Intraseasonal Variability and Predictability over West Equatorial Africa during the Rainy Season

Central Africa and the Gulf of Guinea, among the major areas of tropical convection, are very sensitive to intraseasonal variability during the northern hemisphere spring, summer and fall seasons. The goal of this study is to document the intraseasonal variability of tropical convection and predictability in Equatorial West Africa during the seasons of the year for which ITCZ is located near the equator. Studies, carried out on March to June and September to November seasonal rainfall highlighted the presence of three main modes of variability with great impact on convection and rainfall over the region. During these two seasons, while individual rain-producing systems move westward, they are highly modulated by eastward propagating subregional and regional scale convective systems. Moreover, the role played by westward propagating signals (Rossby wave in particular) and Mediterranean air intrusion are important. These systems by interacting with each other modulate the phases of convective activity in the region. Thus knowledge of these external forces associated with the rain-producing systems can be useful in the predictability of the intraseasonal modes in this region. A multi-model diagnostic study is performed using data available from the TIGGE project in order to evaluate the predictability of each of the main modes of variability. For a typical phase of these modes, there seems to be a statistically significant skill associated with predictability beyond 10 days, especially for predictions initiated from active main sources.