Dear loops friends,
Here is a paper I wrote for the Hinode II conference proceedings. In it, I try to do three things: (1) review the arguments leading to the conclusion that warm EUV loops must by bundles of strands heated by storms of nanoflares (the flow chart some of you have asked about); (2) reconcile the isothermal/multi-thermal debate in terms of the duration of the nanoflare storm; and (3) address the possibility that loops can be explained by thermal nonequilibrium. Comments are welcomed.
Thanks,
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
************************************************************************ ********
Dear Hugh,
Jim Klimchuk sent a great summary of the current status of a nanoflare model around, so it deals with all the PROs. An outside reader who wants to hear both sides might be interested to hear also the CONs, which you could find in the ApJ Letter entitled "An observational test that disproves coronal nanoflare heating models" (Aschwanden 2008, ApJ 672, L135). The arguments made therein do not dismiss nanoflares altogether, but come to the conclusion that they occur in the transition region, rather than in the corona (as Parker originally suggested).
Cheers, Markus
On Mar 3, 2009, at 7:32 AM, Klimchuk, James A. (GSFC-6710) wrote:
Dear loops friends,
Here is a paper I wrote for the Hinode II conference
proceedings. In it, I try to do three things: (1) review the arguments leading to the conclusion that warm EUV loops must by bundles of strands heated by storms of nanoflares (the flow chart some of you have asked about); (2) reconcile the isothermal/multi- thermal debate in terms of the duration of the nanoflare storm; and (3) address the possibility that loops can be explained by thermal nonequilibrium. Comments are welcomed.
Thanks, James A. Klimchuk
____________________________________________ 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 _______________________________________ ____________________________________
Markus et al.,
It is unambiguous that there is a lot of dynamic activity going on in the transition region. However:
. . . a significant fraction of the Sun's magnetic flux closes at low heights (several Mm), so it is unclear how much of this activity is related to what we see in the corona.
. . . my impression of SOT magnetic field measurements is that active region plage (where many active region loops are rooted) is unipolar. It is hard to see how small-scale reconnection in the transition region could be important here. I could be wrong about this! I'm sure that an SOT person could provide a more definitive answer.
Best wishes,
Harry
// --------------------------------------------------------------------- // 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 // ---------------------------------------------------------------------
From: loops-bounces@mithra.physics.montana.edu [mailto:loops-bounces@mithra.physics.montana.edu] On Behalf Of Markus J. Aschwanden Sent: Thursday, March 05, 2009 10:16 AM To: Hugh Hudson; A mailing list for scientists involved in the observation and modeling of solar loop structures Subject: [Loops] summaries on nanoflare debates in "coronal loop workshops"
Dear Hugh,
Jim Klimchuk sent a great summary of the current status of a nanoflare model around, so it deals with all the PROs. An outside reader who wants to hear both sides might be interested to hear also the CONs, which you could find in the ApJ Letter entitled "An observational test that disproves coronal nanoflare heating models" (Aschwanden 2008, ApJ 672, L135). The arguments made therein do not dismiss nanoflares altogether, but come to the conclusion that they occur in the transition region, rather than in the corona (as Parker originally suggested).
Cheers, Markus
On Mar 3, 2009, at 7:32 AM, Klimchuk, James A. (GSFC-6710) wrote:
Dear loops friends, Here is a paper I wrote for the Hinode II conference proceedings. In it, I try to do three things: (1) review the arguments leading to the conclusion that warm EUV loops must by bundles of strands heated by storms of nanoflares (the flow chart some of you have asked about); (2) reconcile the isothermal/multi-thermal debate in terms of the duration of the nanoflare storm; and (3) address the possibility that loops can be explained by thermal nonequilibrium. Comments are welcomed. Thanks, James A. Klimchuk
____________________________________________ 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 _______________________________________ ____________________________________
Dear all, this is an interesting conversation. My tuppence: parker nanoflares work precisely in unipolar reasons, as it is the tangential stresses which are relaxed in the original parker scenario. The presence of multiple polarities changes this in a way which has never been quantitatively estimated. I would like to point you to the 2008/07 papers by Rappazzo and myself which I believe contain the only scalings for the Parker flt scenario which have numerical simulation confirmation.
@ARTICLE{2008ApJ...677.1348R, author = {{Rappazzo}, A.~F. and {Velli}, M. and {Einaudi}, G. and {Dahlburg}, R.~B. }, title = "{Nonlinear Dynamics of the Parker Scenario for Coronal Heating}", journal = {\apj}, archivePrefix = "arXiv", eprint = {0709.3687}, keywords = {Magnetohydrodynamics: MHD, Sun: Corona, Sun: Magnetic Fields, Turbulence}, year = 2008, month = apr, volume = 677, pages = {1348-1366}, doi = {10.1086/528786}, adsurl = {http://adsabs.harvard.edu/abs/2008ApJ...677.1348R }, adsnote = {Provided by the SAO/NASA Astrophysics Data System} }
On Mar 5, 2009, at 7:31 AM, Harry Warren wrote:
Markus et al.,
It is unambiguous that there is a lot of dynamic activity going on in the transition region. However:
. . . a significant fraction of the Sun's magnetic flux closes at low heights (several Mm), so it is unclear how much of this activity is related to what we see in the corona.
. . . my impression of SOT magnetic field measurements is that active region plage (where many active region loops are rooted) is unipolar. It is hard to see how small-scale reconnection in the transition region could be important here. I could be wrong about this! I'm sure that an SOT person could provide a more definitive answer.
Best wishes,
Harry
//
// 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 //
From: loops-bounces@mithra.physics.montana.edu [mailto:loops-bounces@mithra.physics.montana.edu] On Behalf Of Markus J. Aschwanden Sent: Thursday, March 05, 2009 10:16 AM To: Hugh Hudson; A mailing list for scientists involved in the observation and modeling of solar loop structures Subject: [Loops] summaries on nanoflare debates in "coronal loop workshops"
Dear Hugh,
Jim Klimchuk sent a great summary of the current status of a nanoflare model around, so it deals with all the PROs. An outside reader who wants to hear both sides might be interested to hear also the CONs, which you could find in the ApJ Letter entitled "An observational test that disproves coronal nanoflare heating models" (Aschwanden 2008, ApJ 672, L135). The arguments made therein do not dismiss nanoflares altogether, but come to the conclusion that they occur in the transition region, rather than in the corona (as Parker originally suggested).
Cheers, Markus
On Mar 3, 2009, at 7:32 AM, Klimchuk, James A. (GSFC-6710) wrote:
Dear loops friends,
Here is a paper I wrote for the Hinode II conference
proceedings. In it, I try to do three things: (1) review the arguments leading to the conclusion that warm EUV loops must by bundles of strands heated by storms of nanoflares (the flow chart some of you have asked about); (2) reconcile the isothermal/multi-thermal debate in terms of the duration of the nanoflare storm; and (3) address the possibility that loops can be explained by thermal nonequilibrium. Comments are welcomed.
Thanks, James A. Klimchuk
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 _______________________________________ ____________________________________
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
But many transition region explosive events are associated with flux cancelation . . . and (as Ignacio may have already pointed out) very few transition region explosive events are clearly associated with enhanced coronal emission . . .
// --------------------------------------------------------------------- // 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 // ---------------------------------------------------------------------
-----Original Message----- From: Marco Velli [mailto:velli@arcetri.astro.it] Sent: Thursday, March 05, 2009 10:42 AM To: hwarren@nrl.navy.mil; A mailing list for scientists involved in the observation and modeling of solar loop structures Subject: Re: [Loops] summaries on nanoflare debates in "coronal loop workshops"
Dear all, this is an interesting conversation. My tuppence: parker nanoflares work precisely in unipolar reasons, as it is the tangential stresses which are relaxed in the original parker scenario. The presence of multiple polarities changes this in a way which has never been quantitatively estimated. I would like to point you to the 2008/07 papers by Rappazzo and myself which I believe contain the only scalings for the Parker flt scenario which have numerical simulation confirmation.
@ARTICLE{2008ApJ...677.1348R, author = {{Rappazzo}, A.~F. and {Velli}, M. and {Einaudi}, G. and {Dahlburg}, R.~B. }, title = "{Nonlinear Dynamics of the Parker Scenario for Coronal Heating}", journal = {\apj}, archivePrefix = "arXiv", eprint = {0709.3687}, keywords = {Magnetohydrodynamics: MHD, Sun: Corona, Sun: Magnetic Fields, Turbulence}, year = 2008, month = apr, volume = 677, pages = {1348-1366}, doi = {10.1086/528786}, adsurl = {http://adsabs.harvard.edu/abs/2008ApJ...677.1348R }, adsnote = {Provided by the SAO/NASA Astrophysics Data System} }
On Mar 5, 2009, at 7:31 AM, Harry Warren wrote:
Markus et al.,
It is unambiguous that there is a lot of dynamic activity going on in the transition region. However:
. . . a significant fraction of the Sun's magnetic flux closes at low heights (several Mm), so it is unclear how much of this activity is related to what we see in the corona.
. . . my impression of SOT magnetic field measurements is that active region plage (where many active region loops are rooted) is unipolar. It is hard to see how small-scale reconnection in the transition region could be important here. I could be wrong about this! I'm sure that an SOT person could provide a more definitive answer.
Best wishes,
Harry
//
// 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 //
From: loops-bounces@mithra.physics.montana.edu [mailto:loops-bounces@mithra.physics.montana.edu] On Behalf Of Markus J. Aschwanden Sent: Thursday, March 05, 2009 10:16 AM To: Hugh Hudson; A mailing list for scientists involved in the observation and modeling of solar loop structures Subject: [Loops] summaries on nanoflare debates in "coronal loop workshops"
Dear Hugh,
Jim Klimchuk sent a great summary of the current status of a nanoflare model around, so it deals with all the PROs. An outside reader who wants to hear both sides might be interested to hear also the CONs, which you could find in the ApJ Letter entitled "An observational test that disproves coronal nanoflare heating models" (Aschwanden 2008, ApJ 672, L135). The arguments made therein do not dismiss nanoflares altogether, but come to the conclusion that they occur in the transition region, rather than in the corona (as Parker originally suggested).
Cheers, Markus
On Mar 3, 2009, at 7:32 AM, Klimchuk, James A. (GSFC-6710) wrote:
Dear loops friends,
Here is a paper I wrote for the Hinode II conference
proceedings. In it, I try to do three things: (1) review the arguments leading to the conclusion that warm EUV loops must by bundles of strands heated by storms of nanoflares (the flow chart some of you have asked about); (2) reconcile the isothermal/multi-thermal debate in terms of the duration of the nanoflare storm; and (3) address the possibility that loops can be explained by thermal nonequilibrium. Comments are welcomed.
Thanks, James A. Klimchuk
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 _______________________________________ ____________________________________
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Marco et al.,
this is an interesting conversation. My tuppence: parker nanoflares work precisely in unipolar reasons, as it is the tangential stresses which are relaxed in the original parker scenario.
Agreed, that is certainly what Parker described. The problem I have with the Parker scenario is: why loops? Why not a uniform distribution of nanoflares throughout the AR? "Why loops?" also applies to any mechanism that places the origin of the heating in the upper chromosphere or below.
Stick and slip reconnection along separators, a scenario that Dana Longcope has been working on for years, answers the "Why loops?" question seamlessly. I am aware of course that observational studies have so far found no clear relation between separators and loops, except in flaring loops. This may be a resolution issue, or an issue related to the large amount of horizontal flux missed in magnetograms. Or there is no such relation, in which case we are back where we started.
Cheers,
Piet
The presence of multiple polarities
changes this in a way which has never been quantitatively estimated. I would like to point you to the 2008/07 papers by Rappazzo and myself which I believe contain the only scalings for the Parker flt scenario which have numerical simulation confirmation.
@ARTICLE{2008ApJ...677.1348R, author = {{Rappazzo}, A.~F. and {Velli}, M. and {Einaudi}, G. and {Dahlburg}, R.~B. }, title = "{Nonlinear Dynamics of the Parker Scenario for Coronal Heating}", journal = {\apj}, archivePrefix = "arXiv", eprint = {0709.3687}, keywords = {Magnetohydrodynamics: MHD, Sun: Corona, Sun: Magnetic Fields, Turbulence}, year = 2008, month = apr, volume = 677, pages = {1348-1366}, doi = {10.1086/528786}, adsurl = {http://adsabs.harvard.edu/abs/2008ApJ...677.1348R }, adsnote = {Provided by the SAO/NASA Astrophysics Data System} }
On Mar 5, 2009, at 7:31 AM, Harry Warren wrote:
Markus et al.,
It is unambiguous that there is a lot of dynamic activity going on in the transition region. However:
. . . a significant fraction of the Sun's magnetic flux closes at low heights (several Mm), so it is unclear how much of this activity is related to what we see in the corona.
. . . my impression of SOT magnetic field measurements is that active region plage (where many active region loops are rooted) is unipolar. It is hard to see how small-scale reconnection in the transition region could be important here. I could be wrong about this! I'm sure that an SOT person could provide a more definitive answer.
Best wishes,
Harry
//
// 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 //
From: loops-bounces@mithra.physics.montana.edu [mailto:loops-bounces@mithra.physics.montana.edu] On Behalf Of Markus J. Aschwanden Sent: Thursday, March 05, 2009 10:16 AM To: Hugh Hudson; A mailing list for scientists involved in the observation and modeling of solar loop structures Subject: [Loops] summaries on nanoflare debates in "coronal loop workshops"
Dear Hugh,
Jim Klimchuk sent a great summary of the current status of a nanoflare model around, so it deals with all the PROs. An outside reader who wants to hear both sides might be interested to hear also the CONs, which you could find in the ApJ Letter entitled "An observational test that disproves coronal nanoflare heating models" (Aschwanden 2008, ApJ 672, L135). The arguments made therein do not dismiss nanoflares altogether, but come to the conclusion that they occur in the transition region, rather than in the corona (as Parker originally suggested).
Cheers, Markus
On Mar 3, 2009, at 7:32 AM, Klimchuk, James A. (GSFC-6710) wrote:
Dear loops friends,
Here is a paper I wrote for the Hinode II conference
proceedings. In it, I try to do three things: (1) review the arguments leading to the conclusion that warm EUV loops must by bundles of strands heated by storms of nanoflares (the flow chart some of you have asked about); (2) reconcile the isothermal/multi-thermal debate in terms of the duration of the nanoflare storm; and (3) address the possibility that loops can be explained by thermal nonequilibrium. Comments are welcomed.
Thanks, James A. Klimchuk
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 _______________________________________ ____________________________________
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
So many sage comments!
The Parker problem seems now to me too abstract to apply to real observations, for a couple of other reasons. First, at least for flares, I think it is wrong to think of the footpoint perturbations as "random" - the magnetic field is arguably following coherent marching orders from deep in the convection zone. So if the mathematics of "random" is important, that would be a flaw in the concept. Second, the analysis of coronal current systems really must involve consideration of what species carries the currents, and how the conductivity tensor varies through the medium. This seems to be the language of the magnetosphere, where people can directly sample the medium. So I'd relegate the Parker problem to being, well, interesting but abstract.
Hugh
On Mar 5, 2009, at 1:09 PM, Petrus Martens wrote:
Marco et al.,
this is an interesting conversation. My tuppence: parker nanoflares work precisely in unipolar reasons, as it is the tangential stresses which are relaxed in the original parker scenario.
Agreed, that is certainly what Parker described. The problem I have with the Parker scenario is: why loops? Why not a uniform distribution of nanoflares throughout the AR? "Why loops?" also applies to any mechanism that places the origin of the heating in the upper chromosphere or below.
Stick and slip reconnection along separators, a scenario that Dana Longcope has been working on for years, answers the "Why loops?" question seamlessly. I am aware of course that observational studies have so far found no clear relation between separators and loops, except in flaring loops. This may be a resolution issue, or an issue related to the large amount of horizontal flux missed in magnetograms. Or there is no such relation, in which case we are back where we started.
Cheers,
Piet
The presence of multiple polarities
changes this in a way which has never been quantitatively estimated. I would like to point you to the 2008/07 papers by Rappazzo and myself which I believe contain the only scalings for the Parker flt scenario which have numerical simulation confirmation.
@ARTICLE{2008ApJ...677.1348R, author = {{Rappazzo}, A.~F. and {Velli}, M. and {Einaudi}, G. and {Dahlburg}, R.~B. }, title = "{Nonlinear Dynamics of the Parker Scenario for Coronal Heating}", journal = {\apj}, archivePrefix = "arXiv", eprint = {0709.3687}, keywords = {Magnetohydrodynamics: MHD, Sun: Corona, Sun: Magnetic Fields, Turbulence}, year = 2008, month = apr, volume = 677, pages = {1348-1366}, doi = {10.1086/528786}, adsurl = {http:// adsabs.harvard.edu/abs/2008ApJ...677.1348R }, adsnote = {Provided by the SAO/NASA Astrophysics Data System} }
On Mar 5, 2009, at 7:31 AM, Harry Warren wrote:
Markus et al.,
It is unambiguous that there is a lot of dynamic activity going on in the transition region. However:
. . . a significant fraction of the Sun's magnetic flux closes at low heights (several Mm), so it is unclear how much of this activity is related to what we see in the corona.
. . . my impression of SOT magnetic field measurements is that active region plage (where many active region loops are rooted) is unipolar. It is hard to see how small-scale reconnection in the transition region could be important here. I could be wrong about this! I'm sure that an SOT person could provide a more definitive answer.
Best wishes,
Harry
//
// 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 //
From: loops-bounces@mithra.physics.montana.edu [mailto:loops-bounces@mithra.physics.montana.edu] On Behalf Of Markus J. Aschwanden Sent: Thursday, March 05, 2009 10:16 AM To: Hugh Hudson; A mailing list for scientists involved in the observation and modeling of solar loop structures Subject: [Loops] summaries on nanoflare debates in "coronal loop workshops"
Dear Hugh,
Jim Klimchuk sent a great summary of the current status of a nanoflare model around, so it deals with all the PROs. An outside reader who wants to hear both sides might be interested to hear also the CONs, which you could find in the ApJ Letter entitled "An observational test that disproves coronal nanoflare heating models" (Aschwanden 2008, ApJ 672, L135). The arguments made therein do not dismiss nanoflares altogether, but come to the conclusion that they occur in the transition region, rather than in the corona (as Parker originally suggested).
Cheers, Markus
On Mar 3, 2009, at 7:32 AM, Klimchuk, James A. (GSFC-6710) wrote:
Dear loops friends,
Here is a paper I wrote for the Hinode II conference
proceedings. In it, I try to do three things: (1) review the arguments leading to the conclusion that warm EUV loops must by bundles of strands heated by storms of nanoflares (the flow chart some of you have asked about); (2) reconcile the isothermal/multi-thermal debate in terms of the duration of the nanoflare storm; and (3) address the possibility that loops can be explained by thermal nonequilibrium. Comments are welcomed.
Thanks, James A. Klimchuk
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 _______________________________________ ____________________________________
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
+++++++++++++++++++++
In medias res hhudson@ssl.berkeley.edu +1 (510) 643-0333
AST:7731^29u18e3
Hugh,
The Parker problem seems now to me too abstract to apply to real observations, for a couple of other reasons. First, at least for flares, I think it is wrong to think of the footpoint perturbations as "random"
- the magnetic field is arguably following coherent marching orders from
deep in the convection zone. So if the mathematics of "random" is important, that would be a flaw in the concept
Hugh, I think that there is a miscommunication here. I only meant to say that in flares we have good evidence that the flaring loops coincide with separators. I didn't mean to imply that flares are caused by Parker's mechanism.
Second, the analysis of coronal current systems really must involve consideration of what species carries the currents, and how the conductivity tensor varies through the medium. This seems to be the language of the magnetosphere, where people can directly sample the medium. So I'd relegate the Parker problem to being, well, interesting but abstract.
I don't quite see the logical step from a to b. You still have to figure out what drives the currents before you can worry about what dissipates them, and Parker's model focuses on what drives them.
Cheers,
Piet
Hugh
On Mar 5, 2009, at 1:09 PM, Petrus Martens wrote:
Marco et al.,
this is an interesting conversation. My tuppence: parker nanoflares work precisely in unipolar reasons, as it is the tangential stresses which are relaxed in the original parker scenario.
Agreed, that is certainly what Parker described. The problem I have with the Parker scenario is: why loops? Why not a uniform distribution of nanoflares throughout the AR? "Why loops?" also applies to any mechanism that places the origin of the heating in the upper chromosphere or below.
Stick and slip reconnection along separators, a scenario that Dana Longcope has been working on for years, answers the "Why loops?" question seamlessly. I am aware of course that observational studies have so far found no clear relation between separators and loops, except in flaring loops. This may be a resolution issue, or an issue related to the large amount of horizontal flux missed in magnetograms. Or there is no such relation, in which case we are back where we started.
Cheers,
Piet
The presence of multiple polarities
changes this in a way which has never been quantitatively estimated. I would like to point you to the 2008/07 papers by Rappazzo and myself which I believe contain the only scalings for the Parker flt scenario which have numerical simulation confirmation.
@ARTICLE{2008ApJ...677.1348R, author = {{Rappazzo}, A.~F. and {Velli}, M. and {Einaudi}, G. and {Dahlburg}, R.~B. }, title = "{Nonlinear Dynamics of the Parker Scenario for Coronal Heating}", journal = {\apj}, archivePrefix = "arXiv", eprint = {0709.3687}, keywords = {Magnetohydrodynamics: MHD, Sun: Corona, Sun: Magnetic Fields, Turbulence}, year = 2008, month = apr, volume = 677, pages = {1348-1366}, doi = {10.1086/528786}, adsurl = {http://adsabs.harvard.edu/abs/2008ApJ...677.1348R }, adsnote = {Provided by the SAO/NASA Astrophysics Data System} }
On Mar 5, 2009, at 7:31 AM, Harry Warren wrote:
Markus et al.,
It is unambiguous that there is a lot of dynamic activity going on in the transition region. However:
. . . a significant fraction of the Sun's magnetic flux closes at low heights (several Mm), so it is unclear how much of this activity is related to what we see in the corona.
. . . my impression of SOT magnetic field measurements is that active region plage (where many active region loops are rooted) is unipolar. It is hard to see how small-scale reconnection in the transition region could be important here. I could be wrong about this! I'm sure that an SOT person could provide a more definitive answer.
Best wishes,
Harry
//
// Harry P. Warren phone : 202-404-1453 // Naval Research Laboratory fax : 202-404-7997 // Code 7673HW email : hwarren@nrl.navy.mil mailto:hwarren@nrl.navy.mil // Washington, DC 20375 www : http://tcrb.nrl.navy.mil/~hwarren //
From: loops-bounces@mithra.physics.montana.edu mailto:loops-bounces@mithra.physics.montana.edu [mailto:loops-bounces@mithra.physics.montana.edu] On Behalf Of Markus J. Aschwanden Sent: Thursday, March 05, 2009 10:16 AM To: Hugh Hudson; A mailing list for scientists involved in the observation and modeling of solar loop structures Subject: [Loops] summaries on nanoflare debates in "coronal loop workshops"
Dear Hugh,
Jim Klimchuk sent a great summary of the current status of a nanoflare model around, so it deals with all the PROs. An outside reader who wants to hear both sides might be interested to hear also the CONs, which you could find in the ApJ Letter entitled "An observational test that disproves coronal nanoflare heating models" (Aschwanden 2008, ApJ 672, L135). The arguments made therein do not dismiss nanoflares altogether, but come to the conclusion that they occur in the transition region, rather than in the corona (as Parker originally suggested).
Cheers, Markus
On Mar 3, 2009, at 7:32 AM, Klimchuk, James A. (GSFC-6710) wrote:
Dear loops friends,
Here is a paper I wrote for the Hinode II conference
proceedings. In it, I try to do three things: (1) review the arguments leading to the conclusion that warm EUV loops must by bundles of strands heated by storms of nanoflares (the flow chart some of you have asked about); (2) reconcile the isothermal/multi-thermal debate in terms of the duration of the nanoflare storm; and (3) address the possibility that loops can be explained by thermal nonequilibrium. Comments are welcomed.
Thanks, James A. Klimchuk
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 mailto:aschwanden@lmsal.com _______________________________________ ____________________________________
Loops mailing list Loops@solar.physics.montana.edu mailto:Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Loops mailing list Loops@solar.physics.montana.edu mailto: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
mailto:pmartens@cfa.harvard.edu
Loops mailing list Loops@solar.physics.montana.edu mailto:Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
+++++++++++++++++++++
In medias res hhudson@ssl.berkeley.edu mailto:hhudson@ssl.berkeley.edu +1 (510) 643-0333
AST:7731^29u18e3
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Some quick comments....
1. I agree with Markus and Marco that there is, in principle, no problem having impulsive heating (nanoflares) in the low atmosphere (chromosphere and transition region) of unipolar regions, as long as the field is "tangled." The resolvable events that Harry mentions are interesting and important, but different from ordinary coronal heating.
2. However, the transition region is an extremely thin layer that moves up and down flux tubes in response to changes in the coronal pressure resulting from heating and cooling. It is very difficult for me to see why the magnetic energy dissipation that gives rise to heating should always follow this layer. Dissipation in the thicker chromosphere is much easier to swallow.
3. The ten arguments that Markus gives in his paper are consistent with heating in the transition region, but they are also consistent with heating in the corona! Thus, they do not disprove coronal nanoflares. Perhaps we can discuss this in Florence. (Markus: I remember we went over some of this during a wonderful lunch with retsina on a patio in Santorini! How about if we cover the rest with chianti?).
Cheers,
Jim
________________________________
From: loops-bounces@solar.physics.montana.edu [mailto:loops-bounces@solar.physics.montana.edu] On Behalf Of Markus J. Aschwanden Sent: Thursday, March 05, 2009 10:16 AM To: Hugh Hudson; A mailing list for scientists involved in the observation and modelingof solar loop structures Subject: [Loops] summaries on nanoflare debates in "coronal loop workshops"
Dear Hugh,
Jim Klimchuk sent a great summary of the current status of a nanoflare model around,
so it deals with all the PROs. An outside reader who wants to hear both sides might be
interested to hear also the CONs, which you could find in the ApJ Letter entitled
"An observational test that disproves coronal nanoflare heating models" (Aschwanden
2008, ApJ 672, L135). The arguments made therein do not dismiss nanoflares
altogether, but come to the conclusion that they occur in the transition region,
rather than in the corona (as Parker originally suggested).
Cheers,
Markus
On Mar 3, 2009, at 7:32 AM, Klimchuk, James A. (GSFC-6710) wrote:
Dear loops friends,
Here is a paper I wrote for the Hinode II conference proceedings. In it, I try to do three things: (1) review the arguments leading to the conclusion that warm EUV loops must by bundles of strands heated by storms of nanoflares (the flow chart some of you have asked about); (2) reconcile the isothermal/multi-thermal debate in terms of the duration of the nanoflare storm; and (3) address the possibility that loops can be explained by thermal nonequilibrium. Comments are welcomed.
Thanks,
James A. Klimchuk
____________________________________________
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
_______________________________________
____________________________________
Jim Klimchuk wrote:
- However, the transition region is an extremely thin layer that
moves up and down flux tubes in response to changes in the coronal pressure resulting from heating and cooling. It is very difficult for me to see why the magnetic energy dissipation that gives rise to heating should always follow this layer. Dissipation in the thicker chromosphere is much easier to swallow.
Dear Jim,
Well, the transition region was only an extremely thin layer in old hydrostatic models, which nobody believes anymore. The current observations from TRACE, SoHO, and Hinode clearly show a highly dynamic transition region, which shows all kind of variabilities (including the ominous spicules and macrospicules) in a height range of h=2000-8000 km. Since the granular magneto-convection stirs up the magnetic field on horizontal scales of w~1000-2000 km, this is exactly the height range where you have most of the braiding, stressing, and reconnection, which is another plausibility argument for the most likely place of plasma heating that fills up the overlying corona. Of course, dissipation in the upper chromosphere is included, which provides all the mass for coronal filling with heated plasma.
Cheers, Markus
P.S. What Marco Velli alluded to, is most relevant for open-field regions such as coronal holes I gather. So we are talking about two different heating mechanisms for AR and solar wind.
____________________________________________ 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 _______________________________________
To clarify, I was referring to the transition region layer in a (likely sub-resolution) flux tube. This will be ultra thin, but the layers will occur at different heights in different flux tubes, so the transition region plasma will span a wide range of heights in a typical observation.
Jim
________________________________
From: loops-bounces@solar.physics.montana.edu [mailto:loops-bounces@solar.physics.montana.edu] On Behalf Of Markus J. Aschwanden Sent: Thursday, March 05, 2009 5:20 PM To: A mailing list for scientists involved in the observation and modeling ofsolar loop structures Subject: Re: [Loops] summaries on nanoflare debates in "coronal loopworkshops"
Jim Klimchuk wrote:
2. However, the transition region is an extremely thin layer that moves up and down flux tubes in response to changes in the coronal pressure resulting from heating and cooling. It is very difficult for me to see why the magnetic energy dissipation that gives rise to heating should always follow this layer. Dissipation in the thicker chromosphere is much easier to swallow.
Dear Jim,
Well, the transition region was only an extremely thin layer in old hydrostatic models, which nobody
believes anymore. The current observations from TRACE, SoHO, and Hinode clearly show a highly
dynamic transition region, which shows all kind of variabilities (including the ominous spicules and
macrospicules) in a height range of h=2000-8000 km. Since the granular magneto-convection
stirs up the magnetic field on horizontal scales of w~1000-2000 km, this is exactly the height range where
you have most of the braiding, stressing, and reconnection, which is another plausibility argument
for the most likely place of plasma heating that fills up the overlying corona. Of course, dissipation
in the upper chromosphere is included, which provides all the mass for coronal filling with heated
plasma.
Cheers,
Markus
P.S. What Marco Velli alluded to, is most relevant for open-field regions such as coronal holes
I gather. So we are talking about two different heating mechanisms for AR and solar wind.
____________________________________________
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
_______________________________________
Dear All,
A good example (I would say that...) of hot loops in locally unipolar regions as seen by SOT (that Harry mentioned) is video 4 in our paper: http://www.iop.org/EJ/article/1538-4357/689/1/L77/23039.html
It also shows that dynamic events in the chromosphere/transition region cluster around the active region neutral line in mixed flux regions. These are the resolvable events that Jim referred to that don't reach high temperatures.
Best wishes, David Brooks
Dear All, I have been away from coronal heating for a number of years, so I am asking for some guidance.
Here is my problem: The Parker model for heating relied heavily on energy storage throughout a coronal loop. In the absence of reconnection the field lines within a loop would become increasingly tangled: the free energy within a loop then increases as time squared, giving a power input increasing linearly with time. Throw in reconnection, and the system reaches a steady state at some saturation time t_sat. Here the heating power is linear in t_sat. Physically, t_sat tells you the time needed to stress the field up to levels where reconnection takes off, as in the secondary instabilities of Dahlburg, Linton and Antiochos. The curious thing is that the heating rate goes down if reconnection is more easy to trigger, because the saturation time is smaller for easy reconnection.
Having grown up with these ideas, it is difficult to reconcile myself with the newer observations suggesting the location of heating mostly at the base of loops. This causes two problems: first, is there enough volume of stressed field in the chromosphere/transition region to store the saturation level energy (yes, I know B is stronger down there, but still...). Secondly, reconnection may be too easy down there because of lower magnetic Reynolds numbers. Can someone convince me that you can still get 10^7 ergs/cm^2-sec active region heating rates?
Best Wishes Mitchell Berger
On Fri, Mar 6, 2009 at 2:13 AM, Brooks, David (Forn Natl) dhbrooks@ssd5.nrl.navy.mil wrote:
Dear All,
A good example (I would say that...) of hot loops in locally unipolar regions as seen by SOT (that Harry mentioned) is video 4 in our paper: http://www.iop.org/EJ/article/1538-4357/689/1/L77/23039.html
It also shows that dynamic events in the chromosphere/transition region cluster around the active region neutral line in mixed flux regions. These are the resolvable events that Jim referred to that don't reach high temperatures.
Best wishes, David Brooks
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Mitch,
Dear All, I have been away from coronal heating for a number of years, so I am asking for some guidance.
Here is my problem: The Parker model for heating relied heavily on energy storage throughout a coronal loop. In the absence of reconnection the field lines within a loop would become increasingly tangled: the free energy within a loop then increases as time squared, giving a power input increasing linearly with time. Throw in reconnection, and the system reaches a steady state at some saturation time t_sat. Here the heating power is linear in t_sat. Physically, t_sat tells you the time needed to stress the field up to levels where reconnection takes off, as in the secondary instabilities of Dahlburg, Linton and Antiochos. The curious thing is that the heating rate goes down if reconnection is more easy to trigger, because the saturation time is smaller for easy reconnection.
Yes, this has always been a fascinating result. If the energy release process were highly efficient, the corona would be much cooler. The process must have a "switch-on" property whereby it remains dormant while magnetic stresses build to substantial levels and then turns on. The nice thing about the secondary instability is that it occurs at the right level of stress to produce the observed temperatures and loss rates. (By the way, the secondary instability work is Dahlburg, KLIMCHUK, and Antiochos!!!) Note that this switch-on property is generic. It must apply to flares, CMEs, and any magnetically driven process.
Having grown up with these ideas, it is difficult to reconcile myself with the newer observations suggesting the location of heating mostly at the base of loops. This causes two problems: first, is there enough volume of stressed field in the chromosphere/transition region to store the saturation level energy (yes, I know B is stronger down there, but still...). Secondly, reconnection may be too easy down there because of lower magnetic Reynolds numbers. Can someone convince me that you can still get 10^7 ergs/cm^2-sec active region heating rates?
You raise a valid concern. The integral of B^2 over the transition region volume is small. Note that B is the shear component of the field, since we are interested in the free energy available to heat the plasma. One might be even more concerned about the chromosphere, which is also not very thick and which has much greater heating requirements. The situation there is helped by the fact that the field may be more highly concentrated in discrete flux tubes (at least in the low chromosphere). For a given magnetic flux, the volume integral of magnetic energy goes as one over the filling factor. Say we take a magnetic flux density of 100 G, a chromospheric thickness of 2x10^8 cm, and a filling factor of 10%. The energy per unit area is then 10^12 erg/cm^2. For the transition region (h ~ 2x10^7 cm, f ~ 1), the number is more like 10^10 erg/cm^2. To satisfy the coronal energy budget of 10^7 erg/cm^2/s^1 in active regions, the field must be "recharged" every 1000 s. Maybe this isn't so bad, since stresses can propagate down from the corona (ultimately they come from the photosphere motions).
Cheers, Jim
Best Wishes Mitchell Berger
On Fri, Mar 6, 2009 at 2:13 AM, Brooks, David (Forn Natl) dhbrooks@ssd5.nrl.navy.mil wrote:
Dear All,
A good example (I would say that...) of hot loops in locally
unipolar
regions as seen by SOT (that Harry mentioned) is video 4 in our paper: http://www.iop.org/EJ/article/1538-4357/689/1/L77/23039.html
It also shows that dynamic events in the chromosphere/transition
region
cluster around the active region neutral line in mixed flux regions. These
are the
resolvable events that Jim referred to that don't reach high
temperatures.
Best wishes, David Brooks
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
Jim, (By the way, the secondary instability work is Dahlburg, KLIMCHUK, and Antiochos!!!) Ooops!
So maybe it is possible that the place most favoured by the corona to relieve its stresses is at the base. Or maybe there is another possibility, that reconnections in the corona send jets of energetic particles downwards, where they boil the chromospheric material and send that material upwards. In this case, we might first observe what is happening at the chromosphere, because of the much greater densities there -- has this been ruled out? Cheers Mitch
Mitch,
Jim, (By the way, the secondary instability work is Dahlburg, KLIMCHUK, and Antiochos!!!) Ooops!
So maybe it is possible that the place most favoured by the corona to relieve its stresses is at the base. Or maybe there
Could be.
is another possibility, that reconnections in the corona send jets of energetic particles downwards, where they boil the chromospheric material and send that material upwards. In this case, we might first observe what is happening at the chromosphere, because of the much greater densities there -- has this been ruled out?
As far as I am aware, this is a viable possibility. I have simulated the situation where some of the energy released in the corona goes into nonthermal particles (the rest going into direct heating), but the particle beam produces "gentle" evaporation, not "explosive" evaporation, to use the terms of the flare people. I believe Trae Winter and Piet Martens may have worked on this, too.
By the way, I do NOT believe that observations necessarily point to low altitude heating. My view is that observations are consistent with both low altitude and high altitude heating. Perhaps this should be a topic for Loops IV.
Jim
Cheers Mitch _______________________________________________ Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
On Mar 6, 2009, at 8:44 AM, Klimchuk, James A. (GSFC-6710) wrote:
By the way, I do NOT believe that observations necessarily point to low altitude heating. My view is that observations are consistent with both low altitude and high altitude heating. Perhaps this should be a topic for Loops IV.
Jim
There is no way around to heat up first chromospheric material to fill coronal loops to produce the enhanced soft X-ray and EUV emission we see from coronal loops (like in flares). Any heating mechanism that heats directly in the corona, does not increase the local density, so we would not see any loops.
Markus
____________________________________________ 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 _______________________________________ ____________________________________
Markus, you are definitely right that all coronal material originates in the chromosphere. If the energy release (heating) occurs in the corona, a downward thermal conduction flux (and possibly also a downward flux of nonthermal particles) causes material to evaporate into the corona. That is the traditional view. What other people (including you?) are proposing is that the energy release occurs directly in the chromosphere or transition region, and this process both heats the cool plasma and injects it upward.
Jim
________________________________
From: loops-bounces@solar.physics.montana.edu [mailto:loops-bounces@solar.physics.montana.edu] On Behalf Of Markus J. Aschwanden Sent: Friday, March 06, 2009 11:52 AM To: A mailing list for scientists involved in the observation and modeling ofsolar loop structures Subject: Re: [Loops] summaries on nanoflare debates in "coronalloopworkshops"
On Mar 6, 2009, at 8:44 AM, Klimchuk, James A. (GSFC-6710) wrote:
By the way, I do NOT believe that observations necessarily point to low altitude heating. My view is that observations are consistent with both low altitude and high altitude heating. Perhaps this should be a topic for Loops IV.
Jim
There is no way around to heat up first chromospheric material to fill coronal
loops to produce the enhanced soft X-ray and EUV emission we see from
coronal loops (like in flares). Any heating mechanism that heats directly
in the corona, does not increase the local density, so we would not see
any loops.
Markus
____________________________________________
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
_______________________________________
____________________________________
Dear Jim,
Ok, we agree we need heating of chromospheric material to fill coronal loops (i.e. the well-established chromospheric evaporation scenario for flares), which is a kind of a secondary step. What we are not sure is where is the primary energy release that leads up to the chromospheric heating:
(1) Is it in coronal reconnection sites that produces precipitating particles/donward conduction like in flares? (2) Is it coronal nanoflares that could also produce precipitating particles and/or downward conduction? (3) Is it reconnection events in the chromosphere/transition region
Since I see a continous transition from high-lying reconnection regions in large flares to low-lying reconnection regions in microflares or EUV nanoflares, it appears natural to me that there is a continuouity from (1) to (3). But do we need case (2), which was postulated by Parker ? As long we do not have any observational measurements for case (2), it remains a theoretical construct. So, what observational diagnostics can people come up to test case (2) ?
Markus
On Mar 6, 2009, at 11:11 AM, Klimchuk, James A. (GSFC-6710) wrote:
Markus, you are definitely right that all coronal material originates in the chromosphere. If the energy release (heating) occurs in the corona, a downward thermal conduction flux (and possibly also a downward flux of nonthermal particles) causes material to evaporate into the corona. That is the traditional view. What other people (including you?) are proposing is that the energy release occurs directly in the chromosphere or transition region, and this process both heats the cool plasma and injects it upward.
Jim
From: loops-bounces@solar.physics.montana.edu [mailto:loops-bounces@solar.physics.montana.edu ] On Behalf Of Markus J. Aschwanden Sent: Friday, March 06, 2009 11:52 AM To: A mailing list for scientists involved in the observation and modeling ofsolar loop structures Subject: Re: [Loops] summaries on nanoflare debates in "coronalloopworkshops"
On Mar 6, 2009, at 8:44 AM, Klimchuk, James A. (GSFC-6710) wrote:
By the way, I do NOT believe that observations necessarily point to low altitude heating. My view is that observations are consistent with both low altitude and high altitude heating. Perhaps this should be a topic for Loops IV.
Jim
There is no way around to heat up first chromospheric material to fill coronal loops to produce the enhanced soft X-ray and EUV emission we see from coronal loops (like in flares). Any heating mechanism that heats directly in the corona, does not increase the local density, so we would not see any loops.
Markus
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 _______________________________________ ____________________________________
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 _______________________________________ ____________________________________
Dear All,
Hugh has an interesting suggestion about writing a critical and objective review. I think his unfailing identification of interested authors is an excellent first cut. Of course it needs to be discussed who is taking the responsibility to be first author, and who else would like to contribute (and become co-author by default). The first author should be somebody who is willing to sheperd and streamline such a job through all hurdles of writing and editing, carefully balancing different views and arguments of pros and cons, and organizing the review in a logical manner. The review by the Miller et al. Team (1997, JGR 102/A7, p.14631-14660) is an excellent role model. Please check it out with ADS, it shows a total citation count of 168 that steadily continues every year. As I remember, the team (Miller, Cargill, Emslie, Holman, Dennis, LaRosa, Winglee, Benka, Tsuneta) had a couple of meetings to sort out their conclusions, so it was very labor intense. But since we had already 3-4 workshops, it would be timely to tackle a similar critical assessment of the problem. The title could be very similar, such as "A critical assessment in the understanding of coronal loops". We should give this proposal serious consideration during the meeting in Florence.
Just some food for thoughts! Cheers,
Markus
Dear Markus
Well, this email thrash shows who is interested, I guess: Aschwanden, Brooks, Klimchuk, Berger, Hudson, Klimchuk, Martens, Poland, Velli, Warren... have I missed anybody? Maybe these people should be the authors of a "forced marriage" review along the lines of Miller et al. (1997) on particle acceleration.
Hugh
+++++++++++++++++++++
______________________________________ 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,
Just a quick response here....
________________________________
From: loops-bounces@solar.physics.montana.edu [mailto:loops-bounces@solar.physics.montana.edu] On Behalf Of Markus J. Aschwanden Sent: Friday, March 06, 2009 2:25 PM To: A mailing list for scientists involved in the observation and modeling ofsolar loop structures Subject: Re: [Loops] summaries on nanoflare debates in "coronalloopworkshops"
Dear Jim,
Ok, we agree we need heating of chromospheric material to fill coronal loops (i.e. the well-established
chromospheric evaporation scenario for flares), which is a kind of a secondary step. What we are not
sure is where is the primary energy release that leads up to the chromospheric heating:
(1) Is it in coronal reconnection sites that produces precipitating particles/donward conduction like in flares?
(2) Is it coronal nanoflares that could also produce precipitating particles and/or downward conduction?
(3) Is it reconnection events in the chromosphere/transition region
Since I see a continous transition from high-lying reconnection regions in large flares to low-lying
reconnection regions in microflares or EUV nanoflares, it appears natural to me that there is a
continuouity from (1) to (3). But do we need case (2), which was postulated by Parker ?
As long we do not have any observational measurements for case (2), it remains a
theoretical construct. So, what observational diagnostics can people come up to test case (2) ?
First, what is the difference between (1) and (2) other than the magnitude of the energy release? Having asked that, I would make the point that I see a fundamental difference between large erupting flares and smaller compact flares. The evolution of the magnetic field is completely different in the two cases.
I would argue that the observational evidence for (2) is stronger than the observational evidence for (3). However, in both cases the evidence might be thought of as circumstantial. It is quite easy to reproduce loop observations (at least EUV loops) in terms of bundles of strands heated by storms of nanoflares that occur in the corona. To my knowledge, no one has demonstrated that the observations can be reproduced by (3).
Have a nice weekend!
Jim
Markus
On Mar 6, 2009, at 11:11 AM, Klimchuk, James A. (GSFC-6710) wrote:
Markus, you are definitely right that all coronal material originates in the chromosphere. If the energy release (heating) occurs in the corona, a downward thermal conduction flux (and possibly also a downward flux of nonthermal particles) causes material to evaporate into the corona. That is the traditional view. What other people (including you?) are proposing is that the energy release occurs directly in the chromosphere or transition region, and this process both heats the cool plasma and injects it upward.
Jim
________________________________
From: loops-bounces@solar.physics.montana.edu [mailto:loops-bounces@solar.physics.montana.edu] On Behalf Of Markus J. Aschwanden Sent: Friday, March 06, 2009 11:52 AM To: A mailing list for scientists involved in the observation and modeling ofsolar loop structures Subject: Re: [Loops] summaries on nanoflare debates in "coronalloopworkshops"
On Mar 6, 2009, at 8:44 AM, Klimchuk, James A. (GSFC-6710) wrote:
By the way, I do NOT believe that observations necessarily point to low altitude heating. My view is that observations are consistent with both low altitude and high altitude heating. Perhaps this should be a topic for Loops IV.
Jim
There is no way around to heat up first chromospheric material to fill coronal
loops to produce the enhanced soft X-ray and EUV emission we see from
coronal loops (like in flares). Any heating mechanism that heats directly
in the corona, does not increase the local density, so we would not see
any loops.
Markus
____________________________________________
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
_______________________________________
____________________________________
_______________________________________________ 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 (and others),
it is very interesting for me to read all these debates about coronal heating, initiated this time by jim's nice paper. there is one point, however, i'd like to make that most of you do not seem to consider: waves.
i admit that wave heating suffered a bit of a set-back before the soho/trace era. even the initial wave observations by soho/trace did not help too much to promote the wave heating scenario(s), as most of the kink or longitudinal waves reported in loops had just a fraction of energy density needed for coronal radiation.
however, both hinode and very recent rosa observations have shown the omnipotent presence of mhd waves (and let's not go into the debate of alfvenic or kink at the moment as it is irrelevant from the heating perspectives) that have the necessary poyting flux to heat the lower atmosphere or corona. so, it is not just reconnection!
in fact, i still have not fully recovered myself from the very convincing and well-equipped review talk given by david berghmans at the iau gen assembly @ prague where he just "ruled out" the nanoflare concept.
i basically support the fundamental question markus raised below: "What we are not sure is where is the primary energy release that leads up to the chromospheric heating". but his list of options for an answer is far too incomplete, and i'm not even sure whether it captures the essence if waves are neglected. if (IF) we want to get closer to loop fine structure (multi-thread vs whatever) or uncover the operating heating function, a very promising and currently already availble way is of the one by magneto-seismology.
robertus
On Fri, 6 Mar 2009, Markus J. Aschwanden wrote:
Dear Jim,
Ok, we agree we need heating of chromospheric material to fill coronal loops (i.e. the well-established chromospheric evaporation scenario for flares), which is a kind of a secondary step. What we are not sure is where is the primary energy release that leads up to the chromospheric heating:
(1) Is it in coronal reconnection sites that produces precipitating particles/donward conduction like in flares? (2) Is it coronal nanoflares that could also produce precipitating particles and/or downward conduction? (3) Is it reconnection events in the chromosphere/transition region
Since I see a continous transition from high-lying reconnection regions in large flares to low-lying reconnection regions in microflares or EUV nanoflares, it appears natural to me that there is a continuouity from (1) to (3). But do we need case (2), which was postulated by Parker ? As long we do not have any observational measurements for case (2), it remains a theoretical construct. So, what observational diagnostics can people come up to test case (2) ?
Markus
On Mar 6, 2009, at 11:11 AM, Klimchuk, James A. (GSFC-6710) wrote:
Markus, you are definitely right that all coronal material originates in the chromosphere. If the energy release (heating) occurs in the corona, a downward thermal conduction flux (and possibly also a downward flux of nonthermal particles) causes material to evaporate into the corona. That is the traditional view. What other people (including you?) are proposing is that the energy release occurs directly in the chromosphere or transition region, and this process both heats the cool plasma and injects it upward.
Jim
From: loops-bounces@solar.physics.montana.edu [mailto:loops-bounces@solar.physics.montana.edu] On Behalf Of Markus J. Aschwanden Sent: Friday, March 06, 2009 11:52 AM To: A mailing list for scientists involved in the observation and modeling ofsolar loop structures Subject: Re: [Loops] summaries on nanoflare debates in "coronalloopworkshops"
On Mar 6, 2009, at 8:44 AM, Klimchuk, James A. (GSFC-6710) wrote:
By the way, I do NOT believe that observations necessarily point to low altitude heating. My view is that observations are consistent with both low altitude and high altitude heating. Perhaps this should be a topic for Loops IV.
Jim
There is no way around to heat up first chromospheric material to fill coronal loops to produce the enhanced soft X-ray and EUV emission we see from coronal loops (like in flares). Any heating mechanism that heats directly in the corona, does not increase the local density, so we would not see any loops.
Markus
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 _______________________________________ ____________________________________
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 Robertus, hi all,
however, both hinode and very recent rosa observations have shown the
omnipotent presence of mhd waves ... that have the necessary poyting flux to heat the lower atmosphere or corona. so, it is not just reconnection!
There are two important aspects, in my opinion: (a) even if the Poynting flux is sufficient, there also should be sufficiently effective mechanisms for the wave energy dissipation at a reasonable height. The efficiency of both phase mixing and RA is determined by the steepness of the transverse structuring of the waveguiding plasma structures.
Structuring is definitely an unknown parameter, as you've pointed out:
if (IF) we want to get closer to loop fine structure
(multi-thread vs whatever) or uncover the operating heating function, a very promising and currently already available way is of the one by magneto-seismology.
I agree. As I have mentioned in this forum before, there are several coronal seismological indications of the subresolution structuring of the corona. But, what is important is not only the spatial scale of structuring, but also the gradients of the plasma parameters.
(b) The amplitudes of the observed transverse waves are sufficiently high to produce a significant change of the magnetic field in the vicinity of the potential reconnection sites. Hence, the waves can effectively contribute to reconnection, and then the separation of "wave-based" and "reconnection-based" mechanisms for heating seems to be a bit too artificial.
All the best,
Valery
Valery and Robert,
Thanks for bringing up waves. I have two quick points.
1. The internal plasma structure of a loop (multi-stranded or not) is determined by the heating and cannot be decoupled from the wave dissipation (unless the wave is energetically insignificant). See Section 4.3 of the attached.
2. There may be different opinions of what is meant by "nanoflare." Some people define it to be an identifiable point-like brightening that probably occurs in a tiny bipole. Most loops modelers define it to be an impulsive energy release in a long and unresolved magnetic strand. It cannot be directly observed. With this definition, even resonant wave absorption produces nanoflare heating (also explained in Sections 4.3 and 4.2). I'm very curious about David Berghmans' talk and have my doubts about the conclusions!
Cheers,
Jim
________________________________
From: loops-bounces@solar.physics.montana.edu [mailto:loops-bounces@solar.physics.montana.edu] On Behalf Of Nakariakov, Valery Sent: Saturday, March 07, 2009 9:02 AM To: A mailing list for scientists involved in the observation and modeling ofsolar loop structures; A mailing list for scientists involved in the observation and modelingofsolar loop structures Subject: Re: [Loops] summaries on nanoflare debates in "coronalloopworkshops"
Hi Robertus, hi all,
however, both hinode and very recent rosa observations have shown the
omnipotent presence of mhd waves ... that have the necessary poyting flux to heat the lower atmosphere or corona. so, it is not just reconnection!
There are two important aspects, in my opinion: (a) even if the Poynting flux is sufficient, there also should be sufficiently effective mechanisms for the wave energy dissipation at a reasonable height. The efficiency of both phase mixing and RA is determined by the steepness of the transverse structuring of the waveguiding plasma structures.
Structuring is definitely an unknown parameter, as you've pointed out:
if (IF) we want to get closer to loop fine structure
(multi-thread vs whatever) or uncover the operating heating function, a very promising and currently already available way is of the one by magneto-seismology.
I agree. As I have mentioned in this forum before, there are several coronal seismological indications of the subresolution structuring of the corona. But, what is important is not only the spatial scale of structuring, but also the gradients of the plasma parameters.
(b) The amplitudes of the observed transverse waves are sufficiently high to produce a significant change of the magnetic field in the vicinity of the potential reconnection sites. Hence, the waves can effectively contribute to reconnection, and then the separation of "wave-based" and "reconnection-based" mechanisms for heating seems to be a bit too artificial.
All the best,
Valery
Hi Jim,
I was talking about the waves with observed (relatively low, > 2 min) periods and low amplitudes, which are not likely to energetically contribute to heating, but are excellent diagnostics tools. They have already been used for this purpose and gave results which indicate the presence of fine (sub-resolution) structuring.
Concerning triggering of reconnection events by waves: it can be achieved by waves of relatively low amplitude and this option, I think, needs detailed attention.
Cheers,
Valery
-----Original Message----- From: loops-bounces@mithra.physics.montana.edu on behalf of Klimchuk, James A. (GSFC-6710) Sent: Mon 09/03/2009 17:02 To: A mailing list for scientists involved in the observation andmodeling ofsolar loop structures; A mailing list for scientists involved in the observation and modelingofsolar loop structures Subject: Re: [Loops] summaries on nanoflare debates in "coronalloopworkshops"
Valery and Robert,
Thanks for bringing up waves. I have two quick points.
1. The internal plasma structure of a loop (multi-stranded or not) is determined by the heating and cannot be decoupled from the wave dissipation (unless the wave is energetically insignificant). See Section 4.3 of the attached.
2. There may be different opinions of what is meant by "nanoflare." Some people define it to be an identifiable point-like brightening that probably occurs in a tiny bipole. Most loops modelers define it to be an impulsive energy release in a long and unresolved magnetic strand. It cannot be directly observed. With this definition, even resonant wave absorption produces nanoflare heating (also explained in Sections 4.3 and 4.2). I'm very curious about David Berghmans' talk and have my doubts about the conclusions!
Cheers,
Jim
________________________________
From: loops-bounces@solar.physics.montana.edu [mailto:loops-bounces@solar.physics.montana.edu] On Behalf Of Nakariakov, Valery Sent: Saturday, March 07, 2009 9:02 AM To: A mailing list for scientists involved in the observation and modeling ofsolar loop structures; A mailing list for scientists involved in the observation and modelingofsolar loop structures Subject: Re: [Loops] summaries on nanoflare debates in "coronalloopworkshops"
Hi Robertus, hi all,
however, both hinode and very recent rosa observations have shown the
omnipotent presence of mhd waves ... that have the necessary poyting flux to heat the lower atmosphere or corona. so, it is not just reconnection!
There are two important aspects, in my opinion: (a) even if the Poynting flux is sufficient, there also should be sufficiently effective mechanisms for the wave energy dissipation at a reasonable height. The efficiency of both phase mixing and RA is determined by the steepness of the transverse structuring of the waveguiding plasma structures.
Structuring is definitely an unknown parameter, as you've pointed out:
if (IF) we want to get closer to loop fine structure
(multi-thread vs whatever) or uncover the operating heating function, a very promising and currently already available way is of the one by magneto-seismology.
I agree. As I have mentioned in this forum before, there are several coronal seismological indications of the subresolution structuring of the corona. But, what is important is not only the spatial scale of structuring, but also the gradients of the plasma parameters.
(b) The amplitudes of the observed transverse waves are sufficiently high to produce a significant change of the magnetic field in the vicinity of the potential reconnection sites. Hence, the waves can effectively contribute to reconnection, and then the separation of "wave-based" and "reconnection-based" mechanisms for heating seems to be a bit too artificial.
All the best,
Valery
Sounds good!
Jim
________________________________
From: loops-bounces@solar.physics.montana.edu [mailto:loops-bounces@solar.physics.montana.edu] On Behalf Of Nakariakov, Valery Sent: Monday, March 09, 2009 1:29 PM To: A mailing list for scientists involved in the observation and modeling ofsolar loop structures; A mailing list for scientists involved in the observation andmodelingofsolar loop structures; A mailing list for scientists involved in the observation andmodelingofsolar loop structures Subject: Re: [Loops] summaries on nanoflare debates in "coronalloopworkshops"
Hi Jim,
I was talking about the waves with observed (relatively low, > 2 min) periods and low amplitudes, which are not likely to energetically contribute to heating, but are excellent diagnostics tools. They have already been used for this purpose and gave results which indicate the presence of fine (sub-resolution) structuring.
Concerning triggering of reconnection events by waves: it can be achieved by waves of relatively low amplitude and this option, I think, needs detailed attention.
Cheers,
Valery
-----Original Message----- From: loops-bounces@mithra.physics.montana.edu on behalf of Klimchuk, James A. (GSFC-6710) Sent: Mon 09/03/2009 17:02 To: A mailing list for scientists involved in the observation andmodeling ofsolar loop structures; A mailing list for scientists involved in the observation and modelingofsolar loop structures Subject: Re: [Loops] summaries on nanoflare debates in "coronalloopworkshops"
Valery and Robert,
Thanks for bringing up waves. I have two quick points.
1. The internal plasma structure of a loop (multi-stranded or not) is determined by the heating and cannot be decoupled from the wave dissipation (unless the wave is energetically insignificant). See Section 4.3 of the attached.
2. There may be different opinions of what is meant by "nanoflare." Some people define it to be an identifiable point-like brightening that probably occurs in a tiny bipole. Most loops modelers define it to be an impulsive energy release in a long and unresolved magnetic strand. It cannot be directly observed. With this definition, even resonant wave absorption produces nanoflare heating (also explained in Sections 4.3 and 4.2). I'm very curious about David Berghmans' talk and have my doubts about the conclusions!
Cheers,
Jim
________________________________
From: loops-bounces@solar.physics.montana.edu [mailto:loops-bounces@solar.physics.montana.edu] On Behalf Of Nakariakov, Valery Sent: Saturday, March 07, 2009 9:02 AM To: A mailing list for scientists involved in the observation and modeling ofsolar loop structures; A mailing list for scientists involved in the observation and modelingofsolar loop structures Subject: Re: [Loops] summaries on nanoflare debates in "coronalloopworkshops"
Hi Robertus, hi all,
however, both hinode and very recent rosa observations have shown the
omnipotent presence of mhd waves ... that have the necessary poyting flux to heat the lower atmosphere or corona. so, it is not just reconnection!
There are two important aspects, in my opinion: (a) even if the Poynting flux is sufficient, there also should be sufficiently effective mechanisms for the wave energy dissipation at a reasonable height. The efficiency of both phase mixing and RA is determined by the steepness of the transverse structuring of the waveguiding plasma structures.
Structuring is definitely an unknown parameter, as you've pointed out:
if (IF) we want to get closer to loop fine structure
(multi-thread vs whatever) or uncover the operating heating function, a very promising and currently already available way is of the one by magneto-seismology.
I agree. As I have mentioned in this forum before, there are several coronal seismological indications of the subresolution structuring of the corona. But, what is important is not only the spatial scale of structuring, but also the gradients of the plasma parameters.
(b) The amplitudes of the observed transverse waves are sufficiently high to produce a significant change of the magnetic field in the vicinity of the potential reconnection sites. Hence, the waves can effectively contribute to reconnection, and then the separation of "wave-based" and "reconnection-based" mechanisms for heating seems to be a bit too artificial.
All the best,
Valery
Dear all,
It seems to me that the heating is responsible for establishing the temperature profile of a coronal loop. Therefore, there is not much point in asking a-priori whether it occurs in the chromosphere, TR or corona. The crucial issue, I believe, is what are the conditions (magnetic AND plasma) BEFORE the onset of heating? i.e. field strengths, densities, etc. Once these have been established (with great difficulty, I suspect) then one may ask what is it about these conditions that leads to a particular height and / or spatial-scale preference for the heating mechanism. This may help to avoid the apparently messy necessity of specifying the location of the heating with reference to a particular temperature regime...
Regards,
Steve
Dr Stephen J. Bradshaw
NASA Goddard Space Flight Center Solar Physics Laboratory, Code 671 Greenbelt, MD 20771 USA
Tel: 1-301-286-9682
________________________________________ From: loops-bounces@solar.physics.montana.edu [loops-bounces@solar.physics.montana.edu] On Behalf Of Markus J. Aschwanden [aschwanden@lmsal.com] Sent: Friday, March 06, 2009 7:25 PM To: A mailing list for scientists involved in the observation and modeling of solar loop structures Subject: Re: [Loops] summaries on nanoflare debates in "coronalloopworkshops"
Dear Jim,
Ok, we agree we need heating of chromospheric material to fill coronal loops (i.e. the well-established chromospheric evaporation scenario for flares), which is a kind of a secondary step. What we are not sure is where is the primary energy release that leads up to the chromospheric heating:
(1) Is it in coronal reconnection sites that produces precipitating particles/donward conduction like in flares? (2) Is it coronal nanoflares that could also produce precipitating particles and/or downward conduction? (3) Is it reconnection events in the chromosphere/transition region
Since I see a continous transition from high-lying reconnection regions in large flares to low-lying reconnection regions in microflares or EUV nanoflares, it appears natural to me that there is a continuouity from (1) to (3). But do we need case (2), which was postulated by Parker ? As long we do not have any observational measurements for case (2), it remains a theoretical construct. So, what observational diagnostics can people come up to test case (2) ?
Markus
On Mar 6, 2009, at 11:11 AM, Klimchuk, James A. (GSFC-6710) wrote:
Markus, you are definitely right that all coronal material originates in the chromosphere. If the energy release (heating) occurs in the corona, a downward thermal conduction flux (and possibly also a downward flux of nonthermal particles) causes material to evaporate into the corona. That is the traditional view. What other people (including you?) are proposing is that the energy release occurs directly in the chromosphere or transition region, and this process both heats the cool plasma and injects it upward.
Jim
________________________________ From: loops-bounces@solar.physics.montana.edumailto:loops-bounces@solar.physics.montana.edu [mailto:loops-bounces@solar.physics.montana.edu] On Behalf Of Markus J. Aschwanden Sent: Friday, March 06, 2009 11:52 AM To: A mailing list for scientists involved in the observation and modeling ofsolar loop structures Subject: Re: [Loops] summaries on nanoflare debates in "coronalloopworkshops"
On Mar 6, 2009, at 8:44 AM, Klimchuk, James A. (GSFC-6710) wrote:
By the way, I do NOT believe that observations necessarily point to low altitude heating. My view is that observations are consistent with both low altitude and high altitude heating. Perhaps this should be a topic for Loops IV.
Jim
There is no way around to heat up first chromospheric material to fill coronal loops to produce the enhanced soft X-ray and EUV emission we see from coronal loops (like in flares). Any heating mechanism that heats directly in the corona, does not increase the local density, so we would not see any loops.
Markus
____________________________________________ 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 _______________________________________ ____________________________________
_______________________________________________ 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 _______________________________________ ____________________________________
"What is there before the flare?" - I attach a lightweight paper on this seldom-asked question.
Hugh

On Mar 6, 2009, at 2:41 PM, Bradshaw, Stephen J wrote:
Dear all,
It seems to me that the heating is responsible for establishing the temperature profile of a coronal loop. Therefore, there is not much point in asking a-priori whether it occurs in the chromosphere, TR or corona. The crucial issue, I believe, is what are the conditions (magnetic AND plasma) BEFORE the onset of heating? i.e. field strengths, densities, etc. Once these have been established (with great difficulty, I suspect) then one may ask what is it about these conditions that leads to a particular height and / or spatial- scale preference for the heating mechanism. This may help to avoid the apparently messy necessity of specifying the location of the heating with reference to a particular temperature regime...
Regards,
Steve
Dr Stephen J. Bradshaw
NASA Goddard Space Flight Center Solar Physics Laboratory, Code 671 Greenbelt, MD 20771 USA
Tel: 1-301-286-9682
From: loops-bounces@solar.physics.montana.edu [loops- bounces@solar.physics.montana.edu] On Behalf Of Markus J. Aschwanden [aschwanden@lmsal.com] Sent: Friday, March 06, 2009 7:25 PM To: A mailing list for scientists involved in the observation and modeling of solar loop structures Subject: Re: [Loops] summaries on nanoflare debates in "coronalloopworkshops"
Dear Jim,
Ok, we agree we need heating of chromospheric material to fill coronal loops (i.e. the well-established chromospheric evaporation scenario for flares), which is a kind of a secondary step. What we are not sure is where is the primary energy release that leads up to the chromospheric heating:
(1) Is it in coronal reconnection sites that produces precipitating particles/donward conduction like in flares? (2) Is it coronal nanoflares that could also produce precipitating particles and/or downward conduction? (3) Is it reconnection events in the chromosphere/transition region
Since I see a continous transition from high-lying reconnection regions in large flares to low-lying reconnection regions in microflares or EUV nanoflares, it appears natural to me that there is a continuouity from (1) to (3). But do we need case (2), which was postulated by Parker ? As long we do not have any observational measurements for case (2), it remains a theoretical construct. So, what observational diagnostics can people come up to test case (2) ?
Markus
On Mar 6, 2009, at 11:11 AM, Klimchuk, James A. (GSFC-6710) wrote:
Markus, you are definitely right that all coronal material originates in the chromosphere. If the energy release (heating) occurs in the corona, a downward thermal conduction flux (and possibly also a downward flux of nonthermal particles) causes material to evaporate into the corona. That is the traditional view. What other people (including you?) are proposing is that the energy release occurs directly in the chromosphere or transition region, and this process both heats the cool plasma and injects it upward.
Jim
From: loops-bounces@solar.physics.montana.edu<mailto:loops- bounces@solar.physics.montana.edu> [mailto:loops- bounces@solar.physics.montana.edu] On Behalf Of Markus J. Aschwanden Sent: Friday, March 06, 2009 11:52 AM To: A mailing list for scientists involved in the observation and modeling ofsolar loop structures Subject: Re: [Loops] summaries on nanoflare debates in "coronalloopworkshops"
On Mar 6, 2009, at 8:44 AM, Klimchuk, James A. (GSFC-6710) wrote:
By the way, I do NOT believe that observations necessarily point to low altitude heating. My view is that observations are consistent with both low altitude and high altitude heating. Perhaps this should be a topic for Loops IV.
Jim
There is no way around to heat up first chromospheric material to fill coronal loops to produce the enhanced soft X-ray and EUV emission we see from coronal loops (like in flares). Any heating mechanism that heats directly in the corona, does not increase the local density, so we would not see any loops.
Markus
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 _______________________________________ ____________________________________
Loops mailing list Loops@solar.physics.montana.edu<mailto: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 _______________________________________ ____________________________________
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
+++++++++++++++++++++
In medias res hhudson@ssl.berkeley.edu +1 (510) 643-0333
AST:7731^29u18e3
OK, I have to jump in, since there seems to be some confusion about this. Yes, the increase in coronal density comes up from the chromosphere. This has been known for decades and has been well-modeled, especially by the Palermo group. But it is entirely possible for the energy to be deposited in the corona, then travel down (relying on the ambient density) to be deposited and cause evaporation. The pattern of brightness variations that you see does, in fact, change depending on where in the loop the energy is deposited, and can be used to determine where it happened. By seeing how the loop brightens, you can tell where the energy deposition took place. See:
A Brightening Coronal Loop Observed by TRACE. II. Loop Modeling and Constraints on Heating Reale, F.; Peres, G.; Serio, S.; Betta, R. M.; DeLuca, E. E.; Golub, L. Astrophysical Journal, Volume 535, Issue 1, pp. 423-437.
Leon
Markus J. Aschwanden wrote:
On Mar 6, 2009, at 8:44 AM, Klimchuk, James A. (GSFC-6710) wrote:
By the way, I do NOT believe that observations necessarily point to low altitude heating. My view is that observations are consistent with both low altitude and high altitude heating. Perhaps this should be a topic for Loops IV.
Jim
There is no way around to heat up first chromospheric material to fill coronal loops to produce the enhanced soft X-ray and EUV emission we see from coronal loops (like in flares). Any heating mechanism that heats directly in the corona, does not increase the local density, so we would not see any loops.
Markus
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 mailto:aschwanden@lmsal.com _______________________________________ ____________________________________
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
OK, I have to jump in, since there seems to be some confusion about this. Yes, the increase in coronal density comes up from the chromosphere. This has been known for decades and has been well-modeled, especially by the Palermo group. But it is entirely possible for the energy to be deposited in the corona, then travel down (relying on the ambient density) to be deposited and cause evaporation. The pattern of brightness variations that you see does, in fact, change depending on where in the loop the energy is deposited, and can be used to determine where it happened. By seeing how the loop brightens, you can tell where the energy deposition took place. See:
A Brightening Coronal Loop Observed by TRACE. II. Loop Modeling and Constraints on Heating Reale, F.; Peres, G.; Serio, S.; Betta, R. M.; DeLuca, E. E.; Golub, L. Astrophysical Journal, Volume 535, Issue 1, pp. 423-437, 05/2000.
Leon
Markus J. Aschwanden wrote:
On Mar 6, 2009, at 8:44 AM, Klimchuk, James A. (GSFC-6710) wrote:
By the way, I do NOT believe that observations necessarily point to low altitude heating. My view is that observations are consistent with both low altitude and high altitude heating. Perhaps this should be a topic for Loops IV.
Jim
There is no way around to heat up first chromospheric material to fill coronal loops to produce the enhanced soft X-ray and EUV emission we see from coronal loops (like in flares). Any heating mechanism that heats directly in the corona, does not increase the local density, so we would not see any loops.
Markus
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 mailto:aschwanden@lmsal.com _______________________________________ ____________________________________
Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Leon,
Dense as a brick... I am not replying to Markus' input anymore. You're right about our Italian friends though. Once I am done with tons of SDO-SC related organizing and resubmitting my loop paper, there is a whole sequence of papers with Trae on coronal loops and flares in queue.
Cheers,
Piet
Leon Golub wrote:
OK, I have to jump in, since there seems to be some confusion about this. Yes, the increase in coronal density comes up from the chromosphere. This has been known for decades and has been well-modeled, especially by the Palermo group. But it is entirely possible for the energy to be deposited in the corona, then travel down (relying on the ambient density) to be deposited and cause evaporation. The pattern of brightness variations that you see does, in fact, change depending on where in the loop the energy is deposited, and can be used to determine where it happened. By seeing how the loop brightens, you can tell where the energy deposition took place. See:
A Brightening Coronal Loop Observed by TRACE. II. Loop Modeling and Constraints on Heating Reale, F.; Peres, G.; Serio, S.; Betta, R. M.; DeLuca, E. E.; Golub, L. Astrophysical Journal, Volume 535, Issue 1, pp. 423-437, 05/2000.
Leon
Markus J. Aschwanden wrote:
On Mar 6, 2009, at 8:44 AM, Klimchuk, James A. (GSFC-6710) wrote:
By the way, I do NOT believe that observations necessarily point to low altitude heating. My view is that observations are consistent with both low altitude and high altitude heating. Perhaps this should be a topic for Loops IV.
Jim
There is no way around to heat up first chromospheric material to fill coronal loops to produce the enhanced soft X-ray and EUV emission we see from coronal loops (like in flares). Any heating mechanism that heats directly in the corona, does not increase the local density, so we would not see any loops.
Markus
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 mailto:aschwanden@lmsal.com _______________________________________ ____________________________________
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,
I apologize for my prior email. It was obviously not intended for public distribution. I'll just keep my mouth shut for a while, so you can continue a civilized debate among yourselves.
Best regards,
Piet
-------------------------------------------------------------------- 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 --------------------------------------------------------------------
From model calculations I have been doing in 2-D MHD with the Flash code it appears to me that you can deposit the heat in either the transition region or the corona and get pretty much the same result. Conduction has been done in a vector mode, only along the magnetic field lines. The field lines do get distorted some by the energy, but only a little. If the energy is deposited in the transition region, it rapidly "evaporates" the upper chromosphere and sends a visible structure into the corona. If the energy is deposited in the corona, it conducts down to the transition region with little loss and causes the same effect. The results are new, so I need to study them for more subtle differences. Art
Mitchell Berger wrote:
Jim, (By the way, the secondary instability work is Dahlburg, KLIMCHUK, and Antiochos!!!) Ooops!
So maybe it is possible that the place most favoured by the corona to relieve its stresses is at the base. Or maybe there is another possibility, that reconnections in the corona send jets of energetic particles downwards, where they boil the chromospheric material and send that material upwards. In this case, we might first observe what is happening at the chromosphere, because of the much greater densities there -- has this been ruled out? Cheers Mitch _______________________________________________ Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Art,
Neat!
little. If the energy is deposited in the transition region, it rapidly "evaporates" the upper chromosphere and sends a visible structure into the corona.
At what speed?
Piet
If the energy is deposited in the corona, it conducts down
to the transition region with little loss and causes the same effect. The results are new, so I need to study them for more subtle differences. Art
Mitchell Berger wrote:
Jim, (By the way, the secondary instability work is Dahlburg, KLIMCHUK, and Antiochos!!!) Ooops!
So maybe it is possible that the place most favoured by the corona to relieve its stresses is at the base. Or maybe there is another possibility, that reconnections in the corona send jets of energetic particles downwards, where they boil the chromospheric material and send that material upwards. In this case, we might first observe what is happening at the chromosphere, because of the much greater densities there -- has this been ruled out? Cheers Mitch _______________________________________________ Loops mailing list Loops@solar.physics.montana.edu https://mithra.physics.montana.edu/mailman/listinfo/loops
Surely the power input is dictated by the Poynting flux at the base, and so any saturation level of loop tangling has nothing to do with it? Otherwise one would have to be extracting energy out of the corona itself, rather than the convection zone.
Hugh
On Mar 6, 2009, at 8:12 AM, Klimchuk, James A. (GSFC-6710) wrote:
Mitch,
Dear All, I have been away from coronal heating for a number of years, so I am asking for some guidance.
Here is my problem: The Parker model for heating relied heavily on energy storage throughout a coronal loop. In the absence of reconnection the field lines within a loop would become increasingly tangled: the free energy within a loop then increases as time squared, giving a power input increasing linearly with time. Throw in reconnection, and the system reaches a steady state at some saturation time t_sat. Here the heating power is linear in t_sat. Physically, t_sat tells you the time needed to stress the field up to levels where reconnection takes off, as in the secondary instabilities of Dahlburg, Linton and Antiochos. The curious thing is that the heating rate goes down if reconnection is more easy to trigger, because the saturation time is smaller for easy reconnection.
Yes, this has always been a fascinating result. If the energy release process were highly efficient, the corona would be much cooler. The process must have a "switch-on" property whereby it remains dormant while magnetic stresses build to substantial levels and then turns on. The nice thing about the secondary instability is that it occurs at the right level of stress to produce the observed temperatures and loss rates. (By the way, the secondary instability work is Dahlburg, KLIMCHUK, and Antiochos!!!) Note that this switch-on property is generic. It must apply to flares, CMEs, and any magnetically driven process.
Having grown up with these ideas, it is difficult to reconcile myself with the newer observations suggesting the location of heating mostly at the base of loops. This causes two problems: first, is there enough volume of stressed field in the chromosphere/transition region to store the saturation level energy (yes, I know B is stronger down there, but still...). Secondly, reconnection may be too easy down there because of lower magnetic Reynolds numbers. Can someone convince me that you can still get 10^7 ergs/cm^2-sec active region heating rates?
You raise a valid concern. The integral of B^2 over the transition region volume is small. Note that B is the shear component of the field, since we are interested in the free energy available to heat the plasma. One might be even more concerned about the chromosphere, which is also not very thick and which has much greater heating requirements. The situation there is helped by the fact that the field may be more highly concentrated in discrete flux tubes (at least in the low chromosphere). For a given magnetic flux, the volume integral of magnetic energy goes as one over the filling factor. Say we take a magnetic flux density of 100 G, a chromospheric thickness of 2x10^8 cm, and a filling factor of 10%. The energy per unit area is then 10^12 erg/cm^2. For the transition region (h ~ 2x10^7 cm, f ~ 1), the number is more like 10^10 erg/cm^2. To satisfy the coronal energy budget of 10^7 erg/cm^2/s^1 in active regions, the field must be "recharged" every 1000 s. Maybe this isn't so bad, since stresses can propagate down from the corona (ultimately they come from the photosphere motions).
Cheers, Jim
Best Wishes Mitchell Berger
On Fri, Mar 6, 2009 at 2:13 AM, Brooks, David (Forn Natl) dhbrooks@ssd5.nrl.navy.mil wrote:
Dear All,
A good example (I would say that...) of hot loops in locally
unipolar
regions as seen by SOT (that Harry mentioned) is video 4 in our paper: http://www.iop.org/EJ/article/1538-4357/689/1/L77/23039.html
It also shows that dynamic events in the chromosphere/transition
region
cluster around the active region neutral line in mixed flux regions. These
are the
resolvable events that Jim referred to that don't reach high
temperatures.
Best wishes, David Brooks
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
+++++++++++++++++++++
In medias res hhudson@ssl.berkeley.edu +1 (510) 643-0333
AST:7731^29u18e3
Hugh, The saturation level of loop tangling determines the average transverse field strength. Also, I think the loop would presumably distribute its stored energy more or less evenly along its length. That means that the transverse field strength at the base of the loop is affected by the amount of loop tangling. The Poynting flux is proportional to V B_trans B_z, where V is the fluid velocity, B_z the vertical field, and B_trans the horizontal component of the field. The convection zone supplies V and adds some new B_trans, but the boundary conditions on the existing coronal field give you some B_trans as well. Mitch
On Fri, Mar 6, 2009 at 4:53 PM, Hugh Hudson hhudson@ssl.berkeley.edu wrote:
Surely the power input is dictated by the Poynting flux at the base, and so any saturation level of loop tangling has nothing to do with it? Otherwise one would have to be extracting energy out of the corona itself, rather than the convection zone. Hugh
loops@solar.physics.montana.edu