青藏高原表层土壤热通量的时空分布特征

Temporal and Spatial Characteristics of Ground Surface Soil Heat Flux over the Qinghai-Tibetan Plateau

利用青藏高原(简称高原)9个站点的实测数据分析了表层土壤热通量G0的季节变化、日变化特征,然后利用MODIS数据(MOD13Q1和MOD09CMG)、中国西部逐日1 km空间分辨率全天候地表温度数据集和同化数据(ITPCAS-SRad和ITPCAS-LRad),借助G0遥感估算模型Ma模拟了高原四期(2014年7月12日和10月16日,2015年1月1日和4月7日)的G0空间分布特征。结果表明:G0振幅随季节变化,夏季较大,冬季最小,站点之间振幅不同可能与下垫面有关,下垫面植被覆盖度越高,振幅越小;G0在春、夏季以及全年整体为正,而秋、冬季G0则为负。高原G0呈现倒立的"U"型的日变化曲线,夜晚的变化相对白天而言比较平缓;G0日变化曲线为正值的时长存在明显季节差异,四个季节的顺序是夏季>春季>秋季>冬季;高原G0的空间分布特征与高原地表温度的空间分布有较好的正相关,站点数据显示地表温度每增加1℃,G0随之增大2~5 W·m^-2。

We have collected the measured data of 9 observation stations on the Qinghai-Tibetan Plateau.The measured data of these sites on the Qinghai-Tibetan Plateau were used to analyze the seasonal and daily variation characteristics of ground surface soil heat flux,and we discussed the reasons for the differences in the temporal characteristics of ground surface soil heat flux between stations.Then MODIS data(including the Terra Moderate Resolution Imaging Spectroradiometer vegetation indices version 6 data MOD13 Q1 and the surface spectral reflectance of Terra Moderate Resolution Imaging Spectroradiometer bands 1 through 7 product MOD09 CMG),daily land surface temperature dataset in Western China under all-sky condition with 1 km spatial resolution,and assimilation data(ITPCAS-SRad and ITPCAS-LRad)were applied to simulate the spatial distribution of ground surface soil heat flux over the Qinghai-Tibetan Plateau by the scheme Ma on 12 July and 16 October 2014,1 January and 7 April 2015.The results shown that:The amplitude of ground surface soil heat flux varies with the season,the summer is larger,the winter is the smallest,and the amplitude between the stations is different from the underlying surface.The higher the coverage of the underlying surface,the smaller the amplitude;ground surface soil heat flux is positive in spring and summer and throughout the year,while ground surface soil heat flux in autumn and winter is negative.Ground surface soil heat flux is greater than 0,which means that the underground soil absorbs heat from the surface,otherwise,the underground soil releases heat.Ground surface soil heat flux on the the Qinghai-Tibetan Plateau shows an obvious daily variation curve of inverted U-shape,and its change of the night is relatively flat compared with the daytime.There is a significant seasonal difference in the duration of the daily variation curve of ground surface soil heat flux.The order of the four seasons is:summer>spring>autumn>winter.There is a good positive correlation between the spatial distribution characteristics of ground surface soil heat flux and that of land surface temperature on the the Qinghai-Tibetan Plateau.Station data shows that for every 1°C increase in land surface temperature,ground surface soil heat flux will increase by 2~5 W·m^-2.This study further deepens the understanding of ground surface soil heat flux over the Qinghai-Tibetan Plateau,in order to provide basis and help for the prediction of frozen soil evolution,accurate estimation of evapotranspiration and geogas interaction.