A model of the terrestrial ionosphere in the altitude interval 50–4000 km I. Atomic ions (H+, He+, N+, O+)

Abstract

An empirical model of atomic ion densities (H+, He+, N+, O+) is presented up to 4000 km altitude as a function of time (diurnal, annual), space (position, altitude) and solar flux (F10.7) — using observations of satellites (AE-B, AE-C, AE-D, AE-E, ISIS-2, OGO-6) and rockets during quiet geophysical conditions (K p ⩽ 3). The numerical treatment is based upon harmonic functions for the horizontal pattern and cubic splines for the vertical structure. The ion densities increase with increasing height up to a maximum (depending roughly on the ion mass) and decrease beyond that with increasing altitude. Above 200 km, O+ is the main ionic constituent being replaced at approximately 800 km (depending on latitude, local time, etc.) by H+. Around polar regions the light ions, H+ and He+, are depleted (polar wind) and the heavier ones enhanced. During local summer conditions the ion densities increase around polar latitudes and correspondingly decrease during local winter, except He+ which reflects the opposite pattern. Diurnal variations are intrinsically coupled to the individual plasma layers: N+ and O+ peak, in general, during daytime, while the amplitudes and phases of H+ and He+ change strongly with altitude and latitude.