Based on NCEP/NCAR reanalysis daily atmosphere data along with 740 stations precipitation data in China, we have
choosed two typical strong Meiyu years(1998 and 2003) and analyzed propagation characters of baroclinic waves at
upper troposphere during Meiyu period of these years. The results indicate that baroclinic waves of these years have
obvious downstream development effect during Meiyu period. These waves develop near entrance of westerly jet about 3
days before rainstorm happens, then propagate downstream from northwest to southeast and reach the valley at the day
that rainstorm happens. Energy dispersion associated with these wave packets has significant impact on happening and
development of rainstorm. Characters of baroclinic waves during non-Meiyu period are also studied, however, we fail to
find distinct downstream development effect in both years.