Showing papers on "Ocean current published in 1974"

Sea Level and the Seasonal Fluctuations of the Equatorial Currents in the Western Pacific Ocean

Abstract: The seasonal variations of the dynamic topography relative to 500 decibars in the western equatorial Pacific, using data from 6900 hydrographic stations, are compared with the seasonal fluctuations of sea level observed at eleven islands. It is shown that the changes in the meridional profile of sea level correlate with changes in the strength of the major ocean currents measured by their speed or by geostrophic transports. The strength of the North Equatorial Current and that of the Countercurrent vary synchronously, both being strong in fall and weak in spring. The South Equatorial Current varies exactly out of phase with the two Northern Hemisphere currents, but is apparently in phase with the Undercurrent. Investigation of the particular example indicates that large anomalies seem to behave in the same fashion as the seasonal fluctuations of these currents.

The Dynamic Topography of the Pacific Ocean and Its Fluctuations

Abstract: : The dynamic topography of the Pacific Ocean has been mapped for bimonthly periods relative to 500 and 1000 decibars and based on approximately 66,600 hydrographic stations. The maps indicate that the largest seasonal fluctuations are associated with the equatorial current systems. In the subtropical gyres and in higher latitudes, dynamic topography varies seasonally in accordance with the annual cycle of surface layer temperature, but the pattern of isobars does not change much between summer and winter. In the western portion of the North Pacific anticyclonic gyre, a U-shaped ridge is developed, separating the western boundary current from the interior of the gyre and linking the north equatorial ridge with a ridge at the right flank of the Kuroshio. (Modified author abstract)

Nearshore Circulations under Sea Breeze Conditions and Wave-current Interactions in the Surf Zone

Abstract: : Numerical models for nearshore circulation patterns in the surf zone were developed and applied to an observed condition subjected to a sea breeze environment Bottom topography and input waves were derived from observed data to predict surf zone circulation as a function of time of day It was found that many features observed in the surf zone were modeled but wave-current interactions are known to be important Wave-current interactions were modeled for shallow water assuming a two-dimensional motion which included rip current and lonshore current components The refraction effects caused by even small currents produce major changes in the wave induced driving forces in the surf zone which leads to the prediction of entirely different rip-current patterns when wave-current interactions are considered Numerical results are presented and a discussion of the numerical techniques is included A review of water wave theories to include mass transport, vorticity and current was made for a vertical section in shallow water of constant depth

On the Mixed Stability Program for Quasi-Geostrophic Ocean Currents

Abstract: A simple, two-layer, quasi-geostrophic model is used to investigate the stability of baroclinic currents confined to a finite length scale L in a basin of considerably larger dimension (4L). The current distributions studied are typical of oceanic boundary currents and of certain oceanic and atmospheric eddies. The sharp shear zone which couples the relativity broad interior portion of the current to the resting ocean makes it possible for instabilities to arise which can get their energy either from the available potential energy of the tilted interface or from the basic zonal kinetic energy of the current. In a two-layer inviscid ocean of density contrast Δρ on an f-plane, and with a flat bottom, the two parameters governing the stability of a given current are the internal Froude number F=ρf2L2(gΔρH)−1 and the layer depth ratio δ=Htop/Hbottom. The stability calculations show that these finite-width currents can be stable for intermediate values of F if δ is small enough. For moderate δ (0.2 to...

Atlantic Water Circulation in the Canada Basin

Abstract: Circulation of the Atlantic water layer in the Canada Basin of the Arctic Ocean is re-examined using the numerous data acquired in the last decade. Methods of analysis were (1) the core layer method as used ten years previously, (2) a 500/1000-decibar dynamic topography, and (3) the available direct current measurements. The results confirm the general anti-cyclonic circulation deduced previously which has a transport of about 0.6 sverdrups. A new feature is described: a sub-surface counterflow moving southeast along the eastern slope of the Chukchi Rise with a transport of about 0.3 sverdrups.

Satellite photography of eddies in the Gulf Loop Current

Abstract: Cyclonic ocean eddies, approximately 12 to 32 kilometers in diameter, have been photographed in the eastern Gulf of Mexico by SKYLAB. Apparently caused by horizon velocity shear, these features are associated with the Gulf Loop Current, whose position was known a fortnight before and after the observation. The eddies were discovered in sunlight-enhanced patterns of streamlines on the surface, and appear to be embedded in the flow.

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

Abstract: 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.

Eastern Intensification of Ocean Spin-Down: Application to El Niño

Abstract: The El Nino studies carried out by Bjerknes indicate that the anomalous warming of the eastern boundary tropical ocean in 1939 and 1958 extended 1000 km into the interior ocean, corresponding with a diversion of the Humboldt Current offshore south of Peru. Furthermore, these features were associated with a large-scale weakening of the Southern Hemisphere wind systems. This suggests that major changes occurred in the wind-driven eastern boundary circulation during this time. To see if this is plausible from a theoretical viewpoint, we consider a mathematical model of large-scale ocean spin-down, induced by a reduction in the mean strength of the large-scale wind systems. This model shows that spin-down of the interior ocean is intensified along the eastern boundary with de-intensification propagating in time toward the west and extending out to 1000 km after one year. The interior portions of the ocean circulation are only weakly affected. Moreover, the spin-down is asymmetric, with greater de-int...

On Planetary Voltages, Ocean Tides, and Electrical Conductivity below the Pacific

Abstract: Voltages observed between the ends of various underwater telegraph cables up to 9660 km long are analyzed in terms of planetary electric fields, deep ocean tides, wind driven surface currents, and ...

Ocean Current Observations at the AIDJEX 1972 Main Camp. (1) The Oceanic Boundary Layer and Ice-Water Stress During AIDJEX 1972. (2) An Estimate of Internal Wave Drag on Pack Ice. (3).

Abstract: : ;Contents: Ocean current observations at the AIDJEX 1972 main camp; The ocean boundary layer and ice-water stress during AIDJEX 1972; and An estimate of internal wave drag on pack ice.

Design Criteria for Single-Point Mooring Terminals

Abstract: Single-point moorings (SPMs) have come to be accepted as a logical choice for offshore berths for large tankers. The type most commonly used is that in which a single-buoy mooring (SBM) is anchored to the seabed with long catenaries of chain. Site selection for SPMs is governed above all by safety of operation of the tanker in maneuvering and mooring. Site conditions and marine environment play a major part in judging this safety. Detailed information is required on bottom conditions, sea levels, currents, winds, waves, and visibility. In the design of a specific SBM system, the main parameter is the mooring load. Determination of this load requires model tests, since reliable design formulas are not yet available. SBM can be operated without causing pollution to the surrounding coastline and without detrimental effect on the local marine environment.

The influence of surface waves on water circulation in a mid-Atlantic continental shelf region

Abstract: The importance of wave-induced currents in different weather conditions and water depths (18.3 m and 36.6 m) is assessed in a mid-Atlantic continental-shelf region. A review of general circulation conditions is conducted. Factors which perturb the general circulation are examined using analytic techniques and limited experimental data. Actual wind and wave statistics for the region are examined. Relative magnitudes of the various currents are compared on a frequency of annual occurrence basis. Results indicated that wave-induced currents are often the same order of magnitude as other currents in the region and become more important at higher wind and wave conditions. Wind-wave and ocean-swell characteristics are among those parameters which must be monitored for the analytical computation of continental-shelf circulation.

Oceanographic Summary of the Barents Sea South of Bear Island in the Summer.

Abstract: : Using published articles, data reports and other historical data, a brief summary of the oceanography of the region between Bear Island and Norway is presented The main feature of this area is a frontal region formed where the warm Atlantic water and cold Polar water meet; steep temperature, salinity and sound speed gradients occur in this region The position of the front can vary by about 30 nautical miles from year to year (Author)

Drifting ocean buoy

Abstract: A drifting ocean buoy is described which utilizes a drag structure which follows the water mass of the ocean as it flows in the form of the ocean current, and which also has an aerodynamically shaped low wind drag mast to minimize wind induced errors in ocean current drift measurements; the drag structure also being stable and resistant to heaving (pitch and roll) so as to maintain a mast carried antenna above the water even at high sea states.

A Diagnostic Calculation of Continental Shelf Circulation.

Abstract: : An attempt is made to compute from observed density the three-dimensional velocity field in a continental shelf region that is bounded by the coast on one side and open to the ocean along the rest of its perimeter. The bottom topography of the shelf region is found to be of crucial importance. For a nondimensional depth gradient greater than the square root of the Ekman number, E, based on the vertical eddy viscosity and a scale depth, the isobaths become geostrophic contours in the sense that the barotropic part of the velocity field possesses no component normal to the isobaths. In such case, the flow field everywhere away from the coast is determined once the geostrophic velocity vector becomes known at some reference point along each of the isobaths. (Modified author abstract)

On ocean current induced by a prograding ice pack

Abstract: An ice cover which progrades over a shallow ocean may induce a baroclinic flow in the underlying water, providing that the brine excluded from the freezing surface layer is mixed rapidly through out the underlying water column. For a simplified model of the shallow northern part of the Bering Sea the near-surface flow rate is of the order of 2 cm sec−1and directed to the east. Volume transport, assuming a nominal depth of 100 m, is about 0.1 Sverdrup. Over a 3 month freezing period up to 800 km³ are transported through a given meridional section of this model. One might conclude that the process may play a significant role in winter circulation in the Bering Sea.

New England Continental Shelf Dynamics Pilot Experiment

Abstract: : Current and sea level observations made on the New England continental shelf during several winter storms show that these short intense wind events dominate the circulation over the shelf, and account for most of the observed net flow. The observations show that large mass transports westward along the shelf were produced by strong westerly wind stresses, while an easterly stress produced little along-shore flow. Significant cross-shelf and along-shelf surface pressure gradients occur during the storms. A simple conceptual model is proposed to explain the observations. The following engineering and scientific aspects of the experiment are also presented: (a) mooring design; (b) field operations; (c) results of hydrographic and suspended sediment surveys; (d) force balances; and (e) spatial analysis of the observed current, sea level and meteorological variables. (Author)

Computation of Real-Time Currents off Southern California with Multi- Layer Hydrodynamical-Numerical Models

Abstract: : The measurement of currents at various levels in deep water is a difficult and expensive task, and the few available measurements do not allow the construction of a coherent picture of these currents. The available general circulation models have not yet reproduced the general circulation in the desired detail and they are unable to reproduce real-time (synoptic) currents. The only method for computation of real-time currents in the ocean, including wind and tidal currents, is by the use of the Hansen type Multi-Layer Hydrodynamical-Numerical Models.

Some geophysical aspects of deep-sea drilling

Abstract: More than 300 locations covering all the major ocean basins of the world, except the Arctic, have now been explored by deep-sea drilling. Results from deep-sea drilling permit the accurate calibration of seismic reflection profiles but at the same time emphasize the need for caution in interpreting the stratigraphic significance of such records. Basement ages determined from core samples are in close agreement with ages predicted by the concept of sea floor spreading, demonstrating both the validity of that concept and the validity of the paleomagnetic time scale. There also appears to be a demonstrable relationship between the age of the sea floor and its present depth. at many locations permits the documentation of changes in ocean currents, surface and bottom water temperatures, climate, and water depth.

An integrated approach to the study of polLution transport and waves in the coastal zone - Part II: Modeling

Abstract: Among the Applications Activities (the application of NASA technological expertise to civil sector problems) at the Langley Research Center are the study of pollution transport in the Coastal Zone and coastal wave conditions. This paper describes the Coastal Zone modeling work being undertaken in support of these Applications Activities. The analytical models described are being developed to provide a predictive capability for pollution transport and wave conditions in the Coastal Zone. The models include: (1) a Continental Shelf circulation model, (2) a North Atlantic circulation model intended for validation of the general ocean circulation models, (3) two pollution dispersal models, and (4) a first-order coastal wave refraction model.

Marine Environmental Planning Guide for the Hampton Roads/Norfolk Operating Area.

Abstract: : The marine environment of the Atlantic Ocean for about 180 miles east of the costs of Virginia and North Carolina is summarized and evaluated to estimate the effects of introduced pollutants. Winds, currents, waves, temperature, salinity and density of the water, geology and biology, and the marine ecosystem are discussed and summarized in charts and tables. Surface materials in the Hampton Roads/Norfolk Naval Operating Area will be moved offshore into the Gulf Stream by wind-induced surface flow during 10 months of the year. This flow is reversed during September and October and carries these materials toward the coast - more rapidly as distance to shore decreases. A model, using an ellipse technique, predicts dispersion directions of surface or suspended material in the Area. The ellipses are closely related to the surface currents and are elongated in the direction of prevailing flow. A second model predicts the dispersion of dredge spoil or other deposits over the seabed. Orbital and forward drift velocities are sufficient during autumn, winter, and spring to erode and transport sediment, such as dredge spoil, on the Continental Shelf. Bottom transport in the area is predominantly toward the coast regardless of the season. Surface, subsurface, and bottom currents probably will least affect introduced pollutants seaward of the Continental Shelf and north of 36 deg 30 min N. Any stresses that reduce the biomass of autotrophs or cause a loss in their production efficiency will decrease the productivity of the entire ecosystem. (Author)

An evaluation of ERTS data for oceanographic uses through Great Lakes studies

Abstract: The author has identified the following significant results. Prevailing wind direction on Lake Michigan is southwesterly, although during winter northwesterly stresses are common. Along the western shore the current favors a northward direction. ERTS-1 observations indicate that the southward-flowing current along the Michigan shoreline of the thumb is only reversed by southerly resultant wind stress. Along the Canadian shoreline, a northward current was observed north of Kettle Point. ERTS-1 data also reveal that a preferred southward-flowing current is found along the Detroit shoreline of Lake St. Clair. Eastward flow of surface water from the shallow western basin of Lake Erie into the middle basin is most obvious during northwesterly and northerly wind stresses. The reverse wind direction especially east and southeasterly, appear to hold the effluents from the Detroit and Maumee Rivers in the western basin. Across-lake winds from the north and south induce eddy-like circulation in surface waters of Lake Ontario. Counterclockwise alongshore flow persists in the western basin under most wind conditions.

Greenland Sea Studies.

Abstract: : This report is in three parts. Part I is a short paper co-authored with Clark Darnall and Paul Greisman, summarizing the mooring and current measurements in the Greenland-Spitsbergen Passage. Part II is a paper on the Arctic heat and mass budgets, co-authored with Paul Greisman and based on large part on the 1971-72 current measurements. Part III presents the current measurements themselves.

Remote detection of ocean features in the Lesser Antilles using ERTS-1 data

Abstract: The author has identified the following significant results. Photographic data received from the ERTS-1 satellite over the Lesser Antilles Islands shows distinct ocean features on the leeward side of each island. Attempts to relate these features to ocean eddy formations with the aid of ground truth data proved unsuccessful. However, analysis of surface and upper air wind data correlate extremely well with the size, shape, and downwind extent of the ocean features. Studies to date indicate strongly that these features result from horizontal differences in sea surface roughness due to the wind shadow effect of the islands. The results suggest that horizontal variations in the reflectance of the sea surface will make remote sensing of the ocean mixed layer more difficult than previously anticipated. The surface reflection seems to be large enough to mask the smaller variations in backscattered energy from the mixed layer. Efforts to limit the effect of surface reflectance by photographic differencing of two MSS bands were unsuccessful. A supplementary study to enhance the energy reflected from the mixed layer through numerical differencing of ERTS-1 digital data is planned.