Determination of Effective Emittance and a Radiatively Equivalent Microphysical Model of Cirrus from Ground-Based and Satellite Observations during the International Cirrus Experiment: The 18 October 1989 Case Study

Abstract

Abstract Ground-based observations and satellite data have been compared for the 18 October 1989 case study of the International Cirrus Experiment (ICE) field campaign. They correspond to thin cirrus clouds with infrared emittances in the range 0–0.3. Good correspondence was obtained when comparing the time variability of the effective downward beam emittance of the cirrus clouds observed at Nordholz (53.8°N, 8.3°E) to the spatial variability of the effective upward beam emittance derived from NOAA-11 Advanced Very High Resolution Radiometer (AVHRR) data acquired at 1225 UTC. A simple model of cirrus cloud particles was found to satisfy both the ground-based observations of the angular dependence of the scattered solar radiation at 0.85 µm and the satellite observations of the brightness temperatures in channel 4 (11 µm) and channel 5 (12 µm) of NOAA-11 AVHRR. The best fit was obtained for fully randomly oriented hexagonal ice plates with a thickness of 10–20 µm and a diameter of 200–500 µm. Although actu...