Interannual variations of the monthly rainfall anomalies over Tanzania from March to May and their associated atmospheric circulations anomalies

Although long rains (March-May) over Tanzania exhibit significant spatiotemporal variability and the existing literature has studied extensively on a seasonal scale, relatively less research has been geared toward analyzing it at monthly. In this study, the interannual variation in Tanzanian long rains was investigated on a monthly time scale. The study found that in March and April, the enhanced (reduced) surface westerly winds from the Congo basin occur during wet (dry) years. These anomalies arise from a higher geopotential height (GPH) gradient over the Congo basin (western Indian Ocean (IO)) than over the western IO (Congo basin) for wet (dry) years. The westerly winds transport moist air from the Congo basin and act to decelerate the mean flow from the south IO, leading to substantial lower level convergence over Tanzania. In May, surface southwesterly (southeasterly) winds play significant role in modulate rainfall amount in wet (dry) years. The lower-level high GPH anomalies over western IO appears to be related to an enhanced subsidence from upper levels, leading to below-normal rainfall in March to May. Likewise, rainfall anomalies over Tanzania are connected with upper level GPH anomalies over Madagascan region suggesting tropical-subtropical interactions. Overall, this study stresses the atmospheric circulations anomalies related to each monthly rainfall. This would enhance our understanding of climate drivers that control the seasonal rainfall to improve the fidelity of long rains prediction, thereby minimizing its associated disasters.