西北干旱区夏季晴天、阴天边界层结构及其陆面过程对比分析

The Northwest Arid Areas in Summer Sunny Day,Cloudy Day Boundary Layer Structure and Land Surface Process Comparison Analysis

以2006年夏季敦煌野外观测的探空资料为基础,对比研究了西北的荒漠区晴天、阴天大气边界层的构造以及对应的陆面过程。结果表明,西北荒漠区晴天和阴天的对流边界层以及稳定边界层均比中国中部、东部地方发展旺盛。相比而言,晴天的边界层在构造和陆面过程都和阴天存有较大差异。晴天对流边界层高度可达3.5 km,稳定边界层高度约为1 km,而阴天这两者的日最大高度分别仅约为2.5km和0.2 km。除边界层高度外,西北荒漠区的比湿表现为阴天高于晴天,晴天比湿随高度变化幅度大于阴天,阴天从地表开始向上200 m内出现较弱的逆湿现象,而晴天不出现逆湿现象。造成晴天、阴天边界层的不同原因主要是热力因子和动力因子差异。首先,强烈的太阳辐射、较大的感热通量转化率使得晴天比阴天热对流发展更加旺盛;其次,近地面水平风速晴天的速度均比阴天大,这种以湍流形式的动力作用也为晴天边界层的发展高度大于阴天提供了一定的动力背景。对流边界层在发展初期受陆面热力因子影响很大,没有了稳定边界层的限制后就会迅速发展,而且发展在时间上与净辐射、地表温度、感热通量的日变化中表现出一定的滞后性,这与能量的转化和传输有关。

Based on the sounding data of Dunhuang field observation in the summer of 2006, the structure of the atmospheric boundary layer on the sunny and cloudy days in the desert area of Northwest China had been studied. In addition, the corresponding land surface processes were investigated as well. Conclusions were drawn as fol- lows： The convective boundary layer and the stable boundary layer on the sunny and cloudy days of northwest desert are more developed than those in central and eastern of China. In contrast, the boundary layer of sunny days is very different from that of the cloudy days in the structure and land surface processes, the height of con- vective boundary layer is up to 3. 5 km in sunny days, while the height of the stable boundary layer is about 1 km, The maximum daily height of cloudy days for the convective and stable boundary layer is about 2. 5 km and 0. 2 km respectively. In addition to the boundary layer height, the specific humidity of northwest desert on cloudy day and sunny day shares the different characteristics. Sunny specific humidity with height range is greater than the cloudy day, the cloudy day starts from the ground surface up to 200 m, appearing the weaker counter humidity Phenomenon, but sunny days do not appear the phenomenon. The difference between the boundary lay- ers are mainly caused by the thermal and dynamic factors on sunny and cloudy days. First of all, in different background weather, the solar radiation and the heat flux conversion rate lead the heat convection to be different, the solar radiation and sensible heat flux of the sunny days are stronger and greater than that of cloudy days ; Sec- ondly, the speed of the near ground level wind in sunny days is higher than that of cloudy days, This dynamic action in turbulent form also provides a certain dynamic background for the development of boundary layer height in sunny days, which is greater than that of cloudy days. The convective boundary layer is greatly affected by land surface thermodynamic factors in the early stage of the development, without the limitation of the stable boundary layer, it will develop rapidly. In addition, the temporal development in the diurnal variation of the net radiation, surface temperature and sensible heat flux exist a hysteresis quality, it is related to the transformation and transmission of energy.