森林冠层边界层湍流传输的观测和数值模拟

文中分析和模拟了森林冠层上下动量、热量和水汽传输的特征。结果表明：冠层对动量的吸收十分明显，非局地扩散通量在冠层上下的动量传输中起着很大的作用；白天在冠层下层结稳定，但冠层下观测的感热通量向上传输；夜晚冠层下层结不稳定，但冠层下观测的感热通量向下传输，白天和晚上都出现了热量的反梯度传输现象，从而证明在热量输送中，非局地扩散通量不可忽视。同时对冠层上下的水汽交换特征的分析表明：非局地扩散通量是冠层内水汽向冠层上传输的主要机制。

OBSERVING AND NUMERICAL MODELLING OF DISPERSIVE TRANSFER IN FOREST CANOPY BOUNDARY LAYER

A micrometeorological model was developed to simulate momentum, heat and water vapor transfer within and above forests. Simple Biosphere Model (SiB) was also used for providing such parameters as the evapotranspiration rate of the vegetations. In processing dispersive transport term in momentum equation, first order closure scheme by Li (1985) wasused after modification according to analysis of physical processes. After that, the modifiedmethod was also used for calculating various dispersive terms which appeared in the other equations. The vegetation canopy was devided into several layers according to the leaf areadensity. The evapotranspiration rate of vegetation and its latent heat were considered in water vapor conservative equation and heat equation respectively. Absorbed net radiations bydifferent layers were different within the canopy because of various leaf area density.The agreement was shown between the simulated results and observed data. The mo-mentum absorption by the canopy was very obvious. During the daytime, the atmopshericstratification within the canopy was stable. DUring the nighttime, the atmospheric stratification within the canopy was unstable. Form the turbulence data, it was shown that heat fluxwas transferred in countergradient way. The simulated and observed results all indicatedthat the nonlocal dispersive transfer of momentum. heat and water vapor was very importantwithin and immediately above vegetation canopies and couldn't be ignored. Especially, nonlocal turbulent transfer might be the main way to transfer water vapor from within thecanopy to above the canopy. These were special phonomena within and above vegetationcanopies, which should be investigated further both in theory and in experiment.