Linear and nonlinear stratified spindown over sloping topography

Benthuysen, Jessica A.

doi:10.1575/1912/3635

Cited by 5 publications

(4 citation statements)

References 60 publications

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“…Although shelfbreak circulation is complex, simple models can be useful for understanding fundamental aspects of the circulation, such as frontogenesis (Benthuysen 2010). Because density is approximately uniform in the along-shelf direction (Lentz 2010), we employ a 2D (crossshelf and vertical) model based on the 3D temperature and salinity climatology (Fleming and Wilkin 2010) to examine the annual and seasonal mean circulation around the New England shelf break.…”

Section: Introductionmentioning

confidence: 99%

Climatological Mean Circulation at the New England Shelf Break

Zhang

Gawarkiewicz

McGillicuddy

et al. 2011

Journal of Physical Oceanography

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A two-dimensional cross-shelf model of the New England continental shelf and slope is used to investigate the mean cross-shelf and vertical circulation at the shelf break and their seasonal variation. The model temperature and salinity fields are nudged toward climatology. Annual and seasonal mean wind stresses are applied on the surface in separate equilibrium simulations. The along-shelf pressure gradient force associated with the along-shelf sea level tilt is tuned to match the modeled and observed depth-averaged along-shelf velocity. Steady-state model solutions show strong seasonal variation in along-shelf and cross-shelf velocity, with the strongest along-shelf jet and interior onshore flow in winter, consistent with observations. Alongshelf sea level tilt associated with the tuned along-shelf pressure gradient increases shoreward because of decreasing water depth. The along-shelf sea level tilt varies seasonally with the wind and is the strongest in winter and weakest in summer. A persistent upwelling is generated at the shelf break with a maximum strength of 2 m day 21 at 50-m depth in winter. The modeled shelfbreak upwelling differs from the traditional view in that most of the upwelled water is from the upper continental slope instead of from the shelf in the form of a detached bottom boundary layer.

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Section: Introductionmentioning

confidence: 99%

Climatological Mean Circulation at the New England Shelf Break

Zhang

Gawarkiewicz

McGillicuddy

et al. 2011

Journal of Physical Oceanography

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“…Future studies are needed to address the relative importance of EAC versus wind fluctuations to intrusive upwelling in the Central GBR and to compare the impact of the reef passages on shelfbreak upwelling with intrusions arising in other shelf-edge systems [e.g., Benthuysen, 2010;Castelao, 2011]. This work indicates that temperature and salinity gradients, either pre-existing or arising from the intrusion, may play an important role in the intrusion's onshore propagation and process experiments are needed to elucidate this mechanism.…”

Section: Discussionmentioning

confidence: 99%

Intrusive upwelling in the Central Great Barrier Reef

Benthuysen

Tonin

Brinkman

et al. 2016

J. Geophys. Res. Oceans

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In the Central Great Barrier Reef, the outer continental shelf has an open reef matrix that facilitates the exchange of waters with the Coral Sea. During austral summer, cool water intrudes onto the shelf along the seafloor. Temperature observations reveal cool, bottom intrusions during a 6 year period from the Queensland Integrated Marine Observing System's Palm Passage mooring. A metric is used to identify 64 intrusion events. These intrusions predominantly occur from October to March including the wet season. During an event, the outer‐shelf's near‐bottom temperature decreases by 1–3°C typically over 1 week. The near‐bottom salinity tends to increase, while near‐surface changes do not reflect these tendencies. Intrusion events occur predominantly with either weakening equatorward winds or poleward wind bursts. A regional hydrodynamic model for the Great Barrier Reef captures the timing and amplitude of these intrusions. During intrusion events, isotherms tend to uplift over the continental slope and onto the shelf and the East Australian Current intensifies poleward. Over the shelf, a bottom‐intensified onshore current coincides with bottom cooling. For numerous events, the model diagnostics reveal that the cross‐shelf flow is dominated by the geostrophic contribution. A vertical circulation tilts the isopycnals upward on the southern side of the passage, causing an along‐shelf density gradient and geostrophic onshore flow with depth. While wind fluctuations play a major role in controlling the along‐shelf currents, model results indicate that a concurrent topographically induced circulation can assist the onshore spread of cool water.

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“…Chapman 2002). For small Rossby numbers and sufficiently small slope Burger numbers, buoyancy shutdown locally weakens the geostrophic vertical relative vorticity (Benthuysen 2010). Hence both Ekman pumping and Ekman suction are suppressed to the same extent.…”

Section: Stratified Spindown Over a Slopementioning

confidence: 98%

“…At early time, t < 1, nonlinear buoyancy shutdown reduces Ekman pumping and suction in the numerical solutions, although these quantities are systematically larger than the analytical solutions. This systematic error may be explained by an O(E 1/4 ) correction from vertical advection of the laterally uniform buoyancy anomaly in the thermal boundary layer (Benthuysen 2010). This correction causes Ekman pumping and suction to increase from the O(1) solution during SSD over a flat bottom.…”

Section: Asymmetries In Ekman Pumping and Suctionmentioning

confidence: 99%

Nonlinear stratified spindown over a slope

Benthuysen

Thomas

2013

J. Fluid Mech.

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Nonlinear stratified spindown of an along-isobath current over an insulated slope is shown to develop asymmetries in the vertical circulation and vertical relative vorticity field. During spindown, cyclonic vorticity is weakened to a greater extent than anticyclonic vorticity near the boundary because of buoyancy advection. As a consequence, Ekman pumping is weakened over Ekman suction. Momentum advection can weaken Ekman pumping and strengthen Ekman suction. Time-dependent feedback between the geostrophic flow and the frictional secondary circulation induces asymmetry in cyclonic and anticyclonic vorticity away from the boundary. Buoyancy advection over a slope can modify the secondary circulation such that anticyclonic vorticity decays faster than cyclonic vorticity outside the boundary layer. In contrast, momentum advection can cause cyclonic vorticity to spin down faster than anticyclonic vorticity. A scaling and analytical solutions are derived for when buoyancy advection over a slope can have a more significant impact than momentum advection on these asymmetries. In order to test this scaling and analytical solutions, numerical experiments are run in which both buoyancy and momentum advection are active. These solutions are contrasted with homogeneous or stratified spindown over a flat bottom, in which momentum advection controls the asymmetries. These results are applied to ocean currents over continental shelves and slopes.

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Linear and nonlinear stratified spindown over sloping topography

Cited by 5 publications

References 60 publications

Climatological Mean Circulation at the New England Shelf Break

Climatological Mean Circulation at the New England Shelf Break

Intrusive upwelling in the Central Great Barrier Reef

Nonlinear stratified spindown over a slope

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