Chaotic advection, mixing, and property exchange in three-dimensional ocean eddies and gyres

Brett, Genevieve

doi:10.1575/1912/10413

Cited by 2 publications

(3 citation statements)

References 34 publications

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“…Data availability statement. All needed data are available: Brett (2020a) has raw output for daily T, S, and 3D velocities; Brett (2020c) has rotated daily and 148-day mean velocities; Brett (2020b) has all budget terms, manifolds, and their frequency maps. Code for creating manifolds and Eulerian budgets are available as well from Brett (2020d).…”

Section: Appendixmentioning

confidence: 99%

The Western Alboran Gyre: An Analysis of Its Properties and Its Exchange with Surrounding Water

Brett

Pratt

Rypina

et al. 2020

Journal of Physical Oceanography

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One of the largest and most persistent features in the Alboran Sea is the Western Alboran Gyre (WAG), an anticyclonic recirculation bounded by the Atlantic Jet (AJ) to the north and the Moroccan coast to the south. Eulerian budgets from several months of a high-resolution model run are used to examine the exchange of water across the Eulerian WAG’s boundary and the processes affecting the salinity, temperature, and vorticity of the WAG. The volume transport across the sides of the WAG is found to be related to vertical isopycnal movement at the base of the gyre. Advection is found to drive a decay in the salinity minimum and anticyclonic vorticity of the Eulerian WAG. Given the large contributions of advection, a Lagrangian analysis is performed, revealing geometric aspects of the exchange that are hidden in an Eulerian view. In particular, stable and unstable manifolds identify a stirring region around the outer reaches of the gyre where water is exchanged with the WAG on a timescale of weeks. Its complement is an inner core that expands with depth and exchanges water with its surroundings on much longer timescales. The 3D evolution of one parcel, or lobe, of water as it enters the WAG is also described, identifying a general Lagrangian subduction pathway.

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Section: Appendixmentioning

confidence: 99%

The Western Alboran Gyre: An Analysis of Its Properties and Its Exchange with Surrounding Water

Brett

Pratt

Rypina

et al. 2020

Journal of Physical Oceanography

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“…In order to investigate the dynamics of the gyre flow field in more detail, the effects of the different terms in the momentum equation are considered. For this, the vertically averaged horizontal momentum equation over the depth layers influenced by the gyre velocity field (i.e., the thermocline layer and epilimnion) is expressed as (Brett, 2018; Brett et al., 2020; Cimatoribus et al., 2018; Vallis, 2017):

\frac{\partial {\boldsymbol{U}}_{\boldsymbol{h}}}{\partial \boldsymbol{t}}=\boldsymbol{P}+\boldsymbol{N}+\boldsymbol{C}+\boldsymbol{F}-\boldsymbol{D}

where U h = ( u , v ) is the horizontal velocity field,

\boldsymbol{P}=\left(-\frac{1}{\rho }\frac{\partial P}{\partial x},-\frac{1}{\rho }\frac{\partial P}{\partial y}\right)

is the acceleration induced by the barotropic and baroclinic pressure gradients,

\boldsymbol{N}=\left(-\left(\overrightarrow{\boldsymbol{u}}.\nabla \right)u,-\left(\overrightarrow{\boldsymbol{u}}.\nabla \right)v\right)

is the acceleration caused by the nonlinear (advection) terms, C = ( fv , − fu ) is the acceleration caused by the Coriolis effect, F = ( F x , F y ) is the acceleration induced by external forces, and D = (− ν ∇ 2 u ,− ν ∇ 2 v ) is the deceleration due to dissipation (i.e., bulk, lateral, and bottom friction).

\overrightarrow{\boldsymbol{u}}

is the three‐dimensional velocity vector, ν is viscosity, 𝜌 is density, and t is time.…”

Section: Discussionmentioning

confidence: 99%

“…In order to investigate the dynamics of the gyre flow field in more detail, the effects of the different terms in the momentum equation are considered. For this, the vertically averaged horizontal momentum equation over the depth layers influenced by the gyre velocity field (i.e., the thermocline layer and epilimnion) is expressed as (Brett, 2018;Brett et al, 2020;Cimatoribus et al, 2018;Vallis, 2017):…”

Section: Nonlinear Dynamics Associated With a Cyclonic Gyrementioning

confidence: 99%

Chimney‐Like Intense Pelagic Upwelling in the Center of Basin‐Scale Cyclonic Gyres in Large Lake Geneva

et al. 2023

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Basin‐scale quasi‐geostrophic gyres are common features of large lakes subject to Coriolis force. Cyclonic gyres are often characterized by dome‐shaped thermoclines that form due to pelagic upwelling that takes place in their center. At present, the dynamics of pelagic upwelling within the surface mixed layer (SML) of large lakes are poorly documented. A unique combination of high‐resolution 3D numerical modeling, satellite imagery and field observations allowed confirming, for the first time in a lake, the existence of intense pelagic upwelling in the center of cyclonic gyres under strong shallow (summer) and weak deep (winter) stratified conditions/thermocline. Field observations in Lake Geneva revealed that surprisingly intense upwelling from the thermocline to the SML and even to the lake surface occurred as chimney‐like structures of cold water within the SML, as confirmed by Advanced Very High‐Resolution Radiometer data. Results of a calibrated 3D numerical model suggest that the classical Ekman pumping mechanism cannot explain such pelagic upwelling. Analysis of the contribution of various terms in the vertically averaged momentum equation showed that the nonlinear (advective) term dominates, resulting in heterogeneous divergent flows within cyclonic gyres. The combination of nonlinear heterogeneous divergent flow and 3D ageostrophic strain caused by gyre distortion is responsible for the chimney‐like upwelling in the SML. The potential impact of such pelagic upwelling on long‐term observations at a measurement station in the center of Lake Geneva suggests that caution should be exercised when relying on limited (in space and/or time) profile measurements for monitoring and quantifying processes in large lakes.

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Chaotic advection, mixing, and property exchange in three-dimensional ocean eddies and gyres

Cited by 2 publications

References 34 publications

The Western Alboran Gyre: An Analysis of Its Properties and Its Exchange with Surrounding Water

The Western Alboran Gyre: An Analysis of Its Properties and Its Exchange with Surrounding Water

Chimney‐Like Intense Pelagic Upwelling in the Center of Basin‐Scale Cyclonic Gyres in Large Lake Geneva

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