scholarly journals Baroclinic Effects on Wind-Driven Lateral Circulation in Chesapeake Bay

2017 ◽  
Vol 47 (2) ◽  
pp. 433-445 ◽  
Author(s):  
Xiaohui Xie ◽  
Ming Li ◽  
William C. Boicourt
Keyword(s):  
Chesapeake Bay ◽  
Streamwise Vorticity ◽  
Lateral Velocity ◽  
Deep Channel ◽  
Lateral Circulation ◽  
Estuary Circulation ◽  
Stratified Estuary ◽  
Wedderburn Number ◽  
Channel Currents ◽  
Western Half

AbstractThe 2-month-long mooring data were collected in a straight midsection of Chesapeake Bay to document the lateral circulation driven by along-channel winds. Under upestuary winds, the lateral circulation featured a clockwise (looking into estuary) circulation in the surface layer, with lateral Ekman forcing as the dominant generation mechanism. Under downestuary winds, however, the lateral circulation displayed a structure dependent on the Wedderburn number W: a counterclockwise circulation at small W and two counterrotating vortices at large W. The surface lateral velocity was phase locked to the along-channel wind speed. Analysis of the streamwise vorticity equation showed that the strength and structure of the lateral circulation in this stratified estuary were largely determined by the competition between the tilting of planetary vorticity by along-channel currents and lateral baroclinic forcing due to sloping isopycnals. Under strong, downestuary winds, the lateral baroclinic forcing offset or reversed the tilting of planetary vorticity on the western half of the estuarine channel, resulting in two counterrotating lateral circulation cells. A bottom lateral flow was observed in the deep channel and appeared to be generated by lateral Ekman forcing on the along-channel currents.

scholarly journals Generation of Internal Solitary Waves by Lateral Circulation in a Stratified Estuary

2017 ◽  
Vol 47 (7) ◽  
pp. 1789-1797 ◽  
Author(s):  
Xiaohui Xie ◽  
Ming Li ◽  
Malcolm Scully ◽  
William C. Boicourt
Keyword(s):  
Solitary Waves ◽  
Tidal Flow ◽  
Tidal Currents ◽  
Internal Solitary Waves ◽  
Deep Channel ◽  
Mode 2 ◽  
Lee Wave ◽  
Salinity Data ◽  
Lateral Circulation ◽  
Stratified Estuary

AbstractInternal solitary waves are commonly observed in the coastal ocean where they are known to contribute to mass transport and turbulent mixing. While these waves are often generated by cross-isobath barotropic tidal currents, novel observations are presented suggesting that internal solitary waves result from along-isobath tidal flows over channel-shoal bathymetry. Mooring and ship-based velocity, temperature, and salinity data were collected over a cross-channel section in a stratified estuary. The data show that Ekman forcing on along-channel tidal currents drives lateral circulation, which interacts with the stratified water over the deep channel to generate a supercritical mode-2 internal lee wave. This lee wave propagates onto the shallow shoal and evolves into a group of internal solitary waves of elevation due to nonlinear steepening. These observations highlight the potential importance of three-dimensionality on the conversion of tidal flow to internal waves in the rotating ocean.

scholarly journals Modeling Influence of Stratification on Lateral Circulation in a Stratified Estuary

2009 ◽  
Vol 39 (9) ◽  
pp. 2324-2337 ◽  
Author(s):  
Peng Cheng ◽  
Robert E. Wilson ◽  
Robert J. Chant ◽  
David C. Fugate ◽  
Roger D. Flood
Keyword(s):  
Lower Layer ◽  
Cell Structure ◽  
Vertical Mixing ◽  
River Estuary ◽  
Vertical Diffusion ◽  
Lateral Asymmetry ◽  
Differential Diffusion ◽  
Deep Channel ◽  
Lateral Circulation ◽  
Stratified Estuary

Abstract The dynamics of lateral circulation in the Passaic River estuary is examined in this modeling study. The pattern of lateral circulation varies significantly over a tidal cycle as a result of the temporal variation of stratification induced by tidal straining. During highly stratified ebb tides, the lateral circulation exhibits a vertical two-cell structure. Strong stratification suppresses vertical mixing in the deep channel, whereas the shoal above the halocline remains relatively well mixed. As a result, in the upper layer, the lateral asymmetry of vertical mixing produces denser water on the shoal and fresher water over the thalweg. This density gradient drives a circulation with surface currents directed toward the shoal, and the currents at the base of the pycnocline are directed toward the thalweg. In the lower layer, the lateral circulation tends to reduce the tilting of isopycnals and gradually diminishes at the end of the ebb tide. A lateral baroclinic pressure gradient is a dominant driving force for lateral circulation during stratified ebb tides and is generated by differential diffusion that indicates a lateral asymmetry in vertical mixing. Over the thalweg, vertical mixing is strong during the flood and weak during the ebb. Over the shoal, the tidally periodical stratification shows an opposite cycle of that at the thalweg. Lateral straining tends to enhance stratification during flood tides and vertical diffusion maintains the relatively well-mixed water column over the shoal during the stratified ebb tides.

scholarly journals The Relative Importance of Wind Straining and Gravitational Forcing in Driving Exchange Flows in Tidally Energetic Estuaries

2019 ◽  
Vol 49 (3) ◽  
pp. 723-736 ◽  
Author(s):  
Xaver Lange ◽  
Hans Burchard
Keyword(s):  
Cross Sections ◽  
Steady State Solution ◽  
Estuarine Circulation ◽  
Wind Forcing ◽  
Tidal Mixing ◽  
Exchange Flow ◽  
Tidal Straining ◽  
Tidal Estuaries ◽  
Lateral Circulation ◽  
Wedderburn Number

AbstractIn straight tidal estuaries, residual overturning circulation results mainly from a competition between gravitational forcing, wind forcing, and friction. To systematically investigate this for tidally energetic estuaries, the dynamics of estuarine cross sections is analyzed in terms of the relation between gravitational forcing, wind stress, and the strength of estuarine circulation. A system-dependent basic Wedderburn number is defined as the ratio between wind forcing and opposing gravitational forcing at which the estuarine circulation changes sign. An analytical steady-state solution for gravitationally and wind-driven exchange flow is constructed, where tidal mixing is parameterized by parabolic eddy viscosity. For this simple but fundamental situation, is calculated, meaning that the up-estuary wind forcing needs to be 15% of the gravitational forcing to invert estuarine circulation. In three steps, relevant physical processes are added to this basic state: (i) tidal dynamics are resolved by a prescribed semidiurnal tide, leading to caused by tidal straining; (ii) lateral circulation is added by introducing cross-channel bathymetry, smoothly increasing from 0.47 (flat bed) to 1.3 (parabolic bed) due to an increasing effect of lateral circulation on estuarine circulation; and (iii) full dynamics of a real tidally energetic inlet with highly variable forcing, where results from a two-dimensional linear regression.

scholarly journals Lateral Circulation in a Partially Stratified Tidal Inlet

2018 ◽  
Author(s):  
Linlin Cui ◽  
Haosheng Huang ◽  
Chunyan Li ◽  
Dubravko Justic
Keyword(s):  
Pressure Gradient ◽  
Three Dimensional ◽  
Model Performance ◽  
Ocean Model ◽  
Tidal Inlet ◽  
Momentum Balance ◽  
Lateral Velocity ◽  
Short Period ◽  
Lateral Circulation ◽  
Differential Advection

Using a three-dimensional, hydrostatic, primitive-equation ocean model, this study investigates the dynamics of lateral circulation in a partially stratified tidal inlet, the Barataria Pass in the Gulf of Mexico, over a 25.6-hour diurnal tidal cycle. Model performance is assessed against observational data. During flood tide, the lateral circulation exhibits the characteristics similar to that induced by differential advection, i.e., lateral flow consists of two counter-rotating cells and is convergent at the surface. The analysis of momentum balance indicates that, in addition to the pressure gradient and vertical stress divergence, nonlinear advection and horizontal stress divergence are also important contributors. During ebb phase, the lateral circulation is mostly eastward for the whole water column and persisting for almost the whole period. The surface divergence suggested by the differential advection mechanism lasts for a very short period, if it ever exists. The main momentum balance across most of the transect during ebb is between the along-channel advection of cross-channel momentum and pressure gradient. The sectional averaged lateral velocity magnitude during ebb is comparable to that during flood, which is different from the idealized numerical experiment result.

scholarly journals Intratidal Dynamics of Fronts and Lateral Circulation at the Shoal–Channel Interface in a Partially Stratified Estuary

2012 ◽  
Vol 42 (5) ◽  
pp. 869-883 ◽  
Author(s):  
Audric G. Collignon ◽  
Mark T. Stacey
Keyword(s):  
San Francisco ◽  
San Francisco Bay ◽  
Salinity Gradient ◽  
Vertical Mixing ◽  
Tidal Amplitude ◽  
Nonlinear Advection ◽  
Lateral Circulation ◽  
Stratified Estuary ◽  
Differential Advection ◽  
Lateral Variations

Abstract In partially stratified shoal–channel estuaries, variations in bathymetry at the shoal–channel interface generate horizontal shears and density gradients, and foam lines characteristic of convergence fronts are frequently observed. This study is based on transect data collected every 30 min across the shoal–channel interface in south San Francisco Bay to analyze the dynamics of the transverse circulation and convergence fronts at this interface throughout a tidal cycle. During the ebb, a lateral density gradient develops as a result of the competition between differential advection of the longitudinal salinity gradient; lateral variations in vertical mixing; and nonlinear advection terms, which are strongest when convergence fronts develop early and late in the ebb. The lateral circulation over the slope is characterized by a large intratidal variability, reversing three times during the ebb. This variability is driven by a balance dominated by inertia and lateral baroclinic pressure gradient during the ebb but also involving Coriolis and advection terms at leading order. The convergence fronts developing at the edge of the shoal during the ebb are greatly affected by the direction of the lateral circulation on the slope and display similar intratidal variability as a result. Observations from moored instruments suggest that these processes are involved in all partially stratified spring ebbs in south San Francisco Bay and are more sensitive to variations in tidal amplitude than density stratification on the slope.

scholarly journals Lateral Circulation in a Partially Stratified Tidal Inlet

2018 ◽  
Vol 6 (4) ◽  
pp. 159 ◽  
Author(s):  
Linlin Cui ◽  
Haosheng Huang ◽  
Chunyan Li ◽  
Dubravko Justic
Keyword(s):  
Pressure Gradient ◽  
Three Dimensional ◽  
Model Performance ◽  
Ocean Model ◽  
Tidal Inlet ◽  
Momentum Balance ◽  
Lateral Velocity ◽  
Short Period ◽  
Lateral Circulation ◽  
Differential Advection

Using a three-dimensional, hydrostatic, primitive-equation ocean model, this study investigates the dynamics of lateral circulation in a partially stratified tidal inlet, the Barataria Pass in the Gulf of Mexico, over a 25.6 h diurnal tidal cycle. Model performance is assessed against observational data. During flood tide, the lateral circulation exhibits the characteristics similar to those induced by differential advection, i.e., lateral flow consists of two counter-rotating cells and is convergent at the surface. The analysis of momentum balance indicates that, in addition to the pressure gradient and vertical stress divergence, nonlinear advection and horizontal stress divergence are also important contributors. During ebb phase, the lateral circulation is mostly toward the right shoal (when looking into the estuary) for the whole water column and persisting for almost the whole period. The surface divergence suggested by the differential advection mechanism lasts for a very short period, if it ever exists. The main momentum balance across most of the transect during ebb is between the along-channel advection of cross-channel momentum and pressure gradient. The sectional averaged lateral velocity magnitude during ebb is comparable to that during flood, which is different from the idealized numerical experiment result.

scholarly journals Generation of Internal Lee Waves by Lateral Circulation in a Coastal Plain Estuary

2019 ◽  
Vol 49 (7) ◽  
pp. 1687-1697
Author(s):  
Xiaohui Xie ◽  
Ming Li
Keyword(s):  
Internal Waves ◽  
Lateral Flow ◽  
Coastal Plain Estuary ◽  
Deep Channel ◽  
Mode 2 ◽  
Lee Waves ◽  
Lee Wave ◽  
Lateral Circulation ◽  
Internal Hydraulic Jump ◽  
Internal Bores

AbstractRecent mooring observations at a cross-channel section in Chesapeake Bay showed that internal solitary waves regularly appeared during certain phases of a tidal cycle and propagated from the deep channel to the shallow shoal. It was hypothesized that these waves resulted from the nonlinear steepening of internal lee waves generated by lateral currents over channel-shoal topography. In this study numerical modeling is conducted to investigate the interaction between lateral circulation and cross-channel topography and discern the generation mechanism of the internal lee waves. During ebb tides, lateral bottom Ekman forcing drives a counterclockwise (looking into estuary) lateral circulation, with strong currents advecting stratified water over the western flank of the deep channel and producing large isopycnal displacements. When the lateral flow becomes supercritical with respect to mode-2 internal waves, a mode-2 internal lee wave is generated on the flank of the deep channel and subsequently propagates onto the western shoal. When the bottom lateral flow becomes near-critical or supercritical with respect to mode-1 internal waves, the lee wave evolves into an internal hydraulic jump. On the shallow shoal, the lee waves or jumps evolve into internal bores of elevation.

scholarly journals Turbulence Dynamics at the Shoal–Channel Interface in a Partially Stratified Estuary

2013 ◽  
Vol 43 (5) ◽  
pp. 970-989 ◽  
Author(s):  
Audric G. Collignon ◽  
Mark T. Stacey
Keyword(s):  
San Francisco ◽  
San Francisco Bay ◽  
Analytical Framework ◽  
Velocity Gradients ◽  
Simple Scaling ◽  
Lateral Circulation ◽  
Tidally Driven ◽  
Stratified Estuary ◽  
Bed Friction ◽  
Shear Production

Abstract Turbulence observations at the shoal–channel interface in South San Francisco Bay are described and analyzed in this work. Profiles of turbulent kinetic energy (TKE) shear production and dissipation rate are estimated from ADCP beam velocities over a nine-day period during winter 2009 when the estuary was partially stratified. The TKE shear production profiles are consistent with a tidally driven bottom boundary layer, except late in the ebb when shear production intensifies and the region of maximum production is located in the upper half of the water column. A simple scaling for the depth-averaged TKE shear production based on bed friction performs well except during this late ebb period when it fails to predict the peak in shear production, which suggests that a mechanism other than bottom drag drives turbulence dynamics during this period. The profiles of TKE dissipation rates also display a late ebb peak. A lateral circulation develops at the shoal–channel interface during this late ebb period, and its effects on turbulence dynamics are investigated. An analytical framework is developed to identify and quantify these effects. Four mechanisms through which the lateral circulation can impact stability are identified, and two are found to be important during the late ebb period in South San Francisco Bay: the straining of the lateral density and velocity gradients in the lateral circulation. These results suggest that the lateral circulation acts to reduce the gradient Richardson number and is driving the late ebb peak in turbulence production and dissipation.

scholarly journals Coherent Streamwise Vortex Structure of a Three-Dimensional Wall Jet

Fluids ◽  
2021 ◽  
Vol 6 (1) ◽  
pp. 35
Author(s):  
Lhendup Namgyal ◽  
Joseph W. Hall
Keyword(s):  
Coherent Structures ◽  
Near Field ◽  
Three Dimensional ◽  
Streamwise Vortex ◽  
Relative Strength ◽  
Vortex Structures ◽  
Wall Jet ◽  
Streamwise Vorticity ◽  
Lateral Velocity ◽  
Near Wall

The dynamics of the coherent structures in a turbulent three-dimensional wall jet with an exit Reynolds number of 250,000 were investigated using the Snapshot Proper Orthogonal Decomposition (POD). A low-dimensional reconstruction using the first 10 POD modes indicates that the turbulent flow is dominated by streamwise vortex structures that grow in size and relative strength, and that are often accompanied by strong lateral sweeps of fluid across the wall. This causes an increase in the bulging and distortions of streamwise velocity contours as the flow evolves downstream. The instantaneous streamwise vorticity computed from the reconstructed instantaneous velocities has a high level of vorticity associated with these outer streamwise vortex structures, but often has a persistent pair of counter-rotating regions located close to the wall on either side of the jet centerline. A model of the coherent structures in the wall jet is presented. In this model, streamwise vortex structures are produced in the near-field by the breakdown of vortex rings formed at the jet outlet. Separate structures are associated with the near-wall streamwise vorticity. As the flow evolves downstream, the inner near-wall structures tilt outward, while the outer streamwise structures amalgamate to form larger streamwise asymmetric structures. In all cases, these streamwise vortex structures tend to cause large lateral velocity sweeps in the intermediate and far-field regions of the three-dimensional wall jet. Further, these structures meander laterally across the jet, causing a strongly intermittent jet flow.

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