Magnetosheath plasma structures and their relation to foreshock processes

摘要

We present simultaneous Time History of Events andMacroscale Interactions during Substorms observations of plasma parameters upstream in the solar wind and downstream in the magnetosheath (MSH) from 2007 to 2008. We discuss the connection of foreshock (FSH) processes and magnetospheric disturbances to transmission mechanisms in the MSH. In 60% of the analyzed cases, the MSH was strongly influenced by the FSH. We analyze the results as a function of location, time scale, spatial orientation of the observed structures, and the prevailing interplanetary magnetic field (IMF) and solar wind plasma parameters. We find that plasma structures with density enhancement are mostly observed during radial IMF orientations and for small θ_(BN), the angle between the upstream magnetic field and the local bow shock normal; the observed structures are pressure balanced with strong anticorrelation between density and temperature; the scale size of the density fluctuations is about 0.4R_E. We compare the observations with results from a 2.5-dimensional hybrid simulation to investigate the mechanisms by which the foreshock plasma structures are generated, propagate through the bow shock, and evolve.