On the Interannual Variability of the Middle Stratosphere during the Northern Winters

Abstract

The variability of the stratospheric winters is investigated.Monthly mean 30-mbar temperatures over the North Pole which are available for a 26-year period, have been grouped according to the phase of the equatorial QBO at the 50-mbar level, following a suggestion of Holton and Tan (1980).It is shown that the winters are"relatively undisturbed, cold" with an enhanced tendency for the development of a pronounced "normal wave 2 pattern" when the equatorial winds at the 50-mbar level are from the west.Major midwinter warmings seem not to take place in this category, except near the sunspot maxima. In contrast, during the "easterly" phase of the equatorial QBO there is a tendency for an enhanced development of height-wave 1 already in early winter, which leads often to the development of a major warming during midwinter and hence to a generally warmer polar region.