An impact analysis of the surface-cloud damping effect on TOA reflectivity using A 3D radiative transfer model
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ORIGINAL PAPER
An impact analysis of the surface‑cloud damping effect on TOA reflectivity using A 3D radiative transfer model Leidi Wang1,2 · Daren Lü2 · Wenxing Zhang2 Received: 27 June 2019 / Accepted: 17 December 2019 © Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract The I3RC Community Monte Carlo model of three-dimensional (3D) radiative transfer (I3RC-CM) was improved by specifying surfaces with a widely used bidirectional reflectance model known as the RPV (Rahman-Pinty-Verstraete). The surfacecloud damping effect on top-of-atmosphere (TOA) reflectivity (hereafter, the damping effect) is evaluated as the atmospheric attenuation of incoming shortwave radiation on its way down to the surface and shortwave radiation reflected at the surface that is transmitted back to the TOA. A series of simulations were performed using the improved I3RC-CM to investigate this effect over different land covers, in which the land covers are characterized by the 3 RPV parameters: the intensity of surface reflectance, the anisotropy of the surface, and the asymmetry parameter. The damping effect is greatly affected by the land cover, especially the intensity of surface reflectance. The intensity of surface reflectance can lead to an approximate deviation of 0.40 in the damping effect, while the influence of the asymmetry parameter and the surface anisotropy on the damping effect is less than 0.10. The damping effect strengthens as the surface reflectance intensity and asymmetry parameter increase, but slightly weakens as the surface anisotropy increases. The land cover change has a stronger impact on the damping effect at the absorbing wavelengths than at the non-absorbing wavelengths due to the cloud absorption, particularly at 2.13 µm, but the cloud absorption offers only a partial explanation for the differences in damping effect changes with values less 0.10.
1 Introduction The Earth’s top-of-atmosphere (TOA) reflectivity is the ratio of reflected to incident shortwave radiation at the TOA. This reflectivity exerts a profound influence on global glaciation, temperature, atmospheric and oceanic circulation, and cloud and surface feedback processes. It is a function of the optical properties of objects within the atmosphere (e.g., clouds, aerosols, and water vapor) as well as the planet’s surface (Wielicki et al. 1995; Hall 2004). The surface contribution to TOA reflectivity can be attenuated by objects within the atmosphere, especially clouds, in several ways (Qu and Hall 2005; Donohoe and Battisti 2011). With the exception of directly reflecting incident solar radiation back to space, Responsible Editor: S.-W. Kim. * Leidi Wang [email protected] 1
College of Agriculture, South China Agricultural University, Guangzhou 510642, China
LAGEO, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
2
the atmosphere attenuates the effect of the surface on TOA reflectivity by reducing the amount of downward shortwave radiation reaching the surface and the amount of sh
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