Date of Award

Spring 2019

Document Type

Open Access Dissertation

Department

Marine Science

First Advisor

Subrahmanyam Bulusu

Abstract

The Indian summer monsoon is a complex, nonlinear phenomenon involving atmospheric, oceanic, and land-based interactions from June through September. During this period, a strong low-level jet known as the Findlater Jet develops over the western Arabian Sea, advecting seasonally high quantities of warm, moist air to the Indian subcontinent, leading to the largest precipitation rates on the planet. The winds associated with the Findlater Jet seasonally strengthen the Arabian Sea eddy field, known for its intensity and variability. Comparison between the eddies in the western Arabian Sea during monsoon regimes of varying intensities revealed more high-amplitude eddies in strong (high-rainfall) monsoon conditions as well as more extreme coastal upwelling.

Development and application of an eddy tracking algorithm has revealed new insights into the evolution, characteristics, and dissipation of eddies in the Arabian Sea using sea level anomalies. Through its application, this research finds that the highest number of identified eddies are along the coast of the Arabian Peninsula, but the most robust eddies are confined to the Somali Current region. This work explores whether the observed eddies are surface- or subsurface-intensified based on their salinity and temperature characteristics, finding a notable dominance of surface-intensified eddies. The eddy intensification type was clearly identified in this region, as surface-intensified eddies are characterized by warm, fresh cores in anticyclonic eddies and cool, saline cores in cyclonic eddies.

To better understand the role of mesoscale and sub-mesoscale features on the variability of mixed layer depth in the Arabian Sea, eddies and fronts were identified and investigated during strong and weak monsoon conditions. We found through the application of an eddy tracking algorithm, a spatial and temporal analysis of a variety of factors that impact mixed layer depth variability, and a heat budget analysis that there is an overall dominance of larger (smaller) features in strong (weak) monsoon conditions. To better understand how water masses change on longer temporal scales, a decadal analysis was conducted on the salt and volume transports throughout the Indian Ocean, finding that the strongest salinity variability was due to Indian Ocean Dipole and El Niño-Southern Oscillation (ENSO) events.

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