土壤含水量空间尺度分布非均匀对中尺度脉动量和通量的影响研究

本文采用RAMS（Regional Atmospheric Modeling System）模式模拟研究了没有背景风的情况下，土壤湿度非均匀分布的长度尺度分别为40km逐渐减小到2km时，地表通量的分布和大气边界层的响应.运用二维傅里叶变换，分析了地表通量、中尺度脉动量和中尺度通量的二维幅度谱分布，初步探讨大尺度模式中非均匀地表条件下的边界层参数化问题.分析结果显示各试验的地表水、热通量和中尺度脉动量的幅度谱的极大值都出现在与各自非均匀尺度相对应的波数处，当有不同尺度的非均匀斑块共存时，最大的非均匀尺度占主导.但是中尺度水、热通量的结果有所不同，除了在与各自非均匀尺度相对应的波数处有峰值之外，在其他波数还有多个峰值.这些结果表明地表水、热通量的空间分布尺度与非均匀尺度之间存在较好的对应关系，而中尺度水、热通量与非均匀尺度的关系并不明显，说明地表水、热通量的网格平均值的代表性较好，但是不能反映次网格脉动的影响，而中尺度通量的网格平均值的代表性较差.

Impact of spatial heterogeneity of soil moisture on mesoscale fluctuations and mesoscale fluxes

Land surface heat fluxes and atmospheric boundary layer (ABL) are simulated using the Regional Atmospheric Modeling System (RAMS). Eight experiments on land-surface wetness discontinuities with heterogeneous length scales from 40km to 2km are carried out without large-scale background wind. The two-dimensional amplitude spectra of land surface heat fluxes, mesoscale fluctuations and mesoscale heat fluxes are analyzed by two-dimensional fast Fourier transform algorithm (FFT). Then ABL parameterization for large-scale models, such as GCM (General Circulation Model) is discussed. The results show that amplitude spectra of the land surface heat fluxes and the mesoscale fluctuations in each experiment reach maximum, when wave number is corresponding to heterogeneous length scale, and when different length scales coexist, the largest scale is dominant. Differently, amplitude spectra of the mesoscale heat fluxes, besides wave number corresponding to heterogeneous length scale, still have several peaks at other wave numbers. It appears that the relationships between the land surface heat fluxes and the heterogeneous length scale are significant, but the mesoscale heat fluxes don't indicate similar relationships with heterogeneous length scale. The representability of grid-cell averaged surface fluxes is good but that of mesoscale fluxes is not so good.