Tropical lows in southern Africa: tracks, rainfall\ud contributions and the role of ENSO

Southern African tropical lows are synoptic-scale cyclonic vortices that propagate westward across southern Africa in the Austral summer. They strongly influence local rainfall and aggregate in the climatological DJF mean to form the Angola Low. In this study, tropical lows are identified and tracked using an objective feature tracking method. The statistics of tropical low tracks over southern Africa are presented and compared across three reanalysis products. Findings are compared to the literature of tropical low pressure areas elsewhere in the world, where it is found that most tracking statistics compare well, but that the tendency of tropical lows to become semi-stationary over Angola is unique to Southern southern Africa. The hypothesis that tropical lows in Angola have a causal relationship with Tropical Temperate Troughs is tested, and a correlation between occurrence frequencies is found at inter-annual but not daily time-scales. Precipitation is attributed to the tropical lows and it is found that tropical lows are associated with 31% of rainfall across tropical southern Africa, based on gridded precipitation products. The inter-annual variability of the number of tropical lows that form\ud 34 per year (σ = 6 events/annum) is linked to ENSO and the tropical easterly jet. The mean latitude of tropical lows is shifted northwards during El Nino and southwards during La Nina. Much of the inter-annual precipitation variability maximum in Angola is attributed to rainfall associated with tropical lows. These results provide insights into the southern African response to ENSO and into the mechanisms of rainfall in the southern African tropical edge.