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https://doi.org/10.5194/amt-2017-475
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
12 Feb 2018
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).
Reduction in Earth Reflected Radiance during the Eclipse of 21 August 2017
Jay Herman1, Guoyong Wen2, Alexander Marshak3, Karin Blank3, Liang Huang4, Alexander Cede5, Nader Abuhassan1, and Matthew Kowalewski6 1University of Maryland Baltimore County JCET
2Morgan State University, Baltimore Maryland
3NASA Goddard Space Flight Center, Greenbelt, Maryland
4Science Systems and Applications, Lanham, Maryland
5Goddard Earth Sciences Technology & Research (GESTAR) Columbia, Columbia, MD 21046, USA
6SciGlob Instruments and Services, Elkridge, Maryland, USA
Abstract. Ten wavelength channels of calibrated radiance image data from the Sunlit Earth are obtained every 65 minutes during Northern Hemisphere summer from the DSCOVR/EPIC instrument located near the Earth-Sun Lagrange-1 point (L1), 1.5 million km from the Earth. The L1 location permitted seven observations of the Moon’s shadow on the Earth for about 3 hours during the 21 August 2017 eclipse. Two of the observations were timed to be over Casper, Wyoming and Columbia, Missouri. Since, the solar irradiances within 5 channels (λi = 388, 443, 551, 680, and 780 nm) are not strongly absorbed in the atmosphere, they can be used for characterizing eclipse reduction in reflected radiances for the sunlit face of the Earth containing the eclipse shadow. Five channels (λi = 317.5, 325, 340, 688, and 764 nm) that are partially absorbed in the atmosphere give consistent reductions compared to the non-absorbed channels. This indicates that cloud reflectivities dominate the 317.5 to 780 nm radiances reflected back to space from the sunlit Earth’s disk with a strong contribution from Rayleigh scattering for the shorter wavelengths. A reduction of 9.7 ± 1.7 % in the radiance (387 to 781 nm) reflected from the Earth towards L1 was obtained for the set of observations on 21 August 2017, while the shadow was in the vicinity of Casper, Wyoming (42.8666° N, 106.3131° W, centered on 17:44:50 UTC). In contrast, when successive non-eclipse days are compared for each wavelength channel, the change in reflected light is much smaller (less than 1 % for 443 nm compared to 9 % during the eclipse). Also measured was the spatially averaged ratio < RENi) > of reflected radiance within the eclipse totality region to radiances for the same geometry on adjacent non-eclipse days for all 10 wavelength channels. The measured < REN(443 nm) > was smaller for Columbia (35) than for Casper (122), because Columbia had more cloud cover than Casper. RENi) forms a useful test of 3-D radiative transfer models for an eclipse in the presence of optically thin clouds. A previously published clear-sky model (Emde and Mayer, 2007) shows results for a nearly overhead eclipse had REN(340 nm)=1.7 x 104 compared to the maximum measured non-averaged REN(340) at Casper of 515 ± 27 with optically thin clouds under similar geometrical conditions.

Citation: Herman, J., Wen, G., Marshak, A., Blank, K., Huang, L., Cede, A., Abuhassan, N., and Kowalewski, M.: Reduction in Earth Reflected Radiance during the Eclipse of 21 August 2017, Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2017-475, in review, 2018.
Jay Herman et al.
Jay Herman et al.
Jay Herman et al.

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Short summary
The DSCOVR/EPIC instrument located at Lagrange-1 Earth-Sun gravitational balance point is able to view the entire sunlit disk of the Earth. This means that during the eclipse of 21 August 2017 EPIC was able to see the region of totality and the much larger region of partial eclipse. Because of this, EPIC is able to measure the global reduction of reflected solar flux. For the wavelength range 388 nm to 780 nm, we estimated a 9 % reduction in reflected radiation.
The DSCOVR/EPIC instrument located at Lagrange-1 Earth-Sun gravitational balance point is able...
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