613 Seminar: Amin Koorehpazan Dezfuli

USRA-NPP, Code 613

Our analysis suggests that the interannual variability of rainfall in Western and Central Equatorial Africa (WCEA) is more strongly associated with atmospheric parameters, manifested in the form of Walker-like circulations, than with local sea surface temperatures. Changes in both intensity and location of these circulation cells, which control the rainfall variability, appear to be modulated by the remote forcing from the Pacific Ocean via an atmospheric bridge. The causal mechanisms of extreme dry and wet conditions are strongly seasonally and regionally specific due to the fact that the WCEA is a climatic transition zone with extreme spatial heterogeneity of interannual variability. We also examined the intraseasonal variability over the entire equatorial Africa, and found a dipole mode in precipitation during the winter Indian monsoon. Governing factors of the dipole mode involve simultaneous changes in subtropical highs in both hemispheres. This mode, which is the dominant source of synoptic-scale variability in precipitation over the region, provides a mechanism of atmospheric communication between eastern and western equatorial Africa—two regions that are generally treated as climatically separate units. The behavior of the dipole and associated precipitation extremes depends on the position and intensity of subtropical highs, which are projected to change in a warming climate.