We apply well-established flux–gradient relationships to deduce the aerodynamic and radiative properties of a winter wheat crop, using a neglected 1971 dataset (hourly averages), only recently resurrected as part of a historical review of precision CO 2 measurements in Australia (Pearman et al. in Hist Rec Aust Sci 28:111–125, 2017). The aerodynamic roughness length (seasonal variation between 0.07 and 0.14 of the mean crop height) and broadband albedo (seasonal variation between 0.13 and 0.23) are consistent with values published in the literature over the past 50 years. Net radiation at night is found to agree with the net longwave flux only when the dry-bulb temperature exceeds 10 °C, probably the result of dewfall on one or both of the two instruments. During the day, the sum of the four individual radiative flux components (upwards and downwards shortwave and longwave)—the composite net radiation—exceeds the directly measured net radiation, from near zero at sunrise to approximately 100 W m −2 at maximum net radiation ≈ 600 W m −2 , viz. an underestimate in the directly measured net radiation of close to 15%. Again, this is in line with instrument comparisons made in the USA and Europe 15–25 years ago. A novel approach is used in the analysis of terms in the surface energy budget, viz., normalization of all terms by the downwelling shortwave flux. Normalization reveals, (1) near-normal frequency distributions of both the total turbulent heat flux (sensible plus latent) and the implied total storage (the residual); (2) significant diurnal variations in the total turbulent heat flux, whose standard deviations of individual values about any hourly mean during daytime are reduced significantly on those for either the sensible or latent heat flux; (3) an implied storage term with a well-defined diurnal variation, but with an overall mean value of 1% of the shortwave input. Overall, with the above results in mind, the computed momentum and heat fluxes (and also the CO 2 flux) during the daytime, at small to moderate gradient Richardson numbers, provide support for the profile approach when eddy-correlation fluxes are unavailable. Even so, possible errors due to, (1) uncertainties in the zero-plane displacement, and (2) influences of the roughness sublayer, must be borne in mind.

中文翻译：

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澳大利亚小麦作物上微气象观测的回顾性分析

我们应用完善的通量-梯度关系来推断冬小麦作物的空气动力学和辐射特性，使用一个被忽视的 1971 年数据集（每小时平均值），最近才作为澳大利亚精确 CO 2 测量历史回顾的一部分（Pearman等人在 Hist Rec Aust Sci 28:111–125, 2017 中）。空气动力学粗糙度长度（平均作物高度的季节性变化在 0.07 和 0.14 之间）和宽带反照率（季节性变化在 0.13 和 0.23 之间）与过去 50 年文献中发表的值一致。只有当干球温度超过 10 °C 时，才发现夜间的净辐射与净长波通量一致，这可能是两个仪器之一或两个仪器出现露水的结果。白天，四个单独的辐射通量分量（向上和向下的短波和长波）的总和 - 复合净辐射 - 超过了直接测量的净辐射，从日出时接近零到最大净辐射时约为 100 W m -2 ≈ 600 W m −2 ，即。直接测量的净辐射被低估了接近 15%。同样，这与 15-25 年前在美国和欧洲进行的仪器比较一致。一种新颖的方法用于分析表面能量收支中的项，即通过下涌短波通量对所有项进行归一化。归一化揭示，(1) 总湍流热通量（显热加潜热）和隐含总储存量（残差）的接近正态频率分布；(2) 总湍流热通量的显着昼夜变化，与显热通量或潜热通量相比，白天任何小时平均值的单个值的标准差显着降低；(3) 具有明确定义的昼夜变化的隐含存储项，但总体平均值为短波输入的 1%。总体而言，考虑到上述结果，白天计算的动量和热通量（以及 CO 2 通量），在小到中等梯度理查森数下，在涡相关通量不可用时为剖面方法提供支持。即便如此，由于（1）零平面位移的不确定性和（2）粗糙度子层的影响，必须牢记可能的错误。(3) 具有明确定义的昼夜变化的隐含存储项，但总体平均值为短波输入的 1%。总体而言，考虑到上述结果，白天计算的动量和热通量（以及 CO 2 通量），在小到中等梯度理查森数下，在涡相关通量不可用时为剖面方法提供支持。即便如此，由于（1）零平面位移的不确定性和（2）粗糙度子层的影响，必须牢记可能的错误。(3) 具有明确定义的昼夜变化的隐含存储项，但总体平均值为短波输入的 1%。总体而言，考虑到上述结果，白天计算的动量和热通量（以及 CO 2 通量），在小到中等梯度理查森数下，在涡相关通量不可用时为剖面方法提供支持。即便如此，由于（1）零平面位移的不确定性和（2）粗糙度子层的影响，必须牢记可能的错误。当涡相关通量不可用时，为轮廓方法提供支持。即便如此，由于（1）零平面位移的不确定性和（2）粗糙度子层的影响，必须牢记可能的错误。当涡相关通量不可用时，为轮廓方法提供支持。即便如此，由于（1）零平面位移的不确定性和（2）粗糙度子层的影响，必须牢记可能的错误。