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 damages and economic losses. During the LRSE, both temperature and precipitation fields exhibited quasi-biweekly oscillation (QBWO) signals over the CPPRD region. Circulation analysis reveals that the eastward propagation of Rossby waves in mid-high latitudes enhanced the Baikal blocking high and the Mongolian high, facilitating 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 CCPRD region. Meanwhile, deep convective activity originating in the northern Indian Ocean became exceptionally active, propagating to southern China and providing the dynamic lifting conditions for precipitation in the study region. The combined effect of tropical and extratropical weather systems resulted in the LRSE occurrence. Partial lateral forcing (PLF) experiments were performed to quantify contributions of the QBWO signals from different boundaries of the region. It is found that the extratropical QBWO signal from the northern boundary leads 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 causes 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 present study provides quantitative evidence that QBWO is a key factor contributing to the occurrence of the LRSE, which can be used as precursor signals for extended-range forecasts of future LRSEs.