Variations in the Solar Wind Velocity of the Daily Range (Microstreams) in the Near-Earth Space and Remote Areas of the Heliosphere

Abstract

The article studies microstreams, increases in solar wind (SW) currents up to several tens of km/s, with a time scale of the order of a day. A comparative analysis of microstreams present in the polar and low-latitude SW at different heliocentric distances has been carried out. The comparison showed that the properties of microstreams in the near-Earth fast SW are qualitatively similar to the properties of microstreams present in the polar SW during periods close to solar activity minima, at heliocentric distances from 2 to 4.5 AU. At the same time, the quantitative parameters of microstreams (amplitudes of variations in radial and tangential velocity, as well as relative variations in temperature, density, and plasma pressure) show a monotonic decrease with increasing heliocentric distance, which can be interpreted as a consequence of the gradual evolution of microstreams with distance from the Sun. However, comparison with SW measurements in the low-latitude region of the heliosphere at distances of about 5 AU shows some significant differences, which indicate a more rapid evolution of microstreams in the inhomogeneous low-latitude SW.