GRAPES区域模式水汽平流方案的比较与改进

COMPARISONS AND IMPROVEMENT OF WATER VAPOR ADVECTION SCHEMES OF GRAPES REGIONAL MODEL

与欧拉显式时间差分方法相比,GRAPES区域模式采用半隐半拉格朗日时间差分方案可增加时间步长且不影响稳定性,而且模式积分可有较高的计算效率和准确性。半拉格朗日法需要用到内插算法来预测下一时刻的值,对于水汽场的内插值来说,常常会造成预报值的过饱和或者是负值,需要进行特殊处理。比较GRAPES模式的准单调半拉格朗日方案(QMSL)和高精度正定保形方案(PRM),分析模式的降水预报、形势预报,同时初步总结了两方案的优缺点。在参考LCSL(Linear Constraint Semi-Lagarangain)方案的基础上,改进QMSL方案,通过连续试验运行,表明新方案基本稳定可靠,对于降水预报、形势预报有一定的改进,在台风预报试验中也有良好的表现。

Due to the use of the semi- Lagrangian, semi-implicit scheme, the Global/Regional Assimilation PrEdiction System（GRAPES） model can increase the time step without affecting the stability, and model integration may have a higher computational efficiency and accuracy, as compared with Euler explicit time-difference methods. The semi-Lagrangian methods need interpolation algorithms to predict the value of successive time steps. For water vapor, it might be supersaturated or negative, requiring special treatment to solve this problem. In this paper, the schemes of QMSL（Quasi-monotone semi-Lagrangian） and PRM（Piecewise Rational Method） in the GRAPES model were tested and preliminary summaries of the schemes were made from the analysis of the precipitation and situation forecast. Compared to the linearly constraint semi- Lagrangian scheme, the QMSL program was improved. A continuous test run shows that the new program is stable and reliable, precipitation and situation forecasting are improved to a certain degree, and typhoon forecasting experiments also have good results.