Horizontal inhomogeneities in clouds and their effect on remote particle measurements

Abstract

Models of the radiative transport through clouds in most applications use the assumption of horizontally plane-parallel and homogeneous clouds. In fact, as shown for example by this study, real clouds are not homogeneous. They possess strong vertical and horizontal inhomogeneities. This feature is demonstrated with in-situ data from Arctic stratus clouds and midlatitude cirrus clouds. In cirrus clouds, not only variations of bulk quantities such as number density or ice water content are observed but also those of particle size distributions on a horizontal scale of a few hundred meters. Such inhomogeneities of size spectra are also found in simulations with a mesoscale model when cloud microphysical processes are considered in great detail. Furthermore, this paper discusses the different results on cloud structures which would be observed by ground-based or space-borne radar and lidar. The backscatter intensity is calculated from the measured in-situ data, showing that cloud inhomogeneities cannot be neglected for the interpretation of remote sensing data.