Showing papers on "Ocean current published in 1972"

Experimental Approach to the Paleocirculation of the Oceanic Surface Waters

Abstract: Experimental investigations of the pattern of Middle Cretaceous oceanic surface currents in the Northern Hemisphere have been made, using planetary vorticity models developed by Von Arx. The main features of the ocean configuration are an open Tethys seaway and Central American region, an Atlantic Ocean approximately 50 percent of its present size, a Pacific Ocean about 25 percent larger than it is at present, and the ancient Tethys Ocean. Two zonal wind profiles have been considered in the experiments, a “glacial” profile simulating the zonal profile in existence today and a “nonglacial” profile with the westerlies belt about 10° farther north than the glacial profile. Paleoclimatic data support the existence of the non-glacial situation in the Middle Cretaceous, and these results are considered most relevant. The features of this experiment which differ significantly from the present-day oceanic surface circulation are the circum-global flow of the Tethys current, the flow of the Gulf Stream into the Labrador Sea, and cross-polar flow of water from the Atlantic into the North Pacific. In another experiment, the Tethys region was closed off near Malaysia in order to simulate the obstruction of the Tethys current. The Central American region was left open. Weak and variable currents are seen in the Tethys (or ancient Mediterranean), and the circum-global current is absent. North Atlantic circulation occurs from Greenland down to the equator. Atlantic and Pacific waters exchange through the Isthmus of Panama. A net inflow of Pacific water through this gap into the Atlantic maintains the cross-polar flow of “warmer” waters from the Atlantic to the Pacific. Geologic evidence of the first land connections in the Isthmus region can be correlated with the formation of the Labrador Current (3.4 m.y. ago and 3 m.y. ago, respectively). It is proposed that cessation of net inflow of Pacific water into the Atlantic caused cross-polar flow to stop. This, coupled with a deteriorating mean global temperature, was sufficient to trigger the formation of ice in the Arctic region.

A Numerical Calculation of the Circulation in the North Atlantic Ocean

Abstract: A series of numerical experiments are carried out to simulate the three-dimensional circulation in the North Atlantic Ocean and to examine the dynamics therein. The calculations are partly diagnostic in that the density field is not predicted but is given from observations. The main predicted quantities are the velocity and pressure fields. The results of the basic experiment are compared with observations. The surface currents are quite similar to observations based upon ship drift data, and the surface pressure field is nearly identical to the height of the free surface constructed from a level-of-no-motion hypothesis. The deep pressure variations are nowhere flat or level, however, and the predicted deep currents are quite complex. They are, in fact, strongly controlled by bottom topography and tend to follow f/H contours, where f is the Coriolis parameter and H the depth. The Gulf Stream transport is quite large, reaching a maximum value of 81×106 m3 sec−1, despite the lack of important inert...

Negative Oceanic Heat Flux as a Cause of Water-Mass Formation

Abstract: Regions of large (>60 kcal cm−2 year−1) net annual heat flux from the oceans to the atmosphere are found only on the western sides of Northern Hemisphere oceans and in the Norwegian Sea, according to Budyko. It has been assumed that these negative heat fluxes are the result of the transport of warm water to middle and high latitudes by major ocean currents, specifically the Gulf Stream, the North Atlantic Current and the Kuroshio. In the case of the Norwegian Sea, Worthington suggested a mechanism for maintaining the negative heat flux, whereby warm surface water is advected northward to replace the dense, deep water formed within that sea by the cooling action of the atmosphere. The deep water mass so formed overflows the sills of the Norwegian Sea and moves southward into the depths of the Atlantic. It is postulated 1) that this mechanism maintains the negative heat fluxes found at mid-latitudes on the northwestern sides of the oceans, and 2) that water masses are also formed at these latitudes...

Surface Currents off Oregon as Determined from Drift Bottle Returns

Abstract: It is generally known that surface currents off Oregon flow equatorward in summer when winds are from the northwest and poleward in the winter when winds are from the south. A detailed pattern of surface currents has been derived from drift bottle returns and releases observed during a 10-year study from 1961–71. A total of 21,285 drift bottles were released within 165 n mi of the Oregon coast, of which 2937 bottles were eventually recovered. The annual cycle of surface currents indicated from these returns was as follows: Northward–October through February Southward–May through August Variable–March, April and September The Davidson current or (northward) winter current was considered to be any northward prevalence of surface flow. The Davidson current commonly reached 48–50N. Every year of the study, some surface blow off Oregon reached as far north as southeast Alaska to about 55N. Although drift bottle observations often indicate northward surface flow all the way to at least the edge of the ...

Specification of Sea Surface Temperature Anomaly Patterns in the Eastern North Pacific

Abstract: Observed changes in sea surface temperature anomaly patterns on monthly and seasonal time scales are related to anomalous circulation patterns in the overlying atmosphere using data collected from the eastern North Pacific over a 10-year period (1961–70). Three monthly (November 1969, December 1969, January 1970) and four seasonal (fall 1969, winter 1969–70, spring 1970, summer 1970) case studies are described which show that the observed anomalous temperature changes can be explained quite well by relating them to anomalous heat transfer across the air-sea interface and heat advection by anomalous wind-driven ocean surface currents. These interactions are documented by charts showing the anomaly patterns of sea surface temperature change, sea level pressure, types of heat transfer across the air-sea interface, and wind drift currents. In addition, correlations computed between the anomaly patterns for each of the periods studied show that the interactions hypothesized have statistical significan...

A comparison between wind and current observations over the continental shelf off Oregon, summer 1969

Abstract: Wind and current observations made over the continental shelf off Oregon in the summer of 1969 are compared. It is demonstrated that the wind and current are related at periods longer than 2 days. The wind and current data are both filtered to suppress variations of diurnal and higher frequencies. The current behaves similarly to the wind when the wind varies slowly. The amplitude of the current fluctuations seems to depend on the stratification of the water. The current is roughly parallel to the local bottom contours.

A Numerical Model for Circulation in a Homogeneous World Ocean

Abstract: The results for two steady-state models of the world's ocean circulation are presented. The first model is of a homogeneous constant depth ocean with natural coastline geography. The second model, in addition, incorporates realistic sea floor topography. The flow fields indicate that in the constant depth ocean a coefficient of body friction R=1.5×10−6 see−1 is required to produce the observed Circumpolar Transport. For this model the magnitude of the Circumpolar Current is approximately proportional to the inverse of the friction parameter whereas in the variable depth model the effect of the frictional processes on the circumpolar circulation is of minor importance. The circulation is primarily determined by the sea floor topography, and the transport of the Circumpolar Current is small (∼16×1012 gm sec−1). The gyres in the ocean basins, however, are of magnitudes comparable with the constant depth model.

Nonlinear source-sink flow in a rotating pie-shaped basin

Abstract: Source-sink flows in a rotating pie-shaped basin provide a laboratory analogue of wind-driven ocean circulation (Stommel, Arons & Faller 1958). Experiments and theory are presented here for flows which are mildly nonlinear. Theory and experiment show satisfactory agreement for the intense flow in the western boundary-layer region which contains the strongest nonlinear effects. The strengths of the sources and sinks were increased in the experiments in an attempt to induce an instability in the western boundary layer. However, the western boundary layer was always stable, even for relatively large Rossby numbers. Photographs from experiments with a basin of semicircular cross-section show the difference between eastern and western boundary layers in a striking manner.

Upwelling Studies With Satellites

Abstract: Color enhancement and multispectral methods for studying dynamics of upwelling water in connection with Somali, Canary, Benguela, and Agulhas Currents - satellite data

A note on the effect of latitudinally varying bottom topography on the wind‐driven ocean circulation

Abstract: I n recent years the need for a much more realistic modelling of bottom topography has been recognized. Holland (1967), in quite a detailed numerical investigation, considered how the relative sizes of inertial and frictional forces would effect the role played by bottom topography in the large scale, wind driven ocean circulation. Johnson e t al. (1971) used a linear, three dimensional model to investigate the circulations produced in a rectangular ocean for a variety of bottom topographies. DOI: 10.1111/j.2153-3490.1972.tb01544.x

A study of time variability of surface currents at a point in Monterey Bay.

Abstract: The geomagnetic electrokinetograph (GEK) was used to measure surface currents near the center of Monterey Bay during six separate 24-hour periods from May through July, 1972. An average of 244 current vectors were derived for each cruise. The mean currents from these cruises are all southerly and ranged from 4.1 cm/sec to 20.4 cm/sec. The average of these mean currents is 12.1 cm/sec toward 163 °T. These values were compared with individual currents derived from dynamic topographies from the same period. Diurnal and semi-diurnal variations of the current were studied after subjecting the data to a fourier analysis. It was concluded that there must be at least an indirect coupling of the ocean currents with the semi-diurnal tide at the data point. The diurnal component also is important; it may be tidal or inertial, or merely related to the passage

Comments on ocean circulation with regard to satellite altimetry

Abstract: Basic features of sea surface topography are reviewed, to show those oceanographic results which may be of value to a geodetic satellite program: (1) the shape and magnitude of the large scale features of the mean sea surface, relative to a level surface; (2) the position and magnitude of the slopes across the western boundary currents, from a variety of data; (3) an estimate of the position of the geoid, tied into the U.S. leveling network; and (4) a documented change of 60 to 70 cm in mean sea level, with respect to the geoid, between the U.S. east and west coasts.

Coastal currents of pacific northwest

Abstract: To plan and design ocean outfall for sewage, cooling water or other wastes it is necessary to have a knowledge of the nearshore current velocities and directions. An overview is presented of available nearshore current measurement of the Pacific Northwest Coast along with some theoretical methods for calculating velocities. Current contributions are considered from tides, winds, waves and upwelling. Available current data indicate that in nearshore areas effects due to bottom and shore configurations overshadow geostrophic and Ekman layer effects. Generally, theoretical methods for calculation of current velocities in coastal waters (within 5 nautical miles of the coastline) can give approximate values. However, for specific information it is usually necessary to perform local measurements.

How faithfully will the geostrophic currents represent the existing ocean currents

Abstract: It is widely recognized that the geostrophic flows computed by the dynamic method of Bjerknes and collaborators represent the actual currents pretty faithfully. However, what would be the reason that a geostrophic current derived by only retaining the terms of Coriolis and the pressure gradient forces in the hydrodynamical equations agrees so closely with the actual ocean current of the same area? In this attempt was assumed an imaginative ocean of homogeneous water and uniform depth on a rotating earth but with neither continent nor islands. The average wind distribution observed along several meridians over the Pacific Ocean was assumed to prevail in this sea throughout with no variation in east-west direction. Taking the curvature of the earth surface, rotation of the earth, Coriolis forces, pressure gradients and the horizontal and vertical eddy viscosity into account, the equations of motion were solved and velocity components were derived for all latitudes. A comparison of the east-west components thus obtained with the corresponding components of the geostrophic flows, reveals that they agree well in higher latitudes but there appears a remarkable disagreement in lower latitudes. This means that a special care must be taken in replacing the existing currents with the geostrophic flows at lower latitudes.

On the calculation of wind stress curl over open ocean areas from synoptic meteorological data with application to time dependent ocean circulation.

Abstract: Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Science, 1972.

Greenland Sea Currents

Abstract: : The Greenland Sea holds a position of unique importance and interest among all the Arctic seas. There are two essentially different reasons for this. One, the northern portion constitutes the major connection of the Arctic Basin with the rest of the world ocean, both in terms of depth and cross- sectional area, and in terms of the actual flow of water. Two, the Greenland Sea (and the Norwegian and Iceland seas, together with which it forms an intricately combined system) is a large, deep, partially ice-covered sea; it is one of the northern hemisphere's primary heat exchangers. The report discusses preliminary plans to measure the currents in the Greenland Sea.

On the reynolds stress and lateral eddy viscosity due to transient oceanic Rossby waves

Abstract: From numerical solutions of a wind-driven homogeneous ocean model, anegative lateral eddy viscosity of the order 104 cm2 sec−1 is inferred from the large-scale time-dependent currents in the interior of an enclosed shallow basin. The transient Rossby waves in this region produce a systematic convergence of eddy momentum at the latitude of the maximum average eastward current, and thus effect a transfer of zonal momentum from the large-scale eddies to the mean flow. In this sense they are analogous to the Rossby waves in the atmospheric general circulation, and it is speculated that such waves may help to maintain the mean zonal ocean currents. Although this negative viscosity induced by the large-scale transients is relatively small compared with the prescribed lateral viscosity of 108 cm2 sec−1 and should be given a quite different physical interpretation, it is evidently an important viscous effect for the mean flow in the interior of the basin. The prescribed viscosity, on the other hand, is effective in controlling the model's simulated sub-grid scale dissipation, which occurs almost entirely in the nearby steady boundary currents.

Hf radio measurements of ocean currents

Abstract: HF radio waves backscattered from the ocean surface can be used to measure ocean surface currents. Measurements of the range-Doppler spectrum of these signals yields the wavelength and frequency of the scattering ocean waves, and thus their phase velocity. This velocity is subtracted from the velocity the wave would have in still water, and the difference is a measure of the average (over depth) of the surface current. To test these ideas, we measured currents using a conventional and the IiF technique, and found reasonable agreement between the two measurements.