Analyses of the Atmospheric Circulation Characteristics over Tianjin Area in the Years of Anomalous Precipitation in Rainy Season
Based on the 1958-2009 monthly total precipitation data of 4 stations over Tianjin area, 160 stations over China and the NCEP/NCAR reanalysis data set, the variation characteristics of precipitation over Tianjin area and atmospheric circulation features in the same term of July to August as well as in the previous months from the preceding December through June for the anomalous years are investigated respectively by employing the simple correlation and composite analysis. The results show that the precipitation over Tianjin area is mainly concentrated in the rainy season. There exist interannual and interdecadal variations about the rainfall in rainy season. During the simultaneous term of the more precipitation years，the western Pacific subtropical high lies more northward， the low value systems develop on the northwest side of Tianjin area. Positive vorticity develops in the lower troposphere and the convergence ascending movement is more intense accordingly. The South Asia high and the subtropical upper westerly jet lie more northward. Meanwhile， warm and wet flow coming from southwest is stronger. For the less precipitation years the situations are just opposite. Additionally, there is a significant negative correlation between the precipitation and SAM (Southern Hemisphere Annular Mode) in the preceding June, which provides meaningful references for the shortterm climate prediction of precipitation over Tianjin area.