青藏高原中部聂荣半干旱草地夏季近地层能量平衡与输送分析

利用青藏高原中部聂荣地区草地下垫面2014年7~8月近地层气象要素梯度观测及湍流观测数据,分析讨论了该地区观测期间的基本气象要素特征、能量平衡特征以及能量输送特征,主要结论如下:(1)向下、向上短波辐射和净辐射日变化规律一致,向下、向上长波辐射日变化平缓。反照率呈"U"型分布,早晚大,中午小,聂荣夏季地表平均反照率为0.20。(2)在夏季白天,聂荣地区净辐射大部分以潜热的形式加热大气。考虑了土壤浅层热储存和垂直运动引起的平流输送后,能量闭合率由0.65提高到0.80,闭合率有显著的提高。(3)在不稳定层结下,动量总体输送系数CD平均值为4.7×10~(-3)和热量总体输送系数CH平均值为3.5×10~(-3);在稳定层结下,CD平均值为3.4×10~(-3),CH平均值为1.8×10~(-3);C_D和C_H在近中性层结下的平均值分别为4.30×10~(-3)和2.39 10~(-3)。

A Study on Energy Balance and Transfer in the Surface Layer over SemiArid Grassland of Nyainrong Area in Central Tibetan Plateau in Summer

Based on gradient and turbulence data observed in the near surface layer over semi-arid grassland of Nyainrong area in the central Tibetan Plateau from 18 July 2014 to 31 August 2014, characteristics of several basic meteorological elements and energy balance and transfer are analyzed. The main results are:(1) The downward and upward short-wave radiation and net radiation fluxes have a similar diurnal variation pattern, and the diurnal fluctuation of the downward and upward long-wave radiation fluxes are small. The surface albedo shows a "U" type distribution with large values in the morning and evening and small values in the noon. The mean surface albedo over Nyairong area in summer is 0.20. (2) The latent heat flux is obviously larger than the sensible heat flux, which indicates that the latent heat plays a dominate role in the heat transfer between the atmosphere and surface. The closure rate of surface energy balance increases significantly from 0.65 to 0.80 after considering the heat storage in the shallow soil layer and heat advection caused by vertical movement. (3) The bulk transfer coefficients CD and CH for momentum and heat are 4.7×10^-3 and 3.5×10^-3 respectively under unstable stratification; their values are 3.4×10^-3 and 1.8×10^-3 under stable stratification, and 4.30×10^-3 and 2.39×10^-3 under near neutral stratified condition.