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Atmospheric stability effects on penman-monteith evapotranspiration estimates

机译：大气稳定度对Penman-Monteith蒸散量估算的影响

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摘要

This study explores surface-layer stability effects on the Penman-Monteith (P-M) method, one of the most widely used methods to estimate evapotranspiration (ET). Stability correction is applied to the original (neutral stability) formula by using atmospheric exchange coefficients developed by Louis et al. (1981). First, the effects of stability on the P-M formula are explored theoretically. ET is then computed from field data using both P-M formulas and the values are compared to measured ET from Bowen-ratio and lysimeter data. Theoretical investigation of the P-M formula is performed by varying stability conditions for a range of vapor pressure deficit and canopy conductance. Infinitely large canopy conductance (zero canopy resistance) gives potential ET with results similar to Mahrt and Ek (1984): the stability-dependent formula gives larger (smaller) potential ET than the original formula under unstable (stable) conditions. For finite canopy conductance, ET behaves differently from potential ET as a result of coupling between canopy and atmospheric conductances. Stability-dependent ET values become smaller than the original formula values under extreme unstable conditions (when atmospheric conductance becomes large compared to canopy conductance) because stability-dependent sensible heat flux is considerably larger than its neutral counterpart under same net input energy. Field data collected during both wet and dry growing seasons indicate that both P-M formulas track the Bowen-ET estimates and lysimeter measurements quite closely.
机译：这项研究探讨了对Penman-Monteith（P-M）方法的表面层稳定性的影响，Penman-Monteith方法是最常用的估算蒸散量（ET）的方法之一。通过使用Louis等人开发的大气交换系数，将稳定性校正应用于原始（中性稳定性）公式。 （1981）。首先，从理论上探讨了稳定性对P-M公式的影响。然后，使用P-M公式从现场数据中计算出ET，并将其值与Bowen比值和溶渗仪数据测得的ET进行比较。 P-M公式的理论研究是通过针对一定范围的蒸气压不足和冠层电导率改变稳定性条件来进行的。无限大的冠层电导（零冠层阻力）可提供潜在的ET，其结果类似于Mahrt和Ek（1984）：在不稳定（稳定）的条件下，与稳定性有关的公式提供的势能ET比原始公式更大（更小）。对于有限的冠层电导，由于冠层和大气电导之间的耦合，ET的行为不同于潜在的ET。在极端不稳定的条件下（当大气电导率比树冠电导大时），与稳定性有关的ET值变得小于原始公式值，这是因为在相同的净输入能量下，与稳定性有关的显热通量比其中性对应值大得多。在潮湿和干燥生长季节收集的现场数据表明，两个P-M公式都非常紧密地跟踪Bowen-ET的估算值和溶渗仪的测量值。

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