青藏高原东南缘大理地区近地层微气象特征及能量交换分析

Analyses on Micrometeorology Characteristic and Energy Exchange in Surface Layer in Dali Region of the Southeastern Margin of Tibetan Plateau

利用2008年1月-2010年2月青藏高原东南缘大理站的长期观测资料,初步分析了该地区近地层基本气象要素、辐射通量和湍流通量的日变化和季节变化。结果表明,各参数均表现出显著的日循环结构和干、湿季变化特征。近地层的风速、气温和动量通量等均在早晨最小、午后最大;相对湿度、地表温度等均是湿季高于干季。近地层2m高度处的盛行风向,白天以东东南风和东风为主,夜间以静风和偏西风为主,并且盛行风向转变与日出、日落时间有较好的对应关系。地表辐射四分量最高值出现在正午,最低值出现在日出前。除向上短波辐射通量干季大于湿季外,其他辐射分量都是湿季大于干季。地表反照率表现出非对称的"U"形分布,早晨最大、傍晚次之及中午最小。早晚地表反照率差异可能是由于露水、东西两面山体不同程度遮挡以及云的影响造成的。感热、潜热通量全年有相似的日变化过程,变化幅度随季节变化,但潜热通量明显大于感热通量,表明地气热量交换中,感热作用小,潜热输送占主导地位。感热通量一天之中约在20:00出现最小值,这主要是由于风速减弱和地气温差回升影响热量交换系数造成的。地面对大气的加热作用明显,主要是以潜热方式加热大气;地面全年均为大气热源,白天表现为强热源,夜间则表现为较弱的冷源。

Based on the observational data in Dali region of the southeastern margin of the Tibetan Plateau from January 2008 to February 2010, the diurnal and seasonal variations of the basic meteorologi- cal elements, surface radiation and turbulent fluxes are analyzed. The results show that the diurnal cycles, the parameter variations in dry and wet season such as wind speed, air temperature, relative humidity and so on are evident. The wind speed, air temperature, momentum flux and so on in the surface layer reach the maximum in the afternoon and the minimum in the early morning. The relative humidity, soil tempera- ture in the wet season are higher than that in the dry season. The prevailing winds are east-southeast and east winds in the daytime, static and west winds at night at 2 m height in the surface layer, and the shift of prevailing wind has a good correspondence with time of sunrise and sunset. Surface radiation flux reaches the maximum at noon and the minimum before sunrise, apart from the upward short-wave radiation in the dry season is bigger than that in the wet season, other components are in the opposite situation. The diur- nal variation of surface albedo shows asymmetrical ＇U＇ type, and the values of surface albedo are the big- gest in the early morning, bigger in the evening, the smallest at noon. The surface albedo difference be- tween the morning and the afternoon may be due to influences of the dew, cloud and mountain blocking on the eastern and western sides. The sensible heat and latent heat fluxes have the similar daily variation processes in the whole year, the amplitude changes from season to season, but 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, while the sensible heat transfer is secondary. Sensible heat flux reaches the minimum around 20：00 in the evening, which mainly caused by wind speed weakens and Land-atmosphere temperature difference rises again to result in the change of heat exchange coefficient. The heating effect of the surface to atmosphere is evident and mainly through the heating way of latent heat. The land surface is atmospheric heat source in the whole year, with the strong heat source in the daytime and the weak cold source at night.