Analysis of the distribution of the large scale drought/flood of summer in China under different types of the western Pacific subtropical high

The characteristics of the western Pacific subtropical high indices were studied based on the historical data. It was proved that its ridge line index and western extension index could be used to describe the subtropical high well，and the interannual and interdecadal variations of this two indices and their different configurations in space contributed largely to the complexity and variability of the spatial-temporal rainfall distribution and precipitation anomalies in summer of China. Accordingly，anomalies of the summer average ridge index and western extension index of the subtropical high were projected onto a two-dimensional plane，and the subtropical high was classified and the seasonal rainfall was analyzed by the synthesis method based on the different categories. The results indicate that the overall distribution patterns show distinct regulations under the different configurations of the two indices. There are two rain-belts in the summer precipitation respectively in southern and northern China when the subtropical high ridge shifts northward. The normal pattern for the subtropical high ridge is corresponding with that with the precipitation more in the north of the Yangtze River regions and less in southern China. While the distribution of precipitation is opposite when the subtropical high ridge shifts southward. Under the circumstances mentioned， the more the westward extention of the subtropical high is， the larger the precipitation range is. Furthermore， the correlation coefficients between summer precipitation anomalies and the synthesized precipitation based on the classification of the corresponding subtropical high were calculated，and found that the anomaly patterns of summer precipitation anomaly is similar to that of the synthetic one of the same category， which indicated some rationality of the classification to some extent. Finally，the composite analysis was done for the 500 hPa geopotential height field and the 850 hPa wind anomaly field by the nine types of the subtropical high in summer，and the probable mechanisms and background of the large scale circulation were analyzed.