Linkage between the Arctic Oscillation and winter extreme precipitation over central-southern China

Abstract

In this study, we analyzed the relationship between the Arctic Oscillation (AO) and extreme precipitation events over China during boreal winters from 1954 to 2009. The extreme precipitation events are defined as those with daily precipitation above the 80th (or 90th) per- centiles. The AO shows a significantly positive correlation with the frequency of extreme precipi- tation events over China during January to February. Of all 287 stations in China, 238 stations have positive correlation coefficients and 82 stations are positively significant above the 95% con- fidence level. These stations that have significantly positive correlation are mainly located over central-southern China. The correlation between the AO and the average frequency of extreme precipitation events over central-southern China is 0.49, which is significant at the 99% confi- dence level. This correlation is still significant even when the El Nino/Southern Oscillation signal is excluded from the time series. In association with the AO-precipitation extreme linkage, the Middle East jet stream (MEJS) and the southern branch trough (SBT) over the Bay of Bengal covary consistently. A positive AO phase is accompanied by a stronger than normal MEJS and a deepened SBT. The deepened SBT enhances synoptic scale disturbances in vertical motions in the low to middle troposphere over central-southern China. More moisture transport by the deepened SBT and active synoptic scale disturbances in vertical motion over central-southern China would provoke more extreme precipitation events there.