[Loops] preprint: Magnetic energies measured with IRIS and AIA/contradiction?

[Markus J. Aschwanden]

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 at lmsal.com
____________________________________

On Apr 14, 2015, at 5:53 AM, Hugh Hudson <hhudson at 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 at 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 at lmsal.com
>>> ____________________________________
>>> 
>>> 
>>> 
>>> 
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>> 
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