2016年梅雨期间长江中下游强降水与对流层上层斜压波包的关系

2016年6—7月，长江中下游地区发生了自1998年以来最严重的强降水事件，造成了重大的经济损失。利用NCEP/NCAR再分析资料和中国2479站逐月及逐日降水资料，研究了2016年梅雨期间长江中下游地区降水与欧亚大陆对流层上层斜压波包活动的关系，并诊断了两者之间的信息流向。结果表明，梅雨期间的高频斜压波动具有明显的下游频散效应。波动起源于黑海，沿西北—东南方向于3—4 d后传至长江中下游地区。斜压波包为长江中下游地区强降水的发生提供了必要的能量。波作用通量矢量的分布表明，梅雨期间逐日均有来自西风带上游的扰动能量向长江中下游流域传播。而梅雨期间降水与斜压波包的信息流关系表明，二者之间存在信息传递。因此，3—4 d并源于黑海附近的斜压波包活动是2016年长江中下游梅雨期间异常降水的成因。这些结果为深刻认识长江中下游地区强降水事件发生的成因和有效预测提供了线索。 

The relationship between heavy precipitation in the middle and lower reaches of Yangtze River and baroclinic wave packets in the upper troposphere during the Meiyu period of 2016

During June and July of 2016, the most severest rainfall event since 1998 occurred in the middle and lower reaches of Yangtze River, causing huge economic losses there. Using the NECP/NCAR reanalysis data along with monthly and daily precipitation data collected at 2479 weather stations in China, the relationship between precipitation in the middle and lower reaches of Yangtze River and baroclinic wave packets in the upper troposphere over Eurasia is analyzed in the present study. The result demonstrates that high frequency baroclinic disturbances effectively dispersed wave energy downstream to East Asia during the Meiyu period. The disturbances originated in the Black sea, and then propagated southeastward to the middle and lower reaches of Yangtze River in 3-4 days. This wave energy propagation can be well represented by baroclinic wave packets. The wave-activity fluxes also show that disturbance energy dispersed southeastward from the westerlies in the mid-latitudes to the middle and lower reaches of Yangtze River during the Meiyu period. To further understand the relationship between the Rossby wave packets and severe precipitation in the middle and lower reaches of Yangtze River, we calculate the information flow, which shows that there indeed existed information flows between the baroclinic wave packets and precipitation changes in the middle and lower reaches of Yangtze River during the Meiyu period. These results provide clues to understanding and forecasting heavy rainfall events in the middle and lower reaches of Yangtze River.