Original paper
Relationship between the October–December rainfall in Tanzania and the Walker circulation cell over the Indian Ocean
Limbu, Paul Tilwebwa Shelleph; Tan, Guirong
Meteorologische Zeitschrift Vol. 28 No. 6 (2019), p. 453 - 469
39 references
published: Dec 27, 2019
published online: Feb 12, 2019
manuscript accepted: Jan 3, 2019
final revised version received: Dec 29, 2018
manuscript revision requested: Aug 21, 2018
manuscript received: Jul 9, 2018
Open Access (paper may be downloaded free of charge)
Abstract
Like most of the countries in the Great Horn of Africa, Tanzania is prone to floods and droughts. Anomalously wet years over the region are associated with low-level convergence, the advection of moisture from both the Indian Ocean and the Congo and an ascending limb of the Walker circulation cell centered over the western Indian Ocean (WIO). During positive Indian Ocean dipole (IOD) events, the Walker circulation cell over the Indian Ocean is well defined, and more so compared with observed during El Niño years. In El Niño years, the Walker circulation cell becomes weak compared with positive IOD events, where the zonal winds strengthen, resulting in active convective activities over the WIO. A key finding is that the Walker circulation cell developing over the Indian Ocean is strongly connected to IOD activity. The weakening of the Walker circulation cell is likely the reason for the decrease in rainfall during El Niño events compared with that of positive IOD events in recent years over Tanzania during the October–December season. The variability of the Walker circulation cell over the Indian Ocean can lead to extreme weather conditions, making the full understanding of the climate system essential. This is crucial for decision making about adaptation and mitigation measures for coping with climate change and for the minimization of huge socio-economic losses associated with extreme weather events in the region.
Keywords
Walker circulation cell • Rainfall • Indian Ocean Dipole • El Niño–Southern Oscillation • Variability • Tanzania