Impacts of the summertime warm pool in the West Pacific on Huaxi autumn rain and its possible physical mechanism

Stations daily observations including precipitation, rainfall days and sunshine time are combined with sea surface temperature (SST) at different depths to study the relationship between Huaxi autumn rain intensity and summertime heat content in the western Pacific warm pool. The possible physical mechanism is also discussed. Results show that in summer, the variation of heat content in the western Pacific warm pool key area (5°S-5°N, 130°-160°E) is significantly positively correlated with the intensity of Huaxi autumn rain. When the heat content is high (low) over the key area, the intensity of Huaxi autumn rain is strong (weak). Further analysis reveals that when the heat content in the key area is high, it is like an abnormal heat source that leads to abnormal cyclonic circulation near the South China Sea-Indo-China Peninsula to the northwest of the key area. The southerly and easterly flows associated with the cyclonic anomaly are favorable for moisture transport to Huaxi, where the warm, moist airmass converges with dry, cold airmass from the north. Meanwhile, the upper-level westerly jet extends westward abnormally, leading to divergence above Huaxi, which is located to the right of the westerly jet entrance. The coupling between upper and lower circulations results in strong rain in Huaxi, and vice versa.