热储通量对黄土高原北部柠条林地地表能量平衡的影响

地表能量平衡问题一直是陆面过程研究中的重点和难点问题。以2014年8—10月和2015年4—6月黄土高原北部水蚀风蚀交错带柠条林地涡度相关通量观测数据为依据,分析柠条林地热储通量变化特征,在此基础上分析热储通量对能量闭合度的影响。结果表明,柠条林地各热储通量均表现出明显的季节和日变化规律。在能量平衡方程中,考虑热储通量项后能显著提高柠条林地能量闭合度,平均提高幅度为11.91%。其中,土壤表层热储通量对能量闭合度的贡献最大,占总热储通量的95.63%;光合作用热储通量和大气感热存储通量占总热储通量的比例不足5%,光合热储通量略高于大气感热存储通量;而大气潜热存储通量则降低了能量闭合度,平均降低幅度为0.06%。因此,在分析黄土高原柠条林地能量平衡中热储通量项是不可忽略的。影响柠条林地各热储通量的因素主要有太阳辐射、大气温度、土壤温度和水分。植被生长状况是影响柠条林地热储通量各分量项季节和日变化的重要因素,并对能量闭合度产生影响。

Effects of heat storage on surface energy balance in Caragana forest land of northern the Loess Plateau

Surface-energy balance has become a major and difficult problem in the study of surface land processes. The arbitrary neglect of terms for heat-storage flux is one of the main causes preventing closure of the energy balance during measurements or calculations. We analyzed the characteristics of the mean seasonal and daily variations of heat storage, and the influence of heat-storage flux on energy-balance closure, using eddy-covariance data for a Caragana stand in the wind-water erosion crisscross region of the northern the Loess Plateau collected from August to October 2014 and April to June 2015. All terms for heat-storage flux of the Caragana stand varied considerably both seasonally and diurnally. The energy-balance closure increased at an average of 11.91% when the terms for heat-storage fluxes were included. The soil heat flux was the largest contributor to the energy closure, accounting for 95.63% of the total heat-storage fluxes. The sum of the photosynthetic and atmospheric heat-storage fluxes accounted for less than 5% of the total fluxes, and photosynthesis contributed more than the atmosphere to perceptible heat storage. The latent heat-storage flux, however, decreased the energy-balance closure by 0.06%, indicating that the heat-storage flux should not be neglected when analyzing energy balances for the Caragana stands of the northern the Loess Plateau. The heat-storage fluxes in the Caragana stand were influenced by solar radiation, air temperature, and soil temperature and soil moisture. The growing condition of the vegetation was another important factor that influenced the seasonal and diurnal variation of the terms for heat-storage flux, and which also affected energy closure.