[Loops] summaries on nanoflare debates in "coronal loop workshops"
Hugh Hudson
hhudson at ssl.berkeley.edu
Thu Mar 5 15:19:31 MST 2009
So many sage comments!
The Parker problem seems now to me too abstract to apply to real
observations, for a couple of other reasons. First, at least for
flares, I think it is wrong to think of the footpoint perturbations
as "random" - the magnetic field is arguably following coherent
marching orders from deep in the convection zone. So if the
mathematics of "random" is important, that would be a flaw in the
concept. Second, the analysis of coronal current systems really must
involve consideration of what species carries the currents, and how
the conductivity tensor varies through the medium. This seems to be
the language of the magnetosphere, where people can directly sample
the medium. So I'd relegate the Parker problem to being, well,
interesting but abstract.
Hugh
On Mar 5, 2009, at 1:09 PM, Petrus Martens wrote:
> Marco et al.,
>
>> this is an interesting conversation. My tuppence: parker nanoflares
>> work precisely in unipolar reasons, as it is the tangential stresses
>> which are relaxed in the original parker scenario.
>
> Agreed, that is certainly what Parker described. The problem I
> have with
> the Parker scenario is: why loops? Why not a uniform distribution of
> nanoflares throughout the AR? "Why loops?" also applies to any
> mechanism
> that places the origin of the heating in the upper chromosphere or
> below.
>
> Stick and slip reconnection along separators, a scenario that Dana
> Longcope has been working on for years, answers the "Why loops?"
> question
> seamlessly. I am aware of course that observational studies have
> so far
> found no clear relation between separators and loops, except in
> flaring
> loops. This may be a resolution issue, or an issue related to the
> large
> amount of horizontal flux missed in magnetograms. Or there is no such
> relation, in which case we are back where we started.
>
> Cheers,
>
> Piet
>
>
>
>
> The presence of multiple polarities
>> changes this in a way which has never been quantitatively estimated.
>> I would like to point you to the 2008/07 papers by Rappazzo and
>> myself
>> which I believe contain the only scalings for the Parker flt scenario
>> which have numerical simulation confirmation.
>>
>> @ARTICLE{2008ApJ...677.1348R, author = {{Rappazzo}, A.~F. and
>> {Velli},
>> M. and {Einaudi}, G. and {Dahlburg}, R.~B. }, title = "{Nonlinear
>> Dynamics of the Parker Scenario for Coronal Heating}", journal =
>> {\apj}, archivePrefix = "arXiv", eprint = {0709.3687}, keywords =
>> {Magnetohydrodynamics: MHD, Sun: Corona, Sun: Magnetic Fields,
>> Turbulence}, year = 2008, month = apr, volume = 677, pages =
>> {1348-1366}, doi = {10.1086/528786}, adsurl = {http://
>> adsabs.harvard.edu/abs/2008ApJ...677.1348R
>> }, adsnote = {Provided by the SAO/NASA Astrophysics Data System} }
>>
>> On Mar 5, 2009, at 7:31 AM, Harry Warren wrote:
>>
>>> Markus et al.,
>>>
>>> It is unambiguous that there is a lot of dynamic activity going on
>>> in the
>>> transition region. However:
>>>
>>> . . . a significant fraction of the Sun's magnetic flux closes at
>>> low
>>> heights (several Mm), so it is unclear how much of this activity is
>>> related
>>> to what we see in the corona.
>>>
>>> . . . my impression of SOT magnetic field measurements is that
>>> active region
>>> plage (where many active region loops are rooted) is unipolar. It is
>>> hard to
>>> see how small-scale reconnection in the transition region could be
>>> important
>>> here. I could be wrong about this! I'm sure that an SOT person could
>>> provide
>>> a more definitive answer.
>>>
>>> Best wishes,
>>>
>>> Harry
>>>
>>> //
>>> --------------------------------------------------------------------
>>> -
>>> // Harry P. Warren phone : 202-404-1453
>>> // Naval Research Laboratory fax : 202-404-7997
>>> // Code 7673HW email : hwarren at nrl.navy.mil
>>> // Washington, DC 20375 www : http://tcrb.nrl.navy.mil/
>>> ~hwarren
>>> //
>>> --------------------------------------------------------------------
>>> -
>>>
>>>
>>> From: loops-bounces at mithra.physics.montana.edu
>>> [mailto:loops-bounces at mithra.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 modeling of 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 at lmsal.com
>>> _______________________________________
>>> ____________________________________
>>>
>>>
>>>
>>>
>>>
>>>
>>> _______________________________________________
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>>> Loops at solar.physics.montana.edu
>>> https://mithra.physics.montana.edu/mailman/listinfo/loops
>>>
>>
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>
>
> --
> --------------------------------------------------------------------
> Piet Martens Tel: 617-496-7769
> Center for Astrophysics Fax: 617-496-7577
> 60 Garden Street, MS 58 Cell: 617-999-0353
> Cambridge, MA 02138 pmartens at cfa.harvard.edu
> --------------------------------------------------------------------
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+++++++++++++++++++++
In medias res
hhudson at ssl.berkeley.edu
+1 (510) 643-0333
AST:7731^29u18e3
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