Observed variations of the exospheric hydrogen density with the exospheric temperature

International audienceMeasurements of exospheric hydrogen densities at a distance of 3 RE (earth radii) are presented as a function of exospheric temperature. They imply that the density nc at the exobase level decreases with exospheric temperature Tc but not enough to keep the Jeans escape flux FJ constant. The increase of FJ with exospheric temperature may be compensated for by the decrease of Fe, which measures the loss of hydrogen by charge exchange in the plasmasphere. The two fluxes would be equal to 6.6 × 107 atoms cm−2 s−1 at a temperature Tc = 1070°K, giving a total escape flux in agreement with measurements of hydrogen compounds in the region from 30 to 50 km and theoretical mesospheric calculations