黄土高原半干旱区地表能量不闭合及其对二氧化碳通量的影响

利用兰州大学半干旱气候与环境观测站(Semi-Arid Climate and Environment Observatory of Lanzhou University, SACOL) 2008年资料分析了SACOL代表的黄土高原半干旱区稀疏草地下垫面上的能量平衡闭合情况. 不同季节, 白天总体能量平衡比率在0.80左右. 夜间只有0.20左右. 选取不存在局地环流的资料, 考虑土壤热存储和垂直感热平流后, 白天能量平衡比率在85%以上, 春夏秋三季夜间也达到70%, 但冬季夜间能量闭合度仅为29.4%. 白天, 涡动相关系统对湍流热量通量观测的偏差存在季节差异, 冬季低估最多, 秋季次之, 春夏季观测相对较理想; 夜间, 涡动相关系统对湍流热通量严重低估. 湍流热量通量的低估通过空气密度效应修正传递对CO₂通量产生影响, 造成长期净碳交换的不确定性. WPL修正引入的湍流热量误差导致涡动相关系统错误地高估下垫面吸收存储CO₂能力, 全年NEE估计偏高41.2%. 关键词： 黄土高原 涡动相关 能量闭合 密度效应修正

Energy balance analysis over Loess Plateau and the consequences for carbon dioxide flux

This paper examines the surface energy imbalance status over the semi-arid areas of the Loess Plateau, using the data collected by eddy covariance (EC) and boundary layer meteorological measurement systems at the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL). The energy balance ratio is about 0.80 during the daytime in all seasons, while that is only about 0.20 in the night. For the observation time with no local circulation, the energy balance ratio is improved to more than 85% in the daytime. Even in the night of spring, summer or autumn, the energy balance ratio is also improved to 70%. However, the ratio in nighttime of winter is only 29.4%. After taking into consideration all the energy budget items, the surface energy is still not closed, which means that the eddy covariance system underestimated the turbulent heat flux. And the observation error changes with seasons, with maximum in winter and minimum in spring. The errors of sensible heat flux and latent heat flux may impact CO₂ flux through the WPL correction, and cause the uncertainty of long term net ecosystem exchange (NEE), and the NEE throughout the year can be overestimated by 41.2%.
Keywords： Loess Plateau eddy covariance energy balance correction for density effects