Key Laboratory of Meteorological Disaster,Ministry of Education KLME/ International Joint Laboratory on Climate and Environment Change ILCEC/ Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters CIC-FEMD,Nanjing University of Information Science and Technology
Based on NCEP/NCAR reanalysis and datasets of daily basic meteorological elements from China national meteorological stations, the statistical characteristics of The regional daily-precipitation extreme events (RDPEs) in the Yangtze-Huai Rivers (YHR) region in eastern China from 1979 to 2016 and their relationships with Rossby wave activities are investigated. The results show that in the summers (June-July) of 1979－2016, the 95th percentile threshold of regional extreme daily-precipitation in YHR region is 33.95 mm/d. There are 63 RDPEs in total in the past 38 years. When RDPEs occur in YHR region, it is controlled by an anomalous cyclonic circulation in the middle and lower troposphere and an anomalous anticyclonic circulation in the upper troposphere. The water vapor from the Bay of Bengal and the South China Sea has a strong concentration in YHR region. Baroclinic circulation and sufficient water vapor are conducive to the occurrence and development of RDPEs. The eddy enstrophy in the upper troposphere over YHR region reaches its maximum on the day before RDPEs occur and rapidly decreases from then on. Meanwhile, the eddy enstrophy in the middle and lower troposphere reaches its maximum when RDPEs occur. This is dominated by processes including the advection term of the time average flow to the disturbed vorticity and the horizontal divergence term of the disturbed flow. Moreover, Rossby waves originate near the Caspian Sea and the Black Sea and obviously disperse downstream-ward. It takes about 3－5 days to move to YHR region, providing disturbance energy for the formation of RDPEs in this region. Overall, these results have deepened the understanding of the reasons for RDPEs in YHR region and could provide clues for effective predictions.