Influence of the Earth's rotation and of possible perturbations, on the exobase and exospheric hydrogen densities

In this study, we try to refine the relation existing between the exobase temperature and density distributions of atomic hydrogen around the Earth (assuming that the zero net ballistic flux condition is satisfied all over the critical level). We find essentially that neither local heating in high latitude regions, nor the addition of proton fluxes around the Earth, induce large perturbations in the equatorial density distribution (less than 10 per cent). On the other hand, certain local heating can give large perturbations in the global density distribution (more than 50 per cent).

The effect of the Earth's rotation is also studied. We find that at the exobase the density distribution of atomic hydrogen lags about one hour behind the temperature distribution. At higher altitudes this time lag increases, reaching 5-6 hr at 20 Earth radii.

We show also that, due to a density inversion which takes place at 2 Earth radii, if the minimum of density at the exobase is on the dayside, above 2 Earth radii, a maximum of density is then on the dayside when going higher, due to the rotational effect, that density maximum shifts towards the evening, reaching early parts of the night at 20 Earth radii.