Persistent Mode of February-to-March Precipitation over Southern China: Variation, Mechanism, and Prediction

Abstract

Precipitation variations over southern China in February and March have profound influences on local agricultural activities. Therefore, the leading intermonthly variation mode of February-to-March precipitation over southern China is investigated in this study using the extended empirical orthogonal function (EEOF) method. The first leading EEOF (EEOF1) pattern shows a persistent precipitation anomaly from February to March over southern China. Mechanistic analysis indicates that EEOF1's different phases are related to different factors. A dipole sea surface temperature (SST) pattern with warm anomalies in the South China Sea (SCS) and cold anomalies in the western tropical Pacific (WTP) can lead to negative EEOF1 by exciting an anomalous Philippine Sea cyclone. In contrast, positive EEOF1 is influenced jointly by dipole patterns of SST in the southeast Indian Ocean (SEIO)-WTP area and atmospheric circulation over Europe and West Asia. The individual influence of the SST and atmospheric dipole patterns cannot induce persistent precipitation anomalies over southern China from February to March. Furthermore, we check the prediction skill of the National Center for Atmospheric Research (NCEP) Climate Forecast System (CFSv2) for positive and negative EEOF1. The evaluation results show that CFSv2 can predict the relationship between negative EEOF1 and the SCS-WTP dipole SST pattern, consequently showing skillful prediction for negative EEOF1 at the 1-month lead, with a correct rate of approximately 60%. However, CFSv2 cannot reproduce the combined effect of the aforementioned atmospheric dipole pattern and the SEIO-WTP dipole SST pattern and is therefore unskillful for predicting positive EEOF1, with a correct rate of only approximately 36%.