An Improvement of the Linearized Planetary Boundary Layer Parameterization Scheme for CMA-GFS 4DVar

Liu Yongzhu; Zhang Lin; Chen Jiong; Wang Chao

doi:10.11898/1001-7313.20230102

Vol.34, NO.1, 2023

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Article Navigation > Journal of Applied Meteorological Science > 2023 > 34(1): 15-26

Liu Yongzhu, Zhang Lin, Chen Jiong, et al. An improvement of the linearized planetary boundary layer parameterization scheme for CMA-GFS 4DVar. J Appl Meteor Sci, 2023, 34(1): 15-26. DOI: 10.11898/1001-7313.20230102.

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Liu Yongzhu, Zhang Lin, Chen Jiong, et al. An improvement of the linearized planetary boundary layer parameterization scheme for CMA-GFS 4DVar. J Appl Meteor Sci, 2023, 34(1): 15-26. DOI: 10.11898/1001-7313.20230102.

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An Improvement of the Linearized Planetary Boundary Layer Parameterization Scheme for CMA-GFS 4DVar

DOI: 10.11898/1001-7313.20230102

Liu Yongzhu^{1, 2
,
,},
Zhang Lin^{1, 2},
Chen Jiong^{1, 2},
Wang Chao¹

1.
CMA Earth System Modeling and Prediction Center, Beijing 100081
2.
State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing 100081

Received Date: 2022-10-08
Rev Recd Date: 2022-11-24
Publish Date: 2023-01-31

Abstract

Abstract

By continuously developing and optimizing the linearized physical process of the tangent linear model and keeping it consistent with the nonlinear model, the analysis and forecasting performance of four-dimensional variational data assimilation (4DVar) of China Meteorological Administration Global Forecast System (CMA-GFS) can be effectively improved. Currently, the planetary boundary layer (PBL) parameterization scheme adopted by CMA-GFS model is based on Charney-Phillips (C-P) grid, while the linearization PBL parameterization scheme used in CMA-GFS 4DVar is on the basis of Lorenz grid. The zigzag noise of the temperature and moisture in the boundary layer is removed and the correspondent profiles appear to be smooth with C-P PBL parameterization scheme, and the forecast errors of CMA-GFS model are effectively reduced. To improve the analysis and prediction effects of 4DVar on the boundary layer, a new linearized PBL parameterization scheme based on the C-P grid (TL_NMRF_CP) is developed. By making more refined regularization constraints on the disturbances of the surface heat flux, the surface water vapor flux, Richardson coefficient of the free atmosphere, the heat and momentum exchange coefficient of the boundary layer, the influence of the linearization process on the accuracy of the tangent linear approximation is reduced while ensuring stable operation of the tangent linear and adjoint models. Two tests are designed, one is TL_MRF test based on the original TL_MRF scheme and the other is TL_NMRF_CP test based on the TL_NMRF_CP scheme. The tangent linear approximation tests show that, compared with the original scheme, the TL_NMRF_CP scheme can improve the tangent linear model forecast accuracy on the boundary layer, reduce the relative error of the potential temperature of the boundary layer by up to 10%, reduce the relative error of the specific humidity by 5% at the most, and reduce the relative error of zonal wind by up to 12%. In the minimization process of CMA-GFS 4DVar, the TL_NMRF_CP scheme can reduce the relative difference of the cost functions caused by different resolutions between inner and outer loops of the 4DVar system, and improve the convergence efficiency of 4DVar. The batch cycle assimilation forecast experiments of CMA-GFS 4DVar further verify that the TL_NMRF_CP scheme can provide better analysis and prediction results. The TL_NMRF_CP scheme has also been applied to CMA-GFS 4DVar operation system.
- planetary boundary layer;
- linearized physical processes;
- CMA-GFS;
- four-dimensional variational assimilation

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Figures and Tables

Fig. 1 Vertical distribution of global mean relative error of potential temperature perturbation in CMA-GFS tangent linear model

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Fig. 2 Zonal mean absolute errors of potential temperature perturbation for TL_MRF test

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Fig. 3 Improvements in potential temperature perturbation of TL_NMRF_CP test relative to TL_MRF test

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Fig. 4 Vertical distribution of global mean relative error of specific humidity perturbation in CMA-GFS tangent linear model

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Fig. 5 Zonal mean absolute errors of specific humidity perturbation for TL_MRF test

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Fig. 6 Improvements in specific humidity perturbation of TL_NMRF_CP test relative to TL_MRF test

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Fig. 7 Vertical distribution of global mean relative error of zonal wind perturbation in CMA-GFS tangent linear model

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Fig. 8 Mean absolute errors of zonal wind perturbation for TL_MRF test

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Fig. 9 Improvements in zonal wind perturbation of TL_NMRF_CP test relative to TL_MRF test

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Fig. 10 Convergence of the cost function under CMA-GFS 4DVar

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Fig. 11 Anomaly correlations of 700 hPa geopotential height for the Northern Hemisphere and the Southern Hemisphere

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Table 1 Setting of CMA-GFS 4DVar test

设置	详细配置
水平分辨率	外循环为1.0°×1.0°，内循环为1.0°×1.0°
模式积分步长	外循环为450 s，内循环为900 s
垂直层数	87层
同化时间窗长度	6 h
观测剖分间隔	30 m
线性化物理过程	垂直扩散、地形阻塞流拖曳、对流参数化、大尺度凝结
极小化算法	有预调节的Lanczos-CG算法
重力波控制	数字滤波弱约束
最大极小化迭代次数	50次

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