地形非均匀性对网格区地面长波辐射通量计算的影响

THE INFLUENCE OF OROGRAPHIC HETEROGENEITY ON PARAMETERIZATION OFREGIONAL MEAN LONG WAVE RADIATION FLUX

中文关键词:  地形非均匀性，海拔高度，地表温度，地面长波辐射

英文关键词:Topographic heterogeneity, Terrain height, Surface temperature, Surface long wave radiation.

中文摘要:

      从理论和数值试验两个方面证明地形的非均匀性（如海拔高度）对网格区地面长波辐射通量的计算有重要影响，海拔高度场的区域平均值及其变差系数是影响网格区地面长波辐射通量的主要因素，仅仅用地表均匀假定下的区域平均参量（如平均海拔高度和平均温度）所计算的网格区地表有效辐射通量值与其真实值之间存在着一定的误差。由于地表有效辐射通量是海拔高度的非线性函数，在特定情况下,其影响相当大,可产生不容忽略的误差。相对而言，海拔高度自身非均匀性对误差的影响远大于地表温度非均匀性项及其混合扰动项所产生的误差。对于不同的地形平均高度，地形非均匀性影响的程度并不相同。平均高度较小时，非均匀性的影响几乎可以忽略，但随着地形平均高度的增加，地形非均匀性的影响程度呈非线性增长趋势。因而，在复杂地形区域，考虑次网格地形的热力作用非常必要。

英文摘要:

      It is theoretically demonstrated that the influences of terrain height and orographic heterogeneity are important on the flux of surface long wave radiation over a large scale grid area. The results of numerical experiments show that mean terrain height and orographic relative standard deviation over a large scale grid area are two important factors which have influence on the mean flux of surface long wave radiation. Over a complicated topography region, because of the nonlinear increment of the relative standard deviation of topographic elevation with mean terrain height, the mean value of surface long wave radiation flux has a nonlinear increment by the dual-effects. But, the influences of orographic heterogeneity on surface long wave radiation are larger in comparison with the heterogeneity of surface temperature although the latter also has an evident impact on surface long wave radiation flux. It was proved under the homogeneous supposition that there are three parts of the relative errors in calculating the effective radiation flux over a complex orographic region i.e. (1) the deviation of topographic heterogeneity from terrain height; (2) the deviation from surface temperature heterogeneity; (3) the mixed deviations produced by orographic heterogeneity and surface temperature heterogeneity. The first error is larger, which sometimes reaches 40% in the mean effective radiation flux calculated over a heterogeneous topography region. On the other hand, the second error, which is the mixed deviations between the terrain height heterogeneity and surface temperature heterogeneity, is much smaller. Thus, when the effective radiation flux is calculated over a large scale grid area which has a complex topography, the influences of orographic heterogeneity should be considered in the climate model, and the surface temperature heterogeneity effects may be omitted.