Dear all,
Please find attached a new paper on 'Active Region Moss: Basic physical parameters and their temporal variation' which has been accepted for publication in Astronomy and Astrophysics. Below is the abstract of the paper.
Context: Active region moss are transition region phenomena, first noted in the images recorded by the Transition Region and Coronal Explorer (TRACE) in $\lambda$171. Moss regions are thought to be the footpoints of hot loops (3-5~MK) seen in the core of active regions. These hot loops appear 'fuzzy' (unresolved). Therefore, it is difficult to study the physical plasma parameters in individual hot core loops and hence their heating mechanisms. Moss regions provide an excellent opportunity to study the physics of hot loops. In addition, they allow us to study the transition region dynamics in the footpoint regions. Aim: To derive the physical plasma parameters such as temperature, electron density, and filling factors in moss regions and to study their variation over a short (an hour) and a long time period (5 consecutive days). Methods: Primarily, we have analyzed spectroscopic observations recorded by the Extreme-ultraviolet Imaging Spectrometer (EIS) aboard Hinode. In addition we have used supplementary observations taken from TRACE and the X-Ray Telescope (XRT) aboard Hinode. Results: The moss emission is strongest in the \ion{Fe}{xii} and \ion{Fe}{xiii} lines. Based on analyses using line ratios and emission measure we found that moss regions have a characteristic temperature of log~T[K]~=~ 6.2. The temperature structure in moss region remains almost identical from one region to another and it does not change with time. The electron densities measured at different locations in the moss regions using \ion{Fe}{xii} ratios are about 1-3~$\times$~10$^{10}$~cm$^{-3}$ and about 2-4~$\times$~10$^{9}$~cm$^{-3}$ using \ion{Fe}{xiii} and \ion{Fe}{xiv}. The densities in the moss regions are similar in different places and show very little variation over short and long time scales. The derived electron density substantially increased (by a factor of about 3-4 or even more in some cases) when a background subtraction was performed. The filling factor of the moss plasma can vary between 0.1-1 and the path length along which the emission originates is from a few 100 to a few 1000 kms long. By combining the observations recorded by TRACE, EIS and XRT, we find that the moss regions correspond to the footpoints of both hot and warm loops.
Best wishes, -Durgesh Tripathi
Durgesh Tripathi Department of Applied Maths and Theoretical Physics Centre for Mathematical Sciences University of Cambridge Wilberforce Road Cambridge CB3 0WA
Ph. +44 - (0) - 1223 - 337-916
Dear Loop Aficionados,
In case you are interested in magnetic modeling of loops ....
Cheers, Markus
Aschwanden,M.J. and Sandman, A.W. 2010, Astronomical Journal, ... (in press) URL1="http://www.lmsal.com/~aschwand/eprints/2010_bootstrap.pdf" Bootstrapping the coronal magnetic field with STEREO: Unipolar potential field modeling
____________________________________________ 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 Marcus,
thanks for the hint to your recent loop paper. I browsed through it but I stumbled already on page three where you outline your philosophy: You want to test, how close you can fit a potential field to a set of (stereoscopically derived) field lines. The answer could have bee given without numerical tests: as close as your parameter space allows. The same would hold for a NLFField. The field you find is probably not unique, because you may superpose potential fields which vanish along the field lines. Hence from a successful fit no conclusion can be drawn about the nature of the true field. At the end of subsection 2.1: I do not know the paper by Gary (2010), but Conlon and Gallagher (2010) is not NLFFF. And finally: What do you mean by "Abelian"? Commonly this term is used for a group property indicating the the group operation is commutative. What does "Abelian" mean for a magnetic vector field ?
Many regards
Bernd
====================================================================== M M PPPP SSS Dr. Bernd Inhester MM MM P P S Max-Planck-Institut for Solar System Research M M M PPP SS 37191 Katlenburg-Lindau, Germany M M P S Phone:+49 5556 979477 Fax:+49 5556 979240 M M P SSSS Email: binhest@mps.mpg.de ======================================================================
On Fri, 18 Jun 2010, Markus J. Aschwanden wrote:
Dear Loop Aficionados,
In case you are interested in magnetic modeling of loops ....
Cheers, Markus
Aschwanden,M.J. and Sandman, A.W. 2010, Astronomical Journal, ... (in press) URL1="http://www.lmsal.com/~aschwand/eprints/2010_bootstrap.pdf" Bootstrapping the coronal magnetic field with STEREO: Unipolar potential field modeling
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 Bernd,
Thanks for your feedback, which is always interesting from your side. What are you up to with STEREO plus magnetic modeling ? I hope to see you at the COSPAR meeting in Bremen, where we could discuss things.
Cheers, Markus
On Jun 22, 2010, at 1:13 AM, binhest@mps.mpg.de wrote:
Dear Marcus,
thanks for the hint to your recent loop paper. I browsed through it but I stumbled already on page three where you outline your philosophy: You want to test, how close you can fit a potential field to a set of (stereoscopically derived) field lines. The answer could have bee given without numerical tests: as close as your parameter space allows.
Well, within a specific model, such as with unipolar charges or dipoles, you can approximate a set of coronal loops only within a certain tolerance. Once you reach a best fit, you cannot get closer, regardless how many free parameters you add. For instance, if an observed loop is a "square", every model consisting of multiple "semi-circles" cannot improve the fit by adding more semi-circles. So, how close you can fit the data depends very much on your chosen parameterization. In this study we tried with buried magnetic charges, but it was not clear a priori if we get a closer match to the STEREO loops than standard extrapolation models.
The same would hold for a NLFField.
They also have constraints from the photospheric field that does not allow for a better fit than what we measured with the misalignment angles. We wanted to see if the misalignment is due to a wrong boundary condition or due to the inadequacy of NLFFF models.
The field you find is probably not unique, because you may superpose potential fields which vanish along the field lines.
Of course, one best-fit solution is not unique, there are many solutions with similar small misalignment.
Hence from a successful fit no conclusion can be drawn about the nature of the true field.
You are right, we cannot tell whether the true field is potential or not, but we can narrow down the degree of non-potentiality and have a more accurate magnetic field model that is useful for many modeling tasks (like hydrodynamic modeling of an active region).
At the end of subsection 2.1: I do not know the paper by Gary (2010),
Gary's paper contains PTA (parameteric Transform Analysis) that is a general magnetic field deformation concept that can be applied to any model.
but Conlon and Gallagher (2010) is not NLFFF.
You are right, he uses only LFFF (I have to correct that, thanks!)
And finally: What do you mean by "Abelian"? Commonly this term is used for a group property indicating the the group operation is commutative. What does "Abelian" mean for a magnetic vector field ?
Abelian in the sense of commutative and linear. I wanted to emphasize that we can model the superposition of many unipolar charges or dipoles in any commutative permutation (irregardless of the order) and preserve the divergence-free condition.
Many regards
Bernd
====================================================================== M M PPPP SSS Dr. Bernd Inhester MM MM P P S Max-Planck-Institut for Solar System Research M M M PPP SS 37191 Katlenburg-Lindau, Germany M M P S Phone:+49 5556 979477 Fax:+49 5556 979240 M M P SSSS Email: binhest@mps.mpg.de ======================================================================
On Fri, 18 Jun 2010, Markus J. Aschwanden wrote:
Dear Loop Aficionados,
In case you are interested in magnetic modeling of loops ....
Cheers, Markus
Aschwanden,M.J. and Sandman, A.W. 2010, Astronomical Journal, ... (in press) URL1="http://www.lmsal.com/~aschwand/eprints/2010_bootstrap.pdf" Bootstrapping the coronal magnetic field with STEREO: Unipolar potential field modeling
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 _______________________________________ ____________________________________
loops@solar.physics.montana.edu