Low alpha temperatures in the solar wind magnetic closed structures

Summary

As is already known, closed structures in interplanetary magnetic field reduce the solar-wind electron and proton temperatures and possibly diminish the flux of low-rigidity cosmic rays within them. In this analysis, an attempt is made to search for any influence of closed structures on the alpha component,i.e. to detect a possible cooling and rarefaction of these ions like protons, when they are encircled by these structures. Seven isolated events of such features are used for a superposed epoch analysis from a 5-year period data set provided by Helios-1 during its 20 successive trajectories from 0.3 to 1 AU (January 1975-December 1979). This epoch analysis is similar to that of Zhang and Burlaga. Because data are not taken at a fixed (1 AU) but rather at different distances (Helios-1), all hourly values used are normalized to 1 AU (i.e., temperature, density and magnetic field). After the application of the above-mentioned criteria for closed structure development, applied for the whole 5-year period, about 50 hourly values fulfilling them have been found. The selected values are part of several closed structures the characteristic parameters of which are superposed. This analysis shows a unique behaviour of alpha particles inside magnetically closed structures, which however does not exclude their being influenced by such structures.