scholarly journals Impact of Shelf Valleys on the Spread of Surface Trapped River Plumes

2020 ◽  
Author(s):  
Canbo Xiao ◽  
Weifeng (Gordon) Zhang ◽  
Ying Chen
Keyword(s):  
Incident Angle ◽  
Coastal Current ◽  
Current Sensitivity ◽  
Coriolis Parameter ◽  
River Plumes ◽  
Estuary Mouth ◽  
Freshwater Transport ◽  
Bulge Region ◽  
Freshwater Plumes ◽  
Topographic Influence

AbstractThis study focuses on mechanisms of shelf valley bathymetry affecting the spread of riverine freshwater in the nearshore region. In the context of Changjiang River, a numerical model is used with different no-tide idealized configurations to simulate development of unforced river plumes over a sloping bottom, with and without a shelf valley off the estuary mouth. All simulated freshwater plumes are surface-trapped with continuously growing bulges near the estuary mouth and narrow coastal currents downstream. The simulations indicate that a shelf valley tends to compress the bulge along the direction of the valley long axis and modify the incident angle of the bulge flow impinging toward the coast, which then affects the strength of the coastal current. The bulge compression results from geostrophic adjustment and isobath-following tendency of the depth-averaged flow in the bulge region. Generally, the resulting change in the direction of the bulge impinging flow enhances down-shelf momentum advection and freshwater delivery into the coastal current. Sensitivity simulations with altered river discharges (Q), Coriolis parameter, shelf bottom slope, valley geometry, and ambient stratification show that enhancement of down-shelf freshwater transport in the coastal current, ΔQc, increases with increasing valley depth within the bulge region and decreasing slope Burger number of the ambient shelf. Assuming potential vorticity conservation, a scaling formula of ΔQc?Q is developed, and it agrees well with results of the sensitivity simulations. Mechanisms of valley influences on unforced river plumes revealed here will help future studies of topographic influence on river plumes under more realistic conditions.

scholarly journals Enhancement of Alongshore Freshwater Transport in Surface-Advected River Plumes by Tides

2014 ◽  
Vol 44 (11) ◽  
pp. 2951-2971 ◽  
Author(s):  
Shih-Nan Chen
Keyword(s):  
Numerical Study ◽  
Incident Angle ◽  
Ocean Modeling ◽  
Positive Pressure ◽  
Coastal Current ◽  
Current Transport ◽  
Coastal Currents ◽  
Regional Ocean Modeling System ◽  
Tidal Forcing ◽  
Freshwater Transport

Abstract A recent numerical study by Isobe showed that imposing alongshore tidal forcing on buoyant coastal discharge enhances the net freshwater transport in the coastal currents. The mechanisms for this transport enhancement are studied using a three-dimensional, primitive equation ocean model [Regional Ocean Modeling System (ROMS)]. Lagrangian drifters are used to trace the freshwater transport paths. It is found that the river plume bulge circulation largely follows the rigid-body motion (i.e., constant vorticity). The buoyant fluid near the bulge’s outer edge is thinner and faster, behaving as a baroclinic jet. The bulge currents then split after impinging on the coast. The outer fluid feeds the downshelf-flowing coastal currents, while the inner fluid recirculates to form the bulge. The coastal current transport estimated from the present and prior studies corresponds well to a baroclinic jet theory, with the incident angle of bulge currents at the coast being a key parameter. Without tides, the bulge is approximately circular. The incident angle measured with respect to the cross-shore axis is small. With tides, the convergence of tidal momentum fluxes near the upshelf plume front leads to a positive pressure anomaly, which acts to compress the bulge shoreward. As a result, the incident angle increases, which in turn enhances the downshelf momentum input, thus increasing the freshwater transport in the coastal currents. Finally, the parameter space for coastal current transport in the presence of tidal forcing is explored with a conceptual model. A few observational examples are given.

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 The Dispersal of Dense Water Formed in an Idealized Coastal Polynya on a Shallow Sloping Shelf

2014 ◽  
Vol 44 (6) ◽  
pp. 1563-1581 ◽  
Author(s):  
Weifeng G. Zhang ◽  
Claudia Cenedese
Keyword(s):  
Pressure Gradient ◽  
Water Depth ◽  
Velocity Ratio ◽  
Source Region ◽  
Coastal Current ◽  
Scaling Analysis ◽  
Reduced Gravity ◽  
Coriolis Parameter ◽  
Dense Water ◽  
Coastal Polynya

Abstract This study examines the dispersal of dense water formed in an idealized coastal polynya on a sloping shelf in the absence of ambient circulation and stratification. Both numerical and laboratory experiments reveal two separate bottom pathways for the dense water: an offshore plume moving downslope into deeper ambient water and a coastal current flowing in the direction of Kelvin wave propagation. Scaling analysis shows that the velocity of the offshore plume is proportional not only to the reduced gravity, bottom slope, and inverse of the Coriolis parameter, but also to the ratio of the dense water depth to total water depth. The dense water coastal current is generated by the along-shelf baroclinic pressure gradient. Its dynamics can be separated into two stages: (i) near the source region, where viscous terms are negligible, its speed is proportional to the reduced gravity wave speed and (ii) in the far field, where bottom drag becomes important and balances the pressure gradient, the velocity is proportional to Hc[g′/(LCd)]1/2 in which Hc is the water depth at the coast, g′ the reduced gravity, Cd the quadratic bottom drag coefficient, and L the along-shelf span of the baroclinic pressure gradient. The velocity scalings are verified using numerical and laboratory sensitivity experiments. The numerical simulations suggest that only 3%–23% of the dense water enters the coastal pathway, and the percentage depends highly on the ratio of the velocities of the offshore and coastal plumes. This makes the velocity ratio potentially useful for observational studies to assess the amount of dense water formed in coastal polynyas.

Physical properties of Great Barrier Reef lagoon waters near Townsville. I. Effects of Burdekin River floods

1981 ◽  
Vol 32 (3) ◽  
pp. 305 ◽  
Author(s):  
E Wolanski ◽  
M Jones
Keyword(s):  
Physical Properties ◽  
Great Barrier Reef ◽  
River Mouth ◽  
Estuarine Circulation ◽  
Barrier Reef ◽  
River Plumes ◽  
Tidal Flushing ◽  
Reef Lagoon ◽  
Freshwater Plumes ◽  
Land Runoff

Floods from land runoff, principally the Burdekin River. created buoyant freshwater plumes along the coast of the Great Barrier Reef lagoon. From Cape Upstart near the Burdekin River mouth to Innisfail 250 km north. no evidence was found of these plumes directly reaching the Great Barrier Reef. Small buoyant patches, detached from the river plumes, found further offshore might reach the Great Barrier Reef. Classical estuarine circulation in the lagoon. even in flood conditions, and tidal flushing by the ocean do not appear to be significant compared to advective processes.

scholarly journals Detiding Measurement on Transport of the Changjiang-Derived Buoyant Coastal Current

2013 ◽  
Vol 43 (11) ◽  
pp. 2388-2399 ◽  
Author(s):  
Hui Wu ◽  
Bing Deng ◽  
Rui Yuan ◽  
Jun Hu ◽  
Jinghua Gu ◽  
...  
Keyword(s):  
Large River ◽  
Volume Transport ◽  
Surface Velocity ◽  
Coastal Current ◽  
In Situ Data ◽  
Freshwater Transport ◽  
Chinese Coast ◽  
First Time ◽  
O 10

Abstract Measuring the transport of the Changjiang (also known as the Yangtze) River–derived buoyant coastal current, that is, the Min–Zhe Coastal Current, is of great importance for understanding the fate of terrestrial materials from this large river into the open ocean, but it is usually difficult to achieve because of the energetic tidal currents along the Chinese coast. In February 2012, a detiding cruise survey was carried out using the phase-averaging method. For the first time, this coastal current has been quantified with in situ data and has been shown to have a volume transport of 0.215 Sv (1 Sv ≡ 106 m3 s−1) and a maximum surface velocity of ~50 cm s−1. The ratio between the volume transport of the buoyant coastal current and that of the Changjiang is O(10). Freshwater transport by the buoyant coastal current accounts for over 90% of the Changjiang River's discharge. Buoyancy and winds are both important in driving this current.

The freshwater transport and dynamics of the western Maine coastal current

2004 ◽  
Vol 24 (12) ◽  
pp. 1339-1357 ◽  
Author(s):  
W.R. Geyer ◽  
R.P. Signell ◽  
D.A. Fong ◽  
J. Wang ◽  
D.M. Anderson ◽  
...  
Keyword(s):  
Coastal Current ◽  
Freshwater Transport

The impact of spatial wind variations on freshwater transport by the Alaska Coastal Current

2008 ◽  
Vol 66 (6) ◽  
pp. 899-925 ◽  
Author(s):  
John Rogers-Cotrone ◽  
Alexander E. Yankovsky ◽  
Thomas J. Weingartner
Keyword(s):  
Coastal Current ◽  
Freshwater Transport ◽  
Alaska Coastal Current ◽  
The Impact

scholarly journals Evolution of the Freshwater Coastal Current at the Southern Tip of Greenland

2018 ◽  
Vol 48 (9) ◽  
pp. 2127-2140 ◽  
Author(s):  
Peigen Lin ◽  
Robert S. Pickart ◽  
Daniel J. Torres ◽  
Astrid Pacini
Keyword(s):  
Velocity Structure ◽  
Greenland Ice Sheet ◽  
Volume Transport ◽  
The Arctic ◽  
Labrador Sea ◽  
Coastal Current ◽  
Velocity Measurements ◽  
The West ◽  
West Side ◽  
Freshwater Transport

AbstractShipboard hydrographic and velocity measurements collected in summer 2014 are used to study the evolution of the freshwater coastal current in southern Greenland as it encounters Cape Farewell. The velocity structure reveals that the coastal current maintains its identity as it flows around the cape and bifurcates such that most of the flow is diverted to the outer west Greenland shelf, while a small portion remains on the inner shelf. Taking into account this inner branch, the volume transport of the coastal current is conserved, but the freshwater transport decreases on the west side of Cape Farewell. A significant amount of freshwater appears to be transported off the shelf where the outer branch flows adjacent to the shelfbreak circulation. It is argued that the offshore transposition of the coastal current is caused by the flow following the isobaths as they bend offshore because of the widening of the shelf on the west side of Cape Farewell. An analysis of the potential vorticity shows that the subsequent seaward flux of freshwater can be enhanced by instabilities of the current. This set of circumstances provides a pathway for the freshest water originating from the Arctic, as well as runoff from the Greenland ice sheet, to be fluxed into the interior Labrador Sea where it could influence convection in the basin.

Contrast in Scanning Images of Thin Crystals

1972 ◽  
Vol 30 ◽  
pp. 520-521
Author(s):  
S. Kimoto ◽  
H. Hashimoto ◽  
S. Takashima ◽  
R. M. Stern ◽  
T. Ichinokawa
Keyword(s):  
Crystal Surface ◽  
Solid Angle ◽  
Incident Angle ◽  
Intensity Variation ◽  
Lattice Defects ◽  
Scanning Microscope ◽  
Electron Detector ◽  
Backscattered Electrons ◽  
Electron Image ◽  
Backscattered Electron

The most well known application of the scanning microscope to the crystals is known as Coates pattern. The contrast of this image depends on the variation of the incident angle of the beam to the crystal surface. The defect in the crystal surface causes to make contrast in normal scanning image with constant incident angle. The intensity variation of the backscattered electrons in the scanning microscopy was calculated for the defect in the crystals by Clarke and Howie. Clarke also observed the defect using a scanning microscope.This paper reports the observation of lattice defects appears in thin crystals through backscattered, secondary and transmitted electron image. As a backscattered electron detector, a p-n junction detector of 0.9 π solid angle has been prepared for JSM-50A. The gain of the detector itself is 1.2 x 104 at 50 kV and the gain of additional AC amplifier using band width 100 Hz ∼ 10 kHz is 106.

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