Variability of thermospheric neutral densities from satellite observations

The thermosphere is a layer of the atmosphere that extends from about 90 to 500 km. Thermospheric neutral densities are critical in planning of Low Earth Orbit satellite missions, as the neutrals produce perturbations in the orbits due to drag. Because the ionosphere is embedded in the thermosphere, gaining insight into the variability of thermospheric densities improves our understanding of how the thermosphere, ionosphere, and lower atmosphere are coupled. The ionosphere, in turn, affects technologies such as HF communications and GNSS positioning.

Data from the Gravity field and steady-state Ocean Explorer (GOCE) mission are used in this study. The mission provided dawn and dusk neutral densities between about 220 km to 270 km of altitude, with variations in the height of the satellite within one orbit of about 20 km. Thermospheric neutral densities vary with latitude, longitude, solar flux, geomagnetic conditions, seasons and local time. They generally fall off exponentially with altitude, with scale heights varying from 25 to 75 km. Therefore, in order to study other variations, normalization of the densities to a reference altitude is necessary for the GOCE dataset due to the large variations within the same orbit. In this work, we normalize the observed densities for both dawn and dusk in order to study their variability due to other factors.