Detection of clouds and their influence on radiation budget determined by multisensor satellite data

Abstract

In several instances during the International Cirrus Experiment (ICE) 1989, cloud types were detected by multisensor satellite data over the North Sea. The first cloud classification scheme is based on the maximum likelihood method using NOAA AVHRR and Meteosat data. The second is an algorithm using a combination of Meteosat and SSM/I data. By comparing these results together and with synoptical observations, good agreement can be achieved. The discrepancies can be explained either by time delay or different spatial resolution. Comparing the monthly mean cloudiness inferred from NOAA AVHRR-data with ISCCP C2 data, it seems that the ISCCP C2 results underestimate the real cloudiness for the North Sea area (approx. 55 degree(s) N latitude, 5 degree(s) E longitude). To determine the influence of clouds on the earth radiation budget and on the climate the cloud-climate efficiency was used. This index is similar to the cloud forcing, but is valid for an individual classified satellite image pixel. The cloud forcing is the sum of the cloud-climate efficiencies over an area, i.e., the heating or cooling of the earth/atmosphere system can be estimated. Using NOAA-AVHRR data the annual cycle of cloud forcing at top of atmosphere was calculated for the North Sea.