Impact of Multiple Scattering on Infrared Radiative Transfer involving Ice Clouds

Abstract:

General circulation models (GCMs) facilitate a major tool to investigate climate on global scale. Since solar and terrestrial radiation control energy budget of global climate, developing an accurate yet computationally efficient radiative transfer model in GCMs is important. However, in most of the GCMs, absorption of ice cloud is the only mechanism considered for the longwave radiative transfer process. Implementation of longwave scattering in GCMs requires parameterizations of ice cloud. This study utilizes spectrally consistent ice particle model in MODIS collection 6 and more than 14,000 particle size distributions from aircraft in-situ observations to parameterize ice cloud longwave optical properties. The new parameterizations are compared with Fu-Liou parameterization implemented in the RRTM_LW (Longwave Rapid Radiative Transfer Model). As accurate and computationally efficient radiative transfer model is important in GCMs, comparison of different radiative transfer methods are performed. Specifically, RRTMG_LW (GCM version of RRTM_LW), one of the most widely utilized radiative transfer schemes in the GCMs, will be modified to include different scattering approximation methods. To evaluate the accuracy, DISORT (Discrete Ordinates Radiative Transfer Program for a Multi-Layered Plane-Parallel Medium) is implemented and compared with other methods in terms of cloud radiative effect and heating rate.