On the angular radiance closure of tropical cumulus congestus clouds observed by the Multiangle Imaging Spectroradiometer

over a (2.2 km) 2 area, and (5) a vertical-mean b retrieved using off-nadir reflectances. An asymmetry about nadir in the observed reflectance means and skewnesses is not reproduced by any Monte Carlo simulation. The lack of symmetry can be related to differing proportions of unobscured sunlit and shadowed cloudy areas within the different views, even for these cases with viewing angles close to the perpendicular plane. The Monte Carlo simulations do not appear to capture the observed fraction of unobscured sunlit and shadowed cloudy areas, suggesting that radiatively significant cloud variability is occurring at scales smaller than the height field resolution of ±550 m. Results from the Monte Carlo simulation done at a higher vertical resolution are consistent with this. The cases examined also contain a nadir maximum in the observed reflectance skewnesses and a relative maximum for the observed nadir reflectances, attributed to the solar illumination of some optically thick cloud surfaces and to specular reflection pervading through the optically thin cloudy regions. This contrasts with previous modeling results that assume a Lambertian surface. INDEX TERMS: 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 3374 Meteorology and Atmospheric Dynamics: Tropical meteorology; 3394 Meteorology and Atmospheric Dynamics: Instruments and techniques; KEYWORDS: 3-D radiative transfer, cumulus congestus, MISR

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