[A-AS06] 大気圏（成層圏・対流圏）過程とその気候への影響

[AAS06-11] Revisiting the cross-equatorial symmetry in QBO jets

*坂崎 貴俊¹、Hamilton Kevin² (1.京都大学　大学院理学研究科、2.ハワイ大学)

キーワード：準二年周期振動、再解析

The stratospheric Quasi-Biennial Oscillation (QBO) is usually defined by the interannual variability in the deseasonalized zonal-mean zonal wind in the equatorial stratosphere. As shown by many studies, the long-term average QBO jets take their maximum right on the equator with their meridional structure being symmetric with respect to the equator. By using multiple reanalysis datasets, the present study demonstrates that the meridional structure systematically depends on the QBO phase and month. Specifically, in either phase of QBO (westerly or easterly), the QBO jets tend to sit in the winter hemisphere. Such seasonal dependence is likely due to the meridional transport of zonal momentum by cross-equatorial flow associated with the seasonally-varying Brewer-Dobson circulation. The meridional asymmetry may need to be considered when reconstructing a single QBO index time series by synthesizing zonal wind data at different locations (e.g., FUB wind).