Influence of solar activity on penetration of travelling planetary-scale waves from the troposphere into the thermosphere

Abstract

In this study, numerical simulations of planetary-scale waves (PSWs), generated in the troposphere, were performed for altitudes from the Earth’s surface up to 300 km. The influence of thermospheric effects of solar activity (SA) on the amplitudes and phases of westward travelling PSWs with zonal wavenumbers 1 – 2 and periods 4 – 16 days propagating from the troposphere was simulated. Such simulations for a large number of PSW modes in the thermosphere were made for the first time. The effects of SA changes at altitudes above 100 km were involved in the general circulation model MUAM. The ionospheric conductivities for minimum and maximum SA levels were included into the MUAM. The simulation results were averaged over two ensembles of model runs with different PSW phases for conditions corresponding to the high and low SA levels for January – February. PSW atmospheric refractivity index and Eliassen-Palm flux (EP-flux) were calculated. They correspond to simulated changes in PSW amplitudes. Changes in the zonal velocity and temperature caused by the SA variations can modify spatial distributions of the westward travelling PSWs. Wave amplitudes significantly (up to 100%) decrease at the thermospheric heights under high SA, which is accompanied by decreasing vertical component of the EP-flux. The 7-, 10- and 16-day PSWs could have larger partial reflection and worse propagation conditions than the 4- and 5-day waves in the Southern Hemisphere under the high SA. At altitudes below 100 km, minor differences in zonal velocity and PSW amplitudes between high and low SA are found.