Charged-particle temperatures and concentrations in the Earth's exosphere

Abstract

Under the assumption that the earth's magnetospheric plasma between 800 km and the plasmapause is in diffusive equilibrium, charged-particle temperatures and concentrations throughout the region are estimated from experimental electron concentration and scale-height data near the base of the region. Using various plausible models of electron and ion temperature distributions, relative abundances of oxygen, helium, and hydrogen ions near the base level as functions of dip latitude are computed. Ion temperatures and temperature gradients are also deduced. Experimental data employed in the analysis include Alouette 1 midlatitude electron concentration profiles, Explorer 22 electron temperature data, and equatorial electron concentration profiles deduced from whistler observations. It is found that daytime temperature gradients of 1–2°K/km near 30° dip latitude at 1000 km and decreasing with latitude must exist along the field lines for the experimental data to be compatible with thermal equilibrium and a constant temperature gradient above 800 km. For unequal electron and ion temperatures, lower temperature gradients suffice. The relative abundance of hydrogen (oxygen) ions at 1000 km decreases (increases) dramatically with latitude, while the helium abundance shows little systematic variation. The results compare favorably with independent measurements of ion temperature and composition, lending confidence in the basic diffusive equilibrium assumption.