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Studies of and improvements to the parameterized treatment of physical processes is a broad area of CMS research. Collins and Conley have developed a new mathematical method for approximating transmission in radiative transfer calculations, perhaps the most fundamental quantity for describing the propagation of light and heat through the atmosphere. It has proven quite difficult to represent transmission in numerical models because of the enormous range in the optical opacity depending on the color, or wavelength, of light and the chemical composition of the atmosphere. This work has yielded a new approximation for transmission based upon a novel mathematical analysis, and is designed to overcome the severe mathematical and physical limitations of previous ad hoc techniques. It also yields new, mathematical insights into the issue of "anomalous", or enhanced, shortwave absorption in clouds and into the origin of relatively transmissive parts of the solar and terrestrial spectra known as atmospheric "windows". Collins and Conley are now applying this new method to the design of new radiative parameterizations for CCSM. In addition to his IPCC work on radiative forcing of the climate system, Collins collaborated with Dr.Ramaswamy to lead a Radiative Transfer Model Intercomparison Project (RTMIP) (Collins et al, 2006). The objective in RTMIP was to compare the forcings computed by the radiative parameterizations of AOGCMs and against benchmark line-by-line (LBL) codes. Findings of this work show that in order to improve the interpretation of climate change simulations from multimodel ensembles, it will be necessary to collect much more complete information on the forcings applied to each of the AOGCMs than has been customary.