11th Conference on Atmospheric Radiation and the 11th Conference on Cloud Physics

Thursday, 6 June 2002
Allowing for inhomogeneous clouds in the Goddard Earth Observing System GCM Colunm radiation model
Lazaros Oreopoulos, JCET/Univ. of Maryland Baltimore County, Greenbelt, MD; and H. W. Barker, M. D. Chou, R. F. Cahalan, and M. Khairoutdinov
Poster PDF (146.0 kB)
We have implemented a version of the multi-layer Gamma Weighted Two Stream Approximation (GWTSA) algorithm in the Goddard Earth Observing System (GEOS) General Circulation Model (GCM) solar radiative transfer scheme. The algorithm has as its core two-stream solutions to the radiative transfer equation for gamma distributions of optical thickness. The purpose is to capture the radiative effects of inomogeneous clouds. We compare the performance of the new scheme with more accurate Independent Column Approximation (ICA) calculations and demonstrate the improvement over traditional Plane Parallel Homogeneous (PPH) calculations. The inhomogeneous clouds used as input come from Cloud Resolving Models (CRMs) or fractal cascade generators. We are particularly interested in GWTSA algorithm improvements with respect to cloud overlap, and compare the results from new generalized overlap functions with traditional overlap assumptions. We also discuss derivation of these overlap functions from observations and CRMs, and the use of MODIS data to derive and parameterize globally applicable cloud inhomogeneity parameters as a function of grid size.

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