The Relationship of Interannual Variability in Western Equatorial Africa to the Tropical Oceans and Atmospheric Circulation
This study aims to unravel the driving factors of rainfall variability on interannual time-scales and for extreme events over western equatorial Africa (WEA). We first defined homogeneous and contiguous regions with respect to interannual rainfall variability, using different clustering techniques....
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| Format: | Others |
| Language: | English English |
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Florida State University
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| Online Access: | http://purl.flvc.org/fsu/fd/FSU_migr_etd-7176 |
| Summary: | This study aims to unravel the driving factors of rainfall variability on interannual time-scales and for extreme events over western equatorial Africa (WEA). We first defined homogeneous and contiguous regions with respect to interannual rainfall variability, using different clustering techniques. The spatial patterns are seasonally dependent and demonstrate the remarkable heterogeneity of the region. They also are dissimilar to those based on the annual cycle, confirming the difference in their driving factors. Once regionalization was accomplished, we examined how global SST and SLP and well-established modes of variability are related to interannual rainfall variability. The relationships are seasonally and regionally dependent, and we found ocean sectors that detect such links better than the variability modes. That is more crucial when the correlations are evident three months in advance, and provide forecast potential. We then analyzed the driving factors of extreme rainfall events for four select cases. Three of those are the coastal regions. JFM, AMJ and OND are variously considered. The fourth case is the eastern WEA region during OND. The SST-rainfall links are in agreement with the interannual analysis. Moreover, while the extreme rainfall events are associated with the local ocean regions through the induced convective activity and static stability, they are modulated dynamically by remote forcing from the distant oceans via an atmospheric bridge. In addition, we suggest that the moisture availability does not determine the amount of rainfall, and the role of SST as a moisture provider is less important than as a modulator of vertical motion. However, the moisture flux divergence shows apparent contrast between wet and dry composites. === A Dissertation submitted to the Department of Earth, Ocean and Atmospheric Science in partial fulfillment of the
requirements for the degree of Doctor of Philosophy. === Summer Semester, 2011. === June 2, 2011. === Includes bibliographical references. === Sharon E. Nicholson, Professor Directing Dissertation; Allan J. Clarke, University Representative; Jon E. Ahlquist, Committee Member; Guosheng Liu, Committee Member; Philip Sura, Committee Member. |
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