Influences of intraseasonal oscillations on a compound cold and wet event in southern China during the Spring Festival travel rush

Abstract

AbstractIn January 2023 during the Spring Festival travel rush, a compound cold and wet event (CCWE) hit southern China, causing heavy precipitation followed by two cold wave processes. Through an analysis from the intraseasonal oscillation (ISO) perspective, it was found that the cold event is caused by two consecutive cold events, in which upper level midlatitude ISO wave train propagating across the Eurasia favours the formation of blocking high, leading to the expansion of Siberian High and intensification of East Asian winter monsoon. As a result, strong cold advection appeared in the northern boundary of southern China and caused the cooling process. As for the wet event, it was found that a cyclonic ISO anomaly from South China Sea conveyed abundant moisture through the western and southern boundaries and caused the precipitation. It was revealed in the partial lateral forcing (PLF) experiment that the midlatitude ISO signal from the northern boundary caused minimum 2 m temperature to drop by 1.84°C, mainly affecting the northern part of the research area. The tropical ISO from the western and southern boundaries resulted in heavy precipitation for over 40 mm in a belt‐shaped area in 3 days. The combination of the ISOs is the key factor behind this CCWE and our study provides intuitive evidences for this, which is helpful in understanding the mechanisms and providing empirical precursory signals for the forecast of CCWEs.