East African Rains of 1961/62 and The Abrupt Change of The White Nile Discharge

The excessive rainy season 1961/2 over East Africa — causing a discontinuous rise of Lake Victoria and the discharge of the White Nile lasting at least twenty years — coincides with an even larger anomaly of sea surface temperature, surface winds and convective cloudiness at the western equatorial Indian Ocean. Together this anomaly extended over at least 6 x 10 6 km 2 and lasted more than four months. In many respects, it resembles the ENSO events in the equatorial Pacific; in contrast to it it is characterized by a lack of surface westerlies. Eighty to ninety percent of the area-averaged rainfall (in the order of 16-24 mm/d) is contributed by large-scale convergence of water vapour transport; the liberation of latent heat by rainfall during November 1961 surpasses, over areas of more than 10 5 km 2 , the solar constant.