空气热储存、光合作用和土壤垂直水分运动对黄土高原地表能量平衡的影响

地表能量不平衡问题一直是陆面过程研究的一个重要科学难题. 本文利用黄土高原陆面过程试验(LOPEX)资料, 在将垂直感热平流项引入地表能量平衡方程的基础上, 估算了空气热储存和光合作用储存的大小, 并分别用水分守恒关系和两层土壤温度方法计算了浅层土壤水分垂直通量, 考察了空气热储存、光合作用储存和水分垂直运动热量输送对地表能量平衡的影响.结果表明: 黄土高原区自然植被下垫面的空气热储存、光合作用储存和土壤水分垂直运动热量输送平均日变化峰值分别达到1.5, 2.0和7.9 W·m^-2; 在能量平衡方程中引入这三项后, 地表能量闭合度由88.1%提高到89.6%. 空气热储存、光合作用储存和水分垂直运动热量输送对于改善黄土高原地表能量不平衡状况有一定作用, 研究区域的半干旱气候背景和植被状况是导致各热储存量与其他试验区存在差异的根本原因.

The influences of air heat storage, plant photosynthesis and soil water movement on surface energy balance over the loess plateau

The surface energy imbalance problem has become a challenge in the study of surface land process since it was found in the late 1980s. By using data provided by the program "the Loess Plateau Land-surface Process Experiment (LOPEX)" and introducing the vertical sensible heat flux into the surface energy balance equation, in the paper, we estimate the heat storage associated with change of air temperature and humidity as well as the energy stored in plants due to the photosynthesis, determine the water vertical flux in the shadow soil layer both by water conservation principle and two-level soil temperature, and investigate the influences of air and plant photosynthesis energy storages and heat transferred by the soil water movement on the surface energy budget. It is found that the diurnal variation peaks of averaged energy storages of air and plant photosynthesis reach 1.5 and 2.0 W·m^-2 respectively. Additionally, the diurnal variation peak of mean heat transferred by vertical water movement is close to 8.0 W·m^-2. The closure of energy balance is improved from 88.1% to 89.6% by adding the three additional energy terms to the energy balance equation. As a whole, the energy storage related to air and the plant photosynthesis, and the heat transferred by the soil water movement both promote the surface energy balance to some extent. Furthermore, the semi-arid climate and the vegetation condition of Loess Plateau essentially lead to significant differences of energy storage be tween this area and other climatic districts.