Dear All, I have been away from coronal heating for a number of years, so I am asking for some guidance.
Here is my problem: The Parker model for heating relied heavily on energy storage throughout a coronal loop. In the absence of reconnection the field lines within a loop would become increasingly tangled: the free energy within a loop then increases as time squared, giving a power input increasing linearly with time. Throw in reconnection, and the system reaches a steady state at some saturation time t_sat. Here the heating power is linear in t_sat. Physically, t_sat tells you the time needed to stress the field up to levels where reconnection takes off, as in the secondary instabilities of Dahlburg, Linton and Antiochos. The curious thing is that the heating rate goes down if reconnection is more easy to trigger, because the saturation time is smaller for easy reconnection.
Having grown up with these ideas, it is difficult to reconcile myself with the newer observations suggesting the location of heating mostly at the base of loops. This causes two problems: first, is there enough volume of stressed field in the chromosphere/transition region to store the saturation level energy (yes, I know B is stronger down there, but still...). Secondly, reconnection may be too easy down there because of lower magnetic Reynolds numbers. Can someone convince me that you can still get 10^7 ergs/cm^2-sec active region heating rates?
Best Wishes Mitchell Berger
On Fri, Mar 6, 2009 at 2:13 AM, Brooks, David (Forn Natl) dhbrooks@ssd5.nrl.navy.mil wrote:
Dear All,
A good example (I would say that...) of hot loops in locally unipolar regions as seen by SOT (that Harry mentioned) is video 4 in our paper: http://www.iop.org/EJ/article/1538-4357/689/1/L77/23039.html
It also shows that dynamic events in the chromosphere/transition region cluster around the active region neutral line in mixed flux regions. These are the resolvable events that Jim referred to that don't reach high temperatures.
Best wishes, David Brooks
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