Wind in the lower thermosphere and stratospheric warmings

Abstract

Investigations of the winter-time behavior features of the horizontal wind velocity in the lower thermosphere measured by different ground-based methods showed that in periods of winter-time stratospheric warmings there are significant deviations of the azimuth and magnitude of the velocity vector from values typical fo the winter season. It is the winter months: December, January, February and March when the zonal and meridional flows exhibit the largest year-to-year variability. In a series of our papers, by generalizing results of analysis of the stratospheric winter-time warming effects on dynamic characteristics of the lower thermosphere, we stated the fact that the wind reversal in the lower thermosphere in the winter time from westerly to easterly is a fundamental property of the zonal circulation during warming periods in the stratosphere. Sudden stratospheric warmings are one of the main causes of the stability disturbance of zonal westerly winds in the mid-latitude lower thermosphere. The response to these meteorological phenomena changes from year to year and from station to station and depends on the climatic properities of the regions analyzed. The effect of strong stratospheric warmings of the 'major' type that were most frequently observed in the middle or at the end of the winter, manifest themselves in the reversal of westerly prevailing winds in the lower stratosphere. The 'reversal depth' of zonal winds depends on the location and dynamics of development of warm regions and is different for different climatic regions.