江淮地区夏季极端日降水事件变化特征及其与Rossby波活动的联系

利用NCEP/NCAR逐日再分析资料和中国国家级地面气象站基本气象要素日值数据集,研究了1979～2016年(38年)夏季江淮地区区域性极端日降水事件的统计特征及其与Rossby波活动的联系.结果 表明:在38年夏季(6～7月)中,江淮地区区域性极端日降水量的95百分位阈值为33.95 mm d-1,且共有63次极端日...

Variation Features of Summer Regional Daily Precipitation Extreme Events in Yangtze-Huaihe Rivers Region and Their Relationships with Rossby Wave Activities

Based on the NCEP/NCAR reanalysis and the datasets of daily basic meteorological elements from China’s national meteorological stations, this study investigates the statistical characteristics of the regional daily precipitation extreme events (RDPEs) in the Yangtze–Huaihe rivers (YHR) region in eastern China from 1979 to 2016 and their relationships with Rossby wave activities. The results show that in the summer seasons (June–July) of 1979–2016, the 95th percentile threshold of the regional extreme daily precipitation in the YHR region is 33.95 mm d?1. There have been a total of 63 RDPEs in the past 38 years. The occurrence of RDPEs in the YHR region 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 the YHR region. The baroclinic circulation and sufficient water vapor are conducive to the occurrence and development of RDPEs. The eddy enstrophy in the upper troposphere over the YHR region reaches its maximum on the day before RDPEs occur and rapidly decreases thereafter. 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 and Black Seas, and clearly disperse downstream. It takes approximately 3–5 days to move to the YHR region, providing disturbance energy for the formation of RDPEs in this region. Overall, these results have deepened the understanding of the reasons for the occurrence of RDPEs in the YHR region and could provide clues for effective predictions.