地表非均匀性对区域平均水分通量参数化的影响
THE INFLUENCE OF LAND SURFACE HETEROGENEITY ON PARAMETERIZATION OF REGIONAL MEAN WATER VAPOR FLUX
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摘要: 次网格尺度地表非均匀性对于网格区平均通量具有重要影响。若将网格区视为均一地表,并不能真实描述地气通量交换过程,且可造成很大误差。文中从理论上证明,区域平均水分通量的变化率可分解为两部分:第一部分为区域水分通量的算术平均变化率;第二部分为非均匀性所引起的水分通量变化率扰动,它与区域内土壤水分空间分布的变差系数有关。数值试验表明,地表土壤水分的水平空间变差系数集中反映了区域内土壤水分分布的非均匀程度,不同土壤对同样的非均匀程度其敏感性是不同的。变差系数愈大,非均匀性愈强,在相同的土壤水分平均值下,不同土壤类型对地表非均匀程度的敏感性并不相同。例如沙土和粘土受非均匀性的影响就可相差数十倍。Abstract: In this paper it is proved theoret ically that the variation ratio of regional mean water vapor flux can be divided into two components:the variation ratio of mathematical mean of regional mean water vapor flux for a region and,the disturbance variation ratio cont ributed by land surface heterogeneity,which is mainly influenced by variety coefficient of special distribution of soil moisture in the near surface soil layer in the region.It is demonstrated by numerical experiment that the variety coefficient of special distribution of soil moisture content can be used to denote the heterogeneity of soil water content in a spatial region,and the contribution of land surface heterogeneity of soil moisture to the variation ratio of regional mean water vapor flux are also different for diverse soil types.For the same mean of soil water content,the sensitivity of variation ratio of regional mean water vapor flux to land surface heterogeneity of soil moisture is dissimilar completely for different soil types.From this study it can be concluded that the heterogeneous soil moisture distribution on sub-grid scale region imposes import ant influence on estimation of grid-mean water vapor flux.The heterog eneity of soil moisture in near land surface layer on sub-grid scale should be taking into account in est imation of grid mean water vapor flux in land surface process model.The connotative un-realistic hypothesis of homogeneous soil moisture on gridscale region may make un-neglect able error for the est imations of regional mean water vapor flux.
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