极端干旱地区绿洲小气候特征及其生态意义

Microclimatic Characteristics of the Heihe Oasis in the Hyperarid Zone

运用微气象学方法对极端干旱区荒漠绿洲小气候进行了观测,分析我国极端干旱区荒漠绿洲的微气象特征并与林地外进行了对比。同时讨论晴天、阴天和沙尘暴天气的PAR的差异,分析了产生这些差异的原因。结果表明荒漠绿洲具有改变太阳辐射、调节近地层地表及地下温度、缩小温差、降低风速、提高土壤及大气湿度等重要生态作用。绿洲内部的太阳总辐射比林冠层顶部减少49.3%￣49.83%;生长季胡杨和柽柳林内的气温均低于林地外,胡杨林平均比林外低1.62oC,柽柳林比林外低0.83oC,而且森林覆盖率越高降温作用越明显;群落上层气温高于群落下层,气温随高度增加而增加;林内大气相对湿度均高于林地外,生长期,胡杨林内比林地外高8.5%,柽柳林高4.2%;胡杨林地平均风速为0.33m/s,比林地外低2.7m/s;柽柳林平均风速为0.72m/s,比林地外低2.31m/s。在沙尘暴日,PAR明显小于阴天日和晴天日下的值,而!Q非常大,且变化不稳定,该结论对研究大气层的稳定性有极其重要的意义。

The microclimate of a desert oasis in the hyperarid zone of China was monitored using micrometeorological methods and compared with those of areas adjacent to forested land. Differences in ground-level photosynthetically active radiation （PAR） on clear, cloudy and dust storm days and their subtending causes are analysed and discussed. Desert oases serve the ecological functions of altering solar radiation, adjusting near-ground and land surface temperatures, reducing soil temperature differences, lowering wind velocity, and increasing soil and atmospheric humidity. The total solar radiation in the interior of the oasis was roughly half of that outside a forest canopy. During the growing season, air temperatures in Populus euphratica Oliv. （poplar） and Tamarix ramosissima Ledeb. （tamarisk） forests were 1.62 ℃ and 0.83℃ lower, respectively, than those in the areas around the forests. Furthermore, the taller the forest cover, the greater the temperature drops; air temperatures in the upper storey were greater than those in the lower storey, i.e., air temperature rose with increasing height. Over the growing season, the relative humidities of the air in the poplar and tamarisk forests were 8.5% and 4.2% higher, respectively, than those in areas around the forests. Mean wind velocity in poplar-forested lands was 0.33 m s^-, 2.31 m s^-1 lower than that in the surrounding area. During dust storm days the PAR was significantly lower than on cloudy or clear days, when it was high and varied in an irregular manner.