IMP-8 OBSERVATIONS OF A POLEWARD PLASMA CIRCULATION - EVIDENCE OF ENTRY INTO THE PLASMA MANTLE

Plasma data from IMP 8 are used to map the spatial structure of plasma how in Earth's magnetosheath. Plasma and magnetic field data from ins truments on ISEE-3 and WIND are used to normalize the IMP 8 magnetoshe ath data to upstream solar wind conditions. For the majority of the da ta, the magnitude and direction of plasma how inside the magnetosheath agree well with gas-dynamic models. About 8% of the ISEE-3-normalized velocity vectors and 3% of the WIND-normalized velocity vectors exhib it a poleward circulation in the YZ plane. The observed circulation is consistent with predictions for flow within the plasma mantle. The oc currence frequency of these poleward hows increases further down the t ail, consistent with predictions that the mantle width increases tailw ard. Densities are lower where this how is observed, consistent with e xpectations for the plasma mantle, but temperatures are higher and the magnetic field magnitudes lower, the opposite of theoretical expectat ions.