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.