Some quick comments....
1. I agree with Markus and Marco that there is, in principle, no problem having impulsive heating (nanoflares) in the low atmosphere (chromosphere and transition region) of unipolar regions, as long as the field is "tangled." The resolvable events that Harry mentions are interesting and important, but different from ordinary coronal heating.
2. However, the transition region is an extremely thin layer that moves up and down flux tubes in response to changes in the coronal pressure resulting from heating and cooling. It is very difficult for me to see why the magnetic energy dissipation that gives rise to heating should always follow this layer. Dissipation in the thicker chromosphere is much easier to swallow.
3. The ten arguments that Markus gives in his paper are consistent with heating in the transition region, but they are also consistent with heating in the corona! Thus, they do not disprove coronal nanoflares. Perhaps we can discuss this in Florence. (Markus: I remember we went over some of this during a wonderful lunch with retsina on a patio in Santorini! How about if we cover the rest with chianti?).
Cheers,
Jim
________________________________
From: loops-bounces@solar.physics.montana.edu [mailto:loops-bounces@solar.physics.montana.edu] On Behalf Of Markus J. Aschwanden Sent: Thursday, March 05, 2009 10:16 AM To: Hugh Hudson; A mailing list for scientists involved in the observation and modelingof solar loop structures Subject: [Loops] summaries on nanoflare debates in "coronal loop workshops"
Dear Hugh,
Jim Klimchuk sent a great summary of the current status of a nanoflare model around,
so it deals with all the PROs. An outside reader who wants to hear both sides might be
interested to hear also the CONs, which you could find in the ApJ Letter entitled
"An observational test that disproves coronal nanoflare heating models" (Aschwanden
2008, ApJ 672, L135). The arguments made therein do not dismiss nanoflares
altogether, but come to the conclusion that they occur in the transition region,
rather than in the corona (as Parker originally suggested).
Cheers,
Markus
On Mar 3, 2009, at 7:32 AM, Klimchuk, James A. (GSFC-6710) wrote:
Dear loops friends,
Here is a paper I wrote for the Hinode II conference proceedings. In it, I try to do three things: (1) review the arguments leading to the conclusion that warm EUV loops must by bundles of strands heated by storms of nanoflares (the flow chart some of you have asked about); (2) reconcile the isothermal/multi-thermal debate in terms of the duration of the nanoflare storm; and (3) address the possibility that loops can be explained by thermal nonequilibrium. Comments are welcomed.
Thanks,
James A. Klimchuk
____________________________________________
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
_______________________________________
____________________________________