A Multilayer, 1-D Solar Radiative Transfer Algorithm that Accounts for Subgrid-Scale Cloud Variability

A multi-layer, one-dimensional (1-D) solar radiative transfer algorithm that accounts for subgrid-scale cloud variability is presented. This algorithm was implemented in the National Center for Atmospheric Research (NCAR)-Community Climate Model (CCM) broadband column model. A subset of its validation is shown here using a three-dimensional (3-D) inhomogeneous cloud field generated by a cloud-resolving model. Reference calculations were obtained by a 3-D Monte Carlo (MC) simulation. The new code operates on horizontally averaged information, such as cloud fraction, mean, and variance of cloud optical depth, and reduces plane-parallel, homogeneous (PPH)-biases for top of atmosphere (TOA) albedo and surface absorptance by typically more than 85%. Moreover, its estimates of atmospheric heating rate usually differ from MC values by less than 10%