On the distribution of θBn for shocks in the solar wind

Abstract

The distribution of the shock normal angles, θBn, can be calculated for all the heliocentric distances when the distributions of and are available, where θBn is the angle between the upstream magnetic field and the shock normal . The average shock normal is assumed to propagate approximately in the radial direction. However, the distribution of the angles, θnr′ between the shock normals and radial direction is assumed to follow a Rayleigh distribution. The distribution of is obtained by observations by Helios 1 and 2, Voyager 1, and Pioneer 10 spacecraft. The distribution of each component of is assumed to follow a Gaussian. Our results show that even very close to the sun, the probability of observation of parallel and quasi‐parallel shocks is still smaller compared to the observation of quasi‐perpendicular and perpendicular shocks. Therefore it is concluded that the parallel and quasi‐parallel shocks do not easily form in the solar wind because of the fluctuating character of and and not because of any other physical mechanism. The observed distributions of θBn using Helios 1 and 2 at heliocentric distances between 0.3 to 0.5 AU, 0.5 to 0.75 AU, and 0.75 to 1.0 AU are compared with our calculated distributions. The agreement is good, with the agreement at 0.75 to 1.0 AU being the best. The comparison is also made with the results from ISEE 3 observations at 1 AU. Our calculated distribution agrees very well with these observations.