Observations of magnetosheath structure upstream of the magnetopause

It is well known that the flow of the magnetised solar wind over the Earth's magnetosphere establishes an intricate system of upstream wave-fronts and shocks. In the framework of MHD theory, the bow shock is formed by the fast mode, while physical conditions for the Alfven and slow mode waves to stand in the flow behind the bow shock (but upstream of the magnetopause) exist. In this article we survey the multi-instrument data of AMPTE/IRM taken on an inbound orbit leg on 11 December 1984 in the midmorning sector (09:30 LT) of the Earth's magnetosheath. We find that the magnetic field signature exhibits a highly compressive nature, which is in almost perfect anti-correlation with the plasma density throughout the whole magnetosheath crossing. There is also the clear signature of a magnetosheath plasma depletion layer ahead of the magnetopause. Furthermore, we discover strong evidence for the existence of a standing slow mode front in the mid-sheath region, and we suggest that both upstream and downstream of this, mirror mode structures are detected convecting past the spacecraft.