Solar wind signatures associated with magnetic clouds

Abstract

Magnetic clouds are commonly observed in association with bidirectional fluxes of electrons and ions, and in some cases also with shocks and helium enrichments [Gosling, 1990; Richardson, 1997]. In this work we use satellite data in the solar wind near Earth to study 71 magnetic clouds observed between 1967 and 1984 in order to find possible differences in the characteristics of clouds when they are or they are not associated with shocks and with helium enhancements. In our sample we find that 51% of the clouds were preceded by an interplanetary transient shock and that 65% were associated with a helium enhancement observed before, inside, or after the cloud. To investigate the characteristics of magnetic clouds we consider the spatial profiles of magnetic field and plasma parameters (bulk speed, density, temperature, β, and pressure) inside them, observed as temporal variations as clouds pass plasma and magnetic field detectors on board satellites in near‐Earth orbit. The mean magnitudes of these parameters inside the cloud were also considered. We find that the profiles of the magnetic field strength and plasma parameters are different depending on whether the cloud is associated or not with a shock and/or a helium enrichment. The mean values of magnetic field strength, bulk speed, temperature, and pressure are higher for shock‐associated clouds than for clouds without a shock. Mean values of bulk speed, density, temperature, and β are different for clouds associated with helium enrichments and for clouds without this signature. Mean values of the magnetic field strength and pressure are very similar for both types of clouds. Some of these results were previously obtained by other authors.