An exceptional wet June over the Nanling Mountains in South China in 2022: link to anomalous cyclonic circulation over the West Siberian Plain

The Nanling Mountains (NLMs; 24 0 –26 0 N, 108 0 ‒117 0 E) exert a significant influence on weather, climate, and extreme precipitation in South China. In June 2022, an exceptionally wet condition occurred across this region, with precipitation at most meteorological stations on the southern slope of the NLMs exceeding twice the climatological mean. Based on station observations and the JRA-3Q reanalysis, this study investigates the atmospheric moisture budget and its critical role in modulating this record-breaking precipitation. Results indicate that the extreme precipitation anomaly was primarily driven by dynamic effects with the major contribution from vertical velocity enhanced. And the largest contribution is at 500 hPa, followed by that at 900 hPa. A secondary contribution came from anomalous low-level horizontal moisture advection due to the intensified southwesterly winds. In contrast, the thermodynamic component of horizontal moisture advection term exerted a suppressing effect due to the specific humidity anomaly exhibited a negative meridional gradient, thereby partly offsetting rainfall extremes. Further analysis reveals that precipitation anomalies over the NLMs were closely linked to the cyclonic circulation anomaly over the West Siberia Plain (50°‒65°N, 55°‒90°E). This barotropic cyclonic anomaly triggered a southeastward-propagating wave train toward the northwest Pacific, enhancing both the South Asian High and the western North Pacific subtropical high. These enhancements favored upper-level divergence and strengthened mid-to low-level southwesterlies. Coupled with orographic forcing on the windward slope, the combined effects of intensified vertical motion and moisture transport by anomalous southwesterly flows led to heavy rainfall concentrated along the southern slopes of the NLMs.