Ocean currents measured concurrently on and off the Sydney area continental shelf

1974 ◽  
Vol 25 (3) ◽  
pp. 427 ◽  
Author(s):  
GR Cresswell
Keyword(s):  
Internal Waves ◽  
Current Speed ◽  
East Australian Current ◽  
Surface Currents ◽  
M Current ◽  
Variable Surface ◽  
Oscillatory Velocity ◽  
Counter Current ◽  
A Current ◽  
Experiment Duration

Recording current meters, a GEK, and XBT'S were used to study on and off-shelf currents for a 10 day period. Oscillatory currents with frequencies 3-8 cph were observed quite frequently at a mid-shelf mooring (depth 140 m). They were perhaps due to internal waves and were often associated with sudden increases or decreases in current speed. On two occasions the speed increases occurred when meteorological fronts passed over. The horizontal oscillatory velocity components of two of the best wave examples showed clear evidence for clockwise polarization. At the edge of the shelf (180 m), current meters 10 and 50 m above the bottom, while not showing internal waves, showed a current somewhat variable in speed (mean: 20 cm/sec; maximum 50 cm/sec), but reasonably constant in direction (northward) for the experiment duration. At this time the main southward flowing core of the East Australian Current was 120 km out from the edge of the shelf, while the region out to 50 km from the shelf contained variable surface currents. The current in the deeper water at the edge of the shelf was tentatively labelled a counter current.

scholarly journals Stability of a buoyancy-driven coastal current at the shelf break

2002 ◽  
Vol 452 ◽  
pp. 97-121 ◽  
Author(s):  
C. CENEDESE ◽  
P. F. LINDEN
Keyword(s):  
Continental Shelf ◽  
Continental Slope ◽  
Unstable Mode ◽  
Shelf Break ◽  
Coastal Current ◽  
Surface Currents ◽  
Flat Bottom ◽  
Vertical Boundary ◽  
Axisymmetric Disturbances ◽  
A Current

Buoyancy-driven surface currents were generated in the laboratory by releasing buoyant fluid from a source adjacent to a vertical boundary in a rotating container. Different bottom topographies that simulate both a continental slope and a continental ridge were introduced in the container. The topography modified the flow in comparison with the at bottom case where the current grew in width and depth until it became unstable once to non-axisymmetric disturbances. However, when topography was introduced a second instability of the buoyancy-driven current was observed. The most important parameter describing the flow is the ratio of continental shelf width W to the width L* of the current at the onset of the instability. The values of L* for the first instability, and L*−W for the second instability were not influenced by the topography and were 2–6 times the Rossby radius. Thus, the parameter describing the flow can be expressed as the ratio of the width of the continental shelf to the Rossby radius. When this ratio is larger than 2–6 the second instability was observed on the current front. A continental ridge allowed the disturbance to grow to larger amplitude with formation of eddies and fronts, while a gentle continental slope reduced the growth rate and amplitude of the most unstable mode, when compared to the continental ridge topography. When present, eddies did not separate from the main current, and remained near the shelf break. On the other hand, for the largest values of the Rossby radius the first instability was suppressed and the flow was observed to remain stable. A small but significant variation was found in the wavelength of the first instability, which was smaller for a current over topography than over a flat bottom.

Longshore Current Generation by Internal Waves in the Strait of Georgia

1975 ◽  
Vol 12 (3) ◽  
pp. 472-488 ◽  
Author(s):  
Richard E. Thomson
Keyword(s):  
Internal Waves ◽  
Maximum Speed ◽  
Longshore Current ◽  
Delta Area ◽  
Strait Of Georgia ◽  
Wave Characteristics ◽  
Fraser River Delta ◽  
Vertical Eddy ◽  
Measured Water ◽  
A Current

Presented in this paper is a derivation of the longshore current generated by breaking lowest mode internal waves in a two layer fluid of slowly shallowing depth, with emphasis on the nearshore region of the Fraser River delta in the Strait of Georgia. It is proposed that such a current, having a maximum speed of order 104/μv cm3/s2 (equal to 102 cm/s for reasonable vertical eddy viscosities, μv, of 102 cm2/s) and a width of order kilometers based on measured water properties and internal wave characteristics in the Strait, is responsible for the persistent northward flow observed to be associated with the delta in summer. Accordingly, it is suggested that the longshore current would have important implications to sedimentation rates and pollutant dispersal in the delta area, with greatest effects possibly occurring in summer and fall when the stratification in the Strait of Georgia is most pronounced.

scholarly journals V. On the "blaze currents" of the frog's eyeball

1901 ◽  
Vol 194 (194-206) ◽  
pp. 183-233 ◽  
Keyword(s):  
Electrical Stimulation ◽  
Positive Response ◽  
Electrical Response ◽  
Electrical Current ◽  
Positive Direction ◽  
Electrical Stimuli ◽  
Counter Current ◽  
A Current

In a recent communication to the Society I have stated that the normal electrical response of the eye to light consists in a current traversing the eye ball in a positive direction, i. e . from fundus to cornea, and that a similar positive response is aroused by meachanical and by electrical stimuli, whatever be the direction of the latter. I have designated this positive response to non-luminous stimuli as the retainal discharge or blaze. With reference to electrical stimulation, its most characteristic from is when it occurs in the same dorection as the current by which it is excited, i. e . when it cannot be polarisation counter-current. It is in such case analogous with the discharge of an electrical organ excited by an electrical current in the direction of normal discharge, and, indeed, it may be of such magnitued as to lead an observer to regard retain in the light of an electrical organ.

Large-scale influence of the New Zealand seafloor topography on western boundary currents of the South Pacific Ocean.

1985 ◽  
Vol 36 (1) ◽  
pp. 1 ◽  
Author(s):  
RA Heath
Keyword(s):  
New Zealand ◽  
West Coast ◽  
East Coast ◽  
South Pacific ◽  
Surface Flow ◽  
Current Speed ◽  
Western Boundary ◽  
East Australian Current ◽  
South Pacific Ocean ◽  
Tasman Sea

The extensive New Zealand submarine platform lying approximately 1600 km east of Australia has a strong influence on the South Pacific circulation. Together with the Kermadec Ridge, it is the western boundary of the deep South Pacific Ocean with an associated deep western boundary current. Although New Zealand probably influences where the East Australian Current separates from the east Australian coast, at the latitude of northernmost New Zealand, the sloping seafloor on the New Zealand west coast does allow for a meridional flow there. However, the decrease in current speed with depth does decrease the influence of the bottom topography. The net result is that there is both an intensification of the zonal flow across the Tasman Sea at the latitude of northernmost New Zealand, the speed of which is enhanced by the flow over the extensive ridge system, and a general eastwards flow in the Tasman Sea over the latitudinal range of New Zealand, which feeds meridional flows on the New Zealand west coast. It is suggested that the general west to east flow past New Zealand restricts the westward propagation of second- and higher-order baroclinic Rossby waves with the result that, whereas the East Australian Current has rapid near-surface flow which decreases rapidly with depth in the upper 500 m, the surface flow on the east coast of New Zealand is less rapid and decreases more uniformly with depth. One possible consequence of the current speed change with depth is that the flow and eddies on the New Zealand east coast appear to be influenced by the bathymetry whereas the East Australian Current eddies are more a primary component of the current linked to instability in the current system.

scholarly journals Subsurface Jets in the Northwestern Gulf of Mexico

2009 ◽  
Vol 39 (11) ◽  
pp. 2875-2891 ◽  
Author(s):  
Peter Hamilton ◽  
Antoine Badan
Keyword(s):  
Velocity Profile ◽  
Gulf Of Mexico ◽  
Internal Waves ◽  
Vertical Axis ◽  
Surface Currents ◽  
Profile Data ◽  
Near Surface ◽  
Anomalous Density ◽  
Slope Topography ◽  
Upper Slope

Abstract Subsurface jets, defined as having velocity maxima >40 cm s−1 at depths between 100 and 350 m, and being surrounded by much weaker near-surface currents, have been observed over the northwestern Gulf of Mexico continental slope. The observations were from an array of 14 moorings equipped with upward-looking 75-kHz ADCPs deployed at 450–500 m. A total of 10 jet events were observed in 18 ADCP years of velocity profile data, where these events were clearly not the result of downward-propagating inertial internal waves. The jets had durations from about 1 to 8 days and were usually associated with interactions between similarly sized cyclones and anticyclones over the slope or with the interaction of an eddy with upper-slope topography. The jets are associated with potential vorticity anomalies and their inferred length scales indicate that the dynamics depart from simple geostrophic balances. Observed anomalous density gradients present during the jets seem to involve the tilting of the vertical axis of the center of rotation of one or more of the interacting eddies.

The action of a surface current used as a breakwater

1955 ◽  
Vol 231 (1187) ◽  
pp. 466-478 ◽  
Keyword(s):  
Surface Current ◽  
Water Current ◽  
Air Bubbles ◽  
Surface Currents ◽  
Mean Velocity ◽  
Uniform Velocity ◽  
Sea Bottom ◽  
The Mean ◽  
Perforated Tube ◽  
A Current

The conditions under which an outward-flowing surface current can prevent the passage of waves coming in from the sea are investigated mathematically. Two types of current are considered: ( a ) a current with uniform velocity extending to a depth h ; ( b ) a current with velocity decreasing uniformly and vanishing at depth h . They have very similar effects. The mean velocity required to stop waves of given frequency is rather greater in case ( a ) than in case ( b ). The water current produced by a curtain of air bubbles from a perforated tube on the sea bottom is investigated theoretically on the assumption that the bubbles are very small. Evans (1955) has measured the surface currents produced in a tank by a bubble curtain and finds them smaller than predicted. The discrepancy is partly due to the fact that the bubbles were not very small.

Internal waves detected with a continental shelf current-meter array

1981 ◽  
Vol 32 (1) ◽  
pp. 1 ◽  
Author(s):  
GR Cresswell
Keyword(s):  
Shear Flow ◽  
Wave Packet ◽  
Continental Shelf ◽  
Internal Wave ◽  
Internal Waves ◽  
Temperature Structure ◽  
M Current

A 1-km square current-meter array at 130 m depth on the Sydney continental shelf revealed an internal wave packet at 100 m depth propagating coastward at 0.5 m s-1 with a period of c. 15 min and a wavelength of c. 400 m. Current meters at 35 and 70 m depth on one mooring showed what was possibly an independent packet that was detected 20 min before the deeper one and that showed depressions of the temperature structure (of 20 m) and shear flow between the two meters.

Wave Elevation for an Array of Columns Under Wave-Current Interactions

2021 ◽  
pp. 1-15
Author(s):  
Song Gao ◽  
Bin Teng
Keyword(s):  
Free Surface ◽  
Singular Integrals ◽  
Spatial Location ◽  
Current Speed ◽  
Wave Direction ◽  
Wave Elevation ◽  
Diffraction Model ◽  
Nearly Singular Integrals ◽  
Free Surface Wave ◽  
A Current

Abstract A wave and current diffraction model is developed based on the potential flow theory and a high-order boundary element method with the successful treatment of singular and nearly singular integrals. The wave-current diffraction from four mounted cylindrical columns are computed, and the free surface wave elevations among the columns are investigated. The influences of the current speed, wave direction, and column spacing on the wave elevation are examined. Ultimately, the presence of a current has a significant influence on the magnitude, spatial location and occurrence frequency of the maximum wave elevation.

Surface currents on models of force-free solar magnetic flux tubes

1994 ◽  
Vol 51 (1) ◽  
pp. 163-176 ◽  
Author(s):  
D. B. Melrose ◽  
Jennifer Nicholls ◽  
N. G. Broderick
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Flux Tube ◽  
Surface Currents ◽  
Current Profile ◽  
Flux Tubes ◽  
Piecewise Constant ◽  
Cylindrically Symmetric ◽  
Magnetic Flux Tubes ◽  
A Current

A model of a cylindrically symmetric, force-free magnetic field consisting of a sequence of concentric layers with piecewise-constant α is used to construct models of the surface currents on isolated, force-free magnetic flux tubes. Two boundary conditions are considered: a current-neutralized flux tube (Bφ = 0, Bz φ 0, Bz ≠ O at r > r0), and an isolated current-carrying flux tube (Bφ ≠ 0, Bz = 0 at r > r0). A single-a model that is current-neutralized is a reverse-field pinch, and is unacceptable as a model for a solar flux tube. Examples of two-α models for a current-neutralized flux tube are presented. The models of the surface currents satisfying either boundary condition are shown to simplify considerably when the surface layer is thin. A model consisting of several layers, with piecewise-constant α, may be used to find an approximate solution for a force-free flux tube with an arbitrarily specified current profile.

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