ISEE observations of the dayside magnetosheath

Abstract

A survey of the density profile near the stagnation streamline from the bow shock to magnetopause reveals the existence of a slow mode structure, in which the plasma density first increases and then decreases while the magnetic field strength changes oppositely, near the magnetopause. A case study with multiple spacecraft shows that this structure is locally generated and stands in the incoming solar wind flow. The flow speed changes from super-slow to trans-slow across the outer edge of the structure. The waves within the structure appear to be different from those upstream of the structure. The waves upstream are convective but the waves within the structure are propagating. In the plasma frame, the latter propagate upstream from the magnetopause. They are quasi-standing in the Earth's frame. These observations lead to an interpretation that this structure is formed from the slow mode waves launched at the magnetopause to enforce the final boundary condition at the magnetopause. The outer edge of the structure marks the greatest distance that slow modes can propagate upstream into the solar wind. A comprehensive discussion concerning the theoretical significance of this structure is given.