On the radial expansion of the solar wind plasma between 0.3 and 1.0 astronomical units

Abstract

The radial expansion--within 1 AU heliocentric distance--of the extended solar corona is studied. The work was stimulated by the recent availability of solar wind measurements by the Helios 1 solar probe for the period 1974 December--1975 April covering (for the first time) the interplanetary medium between 1 and 0.3 AU. The first part of the work analyzes these data from a theoretical point of view. Thus, in order to classify the plasma states represented by the data, the particle fluxes Jequivalentnupsilonr/sup 2/ are calculated by using measured proton densities, n/sub p/(r), and streaming velocities, upsilonp (r), and are correlated with heliocentric distances as well as with density and streaming velocity fluctuations, ..delta..n/sub p/ and ..delta..upsilon/sub p/, respectively. The quantity J has been chosen as a classifying criterion. The results of these calculations indicated that (i) the normalized particle flux J-barequivalentJ/J/sub E/ (E indicates 1 AU heliocentric distance) varies by a factor of 10 (between approx.0.5 and 5) over the interplanetary range explored by Helios 1; (ii) the strong deviations from the value 1 are found only for states with streaming velocities below about 500 km s/sup -1/, while for the high-speed states J-barapprox. =1; (iii) the deviations /sup 0/J-bar foundmore » for low-speed states are strongly correlated with particle density fluctuations and moderately anticorrelated with streaming velocity fluctuations; and (iv) time-dependent and/or additional process could play a significant role.In the second part of the work we use all observational data representing high-speed flows (i.e., satisfying the condition upsilon> or =600 km s/sup -1/) in conjunction with the fluid equations for a two-component plasma (protons + electrons) in order to estimate unknown properties of the solar wind.« less