Synoptic scale convection and wave activity over tropical Africa and the Atlantic

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منو

" Synoptic scale convection and wave activity over tropical Africa and the Atlantic "
Ademe Mekonnen C. Thorncroft

Document Type	:	Latin Dissertation
Language of Document	:	English
Record Number	:	52921
Doc. No	:	TL22875
Call number	:	‭3312238‬
Main Entry	:	Ademe Mekonnen
Title & Author	:	Synoptic scale convection and wave activity over tropical Africa and the Atlantic\ Ademe Mekonnen
College	:	State University of New York at Albany
Date	:	2007
Degree	:	Ph.D.
student score	:	2007
Page No	:	158
Abstract	:	The objective of this research is to investigate synoptic scale convection and its association with wave disturbances over eastern Atlantic and tropical Africa. Analyses of convection highlight a significant peak periodicity in 2-6 day time scale over the Atlantic and most of tropical North Africa. The 2-6 day convective variance is the same order of magnitude over West and East Africa and accounts for 25%-35% of the total variance. However, dynamical measures of the African easterly wave (AEW) activity showed marked differences, variances over the West being more than the East. The explanation for this is that AEWs are initiated by convective precursors in the east and grow as they propagate westwards along the African easterly jet. Results show two major regions of synoptic time scale convection that are important for AEW initiation: the Darfur mountains (∼20°E) and the Ethiopian highlands (35°-40°E), with the former being more consistent and coherent. This study also shows the presence of eastward moving convective structures over tropical Africa, which are associated with Kelvin waves. The Kelvin waves originate in the Pacific and propagate across Africa. An important aspect of the Kelvin wave activity is its impact on convection and rainfall and its interaction with AEWs. Analysis of July-September 1987 weather events showed that convection and rainfall increase in association with Kelvin waves over tropical Africa. This event also suggested a series of AEWs initiated in association with Kelvin convection over tropical Africa. Spectral analysis of convection indicates a significant 3-4 day periodicity over Central Sudan, a region not known for wave disturbances. Two key factors that are associated with this variance are: (a) convective variability over equatorial Congo, and (b) upper level easterly waves that originate over Bay of Bengal-Southeast Asia. Results show the presence of a dipole pattern between the equatorial and East African convection that oscillates on a 4-day time scale. It is suggested that the two regions interact through a recharge-discharge process. This study also shows that convection over East Africa enhances in association with anomalous northerlies and weakens in association with southerlies in the upper troposphere.
Subject	:	Health and environmental sciences; Earth sciences; Synoptic scale convection; African easterly wave; Kelvin waves; Convective dipole; Easterly jets; Atlantic Ocean; Africa; Atmospheric sciences; Environmental science; 0768:Environmental science; 0725:Atmospheric sciences
Added Entry	:	C. Thorncroft
Added Entry	:	State University of New York at Albany