scholarly journals Idealized Two-Dimensional Modeling of a Coastal Buoyancy Front, or River Plume, under Downwelling-Favorable Wind Forcing with Application to the Alaska Coastal Current

2010 ◽  
Vol 40 (2) ◽  
pp. 279-294 ◽  
Author(s):  
William J. Williams ◽  
Thomas J. Weingartner ◽  
Albert J. Hermann
Keyword(s):  
Wind Stress ◽  
River Plume ◽  
Coastal Current ◽  
Two Dimensional ◽  
Coriolis Parameter ◽  
Final State ◽  
Bottom Boundary Layers ◽  
The Cross ◽  
Alaska Coastal Current ◽  
Bottom Depth

Abstract The cross-shelf structure of a buoyancy-driven coastal current, such as produced by a river plume, is modeled in a two-dimensional cross-shelf slice as a “wide” geostrophically balanced buoyancy front. Downwelling-favorable wind stress applied to this front leads to advection in the surface and bottom boundary layers that causes the front to become steeper so that it eventually reaches a steep quasi-steady state. This final state is either convecting, stable and steady, or stable and oscillatory depending on D/δ* and by /f 2, where D is bottom depth, δ* is an Ekman depth, by is the cross-shelf buoyancy gradient, and f is the Coriolis parameter. Descriptions of the cross-shelf circulation patterns are given and a scaling is presented for the isopycnal slope. The results potentially apply to the Alaska Coastal Current, which experiences strong, persistent downwelling-favorable wind stress during winter, but also likely have application to river plumes subjected to downwelling-favorable wind stress.

scholarly journals Advances on Coastal and Estuarine Circulations Around the Changjiang Estuary in the Recent Decades (2000–2020)

2021 ◽  
Vol 8 ◽  
Author(s):  
Zhiqiang Liu ◽  
Jianping Gan ◽  
Hui Wu ◽  
Jianyu Hu ◽  
Zhongya Cai ◽  
...  
Keyword(s):  
Yellow Sea ◽  
River Plume ◽  
Changjiang Estuary ◽  
Tidal Mixing ◽  
The Yellow Sea ◽  
Coastal Current ◽  
Changjiang River ◽  
The Changjiang Estuary ◽  
The Changjiang River ◽  
The Cross

Advances on the circulation in the Changjiang Estuary and adjacent East China Sea (ECS) and Yellow Sea (YS) coastal waters in the recent decades (2000–2020) are synthesized in this review. The circulation over the complicated bathymetry in the region is locally driven by winds, tides, as well as riverine discharge, and is remotely influenced by shelf currents between the 50 and 100-m isobaths through the cross-shelf exchanges. The interchange of the momentum and the freshwater pathway inside the Changjiang Estuary are jointly determined by tides and seasonally varying discharge and winds over the shelf. The buoyant waters are trapped inside the bulge that forms and expands over the shelf to the west of the 30-m isobath in the vicinity of Hangzhou Bay and the Changjiang Estuary. These buoyant waters are exported offshore by the shelf current, tidal mixing, and variations of wind patterns, forming the Changjiang River plume, which shows notable seasonality due to the reversal of both winds and shelf currents in the ECS and YS. Extensive spatial irregularities in the form of freshwater patches are present along its pathway to the Tsushima Strait in summer and to the Taiwan Strait in winter, respectively. Tides and the bathymetry irregularity have recently been found to play critical roles in determining the cross-shelf exchanges of water mass and momentum along the pathway of the ECS coastal current, and along this pathway, a year-round upslope intrusion of shelf waters appears in both summer and winter. Tides also play an important role in altering the expansion of the Changjiang River plume, cross-shelf extrusion of waters, and variation in the Yellow Sea Coastal Current over the shallow Subei Shoal.

Whether the two-dimensional Eulerian turbulence evolves to a unique final state

2002 ◽  
Vol 14 (11) ◽  
pp. 3937-3945 ◽  
Author(s):  
V. Pavlov ◽  
D. Buisine ◽  
S. Decossin
Keyword(s):  
Two Dimensional ◽  
Final State

scholarly journals Destruction of Potential Vorticity by Winds

2005 ◽  
Vol 35 (12) ◽  
pp. 2457-2466 ◽  
Author(s):  
Leif N. Thomas
Keyword(s):  
Boundary Layer ◽  
Wind Stress ◽  
Potential Vorticity ◽  
Ekman Layer ◽  
Buoyancy Flux ◽  
Coriolis Parameter ◽  
Mode Water ◽  
Ocean Fronts ◽  
Secondary Circulations ◽  
Frictional Forces

Abstract The destruction of potential vorticity (PV) at ocean fronts by wind stress–driven frictional forces is examined using PV flux formalism and numerical simulations. When a front is forced by “downfront” winds, that is, winds blowing in the direction of the frontal jet, a nonadvective frictional PV flux that is upward at the sea surface is induced. The flux extracts PV out of the ocean, leading to the formation of a boundary layer thicker than the Ekman layer, with nearly zero PV and nonzero stratification. The PV reduction is not only active in the Ekman layer but is transmitted through the boundary layer via secondary circulations that exchange low PV from the Ekman layer with high PV from the pycnocline. Extraction of PV from the pycnocline by the secondary circulations results in an upward advective PV flux at the base of the boundary layer that scales with the surface, nonadvective, frictional PV flux and that leads to the deepening of the layer. At fronts forced by both downfront winds and a destabilizing atmospheric buoyancy flux FBatm, the critical parameter that determines whether the wind or the buoyancy flux is the dominant cause for PV destruction is (H/δe)(FBwind/FBatm), where H and δe are the mixed layer and Ekman layer depths, FBwind = S2τo/(ρof ), S2 is the magnitude of the lateral buoyancy gradient of the front, τo is the downfront component of the wind stress, ρo is a reference density, and f is the Coriolis parameter. When this parameter is greater than 1, PV destruction by winds dominates and may play an important role in the formation of mode water.

scholarly journals Synoptic fluctuation of the Taiwan Warm Current in winter on the East China Sea shelf

2016 ◽  
Author(s):  
Jiliang Xuan ◽  
Daji Huang ◽  
Thomas Pohlmann ◽  
Jian Su ◽  
Bernhard Mayer ◽  
...  
Keyword(s):  
Ocean Model ◽  
Coastal Current ◽  
Gradient Term ◽  
Taiwan Warm Current ◽  
Offshore Area ◽  
Warm Current ◽  
Geostrophic Balance ◽  
The North ◽  
The Cross ◽  
The Taiwan Strait

Abstract. The seasonal mean and synoptic fluctuation of the wintertime Taiwan Warm Current (TWC) were investigated using a well validated finite volume community ocean model. The spatial distribution and dynamics of the synoptic fluctuation were highlighted. The seasonal mean of the wintertime TWC has two branches: an inshore branch between the 30 and 100 m isobaths and an offshore branch between the 100 and 200 m isobaths. The Coriolis term is much larger than the inertia term and is almost balanced by the pressure gradient term in both branches, indicating the geostrophic balance of the mean current. Two areas with significant fluctuations of the TWC were identified during wintertime. One of the areas is located to the north of Taiwan with velocities varying in the cross-shore direction. These significant cross-shore fluctuations are driven by barotropic pressure gradients associated with the intrusion of the Taiwan Strait Current (TSC). When a larger TSC intrudes north of Taiwan, the isobaric slope tilts downward from south to north, leading to a cross-shore current from the coastal area to the offshore area. When the TSC intrusion is weak, the cross-shore current to the north of Taiwan is directed from offshore to inshore. The other area of significant fluctuation is located in the inshore area, extending in the region between the 30 and 100 m isobaths. The fluctuations are generally strong in the alongshore direction, in particular at the latitudes 26.5° N and 28° N where they are important for the local cross-shore transports. Wind affects the synoptic fluctuation through episodic events. When the northeasterly monsoon prevails, the southward Zhe-Min Coastal Current dominates the inshore area associated with a deepening of the mixed layer. When the winter monsoon is weakened or the southerly wind prevails, the northward TWC dominates in the inshore area.

scholarly journals Searching for axionlike particles with low masses in pPb and PbPb collisions

2021 ◽  
Vol 81 (6) ◽  
Author(s):  
V. P. Gonçalves ◽  
D. E. Martins ◽  
M. S. Rangel
Keyword(s):  
Detailed Analysis ◽  
Cross Section ◽  
Experimental Analysis ◽  
Mass Range ◽  
Final State ◽  
Lhcb Detector ◽  
The Cross ◽  
Photon Coupling

AbstractThe production of axionlike particles (ALPs) with small masses in ultraperipheral Pb–p and Pb–Pb collisions at the LHC is investigated. The cross section and kinematical distributions associated to the diphoton final state produced in the $$\gamma \gamma \rightarrow a \rightarrow \gamma \gamma $$ γ γ → a → γ γ subprocesses are estimated considering a realistic set of kinematical cuts. A detailed analysis of the backgrounds is performed and the expected sensitivity to the ALP production is derived. Our results demonstrate that a future experimental analysis of the exclusive diphoton production for the forward rapidities probed by the LHCb detector can improve the existing exclusion limits on the ALP–photon coupling in the mass range 2 GeV $$\le m_a \le $$ ≤ m a ≤ 5 GeV.

Atlantic to Mediterranean Sea Level Difference Driven by Winds near Gibraltar Strait

2007 ◽  
Vol 37 (2) ◽  
pp. 359-376 ◽  
Author(s):  
Dimitris Menemenlis ◽  
Ichiro Fukumori ◽  
Tong Lee
Keyword(s):  
Mediterranean Sea ◽  
Sea Level ◽  
Wind Stress ◽  
Coastal Current ◽  
Alboran Sea ◽  
Mean Sea Level ◽  
Level Difference ◽  
Gibraltar Strait ◽  
Sea Level Difference ◽  
Alborán Sea

Abstract Observations and numerical simulations show that winds near Gibraltar Strait cause an Atlantic Ocean to Mediterranean Sea sea level difference of 20 cm peak to peak with a 3-cm standard deviation for periods of days to years. Theoretical arguments and numerical experiments establish that this wind-driven sea level difference is caused in part by storm surges due to alongshore winds near the North African coastline on the Atlantic side of Gibraltar. The fraction of the Moroccan coastal current offshore of the 284-m isobath is deflected across Gibraltar Strait, west of Camarinal Sill, resulting in a geostrophic surface pressure gradient that contributes to a sea level difference at the stationary limit. The sea level difference is also caused in part by the along-strait wind setup, with a contribution proportional to the along-strait wind stress and to the length of Gibraltar Strait and adjoining regions and inversely proportional to its depth. In the 20–360-day band, average transfer coefficients between the Atlantic–Alboran sea level difference and surface wind stress at 36°N, 6.5°W, estimated from barometrically corrected Ocean Topography Experiment (TOPEX)/Poseidon data and NCEP–NCAR reanalysis data, are 0.10 ± 0.04 m Pa−1 with 1 ± 5-day lag and 0.19 ± 0.08 m Pa−1 with 5 ± 4-day lag for the zonal and meridional wind stresses, respectively. This transfer function is consistent with equivalent estimates derived from a 1992–2003 high-resolution barotropic simulation forced by the NCEP–NCAR wind stress. The barotropic simulation explains 29% of the observed Atlantic–Alboran sea level difference in the 20–360-day band. In turn, the Alboran and Mediterranean mean sea level time series are highly correlated, ρ = 0.7 in the observations and ρ = 0.8 in the barotropic simulation, hence providing a pathway for winds near Gibraltar Strait to affect the mean sea level of the entire Mediterranean.

An Instrument for One- or Two-Dimensional Tracking

1965 ◽  
Vol 21 (1) ◽  
pp. 307-312
Author(s):  
William C. Roehrig
Keyword(s):  
Low Cost ◽  
Two Dimensions ◽  
Two Dimensional ◽  
Error Signal ◽  
One Dimensional ◽  
Constant Torque ◽  
Sinusoidal Motion ◽  
The Cross ◽  
Target Path

A rugged electro-mechanical tracking apparatus of simple, low-cost construction is described. The apparatus can be used for one-dimensional tracking by connecting only the longitudinal motor, thus forcing the target to move back and forth in either simple sinusoidal motion or according to the sum of two or three sinusoids. The relative phases of the three sinusoids can be rapidly altered, as can the amplitudes (within limits) of each of the sinusoids. The frequency of the sinusoids can be changed either independently or conjointly. By also connecting the cross-feed motor, an essentially unpredictable target path in two dimensions is obtained, and this path can be rapidly altered by changing cams, and/or frequency, amplitude, and phase of the sinusoids. Movement of the cursor is by low, constant torque lathe-type controls. The distance the cursor moves per each rotation of the controls, can be altered for either or both of the controls. A continuous error signal is generated which is directly proportional to the distance the cursor is off target in any direction.

scholarly journals Wind Modifications to Density-Driven Flows in Semienclosed, Rotating Basins

2010 ◽  
Vol 40 (7) ◽  
pp. 1473-1487 ◽  
Author(s):  
Cristóbal Reyes-Hernández ◽  
Arnoldo Valle-Levinson
Keyword(s):  
Pressure Gradient ◽  
Wind Stress ◽  
Flow Structures ◽  
Pressure Gradients ◽  
Coriolis Parameter ◽  
Maximum Water ◽  
The Right ◽  
Stress Variations ◽  
Wedderburn Number ◽  
Lateral Structure

Abstract An analytical two-dimensional model is used to describe wind-induced modifications to density-driven flows in a semienclosed rotating basin. Wind stress variations produce enhancement, inversion, or damping of density-driven flows by altering the barotropic and baroclinic pressure gradients and by momentum transfer from wind drag. The vertical structure of wind-induced flows depends on αH, the nondimensional surface trapping layer, where α is the inverse of the Ekman layer depth d and H is the maximum water depth. For αH > 5 wind-driven flow structures are similar to the Ekman spiral; for αH < 2 wind-driven flows are unidirectional with depth. The relative importance of density to wind forcing is evaluated with the Wedderburn number W = τ−1ρH2D, which depends on water density ρ, mean depth H, a proxy of the baroclinic pressure gradient D, and wind stress τ. Because D depends on α and therefore on the eddy viscosity of water Az, wind speed and Az both modify W. Moreover, wind direction alters W by modifying the pressure gradient through the sea surface slope. The effect of Az is also evaluated with the Ekman number E = Az/fH2, where f is the Coriolis parameter. The alterations of the density-driven flow by the wind-driven flow are explored in the E and W parameter space through examination of the lateral structure of the resulting exchange flows. Seaward winds and positive transverse winds (to the right facing up basin in the Northern Hemisphere) result in vertically sheared flow structures for most of the E versus W space. In contrast, landward winds and negative transverse winds (to the left facing up basin) result in unidirectional landward flows for most of the E versus W space. When compared to observed and numerically simulated flow structures, the results from the analytical model compare favorably in regard to the main features.

The wall jet in a rotating fluid

1997 ◽  
Vol 335 ◽  
pp. 1-28 ◽  
Author(s):  
MELVIN E. STERN ◽  
ERIC P. CHASSIGNET ◽  
J. A. WHITEHEAD
Keyword(s):  
Vertical Wall ◽  
Three Dimensional ◽  
Point Vortex ◽  
Separation Distance ◽  
Finite Amplitude ◽  
Large Reynolds Number ◽  
Spatial Evolution ◽  
Two Dimensional ◽  
Rotating Fluid ◽  
Coriolis Parameter

The previously observed spatial evolution of the two-dimensional turbulent flow from a source on the vertical wall of a shallow layer of rapidly rotating fluid is strikingly different from the non-rotating three-dimensional counterpart, insofar as the instability eddies generated in the former case cause the flow to separate completely from the wall at a finite downstream distance. In seeking an explanation of this, we first compute the temporal evolution of two-dimensional finite-amplitude waves on an unstable laminar jet using a finite difference calculation at large Reynolds number. This yields a dipolar vorticity pattern which propagates normal to the wall, while leaving some of the near-wall vorticity (negative) of the basic flow behind. The residual far-field eddy therefore contains a net positive circulation and this property is incorporated in a heuristic point-vortex model of the spatial evolution of the instability eddies observed in a laboratory experiment of a flow emerging from a source on a vertical wall in a rotating tank. The model parameterizes the effect of Ekman bottom friction in decreasing the circulation of eddies which are periodically emitted from the source flow on the wall. Further downstream, the point vortices of the model merge and separate abruptly from the wall; the statistics suggest that the downstream separation distance scales with the Ekman spin-up time (inversely proportional to the square root of the Coriolis parameter f) and with the mean source velocity. When the latter is small and f is large, qualitative support is obtained from laboratory experiments.

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