黄土高原塬区地表辐射和热量平衡观测与分析

Observation and Analysis of the Land Surface Radiation and Energy Balance over the Loess Plateau Mesa Region

利用2005年夏季黄土高原塬区陆面过程野外试验（LOPEX05）的观测资料,初步分析了甘肃平凉黄土高原塬区地表辐射收支和热量平衡特征。结果显示,黄土高原塬区地面长波辐射大于大气长波辐射,典型晴天、阴天和雨天情况下两者平均差值分别为65,25和8 W.m^-2;对于地气能量交换各个分量而言,黄土高原塬上和塬下在相同下垫面下的差别不大,但裸地和有植被的下垫面差别很明显;在白天,潜热在净辐射中所占的比重较大,其次是感热,最后是土壤热通量。对能量平衡中的储存项如热通量板上层土壤的热存储和植被冠层存储进行了估算,结果表明,土壤的热储存项在-30~70W.m^-2之间,而植被的热能储存项在-10~25 W.m^-2之间。在考虑估算的存储项之后,能量平衡散布图斜率由0.68提高到0.79,相关系数R由0.90提高到0.93,两者分别提高了11.0%和3.0%,并对能量不平衡有明显的改进,说明能量储存项在地表能量闭合中必须考虑。

The characteristics of land surface radiation and energy flux over the Loess Plateau mesa region was analyzed based on the data collected during land surface process field experiment of the Loess Plateau mesa region,which was conducted from July to September 2005（LOPEX05）.During the experimental period,the surface average albedo over the Loess Plateau mesa region is ranged from 0.08 to 0.22 over the bare soil surface and the millet field.There are not evident differences of surface energy fluxes between the mesa and bottom of the mesa over the same bare soil surface,but obvious differences were founded between the bare soil surface and the millet field.Comparing with the bare soil surface in daytime,latent heat and sensible heat flux of the millet are all bigger than soil heat flux.In order to improve the land surface energy balance closure,the energy storage terms including soil heat storage above the soil heat flux plate（Sg）and canopy heat storage（Sc） were calculated and their proportions in total net radiation were obtained.When all of the storage terms were considered,the energy closure,which is denoted by slopes of the 1：1 line between net radiation and the partitioned fluxes（latent,sensible,ground,and storage）,increased 11.0% and the correlation coefficient decreased 3.0%,this means the storage terms make a large contributions in energy balance closure over the Loess Plateau mesa region.