Satellite-based rainfall estimation for river flow forecasting in Africa. II: African Easterly Waves, convection and rainfall

An investigation has been carried out into the relationship between rainfall and African Easterly Wave (AEW) phase over the Bakoye River catchment in West Africa. Daily values of raingauge data and cold cloud duration (CCD) from satellite imagery, together with humidity and vertical velocity fields (from ECMWF model analyses) have been compared with dominant wave phase also obtained from ECMWF wind fields for three rainy seasons. The average results for this relatively small area agree with previous studies from GATE data for the southern part of the AEW region with strongest convection and rainfall in and ahead of the trough. Observations of rainfall and CCD ahead of the trough are consistent with a simple model of AEW structure, which requires sufficient low-level moisture to trigger convective rain ahead of the trough. There is some indication that the relationship between cold cloud duration and rainfall depends on wave phase. Analysis of storm types shows a higher frequency of active storms ahead of the trough with a minimum around the ridge.