[Loops] summaries on nanoflare debates in "coronalloopworkshops"

[Mitchell Berger]

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 at 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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