[Loops] loops and thermal nonequilibrium

[Harry Warren]

Hugh,

I think that Jim is using the term nanoflare a little more generally than
usual. In this context it appears to refer to small-scale heating events and
not specifically to the Parker model.

There is considerable consistency between steady heating models and
observations of high temperature coronal plasma (I can send references if
desired). Since no one has managed to propose a heating mechanism that is
truly steady, it seems inevitable that we conclude that the coronal heating
occurs on small spatial and temporal scales.

The difficult thing is to reconcile the success of steady heating at high
temperatures with the non-equilibrium behavior observed at low temperatures.
If Jim's modeling had proved successful, it would have lead to a more
general description of the coronal heating mechanism. We would still left
pondering the physical mechanism, however.

Harry


On 12/6/09 8:20 AM, "Hugh Hudson" <hhudson at ssl.berkeley.edu> wrote:

> Dear Jim
> 
> I have some comments. It looks like a nice piece of work, but as usual the
> conclusion that only nanoflares can help is hopelessly quixotic. You set up a
> strawman competing mechanism (why call it "thermal nonequilibrium" when the
> one-syllable alternative "flow" works as well?) and reject it on the basis of
> time scales. Who knows about the time scales of the driver of the flows?
> 
> The model itself seems highly questionable. I had cited its predecessor in
> trying to explain the "chewy nougat" observation of X-rays from prominences
> (http://adsabs.harvard.edu/abs/1999ApJ...513L..83H) but realized later on that
> the model has a very artificial low-temperature boundary and is thus not
> compelling. It is surprising to me that a decade later this has not changed,
> especially since it is just this boundary region in which the heating may be
> taking place.
> 
> To be perfectly clear about nanoflares: I do not think that there is any
> convincing observational evidence that they exist. It is a purely theoretical
> construct.
> 
> Cheers
> 
> Hugh
> 
> p.s. at the Hinode meeting just concluded, a nice poster by Helen Mason made
> it very clear that EIS spectra emphatically do not agree with the various XRT
> suggestions of a high-temperature component in the loop DEM. The discrepancy
> is an order of magnitude.
> 
> On 4 Dec 2009, at 14:04, Klimchuk, James A. (GSFC-6710) wrote:
> 
>> Dear Loops Friends,
>>  
>>     If you are interested, the attached paper shows that coronal loops cannot
>> be explained by thermal nonequilibrium.  The results appear to rule out the
>> widespread existence of coronal heating that is both highly concentrated low
>> in the corona and steady or quasi-steady (slowly varying or impulsive with a
>> rapid cadence).  Comments are welcomed.
>>  
>> Best wishes,
>> Jim
>>  
>> *****************************************************************************
>> ***
>> James A. Klimchuk
>> NASA Goddard Space Flight Center
>> Solar Physics Lab, Code 671
>> Bldg. 21, Rm. 158
>> Greenbelt, MD  20771
>> USA
>>  
>> Phone:  1-301-286-9060
>> Fax:      1-301-286-7194
>> E-mail:  James.A.Klimchuk at nasa.gov <mailto:James.A.Klimchuk at nasa.gov>
>> Home page:  http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html
>> <http://hsd.gsfc.nasa.gov/staff/bios/cs/James_Klimchuk.html>
>>  
>> *****************************************************************************
>> ***
>>  
>> <klimchuk_submitted.pdf>
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> 
> 
> 
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