水体对湍流交换系数的影响*

本文根据边界层理论,计算水体附近湍流交换系数的变化。计算结果表明:白天整个水体上的湍流交换系数都比陆面上同高度的要小,并且有二个低值中心:一个靠近水面,另一个在约100m高度;夜间靠近水面的那层空气的湍流交换系数仍较小,但其上方的湍流交换系数要比陆面上大。水面上的湍流交换系数日变化小于陆面上,特别是靠近水面那层空气日变幅很小。同时指出:水陆间粗糙度的差异和稳定度的差异控制着水陆湍流交换系数的差异;前者是稳定的;后者有周期性的变化。

THE EFFECT OF WATERBODY ON AIR TURBULENT EXCHANGE COEFFICIENT

Based on the theory of atmospheric boundary layer and having synthetically considered various factors which may affect air turbulent intensity, we developed a numerical model for calculating the effect of waterbody on air turbuleat exchange coefficient (ATEC) and obtained the following conclusions.1, The difference of ATEC depends on the differences both on roughness and on atmospheric stability between waterbody and land. As the roughness on water surface is always less than on land surface, its effect on ATEC is stable. However, the difference of atmospheric stability over waterbody and over land has periodic variation, i.e. air over waterbody is more stable than over land in the daytime; in the nightime, the opposite holds. Thus its effect on ATEC is also of periodicity,2, In the daytime, the ATEC over waterbody is less than that over land, and there are two minimum centers. ( 1 ) near water surface; ( 2 ) at the altitude of loom over waterbody.3, In the nightime, the ATEC near water surface is still less than near the land. But in the leeward of waterbody, it is larger than over the land; especially in summer, it may be double as much,4, The profile of ATEC is increasing to the maximum from surface at first, then decreasing to zero with increasing height. The altitides where the maximum ATEC occurs are about 400-500m in the daytime and about 130-200m in the nightime.The ATEC in the daytime may be more than double as much as in the nightime.5, The maximum difference of ATEC over waterbody and over land occurs where the maximum ATEC occurs.The distribution of the difference with height is similar to the profile of ATEC.6. Over water surface, the diurnal variation of ATEC is less than over land, and the diurnal change range near water surface is very small.