区域气候模拟中侧边界嵌套误差的研究

ANALYSIS OF LATERAL BOUNDARY NESTING ERRORS IN REGIONAL CLIMATE MODELING

在复杂地形条件下嵌套细网格模式的基础上 ,建立了与球圈模式相嵌套的区域模式系统 ,对几种不同条件下的嵌套误差进行了比较分析 ,研究了区域模式嵌套误差的特征分布及时空演变特征。初步分析表明 :区域模式嵌套造成的误差在不同区域的分布不同 ,且不同的物理量在时空的分布也不同 ;动能场的误差主要在边界区上层的流入区 ,感热场的误差在边界区上层 ,水汽的误差在边界区上层的流入区 ;侧边界输入时间间隔对模式嵌套误差有一定的影响。有限区细网格模式在上层长波误差大于粗网格环圈模式上层误差 ,在下层短波模拟的误差比粗网格环圈模式的下层误差要小。相速误差对侧边界嵌套误差的影响在下层很严重 ,嵌套误差的大小与大小模式的网格距之比有关 ;在大小模式物理参数化过程一致的条件下 ,无日变化的区域模式其嵌套误差远大于有日变化的区域模式嵌套误差。

In order to study the characteristics of errors associated with the lateral boundary conditions used in regional modeling, especially the regional climate modeling, based on the YH model, a regional model system nested with a spherical-belt type model is established and a set of error diagnosis tools are developed. By means of the software Excel, a series of comparative studies are carried out to analyze the spatial and temporal distribution of the errors due to the different lateral boundary conditions. The results show that the basic methodology for detecting the errors associated with lateral boundary conditions in regional modeling is rational, and the tools are quite useful. Moreover, it might also be applied to other studies, such as for diagnosing other types of errors in the model or developing some new schemes. The preliminary results indicated that the lateral boundary error of a regional model varies with the location in the model domain, and the spatial and temporal distribution of the error associated with different variables is rather different. Relatively, the errors of mass and potential vorticity fields are smaller in the YH model. The errors of kinetic energy and water vapor field are found mainly in the influent part of upper layers in the near-boundary region, while the error of sensitive heat field was in the upper layers of near-boundary region. The fixed lateral boundary conditions cause more serious errors than the nested ones, and the time interval updating the lateral boundary also has some impact on the error. It is interesting to mention that the errors of upper layers in the fine mesh regional model where the long wave motion dominates are larger than the errors found in the coarse mesh spherical-belt one. On the other hand, the errors of lower layers in the same fine mesh regional model where the short wave motion dominates are smaller than the errors found in the coarse mesh spherical-belt one. The impact of phase velocity error on lateral boundary errors is more significant in the lower layers, which is related to the ratio of grid lengths of fine-mesh vis-a-vis coarse-mesh. The errors became much more serious when the diurnal variation cycle is turned off in the regional model.