Journal of Geophysical Research: Atmospheres

Delta-Eddington approximation for solar radiation in the NCAR community climate model


  • Bruce P. Briegleb


Motivated by the desire for a more flexible and general solar radiation calculation in the NCAR community climate model (CCM), the δ-Eddington approximation has been employed in the CCM version 2 (CCM2). Eighteen spectral intervals span the solar spectrum from 0.2 to 5.0 μm. Absorption parameterizations for H2O, O3, CO2, and O2 were developed by making use of the latest theoretical calculations. Water droplet scattering and absorption are parameterized as shown by Slingo (1989). An accurate and efficient convolution of the H2O vapor spectrum with water droplet clouds is presented that yields good agreement with available line-by-line (LBL) calculations for single-layer clouds. A simple and efficient method to simulate partial cloud cover and cloud overlap is included. The simulated albedo-solar zenith angle dependence agrees very well with adding/doubling scattering calculations. The CCM2 δ-Eddington method will make possible many interesting applications of CCM2 in the years to come.