Long-term Variations of Thermospheric Air Mass Density Derived from GRACE Accelerometers

In this study, long-term driver-response relationships of thermospheric mass density variations are derived from 12 year of GRACE accelerometer measurements. In order to obtain long-term variations, diurnal and annual variations have been modeled and removed from the main modes. The global distribution of the averaged thermospheric air mass density shows a clear alignment with vertical magnetic field component. Two asymmetric cells located in each eastern polar side show a southern enhancement and a northern attenuation. The latitudinal variation between the northern and southern polar-regions is positive during all time-span, and strongly controlled by the solar radiation. The reconstructed solution has been averaged and parameterized in terms of the solar-flux F10.7, and geomagnetic Am indices. The results show a considerable magnetospheric forcing on the long-term global thermospheric mass density, which has not been reported previously. With this first results and our planned research, we expect soon to provide an accurate air mass density model for the thermospheric research community.