scholarly journals The Behavior of Jet Currents over a Continental Slope Topography with a Possible Application to the Northern Current

2005 ◽  
Vol 35 (5) ◽  
pp. 790-810 ◽  
Author(s):  
M. M. Flexas ◽  
G. J. F. van Heijst ◽  
R. R. Trieling
Keyword(s):  
High Speed ◽  
Bottom Topography ◽  
Laboratory Model ◽  
Topographic Effects ◽  
Topographic Slope ◽  
Eddy Formation ◽  
Slow Flows ◽  
Bottom Depth ◽  
Source Sink ◽  
Northern Current

Abstract The Northern Current is a slope current in the northwest Mediterranean that shows high mesoscale variability, generally associated with meander and eddy formation. A barotropic laboratory model of this current is used here to study the role of the bottom topography on the current variability. For this purpose, a source–sink setup in a cylindrical tank placed on a rotating table is used to generate an axisymmetric barotropic current. To study inviscid topographic effects, experiments are performed over a topographic slope and also over a constant-depth setup, the latter being used as a reference for the former. With the aim of obtaining a fully comprehensive view of the vorticity balance at play, the flow may be forced in either azimuthal direction, leading to a “westward” prograde current (similar to the Northern Current) or an “eastward” retrograde current. For slow flows, eastward and westward currents showed similar patterns, dominated by Kelvin–Helmholtz-type instabilities. For high-speed flows, eastward and westward currents showed very different behavior. In eastward currents, the variability is observed to concentrate toward the center of the jet and shows strong meandering formation. Westward currents, instead, showed major variability toward the edges of the jet, together with a strong variability over the uppermost slope, which has been associated here with a topographic Rossby wave trapped over the shelf break. The differences between eastward and westward jets are explained through the balance between shear-induced and topographically induced vorticity at play in each case. Moreover, a model of jets over a beta plane is successfully applied here, allowing its extension to any ambient potential vorticity gradient caused either by latitudinal or bottom depth changes.

scholarly journals Mesoscale eddy formation and evolution in the ice-covered ocean

1991 ◽  
Vol 15 ◽  
pp. 139-147 ◽  
Author(s):  
Motoyoshi Ikeda
Keyword(s):  
Deep Convection ◽  
Bottom Topography ◽  
Active Material ◽  
Mesoscale Eddy ◽  
Open Water ◽  
Ekman Pumping ◽  
Strong Current ◽  
Eddy Formation ◽  
Current Instability ◽  
Generation Mechanisms

Generation mechanisms of mesoscale eddies in the ice-covered ocean are studied by using numerical ice–ocean models and discussed with reference to previous papers. The three possible mechanisms of eddy generation, with sea ice as a passive tracer, are current instability, current-eddy interaction and current–bottom topography interaction. The current instability, categorized into barotropic and baroclinic instabilities, may be responsible for eddies near the ice edge associated with a strong current. An eddy can interact with a current, producing additional eddies, where stability of the current is again an important factor for eddy formation. Eddies over bottom topography on the continental shelf are explained by current–topography interaction; i.e. anticyclones are produced over banks. The particular mechanism that includes ice as an active material is an ice–ocean interaction; i.e. a wind stress is larger over the ice than on open water and induces Ekman pumping and suction, which produce dipole eddy motions in the non-uniformly ice-covered ocean. The eddies are suggested to be important for cross-shelf exchanges of ice and heat as well as determining locations of deep convection.

scholarly journals Hydrography, Circulation, and Mixing at the Calypso Deep (the Deepest Mediterranean Trough) during 2006–09

2016 ◽  
Vol 46 (4) ◽  
pp. 1255-1276 ◽  
Author(s):  
H. Kontoyiannis ◽  
V. Lykousis ◽  
V. Papadopoulos ◽  
S. Stavrakakis ◽  
E. G. Anassontzis ◽  
...  
Keyword(s):  
Bottom Topography ◽  
Vertical Mixing ◽  
Average Error ◽  
Surrounding Water ◽  
Local Maxima ◽  
Vertical Diffusivity ◽  
Station Grid ◽  
Vertical Scale ◽  
Bottom Depth ◽  
Lens Center

AbstractThe mass and flow fields from June 2006 to May 2009 in the Calypso Deep (bottom depth ~5.2 km) are investigated using eddy-resolving surface-to-bottom hydrography (station grid spacing ~0.2°) and two tall moorings yielding current-meter records at depths from 700 m to near bottom. A salty warm lens (excess core salinity and temperature are ~0.01 and 0.025°C relative to the surrounding water) of Cretan Deep Water with a core at ~3000 m and a horizontal (vertical) scale of ~50 km (1.5 km) is identified in June 2006 to be locked over the trough. The lens coincides with local maxima in dissolved oxygen. In October 2006 the salinity content of the lens and of all deeper layers is increased; the oxygen maxima are shifted to the bottom layers, indicating an episodic intrusion of higher-density ventilated Adriatic water. The circulation changes from anticyclonic at all depths in June 2006 to cyclonic below ~2.5 km in October 2006, whereas after January 2007 it is cyclonic at all instrumented depths. The measured currents are weak (mean speeds < 5 cm s−1) and persistent in direction, being mostly along the bottom topography at all current-meter depths. After October 2006, the lens erodes due to salt/heat loss caused predominantly by lateral (intrusive) mixing, which works from the outside toward the lens center. The horizontal diffusivity is on the order of ~10 m2 s−1, near the center of the lens, and ~102 to 103 m2 s−1, at its periphery, with an average error ~15 times the diffusivity value. In the deepest part of the trough and in periods of predominance of vertical mixing the vertical diffusivity at 4400 m is ~(4 ± 3) × 10−3 m2 s−1.

Control of Rapid Transit Propulsion System Noise

1984 ◽  
Vol 106 (2) ◽  
pp. 270-277
Author(s):  
P. J. Remington ◽  
N. R. Dixon
Keyword(s):  
High Speed ◽  
Propulsion System ◽  
Laboratory Model ◽  
Rapid Transit ◽  
Blade Passage ◽  
Community Noise ◽  
System Noise ◽  
Cooling Fan ◽  
Urban Rail ◽  
Noise Impact

An extensive series of diagnostic measurements was carried out on an urban rail propulsion system of the type that was found to have the greatest community noise impact. At high speed, 3000 to 4000 rpm, the fan dominates all other sources by 10–15 dBA. At low speed, 1000 to 1500 rpm, fan, gears, and drive motors make comparable noise. A series of tests on a laboratory model of the fan/end housing of a Westinghouse 1447 propulsion motor showed that by modifying the geometry of the end housing posts and reducing the diameter of the cooling fan, the tone at the blade passage frequency was virtually eliminated. In addition, the overall noise was reduced by over 10 dBA while the same airflow was maintained through the fan. When these treatments were applied to the motor itself, it was possible to maintain the same airflow as in the unmodified motor by redesigning the grill over the inlet at the commutator end of the motor. Noise reductions, however, were not as significant as in the laboratory model. Although the blade passage tone was virtually eliminated, overall noise reduction was in the 3 to 6 dBA range, depending on the combination of treatments used.

scholarly journals Eddy Formation near the West Coast of Greenland

2008 ◽  
Vol 38 (9) ◽  
pp. 1992-2002 ◽  
Author(s):  
Annalisa Bracco ◽  
Joseph Pedlosky ◽  
Robert S. Pickart
Keyword(s):  
Vertical Structure ◽  
Labrador Sea ◽  
Boundary Current ◽  
Layer Model ◽  
The West ◽  
Current Configuration ◽  
Topographic Slope ◽  
Eddy Formation ◽  
Perturbation Energy ◽  
Quasigeostrophic Model

Abstract This paper extends A. Bracco and J. Pedlosky’s investigation of the eddy-formation mechanism in the eastern Labrador Sea by including a more realistic depiction of the boundary current. The quasigeostrophic model consists of a meridional, coastally trapped current with three vertical layers. The current configuration and topographic domain are chosen to match, as closely as possible, the observations of the boundary current and the varying topographic slope along the West Greenland coast. The role played by the bottom-intensified component of the boundary current on the formation of the Labrador Sea Irminger Rings is explored. Consistent with the earlier study, a short, localized bottom-trapped wave is responsible for most of the perturbation energy growth. However, for the instability to occur in the three-layer model, the deepest component of the boundary current must be sufficiently strong, highlighting the importance of the near-bottom flow. The model is able to reproduce important features of the observed vortices in the eastern Labrador Sea, including the polarity, radius, rate of formation, and vertical structure. At the time of formation, the eddies have a surface signature as well as a strong circulation at depth, possibly allowing for the transport of both surface and near-bottom water from the boundary current into the interior basin. This work also supports the idea that changes in the current structure could be responsible for the observed interannual variability in the number of Irminger Rings formed.

The source-sink flow in a rotating system and its oceanic analogy

1971 ◽  
Vol 45 (3) ◽  
pp. 441-464 ◽  
Author(s):  
Han-Hsiung Kuo ◽  
George Veronis
Keyword(s):  
Ocean Circulation ◽  
Bottom Topography ◽  
Circulation Model ◽  
Circulation Pattern ◽  
Theoretical Models ◽  
Outer Wall ◽  
Western Boundary ◽  
Shaped Container ◽  
Laboratory Analogue ◽  
Source Sink

Laboratory analogues of theoretical models of wind-driven ocean circulation are based on ideas presented by Stommel (1957). A particularly simple demonstration of the applicability of these ideas is contained in a paper by Stommel, Arons & Faller (1958). The present work develops the source-sink laboratory analogue of ocean circulation models to a point where chosen parametric values allow one to simulate the theoretical models of Stommel (1948) and Munk (1950) exactly. The investigation of the flow in a rotating cylinder generated by a source of fluid near the outer wall leads to a detailed description of the roles of the various boundary layers which occur. This knowledge is used to analyse the more complex source-sink flow in a pie-shaped basin. The laboratory analogue to the Stommel circulation model is analyzed in detail. It is shown that the change in the flow pattern brought about by a radial variation of the position of the eastern boundary in the pie-shaped basin is confined to the interior flow and the boundary layer is largely unaffected. When the bottom of the pie-shaped container slopes, the circulation pattern is changed significantly. For the particular case treated, the depth of the basin along the western boundary is unchanged and the maximum depth occurs at the southeast corner. The circulation generated by a source introduced at the apex of the pie has a gyre whose centre is shifted more toward the southwest corner than the corresponding centre of the gyre for a flat-bottomed basin. Two experiments are reported showing that the western boundary may separate because of the effect of bottom topography or because of the pressure of a cyclonic and an anti-cyclonic gyre generated by suitably placed sources and sinks.

scholarly journals Spring Circulation Associated with the Thermal Bar in Large Temperate Lakes

1995 ◽  
Vol 26 (4-5) ◽  
pp. 331-358 ◽  
Author(s):  
Joakim Malm
Keyword(s):  
Numerical Model ◽  
Water Exchange ◽  
Bottom Topography ◽  
Practical Importance ◽  
Circulation Pattern ◽  
Maximum Density ◽  
Thermal Bar ◽  
Temperature Of Maximum Density ◽  
Induced Currents ◽  
Bottom Depth

The overall circulation pattern in spring is rather specific as density-induced currents may be of significance. The density-driven circulation perpendicular to the shore can be described as consisting of two circulation cells, with a zone of convergence, referred to as thermal bar, in between. The thermal bar, which coincides with the 4°C isotherm (the temperature of maximum density), inhibits horizontal water exchange, implying its practical importance. In this paper, a hydrodynamic numerical model is used to study the relative influence of wind- and density-driven currents in a large temperate lake during spring. The study shows that the general density-driven circulation is strongly dependent on the bottom topography, with a more pronounced circulation and considerable descending motions in the thermal bar zone in lakes with steep sloping bottoms. In shallow lakes, the wind-driven circulation dominates, and the effect of density-induced currents is marginal, except at locations with a drastic change in bottom depth.

scholarly journals Topographic effects on solar radiation distribution in mountainous watersheds and their influence on reference evapotranspiration estimates at watershed scale

2010 ◽  
Vol 14 (12) ◽  
pp. 2479-2494 ◽  
Author(s):  
C. Aguilar ◽  
J. Herrero ◽  
M. J. Polo
Keyword(s):  
Time Series ◽  
Solar Radiation ◽  
High Speed ◽  
Topographic Effects ◽  
Require Time ◽  
Radiation Fields ◽  
Spatially Distributed ◽  
Mountainous Watersheds ◽  
Predicted Values ◽  
Mean Differences

Abstract. Distributed energy and water balance models require time-series surfaces of the climatological variables involved in hydrological processes. Among them, solar radiation constitutes a key variable to the circulation of water in the atmosphere. Most of the hydrological GIS-based models apply simple interpolation techniques to data measured at few weather stations disregarding topographic effects. Here, a topographic solar radiation algorithm has been included for the generation of detailed time-series solar radiation surfaces using limited data and simple methods in a mountainous watershed in southern Spain. The results show the major role of topography in local values and differences between the topographic approximation and the direct interpolation to measured data (IDW) of up to +42% and −1800% in the estimated daily values. Also, the comparison of the predicted values with experimental data proves the usefulness of the algorithm for the estimation of spatially-distributed radiation values in a complex terrain, with a good fit for daily values (R2 = 0.93) and the best fits under cloudless skies at hourly time steps. Finally, evapotranspiration fields estimated through the ASCE-Penman-Monteith equation using both corrected and non-corrected radiation values address the hydrologic importance of using topographically-corrected solar radiation fields as inputs to the equation over uniform values with mean differences in the watershed of 61 mm/year and 142 mm/year of standard deviation. High speed computations in a 1300 km2 watershed in the south of Spain with up to a one-hour time scale in 30 × 30 m2 cells can be easily carried out on a desktop PC.

Nonlinear and time-dependent equivalent-barotropic flows

2019 ◽  
Vol 871 ◽  
pp. 925-951 ◽  
Author(s):  
Luis Zavala Sansón
Keyword(s):  
Wind Stress ◽  
Vertical Structure ◽  
Fluid Velocity ◽  
Bottom Topography ◽  
Bottom Friction ◽  
Time Dependent ◽  
Western Slope ◽  
Topographic Effects ◽  
Specific Level ◽  
Variable Topography

Some oceanic and atmospheric flows may be modelled as equivalent-barotropic systems, in which the horizontal fluid velocity varies in magnitude at different vertical levels while keeping the same direction. The governing equations at a specific level are identical to those of a homogeneous flow over an equivalent depth, determined by a pre-defined vertical structure. The idea was proposed by Charney (J. Met., vol. 6 (6), 1949, pp. 371–385) for modelling a barotropic atmosphere. More recently, steady, linear formulations have been used to study oceanic flows. In this paper, the nonlinear, time-dependent model with variable topography is examined. To include nonlinear terms, we assume suitable approximations and evaluate the associated error in the dynamical vorticity equation. The model is solved numerically to investigate the equivalent-barotropic dynamics in comparison with a purely barotropic flow. We consider three problems in which the behaviour of homogeneous flows has been well established either experimentally, analytically or observationally in past studies. First, the nonlinear evolution of cyclonic vortices around a topographic seamount is examined. It is found that the vortex drift induced by the mountain is modified according to the vertical structure of the flow. When the vertical structure is abrupt, the model effectively isolates the surface flow from both inviscid and viscous topographic effects (due to the shape of the bottom and Ekman friction, respectively). Second, the wind-driven flow in a closed basin with variable topography is studied (for a flat bottom this is the well-known Stommel problem). For a zonally uniform, negative wind-stress curl in the homogeneous case, a large-scale, anticyclonic gyre is formed and displaced southward due to topographic effects at the western slope of the basin. The flow reaches a steady state due to the balance between topographic,$\unicode[STIX]{x1D6FD}$, wind-stress and bottom friction effects. However, in the equivalent-barotropic simulations with abrupt vertical structure, such an equilibrium cannot be reached because the forcing effects at the surface are enhanced, while bottom friction effects are reduced. As a result, the unsteady flow is decomposed as a set of planetary waves. A third problem consists of performing simulations of the wind-driven flow over realistic bottom topography in the Gulf of Mexico. The formation of the so-called Campeche gyre is explored. It is found that such circulation may be consistent with the equivalent-barotropic dynamics.

The Differential Passive Magnetic Bearing for High-Speed Flexible Rotor

2008 ◽  
Vol 144 ◽  
pp. 273-278 ◽  
Author(s):  
Zdzisław Gosiewski ◽  
Krzysztof Falkowski
Keyword(s):  
Mathematical Model ◽  
High Speed ◽  
Magnetic Bearing ◽  
Laboratory Model ◽  
Magnetic Flux Density ◽  
Flexible Rotor ◽  
Neodymium Magnet ◽  
The One ◽  
Neodymium Magnets ◽  
The Mathematical Model

Lab stand of a differential passive magnetic bearing is presented in the paper. The passive bearing will be used in high-speed flexible rotor. The one neodymium magnet MP 41x15x10 – N38 and two neodymium magnets MP 40x22x10 – N38 were used to design the passive magnetic bearing. The mathematical model of differential bearing, laboratory model and distribution of magnetic flux density are presented and analyzed.

Effects of Topography on Baroclinic Instability

2013 ◽  
Vol 43 (4) ◽  
pp. 790-804 ◽  
Author(s):  
Changheng Chen ◽  
Igor Kamenkovich
Keyword(s):  
Numerical Model ◽  
Numerical Simulations ◽  
Potential Vorticity ◽  
Growth Rates ◽  
Vertical Structure ◽  
Bottom Topography ◽  
Baroclinic Instability ◽  
Critical Value ◽  
Zonal Flows ◽  
Topographic Slope

Abstract The importance of bottom topography in the linear baroclinic instability of zonal flows on the β plane is examined by using analytical calculations and a quasigeostrophic eddy-resolving numerical model. The particular focus is on the effects of a zonal topographic slope, compared with the effects of a meridional slope. A zonal slope always destabilizes background zonal flows that are otherwise stable in the absence of topography regardless of the slope magnitude, whereas the meridional slopes stabilize/destabilize zonal flows only through changing the lower-level background potential vorticity gradient beyond a known critical value. Growth rates, phase speeds, and vertical structure of the growing solutions strongly depend on the slope magnitude. In the numerical simulations configured with an isolated meridional ridge, unstable modes develop on both sides of the ridge and propagate eastward of the ridge, in agreement with analytical results.

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