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The Multi-scale Modeling Framework (MMF) version of the NCAR Community Atmospheric Model (CAM - version 1.8) uses 2D Cloud System-Resolving Models (CSRMs) in each of its 8192 columns. Grid-spacings for the CAM and CSRMs are about 256 km and 4 km, respectively. Hence, much cloud structure is resolved explicitly by the MMF. Benchmark radiation calculations were computed for GCM columns by applying the Independent Column Approximation (ICA) to the CSRM domains. Then, profiles of cloud information from the CSRM domains were computed for each GCM column and used in the CAM's regular radiative transfer codes that assume clouds to be plane-parallel and homogeneous (PPH) and to follow the maximum-random overlap (MRO) rule. This map shows the difference between shortwave (SW) cloud radiative effect (forcing) at the TOA between the conventional radiative transfer treatment and the ICA for DJF. For layered cloud systems, neglect of horizontal variations by the conventional model leads to excessive albedos and thus more SW cloud effect (larger negative values). In the tropics, where clouds are both variable in the horizontal and vertically extensive, the MRO assumption underestimates total cloud fraction and so albedos are too small. Globally
averaged, the PPH/MRO simplifications 'reduce' cloud radiative effect by about 1 W/m^2. That is, the impact of the MRO assumption slightly outweights the PPH assumption, thereby darkening Earth. For more details, see the poster by Cole et al.
photo credits: Alexei Korolev; NASA
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| Document Title: | GCM Solar Radiation Code Bias |
| Submission Date: | 01/09/2004 at 09:31 AM |
| Category: | Data |
| Resolution: | 300 dpi |
| Date of Image/Photo: | Jan 9, 2004 |
| Point of contact: | Howard Barker |
| Names of people in photo: | |
| Background: | 2004 cover competition winner for the 14th ARM Science Team Meeting. |
| URL: | http://images.arm.gov/armimages.nsf/by+id/TENG-5V2NK3 |
Note: This image may be reproduced and published at your discretion. Please use the following credit line: "Courtesy: U.S. Department of Energy's Atmospheric Radiation Measurement Program."
