Radiative transfer in the cloudy atmosphere

Abstract
Radiative transfer in clouds is a challenging task, due to their high spatial and temporal variability which is unrivaled by any other atmospheric species. Clouds are among the main modulators of radiation along its path through the Earth’s atmosphere. The cloud feedback is the largest source of uncertainty in current climate model predictions. Cloud observation from satellites, on a global scale, with appropriate temporal and spatial sampling is therefore one of the top aims of current Earth observation missions. In this chapter three-dimensional methods for radiative transfer in cloudy atmospheres are described, which allow to study cloud-radiation interaction at the level needed to better understand the fundamental details driving climate and to better exploit remote sensing algorithms. The Monte Carlo technique is introduced which allows to handle nearly arbitrarily complex atmospheric conditions. The accuracy of the method is discussed by comparison between different models and with observations. Finally, we show some examples and discuss under which conditions three-dimensional methods are actually needed and when commonly-used one-dimensional approximations are applicable. This chapter builds upon the excellent overview of one-dimensional radiative transfer in ERCA Volume 3 [B. Pinty and M.M. Verstraete, ERCA 3, 67 (1998)].