Impact of spring AAO on summertime precipitation in the north China part: observational analysis

Journal article

By using the 160 stations monthly precipitation data and NOAA-ESRL reanalysis data, the effect of spring Antarctic Oscillation (AAO) on Summer Precipitation in North China (SPNC) is studied. The analysis results show that the positive phase of March AAO leads the easterly-southerly and ascend anomalies in the southern part of North China by affecting zonal wind, and meridional circulation in the Northern Hemisphere (NH) late summer, results in more SPNC. Key regions of Antarctic sea-ice may store preceding March AAO signal which is cross-seasonal sustained by the heat exchanging with underlying surface, and the Summer Antarctic Sea-ice Index (SSI) is defined. The upward and poleward propagations of the planetary wave are enhanced in the SouthernHemisphere (SH) high latitude, and there are significant anomalous variabilities of PSI over SH low latitude, high latitude and polar regions in the high SSI years and vice versa. The wave-current interaction weakens the descendingmotion over the Antarctic, strengthens the circumpolar westerlies and deepens the SH polar vortex (AAO positive phase) in the high SSI years and vice versa. The results of observation and CAM5 show that SSI is positively correlated with indices of Quasi-Biennial Oscillation (QBOI). In QBO westerly phase, the SPNC anomaly in the high SSI years shows out of phase with that in the low SSI years. In the low SSI years, Rossby wave has the characteristics of anomalous southward propagation which corresponds to the abnormal weakening of ascend motion (the decrease of precipitation) over North China. Accompanied with a significant PSI anomaly, there exists a region of weak to strong wave energy over North China which is regarded as the source region of wave energy in both high and low SSI years of QBO westerly phase. But in QBO easterly phase, SPNC anomaly is not significant. QBO may be a bridge that connecting the signals of zonal wind anomalies in the stratosphere of the SH and the NH.