Lagrangian Studies of Fluid Exchange between the Gulf Stream and Surrounding Waters

Song, Tao; Rossby, T.; Carter, Everett

doi:10.1175/1520-0485(1995)025<0046:lsofeb>2.0.co;2

Cited by 34 publications

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“…These waters also have different concentrations of tracers, such as oxygen and biological species. Clearly then, the Gulf Stream acts as a boundary between the two water masses, and yet observations of oxygen concentrations [Bower et al, 1985] and Lagrangian subsurface drifters [Song et al, 1995] have shown that exchange does occur within the Gulf Stream system. These studies have spurred several analytical and modeling investigations of the nature of mixing and stirring within a meandering, propagating jet [Bower, 1991 In this study we consider Lagrangian observations of exchange in the continuation of the Gulf Stream, the North north.…”

Section: Introductionmentioning

confidence: 99%

Pathways of cross‐frontal exchange in the North Atlantic Current

Dutkiewicz¹,

Rothstein²,

Rossby³

2001

J. Geophys. Res.

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Abstract. The North Atlantic Current (NAC) forms part of the boundary between the subtropical and subpolar gyres in the North Atlantic Ocean. The current has topographically controlled stationary meanders that appear to grow and decay. A region east of the current in the Newfoundland Basin contains water of mixed subpolar/subtropical properties, suggesting that there is exchange across the NAC. This study considers data from isopycnal RAFOS floats launched in the NAC region from 1993 to 1995. We use the RAFOS data to define the "frontal zone" as a pressure range where the jet is most likely to be found. This definition requires a latitudinal dependence as the NAC shoals to the north. Floats shallower and deeper than this range are defined to be on the subpolar and subtropical side, respectively. These definitions are used to estimate mixing that occurs between the current and its surroundings and to estimate the relative quantity of exchange of water parcels between the two gyres. Only small quantities of mass exchange from one gyre to the other are found, but there is a distinct asymmetry leading to a mean flux from the subpolar to subtropical sides. We also find that floats spend significant time in the frontal region and are frequently exchanged between fast and slow moving waters, particularly at the meander extrema. Diffusion, while in the jet, leads to eddy cross-frontal exchange which is important for the exchange of properties across the NAC. IntroductionRecent studies have explored the mechanisms and frequency of exchange between strong oceanic jets and surrounding slower moving waters and the exchange of water parcels and water properties between two different physical or chemical regions. One of the most intensely studied dynamic fronts is that associated with the Gulf Stream. This ocean current separates the warm, salty Sargasso Sea from the fresher, colder slope water. These waters also have different . The data collected by these floats are discussed in section 2. We differentiate between two processes: the loss of water parcels from the fast moving jet to slower moving surrounding waters and the exchange of mass and properties between the two gyres to either side of the NAC. In section 3 we define specific regimes, such as the "jet" and the "frontal zone," to aid in the investigation of these processes. In section 4 we determine statistics from the float data that provide a measure of the mixing. In section 5 we discuss and summarize these results.

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Section: Introductionmentioning

confidence: 99%

Pathways of cross‐frontal exchange in the North Atlantic Current

Dutkiewicz¹,

Rothstein²,

Rossby³

2001

J. Geophys. Res.

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“…The color in Figure 3 indicates the depth of a float, so tracks trend bluer when curving clockwise in the north and redder when curving anticlockwise in the south. The vertical displacements can be a sizable fraction of the ∼600-m total deepening of isopycnals from one side to the other (Bower & Rossby 1989, Song et al 1995. Bower (1989) identified a well-defined pattern of horizontal convergence and divergence upstream and downstream of meander troughs.…”

Section: Frontsmentioning

confidence: 97%

“…At greater depths, where the downstream velocity is lower, exchange across the stream becomes increasingly possible. This cross-stream leakage from the subpolar to subtropical side happens along the full length of the stream (Song et al 1995) and along its northern branch, the North Atlantic Current (Dutkiewicz et al 2001).…”

Section: Frontsmentioning

confidence: 99%

Visualizing and Quantifying Oceanic Motion

Rossby

2016

Annu. Rev. Mar. Sci.

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Here I review the use of two highly complementary acoustical technologies for measuring currents in the ocean: acoustically tracked neutrally buoyant floats and vessel-mounted acoustic Doppler current profilers (ADCPs). The beauty of floats lies in their ability to efficiently and accurately visualize fluid motion in fronts and vortices and the dispersion caused by mesoscale eddy processes. Floats complement classical hydrography by articulating mechanisms and pathways by which waters spread out from their source region. Vessel-mounted ADCPs can profile the water column at O(1 km) horizontal resolution to depths greater than 1,000 m. These vessel-based scans capture in detail the cross-stream structure of fronts and eddies as well as the impact of bathymetry on currents. Sustained sampling along selected routes builds up valuable databases both for statistical studies of the submesoscale velocity field and for accurate estimates of fluid transport, as well as how these vary over time.

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“…While the filaments are highly visible against the cold waters, the warm outbreaks may actually have a larger volume exchange than do the warm filaments due to the deepening of the GS on the Sargasso Sea side. In possible support of this, Song et al (1995) noted that Lagrangian floats deployed in the center of the GS on the 26.8 t surface (temperature ϭ 15°C in the main thermocline) were more likely to exit the stream to the south than to the north. Of course, both mechanisms could contribute to the tendency for surface drifters to exit the stream to the south.…”

Section: Introductionmentioning

confidence: 96%

“…The warm GS meanders east past the New England Seamount Chain (NESC) where its mean path shifts roughly 1-1.5°to the north (Cornillon, 1986;Song et al, 1995). The meandering structure steepens considerably over and to the east of the NESC.…”

Section: Introductionmentioning

confidence: 99%

Drifters in the Gulf Stream

McGrath¹,

Rossby²,

Merrill³

2010

J Mar Res

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In the past, the Gulf Stream has frequently been viewed as essentially a barrier between the Slope and Sargasso seas. On the other hand, surface drifters have often been observed to leave the stream to the south. To gain a better understanding of surface flow of the Gulf Stream, we used drifter trajectory data to study their drift east and patterns of loss from the current. Two sets of drifter data were used, one from the 1995-1999 Georges Bank GLOBEC program and the other from the Global Drifter Program. We also made use of atmospheric wind stress estimates from a reanalysis data set to evaluate the effect of wind forcing on their movements. Without fail, all drifters that enter into the stream eventually detrain out of the current to the south, indicating significant cross-frontal transport at the surface. A first explanation of these detrainments relies on the Ekman drift to the south due to the westerly winds over the study area. However, the exits to the south are not uniformly distributed, but aggregate in three areas where the meandering is particularly sharp: the New England Seamount Chain, the Southeast Newfoundland Rise, and the 44°N trough in the North Atlantic Current. Although, intuitively, it would seem that the largest Ekman drift losses would occur in the winter, this study shows that the detrainment to the south occurs more effectively in the summer due to a minimum in the mixed layer depth.

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Lagrangian Studies of Fluid Exchange between the Gulf Stream and Surrounding Waters

Cited by 34 publications

References 0 publications

Pathways of cross‐frontal exchange in the North Atlantic Current

Pathways of cross‐frontal exchange in the North Atlantic Current

Visualizing and Quantifying Oceanic Motion

Drifters in the Gulf Stream

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