Heavy Precipitation over the Jing–Jin–Ji Region in Early October: What Controls Its Interannual Variability?

Heavy regional precipitation (HRP) over Beijing, Tianjin, and Hebei Province (the Jing–Jin–Ji region or JJJ) in early October (1–10 October) is a high-impact climate event because of travel and outdoor activities by exceptionally large population during the Chinese National Day Holidays (CNDH). What causes the year-to-year variation of the HRP during early October is investigated through an observational analysis. It is found that the HRP arises from moisture transport by southerly anomalies to the west of an anomalous low-level anticyclone over the subtropical northwestern Pacific (SNWP). Sensitivity numerical experiments reveal that the low-level anticyclonic anomaly is caused by a dipole heating pattern over tropical western and central Pacific associated with a La Niña-like SST anomaly (SSTA) pattern in the Pacific and by a negative heating anomaly over North Europe. The latter connects the SNWP anticyclone through a Rossby wave train. Anomalous ascent associated with a positive heating anomaly over the tropical western Pacific may strengthen the local Hadley Cell, contributing to maintenance of the low-level ano-malous anticyclone over SNWP and extending westwards of the western Pacific subtropical high (WPSH). Therefore, both the tropical Pacific and midlatitude heating signals over North Europe may be potential predictors for HRP forecast in the JJJ region in early October.