1984 Volume 62 Issue 5 Pages 761-774
TIROS-N moisture data and Level III-b humidity fields from European Center for Medium Range Weather Forecasting (ECMWF) have been analyzed during the 1979 summer (May 1-September 15) to obtain fields of Precipitable water in three layers (surface-700mb, 700-500 mb and 500-300mb) at 00 and 12GMT over Africa and the eastern and central Atlantic Ocean (50°W-40°E; 30°N-30°S). The accuracy of the final product has been estimated from a comparison with dropsonde and upper air sounding humidity data. The relative accuracy is about 10%.
The seasonal northward migration of the zone of maximum PW is analyzed from the study of mean fields. May and June are characterizedd by a rapid shift of the zone of maximum PW. A large decrease of the atmospheric water vapor content takes place during early July. In September the zone of maximum PW shifts southward in association with the southward retreat of the monsoon trough. Time series of water vapor content over different areas of the subsaharan region shows the existence of fluctuations related to rainfall variations. The main periodicities of PW lie in the range 3-4 days and 6-9 days. The first type of fluctuations is related to the African easterly waves whereas the second type corresponds to another mode of fluctuation of the tropical atmosphere over Africa and the Atlantic ocean.