THE VERTICAL COUPLING OF UPPER AND LOWER JETS IN A HEAVY RAINFALL CASE DURING THE LATE PERIOD OF MEIYU SEASON——Numerical Experiments

Numerical experiments for a heavy precipitation case during the late period of Meiyu season were carried out by using the ECMWF limited area model. The development of south-west vortex, heavy rainfall area and the spatial and temporal relationship between low level jet (LLJ),subtropical jet (STJ) and Southern Asia easterly jet (EJ) were well simulated in the control experiment (CON).Experiment witho ut latent heating (NLH) also simulated the broad features of the circulation (except those of rain bearing systems),it shows the relative importance of baroclinic and orographyic forcing. In the precipitation area, the simulated upward motion in the NLH was only one tenth of that in the CON. An indirect vertical circulation, with ascending north and descending south, was enhanced by latent heating. The lower branch of the indirect circulation, with northward transverse motion increased the speed of LLJ and the upper branch with southward transverse motion intensified the EJ. In other words, the vertical coupling between LLJ and EJ is quite essential for the occurence of the heavy precipitation and the latent heat release acts as a positive feed back processes for such vertical coupling.