中文摘要：

针对半隐式半拉格朗日数值预报模式GRAPES,研究发展了与之相适合的高精度正定保形的物质平流方案——分段有理函数法（PRM,Piecewise Rational Method）。文中在进行理想试验验证该方案简单、实用、易于编程对于空间变化幅度大的物理量具有较高的平流计算能力且在GRAPES模式中具有可行性的基础上,对2005年7月连续1个月的24小时降水进行实际预报试验。通过细致的个例分析、月平均比较以及TS评分计算,PRM方案实际预报结果与GRAPES模式中原来采用的水物质平流方案预报的主要雨带的分布、走向相一致,但对大雨以上量级的降水预报具有明显优势,对网格尺度的降水的影响比较敏感,进一步验证了高精度正定保形方案对实际降水预报的改进效果,表明该方案对于改进GRAPES模式大到暴雨预报能力具有较大的潜力。PRM平流方案较GRAPES原来采用的准单调正定保形的平流方案能够更加合理地计算水物质场的输送,尤其是能够很好地反映出梅雨季东亚大气下层水汽水平梯度大以及沿梅雨锋水汽的小尺度变率较大的特点描写。

英文摘要：

In a series of papers,for the semi-implicit semi-Lagrangian GRAPES model,the high-accuracy and positive-definite advection scheme called the piecewise rational function methed（PRM）is developed.First,in PartⅠof the papers,it was found that this scheme is simple,practical and easy to code and has great ability in treating the variables of large spatial variation.Its feasibility in the GRAPES can also be confirmed by ideal experiments.In PartⅡ,the 24 hour rainfall forecast has been made continuously for one month;July in 2005.Through detailed case analyses based on a comparison of the monthly mean 24 hour rainfall and the calculation of TS（Threat Score）,it is found that the spatial distribution of forecasted rainbelts by the PRM is similar to that by the original water substances advection scheme utilized in GRAPES model but the PRM shows obvious advantages over the latter in forecasting the rainfall larger than 25 mm/day both for the rainfall amount and occurring location of heavy rainfall and.is more sensitive to the grid scale precipitation.As a result,the high-order accuracy and positive-definite advection scheme can improve the forecast.Particularly,this scheme has great potentialities to improve the heavy rainfall forecast. The PRM advection scheme is more rational to calculate water substance distribution than the original QMSL.Especially, it also has ability in describing the large horizontal gradient of lower atmosphere moisture field over the East Asian region during the Meiyu season as well as the case of larger small scale variability along the Meiyu front.