Results 1 
9 of
9
2006 The meridional flow of sourcedriven abyssal currents in a stratified basin with topography. Part I. Model development and dynamical properties
 University of Alberta, Edmonton
, 1995
"... A numerical simulation is described for sourcedriven abyssal currents in a 3660 km 3660 km stratified Northern Hemisphere basin with zonally varying topography. The model is the twolayer quasigeostrophic equations, describing the overlying ocean, coupled to the finiteamplitude planetary geostrop ..."
Abstract

Cited by 5 (3 self)
 Add to MetaCart
A numerical simulation is described for sourcedriven abyssal currents in a 3660 km 3660 km stratified Northern Hemisphere basin with zonally varying topography. The model is the twolayer quasigeostrophic equations, describing the overlying ocean, coupled to the finiteamplitude planetary geostrophic equations, describing the abyssal layer, on a midlatitude plane. The source region is a fixed 75 km 150 km area located in the northwestern sector of the basin with a steady downward volume transport of about 5.6 Sv (Sv 106 m3 s1) corresponding to an average downwelling velocity of about 0.05 cm s1. The other parameter values are characteristic of the North Atlantic Ocean. It takes about 3.2 yr for the abyssal water mass to reach the southern boundary and about 25 yr for a statistical state to develop. Timeaveraged and instantaneous fields at a late time are described. The timeaveraged fields show an equatorwardflowing abyssal current with distinct up and downslope groundings with decreasing height in the equatorward direction. The average equatorward abyssal transport is about 8 Sv, and the average abyssal current thickness is about 500 m and is about 400 km wide. The circulation in the upper layers is mostly cyclonic and is western intensified, with current speeds about 0.6 cm s1. The upper layer cyclonic circulation intensifies in the source region with speeds about 4 cm s1, and there is an anticyclonic circulation region
Baroclinic characteristics of frictionally destabilized abyssal overflows
 J. Fluid Mech
"... Observations show that the nearsill dynamics of dense abyssal overflows is variable and is governed, to a significant extent, by a balance between rotation, bottom friction and downslope acceleration due to gravity. Numerical simulations indicate that the nearsill downslope velocities are comparab ..."
Abstract

Cited by 5 (2 self)
 Add to MetaCart
(Show Context)
Observations show that the nearsill dynamics of dense abyssal overflows is variable and is governed, to a significant extent, by a balance between rotation, bottom friction and downslope acceleration due to gravity. Numerical simulations indicate that the nearsill downslope velocities are comparable to the phase/group velocities of long internal gravity waves. This suggests the possibility that overflows can become supercritical and destabilized by bottom friction. A theory is presented for the frictional destabilization of rotating abyssal overflows and the accompanying baroclinic coupling with the overlying ocean. This mode of transition allows for the formation of downslope and alongslope propagating periodic bores or pulses in the overflow and the generation of amplifying long internal gravity waves in the overlying ocean, and may help to explain aspects of the observed variability which seem unrelated to purely inertial baroclinic instability. 1.
On the collision between deep anticyclones and seamounts
, 2001
"... Abstract Numerical simulations of the collision between deep topographicallysteered anticyclonic eddies and seamounts are described. The simulations are based on a twolayer intermediate lengthscale model which filters out barotropic processes and focuses on the subinertial baroclinic dynamics ..."
Abstract
 Add to MetaCart
Abstract Numerical simulations of the collision between deep topographicallysteered anticyclonic eddies and seamounts are described. The simulations are based on a twolayer intermediate lengthscale model which filters out barotropic processes and focuses on the subinertial baroclinic dynamics within the context of allowing finiteamplitude height variations in the deep cold eddies and a background topographic vorticity gradient.
Instability of Abyssal Currents
, 2002
"... A theory is developed for the baroclinic destabilization of densitydriven abyssal flows over topography in a rotating environment. The dominant instability mechanism being studied is the release of available potential energy caused by gradual downhill slumping of the abyssal current. The presen ..."
Abstract
 Add to MetaCart
A theory is developed for the baroclinic destabilization of densitydriven abyssal flows over topography in a rotating environment. The dominant instability mechanism being studied is the release of available potential energy caused by gradual downhill slumping of the abyssal current. The present model assumes a twolayer configuration and allows for intersections of the interface with the bottom (i.e. true fronts) as well as continuous stratification in the ambient fluid. We solve the linear instability problem in a channel for a current with parabolic crosssection and show that the perturbation growth rate and most unstable wavenumber both increase with current thickness. A similar trend is evident as the stratification number is increased, or the current width is decreased. The instability manifests itself in the overlying ocean as an amplifying topographic Rossby wave. Alternating positive/negative pressure anomalies in the upper layer are accompanied by a wavelike deformation of the abyssal current that is most pronounced on the downslope side. Upper layer vortical features have a distinct verticallytapered shape, and are to be interpreted as bottomintensified eddies. Longterm evolution of the flow is elucidated in a series of simulations employing the fullynonlinear governing equations.
unknown title
, 2004
"... On the sensitivity of coastal quasigeostrophic edge wave interaction to bottom boundary characteristics: possible implications for eddy parameterizations ..."
Abstract
 Add to MetaCart
On the sensitivity of coastal quasigeostrophic edge wave interaction to bottom boundary characteristics: possible implications for eddy parameterizations
Hydrostatic and nonhydrostatic simulations of dense waters cascading off a shelf: the East Greenland case
"... The cascade of dense waters off the Southeast Greenland shelf during summer 2003 is investigated with two very highresolution (0.5km) simulations. The first simulation is nonhydrostatic. The second simulation is hydrostatic and about 3.75 times less expensive. Both simulations are compared to a 2 ..."
Abstract
 Add to MetaCart
The cascade of dense waters off the Southeast Greenland shelf during summer 2003 is investigated with two very highresolution (0.5km) simulations. The first simulation is nonhydrostatic. The second simulation is hydrostatic and about 3.75 times less expensive. Both simulations are compared to a 2km hydrostatic run, about 31 times less expensive than the 0.5 km nonhydrostatic case. Timeaveraged volume transport values for deep waters are insensitive to the changes in horizontal resolution and vertical momentum dynamics. By this metric, both lateral stirring and vertical shear instabilities associated with the cascading process are accurately parameterized by the turbulent schemes used at 2km horizontal resolution. All runs compare well with observations and confirm that the cascade is mainly driven by cyclones which are linked to dense overflow boluses at depth. The passage of the cyclones is also associated with the generation of internal gravity waves (IGWs) near
On the baroclinic instability of axisymmetric
, 1999
"... The baroclinic stability characteristics of axisymmetric gravity currents in a rotating system with a sloping bottom are determined. Laboratory studies have shown that a relatively dense fluid released under an ambient fluid in a rotating system will quickly respond to Coriolis eects and settle to a ..."
Abstract
 Add to MetaCart
The baroclinic stability characteristics of axisymmetric gravity currents in a rotating system with a sloping bottom are determined. Laboratory studies have shown that a relatively dense fluid released under an ambient fluid in a rotating system will quickly respond to Coriolis eects and settle to a state of geostrophic balance. Here we employ a subinertial twolayer model derived from the shallowwater equations to study the stability characteristics of such a current after the stage at which geostrophy is attained. In the model, the dynamics of the lower layer are geostrophic to leading order, but not quasigeostrophic, since the height deflections of that layer are not small with respect to its scale height. The upperlayer dynamics are quasigeostrophic, with the Eulerian velocity eld principally driven by baroclinic stretching and a background topographic vorticity gradient. Necessary conditions for instability, a semicirclelike theorem for unstable modes, bounds on the growth rate and phase velocity, and a sucient condition for the existence of a highwavenumber cuto are presented. The linear stability equations are solved exactly for the case where the gravity current initially corresponds to an