Influence of the Indian Ocean Subtropical Dipole on the Agulhas current

Master Thesis

2014

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http://hdl.handle.net/11427/9207
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thesis_sci_2014_sovara_mv.pdf (4.19 MB)
Authors
Sovara, Mthetho Vuyo
Supervisors
Hermes, Juliet
Reason, Chris
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University of Cape Town

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Department of Oceanography
Faculty
Faculty of Science
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Abstract
Modern studies have successfully linked Subtropical Dipole (SIOD) events to southern Africa’s austral summer precipitation patterns, however, none have investigated the SIOD’s influence on the Greater Agulhas Current System. Here, the SIOD climatology was developed using a Regional Ocean Modeling System (ROMS) configured with GFDL-CORE v.2b reanalysis winds and heat fluxes for the 1958-2007 period. This configuration allows for a relatively accurate spatial and temporal account of the Sea Surface Temperature (SST) and Sea Surface Height (SSH) variability in the Subtropical Indian Ocean (SIO). Simulation and evaluation of SIOD events was achieved through the application of the Empirical Orthogonal Function (EOF), Wavelet Analysis and Composite Map Analysis. The EOF applied to monthly SST anomalies for the months January to December during the years 1958-2007 in the SIO resulted in the SIOD phenomenon emerging as the second EOF mode and explaining 8.93 of the total variance of the SIO. Moreover, the EOF applied only to the austral summer (JFM) months emerges the SIOD as the first EOF mode and explaining 20.84 of the total variance in the SIO. ROMS model results and statistical correlation results suggest that SIOD SST variability is neither linked to the El Nino-Southern Oscillation (ENSO) nor the Tropical Indian Ocean Dipole (IOD) phenomena, notwithstanding that SIOD events have in the past, coincided with some El Nino and La Nina events. Composite map analysis results suggest no significant influence of SIOD events on anomalous Agulhas Current SST and SSH during positive and negative SIOD years. Examination of lagged statistical correlations also showed no significant relationship between the anomalous SIOD index and the satellite derived geostrophic velocity at the core of the Agulhas Current for the period 1993-2007.
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Includes bibliographical references.

Reference:

Sovara, M. 2014. Influence of the Indian Ocean Subtropical Dipole on the Agulhas current. University of Cape Town.

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