The Relationship and Influence Mechanism Between Circulation Anomaly in Southern Hemisphere and Summer Precipitation Distribution in China

To introduce signal on southern hemisphere circulation anomaly for diagnose and forecast of precipitation trend during flood season, the relationship between southern hemisphere circulation anomalies and its influence mechanism on summer precipitation distribution patterns in China is studied using SVD (Singular Value Decomposition), correlation and analogue methods. Also, the 500 hPa height field and zonal wind shear anomaly from high-level to low-level troposphere (Δu₈₅₀-Δu₂₀₀) in southern hemisphere, and summer precipitation distribution patterns in China are analyzed. Results show that:① When the ridge of Australian high is stronger and zonal wind shear anomaly in the southwest Pacific tropical region is negative, the cold air that comes from the southern hemisphere is weaker. It should be beneficial to the stronger subtropical monsoon and weaker tropical monsoon. And the northwest Pacific subtropical ridge shifts southward, and summer precipitation over the Yangtze River and south of the Yangtze River should be above normal. The rainbelt is located in southern China. On the other hand, when the ridge of Australian high is weaker, the zonal wind shear in southwest Pacific tropical region is positive anomaly, more precipitation appears in northern China. ② The possible mechanism for the influence of circulation anomaly in southern hemisphere on the summer precipitation distribution patterns in China is as follows:there is a close relationship between the anomaly of circulation and cold air activity in southern hemisphere and the monsoon circulation system activity in East Asia. It may also influence positions of the Northwest Pacific subtropical ridge and the rainbelt in China. ③ Furthermore, Australian winter monsoon index is defined. It indicates the circulation anomaly and the intensity of cold air activity in southern hemisphere troposphere. When Australia winter monsoon index is negative, precipitation is richer over the Yangtze River and the north part in the south of the Yangtze River in summer, and less than normal in Northern China. ④ The differences in the origin and intensity of water vapor transfer between strong and weak Australia winter monsoon years may cause the difference of the summer precipitation patterns in China. In weaker Australia winter monsoon year, water vapor is mainly transferred from the Pacific and reaches lower latitudes, and the main rainbelt is over the Yangtze River and south of the Yangtze River. In stronger Australia winter monsoon year, water vapor is mainly transferred from the India Ocean and the South China Sea and reaches high latitudes, and the main rainbelt is in Northern China.