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Rapid Radiative Transfer Model for GCMs

Overview

The calculation of radiative energy flux through the atmosphere is done using the RRTMG radiation package (Iacono et al., 2008;1 Mlawer et al., 19972). The details are consistent with the implementation in CAM5 described in Neale et al. (2012).3 Radiative fluxes are broadly split into shortwave and longwave and computed by separate codes. The shortwave solver uses the 2-stream approximation, while the longwave is an absorption/emission code. Both shortwave and longwave use the correlated k-distribution method for integration of fluxes. Subgrid cloud overlap is accounted for using the Monte Carlo Independent Column Approximation (MCICA; Pincus and Morcrette, 2003),4 assuming the cloudy portions of the column are maximally overlapped in vertically contiguous layers and randomly overlapped when two layers are separated by a completely clear layer. Cloud optics are parameterized as described in Neale et al.(2010).3

Namelist parameters

RRTMG Namelist Parameters

  1. Michael J. Iacono, Jennifer S. Delamere, Eli J. Mlawer, Mark W. Shephard, Shepard A. Clough, and William D. Collins. Radiative forcing by long‐lived greenhouse gases: Calculations with the AER radiative transfer models. Journal of Geophysical Research: Atmospheres, 113(D13):2008JD009944, July 2008. URL: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2008JD009944 (visited on 2024-03-29), doi:10.1029/2008JD009944. ↩

  2. Eli J. Mlawer, Steven J. Taubman, Patrick D. Brown, Michael J. Iacono, and Shepard A. Clough. Radiative transfer for inhomogeneous atmospheres: RRTM, a validated correlated‐k model for the longwave. Journal of Geophysical Research: Atmospheres, 102(D14):16663–16682, July 1997. URL: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/97JD00237 (visited on 2024-03-29), doi:10.1029/97JD00237. ↩

  3. Richard B. Neale, Andrew Gettelman, Sungsu Park, Chih-Chieh Chen, Peter H. Lauritzen, David L. Williamson, Andrew J. Conley, Doug Kinnison, Dan Marsh, Anne K. Smith, Francis M. Vitt, Rolando Garcia, Jean-Francois Lamarque, Michael J. Mills, Simone Tilmes, Hugh Morrison, Philip Cameron-Smith, William D. Collins, Michael J. Iacono, Richard C. Easter, Xiaohong Liu, Steven J. Ghan, Philip J. Rasch, and Mark A. Taylor. Description of the NCAR Community Atmosphere Model (CAM 5.0). UNKNOWN, 2012. URL: https://opensky.ucar.edu/islandora/object/technotes%3A594/ (visited on 2024-04-25), doi:10.5065/wgtk-4g06. ↩↩

  4. Robert Pincus, Howard W. Barker, and Jean‐Jacques Morcrette. A fast, flexible, approximate technique for computing radiative transfer in inhomogeneous cloud fields. Journal of Geophysical Research: Atmospheres, 108(D13):2002JD003322, July 2003. URL: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2002JD003322 (visited on 2024-03-29), doi:10.1029/2002JD003322. ↩