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

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 H 2 O, O 3 , CO 2 , and O 2 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 H 2 O 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.