Abstract:

Based on observational data of daily temperature and precipitation at 97 meteorological stations in Hunan province and the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data, the characteristics and formation of a persistent high temperature and drought events during summer season in 2013 in Hunan province were analyzed. The results showed that the mean number of days with high temperature in Hunan province is 44 d, and these high temperature days occur mostly in the periods of June 15-25, from June 29 to August 18, and August 21-30. The numbers of days with high temperature at 32 stations in 2013 are larger than the historical records in the same period. The large-scale meteorological drought in Hunan province begins in the mid-June of 2013, and the area of severe and even heavier drought is over half area of the province from July 28 to August 20. The Subtropical High over the western Pacific that is abnormally and persistently strong and locates westward controls the Jiangnan region, which is the most important and direct influencing factor  of this high temperature and drought event in Hunan province. In the upper troposphere, the South Asian High is persistently strong and moves eastward or northward, which is favorable to the maintenance of the western Pacific Subtropical High. This leads to the continuous subsidence motions of air flows over the Jiangnan region and the significant suppression of convective activity. Meanwhile, the divergence center of water vapor flux is located at the western of Jiangnan region and the northern part of South China, which is unfavorable to the accumulation of water vapor.

Key words: Day number with high temperature, Drought area, Subtropical High, Abnormal circulation, Water vapor