Influence of Solar Activity on the Amplitudes of Migrating and Non-migrating Atmospheric Tides

Solar thermal tides significantly impact global atmospheric circulation. Being a key factor of the dynamic relationship between atmospheric layers, tides ensure the distribution of the effect of changing solar forcing over all atmospheric layers. Therefore, it is important to study different external factors which can influence solar thermal tide generation and propagation throughout the atmosphere. Using the mechanistic nonlinear numerical general circulation model of the middle and upper atmosphere (MUAM), we examine the influence of variations in solar activity (SA) on the spatiotemporal structure of tides. Two ensembles of MUAM simulations of the global atmospheric circulation in January are considered, each consisting of 16 runs corresponding to high and low SA. An increase in solar forcing at high SA weakens diurnal migrating tide DW1 in the altitude range 100–150 km and intensifies it at higher altitudes. The analysis of the Eliassen–Palm (EP) fluxes shows a significant correlation between changes in the vertical propagation of wave activity and DW1 amplitude: downward flux increments generally correspond to tide weakening in the altitude range 110–150 km, while upward flux increments correspond to tide strengthening above 150 km. Semidiurnal migrating tide SW2 weakens at high SA at altitudes of up to 140 km in the Southern Hemisphere and 190 km in the Northern Hemisphere in the mid- and high-latitude thermosphere. This is mainly accompanied by weakening of the upward EP fluxes. Above 200 km, SW2 amplitude increases by a factor of two to three at high SA in the Northern Hemisphere. Above 150 km in the thermosphere, the amplitude of stationary planetary wave with zonal wavenumber 1 (SPW1) decreases at high SA, while the amplitude of the migrating tides increases. Together, these result in a complex structure of changes in the amplitudes of non-migrating tides. Understanding the complex mechanisms of dynamic interactions between tides and atmospheric circulation is important for improving numerical forecasts of changes in atmospheric processes on different time scales, from days to decades.