ISIS-1 satellite observations of the ionosphere at high southern latitudes

Abstract

Topside sounder data from consecutive passes of ISIS-1 over the south polar region during November 1969 have been used to produce contour ‘maps’ of ƒ 0F2 , and these are compared with observations of the neutral N 2 and electron concentrations reported by other workers. It is shown that at night at longitudes near 90°W large values of ƒ 0F2 occur at latitudes lower than 70°S, but that at higher latitudes the critical frequency decreases rapidly, forming an ionization ‘cliff’ at approximately 60° invariant latitude. Evidence is presented which indicates that on the poleward side of the cliff appreciable heating of the atmosphere occurs and that the low values of ƒ 0F2 are caused by an increase in the electron loss rate associated with an enhancement of the N 2 concentration in the polar region.