Influence of the “Cloud Bow” Effect in SEVIRI Measurements on the Retrieval of the Diurnal Cycle of Land–Sea Cloud Liquid Water Path Contrast in Northern Europe

Abstract

The information on the cloud liquid water path (LWP) is required for many applications including global and regional climate modelling, weather forecasting, and hydrological cycle modelling. The results of derivation of the land–sea LWP contrast from LWP measurements with the satellite SEVIRI (Spinning Enhanced Visible Infra-Red Imager) instrument over land and water bodies in northern Europe are presented. The study of the diurnal cycle of the LWP contrast for some water bodies discovered two maxima nearly symmetrical about the noon UTC. They were observed in most cases at measurement points in the Gulf of Riga and in the Gulf of Finland in the Baltic Sea. Presumably, those maxima were artefacts of observations caused by the so-called “cloud bow effect.” Calculations of a scattering angle for the satellite measurements at these points confirm this conclusion. The problems of data filtering and analyzing in the cases of manifestation of this disturbing effect are discussed. An approach to data analysis is suggested. This approach and the results can be used to assess the quality of LWP measurements by SEVIRI in various regions of the globe.