摘要
A new method is proposed for the effective roughness length (ERL) in heterogeneous terrain based on the principle of equalisation of momentum or heat fluxes calculated by the drag coefficient parameterization scheme used in the ECMWF numerical model. Compared with the area-weighted logarithmically averaged ERL (drag coefficient), the newly calculated ERL (drag coefficient) is about 40% (16%) larger with a roughness step of 2.3. These differences reach their maximum values when the ratio of smooth to rough surface is 60% to 40%. Since the determination by this method is not sensitive to the atmospheric stratification, it is suitable for use in climate models.
A new method is proposed for the effective roughness length (ERL) in heterogeneous terrain based on the principle of equalisation of momentum or heat fluxes calculated by the drag coefficient parameterization scheme used in the ECMWF numerical model. Compared with the area-weighted logarithmically averaged ERL (drag coefficient), the newly calculated ERL (drag coefficient) is about 40% (16%) larger with a roughness step of 2.3. These differences reach their maximum values when the ratio of smooth to rough surface is 60% to 40%. Since the determination by this method is not sensitive to the atmospheric stratification, it is suitable for use in climate models.
基金
This work was supportedjointly by the National Key Basic Research DevelopmentProgram(G1999043400)and the National Natural ScienceFoundation of China under Grant Nos.40275021,and49975016.
