毛乌素沙地凝结水动态变化及其影响因子的研究

Dynamics of Dew Condensation and Its Controlling Factors in Mu Us Desert

基于2002年5～10月间运用直接称重法对毛乌素沙地臭柏（Sabina vulgaris Ant．）群落林间空地的0—1．5cm表层土壤凝结水连续观测资料，分析讨论了凝结水的日变化和季节变化特征以及影响凝结水形成的环境因子。结果表明：毛乌素沙地天然臭柏群落内各月均有凝结水发生，并且可从午后持续至翌日清晨，但各月间凝结水量和凝结持续时间有所不同。5月份凝结水持续时间最短，凝结水量也最少；而9月份凝结水持续时间最长，凝结水量也最多。影响毛乌素沙地凝结水形成的主要环境因子有风速、大气相对湿度、气一地温差及其相互作用。其中，风速与凝结量间存在较高相关性，而气温能否趋近或降至露点产生土壤凝结水是决定夜间水分凝结量的一个关键因素。

In the Mu Us desert, China, dew condensation from soil surface to 1.5 cm in depth under Sabina vulgaris patch gap was measured by directly weighting method from May to October, 2002. Daily and seasonal changes of dew condensation and the controlling factors on dew condensation were analyzed. The results indicated that the net dew deposition of the upper soil layer of S. vulgaris patch gap could be maintained from the late afternoon to the following morning in all seasons. Under natural conditions, the process of dew formation was composed of the following two stages ： （ 1 ） The process of water molecular absorption of sandy soil could last for a long time, however, the amount of dew was limited. （2） The process of soil condensation determined by dew point tempera- ture. Soil condensation lasted a relatively short period and generated considerable dew condensation in volume at the predawn and therefore accounting for the main part of dew condensation. Although dew occurred every month from May to October, the total amount and the time duration of dew condensation changed seasonally. In May, the condensation duration period was shorter and the net total amount was less than other seasons. In September, the condensation duration period was the longest and the largest amount of dew was produced. In Mu Us desert, dew condensation was influenced primarily by wind speed, air - soil surface temperature deficit, humidity and interactions among them. Wind speed showed a high correlation with dew condensation. Higher air -soil surface temperature deficit interacted with lower humidity in daytime promoted strong evaporation generating from soil surface and facilitated the incipience of water molecular absorption condensation at early time. Higher air - soil surface temperature deficit, however, interacted with certain humidity （50% -60% ）, the consequence was reverse. Query whether air temperature could trend or reach the dew - point temperature that soil condensation was produced is critical for the amount of dew condensation during night.