An estimate of large-scale solar wind density and velocity profiles in a coronal hole and the coronal streamer belt

Abstract

With the use of the total electron content data obtained by the Ulysses Solar Corona Experiment (SCE) during the first solar conjunction in summer 1991, two data sets were selected, one associated with a coronal hole and the other associated with coronal streamer belt crossings. To determine a large-scale coronal streamer belt density profile, the electron content of the tracking passes embedded in the coronal streamer belt were corrected for the contributions from coronal hole densities. The inferred large-scale streamer belt electron density profile has a radial falloff exponent of -2.4 for distances greater than 7 Rs implying the acceleration of the slow solar wind according to v(r) ∼ r0.4, in qualitative agreement with SOHO results. The acceleration terminates beyond 60 Rs in agreement with Helios in situ observations. All radial electron density profiles inferred from coronal radio sounding observations, particularly during times of high solar activity, are dominated by coronal streamer contributions. They are applicable to coronal streamers, confined to a limited latitude range about the heliospheric current sheet, and they are not representative of a large-scale mean coronal electron density profile. Because of a lack of data, similar analysis of the coronal hole electron content data was not unequivocally feasible. The coronal hole tracking passes corrected for contributions from coronal streamer areas display large electron content and density fluctuations inconsisting with the plume interpretation by Woo [1996]. Assuming that the lowest densities represent typical hole densities and comparing these with streamer densities at the same distance, we found the streamer-to-hole density ratio to be a factor of 10, which agrees with white light coronagraph results. Copyright 1997 by the American Geophysical Union.