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: 

 

http://adsabs.harvard.edu/abs/2010ApJ...708.1238J

 

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

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                                                                    http://people.hao.ucar.edu/mscott/

 

 

 

 

 

 

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

 

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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