基于变分方法的内蒙古典型草原水热通量估算

Estimation of sensible and latent heat fluxes of typical steppe in Inner Mongolia based on variational method.

利用内蒙古典型草原生长季（2004年8月13—18日、2005年5月21～26日）和非生长季（2004年12月10～15日）共18d的涡动相关系统观测资料（10Hz输出1次）和小气候梯度系统在线输出资料（0．5h输出1次），分析了变分方法对草原陆气通量估算的准确性．结果表明，变分法估算的感热与潜热通量与涡动相关法观测结果的变化趋势较为一致，且能量闭合程度更高．变分法计算的感热通量在白天明显地较涡动相关法得到的通量值高，12：00前后两者通量都达到峰值，两者之差也达到峰值，而夜间则较为接近；变分法计算的潜热通量曲线的相位略微落后于涡动相关法的通量曲线，且夜间的涡动相关法测得的潜热通量负值极少，负值通量的绝对值也很小．这表明夜间大气稳定导致涡动相关法存在一定程度的通量低估现象．变分法与波文比能量平衡法对陆气通量的估算比较表明，变分法可避免能量平衡法计算不稳定导致的虚假峰值现象，计算结果较为稳定．

Based on the observation data and the export data of microclimatic gradient system during growing and non-growing seasons of Stipa krylovii grassland in Inner Mongolia, this paper investigated the accuracy of variational method （VT） on estimating the surface heat fluxes of grassland. The results showed that the changes of sensible and latent heat fluxes estimated by VT were consistent with those obtained by open-path eddy covariance method （EC） , and the fluxes estimated by VT could better satisfy the surface energy balance equation. The sensible heat fluxes （H） from VT were mostly higher than the corrected fluxes from EC, and the values and their difference from these two methods all got the maximum at twelve o＇clock in daytime, and were close in nighttime. The variations of latent heat fluxes from VT lagged behind those from EC. VT could solve the problems that the conventional Bowen ratio energy balance method （BREB） was computationally unstable and produced spurious large values when the Bowen ratio was in vicinity of - 1. Compared with EC and BREB, VT was more of rationality and stability.