Abstract
Abstract
Extreme humid heat (EHH) over South China (SC) has largely been treated as a homogeneous category, obscuring its distinct synoptic origins. Using a circulation clustering method, this study identifies two typical synoptic patterns responsible for summer EHH over SC: a monsoon type and a tropical cyclone (TC) type. The monsoon type features an anticyclonic anomaly over the tropical western North Pacific and enhanced southwesterly flow over SC. The TC type features a cyclonic anomaly with enhanced offshore TC activity. Both produce comparable wet-bulb temperature increases but through fundamentally different mechanisms. In the monsoon type, strong southwesterly flow drives advective moisture replacement, and the warming is dominated by downward longwave radiation from increased moisture and high cloud cover. In the TC type, northeasterly anomalies trap moisture over SC, while peripheral subsidence reduces low- and mid-level cloud; the resulting shortwave increase, with additional enhanced longwave from the trapped moisture, drives stronger warming.