Multiyear Statistics of 2D Shortwave Radiative Effects at Three ARM Sites

Abstract

This study examines the importance of horizontal photon transport effects, which are not considered in the 1D calculations of solar radiative heating used by most atmospheric dynamical models. In particular, the paper analyzes the difference between 2D and 1D radiative calculations for 2D vertical cross sections of clouds that were observed at three sites over 2?3-yr periods. The results show that 2D effects increase multiyear 24-h average total solar absorption by about 4.1, 1.2, and 0.3 W m?2 at tropical, midlatitude, and arctic sites, respectively. However, 2D effects are often much larger than these average values, especially for high sun and for convective clouds. The results also reveal a somewhat unexpected behavior, namely, that horizontal photon transport often enhances solar heating even for oblique sun. These findings underscore the need for fast radiation calculation methods that can allow atmospheric dynamical simulations to consider the inherently multidimensional nature of shortwave radiative processes.