Variation of the ion-temperature gradient along field lines in the outer plasmasphere

Abstract

The equations of thermal diffusion are used to explore the variation of the ion-temperature in the outer plasmasphere, where H + is the dominant positive ion. The ion-temperature gradient component in the direction of the magnetic field is a function of only the ratio of the H + scale height to the He + scale height along the field direction and the gravitational acceleration when the ion and electron temperatures are equal. However, if the scale heights are equal then the ion-temperature gradient is independent of the temperature and depends only on the gravitational acceleration. The ion-temperature gradients are determined throughout the plasmasphere where the H +, He + concentration ratio is assumed to be spatially invariant. At an altitude of 1000 km in the protonosphere, the magnitude of the computed upward directed ion temperature gradient component along the field line increases from 0.9°K/k near L = 1.3 to 1.5°K/km at L = 5. The computed ion-temperature variations are in general agreement with electron-temperature observations in the topside ionosphere and the outer plasmasphere.