Showing papers on "Ocean current published in 1981"

The climate of the Eocene ocean

Abstract: Oxygen isotope palaeotemperature estimates are presented for a number of deep sea sediment samples of Eocene age, covering a wide geographical area. These are plotted on a geographical reconstruction for 50 Ma. The latitudinal temperature gradient at that time was less than half its present value: surface temperature at high latitudes was about 10°C, and at low latitudes little over 20°C. It is concluded that Ocean currents must have contributed a greater proportion of the poleward transport of heat than they do at present.

Temperature and Currents on the Southern California Shelf: A Description of the Variability

Abstract: Temperature and horizontal current observations at three water depths (15, 30 and 60 m) over the Southern California shelf are reported for four discrete periods during 1978–79, roughly corresponding to each of the principal seasons. The vertical structure of temperature changes markedly during the year; the water over the shelf is weakly stratified in the winter (N = 50 cpd) but stratification is stronger in the summer (N = 250 cpd). Seasonal changes in vertically averaged temperature are comparatively unimportant. Long-term averages of the longshore currents are to the south near the surface in all seasons, with amplitudes ranging up to 10 cm s−1 in the winter. During spring and summer, the stratification is accompanied by shear in the vertical structure of these long-term current averages, with surface currents sweeping to the south, but with deeper, colder water flowing in the opposite direction. Currents fluctuating at subtidal frequencies are predominantly alongshore and are strongest durin...

The General Circulation and Meridional Heat Transport of the Subtropical South Atlantic Determined by Inverse Methods

Abstract: The circulation and meridional heat transport of the subtropical South Atlantic Ocean are determined through the application of the inverse method of Wunsch (1978) to hydrographic data from the IGY and METEOR expeditions. Meridional circulation results of the two data sets agree on a northward mass transport of about 20 million metric tons/sec for waters above the North Atlantic Deep Water (NADW), and a comparable southward transport of deep waters. Additional gross features held in common are the Benguela, South Equatorial and North Brazilian Coastal currents' northward transport of the Surface Water, and the deflection of the southward-flowing NADW from the South American Coast into the mid ocean by a seamount chain near 20 deg S. Total heat transport is equatorward, with a magnitude of 0.8 X 10 to the 15th W near 30 deg S and indistinguishable from zero near 8 deg S.

Evolution of physical oceanography : scientific surveys in honor of Henry Stommel

Abstract: The influence of Henry Stommel on the development of physical oceanography over the past four decades has been immense Although he is best known as a major generator of modern concepts of ocean circulation, his research interests have encompassed much of physical oceanography, and the colleagues he influenced have explored every ocean, literally and figuratively In this volume, comprehensive surveys trace the development of major oceanographic fields since Stommel began his professional life and summarize the state of these subjects now--they cover "where we are and how we arrived, what is known and seems probable, and what seem "now" to be the key questions"The book opens with five brief essays offering personal reminiscences of Henry Stommel and assessments of his scientific contributions, written by Arnold B Arons, George Veronis, Raymond B Montgomery, G E R Deacon, and F C Fuglister It then presents eighteen invited survey articles, grouped into four sections: "General Ocean Circulation: " deep circulation of the world ocean (Bruce A Warren), the water masses of the world ocean (L V Worthington), mid-depth circulation of the world ocean (Joseph L Reid), the Gulf Stream System (N P Fofonoff), dynamics of large-scale circulation (George Veronis), equatorial currents (Ants Leetmaa, Julian P McCreary, Jr, and Dennis W Moore), and estuarine and continental-shelf circulation in the Middle Atlantic Bight (Robert C Beardsley and William C Boicourt)"Physical Processes in Oceanography: " small-scale mixing processes (J S Turner), internal waves and small-scale processes (Walter Munk), long waves and ocean tides (Myrl C Hendershott), low-frequency variability of the sea (Carl Wunsch), the amplitude of convection (William V R Malkus), and varieties of biological oceanography (J H Steele)"Techniques of Investigation: " ocean instruments and experimental design (D James Baker, Jr), geochemical tracers and ocean circulation (W S Broecker), and laboratory models and analogues of ocean circulation (Alan J Faller)"Ocean and Atmosphere: " air-sea interaction (H Charnock) and oceanic analogues of large-scale atmospheric motions (Jule G Charney and Glenn R Flierl)

Characteristics of the currents east and south of Madagascar

Abstract: Ocean currents east and south of Madagascar have been studied with the aid of drifting weather buoys and by XBT sections. Detailed XBT sections have been undertaken across the East Madagascar Current at 23°S and also directly south of Madagascar. Taking into account the characteristic T-S relationship existing in the upper 500 m of this area, the velocity shear has been calculated by means of the thermal wind equation. By referring the surface velocity calculated in this way to derived from accurate satellite navigation, it has been possible to arrive at an absolute velocity shear and hence to estimate the volume transports. A southward transport of 41 × 106 m3 s−1 is indicated for the East Madagascar Current. In the area south of Madagascar an intense warm, shallow eastwards flow immediately south of Cape St. Marie is shown to overlie a deep wedge of strong westward flow. Speed and volume transport specifications for these components have been derived. Analysis of the current velocities and temperatures measured by weather buoys drifting in this area has provided additional information on variability and spatial scales, thus enabling us to construct a conceptual image of current behaviour south and east of Madagascar. In this conceptualization the narrow East Madagascar Current is portrayed as having the characteristics of a minor western boundary current. South of Madagascar it is perceived to retroflect, cast off eddies and fragments, and thus to act as a source current to the Agulhas Current system in an intermittent manner only.

Global Ocean Tides. Part II. The Semidiurnal Principal Lunar Tide (M2), Atlas of Tidal Charts and Maps.

Abstract: : In Part I (Schwiderski, 1978a) of this report, a unique hydrodynamical interpolation technique was introduced, extensively tested, and evaluated in order to compute partial global ocean tides in great detail and with a high degree of accuracy. This novel method has been applied to construct the diurnal principal solar (P1) ocean tide with a relative accuracy of better than 5 cm anywhere in the open oceans. The resulting tidal amplitudes and phases are tabulated on a 1 deg X 1 deg grid system in an atlas of 42 deg X 71 deg overlapping charts covering the whole oceanic globe. A corresponding atlas of global corange and cotidal maps is included to provide the reader with a quick general overview of the major tidal phenomena. The specifying hydrodynamical parameters of the model are listed along with quoted sources of empirical tide data, and significant tidal features are explained and discussed. As expected, since the periods of the diurnal tides P1 (24.07h) and K1 (23.93 h) differ by only 0.14 h, these two tides resemble very closely each other (compare Part IV). Significant differences occur only in regions of rapid tidal variations. Of course, P1 resembles also the diurnal 01 tide but to a visibly lesser degree (see Part V). (Author)

Thermohaline steps induced by melting of the Erebus Glacier Tongue

Abstract: A vertically stable, step-like thermohaline structure is observed throughout a continuous, 400 m conductivity-temperature-depth (CTD) profile taken near the Erebus Glacier Tongue, McMurdo Sound, Antarctica The pattern is best developed between the sea surface and 250 m depth, the interval corresponding to that of the irregular underwater profile of the Glacier Tongue The steps average 17 m in thickness and typically display discontinuities of 01°C in temperature, 004‰ in salinity and 35 × 10−4 g cm−3 in density The observations are compared with theory and laboratory experiments of cell development and lateral flow near ice melting into vertically stratified salt water At this location, subsurface seawater is inferred to remain above the in situ freezing point year-round, and contains sufficient heat to account for much of the Glacier Tongue thinning by basal melting An adequate volume of meltwater would result to produce the measured salinity steps We discuss related observations and some implications of this process for ocean circulation and biological productivity in the Antarctic

Ocean circulation and fronts as related to ice melt‐back in the Chukchi Sea

Abstract: The work reported herein was supported in part by the Arctic Submarine Laboratory, Naval Ocean Systems Center, San Diego, California under Project Order Nos. 000007 and 00164.

Satellite‐tracked drift buoy observations of the near‐surface flow in the eastern mid‐latitude North Pacific

Abstract: The surface and near-surface (30 m) currents of the eastern mid-latitude Pacific obtained from 32 satellite-tracked drifting buoys during the period June 1976 through August 1977 are discussed. These observations of oceanic currents are merged with and are compared to Fleet Numerical Weather Center's daily estimates of surface winds for the same period. Statistical comparisons of these data sets reveal that the drifters move systematically approximately 30° to the right of the surface wind at approximately 1.5% of the wind speed. This relationship between drifter movement and surface winds occurs during the entire period except for the summer months of 1976 when independent of the surface winds the buoy trajectories indicate mesoscale eddy motions with 100 km and 30 day time and space scales, respectively. Drifter liftimes exceeded that of the 9-m diameter parachute drogues set at 30 m depth, thus enabling a comparison of the currents derived from the drifter motions at the surface and 30 m. These comparisons reveal no systematic difference in the drifter motions with and without drogues. These results suggest a rather uniform flow in the upper 30 m during periods of steady winds. The estimates of the nature of near-surface currents obtained from the drifters differ from those predicted by Ekman's classical theory of wind-driven flow, in that there is no evidence of either a reduction in speed or change in direction of the currents over the upper 30 m.

Control of Equatorial Ocean Currents by Turbulent Dissipation

Abstract: The importance of turbulence in the flow of equatorial currents has been noted by modelers but not observed. Recent measurements of turbulence show an increase in strength at the equator and confirm its role as a sink of the kinetic energy of currents at the equator.

Ocean surface current measurements by an L band two‐frequency microwave scatterometer

Abstract: Real time current measurements with an L band pulsed two-frequency microwave scatterometer (2FS) were carried out from the German North Sea Research Platform (Forschungsplattform Nordsee) during the 1979 Marine Remote Sensing (Marsen) experiment. The principle of this remote sensing technique consists of measuring the phase velocity of a long ocean wave by resonant scattering of a beat wave produced by two microwave signals. The difference between the measured phase velocity and the phase velocity, as calculated from the dispersion relation for still water, represents a weighted average of the ocean current near the surface. Current measurements over full tidal cycles in various wind conditions (up to 18 m s−1) are presented. At high wind speeds, pronounced differences are found between the 2FS measurements and the in situ current measurements made at depths of 9 m and 23 m. These differences can be explained as the effect of the wind stress acting on the upper layer of the ocean. The measurements indicate that the interaction of the tide- and wind-driven currents strongly depends on the parallel and antiparallel orientation of the currents. The accuracy of the measurements reported here is approximately ±0.12 m s−1, but this can, in principle, be improved.

Model Studies of the Wind-Driven Transient Circulation in the Middle Atlantic Bight. Part 1: Adiabatic Boundary Conditions

Abstract: A numerical model of the wind-driven transient ocean circulation in the Middle Atlantic Bight is described. The model incorporates realistic topography and covers the continental shelf between the coast and the 200 m isobath from Cape Hatteras to the southern tip of Nova Scotia. The traditional shallow-water dynamics are used, i.e., the vertically integrated and linearized equations for the flow of a homogeneous fluid driven by atmospheric pressure and wind stress fluctuations and damped by a quadratic bottom stress. The equations are integrated in time using a simple modification of Platzman's (1972) finite-difference scheme, with a 12.7 km grid spacing. At the coast, normal flow is required to vanish; at non-coastal boundaries, the equivalent surface elevation is held fixed. Several classes of initial value experiments are used to study the free and forced modes of this model, and the damped flow driven by a spatially uniform and stationary wind stress and by an idealized travelling synoptic-sc...

Analysis of current observations on the Georgia shelf

Abstract: An analysis is made of HF radar measurements of surface currents in shallow water near the Georgia coast, and also of vertical profile measurements of current and density. The dominant structure is found to be a clockwise ellipse of semidiurnal periodicity, the ellipses becoming smaller, narrower and turning clockwise with depth. There is a definite phase lead of the bottom currents with respect to the upper currents, and some evidence of veering of the currents in the non-Ekman sense. In order to explain the observed vertical variations, a simple analytical expression is developed for periodic rotary currents in a barotropic ocean of constant eddy viscosity and depth h, when the free-surface elliptic motion is known. The solution depends on the ratios ω/f and h/hEkman, and also on the sense of turning of the free surface ellipse. The model is able to explain several features of the observed vertical variations as frictional effects.

Method for Estimation of Ocean Current Velocity from Satellite Images

Abstract: Barotropic instability waves on a shear interface propagate at the average speed of the water on the two sides. Assuming the instability to be excited by tidal oscillations, the phase speed is the wavelength divided by the tidal period. If the water is at rest on one side of the shear layer the current speed on the other side can be calculated. This method, applied to the Gulf Stream beyond Cape Hatteras as seen in satellite images, gives estimates of current speed in general agreement with in situ observations.

On near-shore surface current measurements by means of radar

Abstract: A radar system is presented which allows the measurement of surface currents in a coastal area of about 50 km×50 km. The basic theoretical ideas of this system are described as well as the measuring equipment and date processing developed by Barrick, Evans and Weber [1977] from NOAA (National Oceanic and Atmospheric Administration). Radar data are available from the German Bight for a 26-hour period during MARSEN 1979 (Marine Remote Sensing Experiment in the North Sea). The data have been evaluated in terms of surface currents and compared with a record from a moored current meter, 7 metres below the surface. According to the comparison surface currents as observed by radar differ from the conventionally measured subsurface currents not more than 15 cm s−1 in speed. With regard to the current direction the agreement between both independent measurements seems to be best (within 10 degrees) when the surface-current speed exceeds 30 cm s−1. However, these comparative numbers do not take into account near-surface vertical shears. Thus, currents measured by means of radar are probably more accurate than those numbers indicate.

A shallow northeastward current in the North Pacific

Abstract: A permanent large-scale longitudinal maximum of sea surface temperature at mid-latitudes in the eastern North Pacific is explained by a permanent circulation. One part of the circulation consists of a northeastward current near the surface, which extends diagonally from low latitudes on the western side to mid-latitudes on the eastern side of the basin, and a southwestward return flow on either side and underneath the northeastward current. The other part of the circulation consists of mid-latitude eastward and low latitude westward surface currents. The complete circulation is driven by the wind and by the sun, and it conserves mass and transports heat and eastward angular momentum poleward, as required of the ocean. The seasonal east-west movement of the longitudinal temperature maximum is explained by the north-south movement of the diagonal circulation, which follows the seasonal movements of the sun and wind systems. Seasonal variations in the complete circulation are consistent with the balances of mass, heat, and eastward angular momentum being satisfied throughout the seasonal cycle.

The Memory of the Ocean

Abstract: The climate of the ocean is defined in terms of the length scale Lβ=(2U/ β) 1/2. Larger motions are treated deterministically, smaller motions statistically. The memory of the smaller motions, the oceanic analogue of weather, is estimated to be a few months according to Lorenz’s (1) criterion based on error growth in numerical models. Such error growth may also limit forecasts of changes in the large scale ocean circulation responding to changes in atmospheric forcing on seasonal and longer periods. The memory of heat anomalies in the ocean is discussed in terms of entropy growth accompanying their dispersion by the fluctuating circulation. It is concluded that the very long oceanic memory sometimes suggested by climatologists could only refer to heat anomalies large enough to emerge with significant sea surface temperature anomalies. Such anomalies in the upper ocean, with relatively short residence times, may offer a signal for climate forecasting.

Eddies of the Western Arctic Ocean - Their Characteristics and Importance to the Energy, Heat, and Salt Balance.

Abstract: : With the undertaking of the main 1975-76 AIDJEX experiment located in the central Beaufort Sea, four manned camps collected for one year the largest and most complete set of oceanographic data within the Arctic Ocean to this date. During this time, a total of 146 separate crossings of eddies were observed. using T-S signatures, 31 of the 146 crossings are found to represent duplicate crossings of 12 individual eddies, making a total of 127 separate eddies observed during the one year. On the basis of the AIDJEX data set, arctic eddies have been found to: (1) be prevalent in the Amerasia Basin and in particular the Beaufort Sea, (2) predominantly reside in the depth range of 50 to 300 meters although deeper eddies are also present, (3) contain more than half of the total amount of kinetic energy in the upper 200 m of the Beaufort Sea, (4) transfer kinetic energy to the mean flow, (5) be predominately anticyclonic in their rotational tendency, (6) apparently originate north of Point Barrow, Alaska as a result of instability in the eastward flowing Alaskan Coastal Current although there are a few eddies in which T-S data may indicate the possibility of local origin, (7) transfer fresher, less saline water into the deep Arctic Ocean from the Chukchi Sea, (8) transfer both warm and cold water into the deep Arctic Ocean in response to the seasonally changing shelf conditions, (9) translate in response to barotropic forcing over short time scales, although over longer time periods move with the mean geostrophic field, and (10) decay in a clockwise pattern from their point of origin, which is consistent with the upper layer movement of the Beaufort Sea.

Coastal boundary layers in ocean modelling: an application to the Adriatic Sea

Abstract: Boundary layers play an important role in modelling geophysical fluid-dynamical flows, in as much as they constitute regions of ageostrophic dynamics in which the physical balances characterizing the main interior of the water mass break down. A short synopsis is given of important boundary layers in ocean circulation modelling with specific emphasis drawn upon side wall boundary layers, namely those adjacent to the coastlines of the considered basin. Application of boundary layer analysis is thereafter made for one specific phenomenological situation, namely the Northern Adriatic Sea and the problem posed by its wintertime seasonal circulation. The analysis furnishes a mathematical model for the coastal strip adjacent to the Italian shoreline, treated as a boundary layer in the density field, starting from general model equations valid throughout the interior of the northern Adriatic. The boundary layer model is consequently used to modify the side wall boundary condition for the interior density field. Related numerical experiments are shown and compared with previous standard experiments in which the boundary layer contribution to the density field has not been considered.

Temporal and spatial variations of the Chesapeake Bay plume

Abstract: Historical records and data obtained during the Superflux experiments are used to describe the temporal and spatial variations of the effluent waters of Chesapeake Bay. The alongshore extent of the plume resulting from variations of freshwater discharge into the Bay and the effects of wind are illustrated. Variations of the cross sectional configuration of the plume over portions of a tidal cycle and results of a rapid underway water sampling system are discussed.

Arctic Ocean Eddies and Baroclinic Instability.

Abstract: : Baroclinic eddies with diameters of about 10 km and maximum current speeds of about 50 cm/s have been widely observed in the central Arctic Ocean north of Alaska and Canada. The possible origin of these eddies through an instability of the mean baroclinic flow is investigated using an ocean model with exponential profiles of mean shear and Vaisala frequency. The model includes Ekman pumping at a rigid bottom and at either a free or rigid upper surface. The central Arctic Ocean where the eddies were found is baroclinically stable with no possibility of eddy production. If the eddies are spawned by this mechanism, they must be formed at a site far from where they were observed. On the periphery of the Arctic Ocean north of Alaska the combination of greater current shear, shallower depth and lack of ice cover leads to unstable conditions and the eddies apparently originate in that region. The instability theory predicts maximum velocity at the surface instead of below the surface as observed. Apparently after formation in open water the eddies are advected beneath the ice cover and dissipate the momentum of their upper layers against the ice. This is demonstrated by calculations for the diffusion of vorticity against the ice in the case of an initial exponential profile. A subsurface maximum then develops which resembles the observed profiles. (Author)

Ocean current power generating apparatus

Abstract: PURPOSE:To increase a rotary torque acting on a turbine by a method wherein the energy density of the ocean current is increased through an inlet duct and a collector and the input angle of the ocean current introduced into the turbine is controlled according to the angle of inclination of a nozzle. CONSTITUTION:An ocean current intake duct 3 opening below the sea level is provided at the central part of a catamaran ship 1. The duct 3 serves as a collector at the rear end thereof and has the function of increasing sharply the effective energy taken out from the ocean current in such a manner that the velocity of the ocean current is increased by choking the inlet sectional area of the current to thereby increase the energy density of the current. Further, there is provided the nozzle 5 adjacent the collector 4 and the current is controlled to have such an inlet angle that the torque acting on the turbine 6 becomes maximum when the current accelerated by the collector 4 is directed to the blades 7 of the turbine 6. With the above structure, electric power can be obtained through effective utilization of the constant ocean current energy and the consumption of oil can be reduced.

An Analysis of Hydrographic Data From Knorr Cruise 74 in HEBBLE Area, September - October 1979.

Abstract: : We present in figure form some of the hydrographic data collected on the Scotian Rise in September-October, 1979 as part of the HEBBLE program (Hollister et al, 1980). Five full water column theta and S cross slope transects are presented together with one sigma-4 transect for comparison. Selected surface to bottom computer geostrophic velocity profiles are also presented. To focus further on conditions near the ocean bottom, six near bottom, cross slope theta transects and theta profiles at all stations in the lowest 350 m are shown. All six near bottom theta transects show a distinct body of cold water above the bottom near the base of the Scotian Rise. The 0-350 mab theta profiles show that in this distinct body of cold water the bottom mixed layer is sometimes layered and is the distinct body of cold water. (Author)

Mechanisms of heat transport through the floor of the equatorial Pacific Ocean

Abstract: Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1981.