The seasonal variability in the surface energy exchange of an alpine grassland on the eastern Qinghai- Tibetan Plateau was investigated using eddy covariance measurements. Based on the change of air temperature and the seasonal distribution of precipitation, a winter season and wet season were identified, which were separated by transitional periods. The annual mean net radiation （Rn） was about 39 % of the annual mean solar radiation （Rs）. Rn was relatively low during the winter season （21% of Rs） compared with the wet season （54 % of Rs）, which can be explained by the difference in surface albedo and moisture condition between the two seasons. Annually, the main consumer of net radiation was latent heat flux （LE）. During the winter season, sensible heat flux （H） was dominant because of the frozen soil condition and lack of precipita- tion. During the wet season, LE expended 66 % of Rn due to relatively high temperature and sufficient rainfall cou- pled with vegetation growth. Leaf area index （LAI） had important influence on energy partitioning during wet season. The high LAI due to high soil water content （θv） contributed to high surface conductance （go） and LE, and thus low Bowen ratio （β）. LE was strongly controlled by Rn from June to August when gc and θv were high. During the transitional periods, H and LE were nearly equally parti- tioned in the energy balance. The results also suggested that the freeze-thaw condition of soil and the seasonal distribution of precipitation had important impacts on the energy exchange in this alpine grassland.
利用ERA40、NCEPI(NCEP/NCAR version I)再分析资料以及高原地区的探空资料和1979年青藏高原地区第1次气象科学试验资料,详细的比较了高原地区位势高度的特征。结果表明,两套再分析资料在高原地区具有一定的相似性,但仍存在着明显的差别。相比较而言,高原北部地区ERA40再分析资料除1980—1990年在200hPa高层优于NCEPI再分析资料外,NCEPI再分析资料在年际变化上更接近探空资料;高原中部和南部地区NCEPI再分析资料除1980—1990年在200 hPa高层优于ERA40再分析资料外,ERA40再分析资料在年际变化上更接近探空资料。与1979年青藏高原地区第1次气象科学试验资料空间相关关系的比较显示,ERA40再分析资料在空间上与试验资料更相似。
