The magnetopause layer and plasma boundary layer of the magnetosphere

Satellite coverage of the sunward magnetopause and plasma boundary layer (PBL) are shown schematically and discussed for four satellites that include both plasma and field measurements. Plasma observations from the VELA satellites first established the continued presence of magnetosheath-like plasma with reduced density and flow velocity in a relatively thin (less than about 1 earth radius) layer bordering the plasma sheet at low latitudes and bordering the lobe environment at high latitudes. Satellite data have demonstrated the presence of PBL over the entire sunward magnetosphere near the magnetopause. A brief summary is presented of recent published results on two distinct regions of the PBL: that bordering open field line regions, and that bordering closed field line regions. Several suggested source mechanisms for the PBL are discussed and compared