Schwarzkopf, Franziska Ulrike (2008) Decadal variability of the Southern Hemisphere Supergyre. (Diploma thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 58 pp.

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Abstract

Recent observational studies have suggested a strengthening gyre circulation in the western south Pacific Ocean over the past 2 decades, possibly representing a main cause of pronounced warming tendencies in the Tasman Sea. The objective of the present study was to examine the nature of these changes in a broader context, the interannual to decadal variability of the Southern Hemisphere Supergyre, by analyzing a sequence of global ocean circulation models with different resolution and forcing. Two hindcast experiments (from 1958 to 2004) with half of a degree and quarter of a degree resolution respectively, reproduce the main patterns of the seasonal variability compared to observational analysis. The solutions reveal large-scale patterns of decadal-scale variations in the gyre intensity of all three ocean basins, reflected in changes in Western Boundary Current transports. A set of sensitivity experiments exposees the gyre circulation in the oceans' interiors being mainly affected by changes in the wind forcing. However, in the Western Boundary Currents, non-linear dynamics dominate the behaviour of the circulation. Local observations of the circulation were compared to their modelled equivalents and mostly recovered
in them. The observed trends over the last 20 years were almost exactly reproduced in the model experiments, but appear embedded in the longer time series as part of variability on interannual to multi-decadal time scales.

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