On the diurnal and seasonal variations of H+, He+, N+, O+, and Ne at 1400-km altitude

Abstract

The diurnal and seasonal variations of H+, He+, N+, O+ and Ne are analyzed at 1400-km altitude. Using longitudinally averaged observations of ISIS-2 (April 1971 to December 1972), the ion and electron densities are decomposed via spherical harmonics and Fourier series into time-independent, seasonal and diurnal terms. The time-independent terms of H+ and He+ show a plateauor trough-like structure at medium to low latitudes and a strong decrease towards the poles; N+ and O+, on the other hand, yield an almost inverse picture with a density increase at high latitudes. All constituents, except He+, show at polar latitudes an enhancement during local summer conditions and a depletion during local winter conditions; He+, however, exhibits a winter bulge and a density minimum during local summer. The diurnal variations are strongly latitude dependent; while the amplitudes (relative) of H+, He+, and Ne are rather small, the heavier ions N+ and O+ show a deep minimum early in the morning and a high but flat maximum during daytime. © 1981.