Publication Date

2016-11-08

Availability

Embargoed

Embargo Period

2017-11-08

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Meteorology and Physical Oceanography (Marine)

Date of Defense

2016-09-15

First Committee Member

William Johns

Second Committee Member

Mohamed Iskandarani

Third Committee Member

Christopher Meinen

Abstract

In this study, the role of westward propagating signals in driving year-to-year changes in the seasonal variability of the Florida Current (FC) transport is investigated based on controlled realistic numerical simulations carried out using the Regional Ocean Modeling System (ROMS). Different sets of idealized numerical experiments are performed with and without background flows associated with the FC to assess the different mechanisms involved, and include experiments initialized: (1) with single eddies of different sizes and intensities in the ocean interior without the background flow (SENS-E0x); (2) with single eddies at different latitudinal locations with the background flow; and (3) with eddy-full configurations in the ocean interior both with and without background flows. The main finding from this study is that westward propagating signals can cause transient seasonal variability in the FC transport by means of both direct and indirect forcing mechanisms, in which the forced response is characterized by seasonal variability associated with variable annual phase. In the direct forcing mechanism, westward propagating signals cause a two stage response in the Florida Straits, in which the first stage is characterized by the development of barotropic velocity anomalies linked with the eddy-induced Rossby wave field, and the second stage is linked with the development of baroclinic wall-jets that propagate through Northwest Providence Channel. In the indirect forcing mechanism, westward propagating signals originating in the open ocean perturb the eddy field offshore of the Gulf Stream in a manner analogous to the “butterfly effect”, which can drive the Gulf Stream variability to evolve into different state. The perturbed Gulf Stream variability is then linked to the Florida Straits through baroclinic coastally trapped signals that travel along the east U.S. coast. Results indicate that the in the real ocean, the indirect forcing mechanism may play a dominant role in linking the open ocean variability from westward propagating signals to the changes in the FC transport, while the direct response mechanism may play a secondary role. The FC response driven by westward propagating signals simulated by this study had an amplitude of ~2 Sv and is essentially linked with transient seasonal variability. Results reported here based on numerical simulations confirm findings from previous studies based on observations, which reported that year-to-year changes in the FC seasonality are largely linked with elevated levels of background transient variability due to westward propagating signals originating in the open ocean. In addition, the mechanisms reported here can be potentially linked to year-to-year changes in the seasonality of the Meridional Overturning Circulation (MOC) and Meridional Heat Transport (MHT), given that the FC corresponds to an important component of the MOC and MHT.

Keywords

Western Boundary Current; Rossby Waves; Meridional Overturning Circulation; Satellite Altimetry; ROMS; Mesoscale Eddies; Coastal Sea-level

Available for download on Wednesday, November 08, 2017

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