[Loops] summaries on nanoflare debates in "coronalloopworkshops"

Mon Mar 9 11:02:07 MDT 2009

Valery and Robert,

    Thanks for bringing up waves.  I have two quick points.

1.  The internal plasma structure of a loop (multi-stranded or not) is
determined by the heating and cannot be decoupled from the wave
dissipation (unless the wave is energetically insignificant).  See
Section 4.3 of the attached.

2.  There may be different opinions of what is meant by "nanoflare."
Some people define it to be an identifiable point-like brightening that
probably occurs in a tiny bipole.  Most loops modelers define it to be
an impulsive energy release in a long and unresolved magnetic strand.
It cannot be directly observed.  With this definition, even resonant
wave absorption produces nanoflare heating (also explained in Sections
4.3 and 4.2).  I'm very curious about David Berghmans' talk and have my
doubts about the conclusions!

Cheers,

Jim

________________________________

From: loops-bounces at solar.physics.montana.edu
[mailto:loops-bounces at solar.physics.montana.edu] On Behalf Of
Nakariakov, Valery
Sent: Saturday, March 07, 2009 9:02 AM
To: A mailing list for scientists involved in the observation and
modeling ofsolar loop structures; A mailing list for scientists involved
in the observation and modelingofsolar loop structures
Subject: Re: [Loops] summaries on nanoflare debates in
"coronalloopworkshops"

Hi Robertus, hi all,

>however, both hinode and very recent rosa observations have shown the
omnipotent presence of mhd waves ... that have the necessary poyting
flux to heat the lower
atmosphere or corona. so, it is not just reconnection!

There are two important aspects, in my opinion:
(a) even if the Poynting flux is sufficient, there also should be
sufficiently effective mechanisms for the wave energy dissipation at a
reasonable height. The efficiency of both phase mixing and RA is
determined by the steepness of the transverse structuring of the
waveguiding plasma structures.

Structuring is definitely an unknown parameter, as you've pointed out:
>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 available way is of the one by
magneto-seismology.

I agree. As I have mentioned in this forum before, there are several
coronal seismological indications of the subresolution structuring of
the corona. But, what is important is not only the spatial scale of
structuring, but also the gradients of the plasma parameters.

(b) The amplitudes of the observed transverse waves are sufficiently
high to produce a significant change of the magnetic field in the
vicinity of the potential reconnection
sites. Hence, the waves can effectively contribute to reconnection, and
then the separation of "wave-based" and "reconnection-based" mechanisms
for heating seems to be a bit too artificial.

All the best,

Valery

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