Latitude dependence of Solar Wind plasma thermal noise: ULYSSES radio observations.

Abstract

Thermal noise spectroscopy was performed on the URAP radio receiver data for the first time out of the ecliptic during the Ulysses spacecraft transit from southern to northern heliolatitudes. We present the results on the solar wind electron density and bulk temperature obtained from -43°S to +43°N. They indicate a rough symmetry of the solar wind electron plasma about the solar equator. The latitudinal gradient of the electron bulk temperature was found to be approximately -830K/° latitude southward and -1100K/° northward. Within +/-20° latitude, large fluctuations in the 1-AU scaled electron density and temperature were observed and presumably linked to the corotating structures existing in the equatorial band. Effects of the solar wind speed on the thermal noise spectra were highest at high latitudes as predicted. They will be fully taken into account in future work.