林带对空气的湍流交换系数影响

本文从近地层动力学和热力学方程出发,用数值方法研究了林带对空气的湍流交换系数影响。研究结果表明:在林冠层以上,林带附近的湍流交换系数比较大;在林冠层以下,林带附近的湍流交换系数比较小。林带影响在高度为2.7—3.5倍树高、透风率为0.35左右铅直范围内最大。

THE EFFECTS OF SHELTERBELT ON THE COEFFICIENT OF ATMOSPHERIC TURBULENT EXCHANGE

The coefficient of atmospheric turbulent exchange is an important factor which affects the climate near the surface and the soil climate. Due to the difficulty of observation, the study of the effects of shelterbelt on the vertical structure of the coefficient of atmospheric turbulent exchange has been scarcely carried out. In this paper, we try to simulate numerically the effects based on the dynamic and thermaldynamic equations in the constant flux layer, and obtain the satisfied results.The movement equation, thermaldynamic equation and continuement equation may be written as follows:, andwhere We take the height of shelterbelt as 10 m, and the permeability as 0.17. 0.35, 0.45 and0.65, which cover a larger range from porous to dense shelterbelts so that the results we have simulated are of universality.Based on this study, we may conclude that: under the crown of the tree, the sheltbelt de-creases the coefficient of atmospheric turbulent exchange; over the crown of the tree, the sheltbelt increases the coefficient. This is because the coefficient is closely related to the ver-tical gradient of wind, under the crown of the tree, the vertical gradient of wind is smallernear the sheltbelt than far from the sheltbelt, and over the crown of the tree, the vertical gradient of wind is larger.