South Asia High Activity And The Relationship Between The Plateau Monsoon Evolution Analysis

Based on ECMWF monthly reanalysis data and monthly rainfall and air temperature data from 160 primary stations in China during 1958-2002, it were discussed that the characteristics of convection and zonal wind over Plateau during summer. Further, we define a new Plateau Summer Monsoon index. Using synthesis analysis, correlation analysis, Morlet wavelet analysis, curve fitting et al to study inter-annual variation and inter-decadal variation of the Plateau Summer Monsoon, the anomalous of the Plateau Summer Monsoon associates with different circulation patterns over Northern Hemisphere, the relationship between the Plateau Summer Monsoon and summer rainfall and air temperature in China. Further, we analyze the relationship between the Plateau Summer Monsoon and precipitation of southwest China in autumn. We find that the longitudinal position of South Asia High (SAH) in summer is correlated with the Plateau Summer Monsoon. Finally, we discuss that SAH and the Plateau Summer Monsoon impact on climate of Sichuan and Chongqing Basin in summer. The main conclusions are:(1) The Plateau Summer Monsoon Indices(PMI) was defined using the difference of anomalous wind between the (27.5~30°N,80~100°E) and (35~37.5°N,80~100°E) at 600hPa by the averaged Jun-Aug. The phenomena have been found that the opposite variation occurred between the latitude (27.5~30°N) and (35~37.5°N) over Plateau for the anomalous zonal wind at 600hPa. The PMI corresponds with summer rainfall and air temperature over China in distinctive patterns. After carrying on the comparison about performance synthesis between the Plateau Summer Monsoon Index and the one which defined by Tang maochang before, it shows that the Plateau Summer Monsoon Index has the better instruction significance to the summer precipitation and the temperature of Sichuan Chongqing area. After analysis the periodic changes of the Plateau Summer Monsoon, we found that it had an increase trend from 1958 to 2002. Before 20th century 60's intermediate stages is the plateau summer monsoon powerful time, afterwards is the plateau summer monsoon weak time, in the end of 80's at the beginning of 90's, also transfers monsoon strong time. The remarkably inter-annual variation and inter-decadal variation of the Plateau Summer Monsoon occur throughout 45 years.(2) Geopotential Height fields, wind fields, vertical velocities, the precipitation and temperature of China in summer, has notable differences in abnormally strong or weak years of the Plateau Summer Monsoon. The change of the Plateau Summer Monsoon has significant impact on the climate of China in summer. There existed obviously positive correlation between the Plateau Summer Monsoon and the precipitation of the west of Xinjiang, east and south of plateau, northwest of Yunnan, east of Sichuan, and the downstream of Yangtze River in summer, and obviously negative correlation between the Plateau Summer Monsoon and the precipitation of the area west of Sichuan, Gansu, Hetao, north China and South China. Similarly, there existed obviously positive correlation between the Plateau Summer Monsoon and the air temperature of the north of Xinjiang, north of Qinghai, northeast of plateau, Hetao, Gansu, and South China in summer, and obviously negative correlation between the Plateau Summer Monsoon and the air temperature of the area west of Xinjiang, east of Sichuan, and the downstream of Yangtze River.(3) There are negative correlations between the Plateau Summer Monsoon and precipitation of southwest China in autumn. Precipitation of southwest China in autumn become weak while the Plateau Summer Monsoon become strong. By contrary, precipitation of southwest China in autumn become strong while the Plateau Summer Monsoon become weak. The Plateau Summer Monsoon and precipitation of southwest China in autumn have the same periods, 7 years of inter-annual variation and 12 years of inter-decadal variation. Using the synthesis analysis, we find that precipitation of southwest China in autumn is closely correlated with circulation patterns over Northern Hemisphere. Precipitation of southwest China in autumn become more when the subtropical high over the western Pacific at 500hPa extend northwestwards, for negative, precipitation of southwest China in autumn become less when the subtropical high over the western Pacific at 500hPa extend southeastwards. Anomaly of 500hPa atmospheric circulation over the East Asia forced by abnormal of the Plateau Summer Monsoon is able to restrict amount of precipitation of southwest China in autumn. Above all, it is useful and significative to forecast the amount of precipitation of southwest China in autumn by the strength of the Plateau Summer Monsoon in the earlier stage.(4) There are good corresponding relations among SAH, the Plateau Summer Monsoon, and the subtropical high over the western Pacific at 500hPa. In abnormally East deviation years of SAH, Geopotential Height fields of Northern Hemisphere generally ascend at 100hPa. Geopotential Height anomaly of Northern Hemisphere have"positive- negative–positive"distribution. There are positive Geopotential Height anomaly in Qinghai and Xizang Plateau. The circulation of anticyclone anomaly appears when the low become weak at 600hPa.The air current disperses from center to all around, then the Plateau Summer Monsoon become weak. The subtropical high over the western Pacific at 500hPa extends to China mainland interior west and its west part influences the east of the Sichuan and Chongqing Basin. Thus, it cause less precipitation in the east and high temperature all over the Basin. The west region of the Basin with more precipitation is associated with its location in the ascendant current on the western edge of the subtropical high over the western Pacific at 500hPa.On the contrary, in abnormally West deviation years of SAH, Geopotential Height fields of Northern Hemisphere generally descend at 100hPa. Geopotential Height anomaly of Northern Hemisphere have"negative- positive–negative"distribution. There are negative Geopotential Height anomaly in Qinghai and Xizang Plateau. The circulation of cyclone anomaly appears when the low become strong at 600hPa.The air current spoke gathers from all around approaches the center, then the Plateau Summer Monsoon become strong. The subtropical high over the western Pacific at 500hPa draws back east to sea. The east region of the Basin with more precipitation is associated with its location in the northwest edge of the subtropical high over the western Pacific at 500hPa. Because of lack of water vapor, the west region of the Basin is less precipitation. The temperature is lower than normal all over the Basin.