Comparison of coincident OGO 3 and OGO 4 hydrogen ion composition measurements

Abstract

Ion composition measurements made on August 8, 1967 and August 28, 1967 by the topside ionospheric polar orbiting satellite OGO 4 and simultaneously by the eccentric orbiting magnetospheric satellite OGO 3 were compared on nightside passes through the plasmasphere. Throughout most of the midlatitude regions sampled, an isothermal diffusive equilibrium model at an ion temperature of 1000°K provides a good approximation for coupling these ionospheric regions. However temperature gradient components directed upwards along the field lines of the order of 1°K/km or greater are required to bring the profiles into agreement near the plasma pause assuming diffusive equilibrium and assuming the magnitude of the temperature gradient does not vary along the field line. Similar gradients are also required along the low latitude field lines traversed on the August 28, 1967 passes. In agreement with previous studies of the average local time asymmetry of the plasmasphere boundary, the plasmapause L coordinates measured by OGO 3 near midnight were greater than the L coordinates associated with the light ion troughs observed near dawn on the coincident OGO 4 pass. In the steady state, if field line preservation is assumed and the convection stream-line pattern in the equatorial plane is known, the H + densities measured at different local times along the OGO 3 trajectory can be transformed into densities at a local time characteristic of the OGO 4 measurements so that the transformed OGO 3 plasma-pause is located on the same field line as the plasmapause determined from the OGO 4 measurements.