Latitudinal Distribution of Electron Concentration from the Alouette-II Topside Sounder

Abstract

Electron density profiles from the Alouctte-II satellite are used to study the latitudinal distribution of electrons to heights up to 3000 km in the topside ionosphere. The electron density in the topside decreases as one goes away from the equator, resulting in a trough at mid to high latitudes for both day and night conditions in the winter hemisphere and only for night conditions in other seasons. This trough, however, is not always seen at the F2 peak. On the dayside, while the trough is not observed for altitudes up to 1000 km, the higher altitudes indicate a tendency towards the formation of the trough. The plasma scale heights, obtained from the electron density profiles, show a sharp decrease at and above the trough latitudes, indicating the dominance of atomic oxygen ions and the depletion of lighter ions at these latitudes. These results are in agreement with the ion composition measurements on various satellites and the polar wind theory which predicts an upward plasma flow at the high latitudes.