Sub-seasonal teleconnections between convection over the Indian Ocean, the East African long rains and tropical Pacific surface temperatures

Since 1999, the increased frequency of dry conditions over East Africa, particularly during the March-May (MAM) season, has heightened concerns in a region already highly insecure about food. The underlying mechanisms, however, are still not yet fully understood. This article analyses a proxy for daily convection variations over a large region encompassing East Africa and the whole Indian Ocean basin by applying a cluster analysis to more than 30 years of daily outgoing longwave radiation (OLR). Focusing on the MAM season to investigate relationships with East African long rains, four recurrent convection regimes associated with wet/dry conditions in East Africa are identified. Interestingly, all four regimes are related to western/central Pacific sea surface temperatures (SSTs) and rainfall. Wet regimes are associated with cool and dry/warm and wet conditions over the Maritime Continent (MC)/tropical Pacific east of the date line. Dry regimes exhibit opposite SST/rainfall dipole patterns in the Pacific compared to wet regimes, with the Indian Ocean found to modulate impacts on East African rainfall. Significant relationships between off-equatorial warming in the west Pacific and a more frequent dry regime in May since 1998-1999 suggest an earlier onset of the monsoon and Somali jet, consistent with the recent abrupt shift observed in East African long rains and their modulation at multi-decadal time scales of the Pacific.