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Interactions of mesoscale ocean dynamics with large-scale ocean and climate variability: case studies in the mid-latitude Pacific and tropical Indian oceans

  • Author(s): Delman, Andrew Spencer
  • Advisor(s): McClean, Julie L
  • Sprintall, Janet
  • et al.
Abstract

The large-scale climate system is driven by imbalances of the reservoirs of heat contained in the world oceans. The transport and redistribution of this heat is determined in part by nonlinear mesoscale eddies (radii ~50-200 km), as well as by planetary waves whose widths approach the size of mesoscale eddies away from the equator. In this dissertation, new analysis techniques are developed and implemented to assess oceanic phenomena in two regions: mesoscale eddy-mean flow interaction in the Kuroshio Extension (KE) region, and the effects of coastal Kelvin waves and mesoscale eddies in the Indian Ocean south of Java. In the KE region, a jet-following coordinate reference frame is used to quantify the contributions of eddies to the vorticity budget along the KE jet in a strongly eddying ocean general circulation model simulation, the Parallel Ocean Program (POP). The jet reference frame preserves synoptic gradients of the jet that are not accurately represented in multi-year Eulerian means. This analysis found that eddies tend to accelerate the jet just downstream of crests in the topographically-induced meanders, implying an intensification of frontal gradients in these areas. In the Indian Ocean, a method involving projections of harmonic basis functions onto altimetry-derived sea level anomaly (SLA) is used to estimate Kelvin wave activity along the equatorial-coastal waveguide. The resulting Kelvin wave coefficient presents a more accurate representation of Kelvin wave activity than that from raw SLA. Moreover, values of the Kelvin wave coefficient in April-June are a robust predictor of positive Indian Ocean Dipole (pIOD) event development later in the calendar year. Finally, a temperature budget using a strongly eddying POP simulation isolates the specific contributions of mesoscale processes south of Java. It shows that Kelvin waves and local wind forcing both contribute substantially to anomalous cooling during pIOD years, while mesoscale eddies have a modest warming effect. These results suggest that mesoscale processes in the study regions have an important influence on the ocean's structure and can trigger a climate response; use of the new analysis techniques may help quantify the effects of mesoscale eddies and planetary waves elsewhere in the oceans.

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