My little nail for Jack Scudders velocity filtration coffin:
Title:
Kinetic electrons in high-speed solar wind streams: Formation of high-energy tails
Authors:
Lie-Svendsen, ØysteinHansteen, Viggo H.Leer, Egil
Publication:
Journal of Geophysical Research, Volume 102, Issue A3, p. 4701-4718 (JGR Homepage)
Publication Date:
03/1997
Origin:
AGU
Keywords:
Interplanetary Physics: Solar wind plasma, Interplanetary Physics: Sources of the solar wind, Solar Physics, Astrophysics, and Astronomy: Corona, and Astronomy: Coronal holes
DOI:
10.1029/96JA03632
Bibliographic Code:
1997JGR...102.4701L

Abstract

We study the evolution of the electron velocity distribution function in high-speed solar wind streams from the collision-dominated corona and into the collisionless interplanetary space. The model we employ solves the kinetic transport equation with the Fokker-Planck collision operator to describe Coulomb collisions between electrons. We use a test particle approach, where test electrons are injected into a prescribed solar wind background. The density, temperature, and electric field associated with the background are computed from fluid models. The test electrons are in thermal equilibrium with the background at the base of the corona, and we study the evolution of the velocity distribution of the test electrons as a function of altitude. We find that velocity filtration, due to the energy dependence of the Coulomb cross section, is a small effect and is not capable of producing significant beams in the distribution or a temperature moment that increases with altitude. The distribution function is mainly determined by the electric field and the expanding geometry and consists of a population with an almost isotropic core which is bound in the electrostatic potential and a beam-like high-energy tail which escapes. The trapped electrons contribute significantly to the even moments of the distribution function but almost nothing to the odd moments; the drift speed and energy flux moments are carried solely by the tail. In order to describe the high-speed solar wind observed near 0.3 AU by the Helios spacecraft, we use a multifluid model where ions are heated preferentially. The resulting test electron distribution at 0.3 AU, in this background, is in very good agreement with the velocity distributions observed by the Helios spacecraft.

1) Electron temperatures are low -> polarization electric field is weak, so no matter how you describe them the electrons don't contribute much to the SW heat flux.
2) Observations at 0.3 AU can be reproduced without any Scudder magic.

Best wishes,
Viggo

On Jul 31, 2012, at 18:42 , Charles C. Kankelborg wrote:

So, Anderson concluded that the velocity filtration model needed to be redone with Coulomb collisions included. Dorelly and Scudder came back in 2003 with a paper concluding that "the electron heat flux is determined by the essentially collisionless high-energy tail" of the distribution:

http://adsabs.harvard.edu/abs/2003JGRA..108.1294D

Does that mean the coulomb collisions don't really affect prediction of energy transport? I haven't followed the trail of citations any farther...

Charles


On 2012 Jul 31, , at 9:27 AM, Dana Longcope wrote:

Stephen Anderson did a very thorough analysis of how Coulomb collisions affect the model.

http://adsabs.harvard.edu/abs/1994ApJ...437..860A

dana

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Dana Longcope    |     Dept. of Physics
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On Jul 31, 2012, at 9:20 AM, Petrus Martens wrote:


   Do you mean velocity filtration, where the corona is simply particles from the
tail of the chromospheric distribution function?  That theory has been largely discredited.

That's news to me.  Do you have a reference?

Piet



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