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首页> 外文期刊>Journal of hydrometeorology >The Diurnal Behavior of Evaporative Fraction in the Soil–Vegetation–Atmospheric Boundary Layer Continuum
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The Diurnal Behavior of Evaporative Fraction in the Soil–Vegetation–Atmospheric Boundary Layer Continuum

机译：土壤-植被-大气边界层连续体中蒸发分数的日变化

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摘要

The components of the land surface energy balance respond to periodic incoming radiation forcing with different amplitude and phase characteristics. Evaporative fraction (EF), the ratio of latent heat to available energy at the land surface, supposedly isolates surface control (soil moisture and vegetation) from radiation and turbulent factors. EF is thus supposed to be a diagnostic of the surface energy balance that is constant or self-preserved during daytime. If this holds, EF can be an effective way to estimate surface characteristics from temperature and energy flux measurements. Evidence for EF diurnal self-preservation is based on limited-duration field measurements. The daytime EF self-preservation using both long-term measurements and a model of the soil–vegetation–atmosphere continuum is reexamined here. It is demonstrated that EF is rarely constant and that its temporal power spectrum is wide; thus emphasizing the role of all diurnal frequencies associated with reduced predictability in its daylight response. Oppositely, surface turbulent heat fluxes are characterized by a strong response to the principal daily frequencies (daily and semi-daily) of the solar radiative forcing. It is shown that the phase lag and bias between the turbulent flux components of the surface energy balance are key to the shape of the daytime EF. Therefore, an understanding of the physical factors that affect the phase lag and bias in the response of the components of the surface energy balance to periodic radiative forcing is needed.Alinearized model of the soil–vegetation–atmosphere continuum is used that can be solved in terms of harmonics to explore the physical factors that determine the phase characteristics. The dependency of these phase and offsets on environmental parameters—friction velocity, water availability, solar radiation intensity, relative humidity, and boundary layer entrainment—is then analyzed using the model that solves the dynamics of subsurface and atmospheric boundary layer temperatures and heat fluxes in a continuum. Additionally, the asymptotical diurnal lower limit of EF is derived as a function of these surface parameters and shown to be an important indicator of the self-preservation value when the conditions (also identified) for such behavior are present.
机译：陆地表面能量平衡的组成部分以不同的幅度和相位特性响应周期性的入射辐射强迫。蒸发分数（EF），即陆地表面潜热与可用能量的比率，据认为使表面控制（土壤水分和植被）与辐射和湍流因素隔离开来。因此，EF被认为是对白天表面能量恒定或自我保存的表面能量平衡的诊断​​。如果这样，EF可能是从温度和能量通量测量值估算表面特性的有效方法。 EF昼夜自我保存的证据基于有限持续时间的现场测量。在此重新检查了使用长期测量和土壤-植被-大气连续体模型的白天EF自我保存。事实证明，EF很少是恒定的，并且其时间功率谱很宽。因此强调了所有昼夜频率在日光响应中与可预测性降低相关的作用。相反，表面湍流通量的特征是对太阳辐射强迫的主要日频率（每天和每天半）有强烈的响应。结果表明，表面能平衡的湍流分量之间的相位滞后和偏差是白天EF形状的关键。因此，需要了解影响表面能平衡各组成部分对周期性辐射强迫响应的相位滞后和偏差的物理因素。采用土壤-植被-大气连续体的线性模型可以解决用谐波术语来探索确定相位特性的物理因素。这些相位和偏移量对环境参数（摩擦速度，水的可利用性，太阳辐射强度，相对湿度和边界层夹带）的依赖性，然后使用求解地下和大气边界层温度和热通量动态的模型进行分析。一个连续体。此外，EF的无症状昼夜下限是这些表面参数的函数，当存在此类行为的条件（也已确定）时，表明它是自我保存值的重要指标。

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