不同下垫面湍流通量计算方法的比较研究

A comparative study of computing methods of turbulent fluxes on different underling surfaces

本文利用1990～1994年在中国内蒙古奈曼市半干旱地区沙丘和植被区下垫面观测的微气象数据,采用变分法、波文比能量平衡方法和空气动力学方法计算了7种下垫面(沙丘、草原、四种放牧强度的草地、玉米田)的湍流通量并进行了比较.结果表明:除沙丘和重度放牧草地外,三种方法计算的湍流通量在大多数时刻是比较一致的,相关性较高,能量闭合程度也较好.在用于计算植被相对茂盛下垫面的湍流通量时,变分法得到的结果更好一些.随着放牧强度的增大,地表生物量、覆盖率和植被高度相应减少,潜热和动量通量相应减小,而感热通量增大.草地等植被茂盛的下垫面能够增加垂直方向的动量输送,增加空气动力学粗糙度,减小风速,阻止地表沙粒的运动和沙丘的起伏,对防止沙漠化能起到较大作用.

Sensible heat flux, latent heat flux and momentum flux on heavy grazing site, medium grazing site, light grazing site, no grazing site, dune, grassland and maize site underlying surfaces, according to the variational method, the conventional Bowen ratio energy balance method and the aerodynamic method, have been computed by utilizing the micrometeorological observed data of dune and vegetation at the semi-arid area at Naiman in Inner Mongolia of China between 1990-1994. The results show that the turbulent fluxes calculated by three methods are comparatively consistent at the most time, which have close correlation and closure degree of the energy balance except on the dune and heavy grazing site. So the variational method will be more applicable at the flourishing underling surface. And also, above-ground biomass, plant coverage, height of vegetation, momentum flux and latent heat flux decreases, along with the increasing of the grazing intensity, which corresponds to the enhancing of sensible heat flux. Flourishing underling surface could increase the vertical momentum transportation and aerodynamic roughness length,decrease the wind speed, prevent the movement of the sand and the fluctuation of dune, and so avoid desertification to a certain degree.