




Wenegrat, Jacob O.; Thomas, Leif N.; Gula, Jonathan; Mcwilliams, James C.. 
Nonconservative processes change the potential vorticity (PV) of the upper ocean, and later, through the subduction of surface waters into the interior, affect the general ocean circulation. Here we focus on how boundary layer turbulence, in the presence of submesoscale horizontal buoyancy gradients, generates a source of potential vorticity at the ocean surface through a balance known as the Turbulent ThermalWind. This source of PV injection at the submesoscale can be of similar magnitude to PV fluxes from the wind and surface buoyancy fluxes, and hence can lead to a net injection of PV onto outcropped isopycnals even during periods of surface buoyancy loss. The significance of these dynamics is illustrated using a highresolution realistic model of the... 
Tipo: Text 
Palavraschave: Ageostrophic circulations; Atmosphereocean interaction; Fronts; Ocean dynamics; Potential vorticity; Boundary layer. 
Ano: 2018 
URL: http://archimer.ifremer.fr/doc/00452/56347/57937.pdf 
 


Vandermeirsch, Frederic; Carton, Xavier; Morel, Yves. 
The interaction between a stable zonal jet and a vortex is studied numerically with two oneandahalf layer models, one with quasigeostrophic dynamics, the other with shallowwater equations. In both models, simulations on the fplane evidence three regimes occuring with increasing vortex strength: (regime 1) weak vortices do not cross the jet and steadily drift along it; (regime 2) stronger vortices cross the jet, tear an oppositesign meander from the jet with which they pair as a dipole; the trajectory of this dipole depends on the strength of the initial vortex; since most dipoles are asymmetric, they veer back towards the jet axis where they are split apart in the ambient shear; (regime 3) even stronger vortices cross the jet and tear a vorticity... 
Tipo: Text 
Palavraschave: Potential vorticity; Vortices; Jets; Nonlinear equations; Stratified flow; Rotating fluids. 
Ano: 2003 
URL: http://archimer.ifremer.fr/doc/2003/publication440.pdf 
 


Vandermeirsch, Frederic; Carton, Xavier; Morel, Yves. 
In a twoandahalflayer quasigeostrophic model, a process study is conducted on the interaction between a vortex and a zonal jet, both with constant potential vorticity. The vortex is a stable anticyclone, initially located north of the eastward jet. The potential vorticity of the jet is allowed to have various vertical structures, while the vortex is concentrated in only one layer. The flow parameters are set to values characteristic of the Azores region. First, the jet is stable. Weak vortices steadily drift north of the jet without crossing it while strong vortices can cross the jet and tear off a cyclone with which they pair as a heton (baroclinic dipole). This heton often breaks later in the shear exerted by the jet; the two vortices finally... 
Tipo: Text 
Palavraschave: Potential vorticity; Vortices; Jets; Nonlinear equations; Stratified flow; Rotating fluids. 
Ano: 2003 
URL: http://archimer.ifremer.fr/doc/2003/publication441.pdf 
 


Morel, Yves; Gula, Jonathan; Ponte, Aurelien. 
Taking advantage of alternative expressions for potential vorticity (PV) in divergence forms, we derive balances between volume integral of PV and boundary conditions, that are then applied to practical computations of PV: • we propose a new method for diagnosing the Ertel potential vorticity from model output, that preserves the balances; • we show how the expression of PV can be derived in general coordinate systems. This is here emphasised with isopycnic coordinates by generalising the PV expression to the general NavierStokes equations; • we propose a generalised derivation for the HaynesMcIntyre impermeability theorem, which highlights the role of the bottom boundary condition choice (e.g. noslip vs freeslip) and mixing near the bottom boundary... 
Tipo: Text 
Palavraschave: Potential vorticity; Boundary conditions; General circulation; Vortex; Fronts; Boundary layers. 
Ano: 2019 
URL: https://archimer.ifremer.fr/doc/00494/60525/63988.pdf 
 

 

 


Buckingham, Christian; Gula, Jonathan; Carton, Xavier. 
In this study, we examine the role of curvature in modifying frontal stability. We first evaluate the classical criterion that the Coriolis parameter f multiplied by the Ertel potential vorticity (PV) q is positive for stable flow and that instability is possible when this quantity is negative. The first portion of this statement can be deduced from Ertel’s PV theorem, assuming an initially positive fq. Moreover, the full statement is implicit in the governing equation for the mean geostrophic flow, as the discriminant, fq, changes sign. However, for curved fronts in cyclogeostrophic or gradient wind balance (GWB), an additional term enters the discriminant owing to conservation of absolute angular momentum L. The resulting expression, (1 + Cu)fq < 0 or... 
Tipo: Text 
Palavraschave: Instability; Ocean dynamics; Potential vorticity; Turbulence; Frontogenesis/frontolysis; Fronts; Vortices; Angular momentum. 
Ano: 2021 
URL: https://archimer.ifremer.fr/doc/00677/78920/81288.pdf 
 


Buckingham, Christian; Gula, Jonathan; Carton, Xavier. 
We continue our study of the role of curvature in modifying frontal stability. In Part I, we obtained an instability criterion valid for curved fronts and vortices in gradient wind balance (GWB): Φ′ = L′q′ < 0, where L′ and q′ are the nondimensional absolute angular momentum and Ertel potential vorticity (PV), respectively. In Part II, we investigate this criterion in a parameter space representative of lowRichardsonnumber fronts and vortices in GWB. An interesting outcome is that, for Richardson numbers near 1, anticyclonic flows increase in q′, while cyclonic flows decrease in q′, tending to stabilize anticyclonic and destabilize cyclonic flow. Although stability is marginal or weak for anticyclonic flow (owing to multiplication by L′), the... 
Tipo: Text 
Palavraschave: Eddies; Fronts; Instability; Ocean circulation; Potential vorticity; Frontogenesis/frontolysis; Vortices; Angular momentum. 
Ano: 2021 
URL: https://archimer.ifremer.fr/doc/00677/78919/81286.pdf 
 


