Activities of baroclinic wave packets in the upper troposphere related to Meiyu of 2003 in the Yangtze River\|Huaihe River valley

Using NCEP/NCAR reanalysis daily data from 1980 to 2003 along with 740-station precipitation data in China, the authors analyze the propagation features of the baroclinic wave packets in middle latitudes of the Northern Hemisphere during the Meiyu period of 2003. The results demonstrate that the baroclinic waves in the upper troposphere organize into the Rossby wave packets during the Meiyu period of 2003, dispersing to their downstream area distinctly. The waves originate from the regions northwest of Lake Balkhash and then spread southeastward to their downstream regions. About 3 days later, wave packets arrive in the Yangtze River-Huaihe River valley. The energy dispersion associated with baroclinic wave packets leads to the energy accumulation for rainstorms in the Yangtze River-Huaihe River valley. To further understand the downstream effect of the baroclinic wave packets, the authors compare the propagation features of the wave packets during the Meiyu periods of 1998 and 1997. It is found that the activities of baroclinic wave packets in flood Meiyu year 1998 are very similar to those in 2003. However, the downstream effect was not clearly observed in 1997 which is known as a dry Meiyu year in the Yangtze River-Huaihe River valley.