Influence of solar activity on the amplitudes of migrating and non-migrating atmospheric tides
A.V. Koval1,2, N.M. Gavrilov1, K.A. Didenko1,3, T.S. Ermakova1,2, A.V. Sokolov1
1Saint Petersburg State University, St. Petersburg, Russia
2Russian State Hydrometeorological University, St. Petersburg, Russia
3Pushkov Institute of Terrestrial Magnetism, Ionosphere, and Radio Wave Propagation, Russian Academy of Sciences, Troitsk, Russia
Keywords: atmospheric tide, migrating and non-migrating tides, solar activity, wave activity, global atmospheric circulation, numerical simutation
Abstract
Solar thermal tides have a significant impact on global atmospheric circulation, making it important to study the various external factors that can influence their generation and propagation throughout the atmosphere. Using the mechanistic nonlinear numerical general circulation model of the middle and upper atmosphere (MUAM), this paper examines the influence of solar activity (SA) variations 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. It is shown that with increasing solar forcing at high SA, the diurnal migrating tide (DW1) weakens in the altitude range 100-150 km and intensifies at higher altitudes. The analysis of the Eliassen-Palm (EP) fluxes demonstrates a significant correlation between changes in the vertical propagation of wave activity and the amplitude of DW1: downward flux increments generally correspond to tide weakening in the range 110-150 km, while upward flux increments correspond to strengthening of the tide above 150 km. The 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 accompanied by mainly weakening of the ascending EP fluxes. Above 200 km, SW2 amplitude in the Northern Hemisphere increases by a factor of 2-3 at high SA. Above 150 km in the thermosphere, the amplitude of the stationary planetary wave with zonal number 1 (SPW1) decreases at high SA, while the amplitude of the migrating tides increases. Taken together, this leads to a complex structure of changes in the amplitudes of non-migrating tides. As an important link in the dynamic relationship between atmospheric layers, tides, in particular, provide the distribution of the effect of changing solar forcing during varying solar activity across all atmospheric layers. Understanding the complex mechanisms of dynamic interactions between tides and atmospheric circulation is important for improving numerical forecasts of changes in atmospheric processes on various time scales, from days to decades.
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