Type

Text

Type

Dissertation

Advisor

Flagg, Charles N. | Hameed, Sultan | Rossby, Thomas | Wilson, Robert | Donohue, Kathleen.

Date

2015-12-01

Keywords

Gulf Stream, Low-frequency variability | Physical oceanography

Department

Department of Marine and Atmospheric Science.

Language

en_US

Source

This work is sponsored by the Stony Brook University Graduate School in compliance with the requirements for completion of degree.

Identifier

http://hdl.handle.net/11401/76015

Publisher

The Graduate School, Stony Brook University: Stony Brook, NY.

Format

application/pdf

Abstract

The Gulf Stream's (GS) main mode of interannual variability, its latitudinal migration, has been shown to be atmospherically forced by the North Atlantic Oscillation (NAO), taking a 2 year lag into account. Observational and model data were used here to examine the structure of the GS's migration and the dynamics linking it to atmospheric forcing. The structure of the GS's interannual variability was investigated from different measures of GS position and transport at 38°N and 27°N (i.e. the Florida Current). Using a zonally averaged index, the local measurements of GS position at 38°N proved good representations of overall meridional shifting of the current. GS position and transport were shown linked to the NAO, though the relationship between the GS and the Florida Current transport was not found statistically significant. This indicated that the Florida Current does not have a detectable interannual signal downstream in the GS. Further investigation of the link between GS position and the NAO revealed the GS position has a more robust correlation with the Icelandic Low (IL) component of the NAO rather than with the NAO itself. Using Sea Surface temperature composites, it was shown that for anomalously low (west) IL pressure (longitude) corresponding to cooler surface temperatures in the Labrador Sea the GS position shifts north after a period of ~2 years. The relationship between GS and IL pressure (longitude) was further used to create a forecasting scheme for GS position one year ahead of time. The correlation between the resulting forecasted GS and the observed GS was 0.60, significant at 95% level. Insight into the 2-year delay between the GS and atmospheric forcing was obtained from mean structure and interannual variability of the Slope Sea and Labrador Current. Observations suggested there is a statistically significant link between the Labrador Current, the Slope Sea, and GS position. On 0.5 to 1 year time scales, increases (decreases) in Slope Sea transport lags southward (northward) shifts in GS position by 1 year (r=0.48, significant at 95% level), and cooler (warmer) SSTs in the Slope Sea lead southward (northward) shifts in GS position by 0.5 years (r=0.65, significant at 95% level). On longer time scales, Labrador Current transport and GS position are found significantly correlated (r=-0.68, significant at 95% level) where increases in Labrador Current transport lead southern shifts in GS position taking a 2 year lag into account. Finally, the connection between GS position, the Atlantic meridional overturning circulation (AMOC) and the regional biogeochemical cycle was investigated using coupled climate models and ocean temperature observations. GS position and the AMOC simulated from GFDL's Climate Model 2.1 found enhanced (weakened) AMOC significantly correlated with south (north) shifts in GS position on decadal time scale. Similarly, results from the GFDL Earth System Models indicated an enhanced (weakened) AMOC leads southward (northward) displacements in GS position and increases (decreases) in regional chlorophyll and nutrient concentrations. | The Gulf Stream's (GS) main mode of interannual variability, its latitudinal migration, has been shown to be atmospherically forced by the North Atlantic Oscillation (NAO), taking a 2 year lag into account. Observational and model data were used here to examine the structure of the GS's migration and the dynamics linking it to atmospheric forcing. The structure of the GS's interannual variability was investigated from different measures of GS position and transport at 38°N and 27°N (i.e. the Florida Current). Using a zonally averaged index, the local measurements of GS position at 38°N proved good representations of overall meridional shifting of the current. GS position and transport were shown linked to the NAO, though the relationship between the GS and the Florida Current transport was not found statistically significant. This indicated that the Florida Current does not have a detectable interannual signal downstream in the GS. Further investigation of the link between GS position and the NAO revealed the GS position has a more robust correlation with the Icelandic Low (IL) component of the NAO rather than with the NAO itself. Using Sea Surface temperature composites, it was shown that for anomalously low (west) IL pressure (longitude) corresponding to cooler surface temperatures in the Labrador Sea the GS position shifts north after a period of ~2 years. The relationship between GS and IL pressure (longitude) was further used to create a forecasting scheme for GS position one year ahead of time. The correlation between the resulting forecasted GS and the observed GS was 0.60, significant at 95% level. Insight into the 2-year delay between the GS and atmospheric forcing was obtained from mean structure and interannual variability of the Slope Sea and Labrador Current. Observations suggested there is a statistically significant link between the Labrador Current, the Slope Sea, and GS position. On 0.5 to 1 year time scales, increases (decreases) in Slope Sea transport lags southward (northward) shifts in GS position by 1 year (r=0.48, significant at 95% level), and cooler (warmer) SSTs in the Slope Sea lead southward (northward) shifts in GS position by 0.5 years (r=0.65, significant at 95% level). On longer time scales, Labrador Current transport and GS position are found significantly correlated (r=-0.68, significant at 95% level) where increases in Labrador Current transport lead southern shifts in GS position taking a 2 year lag into account. Finally, the connection between GS position, the Atlantic meridional overturning circulation (AMOC) and the regional biogeochemical cycle was investigated using coupled climate models and ocean temperature observations. GS position and the AMOC simulated from GFDL's Climate Model 2.1 found enhanced (weakened) AMOC significantly correlated with south (north) shifts in GS position on decadal time scale. Similarly, results from the GFDL Earth System Models indicated an enhanced (weakened) AMOC leads southward (northward) displacements in GS position and increases (decreases) in regional chlorophyll and nutrient concentrations. | 113 pages

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