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Ann. Geophys., 20, 1265-1277, 2002
www.ann-geophys.net/20/1265/2002/
© European Geosciences Union 2002
Estimating random transverse velocities in the fast solar wind from EISCAT Interplanetary Scintillation measurements
A. Canals1, A. R. Breen1, L. Ofman2, P. J Moran1, and R. A Fallows1
1Physics Department, University of Wales, Aberystwyth, Wales, UK
2The Catholic University of America and NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
Correspondence to: A. R. Breen (azb@aber.ac.uk)
Abstract. Interplanetary
scintillation measurements can yield estimates of a large number of solar wind
parameters, including bulk flow speed, variation in bulk velocity along the
observing path through the solar wind and random variation in transverse
velocity. This last parameter is of particular interest, as it can indicate the
flux of low-frequency Alfvén waves, and the dissipation of these waves has
been proposed as an acceleration mechanism for the fast solar wind. Analysis of
IPS data is, however, a significantly unresolved problem and a variety of a
priori assumptions must be made in interpreting the data. Furthermore, the
results may be affected by the physical structure of the radio source and by
variations in the solar wind along the scintillation ray path. We have used
observations of simple point-like radio sources made with EISCAT between 1994
and 1998 to obtain estimates of random transverse velocity in the fast solar
wind. The results obtained with various a priori assumptions made in the
analysis are compared, and we hope thereby to be able to provide some
indication of the reliability of our estimates of random transverse velocity
and the variation of this parameter with distance from the Sun.
Key words. Interplanetary physics (MHD
waves and turbulence; solar wind plasma; instruments and techniques)
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