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

通过ETA模式对"98@7"长江流域暴雨过程的数值试验研究,讨论了行星边界层过程对暴雨数值预报的影响,结果表明边界层过程在这次暴雨预报中有重要作用.具体结论为:(1)降水大范围落区是受大尺度流场所决定的,但边界层过程对暴雨预报具有重要的作用;(2)不考虑边界层过程会影响对天气系统的正确预报,包括影响大气低层的运动场、水汽及大气不稳定度,从而影响暴雨的预报;(3)从时间层次上看,由于地表通量有着显著的日变化,边界层过程的作用不仅与暴雨本身发生发展及消亡的阶段有关,也与各阶段的时间(白天或夜间)有联系;(4)在空间范围内,边界层过程对大气的影响是通过大气流场重新分布来影响降水的环境条件,故地表通量分布和低层流场的相互配置作用十分重要.长江南北的情况有所不同,长江流域南侧区是地表通量的大值区,也是长江流域雨区水汽和不稳定能量的源区,它对长江流域的暴雨可能有着更为重要的作用.

Numerical Experiments of Effects of Planetary Boundary Layer Processes on Prediction of Heavy Rain in the Yangtze River in July 1998

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.