16 Oct 2023
 | 16 Oct 2023

Influence of Cloud Retrieval Errors Due to Three Dimensional Radiative Effects on Calculations of Broadband Cloud Radiative Effect

Adeleke S. Ademakinwa, Zahid H. Tushar, Jianyu Zheng, Chenxi Wang, Sanjay Purushotham, Jianwu Wang, Kerry G. Meyer, Tamas Várnai, and Zhibo Zhang

Abstract. We investigate how cloud retrieval errors due to the threedimensional (3D) radiative effects affect broadband cloud radiative effects (CRE). A framework based on the combination of large eddy simulations (LES) and radiative transfer (RT) models was developed to simulate both onedimensional (1D) and 3D radiance, and shortwave (SW) broadband fluxes. Results show that the broadband SW fluxes reflected at top-of-the-domain, transmitted at the surface, and absorbed in the atmosphere, computed from the cloud retrievals using 1D-RT (called “1D-RT+retrieved clouds”) can provide reasonable broadband radiative energy estimates in comparison with those derived from the true cloud fields using 1D-RT (called “1D-RT+true clouds”). The difference between these 1D-RT simulated fluxes (1D-RT+retrieved clouds simulations, 1D-RT+true clouds simulations) and the benchmark 3D-RT simulations from the true cloud field (called “3D-RT+true clouds”), depends primarily on the horizontal transport of photons in 3D-RT, whose characteristics vary with the Sun’s geometry. When the solar zenith angle (SZA) is 5°, the domain-averaged fluxes simulated based on the 1D-RT+retrieved clouds are in excellent agreement with the 3D-RT+true clouds results, all within 7 % relative CRE bias. When the SZA is 60°, the differences between the results from the 1D-RT+retrieved clouds and 3D-RT+true clouds are determined by how the cloud side-illumination and shadowing effects offset each other in the radiance, retrieval, and broadband fluxes. This study suggests that although the cloud property retrievals based on the 1D-RT theory may be biased due to the 3D radiative effects, they still provide an observational basis for the estimation of broadband fluxes.

Adeleke S. Ademakinwa et al.

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Adeleke S. Ademakinwa et al.

Adeleke S. Ademakinwa et al.


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Short summary
Clouds play a critical role in our climate system. At present and in the near future, satellite based remote sensing is the only means to obtain regional and global observations of cloud properties. The current satellite remote sensing algorithms are mostly based on the so-called 1-D radiative transfer. This deviation from the 3-D wold reality can lead to large errors. In this study we investigate how this error affect our estimation of cloud radiative effects.