湍流动能闭合对区域气候模拟效果影响的机理研究

EFFECTS OF TURBULENCE KINETIC ENERGY CLOSURE SCHEME ON REGIONAL CLIMATE MODELING

利用湍流动能(TKE)闭合改进了RegCM2中原高分辨的边界层参数化方案,并用1998年夏的NCEP/NCAR气候资料对TKE闭合方案影响区域气候模拟效果的机理作了探讨.研究表明,在区域气候模式中采用TKE闭合的边界层方案可以将垂直扩散直接与湍流变化联系起来,改善地表通量及各层垂直扩散项的计算,使地表通量和垂直扩散的日变化及各层分布更为合理,从而改进模式对各预报量及降水的模拟。

The boundary layer parameterization scheme in regional climate model (RegCM2) is improved by applying turbulence kinetic energy closure scheme. The NCEP/NCAR reanalysis data of 1998 is employed to study the effects of the TKE closure scheme on regional climate modeling. The main results may be summarized as follows. The vertical diffusion and the turbulence variation are linked directly after employing TKE closure scheme. The physical process in boundary layer can be described more realistically. By the use of TKE scheme, the estimation of the ground flux and the vertical diffusion at the model levels are improved. The diurnal variation and distribution of the ground flux and the vertical diffusion at each model level are more reasonable. It is found that after adopting the TKE closure scheme, the geopotential height and temperature field are obviously improved, especially, the much distinct improvements occur in the temperature and specific humidity field at low levels that are directly effected by the boundary layer parameterization scheme. An improving also takes place on estimating the height of boundary layer, the results show that the diurnal variation and the diurnal extreme value of boundary layer height can be described more reasonably. After adopting the TKE closure scheme, the simulation of the precipitation is also improved to some extent. The results show that the distribution of precipitation simulated by TKE scheme is closer to the observation than that of simulated by original scheme, and modifies the circumstance of lesser precipitation amounts simulated by the original scheme. Although the capability of simulation can be elevated to some extent after applying TKE scheme, for improving the simulation of precipitation which represents the whole capability of the model, in addition to improve the boundary layer parameterization scheme, other physical process parameterization scheme should also be improved in order to obtain a satisfactory result.