Interannual and climatic variability of breakup date of the stratospheric circulation
The analysis of observations shows that there exists a sufficiently strong interannual variation of breakup date of the stratospheric circulation. In the present paper the interannual and climatic variability of the spring-time transition date of the circulation in the Northern Hemisphere is analyzed on the base of the data assimilated in the UK Met Office and NCEP/NCAR models. As a characteristic of zonal-mean flow the geostrophic wind calculated using the geopotential high of the 10 hPa level at 65.7 N has been used. Оn the averagе, the spring-time transition occurs at the beginning of April, however, sometimes it takes place earlier (in the middle of March) or later (at the beginning or even in the middle of May). The results obtained show that spring-time transition date depends on the planetary-wave activity in the stratosphere and there is a tendency of the shift of а breakup to the later date (the speed of this shift is about 9 days per decade). It is noted that a noticeable dependence of the breakup date on the phase of quasi-biennial oscillations of the zonal wind at low latitudes is observed.