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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >UNCERTAINTIES IN MODELED AND MEASURED CLEAR-SKY SURFACE SHORTWAVE IRRADIANCES
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UNCERTAINTIES IN MODELED AND MEASURED CLEAR-SKY SURFACE SHORTWAVE IRRADIANCES

机译：建模和测量的清晰天空短波辐射度的不确定性

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A comparison of five independent measurements of the clear-sky downward shortwave irradiance at the surface shows that they scatter within a 5% range depending on their calibration constants. When the measurements are corrected using data from two cavity radiometers, three of the five independent measurements agree within 3 W m(-2) over three clear-sky days, which is well within the estimated error limit of +/-1.5%. A comparison of these three sets of irradiance measurements with the computed irradiance by a delta 2-stream model reveals that the model overestimates the irradiance by 5%. Detailed investigation of the approximations and uncertainties associated with the computations (including the measurement error in the water vapor and ozone amounts, neglecting the state of polarization and trace gas absorption, the 2-stream approximation, the neglect of the spectral dependence of the surface albedo, and the uncertainties associated with aerosols) demonstrates that the discrepancy is not due to these approximations. Further analysis of the modeled and measured irradiance shows that the discrepancy is almost entirely due to the difference between modeled and measured diffuse field irradiances. An analysis of narrow-band diffuse to total irradiance ratios shows that this discrepancy is the largest near 400 nm and decreases with wavelength. These results rely on the absolute calibrations of two cavity radiometers, two shaded pyranometers, and one unshaded pyranometer, as well as ratios of irradiances measured by a multifilter rotating shadow-band radiometer. Therefore, in order for instrumental error to account for the diffuse field discrepancy, three independent measurements of the diffuse held irradiance must be biased low by at least 40%. For an aerosol to account for this discrepancy, it must be highly absorbing with a single-scattering albedo as low as 0.3. The unlikelihood of instrumental errors of 40% and aerosol single-scattering albedos of 0.3 suggests a third possibility: the neglect of some gaseous absorption process at visible wavelengths. [References: 44]
机译：对表面处的晴空向下短波辐照度的五个独立测量值的比较显示，取决于其校准常数，它们在5％的范围内散射。当使用来自两个腔辐射计的数据对测量进行校正时，五个独立测量中的三个在三天的晴天在3 W m（-2）内一致，这完全在+/- 1.5％的估计误差范围内。将这三组辐照度测量值与通过德尔塔2流模型计算出的辐照度进行比较后发现，该模型将辐照度高估了5％。详细研究与计算相关的近似和不确定性（包括水蒸气和臭氧量中的测量误差，忽略极化和痕量气体吸收的状态，2流近似，忽略表面反照率的光谱依赖性） ，以及与气溶胶相关的不确定性）表明差异并不是由于这些近似值造成的。对建模和测量的辐照度的进一步分析表明，差异几乎完全是由于建模和测量的散射场辐照度之间的差异引起的。窄带漫射与总辐照比的分析表明，这种差异在400 nm附近最大，并随波长减小。这些结果依赖于两个空腔辐射计，两个带阴影的日射强度计和一个带阴影的日射强度计的绝对校准，以及由多滤光片旋转阴影带辐射计测得的辐照率。因此，为了使仪器误差解决散射场差异，必须将散射保持辐照度的三个独立测量值偏低至少40％。为了解决这种差异，气溶胶必须具有低至0.3的单散射反照率才能具有很高的吸收能力。仪器误差为40％的可能性和气溶胶单散射反照率的可能性为0.3，这表明了第三种可能性：忽略了一些在可见波长处的气体吸收过程。 [参考：44]

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