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Astron. Astrophys. 329, 735-746 (1998)

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Heating of the corona and acceleration of high speed solar wind

H.O. Evje 1 and E. Leer 1, 2

1 Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029, N-0316 Oslo, Norway (h.o.evje@astro.uio.no)
2 High Altitude Observatory, National Center for Atmospheric Research, PO Box CO 3000 Boulder, USA (egil.leer@astro.uio.no)

Received 27 January 1997 / Accepted 12 September 1997

Abstract

We present a parameter study of the corona-solar wind system. The corona is heated by an energy flux from the sun. This energy flux is lost as heat conductive flux into the transition region and as solar wind energy flux. We consider two-fluid models where most of the energy flux is deposited in the proton gas. Heating of the inner corona leads to a significant (electron) heat conductive flux into the transition region and a relatively high coronal electron density. This gives a relatively low coronal proton temperature, a large solar wind proton flux, and a relatively low asymptotic flow speed. In rapidly expanding flow geometries, where the thermal coupling between electrons and protons is weaker, heating of the protons in the inner corona may lead to a somewhat higher proton temperature, and higher asymptotic flow speed, but in order to drive high speed solar wind, a significant fraction of the energy flux from the sun must be deposited in the outer corona, where the protons are collisionless. In such a model only a small fraction of the energy flux is lost as inward heat flux, the transition region pressure is low, and the solar wind proton flux is quite small. The proton temperature in the outer corona is high, and a larger fraction of the energy flux deposited in the proton gas may be lost as solar wind kinetic energy flux.

Key words: Sun: corona – solar wind – acceleration of particles

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© European Southern Observatory (ESO) 1998

Online publication: December 8, 1997
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