Conversion of kinetic energy from synoptic scale disturbance to low-frequency fluctuation over the Yangtze River valley in the summers of 1997 and 1999

In order to investigate the conversion of kinetic energy from a synoptic scale disturbance (SSD; period≤seven days) to a low-frequency fluctuation (LFF; period＞seven days), the budget equation of the LFF kinetic energy is derived. The energy conversion is then calculated and analyzed for the summers of 1997 and 1999.The results show that the energy conversion from the SSD to the LFF is obviously enhanced in the middle and lower troposphere during the heavy rainfall, suggesting this to be one of mechanisms inducing the heavy rainfall, although the local LFF kinetic energy may not be enhanced.