黄土高原半干旱区露水形成的大气物理特征研究

Atmospheric physical characteristics of dew formation in semi-arid in loess plateau

运用2009年在黄土高原典型半干旱区定西的观测资料,分析了半干旱区露水变化特征及其大气影响因子.研究结果表明在黄土高原半干旱区秋季,日最大凝结量可以达到0.33mm,最小日凝结量0.09mm,日平均凝结量为0.23mm,这对半干旱区而言是可观的水分输入;露水凝结持续时间可以长达14h.露水的出现频率与风速、大气相对湿度、气温、地-气温差等大气影响因子有显著关系.露水的形成机理十分复杂,是湿度因子、热力因子和动力因子综合作用的结果.在露水形成过程中,大气湿度是内因,为露水形成提供所需水汽;温度则是露水形成的关键,为露水形成提供"源动力",而风速则是重要的外部影响因素,既可以促进露水形成,也可以阻碍露水形成,是露水形成过程中不确定因子.从露水发生频率的分布特征来看,在风速0.5—2m/s、相对湿度>80及温度-露点差-3—6℃时、地-气温差<±2℃条件下更易形成露水.

Based on the data measured in 2009 in the DingXi,a typical semi-arid region in loess plateau,the temporal variation of condensed water and the influence factors are investigated.Meanwhile,the measurements of condensed water,made by weighing approach and eddy-correlation approach separately,are compared in this work.The results show that in the semiarid regions in Loess Plateau,the daily maximum amount of condensation can reach 0.33 mm,the daily minimum recorded is 0.09 mm,and the average daily amount is 0.23mm.No obvious correlations is found between the amount of condensation and wind velocity,relative humidity,temperature,or land-air temperature difference.In the process of dew formation,the relative humidity which supplies the water vapor for condensing is an internal factor.The temperature which is motive power for condensing process is a key factor.The wind speed has an important effect and is an uncertain factor,which promotes but also can restrain the dew formation.It is also found that the following conditions favor the condensation processwind speed of 0.5—2 m /s,relative humidity 80 and land-air temperature difference ± 2℃.