Water cycle and mesoscale convective systems over West Africa

Satellite and the European Centre for Medium range Weather Forecasting (ECMWF) data have been used to study water vapour flux and Mesoscale Convective Complexes (MCC) in West Africa. The area of interest extends from 15° S to 25° N and from 30°W to 20° E. The characteristics of MCC are analysed using half hourly Meteosat infrared channel full resolution data from 1990 to 1994 and automatic tracking initiated by Yves Arnaud. The results show maximum MCC generation and decay in mountainous regions of Fouta Djalon, Joss highlands and Cameroon mountains. A spatial regular distribution of these extremes is observed in the western part of the area with the impact of south-western monsoon flux at the Guinean coast. Combination of ECMWF water vapour and win data leads to a description of monsoon and water vapour fluxes. The later is weaker in dry period. Sources and well regions of humidity are defined as the area of convergence or divergence of water vapour flux. At larger scale intra-seasonal variation of subsidence (dry) zones is illustrated by the water vapour channel signal from Meteosat. These dry area move northward during the wait season and may influence the regional climate.