Interannual variability of the Gulf Stream position: The role of atmospheric forcing

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The position of the Gulf Stream has a substantial impact on the regional climate of the northeastern United States and the marine environment of the Mid-Atlantic Bight. The northern edge of the Gulf Stream is marked by a sharp temperature front called the North Wall. While the point where the Gulf Stream diverges from the coast is remarkably stable, the latitude of the North Wall varies on a wide range of time scales east of Cape Hatteras. The proposed study will diagnose the dynamical processes linking interannual fluctuations in North Wall position to atmospheric forcing using observational products, high-resolution ocean reanalyses, and an eddy-resolving regional model of the Atlantic Ocean subjected to atmospheric forcing perturbations. Each of these tools will complement each other: the analysis of the observations will guide the selection of forcing perturbations applied to the regional model, the evolution of the regional model will inform the analysis of the observations by highlighting fields and regions of possible interest, and finally, the ocean reanalysis products will allow the evolution of the flow to be examined in a level of detail not available from observations alone. The proposed research will result in an improved understanding of the dynamical processes that contribute to the predictability of North Wall and form the basis for dynamical predictions of its position. This information could have significant utility for fisheries managers and local governments involved with planning responses to severe weather events. In addition, the graduate student involved in the project will be trained in oceanic and atmospheric dynamics, modern approaches to the numerical modeling of oceanic flows, and the statistical analysis of data; publications associated with this research will form the core of a doctoral thesis.Interannual variations in North Wall position have been linked to changes in the North Atlantic Oscillation (NAO), with low (high) NAO phases preceding southward (northward) shifts of the Gulf Stream by several years, although there is uncertainty concerning the time lag between the two systems. Correlations between North Wall position and the NAO are significantly enhanced when the NAO is decomposed into its component centers of action (CoAs), the Icelandic Low and the Azores High. Each of these CoAs has its own dynamics and evolution which can be characterized by pressure, latitude, and longitude. The NAO represents just one possible linear combination of these characteristics. Several mechanisms linking the North Wall's position and the NAO or its component CoAs have been proposed, including changes in the Eastern Atlantic wind regime communicated by baroclinic Rossby waves, variations of deep western boundary current transport due to changes in deep water production, and fluctuations in Labrador Current transport which alter the transport and composition of the Slope Sea. There is currently no consensus on which mechanisms are significant in the latitudinal movement of the Gulf Stream North Wall. The proposed research seeks address this gap in our knowledge.