Study Of The Conservation Semi-Lagrange Scheme Of The Limited-Area Model

It is important to achieve conservation or break-even calculations for variables such as water substances in global or regional numerical models,and lack of conservation of mass may lead to spurious water vapor movement and excessive local precipitation.At present,the advection scheme used in the treatment of water matter in China’s CMA-MESO model is PRM(Piece-wise Rational Method)scheme,although the scheme has high accuracy and positive definite conformity and can be conserved in the global model,but in the limited area mode,due to the treatment of side boundaries,it is difficult to achieve conservation or balance in the limited area mode.In addition,the advection scheme of CMA-MESO mode in processing physical quantities such as air pressure,temperature,and wind field is the semi-Lagrangian advection scheme,and the error caused by upstream point interpolation in the divergent flow is not a conserved advection scheme.In order to solve the conservation problem of modal advection schemes in finite region models,two different conservation semi-Lagrangian schemes of finite region modes are studied.A new simple and negligible computational cost finite mode semiLagrangian scheme is a method for conservation of mass based on the idea of mass recovery,and the zero-lateral boundary flux scheme(ZLF)is applied in the advection of water in the CMA-MESO model.The results of the ideal test show that the ZLF scheme has good conservation and conformality,and can better maintain the distribution of physical quantity fields and the conservation of strong intermittent physical quantity fields.Then,the scheme is added to the CMA-MESO model,and the results of the actual individual prediction test and continuous forecast test show that the ZLF scheme can suppress overestimated precipitation,reduce false precipitation forecast,and significantly improve the precipitation fall area forecast.For extreme rainstorms and continuous rainstorms,the ZLF scheme has a significant effect on the improvement of precipitation level and precipitation fall area forecasting.The ZLF scheme effectively improves the imbalance and non-conservation of water substances in the limited-area caused by the CMA-MESO advection scheme and improves the precipitation prediction effect of the model.The other is the self-conserved upstream point continuous mapping scheme COMAD(Continuous Mapping about Departure points)scheme designed based on the idea of tectonic conservation form in the CMA-MESO mode in the atmospheric pressure,temperature and wind field advection scheme step by step,the results show that the conserved COMAD scheme can effectively improve the forecast effect of the original upstream point semi-Lagrangian scheme and improve the precipitation intensity in the center of the rainstorm.Suppression of excessive precipitation also improved precipitation forecast scores,and the COMAD scheme was able to improve forecasting of model variables.The COMAD scheme effectively improves the problem of non-conservation of the scheme caused by the interpolation error of the traditional semi-Lagrangian scheme of upstream points,improves the prediction accuracy of model variables,and improves the precipitation prediction effect of the model.