Lateral diffusivity and Lagrangian scales in the Pacific Ocean as derived from drifter data

Zhurbas, Victor; Oh, Im Sang

doi:10.1029/2002jc001596

Cited by 96 publications

(99 citation statements)

References 19 publications

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“…The western Coral Sea atmospheric circulation is dominated by trade winds that vary in intensity and direction with the South Pacific Convergence Zone position [Vincent, 1994].The seasons in the western Coral Sea can be defined as the dry season which extends from April to September and the wet season, from October to March. Fratantoni [2001] defined an independent measurement as either being the result of more than one drifter per bin, or one drifter remained in a single bin for more than one Lagrangian integral time scale, taken here to be 6 d. This is the maximum Lagrangian time scale calculated in the Pacific [Zhurbas and Oh, 2003].…”

Section: Methodsmentioning

confidence: 99%

On the surface circulation in the western Coral Sea and residence times in the Great Barrier Reef

Choukroun¹,

Ridd²,

Brinkman³

et al. 2010

J. Geophys. Res.

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[1] Surface velocity observations from satellite tracked drifters made between 1987 and 2008 were used to resolve the surface circulation of the western Coral Sea, west of 158°E, and the Great Barrier Reef (GBR). The mean surface current map depicts well the major circulation patterns of the region, such as the position of the north Vanuatu and north Caledonia jets (NVJ and NCJ) and the western boundary currents. The North Queensland Current (NQC) and the East Australian Current (EAC) are well defined, flowing at speeds greater than 50 cm s −1 to the north, south of 15°S and 19°S, respectively. The NQC/EAC is mainly formed by the NVJ/NCJ flows, respectively. The presence of the Queensland Plateau greatly affects the westward flow, causing a zone of weak and highly variable currents that extends from 15°S to 18°S between the Queensland Plateau and the GBR shelf. Of the 235 drifters that crossed the western Coral Sea, 75 entered the GBR. Analysis of the drifter trajectories inside the GBR reveals the presence of a northwestward circulation at speeds of 22 cm s −1 north of 18°S and 0.5 cm s −1 south of 18°S. Drifter travel times used to evaluate the water residence times within the GBR indicate residence times of a few weeks for most of the lagoon.

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Section: Methodsmentioning

confidence: 99%

On the surface circulation in the western Coral Sea and residence times in the Great Barrier Reef

Choukroun¹,

Ridd²,

Brinkman³

et al. 2010

J. Geophys. Res.

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“…Although the following geophysical flows are inhomogeneous, using representative published values for the transverse eddy-diffusivity (κ), the transverse scale of the mean current (L), and transverse Lagrangian time scale (τ L ), the ratio τ L /τ D can be estimated. In the surfzone, τ L /τ D is as large as 0.5 (Spydell, Feddersen & Guza 2009), for surface currents in the Santa Barbara Channel it is as large as 0.1 (Dever, Hendershott & Winant 1998), as large as 0.5 for the Gulf Stream extension (McClean, Poulain & Pelton 2002), as large as 0.3 for the Kuroshio extension (Zhurbas 2003), as large as 0.25 for the California Current (Davis 1985), and as large as 0.1 for the Antarctic Circumpolar Current (Sallée et al 2008). For these flows, the effective longitudinal diffusivity may be affected by the presence of correlated random transverse motions (i.e.…”

Section: Shear Dispersion With a Non-zero Lagrangian Time Scalementioning

confidence: 99%

The effect of a non-zero Lagrangian time scale on bounded shear dispersion

Spydell

Feddersen

2011

J. Fluid Mech.

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Previous studies of shear dispersion in bounded velocity fields have assumed random velocities with zero Lagrangian time scale (i.e. velocities are$\delta $-function correlated in time). However, many turbulent (geophysical and engineering) flows with mean velocity shear exist where the Lagrangian time scale is non-zero. Here, the longitudinal (along-flow) shear-induced diffusivity in a two-dimensional bounded velocity field is derived for random velocities with non-zero Lagrangian time scale${\tau }_{L} $. A non-zero${\tau }_{L} $results in two-time transverse (across-flow) displacements that are correlated even for large (relative to the diffusive time scale${\tau }_{D} $) times. The longitudinal (along-flow) shear-induced diffusivity${D}_{S} $is derived, accurate for all${\tau }_{L} $, using a Lagrangian method where the velocity field is periodically extended to infinity so that unbounded transverse particle spreading statistics can be used to determine${D}_{S} $. The non-dimensionalized${D}_{S} $depends on time and two parameters: the ratio of Lagrangian to diffusive time scales${\tau }_{L} / {\tau }_{D} $and the release location. Using a parabolic velocity profile, these dependencies are explored numerically and through asymptotic analysis. The large-time${D}_{S} $is enhanced relative to the classic Taylor diffusivity, and this enhancement increases with$ \sqrt{{\tau }_{L} } $. At moderate${\tau }_{L} / {\tau }_{D} = 0. 1$this enhancement is approximately a factor of 3. For classic shear dispersion with${\tau }_{L} = 0$, the diffusive time scale${\tau }_{D} $determines the time dependence and large-time limit of the shear-induced diffusivity. In contrast, for sufficiently large${\tau }_{L} $, a shear time scale${\tau }_{S} = \mathop{ ({\tau }_{L} {\tau }_{D} )}\nolimits ^{1/ 2} $, anticipated by a simple analysis of the particle’s domain-crossing time, determines both the${D}_{S} $time dependence and the large-time limit. In addition, the scalings for turbulent shear dispersion are recovered from the large-time${D}_{S} $using properties of wall-bounded turbulence.

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“…Therefore, A4 and F10 are not different, (c) the residual flux was not presented in A4 and F10. We have shown that in both A4,F10 it is of the diffusive type with a mesoscale diffusivity that vanishes at the bottom of the ML, (d) however, the value of the surface diffusivity in such models is roughly h/H times smaller than what Zhurbas and Oh (2003) have derived using drifter data.…”

Section: A4 and F10 Modelsmentioning

confidence: 56%

“…The results of the four models intercomparison can be summarized as follows: (a) the F8 bolus velocity does not entail ML restratification which is known to exist, (b) the A4, F10 bolus velocities induce re-stratification but at the lowest order in the smallness parameter h/H, A4,F10 are not different (h, H are the ML and ocean depths, respectively), (c) using the W of A4, F8,10, we construct the corresponding F r 's; we reproduce the F8 result while the F r of A4, F10 are new since they were not given in the original work, (d) in both A4, F10, F r is diffusive with a mesoscale diffusivity that vanishes at the bottom of the ML, as expected, (e) however, their values at the surface is h/H times smaller than the value obtained by Zhurbas and Oh (2003), and finally, (f) only the C11 model accounts for wind and mean flow, which affect both the mesoscale fluxes and their kinetic energy.…”

Section: Introductionmentioning

confidence: 61%

See 1 more Smart Citation

Comparison of four mixed layer mesoscale parameterizations and the equation for an arbitrary tracer

Canuto¹,

Dubovikov²

2011

Ocean Modelling

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a b s t r a c tIn this paper we discuss two issues, the inter-comparison of four mixed layer mesoscale parameterizations and the search for the eddy induced velocity for an arbitrary tracer. It must be stressed that our analysis is limited to mixed layer mesoscales since we do not treat sub-mesoscales and small turbulent mixing.As for the first item, since three of the four parameterizations are expressed in terms of a stream function and a residual flux of the RMT formalism (residual mean theory), while the fourth is expressed in terms of vertical and horizontal fluxes, we needed a formalism to connect the two formulations. The standard RMT representation developed for the deep ocean cannot be extended to the mixed layer since its stream function does not vanish at the ocean's surface.We develop a new RMT representation that satisfies the surface boundary condition. As for the general form of the eddy induced velocity for an arbitrary tracer, thus far, it has been assumed that there is only the one that originates from the curl of the stream function. This is because it was assumed that the tracer residual flux is purely diffusive.On the other hand, we show that in the case of an arbitrary tracer, the residual flux has also a skew component that gives rise to an additional bolus velocity. Therefore, instead of only one bolus velocity, there are now two, one coming from the curl of the stream function and other from the skew part of the residual flux. In the buoyancy case, only one bolus velocity contributes to the mean buoyancy equation since the residual flux is indeed only diffusive.Published by Elsevier Ltd.

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Lateral diffusivity and Lagrangian scales in the Pacific Ocean as derived from drifter data

Cited by 96 publications

References 19 publications

On the surface circulation in the western Coral Sea and residence times in the Great Barrier Reef

On the surface circulation in the western Coral Sea and residence times in the Great Barrier Reef

The effect of a non-zero Lagrangian time scale on bounded shear dispersion

Comparison of four mixed layer mesoscale parameterizations and the equation for an arbitrary tracer

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