and pleased, at the interest this paper
has > > > > generated! Let me first respond to Leon's comment. As Harry said > > > > (thanks!), in order to get the extreme excess densities that are > > > > observed in most warm loops, the footpoint heating needs to be so > > > > concentrated that no equilibrium exists (which strictly speaking > > > > is different from an instability). Hence, thermal nonequilibrium. > > > > A few years back, Spiros P. and I addressed your suggestion with > > > > Amy that asymmetric heating and steady flows might explain the > > >
observations. Our modeling showed that the density enhancement was
> > adequate to explain some loops, but the scale height is too
small > > > > and the filter-ratio temperature profile is far too structured > > > > (paper attached). We thus rejected this explanation. Sorry!
> > > > > > Thanks for your comment, > > Jim > > > > > > > -----Original Message----- > > > From: loops-bounces@solar.physics.montana.edu > > > [mailto:loops- > > > bounces@solar.physics.montana.edu] On Behalf Of Harry > > > Warren > > > Sent: Sunday, December 06, 2009 6:19 PM > > > To: A mailing list for scientists involved in the
observation > > > > > and modeling of
> > > solar loop structures > > > Subject: Re: [Loops] loops and thermal nonequilibrium > > > > > > > > > > > > > Leon, > > > > > > > > As I recall, your paper with Amy relied on
footpoint heating, > > > > > which does
> > > lead to higher apex densities and flatter temperature
ratios. > > > > > The observed
> > > densities near 1 MK are so high, however, that the loops
become
> > > thermodynamically unstable. Also, the high speed EIS flows
are > > > > > typically
> > > seen in faint regions and are not associated with the
types of > > > > > loops that
> > > Jim is attempting to model. > > > > > > > > Harry > > > > > > > > > > > > > On 12/5/09 3:16 PM, "Leon Golub"
golub@cfa.harvard.edu wrote:
> > > > > > > > > Jim, > > > > > > > > > > Amy and I addressed the issues of excess
density, flat > > > > > > temperature
> > > > profiles and large scale height about 10 years ago.
Having > > > > > > flows of
> > > > 30-40 km/sec, as is observed in TRACE and now verified
by EIS, > > > > > > solves
> > > > these problems quite nicely. So there is a viable
mechanism > > > > > > other than
> > > > nanoflares. > > > > > > > > > > Leon > > > > > > > > > > > > > > > > Klimchuk, James A. (GSFC-6710)
wrote:
> > > > > Dear Loops Friends, > > > > > > > > > > > > > > > > > > > > > > > > > > If you
are interested, the attached paper shows that > > > > > > > coronal loops
> > > > > cannot be explained by thermal nonequilibrium. The
results > > > > > > > appear to
> > > > > rule out the widespread existence of coronal heating
that is > > > > > > > both highly
> > > > > concentrated low in the corona and steady or
quasi-steady > > > > > > > (slowly
> > > > > varying or impulsive with a rapid cadence). Comments
are > > > > > > > welcomed.
> > > > > > > > > > > > > > > > > > > > > > > > > > Best wishes, > > > > > > > > > > > > Jim > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
> > > *************** > > > > > *** > > > > > > > > > > > > James A. Klimchuk > > > > > > > > > > > > NASA Goddard Space Flight Center > > > > > > > > > > > > Solar Physics Lab, Code 671 > > > > > > > > > > > > Bldg. 21, Rm. 158 > > > > > > > > > > > > Greenbelt, MD 20771 > > > > > > > > > > > > USA > > > > > > > > > > > > > > > > > > > > > > > > > > Phone:
1-301-286-9060
> > > > > > > > > > > > Fax: 1-301-286-7194 > > > > > > > > > > > > E-mail: James.A.Klimchuk@nasa.gov > > > mailto:James.A.Klimchuk@nasa.gov > > > > > Home page: > > > > > > >
http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html
> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
> > > *************** > > > > > *** > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
> > > > > _______________________________________________ > > > > > Loops mailing list > > > > > Loops@solar.physics.montana.edu > > > > > https://mithra.physics.montana.edu/mailman/listinfo/loops > > > > _______________________________________________ > > > > Loops mailing list > > > > Loops@solar.physics.montana.edu > > > > https://mithra.physics.montana.edu/mailman/listinfo/loops > > > -- > > > > > // > > > > >
> > > // Harry P. Warren phone : 202-404-1453 > > > // Naval Research Laboratory fax : 202-404-7997 > > > // Code 7673HW email : hwarren@nrl.navy.mil > > > // Washington, DC 20375 www : > > > > >
http://tcrb.nrl.navy.mil/~hwarren
> > > // > > > > >
> > > > > > > > > > > > > > > > > > > > > > > > > > > >
> > > Loops mailing list > > > Loops@solar.physics.montana.edu > > > https://mithra.physics.montana.edu/mailman/listinfo/loops > > _______________________________________________ > > Loops mailing list > > Loops@solar.physics.montana.edu > > https://mithra.physics.montana.edu/mailman/listinfo/loops > > > > -- > > >
> Leon Golub Smithsonian Astrophysical Observatory > 60 Garden Street > Cambridge, MA 02138 > 617 495 7177 > FAX 496 7577 > lgolub@cfa.harvard.edu >
> _______________________________________________ > Loops mailing list > Loops@solar.physics.montana.edu > https://mithra.physics.montana.edu/mailman/listinfo/loops > > _______________________________________________ Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops > > > -- >
Piet Martens Tel: 617-496-7769 Center for Astrophysics Fax: 617-496-7577 60 Garden Street, MS 58 Cell: 617-999-0353 Cambridge, MA 02138 pmartens@cfa.harvard.edu
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Dear Tongjiang,
I see that this subject is going to be debated for many years to come, which is good. We'll have to discuss this in person some time, where we show each other the observations and both be looking at the same thing. In particular, it is exactly in those fan-like features that we see the clearest flows, and indeed there is some question about the temperature. We need simultaneous observations, in the same spectral lines, with EIS and AIA. These should be available in a few months, once SDO launches. Since TRACE sees upflows at both ends of the large loop systems, it seems likely that there are interlaced loops (or threads) and that the flows go up warm and are cooler coming down. With low-resolution (~1") imaging, it would seem as if the blue shifts and red shifts are on top of each other, but this is an illusion cause by failure to resolve the different structures.
Leon
Tongjiang Wang wrote:
Dear Leon,
I just would like to remind you that the regions showing tens of km/s upflows seen in EIS coronal lines are typically for weak or dark fan structure in TRACE and XRT, while the propagating wave features are often seen in bright fan-like loops (like those shown in my paper, where the brighter part of fan loops show RED-SHFIT!). Indeed there are other EIS observations show bright fan-like loops show redshift while not blue shifts. Moreover, as you mentioned the steady flow is not possibly seen in imaging observations, that means that the moving brobs features correspond to episodic jets or pulsive flows, thus Doppler shift fluctuations of tens of km/s amplitudes are expected for a upflow of 100-120 km/s for fan-like loops with a typical inclination of 50-60 deg (see Marsh et al. 2009 who derived the inclination from STEREO/EUVI obs), but my study did not show this is the case. Finally, in the dark region showing tens of km/s EIS blue shifts, the waves may co-exist with upflows, therefore, the upwards moving blobs are not necessary to be the upflows. I'll try to look for more examples to support my view. Thank you for your discussions.
Best Regards
Tongjiang
On Mon, 21 Dec 2009, Leon Golub wrote:
Dear Tongjiang,
This is exactly the "argument" I've been having for the past ten years, starting with Nakariakov in 1999. I've been waiting for the Doppler data since then, because where I see flows, other people see waves. I do think that the EIS results are now showing higher velocities of some tens of km/sec, and in TRACE the flows do start out slow at the footpoints, so there's no inconsistency with what you're saying about the speeds. There is a difference in that EIS sees the upflows at somewhat higher temperatures than we do with TRACE, and XRT sees them too, meaning higher T. I'm hoping that AIA will help sort this out.
What I can tell you is that when we see waves in the corona, they are quite clearly periodic and there's no doubt about it. Just look at any movie (with high time cadence) taken above sunspots: it looks like a loudspeaker pulsing away. These fans are different, and if you look closely at your time-distance plots, you'll see the lower portions curving upward, as the flows accelerate on their way up.
Leon
Dear Leon and Piet
Thank you very much for your comments and suggestions. Yes, I agree it is important to determine whether those propagating wave (or upflow) features are only seen in the cool loops (evident in TRACE or EUV 171) or they may be existing in hot loops. Whether the propagating speed depending on the temperature of the loop may provide additional evidence to tell the truth. I wish SDO/AIA will be successfully lauched next year and can significantly contribute to solve this question.
But whatever how obvious the flow patterns look like, the feature of clear periodicities of this phenomenon should not be negligible, and need a reasonable explanation.
Hope I can find a chance to visit Harvard-Smithsonian Center some time.
Merry Christmas and Happy New Year!
Tongjiang
------------------- Tongjiang Wang
NASA GSFC - Code 671 Bldg 21 - RM 177B Greenbelt, MD 20771
Tel. 301-286-6575 Fax. 301-286-1617
On Tue, 22 Dec 2009, Leon Golub wrote:
Dear Tongjiang,
I see that this subject is going to be debated for many years to come, which is good. We'll have to discuss this in person some time, where we show each other the observations and both be looking at the same thing. In particular, it is exactly in those fan-like features that we see the clearest flows, and indeed there is some question about the temperature. We need simultaneous observations, in the same spectral lines, with EIS and AIA. These should be available in a few months, once SDO launches. Since TRACE sees upflows at both ends of the large loop systems, it seems likely that there are interlaced loops (or threads) and that the flows go up warm and are cooler coming down. With low-resolution (~1") imaging, it would seem as if the blue shifts and red shifts are on top of each other, but this is an illusion cause by failure to resolve the different structures.
Leon
Tongjiang Wang wrote:
Dear Leon,
I just would like to remind you that the regions showing tens of km/s upflows seen in EIS coronal lines are typically for weak or dark fan structure in TRACE and XRT, while the propagating wave features are often seen in bright fan-like loops (like those shown in my paper, where the brighter part of fan loops show RED-SHFIT!). Indeed there are other EIS observations show bright fan-like loops show redshift while not blue shifts. Moreover, as you mentioned the steady flow is not possibly seen in imaging observations, that means that the moving brobs features correspond to episodic jets or pulsive flows, thus Doppler shift fluctuations of tens of km/s amplitudes are expected for a upflow of 100-120 km/s for fan-like loops with a typical inclination of 50-60 deg (see Marsh et al. 2009 who derived the inclination from STEREO/EUVI obs), but my study did not show this is the case. Finally, in the dark region showing tens of km/s EIS blue shifts, the waves may co-exist with upflows, therefore, the upwards moving blobs are not necessary to be the upflows. I'll try to look for more examples to support my view. Thank you for your discussions.
Best Regards
Tongjiang
On Mon, 21 Dec 2009, Leon Golub wrote:
Dear Tongjiang,
This is exactly the "argument" I've been having for the past ten years, starting with Nakariakov in 1999. I've been waiting for the Doppler data since then, because where I see flows, other people see waves. I do think that the EIS results are now showing higher velocities of some tens of km/sec, and in TRACE the flows do start out slow at the footpoints, so there's no inconsistency with what you're saying about the speeds. There is a difference in that EIS sees the upflows at somewhat higher temperatures than we do with TRACE, and XRT sees them too, meaning higher T. I'm hoping that AIA will help sort this out.
What I can tell you is that when we see waves in the corona, they are quite clearly periodic and there's no doubt about it. Just look at any movie (with high time cadence) taken above sunspots: it looks like a loudspeaker pulsing away. These fans are different, and if you look closely at your time-distance plots, you'll see the lower portions curving upward, as the flows accelerate on their way up.
Leon
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Dear Leon and all,
It is interesting to see the reanimation of the discussion which I considered closed about 10 years ago :). There is a very clear observational evidence of the propagating slow magnetoacoustic waves in the magnetic fans above sunspots and other magnetic elements. The observed (or deduced) disbalance of the blue and red shifts can be explained by a number of causes, e.g. the stratification of the medium. Hopefully, AIA will shed some additional light on this issue.
Concerning the need for the separation of the "periodic upflows" (nonlinear waves?) and "waves" in the automated detection, I am not sure that such a separation is important. If detected, such phenomena attract our attention anyway. The main task of the automated detection is to process the data much faster than they are accumulated, not missing important events. In other words, in my opinion, automated detection software should not be meant to produce a research paper about the detected event, but to attract researcher's attention to it, specifying its spatial location and time interval. I believe that our periodmapping approach does it sufficiently well. (By the way, last week we applied it to the preprocessing of the TESIS data obtained with the Russian CORONAS-PHOTON satellite).
All the best,
Valery
-----Original Message----- From: loops-bounces@mithra.physics.montana.edu on behalf of Leon Golub Sent: Tue 22/12/2009 08:10 To: A mailing list for scientists involved in the observation and modeling ofsolar loop structures Subject: Re: [Loops] loops and thermal nonequilibrium
Dear Tongjiang,
I see that this subject is going to be debated for many years to come, which is good. We'll have to discuss this in person some time, where we show each other the observations and both be looking at the same thing. In particular, it is exactly in those fan-like features that we see the clearest flows, and indeed there is some question about the temperature. We need simultaneous observations, in the same spectral lines, with EIS and AIA. These should be available in a few months, once SDO launches. Since TRACE sees upflows at both ends of the large loop systems, it seems likely that there are interlaced loops (or threads) and that the flows go up warm and are cooler coming down. With low-resolution (~1") imaging, it would seem as if the blue shifts and red shifts are on top of each other, but this is an illusion cause by failure to resolve the different structures.
Leon
Tongjiang Wang wrote:
Dear Leon,
I just would like to remind you that the regions showing tens of km/s upflows seen in EIS coronal lines are typically for weak or dark fan structure in TRACE and XRT, while the propagating wave features are often seen in bright fan-like loops (like those shown in my paper, where the brighter part of fan loops show RED-SHFIT!). Indeed there are other EIS observations show bright fan-like loops show redshift while not blue shifts. Moreover, as you mentioned the steady flow is not possibly seen in imaging observations, that means that the moving brobs features correspond to episodic jets or pulsive flows, thus Doppler shift fluctuations of tens of km/s amplitudes are expected for a upflow of 100-120 km/s for fan-like loops with a typical inclination of 50-60 deg (see Marsh et al. 2009 who derived the inclination from STEREO/EUVI obs), but my study did not show this is the case. Finally, in the dark region showing tens of km/s EIS blue shifts, the waves may co-exist with upflows, therefore, the upwards moving blobs are not necessary to be the upflows. I'll try to look for more examples to support my view. Thank you for your discussions.
Best Regards
Tongjiang
On Mon, 21 Dec 2009, Leon Golub wrote:
Dear Tongjiang,
This is exactly the "argument" I've been having for the past ten years, starting with Nakariakov in 1999. I've been waiting for the Doppler data since then, because where I see flows, other people see waves. I do think that the EIS results are now showing higher velocities of some tens of km/sec, and in TRACE the flows do start out slow at the footpoints, so there's no inconsistency with what you're saying about the speeds. There is a difference in that EIS sees the upflows at somewhat higher temperatures than we do with TRACE, and XRT sees them too, meaning higher T. I'm hoping that AIA will help sort this out.
What I can tell you is that when we see waves in the corona, they are quite clearly periodic and there's no doubt about it. Just look at any movie (with high time cadence) taken above sunspots: it looks like a loudspeaker pulsing away. These fans are different, and if you look closely at your time-distance plots, you'll see the lower portions curving upward, as the flows accelerate on their way up.
Leon
_______________________________________________ Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Dear Valery,
I think that nothing has been settled at all, even now. I look forward to at least several more years of vigorous debate about this.
Leon Sent from my Verizon Wireless BlackBerry
-----Original Message----- From: "Nakariakov, Valery" V.Nakariakov@warwick.ac.uk Date: Wed, 23 Dec 2009 10:29:25 To: A mailing list for scientists involved in the observation and modeling ofsolar loop structuresloops@mithra.physics.montana.edu Subject: Re: [Loops] loops and thermal nonequilibrium
_______________________________________________ Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Leon and Tongjiang,
At the AGU Bart De Pontieu showed me very interesting data that indicate persistent blue-shifts at the basis of fan-like bundles of loops, in addition to "puffs" going up the legs of the same loops.
The interpretation seems obvious and is consistent with the previous emails. I have little to add to this since I am not so familiar with the data, but this will be interesting, and fairly easy in my opinion, to simulate with hydro codes.
What is important to me is that the signatures of oscillations that we detect with our feature finding codes could indicate any of the options discussed here: pure waves, puffs, oscillatory flows. So it is important that we label the output of our oscillation code correctly, not just as the detection of pure waves.
Is it lot of trouble to put together a web-site showing some of the best examples of the phenomena discussed here? That would certainly help modelers.
Cheers,
Piet
Leon Golub wrote:
Dear Gordon and Piet,
All I can contribute to this discussion is the observation that the flows are steady and continual, lasting for at least several days if not longer. The individual strands may come and go, but the overall structure of the fan only changes slowly. Meanwhile, the flows go on and on. My measurement (unpublished, sorry to say - long story) is that the flows increase in velocity, reaching up to 140 km/sec by the time they get to heights of ~10^5 km. After that they become too faint to see.
These are very long closed loops, about as near to being open structures as they can be and still be closed. I suspect that the material cools as it flows and it comes down at transition region temperatures. Going up, it's at ~1 MK in TRACE (Fe IX/X and Fe XII), probably hotter as seen in XRT. AIA should be able to see the cooler material (Fe VIII at 131A) and tell us if it's coming down.
So the puzzle in my mind is why we don't see the instabilities that you folks insist should be present. There are, of course, lumps in the flow; if there weren't then we would not be able to tell that anything is moving. But those start at the footpoints and move upward - they are, in fact, what we measure to determine the velocities.
Cheers,
Leon
Gordon Petrie wrote:
Dear Piet,
If I understand the steady isothermal theory correctly, the scale height can become unbounded wherever the flow approaches the sonic point, v -> c_s, because of a v^2-c_s^2 factor. Beyond a (generally different) critical point, v=sqrt(g_s Z_0) where g_s is the solar surface gravitational acceleration and Z_0 a length scale of the flux tube spatial expansion, mass conservation demands that the density invert.
Best regards,
Gordon
On Mon, 07 Dec 2009 10:11:07 -0700 Petrus Martens pmartens@cfa.harvard.edu wrote:
Gordon,
I agree with your comment. In fact, it is fairly easily shown directly from the momentum equation that flows up to the sound speed increase the pressure scale height by at most a factor two, when v~c_s, much less when v<c_s because the flow effect scales as (v/c_s)^2.
A really original solution as to why observed loops can be overdense near their apexes was presented by Craig Deforest in 2007. If the unresolved strands that make up the observed loop increase in cross- section from footpoints to apex an observer would conclude that the loop is overdense and has a scale height much larger than what follows from the loop temperature. In reality there is simply more emitting volume near the apex. Of course one has to explain why strands increase in cross-section, while the loops that they collectively form appear not to, but Craig shows some nice images in his paper that seem to support his suggestion.
There are ways to verify this from observations.
Cheers,
Piet
Gordon Petrie wrote:
Dear All,
In a basic model of steady, isothermal hydrodynamic flow (http://adsabs.harvard.edu/abs/2006ApJ...649.1078P), steady flows can only affect hydrostatic scale heights under exceptional conditions. These states have fast flows approaching the sound speed and form a small part of the solution space right next to unphysical regimes with density inversions. If significantly many loops really are of this kind, it would be an interesting problem explaining why. On the other hand, it's clear from rho*V*A why steady flows decrease densities.
Best regards,
Gordon
On Mon, 07 Dec 2009 09:11:07 -0500 Leon Golub golub@head.cfa.harvard.edu wrote:
Jim,
We were indeed modelling the long, relatively faint loops seen in the plage regions surrounding sunspots, which are exactly where EIS is seeing the flows. It's been known for a long time (the Palermo people did such modelling 20 years ago) that flows in coronal loops drop the density ("When you start a flow going, the loop disappears.") or alternatively, if you see the loop it means the density is enhanced. I'm not sure why your modelling failed, but we were able to reproduce the scale height quite well. Having the flow (in either direction) extends the emission scale height quite a bit beyond the hydrostatic value.
As you know, the AIA on SDO will have far more extensive temperature coverage than TRACE does. There is a puzzle right now in that EIS sees the flows at higher temperatures than we saw in TRACE. I think that this topic is going to be a major one in the coming years.
Leon
Klimchuk, James A. (GSFC-6710) wrote:
Wow, I'm surprised, and pleased, at the interest this paper has generated! Let me first respond to Leon's comment. As Harry said (thanks!), in order to get the extreme excess densities that are observed in most warm loops, the footpoint heating needs to be so concentrated that no equilibrium exists (which strictly speaking is different from an instability). Hence, thermal nonequilibrium. A few years back, Spiros P. and I addressed your suggestion with Amy that asymmetric heating and steady flows might explain the observations. Our modeling showed that the density enhancement was adequate to explain some loops, but the scale height is too small and the filter-ratio temperature profile is far too structured (paper attached). We thus rejected this explanation. Sorry!
Thanks for your comment, Jim
> -----Original Message----- > From: loops-bounces@solar.physics.montana.edu [mailto:loops- > bounces@solar.physics.montana.edu] On Behalf Of Harry Warren > Sent: Sunday, December 06, 2009 6:19 PM > To: A mailing list for scientists involved in the observation and > modeling of > solar loop structures > Subject: Re: [Loops] loops and thermal nonequilibrium > > > Leon, > > As I recall, your paper with Amy relied on footpoint heating, > which does > lead to higher apex densities and flatter temperature ratios. The > observed > densities near 1 MK are so high, however, that the loops become > thermodynamically unstable. Also, the high speed EIS flows are > typically > seen in faint regions and are not associated with the types of > loops that > Jim is attempting to model. > > Harry > > > On 12/5/09 3:16 PM, "Leon Golub" golub@cfa.harvard.edu wrote: > >> Jim, >> >> Amy and I addressed the issues of excess density, flat temperature >> profiles and large scale height about 10 years ago. Having flows of >> 30-40 km/sec, as is observed in TRACE and now verified by EIS, >> solves >> these problems quite nicely. So there is a viable mechanism >> other than >> nanoflares. >> >> Leon >> >> >> Klimchuk, James A. (GSFC-6710) wrote: >>> Dear Loops Friends, >>> >>> >>> >>> If you are interested, the attached paper shows that >>> coronal loops >>> cannot be explained by thermal nonequilibrium. The results >>> appear to >>> rule out the widespread existence of coronal heating that is >>> both highly >>> concentrated low in the corona and steady or quasi-steady (slowly >>> varying or impulsive with a rapid cadence). Comments are >>> welcomed. >>> >>> >>> >>> Best wishes, >>> >>> Jim >>> >>> >>> >>> > ************************************************************** > *************** >>> *** >>> >>> James A. Klimchuk >>> >>> NASA Goddard Space Flight Center >>> >>> Solar Physics Lab, Code 671 >>> >>> Bldg. 21, Rm. 158 >>> >>> Greenbelt, MD 20771 >>> >>> USA >>> >>> >>> >>> Phone: 1-301-286-9060 >>> >>> Fax: 1-301-286-7194 >>> >>> E-mail: James.A.Klimchuk@nasa.gov > mailto:James.A.Klimchuk@nasa.gov >>> Home page: >>> http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html >>> >>> >>> >>> > ************************************************************** > *************** >>> *** >>> >>> >>> >>> >>> ------------------------------------------------------------------------ >>> _______________________________________________ >>> Loops mailing list >>> Loops@solar.physics.montana.edu >>> https://mithra.physics.montana.edu/mailman/listinfo/loops >> _______________________________________________ >> Loops mailing list >> Loops@solar.physics.montana.edu >> https://mithra.physics.montana.edu/mailman/listinfo/loops > -- > // > --------------------------------------------------------------------- > > // Harry P. Warren phone : 202-404-1453 > // Naval Research Laboratory fax : 202-404-7997 > // Code 7673HW email : hwarren@nrl.navy.mil > // Washington, DC 20375 www : > http://tcrb.nrl.navy.mil/~hwarren > // > --------------------------------------------------------------------- > > > > > > > _______________________________________________ > Loops mailing list > Loops@solar.physics.montana.edu > https://mithra.physics.montana.edu/mailman/listinfo/loops _______________________________________________ Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
-- ______________________________________________________________________________ Leon Golub Smithsonian Astrophysical Observatory 60 Garden Street Cambridge, MA 02138 617 495 7177 FAX 496 7577 lgolub@cfa.harvard.edu ______________________________________________________________________________ _______________________________________________ Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
--
Piet Martens Tel: 617-496-7769 Center for Astrophysics Fax: 617-496-7577 60 Garden Street, MS 58 Cell: 617-999-0353 Cambridge, MA 02138 pmartens@cfa.harvard.edu
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Yes, we can certainly provide examples - movies, in this case.
Leon Sent from my Verizon Wireless BlackBerry
-----Original Message----- From: Petrus Martens pmartens@cfa.harvard.edu Date: Tue, 22 Dec 2009 08:51:34 To: A mailing list for scientists involved in the observation and modeling ofsolar loop structuresloops@mithra.physics.montana.edu Cc: petrie@email.noao.edu Subject: Re: [Loops] loops and thermal nonequilibrium
Leon and Tongjiang,
At the AGU Bart De Pontieu showed me very interesting data that indicate persistent blue-shifts at the basis of fan-like bundles of loops, in addition to "puffs" going up the legs of the same loops.
The interpretation seems obvious and is consistent with the previous emails. I have little to add to this since I am not so familiar with the data, but this will be interesting, and fairly easy in my opinion, to simulate with hydro codes.
What is important to me is that the signatures of oscillations that we detect with our feature finding codes could indicate any of the options discussed here: pure waves, puffs, oscillatory flows. So it is important that we label the output of our oscillation code correctly, not just as the detection of pure waves.
Is it lot of trouble to put together a web-site showing some of the best examples of the phenomena discussed here? That would certainly help modelers.
Cheers,
Piet
Leon Golub wrote:
Dear Gordon and Piet,
All I can contribute to this discussion is the observation that the flows are steady and continual, lasting for at least several days if not longer. The individual strands may come and go, but the overall structure of the fan only changes slowly. Meanwhile, the flows go on and on. My measurement (unpublished, sorry to say - long story) is that the flows increase in velocity, reaching up to 140 km/sec by the time they get to heights of ~10^5 km. After that they become too faint to see.
These are very long closed loops, about as near to being open structures as they can be and still be closed. I suspect that the material cools as it flows and it comes down at transition region temperatures. Going up, it's at ~1 MK in TRACE (Fe IX/X and Fe XII), probably hotter as seen in XRT. AIA should be able to see the cooler material (Fe VIII at 131A) and tell us if it's coming down.
So the puzzle in my mind is why we don't see the instabilities that you folks insist should be present. There are, of course, lumps in the flow; if there weren't then we would not be able to tell that anything is moving. But those start at the footpoints and move upward - they are, in fact, what we measure to determine the velocities.
Cheers,
Leon
Gordon Petrie wrote:
Dear Piet,
If I understand the steady isothermal theory correctly, the scale height can become unbounded wherever the flow approaches the sonic point, v -> c_s, because of a v^2-c_s^2 factor. Beyond a (generally different) critical point, v=sqrt(g_s Z_0) where g_s is the solar surface gravitational acceleration and Z_0 a length scale of the flux tube spatial expansion, mass conservation demands that the density invert.
Best regards,
Gordon
On Mon, 07 Dec 2009 10:11:07 -0700 Petrus Martens pmartens@cfa.harvard.edu wrote:
Gordon,
I agree with your comment. In fact, it is fairly easily shown directly from the momentum equation that flows up to the sound speed increase the pressure scale height by at most a factor two, when v~c_s, much less when v<c_s because the flow effect scales as (v/c_s)^2.
A really original solution as to why observed loops can be overdense near their apexes was presented by Craig Deforest in 2007. If the unresolved strands that make up the observed loop increase in cross- section from footpoints to apex an observer would conclude that the loop is overdense and has a scale height much larger than what follows from the loop temperature. In reality there is simply more emitting volume near the apex. Of course one has to explain why strands increase in cross-section, while the loops that they collectively form appear not to, but Craig shows some nice images in his paper that seem to support his suggestion.
There are ways to verify this from observations.
Cheers,
Piet
Gordon Petrie wrote:
Dear All,
In a basic model of steady, isothermal hydrodynamic flow (http://adsabs.harvard.edu/abs/2006ApJ...649.1078P), steady flows can only affect hydrostatic scale heights under exceptional conditions. These states have fast flows approaching the sound speed and form a small part of the solution space right next to unphysical regimes with density inversions. If significantly many loops really are of this kind, it would be an interesting problem explaining why. On the other hand, it's clear from rho*V*A why steady flows decrease densities.
Best regards,
Gordon
On Mon, 07 Dec 2009 09:11:07 -0500 Leon Golub golub@head.cfa.harvard.edu wrote:
Jim,
We were indeed modelling the long, relatively faint loops seen in the plage regions surrounding sunspots, which are exactly where EIS is seeing the flows. It's been known for a long time (the Palermo people did such modelling 20 years ago) that flows in coronal loops drop the density ("When you start a flow going, the loop disappears.") or alternatively, if you see the loop it means the density is enhanced. I'm not sure why your modelling failed, but we were able to reproduce the scale height quite well. Having the flow (in either direction) extends the emission scale height quite a bit beyond the hydrostatic value.
As you know, the AIA on SDO will have far more extensive temperature coverage than TRACE does. There is a puzzle right now in that EIS sees the flows at higher temperatures than we saw in TRACE. I think that this topic is going to be a major one in the coming years.
Leon
Klimchuk, James A. (GSFC-6710) wrote:
Wow, I'm surprised, and pleased, at the interest this paper has generated! Let me first respond to Leon's comment. As Harry said (thanks!), in order to get the extreme excess densities that are observed in most warm loops, the footpoint heating needs to be so concentrated that no equilibrium exists (which strictly speaking is different from an instability). Hence, thermal nonequilibrium. A few years back, Spiros P. and I addressed your suggestion with Amy that asymmetric heating and steady flows might explain the observations. Our modeling showed that the density enhancement was adequate to explain some loops, but the scale height is too small and the filter-ratio temperature profile is far too structured (paper attached). We thus rejected this explanation. Sorry!
Thanks for your comment, Jim
> -----Original Message----- > From: loops-bounces@solar.physics.montana.edu [mailto:loops- > bounces@solar.physics.montana.edu] On Behalf Of Harry Warren > Sent: Sunday, December 06, 2009 6:19 PM > To: A mailing list for scientists involved in the observation and > modeling of > solar loop structures > Subject: Re: [Loops] loops and thermal nonequilibrium > > > Leon, > > As I recall, your paper with Amy relied on footpoint heating, > which does > lead to higher apex densities and flatter temperature ratios. The > observed > densities near 1 MK are so high, however, that the loops become > thermodynamically unstable. Also, the high speed EIS flows are > typically > seen in faint regions and are not associated with the types of > loops that > Jim is attempting to model. > > Harry > > > On 12/5/09 3:16 PM, "Leon Golub" golub@cfa.harvard.edu wrote: > >> Jim, >> >> Amy and I addressed the issues of excess density, flat temperature >> profiles and large scale height about 10 years ago. Having flows of >> 30-40 km/sec, as is observed in TRACE and now verified by EIS, >> solves >> these problems quite nicely. So there is a viable mechanism >> other than >> nanoflares. >> >> Leon >> >> >> Klimchuk, James A. (GSFC-6710) wrote: >>> Dear Loops Friends, >>> >>> >>> >>> If you are interested, the attached paper shows that >>> coronal loops >>> cannot be explained by thermal nonequilibrium. The results >>> appear to >>> rule out the widespread existence of coronal heating that is >>> both highly >>> concentrated low in the corona and steady or quasi-steady (slowly >>> varying or impulsive with a rapid cadence). Comments are >>> welcomed. >>> >>> >>> >>> Best wishes, >>> >>> Jim >>> >>> >>> >>> > ************************************************************** > *************** >>> *** >>> >>> James A. Klimchuk >>> >>> NASA Goddard Space Flight Center >>> >>> Solar Physics Lab, Code 671 >>> >>> Bldg. 21, Rm. 158 >>> >>> Greenbelt, MD 20771 >>> >>> USA >>> >>> >>> >>> Phone: 1-301-286-9060 >>> >>> Fax: 1-301-286-7194 >>> >>> E-mail: James.A.Klimchuk@nasa.gov > mailto:James.A.Klimchuk@nasa.gov >>> Home page: >>> http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html >>> >>> >>> >>> > ************************************************************** > *************** >>> *** >>> >>> >>> >>> >>> ------------------------------------------------------------------------ >>> _______________________________________________ >>> Loops mailing list >>> Loops@solar.physics.montana.edu >>> https://mithra.physics.montana.edu/mailman/listinfo/loops >> _______________________________________________ >> Loops mailing list >> Loops@solar.physics.montana.edu >> https://mithra.physics.montana.edu/mailman/listinfo/loops > -- > // > --------------------------------------------------------------------- > > // Harry P. Warren phone : 202-404-1453 > // Naval Research Laboratory fax : 202-404-7997 > // Code 7673HW email : hwarren@nrl.navy.mil > // Washington, DC 20375 www : > http://tcrb.nrl.navy.mil/~hwarren > // > --------------------------------------------------------------------- > > > > > > > _______________________________________________ > Loops mailing list > Loops@solar.physics.montana.edu > https://mithra.physics.montana.edu/mailman/listinfo/loops _______________________________________________ Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
-- ______________________________________________________________________________ Leon Golub Smithsonian Astrophysical Observatory 60 Garden Street Cambridge, MA 02138 617 495 7177 FAX 496 7577 lgolub@cfa.harvard.edu ______________________________________________________________________________ _______________________________________________ Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
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Hi all,
I would just want to add to Leon's comment on cool downflows, that EIS/Hinode in its wide slit mode can make movies in a couple of transition region lines (Mg VI 269.0, Si VII 275.3) and we have in fact observed and recently reported (http://adsabs.harvard.edu/abs/2009ApJ...695..642U) downflows of 100km/s at those temperatures.
A short movie not included in the paper: http://tcrb.nrl.navy.mil/~iuu/out/offlimb/20071219_eis_slot_offlimb.mpeg
Cheers, Ignacio
Hi Leon,
A couple quick points of clarification....
Spiros and I were comparing models with the same peak temperature. In that case, shorter heating scale heights (greater footpoint concentration) produce higher densities because the amplitude of the heating must be increased to achieve the same peak temperature. You and Amy found the same thing.
I need to qualify my statement about the pressure scale height. The presence of a steady flow requires that the pressure scale height be smaller than the local gravitational scale height (at the local temperature). A smaller scale height means a larger pressure gradient, and you need a super-hydrostatic pressure gradient to accelerate the plasma in the upflowing leg and decelerate the plasma in the downflowing leg. Otherwise, it would be in force balance with gravity and the loop would be static. Things can get complicated when you compare static and steady flow loops because they have different temperature profiles, so the pressure gradient at a given position in the loop can be bigger in one or the other.
Cheers, Jim
-----Original Message----- From: loops-bounces@solar.physics.montana.edu [mailto:loops- bounces@solar.physics.montana.edu] On Behalf Of Leon Golub Sent: Monday, December 07, 2009 9:11 AM To: A mailing list for scientists involved in the observation and modeling of solar loop structures Subject: Re: [Loops] loops and thermal nonequilibrium
Jim,
We were indeed modelling the long, relatively faint loops seen in the plage regions surrounding sunspots, which are exactly where EIS is seeing the flows. It's been known for a long time (the Palermo people did such modelling 20 years ago) that flows in coronal loops drop the density ("When you start a flow going, the loop disappears.") or alternatively, if you see the loop it means the density is enhanced. I'm not sure why your modelling failed, but we were able to reproduce the scale height quite well. Having the flow (in either direction) extends the emission scale height quite a bit beyond the hydrostatic value.
As you know, the AIA on SDO will have far more extensive temperature coverage than TRACE does. There is a puzzle right now in that EIS sees the flows at higher temperatures than we saw in TRACE. I think that this topic is going to be a major one in the coming years.
Leon
Klimchuk, James A. (GSFC-6710) wrote:
Wow, I'm surprised, and pleased, at the interest this paper has generated!
Let me first respond to Leon's comment. As Harry said (thanks!), in order to get the extreme excess densities that are observed in most warm loops, the footpoint heating needs to be so concentrated that no equilibrium exists (which strictly speaking is different from an instability). Hence, thermal nonequilibrium. A few years back, Spiros P. and I addressed your suggestion with Amy that asymmetric heating and steady flows might explain the observations. Our modeling showed that the density enhancement was adequate to explain some loops, but the scale height is too small and the filter-ratio temperature profile is far too structured (paper attached). We thus rejected this explanation. Sorry!
Thanks for your comment, Jim
-----Original Message----- From: loops-bounces@solar.physics.montana.edu [mailto:loops- bounces@solar.physics.montana.edu] On Behalf Of Harry Warren Sent: Sunday, December 06, 2009 6:19 PM To: A mailing list for scientists involved in the observation and modeling of solar loop structures Subject: Re: [Loops] loops and thermal nonequilibrium
Leon,
As I recall, your paper with Amy relied on footpoint heating, which does lead to higher apex densities and flatter temperature ratios. The observed densities near 1 MK are so high, however, that the loops become thermodynamically unstable. Also, the high speed EIS flows are typically seen in faint regions and are not associated with the types of loops that Jim is attempting to model.
Harry
On 12/5/09 3:16 PM, "Leon Golub" golub@cfa.harvard.edu wrote:
Jim,
Amy and I addressed the issues of excess density, flat temperature profiles and large scale height about 10 years ago. Having flows of 30-40 km/sec, as is observed in TRACE and now verified by EIS, solves these problems quite nicely. So there is a viable mechanism other than nanoflares.
Leon
Klimchuk, James A. (GSFC-6710) wrote:
Dear Loops Friends,
If you are interested, the attached paper shows that coronal loops
cannot be explained by thermal nonequilibrium. The results appear to rule out the widespread existence of coronal heating that is both highly concentrated low in the corona and steady or quasi-steady (slowly varying or impulsive with a rapid cadence). Comments are welcomed.
Best wishes,
Jim
James A. Klimchuk
NASA Goddard Space Flight Center
Solar Physics Lab, Code 671
Bldg. 21, Rm. 158
Greenbelt, MD 20771
USA
Phone: 1-301-286-9060
Fax: 1-301-286-7194
E-mail: James.A.Klimchuk@nasa.gov
mailto:James.A.Klimchuk@nasa.gov
Home page:
http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html
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-- // --------------------------------------------------------------------- // Harry P. Warren phone : 202-404-1453 // Naval Research Laboratory fax : 202-404-7997 // Code 7673HW email : hwarren@nrl.navy.mil // Washington, DC 20375 www : http://tcrb.nrl.navy.mil/~hwarren // ---------------------------------------------------------------------
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-- ______________________________________________________________ ________________ Leon Golub Smithsonian Astrophysical Observatory 60 Garden Street Cambridge, MA 02138 617 495 7177 FAX 496 7577 lgolub@cfa.harvard.edu ______________________________________________________________ ________________ _______________________________________________ Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Oops, forgot to attach the paper. Here it is.
Jim
-----Original Message----- From: loops-bounces@solar.physics.montana.edu [mailto:loops- bounces@solar.physics.montana.edu] On Behalf Of Harry Warren Sent: Sunday, December 06, 2009 6:19 PM To: A mailing list for scientists involved in the observation and modeling of solar loop structures Subject: Re: [Loops] loops and thermal nonequilibrium
Leon,
As I recall, your paper with Amy relied on footpoint heating, which does lead to higher apex densities and flatter temperature ratios. The observed densities near 1 MK are so high, however, that the loops become thermodynamically unstable. Also, the high speed EIS flows are typically seen in faint regions and are not associated with the types of loops that Jim is attempting to model.
Harry
On 12/5/09 3:16 PM, "Leon Golub" golub@cfa.harvard.edu wrote:
Jim,
Amy and I addressed the issues of excess density, flat temperature profiles and large scale height about 10 years ago. Having flows of 30-40 km/sec, as is observed in TRACE and now verified by EIS, solves these problems quite nicely. So there is a viable mechanism other than nanoflares.
Leon
Klimchuk, James A. (GSFC-6710) wrote:
Dear Loops Friends,
If you are interested, the attached paper shows that coronal loops
cannot be explained by thermal nonequilibrium. The results appear to rule out the widespread existence of coronal heating that is both highly concentrated low in the corona and steady or quasi-steady (slowly varying or impulsive with a rapid cadence). Comments are welcomed.
Best wishes,
Jim
James A. Klimchuk
NASA Goddard Space Flight Center
Solar Physics Lab, Code 671
Bldg. 21, Rm. 158
Greenbelt, MD 20771
USA
Phone: 1-301-286-9060
Fax: 1-301-286-7194
E-mail: James.A.Klimchuk@nasa.gov
mailto:James.A.Klimchuk@nasa.gov
Home page: http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
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-- // --------------------------------------------------------------------- // Harry P. Warren phone : 202-404-1453 // Naval Research Laboratory fax : 202-404-7997 // Code 7673HW email : hwarren@nrl.navy.mil // Washington, DC 20375 www : http://tcrb.nrl.navy.mil/~hwarren // ---------------------------------------------------------------------
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Dear Jim
I have some comments. It looks like a nice piece of work, but as usual the conclusion that only nanoflares can help is hopelessly quixotic. You set up a strawman competing mechanism (why call it "thermal nonequilibrium" when the one-syllable alternative "flow" works as well?) and reject it on the basis of time scales. Who knows about the time scales of the driver of the flows?
The model itself seems highly questionable. I had cited its predecessor in trying to explain the "chewy nougat" observation of X- rays from prominences (http://adsabs.harvard.edu/abs/1999ApJ...513L.. 83H) but realized later on that the model has a very artificial low- temperature boundary and is thus not compelling. It is surprising to me that a decade later this has not changed, especially since it is just this boundary region in which the heating may be taking place.
To be perfectly clear about nanoflares: I do not think that there is any convincing observational evidence that they exist. It is a purely theoretical construct.
Cheers
Hugh
p.s. at the Hinode meeting just concluded, a nice poster by Helen Mason made it very clear that EIS spectra emphatically do not agree with the various XRT suggestions of a high-temperature component in the loop DEM. The discrepancy is an order of magnitude.
On 4 Dec 2009, at 14:04, Klimchuk, James A. (GSFC-6710) wrote:
Dear Loops Friends,
If you are interested, the attached paper shows that coronal
loops cannot be explained by thermal nonequilibrium. The results appear to rule out the widespread existence of coronal heating that is both highly concentrated low in the corona and steady or quasi- steady (slowly varying or impulsive with a rapid cadence). Comments are welcomed.
Best wishes, Jim
James A. Klimchuk NASA Goddard Space Flight Center Solar Physics Lab, Code 671 Bldg. 21, Rm. 158 Greenbelt, MD 20771 USA
Phone: 1-301-286-9060 Fax: 1-301-286-7194 E-mail: James.A.Klimchuk@nasa.gov Home page: http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html
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Hugh,
I think that Jim is using the term nanoflare a little more generally than usual. In this context it appears to refer to small-scale heating events and not specifically to the Parker model.
There is considerable consistency between steady heating models and observations of high temperature coronal plasma (I can send references if desired). Since no one has managed to propose a heating mechanism that is truly steady, it seems inevitable that we conclude that the coronal heating occurs on small spatial and temporal scales.
The difficult thing is to reconcile the success of steady heating at high temperatures with the non-equilibrium behavior observed at low temperatures. If Jim's modeling had proved successful, it would have lead to a more general description of the coronal heating mechanism. We would still left pondering the physical mechanism, however.
Harry
On 12/6/09 8:20 AM, "Hugh Hudson" hhudson@ssl.berkeley.edu wrote:
Dear Jim
I have some comments. It looks like a nice piece of work, but as usual the conclusion that only nanoflares can help is hopelessly quixotic. You set up a strawman competing mechanism (why call it "thermal nonequilibrium" when the one-syllable alternative "flow" works as well?) and reject it on the basis of time scales. Who knows about the time scales of the driver of the flows?
The model itself seems highly questionable. I had cited its predecessor in trying to explain the "chewy nougat" observation of X-rays from prominences (http://adsabs.harvard.edu/abs/1999ApJ...513L..83H) but realized later on that the model has a very artificial low-temperature boundary and is thus not compelling. It is surprising to me that a decade later this has not changed, especially since it is just this boundary region in which the heating may be taking place.
To be perfectly clear about nanoflares: I do not think that there is any convincing observational evidence that they exist. It is a purely theoretical construct.
Cheers
Hugh
p.s. at the Hinode meeting just concluded, a nice poster by Helen Mason made it very clear that EIS spectra emphatically do not agree with the various XRT suggestions of a high-temperature component in the loop DEM. The discrepancy is an order of magnitude.
On 4 Dec 2009, at 14:04, Klimchuk, James A. (GSFC-6710) wrote:
Dear Loops Friends,
If you are interested, the attached paper shows that coronal loops cannot
be explained by thermal nonequilibrium. The results appear to rule out the widespread existence of coronal heating that is both highly concentrated low in the corona and steady or quasi-steady (slowly varying or impulsive with a rapid cadence). Comments are welcomed.
Best wishes, Jim
James A. Klimchuk NASA Goddard Space Flight Center Solar Physics Lab, Code 671 Bldg. 21, Rm. 158 Greenbelt, MD 20771 USA
Phone: 1-301-286-9060 Fax: 1-301-286-7194 E-mail: James.A.Klimchuk@nasa.gov mailto:James.A.Klimchuk@nasa.gov Home page: http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html
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Hi Hugh,
Thanks also to you for your comments. Harry (thanks again!) is completely correct that my use of the term "nanoflare" simply means an impulsive energy release on a magnetic strand. There are many possible mechanisms that have this property, including waves. In fact, I do not know of a single mechanism that does not have this property under realistic conditions! Having said that, if the impulsive bursts repeat sufficiently rapidly on a given strand, the plasma conditions will not be greatly different from quasi-static. I'm confused by your suggestion that "flow" is the same as "thermal nonequilibrium." Flows can happen for many reasons, with varying effects on the loop properties. As I indicated in my response to Leon, steady flows cannot reproduce most observed warm loops, and neither can the flows associated with thermal nonequilibrium. Regarding nanoflares being a purely theoretical construct with no observational support, all I can say is that impulsive sub-resolution energy bursts are the only known way to explain the observed properties of warm loops (fan loops at the perimeters of active regions, of the type Leon has mentioned, may have an alternate explanation?). If you can point to a rigorous paper that offers another explanation, please let me know. As Harry stated, quasi-steady heating seems to be a valid explanation of hot loops. Impulsive heating (with long intervals between repeats in a given strand) may also be a valid explanation for these loops, although a lack of cospatial warm emission in the predicted quantities might rule this out. We still need to work out the numbers. I was interested to hear about Helen's EIS results and look forward to learning more. As you know, RHESSI observations are consistent with there being a weak super-hot component at the levels found by XRT and predicted by the nanoflare models. Kuen Ko and her colleagues at NRL found that the sensitivity of EIS to Ca XVII (one of the strongest hot lines in the EIS spectrum) is inadequate to prove or disprove nanoflares. The intensities predicted by the models are too weak. I'm not sure what to make of your comment about the low-temperature boundary in the models apparently negating the results in your view. We never claim to model the chromosphere in enough detail to compare with chromospheric observations. Our goal is to study the corona, and our model accurately treats the energetic and dynamic interaction between the corona and chromosphere (i.e., evaporation and condensation). Do you have some reason to believe that our treatment of the chromosphere adversely affects the coronal solution? If so, please explain in detail.
Thanks again for your interest, Jim
From: loops-bounces@solar.physics.montana.edu [mailto:loops-bounces@solar.physics.montana.edu] On Behalf Of Hugh Hudson Sent: Saturday, December 05, 2009 6:20 PM To: A mailing list for scientists involved in the observation and modeling of solar loop structures Subject: Re: [Loops] loops and thermal nonequilibrium
Dear Jim
I have some comments. It looks like a nice piece of work, but as usual the conclusion that only nanoflares can help is hopelessly quixotic. You set up a strawman competing mechanism (why call it "thermal nonequilibrium" when the one-syllable alternative "flow" works as well?) and reject it on the basis of time scales. Who knows about the time scales of the driver of the flows?
The model itself seems highly questionable. I had cited its predecessor in trying to explain the "chewy nougat" observation of X-rays from prominences (http://adsabs.harvard.edu/abs/1999ApJ...513L..83H) but realized later on that the model has a very artificial low-temperature boundary and is thus not compelling. It is surprising to me that a decade later this has not changed, especially since it is just this boundary region in which the heating may be taking place.
To be perfectly clear about nanoflares: I do not think that there is any convincing observational evidence that they exist. It is a purely theoretical construct.
Cheers
Hugh
p.s. at the Hinode meeting just concluded, a nice poster by Helen Mason made it very clear that EIS spectra emphatically do not agree with the various XRT suggestions of a high-temperature component in the loop DEM. The discrepancy is an order of magnitude.
On 4 Dec 2009, at 14:04, Klimchuk, James A. (GSFC-6710) wrote:
Dear Loops Friends,
If you are interested, the attached paper shows that coronal loops cannot be explained by thermal nonequilibrium. The results appear to rule out the widespread existence of coronal heating that is both highly concentrated low in the corona and steady or quasi-steady (slowly varying or impulsive with a rapid cadence). Comments are welcomed.
Best wishes, Jim
******************************************************************************** James A. Klimchuk NASA Goddard Space Flight Center Solar Physics Lab, Code 671 Bldg. 21, Rm. 158 Greenbelt, MD 20771 USA
Phone: 1-301-286-9060 Fax: 1-301-286-7194 E-mail: James.A.Klimchuk@nasa.govmailto:James.A.Klimchuk@nasa.gov Home page: http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html
********************************************************************************
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Dear Jim (et al),
there is no doubt that high temp emission (log T>6.7) can be seen in the hot dense core of the AR, however the EIS data do not show high temp emission (down to 3 orders of magnitude below the peak DEM) in the 'warm' loops. The XRT DEMs have large uncertainties. There seems to be some inconsistencies between EIS and XRT DEMs, but perhaps these might be resolved with the revised calibration presented at Hinode-3.
Best wishes, helen
Dear Helen Did you get some time to look at my EIS files on the AR 1026?
HAPPY NEW YEAR Brigitte
Dear Jim (et al),
there is no doubt that high temp emission (log T>6.7) can be seen in the hot dense core of the AR, however the EIS data do not show high temp emission (down to 3 orders of magnitude below the peak DEM) in the 'warm' loops. The XRT DEMs have large uncertainties. There seems to be some inconsistencies between EIS and XRT DEMs, but perhaps these might be resolved with the revised calibration presented at Hinode-3.
Best wishes, helen
--
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Hi all. I have a quick comment about DEMs because I worry that some of the earlier e-mails may have left a wrong impression. I've taken a look at Helen's DEM curves, and they are very much consistent with nanoflare heating. The DEM at logT = 6.7 is what many of the models predict. This does not prove nanoflare heating, but rather leaves it open as a possibility. Helen's much reduced DEM at logT = 7.1 suggests that the nanoflares cannot be exceptionally strong. I would caution, however, that ionization nonequilibrium effects are expected to be very important in the early stages of an event, and the true DEM may be much larger than what the observations suggest (as demonstrated by Steve and Fabio). I also want to give credit to Brendan O'Dwyer, Helen's student who is the lead author on the paper with these results.
Happy, healthy, and productive 2010 to all! Jim
-----Original Message----- From: loops-bounces@solar.physics.montana.edu [mailto:loops- bounces@solar.physics.montana.edu] On Behalf Of brigitte Schmieder Sent: Friday, January 08, 2010 11:26 AM To: A mailing list for scientists involved in the observation and modeling of solar loop structures Subject: Re: [Loops] EIS DEM for September 24-29 2010
Dear Helen Did you get some time to look at my EIS files on the AR 1026?
HAPPY NEW YEAR Brigitte
Dear Jim (et al),
there is no doubt that high temp emission (log T>6.7) can be seen in the hot dense core of the AR, however the EIS data do not show high temp emission (down to 3 orders of magnitude below the peak DEM) in the 'warm' loops. The XRT DEMs have large uncertainties. There seems to be some inconsistencies between EIS and XRT DEMs, but perhaps these might be resolved with the revised calibration presented at Hinode-3.
Best wishes, helen
--
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Further to Jim's email (below) and his comment concerning the importance of non-equilibrium ionisation states during the early stages of nanoflare-type heating; anyone wishing to examine its likely importance (or otherwise) to their own investigations are welcome to use a code I have recently developed for exactly this purpose. Full details are provided in:
Bradshaw, S.J., 2009, A&A (Suppl. Ser.), 502, 409 (http://adsabs.harvard.edu/abs/2009A%26A...502..409B).
Briefly: the user supplies tabulated electron temperature and density values as a function of time (could be from analytical / numerical models or observations) and the solver will return the evolution of the ionisation state for the element(s) of choice. It will run in just a few seconds on a standard desktop PC and the output can then be used to calculate quantities such as emission line intensities.
Just drop me an email if you would like a copy of the code.
Best wishes,
Steve
Dr Stephen J. Bradshaw
NASA Goddard Space Flight Center, Solar Physics Lab., Code 671, Greenbelt, MD 20771, USA.
Tel: 1-301-286-9682
Email: stephen.bradshaw@nasa.gov
-----Original Message----- From: loops-bounces@solar.physics.montana.edu [mailto:loops-bounces@solar.physics.montana.edu] On Behalf Of Klimchuk, James A. (GSFC-6710) Sent: Friday, January 08, 2010 2:48 PM To: A mailing list for scientists involved in the observation and modeling of solar loop structures Subject: Re: [Loops] EIS DEM for September 24-29 2010
Hi all. I have a quick comment about DEMs because I worry that some of the earlier e-mails may have left a wrong impression. I've taken a look at Helen's DEM curves, and they are very much consistent with nanoflare heating. The DEM at logT = 6.7 is what many of the models predict. This does not prove nanoflare heating, but rather leaves it open as a possibility. Helen's much reduced DEM at logT = 7.1 suggests that the nanoflares cannot be exceptionally strong. I would caution, however, that ionization nonequilibrium effects are expected to be very important in the early stages of an event, and the true DEM may be much larger than what the observations suggest (as demonstrated by Steve and Fabio). I also want to give credit to Brendan O'Dwyer, Helen's student who is the lead author on the paper with these results.
Happy, healthy, and productive 2010 to all! Jim
Stephen et al,
Further to the interesting discussion on non-equilibrium processes in the corona, I unashamedly advertise two relevant pieces of my own work:
1. the DIPER package which handles these (among other) things,
http://www.hao.ucar.edu/modeling/haos-diper/
(see the image displayed at this url).
2. a paper discussing the analytical evolution of atomic systems based upon an eigen-expansion. It enables one to understand how multi-level systems evolve and corrects some misconceptions in the literature:
"Understanding the time dependence of atomic level populations in evolving plasmas", Judge, P. G., Journal of Quantitative Spectroscopy and Radiative Transfer, 92, p. 479-510 (2005).
Best wishes
Philip Judge HAO.
Dear Helen, sorry for the delay of this reply, but I think that this discussion is very important: can you really really exclude a hot emission component down to 3 orders of magnitude below the highest signal in the UV band? Are uncertainties so small? What is the confidence of this result? Can you provide a quantitative upper limit? Is this result published and can you provide a reference (it is very important)? Best regards Fabio
Dear Jim (et al),
there is no doubt that high temp emission (log T>6.7) can be seen in the hot dense core of the AR, however the EIS data do not show high temp emission (down to 3 orders of magnitude below the peak DEM) in the 'warm' loops. The XRT DEMs have large uncertainties. There seems to be some inconsistencies between EIS and XRT DEMs, but perhaps these might be resolved with the revised calibration presented at Hinode-3.
Best wishes, helen
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Dear Fabio,
we are just awaiting acceptance of our paper O'Dwyer et al, and then Brendan (my grad student) will circulate it.
I'm in the Antarctic at the moment with very basic and intermittant email. I'll be back in Cambridge at the begining of Feb.
We are pretty confident in our results, but are looking to get more EIS datasets and carry out more analyses.
Best wishes, Helen
On Jan 13 2010, reale@astropa.unipa.it wrote:
Dear Helen, sorry for the delay of this reply, but I think that this discussion is very important: can you really really exclude a hot emission component down to 3 orders of magnitude below the highest signal in the UV band? Are uncertainties so small? What is the confidence of this result? Can you provide a quantitative upper limit? Is this result published and can you provide a reference (it is very important)? Best regards Fabio
Dear Jim (et al),
there is no doubt that high temp emission (log T>6.7) can be seen in the hot dense core of the AR, however the EIS data do not show high temp emission (down to 3 orders of magnitude below the peak DEM) in the 'warm' loops. The XRT DEMs have large uncertainties. There seems to be some inconsistencies between EIS and XRT DEMs, but perhaps these might be resolved with the revised calibration presented at Hinode-3.
Best wishes, helen
--
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Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Jim,
I find your paper a more convincing than Hugh. Still, a TRACE image or two to illustrate the morphology of the actual corona would be helpful.
Also, using "high frequency nanoflare" (or similar variants) as a synonym for "steady heating" is invariably confusing.
Finally, how much low temperature emission (less than ~ 5.5, for example) does the nanoflare model predict? If loops are cooling all of the way down we should see some transition region emission in the corona all the time over active regions. This seems like an analog of the "insufficient observed coronal rain" problem. Of course, it might be too faint to see considering how bright the transition region on the disk is.
Harry
On 12/5/09 7:04 AM, "Klimchuk, James A. (GSFC-6710)" james.a.klimchuk@nasa.gov wrote:
Dear Loops Friends,
If you are interested, the attached paper shows that coronal loops cannot
be explained by thermal nonequilibrium. The results appear to rule out the widespread existence of coronal heating that is both highly concentrated low in the corona and steady or quasi-steady (slowly varying or impulsive with a rapid cadence). Comments are welcomed.
Best wishes, Jim
** James A. Klimchuk NASA Goddard Space Flight Center Solar Physics Lab, Code 671 Bldg. 21, Rm. 158 Greenbelt, MD 20771 USA
Phone: 1-301-286-9060 Fax: 1-301-286-7194 E-mail: James.A.Klimchuk@nasa.gov mailto:James.A.Klimchuk@nasa.gov Home page: http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html
**
Dear Jim,
I read your paper with interest. You made a faithful attempt to explain five observed loop properties, which I really appreciate. The hydrodynamic simulations indeed show some puzzling condensation blobs that remain at stationary locations that seem not to correspond to observations. However, I have the impression that this puzzling effect, which you use as main argument that cooling loops are not consistent with observations, is an artifact of the perfect pressure balance in your model. When you watch TRACE movies, you will see that real coronal loops always evolve: sway, expand, twist, or shrink on time scales of an hour, which slowly changes the pressure balance along the loop and would move condensation blobs to one side. Loops are also always asymmetric, have diverging and converging cross-sections, which causes siphon flows and drains condensation blobs to one side. So, I think that the simulations are too idealized to tell us the long-term evolution. It is like balancing a ball on the Eiffeltower - an equilibrium solution is mathematically possible - but is impossible in reality, there are always vibrations or wind ... Perhaps you can repeat a simulation by superimposing some slowly-varying pressure disturbances, use a varying cross-section, and fill it by upflows from gentle chromospheric evaporation (more like in flares).
Cheers, Markus
On Dec 4, 2009, at 2:04 PM, Klimchuk, James A. (GSFC-6710) wrote:
Dear Loops Friends,
If you are interested, the attached paper shows that coronal loops cannot be explained by thermal nonequilibrium. The results appear to rule out the widespread existence of coronal heating that is both highly concentrated low in the corona and steady or quasi-steady (slowly varying or impulsive with a rapid cadence). Comments are welcomed.
Best wishes, Jim
James A. Klimchuk NASA Goddard Space Flight Center Solar Physics Lab, Code 671 Bldg. 21, Rm. 158 Greenbelt, MD 20771 USA
Phone: 1-301-286-9060 Fax: 1-301-286-7194 E-mail: James.A.Klimchuk@nasa.gov Home page: http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html
<klimchuk_submitted.pdf>_______________________________________________ Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
____________________________________________ Dr. Markus J. Aschwanden Solar & Astrophysics Laboratory Lockheed Martin Advanced Techology Center Org. ADBS, Bldg. 252 3251 Hanover St., Palo Alto, CA 94304, USA Phone: 650-424-4001, FAX: 650-424-3994 URL: http://www.lmsal.com/~aschwand/ e-mail: aschwanden@lmsal.com _______________________________________ ____________________________________
Hi Markus,
Maybe the paper wasn't clear, but all the simulations we present have asymmetric heating. That's what the asymmetry factor in the third column of the table refers to. The condensations are definitely not stationary, as we discuss in several places and can be clearly seen in Figure 1, for example. All of the condensations are eventually pushed to the chromosphere by a pressure imbalance. Also, there is evaporation happening during most of the evolution, as discussed on page 10, for instance. Please let me know if you need more details.
Thanks, Jim
From: loops-bounces@solar.physics.montana.edu [mailto:loops-bounces@solar.physics.montana.edu] On Behalf Of Markus J. Aschwanden Sent: Monday, December 07, 2009 4:47 PM To: A mailing list for scientists involved in the observation and modeling of solar loop structures Subject: Re: [Loops] loops and thermal nonequilibrium
Dear Jim,
I read your paper with interest. You made a faithful attempt to explain five observed loop properties, which I really appreciate. The hydrodynamic simulations indeed show some puzzling condensation blobs that remain at stationary locations that seem not to correspond to observations. However, I have the impression that this puzzling effect, which you use as main argument that cooling loops are not consistent with observations, is an artifact of the perfect pressure balance in your model. When you watch TRACE movies, you will see that real coronal loops always evolve: sway, expand, twist, or shrink on time scales of an hour, which slowly changes the pressure balance along the loop and would move condensation blobs to one side. Loops are also always asymmetric, have diverging and converging cross-sections, which causes siphon flows and drains condensation blobs to one side. So, I think that the simulations are too idealized to tell us the long-term evolution. It is like balancing a ball on the Eiffeltower - an equilibrium solution is mathematically possible - but is impossible in reality, there are always vibrations or wind ... Perhaps you can repeat a simulation by superimposing some slowly-varying pressure disturbances, use a varying cross-section, and fill it by upflows from gentle chromospheric evaporation (more like in flares).
Cheers, Markus
On Dec 4, 2009, at 2:04 PM, Klimchuk, James A. (GSFC-6710) wrote:
Dear Loops Friends,
If you are interested, the attached paper shows that coronal loops cannot be explained by thermal nonequilibrium. The results appear to rule out the widespread existence of coronal heating that is both highly concentrated low in the corona and steady or quasi-steady (slowly varying or impulsive with a rapid cadence). Comments are welcomed.
Best wishes, Jim
******************************************************************************** James A. Klimchuk NASA Goddard Space Flight Center Solar Physics Lab, Code 671 Bldg. 21, Rm. 158 Greenbelt, MD 20771 USA
Phone: 1-301-286-9060 Fax: 1-301-286-7194 E-mail: James.A.Klimchuk@nasa.govmailto:James.A.Klimchuk@nasa.gov Home page: http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html
********************************************************************************
<klimchuk_submitted.pdf>_______________________________________________ Loops mailing list Loops@solar.physics.montana.edumailto:Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
____________________________________________ Dr. Markus J. Aschwanden Solar & Astrophysics Laboratory Lockheed Martin Advanced Techology Center Org. ADBS, Bldg. 252 3251 Hanover St., Palo Alto, CA 94304, USA Phone: 650-424-4001, FAX: 650-424-3994 URL: http://www.lmsal.com/~aschwand/ e-mail: aschwanden@lmsal.commailto:aschwanden@lmsal.com _______________________________________ ____________________________________
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