Abstract:Several heavy rain cases in recent years and in history were analyzed. The results show that the downstream development effects caused by the energy dispersal of Rossby waves through Asia jet have important impacts on the formation and development of high level troughs and the path and long life period of landed typhoons in East Asia. If the energy of stationary Rossby waves through Asia jet could form an intensive upper level trough or deepen a pre exiting one near 110°E, the strong upward motion induced by large scale forcing is in favor of the development of heavy rainfall in eastern China. When the downstream effects help developing an intense close anticyclone at high and middle levels of troposphere around 40°N in East Asia, and there is a typhoon or tropical storm from the West Pacific to mainland China, the landed tropical cyclone would tend to move towards west or northwest under the steering current around the anticyclonic edge. At the same time if the monsoon surges from the South China Sea are strong enough, the landed tropical cyclone will have a long journey over the land and produce heavy rainfall and floods.  　It was found that the global NWP models used in operation could, to some extent, forecast the downstream development of Rossby waves at medium range scale. Therefore, it is possible to monitor the abrupt changes or adjustment of large scale circulation caused by downstream effects at Asia jet in operational forecast process. The Hovmller diagram is a simple, intuitional, and effective tool for analyzing the Rossby wave downstream effects in forecast operation.