Showing papers on "Ocean current published in 1983"

Eddies in marine science

Abstract: 1. Overview and Summary of Eddy Science.- 1.1 Eddy Currents in the Ocean.- 1.1.1 Observing the Eddies.- 1.1.2 Modeling the Eddies.- 1.2 Status of Eddy Science.- 1.2.1 Distribution and Generation.- 1.2.2 Physics.- 1.2.3 Role in the General Circulation.- 1.3 Influences of Eddies.- 1.3.1 Scientific Processes and Practical Consequences.- 1.3.2 Dispersion and Mixing.- 1.3.3 Description and Prediction.- 1.4 Evolution and Outlook.- 1.4.1 A Time of Transition.- 1.4.2 A Decade of Eddy Research.- 1.4.3 Eddies in Marine Science.- Regional Kinematics, Dynamics, and Statistics.- 2. Gulf Stream Rings.- 2.1 Introduction.- 2.2 History.- 2.3 Cold-Core Rings.- 2.3.1 Formation.- 2.3.2 Structure and Velocity.- 2.3.3 Distribution and number.- 2.3.4 Movement.- 2.3.5 Interaction and Coalescence with Gulf Stream.- 2.3.6 Decay.- 2.4 Warm-Core Rings.- 2.5 Gulf of Mexico Rings.- 2.6 Eastern Rings.- 2.7 Current Rings from Other Currents.- 3. Western North Atlantic Interior.- 3.1 Introduction.- 3.2 Observations.- 3.2.1 Spectrum and Time Scales.- 3.2.2 Spatial Scales.- 3.2.3 Kinetic and Potential Energy.- 3.3 Other Data.- 3.4 Some Simple Conclusions.- 4. The Western North Atlantic - A Lagrangian Viewpoint.- 4.1 Introduction.- 4.2 The Data Base.- 4.3 The Mean Field.- 4.3.1 The Lagrangian View.- 4.3.2 The Equivalent Eulerian View, and the Eddy Kinetic Energy Distribution.- 4.4 Mixing and Dispersion.- 4.5 Topographic Influences.- 4.6 The Eastward Flow in the Subtropical Gyre.- 4.7 Discrete Eddies.- 4.8 The Path of the Gulf Stream.- 4.9 Concluding Remarks.- 5. The Local Dynamics of Eddies in the Western North Atlantic.- 5.1 Introduction.- 5.2 Scientific Objectives.- 5.2.1 Dynamical Balances.- 5.2.2 Synoptic Structures.- 5.2.3 Geostrophic Fine Scales.- 5.2.4 Surface Layer Mesoscale Eddies.- 5.2.5 The General Circulation.- 5.3 The Experiment.- 5.4 The Phenomena.- 5.5 Summary.- 6. Gulf Stream Variability.- 6.1 Introduction.- 6.2 The Gulf Stream Path.- 6.3 Current Structure and Transport.- 6.4 Water Masses.- 6.5 Dynamics.- 6.6 Summary.- 7. The Northeast Atlantic Ocean.- 7.1 Introduction.- 7.2 General Oceanographic Conditions and Mean Circulation..- 7.3 Data Sources.- 7.3.1 Hydrographic Data.- 7.4 XBT Observations.- 7.5 Direct Observation of Currents.- 7.6 Satellite Observations.- 7.7 Surveys of Individual Eddies.- 7.8 Summary.- 8. Eddy Structure of the North Pacific Ocean.- 8.1 Introduction.- 8.2 Coastal Regions.- 8.3 Mid-Latitude Open Ocean.- 8.4 Tropical Region.- 8.5 Direct Current Measurements.- 9. Subpolar Gyres and the Arctic Ocean.- 9.1 Introduction.- 9.2 The Arctic Ocean.- 9.3 Labrador Sea and Northwestern Atlantic.- 9.4 The Norwegian and Greenland Seas and Their Overflows.- 9.5 The Northeast North Pacific and Bering Sea.- 9.6 Summary.- 10. Tropical Equatorial Regions.- 10.1 Latitudinal Changes of Mesoscale Processes.- 10.2 Eddy-Resolving Arrays in the Tropics.- 10.3 Mesoscale Features in Sections.- 10.4 Mesoscale Energy in the Tropics.- 11. Eddies in the Indian Ocean.- 11.1 Introduction.- 11.2 Kinetic Energy of the Seasonal Circulation.- 11.3 Arabian Sea.- 11.4 Somali Current.- 11.5 Bay of Bengal.- 11.6 Equatorial Zone.- 11.7 South Equatorial Current.- 11.8 Deep Currents in the Indian Ocean.- 11.9 Significance of Indian Ocean Eddies.- 12. The South Pacific Including the East Australian Current.- 12.1 Introduction: The Subtropical South Pacific.- 12.2 Observations: The Tasman Sea.- 12.2.1 The East Australian Current.- 12.2.2 The Tasman Front.- 12.3 Theories.- 12.3.1 A Line Vortex and a Wall.- 12.3.2 A Free Inertial Jet.- 12.3.3 Baroclinic Instability of a Western Boundary Flow..- 12.4 The Significance of Eddies.- 12.4.1 Physical Significance.- 12.4.2 Biological Significance.- 12.5 Future Research.- 12.5.1 The Mid-Ocean.- 12.5.2 The East Australian Current.- 13. Eddies in the Southern Indian Ocean and Agulhas Current.- 13.1 Introduction.- 13.2 South Eastern Indian Ocean.- 13.2.1 Vicinity of the South Equatorial Current.- 13.2.2 West of Australia.- 13.2.3 Vicinity of the Subtropical Convergence.- 13.3 South Western Indian Ocean.- 13.3.1 Eddies South of Madagascar.- 13.3.2 Larger Southwestern Indian Ocean.- 13.3.3 Adjacent to the Agulhas Current.- 13.3.4 The Agulhas Retroflection Area.- 13.3.5 The Vicinity of the Agulhas Plateau.- 13.4 Discussion.- 14. The Southern Ocean.- 14.1 Introduction.- 14.2 Observations of Eddies in the Southern Ocean.- 14.3 Eddy Generation and Decay.- 14.4 Effects Eddies and Implications for Models the Southern Ocean.- 15. Global Summaries and Intercomparisons: Flow Statistics from Long-Term Current Meter Moorings.- 15.1 Introduction.- 15.2 Global Kinetic Energy Estimates from Shift-Drift Analysis.- 15.3 The North Atlantic.- 15.3.1 Introduction.- 15.3.2 Ocean-Scale Patterns of Kinetic Energy.- 15.3.3 A Transect of the Western Basin.- 15.3.4 A Transect of the Eastern Basin.- 15.4 The North Pacific.- 15.4.1 The Kuroshio.- 15.4.2 Western Pacific.- 15.4.3 East-Central Pacific.- 15.4.4 Central and Eastern Tropical Pacific.- 15.5 The Equatorial Zone.- 15.6 South Atlantic.- 15.7 High Latitudes.- 15.7.1 The Antartic Circompolar Current.- 15.7.2 Weddell Sea.- 15.7.3 The West Spitsbergen Current.- 15.7.4 Arctic Ocean.- 15.8 Summary.- 15.8.1 Horizontal Distribution of Eddy Kinetic Energy at Midlatitudes.- 15.8.2 Vertical Structure of the Eddy Field at Midlatitudes.- 15.8.3 Vertical Eddy Structure in Ice-Covered Seas.- 15.8.4 Eddy Time Scales at Midlatitudes.- 15.8.5 Eddy Time Scales in the Equatorial Zone.- 15.8.6 Relationship of KE to KM Worldwide.- 16. Global Summary: Review of Eddy Phenomena as expressed in Temperature Measurements.- 16.1 Introduction.- 16.2 Standard Deviation of Temperature.- 16.3 The North and Equatorial Atlantic.- 16.4 The North and Equatorial Pacific.- 16.5 Discussion.- Models.- 17. Eddy-Resolving Numerical Models of Large-Scale Ocean Circulation.- 17.1 Introduction.- 17.2 Review of EGCM Results.- 17.2.1 What Processes Account for the Presence of Mesoscale Variability?.- 17.2.2 Do Mesoscale Phenomena Play a Fundamental Role in the Character and Dynamics of the Time-Mean Circulation?.- 17.2.3 Where the Effects of Mesoscale Circulations Are Important, Can They Be Parametrized in Terms of Mean-Field Quantities?.- 17.2.4 How Do the Answers to Questions About the Role of Mesoscale Eddies Change as the Model Physical Processes Change?.- 17.3 Comparisons with Observations.- 17.4 Unsolved Problems and Future Prospects.- 18. Periodic and Regional Models.- 18.1 Introduction.- 18.2 Two-Dimensional Turbulence.- 18.3 The Effects of ?.- 18.4 Mean Flow Generation by Localized Forcing.- 18.5 Turbulent Cascades in a Stratified Fluid.- 18.6 Scattering by Topography.- 18.7 Regional Models and Non-Local Effects.- 18.8 Comparison with Observations.- 18.9 Conclusions and Future Directions.- Effects and Applications.- 19. Eddies in Relation to Climate.- 19.1 Introduction.- 19.2 Heat Flux Carried by Eddies.- 19.3 Indirect Effects of Eddies on the Heat Balance.- 20. Eddies and Coastal Interactions.- 20.1 Introduction.- 20.2 Theoretical Considerations.- 20.2.1 Stratification, P-Effect.- 20.2.2 Abrupt Topography: Scattering and Reflection.- 20.2.3 Refractive Effects.- 20.2.4 Bottom Friction.- 20.2.5 Longshore Currents.- 20.2.6 Generating Mechanisms and Initial Value Problems.- 20.3 Observations and Analysis.- 20.3.1 The New England Continental Rise.- 20.3.2 The East Australian Shelf.- 20.3.3 The Southeastern Coast of the U.S.- 20.3.4 The West Florida Shelf.- 20.3.5 The Scotian Shelf.- 20.4 Anatomy of a Warm-Core Ring Interaction with the Continental Margin.- 20.4.1 Low-Frequency Current Data, Summer 1976.- 20.4.2 Offshore Forcing.- 20.4.3 Analysis and Interpretation.- 20.5 Conclusions.- 21. Eddy-Induced Dispersion and Mixing.- 21.1 Introduction.- 21.2 Two-Dimensional Dispersal in the Mid-Ocean.- 21.3 Streakiness.- 21.4 Particle Motions.- 21.5 Gyre-Scale Dispersal Effects.- 21.6 Tracer Evidence for Dispersal Processes.- 22. Eddies and Biological Processes.- 22.1 Introduction.- 22.2 Frontal Eddies.- 22.2.1 Formation.- 22.2.2 Air-Sea Interaction Within a Ring.- 22.2.3 Horizontal Exchanges Between the Ring and Its Surroundings.- 22.2.4 Horizontal Exchange of Plankton Between a Ring and Its Surrounding Water.- 22.3 Mid-Ocean Eddies.- 22.3.1 Biological Processes in a Single Eddy.- 22.3.2 Spatial Spectrum.- 22.4 Observational Data.- 22.4.1 Scripps Transects.- 22.4.2 Gulf Stream Ring Structures.- 22.4.3 East Australian Current Rings.- 22.4.4 Incidental Observations.- 22.5 Sampling Procedures.- 22.6 Conclusions.- 23. Eddies and Acoustics.- 23.1 Introduction.- 23.2 Dynamic Ocean.- 23.3 Sound Propagation in a Range-Dependent Environment.- 23.3.1 Geometrical Acoustics.- 23.3.2 Normal Modes.- 23.3.3 The Parabolic Approximation.- 23.4 Analytical and Numerical Studies of Sound Propagation Through Eddies.- 23.5 Acoustic Measurements in Eddies.- 23.6 Acoustic Eddy Monitoring.- 23.7 Conclusions.- 24. Instruments and Methods.- 24.1 Introduction.- 24.2 Moored Instrumentation.- 24.2.1 Moorings.- 24.2.2 Fixed Depth Moored Current Meters.- 24.3 Moored Profiling Current Meters.- 24.4 Temperature Recorders.- 24.5 Other Moored Instrumentation.- 24.6 Drifting Instruments.- 24.6.1 Surface Drifters.- 24.6.2 Deep Drifters.- 24.6.3 Problems and Interpretations.- 24.7 Profiling Instruments.- 24.7.1 Temperature and Salinity Instruments.- 24.7.2 Nansen Bottles.- 24.7.3 CTD and STD.- 24.8 Expendable Bathythermographs.- 24.9 Current Profilers.- 24.9.1 Electromagnetic Velocity Profiler.- 24.9.2 The White Horse.- 24.9.3 Schmitz-Richardson Profiler.- 24.9.4 Other Velocity Profilers.- 24.9.5 Calibration and Intercomparison.- 24.10 Remote and Inverse Techniques.- 24.10.1 Satellite and Airborne Measurements.- 24.10.2 Tomography.- 24.11 Intercomparison Between Instrument Types.- References.

Global mesoscale variability from collinear tracks of SEASAT altimeter data

Abstract: Eight to nine sets of global collinear altimeter data with a cross-track grid spacing of approximately 900 km at the equator and 600 km at midlatitude have been obtained from the last 25 days of the 1978 SEASAT mission. Since the geoid is time-invariant, such observations can reveal sea surface height variability caused by dynamic ocean phenomena. Variations due to deep ocean mesoscale features are presently solved for by eliminating the longer wavelength deviations, yielding sea height profiles with an accuracy of a few cm, and a global variability map constructed from these data which reveal an exceptionally realistic perspective of mesoscale energetics. The dominance of exceedingly small variability over extensive regions of the oceans is noted. In both the Atlantic and the Pacific, the North Equatorial Current systems were clearly expressed as zonal bands of higher variability.

Low‐frequency current and temperature variability from Gulf Stream frontal eddies and atmospheric forcing along the southeast U.S. outer continental shelf

Abstract: Low-frequency current and temperature time series from the outer shelf between Cape Canaveral, Florida, and Cape Romain, South Carolina, are compared with shipboard hydrographic data, satellite VHRR, coastal and buoy winds, and coastal sea level during the period from February to June 1980. Low-frequency current and temperature variability along the shelf break was primarily produced by cyclonic, cold core Gulf Stream frontal eddies. These disturbances traveled to the north at speeds of 50 to 70 cm s−1 with periods of 5 to 9 days throughout the experiment and produced cold cyclonic perturbations of the northward mean flow and temperature fields over an along-shelf coherence scale of 100 km. Frontal eddies appear to be an important mechanism in the observed eastward transport of northward momentum and heat along the shelf edge. They also appear to play a key role in the transfer of eddy kinetic and potential energy back to the mean flow, which suggests an upstream formation region and shear-induced dissipation. Upwelling velocities of about 10−2 cm s−1 in the cold core provide the major source of new nutrients to the outer shelf. Subtidal flow variability at the 40-m isobath was a mixed response to Gulf Stream and wind forcing. Barotropic along-shelf current oscillations were coherent with the local winds and coastal sea level at periods of 3–4 and 10–12 days over along-shelf scales of 400 km with small phase lags, suggesting a nearly simultaneous frictional equilibrium response to coherent wind-induced sea level slopes.

Abyssal circulation in the Japan Sea

Abstract: The water below a depth of 1,000 m in the Japan Sea was found to consist of two water masses, the upper layer (the Deep Water) and the lower layer (the Bottom Water). The boundary of these water masses is marked by discontinuity of potential temperature, dissolved oxygen and silicate at about 2,000 m depth. The mean residence time of the Bottom Water was calculated to be 300 years from analysis of carbon-14 data using a box model. By applying a one dimensional diffusion advection model to the profiles of potential temperature and dissolved oxygen, it was suggested that the upward advection in the Deep Water occurs most intensively in the basin south of the Yamato Rise. The Bottom Water seems to be formed not in the northernmost region of the Japan Sea but in the northwestern area, judging from the distributions of potential temperature and dissolved oxygen.

Reduced advection into Atlantic Ocean deep eastern basins during last glaciation maximum

Abstract: Causes of change in deep water δ13C can be either global or local in extent. Global causes include (1) climatically-induced changes in the amount of terrestrial biomass which alter the average carbon isotopic composition of the oceanic reservoir1, and (2) erosion and deposition of organic-rich, continental shelf sediments during sea level fluctuations which change the mean oceanic carbon: phosphorus ratio2. Regional gradients of δ13C are created by remineralization of organic detritus within the deep ocean itself thus reflecting the distribution of water masses and modern thermohaline flow. Changes in a single geological record of benthic foraminiferal δ13C can result from any combination of these global and abyssal circulation effects. By sampling a large number of cores collected over a wide bathymetric range yet confined to a small geographical region we have minimized the ambiguity. We can assume that each δ13C record was equally affected by global causes of δ13C variation. The differences seen between the δ13C records must, therefore, reflect changes in the distribution of δ13C in the deep ocean. We interpret these differences in distribution in terms of changes in the ocean's abyssal circulation. Benthic foraminiferal carbon isotopic evidence from a suite of Sierra Leone Rise cores indicates that the deeper parts of the eastern Atlantic basins underwent a reduction in [O2] during the maximum of the last glaciation. Reduced advection of O2-rich deep water through low-latitude fracture zones, associated with increased delivery of organic matter to the deep ocean, lowered the δ13C of deep water ΣCO2 at all depths below the sill separating the eastern and western Atlantic basins.3 This decreased advection into the eastern Atlantic Ocean coincides with the overall decrease in deep water production in the North Atlantic during the last glacial maximum4–7.

Testing a Dynamical Model for Mid-Latitude Sea Surface Temperature Anomalies

Abstract: The present investigation is concerned with the development and testing of a dynamical model for sea surface temperature (SST) anomalies in the midlatitudes. The model is an extension of the stochastic forcing model, suggested by Frankignoul and Hasselmann (1977), in which SST anomalies arise naturally as a response of the slowly varying upper ocean to the rapidly varying air-sea fluxes. The conducted analysis confirms strongly the validity of this model. The results suggest that advection by mean ocean currents plays an important role in some regions. Attention is given to the governing equations, a statistical model, SST anomaly advection, heat flux anomalies, wind-driven mass transport in the mixed layer, mixed-layer depth, aspects of model testing, and the atmospheric forcing.

A Simulation of Bomb Tritium Entry into the Atlantic Ocean

Abstract: Tritium is used in a model calibration study that is aimed at developing three-dimensional ocean circulation and mixing models for climate and geochemical simulations. The North Atlantic tritium distribution is modeled using a three-dimensional advective field predicted by a primitive equation ocean circulation model. The effect of wintertime convection is parameterized by homogenizing the tracer to the observed March mixed-layer depth. Mixing is parameterized by horizontal and vertical Fickian diffusivities of 5 × 10−6 cm2 s−1 and 0.5 cm2 s−1, respectively. The spreading of tritium in the model is dominated by advection in the horizontal, and by wintertime convection and advection in the vertical. The horizontal and vertical mixing provided by the model have negligible effect. A comparison of the model tracer fields with observations shows that most of the basic patterns of the tritium field are reproduced. The model's mean vertical penetration of 543 m in 1972 is comparable to the 592 m penetra...

The West Spitsbergen Current: Transport, Forcing, and Variability.

Abstract: : The West Spitsbergen Current is commonly considered to be the northern extension of the Norwegian Atlantic Current, and it forms one of the branches of the circulation pattern of the Greenland-Norwegian sea system. It flows northward along the continental margin west of Spitsbergen, entering the Arctic basin on the east side of the Greenland-Spitsbergen passage (Fram Strait). Previous work (Aagaard and Greisman, 1975) has shown that it provides the major component in the mass and heat balances of the Polar Basin. Beginning in summer 1976, moored current and temperature recorders have been deployed in the WSC at 79 N, and the data records from 1976-79 and 1980-81 provide the basis for this work. The data have been used to estimate the volume and heat transports by the current and to define the structure and variability of the flow. In addition to the presentation of basic results, there is a discussion of the dynamics of the current with emphasis on explaining the length and time scales of the observed variability and on ascertaining the nature of the forces driving the flow.

The simultaneous use of tracers for ocean circulation studies

Abstract: A method for the simultaneous use of tracers for oceanic circulation studies is developed. To permit the inclusion of tracers that are subject to biochemical transformation a simple model for photosynthesis, bacterial decomposition and chemical dissolution is formulated based on the use of Redfield ratios for the chemical compounds interaction. The finite difference analogue to the steady state tracer continuity equation, applied to the tracers chosen, leads to a set of simultaneous algebraic equations that in principle can be solved by matrix inversion methods. Two cases are considered: (1) The problem is indeterminate, which may be the case when too few tracers are available and/or some tracer equations are redundant. A solution is obtained by minimizing the transport vector; (2) The problem is incompatible, which may result from making use of many tracers. A solution is obtained by minimizing the errors in satisfying the tracer continuity equations. The method is applied to a 12-box model of the world oceans by considering the surface water, intermediate water, deep water and bottom water of the Arctic, Atlantic, Antarctic and Pacifichndian Oceans (with some simplification for the polar seas). Total dissolved inorganic carbon, alkalinity, phosphorus, oxygen and radiocarbon are used as tracers. A series of steady state solutions are presented and the uncertainties as dependant on box configuration and erroneous or nonrepresentative data are analysed. In the reference solution, circulation cells emerge where Antarctic surface water penetrates into intermediate levels of the two major oceans, from where it undergoes lifting and, at the surface, advection back towards the south. In the Atlantic, much of the penetrating water reaches as far north as to involve the Arctic deep water, which sinks and moves towards the deep Antarctic Ocean through the deep Atlantic. The total upwelling in the Antarctic Ocean is about 30 Sv. Turbulent exchange prevails between surface and intermediate waters in both major oceans with an average K, of about 1 cm 2 s -1 . Particular consideration is given to the transfer of carbon by computing the changes in total carbon and radiocarbon that are induced by fossil fuel combustion and nuclear bomb testing by using the steady state circulation and turbulent transfer deduced. It is concluded that better spatial resolution is required to determine the role of the ocean as a sink for injections of carbon and radiocarbon. DOI: 10.1111/j.1600-0889.1983.tb00025.x

Waves and circulation driven by oscillatory winds in an idealized ocean basin

Abstract: We examine, via direct numerical integration, the transient and rectified response of a flat-bottomed barotropic ocean to a spatially localized oscillatory wind-stress pattern. These experiments exemplify in many respects the dynamics which drive the deep motion in recent eddy-resolving ocean circulation studies [e.g., Holland and Rhines (1980)], and may be contrasted with the results of Pedlosky (1965) and Veronis (1966) for spatially broad, time-dependent forcing. By considering doubly re-entrant (periodic) and closed basin geometries, the structure and magnitude of the induced circulation is shown to depend most critically on the form of the mean quasi-geostrophic contours (which are closed and blocked, respectively, in the periodic and basin geometries). In both situations, however, the forced primary wave field may be usefully understood by appeal to the radiation pattern of a time-periodic Green's function, and (in a basin) its image in the western boundary. The dynamics of the prograde and...

Recent progress in the application of satellite altimetry to observing the mesoscale variability and general circulation of the oceans

Abstract: Recent progress in the application of satellite altimetry from Seasat and GEOS 3 to the observation of the oceanic mesoscale variability and general circulation is reviewed. The lack of accurate geoid models has been the major obstacle in the study of the general ocean circulation from altimetry. The use of geoid-independent methods that utilize the temporal differences in altimetric measurements taken at fixed locations, however, has made significant contributions to our knowledge of the mesoscale variability of the ocean. The mesoscale energies of the sea surface height and geostrophic current have been mapped on a global basis. Their distributions in wave number space have also been analyzed. Because of many of the deficiencies of existing altimeter data (short duration, inadequate orbit, poor accuracy, etc.) most of these results describe only a small portion of the frequency-wave number spectrum of the variability, but they have nonetheless demonstrated the great value of an optimally designed altimetric mission in advancing our knowledge of the global mesoscale variability. The current technology allows satellite altimetry to detect oceanic variability at periods from a few days to 3–5 years, and wavelengths from 50 to 10,000 km. Determining the time-averaged general ocean circulation from altimetry is more problematic because an accurate geoid is indispensable. The currently available global geoid models have useful accuracies only at wavelengths greater than about 7000 km. There have been several attempts at mapping the global ocean circulation at those scales using existing altimeter data and geoids. When these results are compared with hydrographic surveys, some qualitative agreement can be observed, but the quantitative differences are mostly inconclusive because of the geoid and orbit errors. It has been suggested, however, that an altimetric mission that is optimally designed with the current technology, when complemented by a state-of-the-art gravimetric mission to map the earth's gravity field, is able to determine the ocean circulation quantitatively at scales from the ocean basin to about 200 km.

Overview and Summary of Eddy Science

Abstract: Ocean currents and their associated fields of pressure, temperature, and density vary energetically in both time and space throughout the ocean. Such variability in fact contains more energy than any other form of motion in the sea. Partly organized, yet highly irregular, these motions have dominant spatial scales in the range of tens to hundreds of kilometers and dominant temporal scales in the range of weeks to months. The variability is distributed unevenly with energy levels and dominant scales changing substantially from place to place in the ocean. These turbulent motions are the internal weather of the deep sea, and many types of synoptic events and peculiar marine internal storm systems are now known to occur. Types of variability which have been identified and studied include the meandering and filamenting of intense current systems, semi-attached and cast-off ring currents, advective vortices extending throughout the entire water column, lens vortices, planetary waves, topographic waves and wakes, etc. All of these types of variable flow are commonly referred to by physical oceanographers by the generic term “eddies”.

On the theory of electromagnetic induction in the Earth by ocean currents

Abstract: of the electrical conductivity structure of the earth. TM modes are closely associated with the Coriolis force deflection of water currents and with coastline effects that limit the source currents to the ocean basin. PM modes are induced by nondivergent electric currents that are fully contained within the ocean. Surface gravity waves and a Kelvin wave are examined in detail. The Kelvin wave result of Larsen (1968) is reevaluated, and because the upper lithosphere was modeled as an insulator, significant errors in his magnetic induction values, caused by neglect of the TM mode, are revealed. The sensitivity of the TM mode magnetic field to lithospheric electrical conductivity suggests the use of tidal induced electromagnetic fields to probe the earth's conductivity structure. Electromagnetic fields are induced in the earth by exter- nal, ionospheric and magnetospheric, current systems and have long been used to investigate the electrical conduc- tivity structure of the earth by the geomagnetic depth sounding or magnetotelluric methods. An additional natural source, the dynamo interaction of ocean currents with the ambient geomagnetic field, is important in the world oceans. Since the crust and mantle of the earth are electrical conductors that couple to the ocean both conduc- tively and inductively, observations of low-frequency elec- tromagnetic fields in the ocean contain information about both the electrical conductivity of the earth and the circu- lation of the oceans. Electromagnetic fields produced by ocean flows are dis- cussed by Cox et al. (1971), Sanford (1971), and Larsen (1973). Solutions of the Maxwell equations for surface gravity waves were obtained by Weaver (1965) for an infinitely deep ocean and were extended to long waves in a finite depth ocean by Larsen (1971). The surface and internal wave problem was also investigated by Podney (1975), who presented a general method for solving fluid induction problems using a magnetic vector potential when the flow is incompressible. All of these studies indicate that the induced electromagnetic fields are small, amount- ing to fractions of a/xV/m or a few nanoteslas (nT) near the sea surface. At lower frequencies, tidal signals have been detected in both seafloor- and island-based elec- tromagnetic data (Larsen, 1968). Low-frequency, meso- scale and large-scale, ocean-induced electromagnetic fields are discussed by Cox (1980, 1981), who emphasized the influence of shallow electrical conductivity structure on the observed fields.

Mid‐latitude mesoscale variability

Abstract: Neither homogeneous quasi-geostrophic turbulence nor the effect of eddies on the interior ocean circulation remains the major focus of mesoscale research as was the case for much of the preceding 20 years following identification of the phenomena. Concentration on basin-wide geographical exploration of eddy properties was rather well established by 1978. Over the last few years, a promising zero-order description and rationalization of the mesoscale field has become available. That is, eddy energy is largest near strong flows (intensification not only in western boundary currents, but along their mid-latitude open-ocean extension), roughly as indicated by gyre-scale numerical models where eddies develop as a result of instability processes in the mid-latitude jet and recirculation regimes, and then propagate into the ocean interior. Our point of view is that mesoscale eddies drive recirculations but do not play a crucial role in the dynamics of the mean flow in the ocean interior [in the North Atlantic, for example, the idea is that the downstream increase in transport of the Gulf Stream is eddy-driven but not the flow through the Florida Straits]. In addition, the fluctuating response to forcing by variable winds may now be widely perceived as forming the horizontally homogeneous background signal in subtropical gyres. The time-dependent field associated with thermohaline flows at abyssal depths also has a special character.

Multifrequency HF radar observations of currents and current shears

Abstract: Techniques have been developed for using high-frequency (HF) surface-wave radar to measure ocean currents and vertical current shears in the upper 1 or 2 m of the ocean surface. An HF radar can precisely measure the phase velocity and direction of propagation of ocean waves whose wavelength is one.half the radar wavelength. In the absence of a current, the speed of the waves is given by the still-water dispersion relation. An underlying current will modify this speed. The radar measures the actual phase velocity through a Doppler shift, and the wavelength of the ocean wave is known through the first-order Bragg scattering relation, so a difference between observed and theoretical stillwater phase velocity can be calculated. In addition, longer ocean waves are affected by currents at deeper depths than are shorter ocean waves. By measuring the phase velocity at several different wavelengths, it is possible to measure a vertical current shear in the top 1 or 2 m of the ocean surface. This is a measurement that is very difficult to make by any other means. A portable coherent pulsed-Doppler HF radar system was developed at Stanford and used in several experiments, both on land on the California coast and on board a ship during the Joint Air-Sca Interaction (JASIN) experiment. The land-based experiments demonstrated that a current could be measured by an HF radar, and that its value agreed well with that measured by in-situ drifting spar buoys. In addition, there was evidence of a vertical current shear, both from the radar measurements and from the buoy measurements. The JASIN experiment was an attempt to apply these techniques to the measurement of surface current and current shear in the open ocean. The radar system was installed on board a ship, along with a receiving antenna consisting of a steerable phased array of eight wide-band loops. The steerable antenna was quite rugged and performed as expected. It produced antenna patterns consistent with the physical aperture of the array. The wind velocity during the JASIN experiment was quite low, so wind- and wave-generated currents were quite small. Nevertheless, there is some evidence of a current shear. Its magnitude is small and near the resolution limit of the radar, but it appears to be somewhat higher than estimates based on either the wind or wave conditions alone, but less than the estimates based on the sum of the two components.

Observations of near‐surface currents and temperature in the central and western tropical Atlantic Ocean

Abstract: Eleven satellite-tracked drifting buoys were deployed in the central South Atlantic Ocean during two austral summer and two austral winter cruises. Between 7°S and 11°S and 23°W and 31°W during austral winter, net buoy drift was to the west. Surface geostrophic flow was to the east between 7°S and 9°S. It is proposed that strong southeast trade winds can induce directly driven surface flows to the west that are more intense than the eastward geostrophic flows associated with the South Equatorial Countercurrent (SECC). A sustained period of eastward drift within the SECC was observed during austral summer, when the trades are weaker. The trajectories indicate surface waters north of 8°S have a mean northward meridional component and those south of 8°S a southward component. The buoys which drifted north became entrained into the North Brazilian Coastal Current (NBCC) and those that drifted south into the Brazil Current. One buoy left the NBCC at about 5°N to drift northeastward in the North Equatorial Countercurrent (NECC). This trajectory and historical ship drift reports suggest that the NECC may extend only to 35°W to 40°W during boreal winter. Temperature data obtained as the buoys drifted westward and northward suggest that increases in upper layer heat content can be attributed to heat fluxes through the sea surface.

Eddy-Resolving Numerical Models of Large-Scale Ocean Circulation

Abstract: During the decade of the 1970’s, in association with large field programs (Mode, Polymode, Isos, Norpax), fine resolution (grid size < 100 km) numerical models of ocean circulation were developed to examine the role of mesoscale eddies in the oceanic general circulation. These models have sought to develop an understanding of dynamics of flow in closed, wind-driven (and in some cases thermally driven) ocean basins, a flow in turbulent equilibrium. The eddy fields in these studies, maintained by instabilities in the currents of the large-scale ocean gyres, radiate energy to distant regions of the basin, interact actively with the mean flow, and ultimately dissipate much of the energy input by wind and heating in bottom or lateral friction.

Absolute measurement by satellite altimetry of dynamic topography of the Pacific Ocean

Abstract: The three-month Seasat mission has shown that altimetry is capable of providing global observations of oceanic variability. It is shown that data from this short, suboptimum mission are also adequate for a determination of the absolute sea-surface topography of the ocean on large scales. An absolute determination of the subtropical gyre of the North Pacific Ocean is obtained. This is believed to be the first direct measurement showing the existence of such a feature that does not depend on conventional hydrography and a series of assumptions.

An Analysis of Monthly Mean Wind Stress Over the Global Ocean

Abstract: The annual mean and four monthly means are calculated for the global ocean wind stress fields. The main data base was gathered by observations along continental coasts and on shipping routes, expressed in terms of the monthly mean speed, eight direction categories, and the rms of the speeds. The stress fields were estimated by assuming a Gaussian distribution for the speed frequency distribution histogram. The resulting data set is concluded useful for general circulation modeling, although the 5 deg resolution could lead to an underestimation of the curl.

Interaction of the Antarctic Circumpolar Current with bottom topography: An investigation using satellite altimetry

Abstract: Theoretical studies on the interaction of a zonal current with a zonal ridge, an isolated bump, and a meridional ridge compare favorably with hydrographic observations within the eastward flowing Antarctic Circumpolar Current where it flows over similar topographic features. However, the existing hydrographic data are insufficient for examining the temporal stability and kinematic behavior of the resulting mesoscale structures. In this study, some of these transient features have been compared with patterns in sea surface variability, derived from collinear satellite altimetric data. When these features occurred near the crossing point of two satellite ground traces, it was possible to characterize their length scales, dynamic height relief, and translational and surface geostrophic velocities.

The Wind Field in the Western Indian Ocean and the Related Ocean Circulation

Abstract: Monthly wind stress contoured for the western Indian Ocean clearly shows the southwest monsoon from May through September (with values over 4 dyn cm−2 during July) to be considerably stronger than the northeast monsoon with a maximum in January. Maps of wind stress curl during the southwest monsoon show a large region of negative curl (over −4 × 10−8 dyn cm−3) to the northeast off the Somali coast, whereas a region of high positive curl occurs off the Arabian coast and in a small band off the Somali east coast north of 5°N. Sverdrup mass transports of up to 40 × 10−12 g s−1 to the north off the Somali coast are in rough agreement with observed values.

A vertical section of eddy kinetic energy through the Gulf Stream system

Abstract: Ocean current observations made by drifting buoys, SOFAR floats, and current meters are combined to produce the first section of eddy kinetic energy through the Gulf Stream and subtropical gyre along 55°W. Eddy kinetic energy peaks at 2000 cm2 s−2 in the surface Gulf Stream near 39°N and decreases latitudinally and vertically to a low of 0.5 cm2 s−2 in the abyssal gyre interior (4000 m, 28°N). Still further south, eddy energy increases slightly in the region of the North Equatorial Current.

On determining the large-scale ocean circulation from satellite altimetry

Abstract: It is contended that a spherical harmonic expansion of the difference between the altimeter-derived mean sea surface and the geoid estimate should reveal the large-scale circulation of the ocean surface layer when the low-degree terms are examined. Methods based on this principle are proposed and partially demonstrated over the Pacific Ocean with the aid of the mean sea surface derived from the Seasat altimeter and the Goddard Earth Model 9 earth gravity model. The preliminary results reveal a well-defined clockwise gyre in the North Pacific and a much less well defined counterclockwise gyre in the South Pacific. When the dynamic topography thus obtained is compared with Wyrtki's (1975) dynamic topography derived from hydrographic data, the agreement is found to be within the limit of geoid uncertainties and satellite orbital errors.

Model for the three-dimensional structure of wind-driven and tidal circulation in Bass Strait

Abstract: Earlier models of the circulation in Bass Strait have been extended to include vertical structure. Time- dependent circulation fields in Bass Strait, induced by wind driving at the surface and tidal oscillations along open-sea boundaries, are computed at a number of selected depths. The original two-dimensional model is combined with an analytical solution of the Ekman equations, which at each grid point provides an expression for the time-dependent flow at any depth in terms of a convolution integral over the sea- surface slope and wind stress. This model should be applicable to winter conditions when the strait is well mixed vertically and hence the dynamical effects of density stratification negligible. The predicted wind-induced circulation fields are highly depth dependent, with equilibrium surface currents in the central Bass Strait basin flowing in a direction approximately 45o to the left of the wind. At lower levels, currents are controlled by pressure gradient forces due to the sea-surface slope and friction. Significant upwelling and downwelling motions along the Victorian and Tasmanian coastlines can be inferred from these circulation fields. In the deep water off the continental shelf, currents in the upper 100 m are dominated by the (Ekman) drift current which rotates in an anticlockwise direction with increasing depth, such that the wind drift at the surface is accompanied by a measure of return flow at depth. Tidal currents are predicted in the absence of wind stress, but include the effects of bottom topography. Considerable variation with depth is found and the distinctive features are explained in terms of the relative importance of Coriolis force, bottom friction, and water depth. Comparison with the few existing observations reveals that the present model is producing realistic results.

Generation mechanisms of tidal residual circulation

Abstract: Two new types of mechanism for the generation of tidal residual flow are revealed with the use of a hydraulic model experiment. A remarkable anticlockwise tidal residual circulation is formed in a model bay due to the presence of a tidal current, the Coriolis force and a horizontal boundary. A similar circulation is also formed due to the presence of a bottom slope, a horizontal boundary and a tidal current which flows normal to the inclination of the bottom slope. The residual circulation in the Sea of Iyo in the Seto Inland Sea is considered to be due to a combination of the effects of the Coriolis force, a bottom slope, a horizontal boundary and the tidal current. We classified some of the generation mechanisms of tidal residual flow which have been described to date into seven types on the basis of vorticity considerations.