Longitudinal Variation in the Mass Density of the Thermosphere: A GAIA Simulation

Using a whole atmosphere-ionosphere coupled model, we investigate the longitudinal variation in the mass density of the upper thermosphere. The simulation results indicate that wave-3 and wave-4 structures in the longitudinal direction at a fixed local time frame are mainly generated by an eastward-moving diurnal tide with zonal wavenumbers of 2 and 3, respectively. However, other nonmigrating tides also contribute to the generation of the longitudinal variation. In particular, nonmigrating terdiurnal and 6 h tides play important roles. The nonmigrating tides that generate the longitudinal variation in the upper thermosphere are excited in the lower atmosphere and propagate into the upper thermosphere. This result implies that spatiotemporal variations in the lower atmosphere affect the longitudinal/local time variation in the thermospheric mass density through the vertical propagation of nonmigrating tides.