A COMPARISON OF IN-SITU MEASUREMENTS OF (E)OVER-RIGHT-ARROW AND -(V)OVER-RIGHT-ARROW X (B)OVER-RIGHT-ARROW FROM DYNAMICS EXPLORER-2

Dynamics Explorer-2 provided the first opportunity to make a direct co mparison of in situ measurements of the high-latitude convection elect ric field by two distinctly different techniques. The vector electric field instrument (VEFI) used antennae to measure the intrinsic electri c fields and the ion drift meter (IDM) and retarding potential analyze r (RPA) measured the ion drift velocity vector, from which the convect ion electric field can be deduced. The data from three orbits having l arge electric fields at high latitude are presented, one at high, one at medium, and one at low altitudes. The general agreement between the two measurements of electric field is very good, with typical differe nces at high latitudes of the order of a few millivolts per meter, but there are some regions where the particle fluxes are extremely large (e.g., the cusp) and the disagreement is worse, probably because of ID M difficulties. The auroral zone potential patterns derived from the t wo devices are in excellent agreement for two of the cases, but not in the third, where bad attitude data may be the problem. At low latitud es there are persistent differences in the measurements of a few milli volts per meter, though these differences are quite constant from orbi t to orbit. This problem seems to arise from some shortcoming in the V EFI measurements. Overall, however, these measurements confirm the con cept of ''frozen-in'' plasma that drifts with velocity E over arrow po inting right x B over arrow pointing right/B2 within the measurement e rrors of the two techniques.