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Astron. Astrophys. 338, 747-755 (1998)


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An eight-moment model parameter study of the solar wind: dependence on variations in coronal heating

Espen Lyngdal Olsen 1, Egil Leer 2 and Oystein Lie-Svendsen 3

1 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street MS 50, Cambridge, MA 02138, USA
2 Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029, Blindern, N-0315 Oslo, Norway
3 Norwegian Defence Research Establishment (FFI), division for electronics, P.O. Box 25, N-2007 Kjeller, Norway

Received 13 January 1998 / Accepted 21 April 1998

Abstract

The eight-moment two-fluid model describes, self-consistently, the proton (and electron) heat flux in the solar wind. This is a crucial parameter in solar wind models with a high coronal proton temperature. In the present study the eight-moment description is used to study how the solar wind outflow from an electron-proton corona responds to variations in coronal heating. Most of the energy flux is deposited in the proton gas. We find that the asymptotic flow speed of the solar wind is only weakly dependent on the amplitude of the energy flux, but it increases with increasing dissipation length. When most of the energy flux is dissipated in the extended corona, where the protons are collisionless, we obtain flow speeds characteristic of high-speed solar wind streams: For a dissipation length of 1 to 2 solar radii the asymptotic flow speed is 700-1000 km s-1. A relatively modest electron heating in the inner corona may lead to an increased transition region pressure and hence a large increase in the solar wind proton flux. This increase in proton flux may be so large that there is not enough energy available to drive a high-speed wind.

Key words: Sun: corona – solar wind

Send offprint requests to: Egil Leer
Corrspondence to: Egil Leer, Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029, Blindern, N-0315 Oslo, Norway (elols@statoil.no; egil.leer@astro.uio.no; Oystein.Lie-Svendsen@ffi.no)

© European Southern Observatory (ESO) 1998

Online publication: September 14, 1998

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