The evolution of various nonlinear processes associated with the propagation of stationary planetary waves (SPW) during sudden stratospheric warmings (SSW) is studied from the troposphere up to the lower mesosphere levels. Based on data of the UK Met Office (UKMO), the spatiotemporal structure of the processes of planetary waves interaction with each other and with the mean flow, as well as wave activity, potential enstrophy flux divergence and advection, was analyzed. Such an analysis was performed for the 2008-2009 winter, when an SSW, accompanied by the splitting of the stratospheric polar vortex, was observed and for the 2018-2019 winter, when an SSW with the displacement of the stratospheric polar vortex was observed. The results show that these SSWs are succeeded by significant differences in the nonlinear processes under consideration. It is also demonstrated that during the SSW with the stratospheric polar vortex displacement the contribution of various processes to the balance of the disturbed potential enstrophy for SPWs with different zonal wavenumbers is comparable. In addition, during the SSW with the stratospheric polar vortex splitting, the exchange of waves with the mean flow makes the greatest contribution to the perturbed potential enstrophy balance.
In the stratosphere, there is a correlation between changes in the amplitudes of stationary planetary waves. This correlation is most clearly manifested during sudden stratospheric warmings (SSWs). An analysis of wave-wave and wave-mean flow interactions during winter 2008-2009 and 2018-2019 sudden stratospheric warmings was made using the equation of perturbed potential enstrophy. It is shown that wave-wave interactions make the least contribution to the wave activity variation during the 2008-2009 SSW, the contribution of all interactions is comparable during the 2018-2019 SSW.
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.
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