荒漠草原区显热通量变化特征及源区分布

对荒漠草原下垫面显热通量的时空特征分析对于提高区域水热交换规律认识和了解其在气候变化中的作用有重要意义。本研究基于内蒙古荒漠草原2021年5—12月的大孔径闪烁仪观测与相应的气象、环境观测资料，分析了荒漠草原区不同时间尺度显热通量变化特征及其源区分布。结果表明：大气不稳定条件下显热通量日变化曲线呈单峰型，相比于晴天，多云和阴天的日变化存在无规律波动；显热通量季节变化明显，5月以后不断减少；通量源区按照闪烁仪光径走向朝上风向延伸分布，越靠近光径对通量贡献能力越大；受稳定度、风速风向和下垫面植被特征共同影响，各时间尺度的通量源区特征不同，源区范围日变化与大气稳定度变化基本一致，研究期间11月源区面积最大，7月最小，相差约70 000 m²,整个生长季的通量贡献区小于非生长季；大气稳定度和风向是影响通量源区分布的重要因素。

Characterization of Variations of Sensible Heat Flux and Its Source Area Distribution over the Desert Steppe

The spatial-temporal characteristics of sensible heat flux over a desert steppe were key to improve the understanding of regional water-heat exchange and its role in climate change. In this study,the large-aperture scintillometer observation and corresponding meteorological and environmental data was collected over the desert steppe of Inner Mongolia from May to December in 2021,to explore the variations of sensible heat flux and its source area distribution at different temporal scales. The results showed that the diurnal variation curves of sensible heat flux under unstable atmospheric condition presented a unimodal trend,while irregular fluctuation was observed in cloudy and overcast days compared with sunny days. The seasonal variations of sensible heat flux over the desert steppe were found,and the sensible heat flux decreased continuously after May. Based on the scintillometer optical path,the source area of flux measurement extended and distributed in the upward wind direction,and closer it was to the optical path,more contributions to flux measurement. Affected by the stability,wind speed,wind direction,and vegetation characteristics of the underlying surface,the characteristics of flux footprint at different temporal scales showed different variances. The diurnal variation of source area of flux measurement was basically consistent with the variation trend of atmospheric stability. During the study period,the source area range was the largest in November and the smallest in July,with a difference of about 70 000 m². The flux contribution area in the whole growing season was smaller than that in the non-growing season. Atmospheric stability and wind direction were key factors affecting the source distribution of flux measurement.