Numerical Experiments of Effects of Planetary Boundary Layer Processes on Prediction of Heavy Rain in the Yangtze River in July 1998
边界层过程对"98·7"长江流域暴雨预报影响的数值试验研究

The effects of planetary boundary layer processes on the prediction of heavy rain in the Yangtze River in July 1998 are studied by utilizing the ETA model. It is demonstrated that boundary layer is important in the forecast of heavy rain. The major results are as follows: (1) Large\|scale location of rainband is decided by the large\|scale flow patterns. However, boundary layer plays an important role in the prediction of heavy rain. (2) Without boundary layer processes, it is impossible to predict the weather system accurately because the flow patterns, moisture and instability in lower troposphere could not be described correctly, sequentially the forecast of heavy rain is unsuccessful (3) The surface fluxes assume a significant diurnal variation. So, the effects of boundary layer processes relate not only with the stages of formation, development and dissipation of heavy rain, but also the time (day or night) of formation, development and dissipation (4) The conditions between north and south area of the Yangtze River are quite different. There are the strong surface fluxes and sources of moisture and instability energy for the rain in south area of the Yangtze River.This area may has more important effects on the rain occurred in the Yangtze River.