[Loops] loops and thermal nonequilibrium

[Leon Golub]

Jim,

We were indeed modelling the long, relatively faint loops seen in the 
plage regions surrounding sunspots, which are exactly where EIS is 
seeing the flows. It's been known for a long time (the Palermo people 
did such modelling 20 years ago) that flows in coronal loops drop the 
density ("When you start a flow going, the loop disappears.") or 
alternatively, if you see the loop it means the density is enhanced. I'm 
not sure why your modelling failed, but we were able to reproduce the 
scale height quite well. Having the flow (in either direction) extends 
the emission scale height quite a bit beyond the hydrostatic value.

As you know, the AIA on SDO will have far more extensive temperature 
coverage than TRACE does. There is a puzzle right now in that EIS sees 
the flows at higher temperatures than we saw in TRACE. I think that this 
topic is going to be a major one in the coming years.

Leon


Klimchuk, James A. (GSFC-6710) wrote:
> Wow, I'm surprised, and pleased, at the interest this paper has generated!  Let me first respond to Leon's comment.  As Harry said (thanks!), in order to get the extreme excess densities that are observed in most warm loops, the footpoint heating needs to be so concentrated that no equilibrium exists (which strictly speaking is different from an instability).  Hence, thermal nonequilibrium.  A few years back, Spiros P. and I addressed your suggestion with Amy that asymmetric heating and steady flows might explain the observations.  Our modeling showed that the density enhancement was adequate to explain some loops, but the scale height is too small and the filter-ratio temperature profile is far too structured (paper attached).  We thus rejected this explanation.   Sorry!
> 
> Thanks for your comment,
> Jim
> 
>> -----Original Message-----
>> From: loops-bounces at solar.physics.montana.edu [mailto:loops-
>> bounces at solar.physics.montana.edu] On Behalf Of Harry Warren
>> Sent: Sunday, December 06, 2009 6:19 PM
>> To: A mailing list for scientists involved in the observation and modeling of
>> solar loop structures
>> Subject: Re: [Loops] loops and thermal nonequilibrium
>>
>>
>> Leon,
>>
>> As I recall, your paper with Amy relied on footpoint heating, which does
>> lead to higher apex densities and flatter temperature ratios. The observed
>> densities near 1 MK are so high, however, that the loops become
>> thermodynamically unstable. Also, the high speed EIS flows are typically
>> seen in faint regions and are not associated with the types of loops that
>> Jim is attempting to model.
>>
>> Harry
>>
>>
>> On 12/5/09 3:16 PM, "Leon Golub" <golub at cfa.harvard.edu> wrote:
>>
>>> Jim,
>>>
>>> Amy and I addressed the issues of excess density, flat temperature
>>> profiles and large scale height about 10 years ago. Having flows of
>>> 30-40 km/sec, as is observed in TRACE and now verified by EIS, solves
>>> these problems quite nicely. So there is a viable mechanism other than
>>> nanoflares.
>>>
>>> Leon
>>>
>>>
>>> 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
>>>>
>>>>
>>>>
>>>>
>> **************************************************************
>> ***************
>>>> ***
>>>>
>>>>
>>>>
>>>>
>>>> ------------------------------------------------------------------------
>>>>
>>>> _______________________________________________
>>>> Loops mailing list
>>>> Loops at solar.physics.montana.edu
>>>> https://mithra.physics.montana.edu/mailman/listinfo/loops
>>> _______________________________________________
>>> Loops mailing list
>>> Loops at solar.physics.montana.edu
>>> https://mithra.physics.montana.edu/mailman/listinfo/loops
>> --
>> // ---------------------------------------------------------------------
>> // 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
>> // ---------------------------------------------------------------------
>>
>>
>>
>>
>>
>> _______________________________________________
>> Loops mailing list
>> Loops at solar.physics.montana.edu
>> https://mithra.physics.montana.edu/mailman/listinfo/loops
> _______________________________________________
> Loops mailing list
> Loops at solar.physics.montana.edu
> https://mithra.physics.montana.edu/mailman/listinfo/loops

-- 
______________________________________________________________________________
Leon Golub	
Smithsonian Astrophysical Observatory
60 Garden Street
Cambridge, MA 02138
617 495 7177
FAX 496 7577
lgolub at cfa.harvard.edu
______________________________________________________________________________