Seasonal/regional comparisons of rain rates and rain characteristics in West Africa using TRMM observations

Abstract

West African rain estimates from a number of global rain data sets (surface and satellite derived), including the TRMM precipitation radar and merged data sets are compared for the 1998–2000 May through September period. Rain intensity and classification (convective/stratiform) from the TRMM precipitation radar are also included in this study. All of the rainfall estimates, including the TRMM products, show that the highest rain rates occur during the month of August for West Africa and its sub region, the Sahel. High negative correlations (<−0.8) are found among the wet season rain estimates and outgoing longwave radiation for West Africa and the Sahel. In the Guinea region, correlations are considerably lower because of a significant longitudinal variation in OLR during the wet season. The TRMM Precipitation Radar derived rain estimates show that stratiform rain becomes increasingly important as the wet season evolves with 35–40% of the rain being stratiform during August and September. Surprisingly the total number of lightning flashes in the Sahel is higher than those in the Guinea region by a factor of 1.5. During August, the Sahelian lightning flashes outnumber those in the Guinea region by more than a factor of 4. Furthermore, in the Sahel, the majority of the flashes occur during the nighttime but during the daytime in the Guinea region. Because of spatial and temporal under‐sampling, the TRMM rain estimates are lower than other rain estimates with the TRMM PR producing the lowest rain rates.