Observed Trends in Dry Season Convection over the Congo Basin Using Multiple Satellite Datasets

The Congo rainforest located in equatorial Africa is the second largest rainforest in the world. While the seasonal cycle of the Inter-Tropical Convergence Zone (ITCZ) that results in a bimodal annual precipitation distribution peaking around March-May and September-November is responsible for close to 60% of the observed total precipitation over the rainforest, the dry season from June-August (JJA) accounts for about 20% of the total annual rainfall. While the magnitude of thunderstorm activity follows the seasonal cycle of precipitation over the Congo, intriguingly deep tropical convection is observed over the rainforest year round, and recent studies have documented a long-term drying trend over the Congo Basin. The work presented here focuses on documenting observed trends in convection over the Congo from 1982–2016 using multiple longstanding satellite datasets during the dry season. The key findings from this work includes an overall increase in the daily mean frequency of thunderstorm activity over the rainforest, a significant increase in the spatial extent of cold (i.e., T<-60°C) cloud top brightness temperatures coupled with a slight decrease in the mean size of thunderstorms at higher brightness temperatures (-45°C to -30°C). These results were also verified using an independent OLR dataset that suggests an increase in high altitude cirrus clouds and an increasing trend towards tall and relatively small thunderstorm cells over the rainforest. It was also found that precipitation and convection over the northern regions of the Congo (0-8°N) have declined substantially. In contrast, no significant changes were observed over southern Congo (0-8°S).