Evaluation of a Stochastic Radiative Transfer Model Using Ground-Based Measurements

Scientists have long been aware there is a need for a stochastic description of radiative transfer through media with statistically distributed parameters (Stephens 1984; Ramanathan et al. 1989; Stephens et al. 1991). This study used a shortwave stochastic band model to investigate radiative transfer through a broken cloud field for several days when low-lying fair-weather cumulus and cumulus fractus clouds were present at the Atmospheric Radiation Measurement (ARM) Program’s Southern Great Plains (SGP) site. The stochastic model distributes clouds in a clear sky according to the statistics of the cloud field and then calculates the ensemble-averaged radiation field. A one-dimensional shortwave radiation routine used in many modern general circulation models (GCMs) is used to evaluate the performance of the stochastic model. Numerical tests are performed to assess model sensitivity and to verify the realism of several parameters. The stochastic model appears promising in its ability to predict the observed downwelling radiation under a broken cloud field relative to the two-stream model.