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Top-of-atmosphere albedo bias from neglecting three-dimensional cloud radiative effects
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  • Clare E. Singer,
  • Ignacio Lopez-Gomez,
  • Xiyue Zhang,
  • Tapio Schneider,
  • Xiyue Zhang
Clare E. Singer
Department of Environmental Science and Engineering, California Institute of Technology, Department of Environmental Science and Engineering, California Institute of Technology

Corresponding Author:[email protected]

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Ignacio Lopez-Gomez
Department of Environmental Science and Engineering, California Institute of Technology, Department of Environmental Science and Engineering, California Institute of Technology
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Xiyue Zhang
Department of Environmental Science and Engineering, California Institute of Technology
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Tapio Schneider
Department of Environmental Science and Engineering and Jet Propulsion Laboratory, California Institute of Technology, Department of Environmental Science and Engineering and Jet Propulsion Laboratory, California Institute of Technology
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Xiyue Zhang
Department of Environmental Science and Engineering
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Abstract

Clouds cover on average nearly 70% of Earth’s surface and regulate the global albedo. The magnitude of the shortwave reflection by clouds depends on their location, optical properties, and three-dimensional (3D) structure. Due to computational limitations, Earth system models are unable to perform 3D radiative transfer calculations. Instead they make assumptions, including the independent column approximation (ICA), that neglect effects of 3D cloud morphology on albedo. We show how the resulting radiative flux bias (ICA-3D) depends on cloud morphology and solar zenith angle. Using large-eddy simulations to produce 3D cloud fields, a Monte Carlo code for 3D radiative transfer, and observations of cloud climatology, we estimate the effect of this flux bias on global climate. The flux bias is largest at small zenith angles and for deeper clouds, while the negative albedo bias is most prominent for large zenith angles. In the tropics, the radiative flux bias from neglecting 3D radiative transfer is estimated to be 4.0 +/- 2.4 Wm-2 in the mean and locally as large as 9 Wm-2.