[Loops] summaries on nanoflare debates in "coronalloopworkshops"

[Bradshaw, Stephen J]

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


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From: loops-bounces at solar.physics.montana.edu [loops-bounces at solar.physics.montana.edu] On Behalf Of Markus J. Aschwanden [aschwanden at 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 at solar.physics.montana.edu<mailto:loops-bounces at solar.physics.montana.edu> [mailto:loops-bounces at 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 at lmsal.com<mailto:aschwanden at lmsal.com>
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____________________________________________
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 at lmsal.com<mailto:aschwanden at lmsal.com>
_______________________________________
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