[Loops] loops and thermal nonequilibrium
Gordon Petrie
petrie at email.noao.edu
Mon Dec 7 09:07:53 MST 2009
Dear All,
In a basic model of steady, isothermal hydrodynamic flow
(http://adsabs.harvard.edu/abs/2006ApJ...649.1078P),
steady flows can only affect hydrostatic scale heights
under exceptional conditions. These states have fast
flows approaching the sound speed and form a small part of
the solution space right next to unphysical regimes with
density inversions. If significantly many loops really
are of this kind, it would be an interesting problem
explaining why. On the other hand, it's clear from
rho*V*A why steady flows decrease densities.
Best regards,
Gordon
On Mon, 07 Dec 2009 09:11:07 -0500
Leon Golub <golub at head.cfa.harvard.edu> wrote:
> 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
>>>>>
>>>>>
>>>>>
>>>>>
>>> **************************************************************
>>> ***************
>>>>> ***
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> ------------------------------------------------------------------------
>>>>>
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>>> --
>>> //
>>>---------------------------------------------------------------------
>>> // 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
>>> //
>>>---------------------------------------------------------------------
>>>
>>>
>>>
>>>
>>>
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> --
> ______________________________________________________________________________
> Leon Golub
> Smithsonian Astrophysical Observatory
> 60 Garden Street
> Cambridge, MA 02138
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> lgolub at cfa.harvard.edu
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