The Continual Intercomparison of Radiation Codes: Results from Phase I

Abstract

.[1] We present results from Phase I of the Continual Intercomparison of Radiation Codes (CIRC), intended as an evolving and regularly updated reference source for evaluation of radiative transfer (RT) codes used in global climate models and other atmospheric applications. CIRC differs from previous intercomparisons in that it relies on an observationally validated catalog of cases. The seven CIRC Phase I baseline cases, five cloud free and two with overcast liquid clouds, are built around observations by the Atmospheric Radiation Measurements program that satisfy the goals of Phase I, namely, to examine RT model performance in realistic, yet not overly complex, atmospheric conditions. Besides the seven baseline cases, additional idealized "subcases" are also employed to facilitate interpretation of model errors. In addition to quantifying individual model performance with respect to reference line-by-line calculations, we also highlight RT code behavior for conditions of doubled CO 2 , issues arising from spectral specification of surface albedo, and the impact of cloud scattering in the thermal infrared. Our analysis suggests that improvements in the calculation of diffuse shortwave flux, shortwave absorption, and shortwave CO 2 forcing as well as in the treatment of spectral surface albedo should be considered for many RT codes. On the other hand, longwave calculations are generally in agreement with the reference results. By expanding the range of conditions under which participating codes are tested, future CIRC phases will hopefully allow even more rigorous examination of RT codes.

The Canadian Fourth Generation Atmospheric Global Climate Model (CanAM4). Part I: Representation of Physical Processes

“…For instance, radiation schemes based on correlated-k distribution and McICA are increasingly replacing other, less accurate radiation schemes in climate models (Barker et al, 2008;Oreopoulos et al, 2012). As another example, the parameterization for transient shallow convection by von Salzen and McFarlane (2002) has led to improved representations of low clouds and convective mixing in CanAM4 and the global climate model ECHAM5-HAM (Isotta, Spichtinger, Lohmann, and von Salzen, 2011).…”

Accuracy tests of radiation schemes used in hot Jupiter global circulation models

“…They have both been found to yield results with satisfactory accuracy when comparing to more accurate solutions obtained from e.g. discrete ordinate (DO), line-by-line (LbL) calculations and when different schemes are compared through intercomparison projects (Ellingson et al 1991;Collins et al 2006;Oreopoulos et al 2012). They are, however, still under investigation (Goldblatt et al 2009) and are still one of the limiting factors of the accuracy of both weather prediction and climate modelling.…”

“…The dynamical cores are tested using benchmarks (see e.g. Held & Suarez 1994;Reed & Jablonowski 2011;Ullrich et al 2013), and both dynamical cores 1 and radiation schemes (Ellingson et al 1991;Collins et al 2006;Oreopoulos et al 2012) are tested through intercomparison projects.…”

Application of Improved Radiation Modeling to General Circulation Models

“…Further model validation was accomplished through participation in the DOE-supported Atmospheric Radiation Measurement (ARM) Continual Intercomparison of Radiation Codes (CIRC; Oreopoulos and Mlawer, 2010) in collaboration with Dr. Lazaros Oreopoulos. This program has the objective of providing a continuously updated framework for evaluating radiation models with an emphasis on using observations to define the cases examined.…”