Global Consequences of Interactions between Clouds and Radiation at Scales Unresolved by Global Climate Models

Horizontal grid-spacings in conventional atmospheric gen-eral circulation models (GCMs) are typically between 100 km and 500 km. Hence, many processes are unresolved and must be parametrized in terms of resolved variables. Development of satisfactory parametrizations of mean-field (or domain-average) cloud and radiative processes has been frustratingly slow. Moreover, the importance of interactions between cloud and radiation at scales unresolved by con-ventional GCMs is unknown. In this study, the native cloud parameterization of a GCM was replaced, in each GCM grid column, by a two-dimensional cloud system-resolving model (CSRM). The CSRMs used a horizontal grid-spacing of 4 km. They were employed to assess the relative importance of accurate domain-average radiative flux profiles and inter-actions between cloud and radiation at unresolved scales. It is shown here that, for a simulation spanning one season, the unresolved interactions are at least as important as accurate domain-averages. 1