3-dimensional numerical nonlinear model of general circulation of the middle and upper atmosphere (MUAM) is used to investigate reaction of the atmospheric circulation in the middle and upper atmosphere to changes in phases of equatorial stratospheric quasi-biennial oscillation (QBO). To estimate changes in transport of atmospheric gas species, residual meridional circulation (RMC) is calculated based on the modelled atmospheric hydrodynamic fields for easterly, westerly and transitional (so-called “easterly-shear” and “westerly-shear”) QBO phases. For this purpose, four 10-members ensembles of MUAM simulations have been obtained corresponding to the aforementioned QBO phases. To determine QBO phases, empirical orthogonal functions (EOF) are applied for the equatorial zonal wind profiles. Statistically significant results are obtained illustrating how changes in direction of equatorial stratospheric winds influence extratropical circulation. It is shown in particularly, that the strongest changes in thermal and dynamical conditions of the middle- and high-latitude stratosphere-mesosphere occur during easterly-shear QBO phase.
The study of wave motions in the atmosphere, in particular, atmospheric solar tides is considered in this research. Using the middle and upper atmosphere model (MUAM) data, the latitudinal-high cross-sections of the amplitude and phase of individual tidal components, as well as their temporal variability, were shown. The most suitable periods for the complex Morlet wavelet transform of data were specified for the further use. The results obtained were used to study nonlinear interactions both between atmospheric tides and the mean flow and with each other.
Spectra of the critical frequency of the F2 ionospheric layer in the range of periods 0.5 – 40 days are analyzed using the data of measurements with the ionosonde DPS-4 at the Peterhof scientific station of Saint Petersburg State University (60°N, 30°E). Spectral analysis is executed using the Lomb –Skargle method for 60-day running intervals. Spectra show maxima at periods of 1 day and 0.5 day corresponding to diurnal and semidiurnal changes, and maxima in the range of periods 2 – 40 days. These waves have frequently maximum amplitudes in spring and summer, which is opposite to the PW amplitudes observed in the lower and middle atmosphere. This may be caused by different mechanisms including possible PW propagation from the middle atmosphere of the winter hemisphere to the summer thermosphere along the waveguides crossing the equator at altitudes above 60 km.
Numerical simulations have been performed to estimate sensitivity of ozone fluxes to the impact of mesoscale orographic gravity waves (OGWs) in the middle atmosphere at different phases of simulated stratospheric warming (SW) events during boreal winter. The numerical model of general circulation of the middle and upper atmosphere (MUAM) with implemented OGW parameterization has been used. The simulations demonstrate a weakening of the vertical ozone fluxes during and after simulated SW compared to the time intervals before SW, which corresponds to the changes in meridional mean circulation. The most significant differences in ozone fluxes due to OGW effects are obtained in the Northern Hemisphere. These differences are up to 20% at middle latitudes and may reach 100% at high latitudes. The results indicate a strong sensitivity of the meridional circulation and hence, the ozone fluxes to the influence of OGWs at different phases of simulated SWs.
A parameterization of the dynamical and thermal effects of orographic gravity waves (OGWs) and assimilation quasibiennial oscillations (QBOs) of the zonal wind in the equatorial lower atmosphere are implemented into the numerical model of the general circulation of the middle and upper atmosphere MUAM. The sensitivity of vertical ozone fluxes to the effects of stationary OGWs at different QBO phases at altitudes up to 100 km for January is investigated. The simulated changes in vertical velocities produce respective changes in vertical ozone fluxes caused by the effects of the OGW parameterization and the transition from the easterly to the westerly QBO phase. These changes can reach 40 - 60% in the Northern Hemisphere at altitudes of the middle atmosphere.
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