MMS Observations of Magnetosheath Field Enhancements and Pressure Pulses: Causes and Consequences

The supersonic solar wind is slowed by the bow shock and deflected by the magnetosphere. At the magnetopause, the dynamic pressure has been converted to thermal and magnetic pressure that is in balance with the pressure of the magnetosphere. As observed by MMS, the magnetosheath is a very dynamic and structured region. There are flux ropes (FRs), flux transfer events (FTEs) and high-speed jets (HSJs) as well as pressure enhancements with central current sheet that we have called magnetosheath field enhancements (MFEs). We use the MMS tetrahedron of measurements to examine this current sheet and the pressure enhancement. We contrast these features with magnetopause crossings and flux transfer events.

A possible cause of MFEs is charged-dust mass loading of the solar wind which is slowed minimally in crossing the bow shock. The MFE is gradually slowed and deflected by the magnetosheath plasma and ultimately by the magnetopause. This process is essentially the inverse of the acceleration in the solar wind, which create structures called interplanetary field enhancements (IFEs). The IFE and MFE share a common structured plasma and field pattern, suggesting their similar origin - produced by acceleration and ended by deceleration of a magnetized plasma construct.