Inpact of interactive radiative transfer on the macroscopic behavior of cumulus ensembles. Part I: radiation parameterization and sensitivity tests

Abstract

Implementation of a broadband radiation parameterization in the UCLA cumulus ensemble model (CEM) is discussed in this study, with emphasis on the specific problems associated with adequate calculation of radiative transfer processes in the CEM. The lowest CEM layer is divided into a thick layer and a very thin layer near the surface for the longwave radiation calculation. Diagnostic tests have been performed to compare the accuracy of this parameterization with results from a more complicated radiative transfer model. Simulations with fully interactive radiation are performed to compare two methods for invoking the radiation module. Additional sensitivity tests are also performed to justify the omission of the radiative effects of rapidly falling precipitating particles. Other sensitivity tests are related to the adequacy of the domain size and horizontal resolution for studying the cloud-radiation interaction problems discussed in Part II. -from Authors