Boundaries and internal structure of mixed phase clouds as deduced from ground-based 95-GHz radar and airborne lidar measurements

Abstract

Knowledge on the occurrence of multiple cloud layers, the heights of their boundaries, their internal structure and phase is important for an accurate determination of radiative fluxes through the atmosphere. Multi-layer mixed phase clouds have simultaneously been profiled with a ground-based 95-GHz radar and Ne:YAG based airborne lidars. Due to their different attenuation and sensitivity to particle size and phase these instruments provide complementary information of cloud boundaries and cloud structure. Case studies from a field campaign over Southern UK are presented. In one case a narrow altostratus layer of mainly spherical, liquid particles was embedded in an ice cloud of larger vertical extent. The liquid layer was resolved in detail by the lidar but did not appear distinguishably in the radar profile, which was much more sensitive to the ice particles. Fallstreaks below the cloud base show a signature in the radar signals only. In another case the lidar beam was blocked in the upper part of a mid-level cloud layer with band like structure, while this cloud hardly appeared in the radar reflectivity which instead was dominated by another band 1 km below. Both instruments detected nearly the same cloud boundaries and structures when the liquid layer disappeared and an optically thin ice cloud remained. This study clearly reveals the tremendous information gain by a synergetic use of radar and lidar for cloud profiling. (C) 2000 Elsevier Science Ltd. All rights reserved.