基于通量方差法对青藏高原东侧高寒草甸地表通量的估算

摘要

Based on the observed data in 2008 at Litang site over the alpine meadow surface on the east edge of Ti-betan Plateau,the temporal variations of surface fluxes measured by an eddy-covariance system were analyzed,and the flux-variance relationships of normalized standard deviations of temperature,water vapor and CO2 concentration as a function of stability parameter were determined.Sensible heat,latent heat and CO2 fluxes were computed by u-sing a flux-variance method,and they were compared with results from eddy-covariance measurements.The results indicate that there is a regular daily variation for surface fluxes,and seasonal variations are also significant.Latent heat flux is greater than sensible heat flux in a rainy season (May to September),whereas sensible heat flux is dominant in a dry season,and CO2 flux is overwhelming during June to September.Under unstable conditions,the normalized variances of the scalars and stability parameter satisfy the similarity,and their universal functions also can be fitted according to the law of“-1/3 fractional power”.Similarity constants of heat,water vapor and CO2 are 1.2,1.4,and 0.9,respectively.Flux estimations are found to be in good agreement with observation.Among three parameters,estimation of sensible heat flux is better than that of other two fluxes.In general,this method o-verestimates the sensible heat flux and latent heat flux,while it underestimates CO2 flux.Prediction accuracy of la-tent heat and CO2 fluxes can be improved if predictions are obtained using the flux-variance method in combination with the measured sensible heat flux.%利用位于青藏高原东侧理塘大气综合观测站2008年观测资料，分析了高寒草甸下垫面地表通量的时间变化特征，确定了温度、水汽和CO2的归一化标准差在不稳定情况下随稳定度变化的通量方差关系，采用通量方差法对感热、潜热和CO2通量进行计算，并与涡旋相关系统的观测结果进行比较。结果表明：地表通量月平均日变化呈较规则的日循环特征，季节变化特征也较明显，雨季（5—9月）潜热大于感热，干季则以感热为主，CO2通量以6—9月最大。在不稳定条件下，温度、水汽和CO2的归一化标准差随稳定度的变化均满足－1／3规律，其通量方差相似性常数分别为1.2、1.4和0.9。通量方差法估算的通量值与涡旋相关观测的通量值有较好的一致性，但估算感热通量的效果优于潜热通量和CO2通量。该方法高估了感热通量尤其是潜热通量，而低估了CO2通量。利用直接观测的感热通量计算潜热通量和CO2通量可改善计算结果。