黄土高原半干旱草地地表能量通量及闭合率

Surface heat flux and energy budget for semi-arid grassland on the Loess Plateau

利用兰州大学半干旱气候与环境观测站(简称SACOL站)2008年的湍流、辐射、土壤温度和通量梯度观测资料,分析了地表能量通量的日变化、季节变化及能量分配特征,讨论了典型黄土高原沟壑区土壤热量储存对地表能量闭合率的影响。结果表明:黄土高原半干旱草地全年获得的净辐射约为2.269×103 MJ/m2,感热、潜热和土壤热通量年总量分别为1.210×103 MJ/m2、1.117×103 MJ/m2和0.069×103 MJ/m2;能量平衡各分量季节变化明显,日变化呈单峰型。从各能量分量占净辐射的比例来看,黄土高原半干旱草地净辐射主要以感热形式加热大气。草原生长期的能量闭合率为86.8%,非生长期的能量闭合率为76.5%。与未考虑0—5cm深度的土壤热量储存相比,草原生长期能量闭合率提高了11.3%,非生长期能量闭合率提高了12.0%。

The atmospheric boundary layer is a passage between the atmosphere and the Earth,through which atmospheric momentum,energy and various substances are transported upwards and downwards.Turbulent transport in the lower atmospheric planetary boundary layer is an important link for substance and energy exchanges between the atmosphere and the Earth.The Loess Plateau ranges from the Qinling Mountains to the Yin Mountains in a south-north direction,and from the Riyue Mountains to the Taihang Mountains in a west-east direction.The plateau stretches across seven provinces or autonomous regions and has a total area of more than 6.268 × 105 km2 and unique land type and ecological environment.It lies on the edge of the southeast monsoon area;i.e.,a transition zone from the humid monsoon climate in southeast China to the inland arid climate in northwest China.The average annual precipitation is generally around 400 mm.The ecological environment and agricultural production on the Loess Plateau are sensitive to precipitation change,and therefore,the Loess Plateau is a typical area sensitive to climate change and has vulnerable ecology and agriculture.However,there have been few studies on the surface energy balance for the typical highland terrain of the Loess Plateau,where the underlying surface is distinctively heterogeneous but less affected by human activity. The diurnal and seasonal variations in energy balance components and energy balance characteristics for semi-arid grassland on the Loess Plateau were studied on the basis of radiation,turbulence flux,soil temperature and soil heat flux data recorded at the Semi-Arid Climate and Environment Observatory of Lanzhou University in 2008.The results show that diurnal variations in energy balance components had the expected single peaks.The yearly net radiation over the grassland was 2.269 × 103 MJ/m2.The yearly sensible heat flux,latent heat flux and soil heat flux were 1.210 × 103,1.117 × 103 and 0.069 × 103 MJ/m2,respectively.The energy balance components had obvious seasonal variations.According to the ratios of energy balance components to net radiation,the sensible heat flux was the main component of net radiation,and the function of surface soil heat flux was the second factor of the energy balance.The energy balance closure averaged 86.8% during the growing season but only 75.5% during the non-growing season.The closure of the surface energy balance for the semi-arid grassland increased 11.3% during the growing season and 12.0% during the non-growing season after considering heat storage from the surface to a soil depth of 5 cm.