Impacts of Tropical and Extratropical Quasi-Biweekly Oscillation on a Persistent Low-Temperature Rain and Snow Event in Southern China in February 2022

In February 2022, a persistent low-temperature rain and snow event (LRSE) occurred in the central Pan-Pearl River Delta (CPPRD) region of southern China, causing severe damage and economic losses. During the LRSE, both the temperature and precipitation fields exhibited quasi-biweekly oscillation (QBWO) signals over the CPPRD region. Circulation analysis revealed that the eastward propagation of Rossby waves at mid–high latitudes enhanced the Baikal blocking high and the Mongolian high, facilitating the continuous southward migration of cold air. The strengthening India–Burma trough (i.e., the southern branch trough) brought abundant warm and humid airflow, converging with cold air from the north in the CPPRD region. Moreover, deep convective activity originating in the northern Indian Ocean became exceptionally active, propagating to southern China and providing dynamic lifting conditions for precipitation in the study region. The combined effects of tropical and extratropical weather systems resulted in the LRSE occurrence. Partial lateral forcing (PLF) experiments were performed to quantify the contributions of the QBWO signals from different boundaries of the region. The extratropical QBWO signal from the northern boundary led to a temperature decrease of 1.61°C, with 77.83% of the whole region experiencing cooling greater than 1°C, whereas the tropical QBWO signal from the southwestern boundary caused an increase in precipitation of 13.1 mm day⁻¹, with more than 40% of the entire region experiencing a precipitation increase of over 5 mm day⁻¹. This study provides quantitative evidence that the QBWO was a key factor contributing to the occurrence of the LRSE, which can be used as a precursor signal for extended-range forecasts of future LRSEs.