THE MAGNETOPAUSE AND BOUNDARY-LAYER FOR SMALL MAGNETIC SHEAR - CONVECTION ELECTRIC-FIELDS AND RECONNECTION

Convection electric fields, Ec = −Vp×B, measured during a magnetopause/boundary layer encounter at low latitude by the AMPTE/IRM spacecraft, are shown to yield an accurate determination of the magnetopause normal vector, N, even though the magnetic shear across the magnetopause was small. The average plasma velocity along N is used to deduce a boundary layer thickness of about 1.3 RE. Analysis of Ec in the magnetopause itself reveals the existence of a deHoffmann‐Teller frame in which the flow is nearly field aligned and approximately Alfvénic, indicating that the magnetopause was a rotational discontinuity; this is interpreted as a signature that magnetic‐field reconnection was occurring somewhere on the magnetopause. Copyright 1990 by the American Geophysical Union.