A critical revision of the estimation of the latent heat flux from two‐wavelength scintillometry
A critical revision of the estimation of the latent heat flux from two‐wavelength scintillometry
复制标题
双波长闪烁测量潜热通量估计的重要修订
DOI：
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
C. Grimmond
中科院分区：
文献类型：
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作者：
H. C. Ward;Jonathan G. Evans;O. Hartogensis;A. Moene;H. D. Bruin;C. Grimmond
多波长的同时闪烁计测量(可见或红外与毫米波或无线电波配对)有可能提供对路径平均地表感热和潜热通量的估计。传统上，从两个波长的折射率结构参数的测量中推导出通量的方程是根据绝对湿度来表示的。在这里，它表明，在比湿度方面的配方有几个优点。比湿度满足相似理论中守恒变量的要求，并从本质上解释了使用绝对湿度错误分配密度效应的原因。评估了这两种公式的有效性和解释力，并讨论了与开路红外气体分析仪密度校正的类比。用绝对湿度表示水汽影响的原始导数被证明是错误地表示潜热通量。通量中的误差取决于鲍文比(对于较干燥的条件较大)，可能在10%量级。感热通量保持不变。还证实了在光学波长上使用单个闪烁计基本上不受这些新配方的影响。在可能无法重新处理双波长结果的情况下，建议对闪烁法的潜热通量进行密度校正，这可以回溯应用以减小误差。
Simultaneous scintillometer measurements at multiple wavelengths (pairing visible or infrared with millimetre or radio waves) have the potential to provide estimates of path‐averaged surface fluxes of sensible and latent heat. Traditionally, the equations to deduce fluxes from measurements of the refractive index structure parameter at the two wavelengths have been formulated in terms of absolute humidity. Here, it is shown that formulation in terms of specific humidity has several advantages. Specific humidity satisfies the requirement for a conserved variable in similarity theory and inherently accounts for density effects misapportioned through the use of absolute humidity. The validity and interpretation of both formulations are assessed and the analogy with open‐path infrared gas analyser density corrections is discussed. Original derivations using absolute humidity to represent the influence of water vapour are shown to misrepresent the latent heat flux. The errors in the flux, which depend on the Bowen ratio (larger for drier conditions), may be of the order of 10%. The sensible heat flux is shown to remain unchanged. It is also verified that use of a single scintillometer at optical wavelengths is essentially unaffected by these new formulations. Where it may not be possible to reprocess two‐wavelength results, a density correction to the latent heat flux is proposed for scintillometry, which can be applied retrospectively to reduce the error.