Combined Effect of Sea Surface Temperature in the Central-eastern Tropical Pacific and North Atlantic on Winter Extreme Precipitation over Southeast China

Based on daily precipitation observations and NCEP reanalysis data from 1961 to 2020, this study examines the interannual variability of winter extreme precipitation frequency (EPF) over Southeast China (SEC) and its possible association with sea surface temperature (SST) anomalies. The results show that winter EPF over SEC is closely linked to a north-south dipole pattern in circulation anomalies over East Asia, as well as the anomalous Philippine Sea anticyclone. The dipole pattern is characterized by a cyclonic anomaly over southern East Asia and an anticyclonic anomaly over northeastern Asia. This pattern enhances upper-level divergence and lower-level convergence over SEC, which enhances ascending motion and favors moisture convergence. The anomalous Philippine Sea anticyclone which is a classic response to El Niño, facilitates the transport of warm and humid air into SEC. Further analysis indicates that the dipole pattern is not a localized phenomenon but is instead an integral component of two large-scale Rossby wave trains: the Indo-western Pacific and East Asia (IWP-EA) pattern and the circumglobal teleconnection (CGT) pattern. The IWP-EA pattern originates over the Indo-western Pacific and is related to ENSO events. The CGT pattern is influenced by both ENSO and a North Atlantic east-west SST dipole pattern (NAEW). Therefore, both El Niño and the positive phase of NAEW collaboratively excite the CGT and IWP-EA wave trains, exerting a synergistic effect on the winter EPF over SEC.