The semi-Lagrangian advection scheme is implemented on a new quasi-uniform overset （Yin-Yang） grid on the sphere. The Yin-Yang grid is a newly developed grid system in spherical geometry with two perpendicularly-oriented latitude-longitude grid components （called Yin and Yang respectively） that overlapp each other, and this effectively avoids the coordinate singularity and the grid convergence near the poles. In this overset grid, the way of transferring data between the Yin and Yang components is the key to maintaining the accuracy and robustness in numerical solutions. A numerical interpolation for boundary data exchange, which maintains the accuracy of the original advection scheme and is computationally efficient, is given in this paper. A standard test of the solid-body advection proposed by Williamson is carried out on the Yin-Yang grid. Numerical results show that the quasi-uniform Yin-Yang grid can get around the problems near the poles, and the numerical accuracy in the original semi-Lagrangian scheme is effectively maintained in the Yin-Yang grid.
A new generation of numerical prediction system GRAPES (a short form of Global/Regional Assimilation and PrEdiction System) was set up in China Meteorological Administration (CMA). This paper focuses on the scientific design and preliminary results of the numerical prediction model in GRAPES, including basic idea and strategy of the general scientific design, multi-scale dynamic core, physical package configuration, architecture and parallelization of the codes. A series of numerical experiments using the real data with horizontal resolutions from 10 to 280 km and idealized experiments with very high resolution up to 100 m are conducted, giving encouraging results supporting the multi-scale application of GRAPES. The results of operational implementation of GRAPES model in some NWP centers are also presented with stress at evaluations of the capability to predict the main features of precipitation in China. Finally the issues to be dealt with for further development are discussed.
According to the modularization and standardization of program structure in Global/Regional Assimilation and Prediction System (GRAPES), the plug-compatible and transplantable regional meso-scale and global middle-range physics software package is established. The package's component integrality is comparative with the other advanced models physics. A three-level structure of connecting GRAPES physics and dynamic frame has been constructed. The friendly interface is designed for users to plug in their own physics packages. Phenomenon of grid-point storm rainfall in numerical prediction is analyzed with the numerical tests. The scheme of air vertical velocity calculation is improved. Optimizing tests of physics schemes are performed with the correlative parameters adjusting. The results show that the false grid-point storm rainfall is removed by precipitation scheme improving. Then the score of precipitation forecast is enhanced.
新一代全球/区域多尺度统一的同化与数值预报系统(global/regional assimilation and prediction system,缩写为GRAPES)已在中国气象局研究建立.该系统的核心技术包括:资料变分同化;半隐式-半拉格朗日差分方案和全可压/非静力平衡动力框架;可自由组合的、优化的物理过程参数化方案;全球、区域一体化的同化与预报系统;标准化、模块化、并行化的同化与模式程序.针对GRAPES系统的正确性、有效性,已经进行了一系列的标准测试和应用模拟试验,包括常规资料分析应用、雷达和卫星非常规资料直接分析应用试验.该系统已在国家级、区域级气象业务中心运行,在实际气象业务中发挥了重要应用.本文重点介绍数值预报模式,包括总体设计思路与策略、多尺度统一动力模式构建、物理过程参数化方案组合优化、模式程序结构设计等;同时,还通过介绍GRAPES模式的模拟试验和实际应用结果等,展示多尺度统一模式的可行性和科学性、实际应用的能力和水平.
