Numerical Modeling of the Impact of Natural Tropical Oscillations on the Amplitudes of Atmospheric Tides During Sudden Stratospheric Warming

In order to study the evolution of atmospheric tides, model simulations of the general atmospheric circulation were carried out using a 3-dimensional nonlinear mechanistic model “MUAM”. The following are considered as natural tropical oscillations: the quasi-biennial oscillation of the equatorial zonal wind (QBO) in the stratosphere and the El Ni˜no Southern Oscillation (ENSO). Changes in tidal amplitudes are analyzed at three 10-day time intervals before, during and after a sudden stratospheric warming (SSW). Composite SSWs consisting of 6 events within the calculation ensembles are considered for each QBO/ENSO combination. Migrating and non-migrating diurnal and semi-diurnal tides with zonal wave numbers 1 and 2 are studied. Numerical experiments have shown in particular, that the structure of tides is susceptible to the effects of SSW, while during SSWs the amplitudes of tides for different combinations of QBO – ENSO change differently. For example, during El Ni˜no and the easterly QBO phase, there is a noticeable weakening of the diurnal migrating tide during the SSW, while during La Ni˜na and the easterly QBO phase, on the contrary, the amplitude of the diurnal tide increases during the event, and after the SSW it weakens. Analysis of numerical experiments confirms existing ideas about significant variability of tides during SSW and demonstrates the most important source of this variability associated with combinations of QBO-ENSO dynamic effects.