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首页> 外文期刊>Atmospheric chemistry and physics >Measurements of spectral irradiance during the solar eclipse of 21?August?2017: reassessment of the effect of solar limb darkening and of changes in total ozone
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Measurements of spectral irradiance during the solar eclipse of 21?August?2017: reassessment of the effect of solar limb darkening and of changes in total ozone

机译：测量2017年8月21日日食期间的光谱辐照度：重新评估太阳肢体变暗的影响和总臭氧的变化

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Measurements of spectral irradiance between 306 and 1020?nm were performed with a GUVis-3511 multi-channel filter radiometer at Smith Rock State Park, Oregon, during the total solar eclipse of 21?August?2017. The radiometer was equipped with a shadowband, allowing the separation of the global (sun and sky) and direct components of solar radiation. Data were used to study the wavelength-dependent changes in solar irradiance at Earth's surface. Results were compared with theoretical predictions using three different parameterizations of the solar limb darkening (LD) effect, which describes the change in the solar spectrum from the Sun's center to its limb. Results indicate that the LD parameterization that has been most widely used during the last 15?years underestimates the LD effect, in particular at UV wavelengths. The two alternative parameterizations are based on two independent sets of observations from the McMath–Pierce solar telescope. When these parameterizations are used, the observed and theoretical LD effects agree to within 4?% for wavelengths larger than 400?nm and occultation of the solar disk of up to 97.8?%. Maximum deviations for wavelengths between 315 and 340?nm are 7?%. These somewhat larger differences compared to the visible range may be explained with varying aerosol conditions during the period of observations. The aerosol optical depth (AOD) and its wavelength dependence was calculated from measurements of direct irradiance. When corrected for the LD effect, the AOD decreases over the period of the eclipse: from 0.41 to 0.34 at 319?nm and from 0.05 to 0.04 at 1018?nm. These results show that AODs can be accurately calculated during an eclipse if the LD effect is corrected. The total ozone column (TOC) was derived from measurements of global irradiance at 306 and 340?nm. Without correction for the LD effect, the retrieved TOC increases by 20?DU between the first and second contact of the eclipse. With LD correction, the TOC remains constant to within natural variability ( ±2.6 DU or ±0.9 % between first and second contact and ±1.0 DU or ±0.3 % between third and fourth contact). In contrast to results of observations from earlier solar eclipses, no fluctuations in TOC were observed that could be unambiguously attributed to gravity waves, which can be triggered by the supersonic speed of the Moon's shadow across the atmosphere. Furthermore, systematic changes in the ratio of direct and global irradiance that could be attributed to the solar eclipse were not observed, in agreement with results of three-dimensional (3-D) radiative transfer (RT) models. Our results advance the understanding of the effects of solar LD on the spectral irradiance at Earth's surface, the variations in ozone during an eclipse, and the partitioning of solar radiation in direct and diffuse components.
机译：在2017年8月21日的日全食期间，使用GUVis-3511多通道滤光辐射计在俄勒冈州史密斯洛克州立公园进行了306至1020 nm的光谱辐照度测量。辐射计配备了一个阴影带，可以将太阳辐射的整体（太阳和天空）和直接分量分开。数据用于研究地球表面太阳辐照度的波长依赖性变化。使用三个不同的太阳肢体变暗（LD）效果参数化将结果与理论预测进行比较，该参数化描述了太阳光谱从太阳中心到其肢体的变化。结果表明，在过去15年中使用最广泛的LD参数设置低估了LD效果，尤其是在紫外线波长下。这两个替代参数化基于麦克马斯-皮尔斯太阳望远镜的两组独立观测值。当使用这些参数设置时，对于大于400？nm的波长和最高97.8？％的太阳圆盘掩星，观察到的和理论上的LD效应在4？％以内。波长介于315和340 nm之间的最大偏差为7％。与可见范围相比，这些较大的差异可以用观察期间变化的气溶胶条件来解释。气溶胶光学深度（AOD）及其波长依赖性是通过直接辐照度的测量计算得出的。如果校正了LD效应，则日食期间的AOD会降低：在319？nm处从0.41降至0.34，在1018？nm处从0.05降至0.04。这些结果表明，如果纠正了LD效应，则在日食期间可以准确计算AOD。总臭氧柱（TOC）来自在306和340？nm处的总辐照度的测量值。如果不对LD效应进行校正，则在日食的第一次和第二次接触之间检索到的TOC将增加20？DU。通过LD校正，TOC保持恒定在自然可变范围内（第一和第二触点之间为±2.6 DU或±0.9％，第三和第四触点之间为±1.0 DU或±0.3％）。与早期日食观测的结果相反，没有观察到TOC的波动可以明确地归因于重力波，而重力波可以由月球阴影穿过大气层的超音速触发。此外，与三维（3-D）辐射传输（RT）模型的结果一致，未观察到可归因于日食的直接和全球辐照比的系统变化。我们的研究结果进一步了解了太阳LD对地球表面光谱辐照度的影响，日食期间臭氧的变化以及太阳辐射在直接分量和扩散分量中的分配。

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