Dear Serge and Hugh,
Thanks for your feedback. You are correct that it appears that there is more free energy available during the flare duration than before or after. However, a similar behavior appears in all flares, as you can see in the analysis of the free energy in some 200 flares analyzed from HMI and AIA (see Aschwanden, Xu, and Jing 2014, ApJ 797:50). This apparently counter-intuitive behavior has been interpreted as a “coronal illumination effect” (see Fig.3 in the quoted paper above). In short, most of the highly twisted helical flare loops that carry non-potential magnetic energy are invisible or undetectable before the start of the flare, but become visible once they become filled up with heated plasma by the chromospheric evaporation process that usually occurs in flares. So, it is not a contra- diction, but just an observational problem. It is similar to the missing mass problem in the universe: We detect only 4% luminous mass, but when you add up all the dark matter and neutrinos you get to a much more massive universe that may even be closed/ And nobody calls the missing mass problem as contradictory, it’s just an observational problem.
Regarding Hugh’s comment, the NLFFF model that has been used to calculate the free energy is based on an analytical solution of the force-free field in terms of vertical currents that introduce a helical twist (Aschwanden 2013, Solar Phys. 287, 323). It is only an approximation, but it should give the first-order non-potential field pretty accurately. There is some consistency with standard NLFFF models, or at least some correlation (e.g., Wiegelmann code). The boundary conditions have been discussed in great detail in a NLFFF comparison paper (DeRosa et al. 2009). The biggest problem with standard NLFFF codes is that they extrapolate from a not force-free boundary. In contrast, the analytical NLFFF model that fits the geometry of coronal loops circumvents this problem and thus yields complementary information. If you wish I can give your more references on this “high-order theoretical matter”.
Thanks for the comments, Best regards,
Markus
____________________________________ Dr. Markus J. Aschwanden Solar & Astrophysics Laboratory Lockheed Martin Advanced Techology Center A021S, 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 ____________________________________
On Apr 14, 2015, at 5:53 AM, Hugh Hudson hhudson@ssl.berkeley.edu wrote:
That’s how it appears to me too. I’d add that the localization of the free energy is a difficult subject, and it may be misleading just to identify it with the B^2/8pi excess. This is because the realization of the free energy, i.e. its actual definition, depends on the nature of the instability that releases it. Understanding this requires understanding the boundary conditions, so it must be a higher-order theoretical matter.
Hugh
On Apr 14, 2015, at 8:42 AM, Serge Koutchmy koutchmy@iap.fr wrote:
Thank you Markus for the preprint. Looking at your most important Fig. 3, you give the impression that MORE free energy is available in the corona AFTER the peak of the flare (GOES HXR, SXR emissions, etc) than before. Is not exactly the opposite of what we would wait following your Introductory presentation of the topic and even the title of the paper? Or did I miss something fundamental? Best, S.
Le 13/04/2015 21:06, Markus J. Aschwanden a écrit :
Aschwanden,M.J. . 2015, ApJL ... (revised, 2015 Apr 2) URL1="http://www.lmsal.com/~aschwand/eprints/2015_iris.pdf" Magnetic energy dissipation during the 2014 Mar 29 flare: Consistent measurements in the transition region and corona with IRIS and AIA/SDO
Dr. Markus J. Aschwanden Solar & Astrophysics Laboratory Lockheed Martin Advanced Techology Center A021S, 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 ____________________________________
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