Solar cycle variation of ionosphere-thermosphere parameters

The recent solar minimum seems to be extra ordinary in several aspects. The long duration of solar quietness causes upper atmospheric conditions that have rarely been observed before. We make use of observations from the two LEO satellites CHAMP and GRACE for characterising the differences of key ionospheric-thermospheric parameters between times of high and low solar activity. From time to time CHAMP and GRACE orbits are coplanar for about 2 months. These periods are exploited in terms of altitude gradients between about 400 and 500km. We present latitudinal profiles of electron density at the two altitudes for different local times and solar flux levels. The differences are compared with concurrent measurements of the electron temperature by CHAMP. Gradients are interpreted in terms of ion fountain and equatorial ionisation anomaly (EIA) activity. Similarly, the thermospheric mass density is sampled at both altitudes. Again the ratio between the densities is correlated with solar flux separately for different local times. We compare the observed gradients with atmospheric model predictions and make inferences about scale height changes and related compositions. Results will be compared with initial C/NOFS observations.