[Loops] summaries on nanoflare debates in "coronalloopworkshops"

[Robert von Fay-Siebenburgen]

hi markus (and others),

it is very interesting for me to read all these debates about coronal 
heating, initiated this time by jim's nice paper. there is one point, 
however, i'd like to make that most of you do not seem to consider: waves.

i admit that wave heating suffered a bit of a set-back before the 
soho/trace era. even the initial wave observations by soho/trace did not 
help too much to promote the wave heating scenario(s), as most of the kink 
or longitudinal waves reported in loops had just a fraction of energy 
density needed for coronal radiation.

however, both hinode and very recent rosa observations have shown the 
omnipotent presence of mhd waves (and let's not go into the debate of 
alfvenic or kink at the moment as it is irrelevant from the heating 
perspectives) that have the necessary poyting flux to heat the lower 
atmosphere or corona. so, it is not just reconnection!

in fact, i still have not fully recovered myself from the very convincing 
and well-equipped review talk given by david berghmans at the iau gen 
assembly @ prague where he just "ruled out" the nanoflare concept.

i basically support the fundamental question markus raised below: "What 
we are not sure is where is the primary energy release that leads up to 
the chromospheric heating". but his list of options for an answer is far 
too incomplete, and i'm not even sure whether it captures the essence if 
waves are neglected. if (IF) we want to get closer to loop fine structure 
(multi-thread vs whatever) or uncover the operating heating function, a 
very promising and currently already availble way is of the one by 
magneto-seismology.

robertus


On Fri, 6 Mar 2009, Markus J. Aschwanden wrote:

> 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] 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
>> _______________________________________
>> ____________________________________
>> 
>> 
>> 
>> 
>> _______________________________________________
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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
> _______________________________________
> ____________________________________
>
>
>