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Discussion papers
https://doi.org/10.5194/acp-2019-961
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-961
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 27 Jan 2020

Submitted as: research article | 27 Jan 2020

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This preprint is currently under review for the journal ACP.

Changes in Surface Broadband Shortwave Radiation Budget during the 2017 Eclipse

Guoyong Wen1,2, Alexander Marshak1, Si-Chee Tsay1, Jay Herman1,3, Ukkyo Jeong1,4, Nader Abuhassan1,3, Robert Swap1, and Dong Wu1 Guoyong Wen et al.
  • 1NASA/Goddard Space Flight Center, Code 613, Greenbelt, Maryland,20771, USA
  • 2GESTAR/Morgan State University, Baltimore, Maryland, 21251, USA
  • 3JCET, University of Maryland Baltimore County, Baltimore, Maryland, 21250, USA
  • 4ESSIC, University of Maryland, College Park, Maryland, 20742, USA

Abstract. While solar eclipses are known to greatly diminish the visible radiation reaching the surface of the Earth, less is known about the magnitude of the impact. We explore both the observed and modelled level of change in surface radiation during the eclipse of 2017. We deployed a pyranometer and Pandora spectrometer instrument to Casper, Wyoming and Columbia, Missouri to measure surface broadband shortwave (SW) flux and atmospheric properties during the 21 August 2017 solar eclipse event. We performed detailed radiative transfer simulations to understand the role of clouds in spectral and broadband solar radiation transfer in the Earth’s atmosphere for the normal (non-eclipse) spectrum and red-shift solar spectra for eclipse conditions. The theoretical calculations showed that the non-eclipse-to-eclipse surface flux ratio depends strongly on the obscuration of solar disk and slightly on cloud optical depth. These findings allowed us to estimate what the surface broadband SW flux would be for non-eclipse conditions from observations during the eclipse and further to quantify the impact of the eclipse on the surface broadband SW radiation budget. We found that the eclipse caused local reductions of time-averaged surface flux of about 379 W m−2 (50 %) and 329 W m−2 (46 %) during the ∼3 hours course of the eclipse at the Casper and Columbia sites, respectively. We estimated that the Moon’s shadow caused a reduction of approximately 7–8 % in global average surface broadband SW radiation. The eclipse has a smaller impact on surface flux reduction for cloudy conditions than a clear atmosphere; the impact decreases with the increase of cloud optical depth. However, the relative time-averaged reduction of local surface SW flux during a solar eclipse is approximately 45 % and it is not sensitive to cloud optical depth. The reduction of global average SW flux relative to climatology is proportional to the non-eclipse and eclipse flux difference in the penumbra area and depends on cloud optical depth in the Moon’s shadow and geolocation due to the change of solar zenith angle. We also discuss the influence of cloud inhomogeneity on the observed SW flux. Our results not only quantify the reduction of the surface solar radiation budget but also advance the understanding of broadband SW radiative transfer under solar eclipse conditions.

Guoyong Wen et al.

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Short summary
We combine the ground-based observations and radiative transfer model to quantify the impact of 2017 solar eclipse on surface shortwave irradiation reduction. We find that the eclipse caused local reductions of time-averaged surface flux of about 379 W m−2 (50 %) and 329 W m−2 (46 %) during the ∼3 hours course of the eclipse at the Casper and Columbia sites, respectively. We estimate that the Moon’s shadow caused a reduction of approximately 7–8 % in global average surface broadband SW radiation.
We combine the ground-based observations and radiative transfer model to quantify the impact of...
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