Interannual and intraseasonal variability of stratospheric dynamics and stratosphere-troposphere coupling during northern winter

The UK Met Office reanalysis data have been used to investigate the interannual and intraseasonal variability of the stratospheric dynamics and thermal structure. The results obtained show that the maximum of interannual variability of the mean zonal flow associated with the quasi-biennial oscillation (QBO) is observed at the altitude of about 30 km. It is shown that there is a statistically significant influence of the QBO phase on the extratropical stratosphere, the so-called, Holton-Tan effect. The results of data analysis show that the conditions under the easterly QBO phase are more favorable for the development of the sudden stratospheric warmings (SSW). The statistical analysis of 15 major SSW observed during two last decades has been performed. The obtained results demonstrate that in recent years internal processes associated with nonlinear interactions of stationary planetary waves (SPW) with the mean flow played a dominant role. It is shown that the first enhancement of the SPW1 in the upper stratosphere takes place because of an amplification of nonlinear interactions between this wave and the mean flow. This enhancement is accompanied by a subsequent increase in the wave activity flux from the stratosphere into the troposphere with further redistribution of wave activity in the horizontal plane. Then, an increase of the upward flux from the troposphere into the stratosphere in another region occurs. The secondary enhancement of the planetary wave activity in the stratosphere is accompanied by the heating of the polar region and the weakening, or even reversal of the stratospheric jet. Additionally to the well-known result that meridional refraction of SPW to the polar region in stratosphere is one of the preconditions of development SSW, the nonlinear wave-wave and wave-mean flow interactions can play an important role before and during SSW. It is shown that the upper stratosphere can be considered as the region where SPW2 is generated during SSW. (C) 2015 Elsevier Ltd. All rights reserved.