Third Intercomparison of Radiation Codes in Climate Models: Longwave Cloudy Sky Benchmarks and Comparisons with Approximate Methods

• Other Authors: Kablick, George P. (authoraut)
• Format: Others
• Language: English; English
• Published: Florida State University
• Subjects: Meteorology
• Online Access: http://purl.flvc.org/fsu/fd/FSU_migr_etd-3405

As a continuation to the shortwave phase of the third Intercomparison of Radiation Codes in Climate Models (ICRCCM III) by Barker et al. (2003), this study establishes longwave benchmarks for inhomogeneous cloud fields and compares the performance of three approximate, one-dimensional (1D) radiation models. The benchmarks are calculated using a correlated-k three-dimensional Monte Carlo (3DMC) algorithm that is validated via comparisons to line-by-line calculations for simple atmospheres. The approximate methods include an independent pixel approximation (IPA) and two cloud-overlap schemes: maximum/random (MRO) and random (RO). The test cases are the same as those used in the shortwave ICRCCM III, and were generated from various cloud resolving models (CRMs). These cases represent a variety of inhomogeneous cloud types that are important radiative forcing mechanisms of general circulation models (GCMs). Domain-averaged fluxes and heating rates from these six "real cloud" atmospheres show that the IPA is consistently more accurate than the cloud-overlap models with respect to the benchmarks. For example, comparisons of model results for the ATEX case yield a maximum cloud layer heating rate error of -20 K/day from using cloud-overlap models, whereas the IPA error is only -2.5 K/day. These differences can be attributed to the 3D effects of cloud radiation, and indicate the need to refine longwave 1D climate radiation codes so that they compensate for unresolved clouds. === A Thesis submitted to the Department of Meteorology in partial fulfillment of the requirements for the degree of Master of Science. === Summer Semester, 2008. === July 8, 2008. === Includes bibliographical references. === Robert G. Ellingson, Professor Directing Thesis; Ming Cai, Committee Member; Guosheng Liu, Committee Member.