Mechanisms and prediction of climate variability in tropical North Africa
| dc.contributor.advisor | Jury, M. | |
| dc.contributor.author | Yeshanew, Adebe | |
| dc.date.accessioned | 2013-01-28T09:17:16Z | |
| dc.date.available | 2013-01-28T09:17:16Z | |
| dc.date.issued | 2003 | |
| dc.description | Submitted to the Faculty of Science in partial fulfillment of the degree of Doctor of Philosophy in the Department of Environmental Studies at the University of Zululand, South Africa, 2003. | en_US |
| dc.description.abstract | One of the monsoon regions of the world is the tropical North Africa. The Sahara Desert lies in contrast with the cool South Atlantic. The monsoon systems control the mean circulation of this region. Superimposed on this basic state, large-scale variability dictates the life of the people and their socio-economic activities. The tropical North Africa climate exhibits a spectra! energy mainly in the ENSO and decadal temporal band as revealed by wavelet transform. The lowland Sahelian climate swing reveals low frequency signals. The mountainous regions of tropical Northeast Africa exhibit higher frequency variability. This variability has one common factor: a large-scale east-west overturning that connects the Pacific and Atlantic. An upper-level velocity dipole is established that induces convection polarity between tropical North Africa and South America. The strength and the sign of opposing poles are determined by the Atlantic and Walker Circulations. This is verified using correlation based on longer timeseries (1950-2000). ENSO signal modulates tropical North Africa climate by surpassing other tropical SST through these Circulations. Tropical Atlantic SST modes and Indian Ocean SST dipole influence tropical North Africa climate variability through the connection of Atlantic Circulation. The impacts of these SSTs are more pronounced during non-ENSO years as their influences are masked by global ENSO mode of variability. The modulation of transverse Monsoon Circulation (in Indian Ocean where Tropical Easterly Jet is the upper limb) on this part of Africa climate operates in phase with Atlantic Circulation. More than 80% of the variance of the Sahelian climate variability is associated to this circulation. It as well imparts equally the Brazilian rainfall following the sign of the Atlantic Circulation velocity potential. One of the aspects that the Indian Ocean differs from other east-west Circulations is that the Monsoon Circulation leads the global ENSO in coherent mode and it explains 60% of the indo-Pacific SST variation. Locally, the African Easteriy Jet determines the north-south moisture and convection between Sahel and Guinea through Hadley Circulation. To understand the ocean's role in the tropical North Africa and South America convection polarity, subsurface thermocline temperature and heat content are analysed using singular value decomposition, correlation and composite analyses. One of the main results that come from these analyses is that the convection over tropical North Africa and South America are closely tied to subsurface properties of the tropical oceans. The nnost important ocean signal that is sensitive to Atlantic Zonal Circulation convection is the east-west sea-saw of the equatorial thermocline. The east-west upper-ocean dipole is manifested in the leading EOF modes in thermocline temperature and in heat content anomaly (HCA) in the Pacific Ocean and Indian Ocean. In the Atlantic however, the main climate signal is in the kinematic fields. In developing predictive equations for tropical North Africa climate variability, stable predictors were found: lower-level Atlantic and Pacific zonal wind. The key factor that leads to high hit rates in the prediction models is the 'memory' and stability of the equatorial ocean winds. The kinematic predictors outperfonn SST in hindcast fit by 33% with respect to Sahelian climate and river flow. The multi- decadal oscillation of angular momentum is shown to play a role in the predictability. The study therefore contributes to understanding of the climate variability and prediction of tropical North Africa climate by inclusion of the kinematic component of the climate system that is the means of ENSO transmission to Africa. | en_US |
| dc.identifier.uri | https://hdl.handle.net/10530/1135 | |
| dc.language.iso | en | en_US |
| dc.publisher | University of Zululand | en_US |
| dc.subject | Climate variability | en_US |
| dc.title | Mechanisms and prediction of climate variability in tropical North Africa | en_US |
| dc.type | Thesis | en_US |