Foreshock Cavities: Direct Transmission Through the Bow Shock

Abstract

AbstractGlobal hybrid code simulations predict enhanced densities and magnetic field strengths not only in foreshock compressional boundaries on the flanks of the steady‐state dayside foreshock under near‐radial IMF conditions but also on the edges of the traveling foreshock cavities formed when slabs of interplanetary magnetic field (IMF) lines connect to the bow shock. The simulations predict only modest velocity or temperature perturbations attending the foreshock compressional/cavity boundaries. However, they predict pronounced flow enhancements and depressed temperatures accompanying the enhanced densities and magnetic field strengths on foreshock compressional/cavity boundaries transmitted into the magnetosheath. Many of these properties are similar to those of magnetosheath jets, previously attributed to processes occurring at locations where the solar wind flow makes a grazing encounter with a locally oblique bow shock. Simultaneous THEMIS observations upstream and downstream from the Earth’s bow shock from 1430 to 1630 UT on June 14, 2007 confirm simulation predictions for the direct transmission of foreshock cavities into the magnetosheath. Foreshock cavity density and magnetic field strength perturbations diminish very rapidly with distance upstream from the bow shock.