Feature of Atmospheric Circulation Anomalies of the Extremely Severe Drought in Northwestern Guangxi from July to August 2011

On the basis of the NCEP/NCAR monthly mean reanalysis data, NOAA outgoing long-wave radiation data, circulation feature data given by the National Climate Center, and the monthly precipitation data of the 16 stations in northwestern Guangxi from 1960 to 2011, the characteristics of the middle-high latitude circulation, the western Pacific subtropical high (WPSH), and the moisture transport for all the drought years are studied. In particular, the anomalous atmospheric circulation of the extremely severe drought occurring from July to August 2011 is examined. The results show that the mid-summer precipitation in 2011 was the least since 1960. The extremely severe drought of northwestern Guangxi in mid-summer 2011 is obviously different from other drought events. The WPSH was weaker and was eastward and shifted northward, and the straight flow prevailed over mid-high latitude region. In addition, no obvious blocking high over the Ural Mountains and Northeast Asia was noted. Moreover, the cold air activities, the activities of the India-Burma trough, water vapor transport from south to north with weak positive moisture flux divergence, vertical movement, and convective activities in mid-summer 2011 were all weaker than normal. All of these features are not conducive to precipitation and jointly resulted in the extremely severe drought event in northwestern Guangxi.