Multiple-Timescale Variations of the Winter Extreme Cold-Wet Events over South China

Abstract Extreme cold-wet (ECW) events are among the most destructive winter weather extremes over South China. ECW events are the joint results of circulation anomalies at multiple timescales. They can occur under cold, wet, cold-wet, and neutral interannual backgrounds, but differ in frequency and intensity, and are modulated by different configurations of the South Asian jet wave train (SAJW) and the Eurasian (EU) teleconnection. ECW events occur most frequently under the neutral background, whereas they are strongest under the cold-wet background. Under the neutral and cold-wet backgrounds, ECW events are linked to the coupling between the SAJW and the EU teleconnection at the 10–30-day timescale, but with different phase configurations and strengths. The coupling is strong and out-of-phase under the neutral background, modulating the India-Burma trough and the East Asian trough separately, and favoring the co-occurrence of intraseasonal wetness and coldness. In contrast, the coupling is in phase but relatively weak under the cold-wet background, jointly modulating geopotential height over East Asia–Japan and leading to either wetness or coldness alone. Only a single wave train is evident under the other two backgrounds. The SAJW is dominant under the cold background, regulating the early-stage 10–30-day warm-moist flow and its oscillation. Precipitation is subsequently triggered by weak intraseasonal cold-air intrusions. While the EU teleconnection is the key driver under the wet background, it strengthens the East Asian trough and enhances intraseasonal cold-air intrusions, which in turn interact with the interannual southwesterly warm-moist transport. Additionally, the SAJW plays a role in modulating the synoptic precipitation extremity in all backgrounds.