Scott,
I fully agree with most of what you
say. We need to be very cautious. The whole point of the paper (and
Phil’s) is to show that various uncertainties limit what you can infer
about the thermal properties of an observed plasma. We propose a simple method
to set approximate bounds on the range of valid interpretations. I
disagree with what you seemed to say about not being able to do much with
DEM/EM. We can learn a great deal about the physics of the corona and transition
region if we know the thermal distribution of the plasma. The key
question is whether we can determine DEM/EM reliably from observations. You
make an excellent point that all of the “inversion” methods,
including ours, assume ionization equilibrium. There are many situations where
this is not valid (e.g., early in a nanoflare event). Expect to see more
on this in the near future….
Thanks for your comments,
Jim
From: loops-bounces@solar.physics.montana.edu
[mailto:loops-bounces@solar.physics.montana.edu] On Behalf Of Scott W.
McIntosh
Sent: Thursday, September 23, 2010 8:54 PM
To: A mailing list for scientists involved in the observation and
modeling of solar loop structures
Subject: Re: [Loops] EM loci
Can I point out a paper to the list:
This paper encapsulates the problem in a concise form. I
could point out a couple more, but those are nearly 10 years old now, wow how
time flies. I have drawn my line in the sand with emission measures as a
practical diagnostic - once we have a DEM/EM, etc what can we do with it? As
far as I can tell there are only a few papers in the literature that deal with
that particular issue in a real sense and those are from further back in the
80s [look for papers by Carole Jordan].
I am all for learning something about the solar plasma from
a zeroth order approach. However, no EM/DEM/Line Ratio estimation deals
with the real time-varying corona (or outer solar atmosphere as we need to deal
with a intrinsically coupled system). By definition, these diagnostic deal
with equilibrium processes and thermal populations - I am not entirely sure
that we have that in place and if we do is, is that the process doing the
"heavy lifting" or just the after effect procing the apparent
stationary state.....there is strong evidence of non-thermal processes
affecting the chromospheric, TR and coronal plasmas in the very same spectra
from which such diagnostics are derived [probably even worse for broadband EUV
imagers].
Sorry, to be a bummer!
-S.
**---------------------------------------------------------------------------------------------**
Dr.
Scott W. McIntosh
National Center for Atmospheric Research
Phone: 303 497 1544
(Room 3624) High Altitude Observatory
Fax:
303 497 1589
3080 Center Green Drive - CG1
email: mscott@ucar.edu
Boulder,
CO 80301
On Sep 23, 2010, at 7:25 AM, Klimchuk, James A. (GSFC-6710)
wrote:
Friends,
The EM loci technique is frequently used to access whether a plasma is
isothermal. The attached paper addresses the uncertainty in this
technique and proposes a way to determine the range of thermal distribution
widths that are consistent with a set of emission line data.
Cheers,
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@nasa.gov
No
endorsement by NASA is implied for any correspondence related to my role as an
officer of professional organizations (American Geophysical Union, American
Astronomical Society, International Astronomical Union).
********************************************************************************
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