Master's thesis defense by Peder Heiselberg – Niels Bohr Institute - University of Copenhagen

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Master's thesis defense by Peder Heiselberg

Title: The effect on Agulhas Rings by the Southern Ocean wind stress

Abstract: High resolution 1/10 ◦ General Circulationn Model (GCM) simulation data is analyzed to investigate the effects on Agulhas leakage via Agulhas Rings by change in
Southern Ocean wind stress. 11 years of control data and 16 years of data with a
15% increase in Southern Ocean wind stress (tau15) is used. By developing a tay-
lored search and track algorithm, 45 and 73 Agulhas Rings were detected in their
respective dataset. A 12% increase in Agulhas Ring generation is found indicating
a correlation but this is within one standard deviation of statistical fluctuations. A
seasonal cycle in Agulhas Ring formation is visible in the tau15 data. The Agul-
has Rings were found to have a mean radius of 140km and a translational velocity
of 6cm/s. A 14.5% increase in velocity were found in the tau15 data. The poten-
tial vorticity of the Agulhas Rings were found to be constant in the first 1000km of
the Agulhas Current retroflection. Four years of low Agulhas Ring generation is
observed to coincide with a lack of Natal Pulses in the Agulhas Current strongly
indicating a relation. The excess production of Agulhas Rings by Natal Pulses is,
however, within statistical fluctuations.