Dear Loopers,
Our paper, 'Evidence for Widespread Cooling in an Active Region Observed with the SDO Atmospheric Imaging Assembly' recently came out in ApJ: http://stacks.iop.org/0004-637X/753/35.
NASA did a really nice press release on it: http://svs.gsfc.nasa.gov/vis/a010000/a011000/a011046/ They made a video visualization of the technique we used, and to be honest, the video does a better job explaining the technique than I am able to do sometimes!
Cheers,
Nicki
**************
Nicholeen Viall
Code 671
NASA/Goddard Space Flight Center
Greenbelt, MD 20771
Email: Nicholeen.M.Viall(a)nasa.gov<https://mail02.ndc.nasa.gov/owa/UrlBlockedError.aspx>
Phone: 301-286-4054
Dear friends,
You might be interested in my recent paper on "The Role of Type II Spicules in the Upper Solar Atmosphere," which can be downloaded at http://arxiv.org/abs/1207.7048
Cheers,
Jim
ABSTRACT:
We examine the suggestion that most of the hot plasma in the Sun's
corona comes from type II spicule material that is heated as it is
ejected from the chromosphere. This contrasts with the traditional
view that the corona is filled via chromospheric evaporation that
results from coronal heating. We explore the observational
consequences of a hypothetical spicule dominated corona and conclude
from the large discrepancy between predicted and actual observations
that only a small fraction of the hot plasma can be supplied by
spicules (<2% in active regions and <5% in the quiet Sun). The
red-blue asymmetries of EUV spectral lines and the ratio of lower
transition region (LTR; T<0.1 MK) to coronal emission measures
are both predicted to be 2 orders of magnitude larger than observed.
Furthermore, hot spicule material would cool dramatically by
adiabatic expansion as it rises into the corona, so coronal heating
would be required to maintain the high temperatures that are seen at
all altitudes. The necessity of coronal heating is inescapable.
Traditional coronal heating models predict far too little emission
from the LTR, and we suggest that this emission comes primarily from
the bulk of the spicule material that is heated to <0.1 MK and
is visible in He II (304 A) as it falls back to the surface.
********************************************************************************
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(a)nasa.gov<mailto:James.A.Klimchuk@nasa.gov>
Homepage: https://sedupdate.gsfc.nasa.gov/sed/index.cfm?fuseAction=people.jumpBio&&iP…
No endorsement by NASA is implied for any correspondence related to my role as an officer of professional organizations (American Geophysical Union, International Astronomical Union, American Astronomical Society).
********************************************************************************
Hi Loopsters,
We enjoyed a very successful workshop in Mallorca. Many thanks to the SOC and LOC and especially to their chairs, Inaki Ugarte Urra and Jose Luis Ballester, respectively. These guys put in a lot of hard work.
We also thank Spiro Antiochos, Joan Schmelz, and Robert Walsh, whose terms on the Steering Committee are ending. Please send me nominations for their replacements, including self nominations. The Steering Committee will then vote from a list of candidates. (Spiro, Joan, and Robert are eligible to serve again.)
It's never too early to start planning for the next workshop, in 2 years. Please contact me if you are interested in hosting. We have some tentative offers already, but they are highly tentative at this time.
Best wishes,
Jim
********************************************************************************
James A. Klimchuk
NASA Goddard Space Flight Center
Solar Physics Lab, Code 671
Bldg. 21, Rm. 158
Greenbelt, MD 20771
USA
Phone: 1-301-286-9060
Fax: 1-301-286-7194
E-mail: James.A.Klimchuk(a)nasa.gov<mailto:James.A.Klimchuk@nasa.gov>
Home page: http://science.gsfc.nasa.gov/671/staff/bios/cs/James_Klimchuk_ssi.html
No endorsement by NASA is implied for any correspondence related to my role as an officer of professional organizations (American Geophysical Union, American Astronomical Society, International Astronomical Union).
********************************************************************************
Dear colleagues
please find at the following link the preprint of a work accepted
for publication in Astronomy & Astrophysics, showing the detection of a
minor but significant very hot (~ 7MK) component in quiescent active
regions, with the SphinX instrument on-board CORONAS-PHOTON:
http://arxiv.org/abs/1207.4665
This hot component is invariably present both at high and low emission
regimes, i.e. even excluding resolvable microflares.
The abstract is below.
Best regards
Fabio Reale
X-raying hot plasma in solar active regions with the SphinX spectrometer
M. Miceli, F. Reale, S. Gburek, S. Terzo, M. Barbera, A. Collura, J.
Sylwester, M. Kowalinski, P. Podgorski, M. Gryciuk
The detection of very hot plasma in the quiescent corona is important
for diagnosing heating mechanisms. The presence and the amount of such
hot plasma is currently debated. The SphinX instrument on-board
CORONAS-PHOTON mission is sensitive to X-ray emission well above 1 keV
and provides the opportunity to detect the hot plasma component. We
analyzed the X-ray spectra of the solar corona collected by the SphinX
spectrometer in May 2009 (when two active regions were present). We
modelled the spectrum extracted from the whole Sun over a time window of
17 days in the 1.34-7 keV energy band by adopting the latest release of
the APED database. The SphinX broadband spectrum cannot be modelled by a
single isothermal component of optically thin plasma and two components
are necessary. In particular, the high statistics and the accurate
calibration of the spectrometer allowed us to detect a very hot
component at ~7 million K with an emission measure of ~2.7 x 10^44
cm^-3. The X-ray emission from the hot plasma dominates the solar X-ray
spectrum above 4 keV. We checked that this hot component is invariably
present both at high and low emission regimes, i.e. even excluding
resolvable microflares. We also present and discuss a possible
non-thermal origin (compatible with a weak contribution from
thick-target bremsstrahlung) for this hard emission component. Our
results support the nanoflare scenario and might confirm that a minor
flaring activity is ever-present in the quiescent corona, as also
inferred for the coronae of other stars.
--
*****************************************************************************
Dr. Fabio Reale, Ph.D.
Professore Associato
Dipartimento di Fisica, Universita` di Palermo
P.za Parlamento 1, 90134 Palermo - ITALY
Tel: +39 091 233 237
Fax: +39 091 233 444
*****************************************************************************
I am pleased to announce that Susanna Parenti, Inaki Ugarte Urra, and Nicki Viall have been elected to the Coronal Loops Workshops Steering Committee to replace outgoing members Spiro Antiochos, Joan Schmelz, and Robert Walsh. In addition, Fabio Reale has been elected the new chair. The committee will now begin to evaluate the proposals we have received for hosting the summer 2013 workshop. Additional proposals are still 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(a)nasa.gov<mailto:James.A.Klimchuk@nasa.gov>
Homepage: https://sedupdate.gsfc.nasa.gov/sed/index.cfm?fuseAction=people.jumpBio&&iP…
No endorsement by NASA is implied for any correspondence related to my role as an officer of professional organizations (American Geophysical Union, International Astronomical Union, American Astronomical Society).
********************************************************************************
Dear All,
Please find at the following link the preprint of a work accepted for publication on the ApJ Letters on upflows in warm coronal loops.
http://www.iucaa.ernet.in/~durgesh/papers/accepted_version.pdf
The details are below:
Title: Observations of plasma upflow in a warm loop with Hinode/EIS
Authors: Durgesh Tripathi, Helen Mason, Giulio Del Zanna and Steve Bradshaw
Abstract: A complete understanding of Doppler shift in active region loops can help probe the basic physical mechanism involved into the heating of those loops. Here we present
observations of upflows in coronal loops detected in a range of temperature temperatures (log T = 5.8-6.2). The loop was not discernible above these temperatures. The speed of
upflow was strongest at the footpoint and decreased with height. The upflow speed at the footpoint was about 20 km/s in Fe VIII which decreased with temperature being about
13 km/s in Fe X, about 8 km/s in Fe XII and about 4 km/s in Fe XIII. To the best of our knowledge this is the first observation providing evidence of upflow of plasma in coronal
loop structures at these temperatures. We interpret these observations as evidence of chromospheric evaporation in quasi-static coronal loops.
Regards
-Durgesh
Dear colleagues
please find at the following link the preprint of a work accepted
for publication in Astronomy & Astrophysics, showing the importance of
updating the radiative losses on loop modeling, in particular on the
very late phases of pulse-heated loop evolution:
http://arxiv.org/abs/1205.4553
This work may help to understand, for instance, why we see much fewer
warm loops in active regions, than expected from a model of loop cooling
from a hotter status. Special thanks to Peter Cargill for useful
suggestions on the analytic part. Please contact me if you wish to have
a 2-column version of the preprint.
The abstract is below.
Best regards
Fabio Reale
The role of radiative losses in the late evolution of pulse-heated
coronal loops/strands
F. Reale, E. Landi
Abstract: Radiative losses from optically thin plasma are an important
ingredient for modeling plasma confined in the solar corona. Spectral
models are continuously updated to include the emission from more
spectral lines, with significant effects on radiative losses, especially
around 1 MK. We investigate the effect of changing the radiative losses
temperature dependence due to upgrading of spectral codes on predictions
obtained from modeling plasma confined in the solar corona. The
hydrodynamic simulation of a pulse-heated loop strand is revisited
comparing results using an old and a recent radiative losses function.
We find significant changes in the plasma evolution during the late
phases of plasma cooling: when the recent radiative loss curve is used,
the plasma cooling rate increases significantly when temperatures reach
1-2 MK. Such more rapid cooling occurs when the plasma density is larger
than a threshold value, and therefore in impulsive heating models that
cause the loop plasma to become overdense. The fast cooling has the
effect of steepening the slope of the emission measure distribution of
coronal plasmas with temperature at temperatures lower than ~2 MK. The
effects of changes in the radiative losses curves can be important for
modeling the late phases of the evolution of pulse-heated coronal loops,
and, more in general, of thermally unstable optically thin plasmas.
--
*****************************************************************************
Dr. Fabio Reale, Ph.D.
Professore Associato
Dipartimento di Fisica, Universita` di Palermo
P.za Parlamento 1, 90134 Palermo - ITALY
Tel: +39 091 233 237
Fax: +39 091 233 444
*****************************************************************************
Dear all,
here is the arxiv link to a new paper that has just been published on
ApJ Letters
http://arxiv.org/abs/1204.0041
The paper addresses diagnostics of hot plasma using AIA data and
validating the method with simultaneous EIS spectroscopic data. Please
find the title and abstract below.
cheers,
Paola
"Hinode/EIS spectroscopic validation of very hot plasma imaged
with Solar Dynamics Observatory in non-flaring active region cores"
Testa P. & Reale F.
Abstract:
We use coronal imaging observations with SDO/AIA, and Hinode/EIS spectral
data, to explore the potential of narrow band EUV imaging data for
diagnosing
the presence of hot (T >~ 5 MK) coronal plasma in active regions. We
analyze observations of two active regions (AR 11281, AR 11289) with
simultaneous
AIA imaging, and EIS spectral data, including the Ca xvii line (at 192.8A)
which is one of the few lines in the EIS spectral bands sensitive to hot
coronal
plasma even outside flares. After careful coalignment of the imaging and
spectral
data, we compare the morphology in a 3 color image combining the 171,
335, and
94A AIA spectral bands, with the image obtained for Ca xvii emission
from the
analysis of EIS spectra. We find that in the selected active regions the
Ca xvii
emission is strong only in very limited areas, showing striking
similarities with
the features bright in the 94A (and 335A) AIA channels and weak in the 171A
band. We conclude that AIA imaging observations of the solar corona can be
used to track hot plasma (6-8 MK), and so to study its spatial
variability and
temporal evolution at high spatial and temporal resolution.
Dear colleagues
please find at the following link the preprint of a work accepted
for publication in Astronomy & Astrophysics, showing tests on the
capability of MCMC method to reconstruct isothermal DEMs:
http://arxiv.org/abs/1112.2857
The abstract is below.
Best regards
Fabio Reale
Monte Carlo Markov Chain DEM reconstruction of isothermal plasmas
E. Landi, F. Reale, P. Testa
In this paper, we carry out tests on the Monte Carlo Markov Chain (MCMC)
technique with the aim of determining: 1) its ability to retrieve
isothermal plasmas from a set of spectral line intensities, with and
without random noise; 2) to what extent can it discriminate between an
isothermal solution and a narrow multithermal distribution; and 3) how
well it can detect multiple isothermal components along the line of
sight. We also test the effects of 4) atomic data uncertainties on the
results, and 5) the number of ions whose lines are available for the DEM
reconstruction. We find that the MCMC technique is unable to retrieve
isothermal plasmas to better than Delta log T = 0.05. Also, the DEM
curves obtained using lines calculated with an isothermal plasma and
with a Gaussian distribution with FWHM of log T = 0.05 are very similar.
Two near-isothermal components can be resolved if their temperature
separation is Delta log T = 0.2 or larger. Thus, DEM diagnostics has an
intrinsic resolving power of log T = 0.05. Atomic data uncertainties may
significantly affect both temperature and peak DEM values, but do not
alter our conclusions. The availability of small sets of lines also does
not worsen the performance of the MCMC technique, provided these lines
are formed in a wide temperature range. Our analysis shows the present
limitations in our ability to identify the presence of strictly
isothermal plasmas in stellar and solar coronal spectra.
Dear colleagues
please find at the following link the preprint of a work accepted
for publication in ApJ, showing interesting evidence of thermal
instability in UV light curves late in a flare. This analysis is done on
SoHO/SUMER data but may be useful for flare observations with SDO/EVE:
http://arxiv.org/abs/1111.3579
The abstract is below.
Best regards
Fabio Reale
Post-flare UV light curves explained with thermal instability of loop plasma
F. Reale, E. Landi, S. Orlando
In the present work we study the C8 flare occurred on September 26, 2000
at 19:49 UT and observed by the SOHO/SUMER spectrometer from the
beginning of the impulsive phase to well beyond the disappearance in the
X-rays. The emission first decayed progressively through equilibrium
states until the plasma reached 2-3 MK. Then, a series of cooler lines,
i.e. Ca x, Ca vii, Ne vi, O iv and Si iii (formed in the temperature
range log T = 4.3 - 6.3 under equilibrium conditions), are emitted at
the same time and all evolve in a similar way. Here we show that the
simultaneous emission of lines with such a different formation
temperature is due to thermal instability occurring in the flaring
plasma as soon as it has cooled below ~ 2 MK. We can qualitatively
reproduce the relative start time of the light curves of each line in
the correct order with a simple (and standard) model of a single flaring
loop. The agreement with the observed light curves is greatly improved,
and a slower evolution of the line emission is predicted, if we assume
that the model loop consists of an ensemble of subloops or strands
heated at slightly different times. Our analysis can be useful for flare
observations with SDO/EVE.