Rotational effects on turbulence structure and mixing are investigated using a second-moment closure model. Both explicit and implicit Coriolis terms are considered. A general criterion for rotational effects to be small is established in terms of local turbulent Rossby numbers. Characteristic length scales are determined for rotational effects and Monin–Obukhov type similarity theory is developed for rotating stratified flows. A one-dimensional version of the closure model is then applied to simulate oceanic mixed layer evolution. It is shown that the effects of rotation on mixed layer depth tend to be small because of the influence of stable stratification. These findings contradict a hypothesis of Garwood et al. that rotational effects on turbulence are responsible for the disparity in the mixed-layer depths between the eastern and western regions of the equatorial Pacific Ocean. The model is also applied to neutrally stratified flows to demonstrate that rotation can either stabilize or destabilize the flow

Galperin, B.

Kantha, L. H.

Mellor, G. L.

Rosati, A.

Journal of Physical Oceanography

English

Monahan, Edward C.

Woolf, David K.

Heriot Watt Pure

Comments on “Variations of Whitecap Coverage with Wind stress and Water Temperature"

Suga, Toshio

12949

Hanawa, Kimio

12950

Toba, Yoshiaki

12951

Tohoku University Repository (TOUR) / 東北大学機関リポジトリ

Subtropical Mode Water in the 137°E Section著者 Suga  Toshio, Hanawa  Kimio, Toba  Yoshiakijournal orpublication titleJournal of Physical Oceanographyvolume 19number 10page range 1605-1618year 1989URL http://hdl.handle.net/10097/51867doi: 10.1175/1520-0485(1989)019<1605:SMWITS>2.0.CO;2

Subtropical Mode Water in the 137°E Section

Correlations of monthly mean sea level variations along the Pacific Ocean margin are used to define length scales. In the northeast quadrant a minimum length scale at about 38°N separates two distinct regimes of longer length scale. This transition corresponds to a change from a regime north of 38° that is dominated by local atmospheric forcing to a regime south of 38° that is dominated by remote forcing. In the northwest quadrant a transition occurs near 35°N near the point of the separation of the Kuroshio. A transition at about 30°S in the southwest quadrant is associated with the southernmost extent of the Great Barrier Reef off the coast of Australia. In the southeast quadrant, a transition is observed at 18°S that may be due to a sharp change in the direction of the South American coastline. In general. tropical length scale values of 800 to 3100 km are separated from midlatitude values of 700 to 1300 km by a narrow region in which length scales are as short as 250 km. These results suggest the need for latitude-dependent criteria for the spacing of tide gauges in a global oceanographic sea level system

Roach, David

Mitchum, Gary T.

Wyrtki, Klaus

Scholar Commons - University of South Florida

Length Scales of Interannual Sea Level Variations along the Pacific Margin

Analytic solutions am obtained for the barotropic shelf circulation caused by wind and deep-ocean forcing at subinertial frequencies. An Inclined beach model of the continental shelf is used and only situations in which bottom friction is important are considered. Three different alongshore forces are considered: pressure gradients and currents (maintained by the deep ocean) at the shelf break and wind stress, over the shelf. In each case the model is formulated as a boundary value problem in which the boundary conditions are determined by the forcing mechanism. In general, a damped resonant response occurs when the forcing function has the same longshore velocity as an unforced continental shelf wave and is most significant for the fim mode. In the case of forcing by an alongshore pressure gradient at the edge of the shelf, this leads to the amplification of the pressure signal toward the coast. The model frequencies and structures are determined for various frictional values. When friction is small the results are consistent with those of Brink and Allen in that phase speeds remain unchanged and cross-shelf phase differences are introduced. At larger frictional values, however, phase speeds are reduced, and the model structures and cross-shelf phase differences are further altered

Power, Scott B.

Middleton, Jason H.

Grimshaw, R. H. J.

University of Southern Queensland ePrints

Frictionally Modified Continental Shelf Waves and the Subinertial Response to Wind and Deep-Ocean Forcing

Modeling Rotating Stratified Turbulent Flows with Application to Oceanic Mixed Layers

Historical data from the region between the Greenwich meridian and the African continental shelf are used to compute the offshore geostrophic transport of the Benguela Current. At 32°S, the Benguela Current is located near the African coast, transporting about 21 Sv (1 Sv = 106 m3 s−1) of surface water toward the north relative to a potential density surface lying between the upper branch of Circumpolar Deep Water and the North Atlantic Deep Watar. Two warm core eddies of probable Agulhas Current origin an observed west of the Benguela Current at 32°S. Near 30°S, the Benguela Current turns toward the northwest and begins to separate from the eastern boundary. It carries about 18 Sv of surface water across 28°S. The current then turns mainly toward the west to flow over a relatively deep segment of the Walvis Ridge south of the Valdivia Bank. A surface current with northward surface of about 10 cm s−1 flows along the western side of the Valdivia Bank, while another northward surface current flows at about 20 cm s−1 some 300 km west of the bank. About 3 Sv of surface now do not leave the Cape Basin south of the Vaidivia Bank, but instead drift northward as a wide. sluggish flow out of the northern end of the Cape Basin. Because of the more southerly seaward extensions of most of the Benguela Current, there are no deep-reaching interactions observed between this current and the cyclonic gyre in the Angola Basin east of the Greenwich meridian. Beneath the surface layer, about 4–5 Sv of Antarctic Intermediate Water are carried northward across 32° and 28°S by the Benguela Current, essentially all of which turns westward to cross the Greenwich meridian south of 24°S

Stramma, Lothar

Peterson, Ray G.

OceanRep

Geostrophic Transport in the Benguela Current Region

Boundary layer potential vorticity dynamics for a quasi-geostrophic, eddy-resolving general circulation ocean model are studied using both Lagrangian and Eulerian analyses. Active western boundary layers are found not only in the upper wind-driven layer but also in the lower layers, despite the lack of a direct vorticity input to the deep ocean. At the western wall dissipative and inertial boundary regimes are exclusively controlled by the time-mean dynamics except for the deepest layer where eddy fluxes drive the mean flow across mean potential vorticity contours. Boundary layers formed at the southern wall in this model are dynamically distinct from the  western boundary layers; they are controlled solely by the eddy flux of potential vorticity found in this region of active baroclinic instability. Basin-integrated vorticity balances reveal a strong contribution to the vorticity cycle by the lateral boundaries with such input overshadowed by the vorticity exchange across the midbasin gyre boundary in the surface layer

Lozier, M Susan

Riser, Stephen C

DukeSpace (Duke Univ.)

Potential vorticity dynamics of boundary currents in a quasigeostrophic ocean.

We report a study of a coastal frontal zone of the southeastern United States based on a field experiment and numerical modeling. The study was conducted in the spring of 1985 during weak to moderate wind stress and strong input of buoyancy from solar radiation and river discharge. The study confirms that the structure and slope of the frontal zone depends on a combination of wind stress and cross-shelf advection of buoyancy.



A cross-shelf/depth two-dimensional (x, y), time-dependent numerical model illustrated the response of the frontal zone to the local wind stress regimes. A comparison of model results with field data showed that the model successfully predicted onsets of stratification and mixing. When alongshore wind stress was negative (southward), isopycnals in the frontal zone steepened due to a combination of horizontal advection and vertical convection. When stress was positive (northward), the offshore advection of low density water flattened the isopycnals and potential energy decreased, demonstrating that horizontal advection terms are important in the equation of conservation of buoyancy. The model predicts die offshore advection of lenses of less dense water during upwelling-favorable wind stress. These lenses are of the order of 20 km in cross-shelf scale and represent an efficient mechanism to export nearshore water. The lenses consist of a mixture of low-salinity coastal water and continental shelf water originating further offshore and advected onshore along the bottom.



The mean flow inside the frontal zone opposed the mean alongshore wind stress. Part of the alongshore flow was in geostrophy with the cross-shore pressure gradient; the other part was due to an alongshore pressure gradient force (kinematic) of about 1 × 10−6 m s−2 (equivalent sea surface slope = 1 × 10−7), which was trapped along the coast with an offshore width scale of O(10 km). It is likely that the alongshore extent of this pressure gradient was governed by the scale at which freshwater is injected to the continental shelf, i.e., 20–30 km. The pressure gradient force immediately outside of the frontal zone was about −5 × 10−7 m s−2 in the direction of the mean alongshore wind stress. It is hypothesized that, as a result of wind setup and freshwater influx, the northward pressure gradient forced over outer shelf/slope by the Gulf Stream decreases in magnitude onshore, and can even change sign across a nearshore frontal zone of O(10 km). The implied flow field near the frontal zone is therefore highly three-dimensional with |∂v/∂y|≈|∂u/∂x|, where (u, v) are velocities in the cross-shore (x) and alongshore (y) directions, respectively

Böning, Claus W.

Influences of a rough bottom topography on flow kinematics in an eddy-resolving circulation model

https://tohoku.repo.nii.ac.jp/?action=repository_action_common_download&item_id=5248&item_no=1&attribute_id=18&file_no=1

Subtropical Mode Water in the 137°E Section

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Heriot Watt Pure

Tohoku University Repository (TOUR) / 東北大学機関リポジトリ

Scholar Commons - University of South Florida

University of Southern Queensland ePrints

Scholar Commons - University of South Florida

OceanRep

DukeSpace (Duke Univ.)

OceanRep