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Astron. Astrophys. 350, 302-309 (1999)

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A determination of the outflow speeds in the lower solar wind

S.J. Tappin, G.M. Simnett and M.A. Lyons

School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, UK

Received 12 January 1999 / Accepted 19 July 1999


The acceleration of the low-latitude solar wind, which comes from regions of the corona above large, closed magnetic loops, is a theoretical challenge. Until recently we have lacked direct measurements close to the Sun with which to constrain the theory. When a series of high-resolution coronagraph images is viewed in the form of a movie the continuous outflow of matter from the Sun is very obvious. We report here the results of a correlation analysis of the LASCO coronagraph images from the SOHO spacecraft which we have used to estimate the low-latitude solar wind speed from 3-27 [FORMULA]. Acceleration occurs to the outer parts of this radial range, by which time the solar wind has approached its measured speed at 1AU, implying little acceleration beyond [FORMULA]30 [FORMULA]. A very significant result is the detection of a component flowing out at speeds up to [FORMULA]1500 km s-1, which is energetically very important and possibly dominant.

Key words: Sun: solar wind – Sun: corona

Send offprint requests to: S.J. Tappin

Correspondence to: S.J. Tappin (sjt@star.sr.bham.ac.uk)

© European Southern Observatory (ESO) 1999

Online publication: September 24, 1999