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Astron. Astrophys. 352, 670-678 (1999)


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Fast solar wind acceleration by Alfvén waves: observable effects on the EUV lines detected by SOHO/UVCS

R. Ventura 1, S. Orlando 2,3, G. Peres 2 and D. Spadaro 1

1 Osservatorio Astrofisico, Città Universitaria, V. le A. Doria 6, 95125 Catania, Italy
2 Dipartimento di Scienze Fisiche ed Astronomiche, Sezione di Astronomia, Piazza del Parlamento 1, 90134 Palermo, Italy
3 Solar System Division, ESA Space Science Department, ESTEC, Postbus 299, 2200 AG Noordwijk, The Netherlands

Received 12 February 1999 / Accepted 27 October 1999

Abstract

SOHO/UVCS observations of the most intense EUV spectral lines emitted by the solar corona have been providing us a good opportunity to study in detail the acceleration regions of the solar wind. In this work we aim at deriving useful diagnostics and identifying possible signatures of Alfvén waves momentum deposition. More specifically we investigate, with the help of a detailed wind model (Orlando et al. 1996), the insight and the constraints that these observations give on the presence of Alfvén waves, as deduced from the influence of the waves on the solar wind structure and dynamics.

The model developed by Orlando et al. (1996) accounts for the momentum deposition by a spectrum of non-WKB Alfvén waves, generated in the Sun's lower atmosphere and undergoing significant reflection across the transition region. We compute a set of wind solutions characterized by different physical conditions, synthesize, from them, the emission in the Ly[FORMULA], Ly[FORMULA] and O VI doublet (1032 Å, 1038 Å) lines and derive possible diagnostics. We finally compare our results with the most recent SOHO/UVCS data.

Key words: Sun: corona – Sun: solar wind – Sun: UV radiation

Send offprint requests to: R. Ventura (rventura@alpha4.ct.astro.it)

© European Southern Observatory (ESO) 1999

Online publication: December 2, 1999

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