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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/acp-2019-609
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-609
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 27 Aug 2019

Submitted as: research article | 27 Aug 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Accurate 3D radiative transfer simulation of spectral solar irradiance during the total solar eclipse of August 21, 2017

Paul Ockenfuß1, Claudia Emde1, Bernhard Mayer1, and Germar Bernhard2 Paul Ockenfuß et al.
  • 1Meteorological Institute, Ludwig-Maximilians-University, Theresienstr. 37, 80333 Munich, Germany
  • 2Biospherical Instruments Inc., San Diego, CA 92110, USA

Abstract. We calculate the variation of spectral solar irradiance in the umbral shadow of the total solar eclipse of August 21, 2017 and compare it to observations. Starting from the sun's and moon's positions, we derive a realistic profile of the lunar shadow at the top of the atmosphere, including the effect of solar limb darkening. Subsequently, the Monte-Carlo model MYSTIC is used to simulate the transfer of solar radiation through the earth's atmosphere. Among the effects taken into account are the atmospheric state (pressure, temperature), concentrations of major gas constituents and the curvature of the earth, as well as the reflectance and elevation of the surrounding area. We apply the model to the total solar eclipse on August 21, 2017 at a position located in Oregon, where irradiance observations were performed for wavelengths between 306 nm and 1020 nm. The influence of the surface reflectance, the ozone profile and mountains surrounding the observer is investigated. An increased sensitivity during totality is found for the reflectance and topography, compared to non-eclipse conditions. During the eclipse, the irradiance at the surface does not only depend on the total ozone column (TOC) but also the vertical ozone distribution, which in general complicates derivations of the TOC from spectral surface irradiance. The findings are related to an analysis of the prevailing photon path and its difference compared to non-eclipse conditions. Using the most realistic estimate for each parameter, the model is compared to the irradiance observations. During totality, the relative difference between model and observations is less than 10 % in the spectral range from 400 nm to 1020 nm. Slightly larger deviations occur in the ultraviolet range below 400 nm and at 665 nm.

Paul Ockenfuß et al.
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Paul Ockenfuß et al.
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Short summary
We model solar radiation as it would be measured on the earth's surface in the core shadow of a total solar eclipse. Subsequently, we compare our results to observations during the total eclipse 2017 for ultraviolet, visible and near-infrared wavelengths. Moreover, we analyze the effect of the surface reflectance, the ozone profile and the topography and give a visualization of the prevailing photons paths in the atmosphere during the eclipse.
We model solar radiation as it would be measured on the earth's surface in the core shadow of a...
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