西南地区夏季降水异常大气环流特征

Characteristics of Anomalous Atmospheric Circulation of Summer Precipitation in Southwest China

为了更好地分析中国西南地区近60年来夏季降水变化异常的大气环流形势,利用1961~2017年西南地区76个气象站点的降水量资料和NCEP/NCAR月平均再分析资料,网格距2.5˚ ×2.5˚,主要运用标准化距平和合成分析对该地区近60年夏季降水量异常的高低空大气环流及水汽输送特征进行了详细研究。结果表明:1) 将西南地区近60年夏季降水量平均值标准化,以±1倍标准差为标准,选取1966,1968,1979,1991,1995,1998和1999年共7年为降水异常偏多年,选取1972,1975,1978,1989,1992,2006,2011和2013年共8年为降水异常偏少年。2) 西南地区100 hPa环流场表明:降水较多年,南亚高压较弱,垂直活动较强;降水较少年,南亚高压较强,盛行下沉气流。3) 500 hPa环流场表明:降水较多年和降水较少年的亚欧大陆中高纬均有两槽一脊。降水较多年,中纬度以经向环流为主;降水较少年,中纬度以纬向环流为主。4) 700 hPa环流场与500hPa环流场相似,但波动更大。5) 850 hPa环流场表明:降水较多年,西南季风输送水汽较弱,东南季风输送水汽较强,配合辐合上升的动力条件,有利于夏季降水的发生发展;降水较少年,西南季风和东南季风相对降水较多年偏弱配合辐散下沉的动力条件,不利于夏季降水的发生发展。

In order to better analyze the atmospheric circulation pattern of anomalous summer precipitation changes in southwest China during the past 60 years, the precipitation data of 76 meteorological stations and NCEP/NCAR monthly mean reanalysis data from 1961 to 2017 were used, and the grid distance was 2.5˚ ×2.5˚. The characteristics of atmospheric circulation and transport of water vapor of summer precipitation anomalies in the past 60 years were studied in detail by using Normalized anomaly and Synthetic analysis. The results show that: 1) Standardizing the mean summer precipitation in the past 60 years in southwest China, using ±1 standard deviation as the standard, seven years including 1966, 1968, 1979, 1991, 1995, 1998 and 1999 were selected as the years of precipitation anomaly. Eight years (1972, 1975, 1978, 1989, 1992, 2006, 2011 and 2013) were selected as precipitation deviant adolescents. 2) The 100 hPa circulation field in southwest China shows that the South Asia high is weak and the vertical activity is strong due to the years of precipitation. Precipitation is relatively young, the South Asia high is strong, prevailing downdraft. 3) The 500 hPa circulation field shows that there are two troughs and one ridge in the middle and high latitudes of The Eurasian continent where the precipitation is relatively old and relatively young. The precipitation was more frequent, and the meridional circulation dominated the middle latitude. The precipitation is juvenile, and the latitudes are mainly zonal circulation. 4) The 700 hPa circulation field is similar to the 500 hPa circulation field, but the fluctuation is larger. 5) The circulation field of 850 hPa shows that the water vapor transported by southwest monsoon is weak and that transported by southeast monsoon is strong, which is conducive to the occurrence and development of summer precipitation with the dynamic condition of convergence rising. The relative precipitation of south-west monsoon and southeast monsoon is weaker than that of many years, which is not conducive to the occurrence and development of summer precipitation due to the dynamic condition of divergence sinking.