Interannual variability of the northern winter stratospheric circulation related to the QBO and the solar cycle

A statistical study is made of the interannual variability of the northern winter stratospheric circulation in connection with the equatorial quasi-biennial oscillation (QBO) and the solar cycle, by using the 37-year stratospheric dataset of the Freie Universitat Berlin and the 31-year NMC global data. During the period 1962/63-1977/78, analyzed first by Holton and Tan (1980, referred to as HT), the polar-night jet is stronger in the W (westerly) than in the E (easterly), as was mentioned by Holton and Tan (1980). However, the difference between the W and the E is barely significant in 'the latter half period' (1978/79-1993/94). When the whole period is classified into two groups defined as 'Min' and 'Max' with respect to the intensity of the 10.7-cm solar flux, it is clearly shown that the late-winter jet in the W is much stronger than in the E (the value of Student's t test exceeds 6) in the Min group, whereas it is no stronger in the Max group. The reason why the result from the BT period resembles that from the Min is probably because the HT period includes two solar minima and one maximum. In early winter, the circulation seems to be correlated with the QBO irrespective of the solar cycle. This difference between early and late winter suggests that the equatorial QBO influences the extratropical circulation in early winter and that the solar cycle modifies it in late winter. An extensive analysis of wave components is also made. The result from the Min is similar to that of the HT period, and the difference between the W and the E is larger than in the HT period. In late winter, the result from the Max is the inverse of the Min result. Finally, the occurrence of major warmings is shown to be related significantly to the QBO and the solar cycle. Such a relationship is clearly illustrated by plotting the occurrence of the major warming onto a 2D phase space of the solar flux and the equatorial wind.