Total and low cloud amounts over France and southern Britain in the summer of 1983: Comparison of surface-observed and satellite-retrieved values

Cloud observations from 124 surface stations for 12.00 hours G.M.T. for the 20 day period 22 July to 10 August 1983 have been compared with retrievals made using the cluster technique of Desbois et al. from METEOSAT radiances measured at 11.30hours G.M.T. The location, France and southern Britain, and time period, summer 1983, were selected to coincide with one of the regions designated for special study in the validation phase of the International Satellite Cloud Climatology Project (ISCCP). Total and low cloud amounts were compared. For total cloud amount 29 percent of the retrievals were fully in agreement with the surface observations and 64 per cent of differences were within ± 1 okta. In the case of low cloud, 33 per cent agreed fully and 64 per cent of the differences were within ± 1 okta. It must be noted that many of these successes (55 per cent in the total cloud amount and 71 per cent in the low cloud amount) were for cases of totally clear or totally cloudy skies and often when only one cloud layer was present.