[Loops] summaries on nanoflare debates in "coronal loop workshops"
Petrus Martens
pmartens at cfa.harvard.edu
Thu Mar 5 15:32:06 MST 2009
Hugh,
> 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
Hugh, I think that there is a miscommunication here. I only meant to say
that in flares we have good evidence that the flaring loops coincide with
separators. I didn't mean to imply that flares are caused by Parker's
mechanism.
> 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.
I don't quite see the logical step from a to b. You still have to figure
out what drives the currents before you can worry about what dissipates
them, and Parker's model focuses on what drives them.
Cheers,
Piet
>
> 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
>>>> <mailto: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>
>>>> [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 <mailto:aschwanden at lmsal.com>
>>>> _______________________________________
>>>> ____________________________________
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
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>>>
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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
>> <mailto:pmartens at cfa.harvard.edu>
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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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