Showing papers on "Ocean current published in 1978"

The Role of Mesoscale Eddies in the General Circulation of the Ocean—Numerical Experiments Using a Wind-Driven Quasi-Geostrophic Model

Abstract: Results from a two-layer, quasi-geostrophic, general circulation model of the ocean with fine horizontal resolution are presented. As in Holland and Lin (1975a.b), mesoscale eddies spontaneously arise due to instabilities in the oceanic currents, giving rise to transient oceanic circulations that reach a statistical equilibrium. In these final equilibrium states, the interaction of the eddy field with the mean state is examined, and it is shown that the eddies determine the character of the large-scale mean flow. In particular, the eddies act to limit the amplitude of the mean flow in the upper ocean, are responsible for a downward energy propagation that fills the deep sea with eddy energy, and create a downward momentum flux which is responsible for the creation of deep, time-mean, abyssal gyres that are an important component of the vertically averaged mass transport in the ocean. Three new aspects of the mesoscale eddy problem are discussed. First, the Holland and Lin (1975a,b) results are ex...

Introduction to physical oceanography

Abstract: Preface. 1. Overview. 2. A Stratified Ocean. 3. The Transfer of Heat Across the Ocean Surface. 4. Global Balances: The Conservation Equations. 5. Equations of Motion. 6. The Effect of the Earth's Rotation. 7. Major Ocean Currents. 8. The Distribution of Temperature and Salinity. 9. Wind-Generated Waves. 10. Tides and Other Waves. 11. The Coastal Ocean and Semienclosed Seas. 12. Sound and Optics. Appendix 1: Selected Reading. Appendix 2: Units--Definitions, Abbreviations, and Conversions. Appendix 3: Some Useful Values. Index.

A survey of worldwide sea surface temperature fronts detected by environmental satellites

Abstract: The recent improvement of infrared scanners on the polar and geostationary environmental satellites operated by the National Oceanic and Atmospheric Administration has enabled the detection of many sea surface temperature fronts associated with ocean currents and upwelling. The present capabilities and limitations of these satellites in ocean applications are summarized. Examples of infrared imagery are used to illustrate the horizontal temperature distribution at the ocean thermal fronts. It is postulated that future improvements in satellite systems will increase further our capability to detect ocean fronts.

Ocean Circulation and Marine Life

Abstract: The geostrophic nature of the gross patterns of ocean circulation, with the wind-driven convergences within the anticyclonic gyres and the divergences within the cyclonic gyres, along the equator and the eastern boundaries, provides a set of quite different biological provinces. Because of their several climates and differences in vertical circulation, the various gyres contain different sets of nutrient and temperature characteristics, and these provide separate oceanic habitats. The principal cyclonic gyres are in the subarctic and subantarctic latitudes and have equatorward extensions along the eastern boundaries. They are cold, high in nutrients, and undergo large seasonal changes: a relatively small number of species is indigenous to these gyres, but the biomass is relatively large.

Measurements and models of fine structure, internal gravity waves, and wave breaking in the deep Ocean

Abstract: Thesis. 1977. Ph.D.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Sciences.

Ocean surface currents mapped by radar

Abstract: A high-frequency radar remote-sensing system for measuring and mapping near-surface ocean currents in coastal waters has been analyzed and described. A transportable prototype version of the system was designed, constructed, and tested. With two units operating tens of kilometers apart, the currents were mapped in near real time at a grid of points 3 by 3 km covering areas exceeding 2000 kM2, out to a distance of about 70 km from the shore. Preliminary estimates of the precision of current velocity measurements show it to be better than 30 cm/sec.

The Stability of Ocean Currents in Eddy-Resolving General Circulation Models

Abstract: The stability of currents generated in an oceanic eddy-resolving general circulation model EGCM (Holland, 1978) is investigated by solving the eigenvalue problem associated with the finite-difference quasi-geostrophic vorticity equations which govern the flow. In general, both barotropically and baroclinically unstable waves are shown to exist for instantaneous currents found in the EGCM. Although these simulated flows are not always quasi-steady in the sense required by the theory and are themselves modified by the presence of the finite-amplitude eddies, many characteristics of the eddy field and its interaction with the time-mean circulation can nevertheless be deduced by the linear stability analysis. In particular, these investigations show that linear stability considerations correctly identify regions of instability in the ocean circulation model and accurately predict the low-order statistical features of the eddy field such as wavelength, period and phase speed. The effects of weakly uns...

A Coupled Air and Sea Model for the Tropical Pacific

Abstract: Several sets of model equations are presented which represent coupled processes in the tropical atmosphere and ocean. The distribution of ocean surface temperature generates large-scale convective motions in the atmosphere. These winds in turn drive ocean currents which advect ocean temperatures. Under most parametric circumstances, the model solutions have the character of moderately damped oscillations of several year period. This period is characteristic of either ocean particle advection across the zonal extent of the basin or potential energy release associated with the ocean temperature distribution. Less stable model solutions can also occur—limit cycle oscillations, alternative mean climatic balances for fixed parameters—but these are not typical of the parameters selected for application to the tropical Pacific. Simulations of possible El Nino sequences are discussed; in general the responses seem weaker than observed.

Electromagnetic response of an ocean-coast model to E-polarization induction

Abstract: summary. An ocean-coast model which consists of a uniformly conducting half-space screened by a perfectly conducting half-plane (the model ocean) is studied. On the land the electric field decreases continuously to zero as the coast is approached. The horizontal magnetic field component is found to vary rapidly, but remains finite; the vertical component on the other hand, increases to infinity at the coast. On the surface of the model ocean as well as on the sea floor, electric field and vertical magnetic field are both nil, but the horizontal magnetic field becomes singular as the seashore is approached. This horizontal magnetic field however, is different on the sea floor and at the ocean surface, because the integrated ocean current is finite, even growing to infinity as the shore is approached. The very large ocean currents near the shore act as an extremely long line antenna, which radiates far afield. This antenna feature explains the very long range of the ocean-coast effects observed under E-polarization induction, compared to the corresponding H-polarization effects where no such antenna-like feature occurs. A similarly large difference of ranges can be expected for all shallow structures with large lateral conductivity contrasts. The present study may therefore be of some interest in relation to geomagnetic depth soundings by the inductive and magnetotelluric methods, as well as in understanding the ocean-coast effect known for some time from records of coastal observatories.

Coastal currents and an associated sand stream off Virginia Beach, Virginia

Abstract: Synoptic data on near-surface and near-bottom currents for two 1-month periods are analyzed for six stations located 3.5–7 km offshore. Tidal currents are rotary with long ellipse axes approximately parallel to the shoreline and are nearly synchronous. On the basis of amplitude the seven largest constituents of the currents were identified as M2, S2, N2, K1, O1, J1, and SO1. Maximum tidal current speed decreases with distance to the south away from the entrance to Chesapeake Bay. Near the bottom, tidal currents at spring strength decrease from 32.4 cm/s at the entrance to 8.2 cm/s at a point 22 km to the south. Near-bottom tidal currents are incompetent by themselves to move fine sand except in the entrance area. Forty-hour low-pass currents are generated by winds and by sea surface slopes. They reach peak speeds near the surface of 48 cm/s in events of up to 6 days' duration. In summer a strong pycnocline inhibits downward propagation of these high-speed surface currents. In the fall the surface currents penetrate more readily to the bottom. Winds to the south in summer generate stronger currents than winds to the north having the same speed. Seasonal variations in wind regimes and corresponding currents seem to require a strong south slope to the sea surface in summer and a very gentle slope to the north in the fall. Waves entrain the bed sediment 60–83% of the time in depths of 8–13 m. With a threshold taken at 20 cm/s, only the south-directed low-pass currents supplement the incompetent tidal currents so as to produce sediment transport. Threshold exceedance in 8–13 m occurs 1–2% of the time under south-flowing low-pass currents in summer and 3–5% of the time under southerly low-pass currents in the fall. At 15 m the transport threshold was not reached during the observation period. A coastwise parallel stream of intermittent bed sediment transport is thus defined. The frequency of exceedance decreases to the south away from the entrance area. This decrease is consistent with the seaward bulging configuration of isobaths east of Cape Henry.

Tidal perturbations on the satellite 1967-92A

Abstract: The orbit of the 1967-92A satellite was studied to ascertain the extent to which tidal forces contribute to orbital perturbations. Parameters describing the ocean tide potential-in particular for the M2 and S2 constituents-were estimated. Since the ocean tide potential is less well known than the solid Earth tide, the ocean tide parameter estimation is based upon the use of a value of 0.3 for the solid Earth tide Love number in the orbit determination procedure. These tidal parameter values are in good agreement with those appearing in numerical models of the M2 and S2 tides derived from surface data.

Melting of Antarctic icebergs

Abstract: PROPOSALS for supplying water to arid regions through the towing and utilisation of Antarctic icebergs1–5 have generated considerable interest. Simulation studies on the towing of unprotected icebergs to southern continents6 suggest that the towing distance, ocean currents and the iceberg deterioration rate are of major importance. The distance and current components may be optimised by a careful choice of iceberg position, although much further study of currents in southern latitudes is required. The rate of deterioration is probably more difficult to calculate as a number of melting and calving mechanisms may be operating. In this note some initial studies of iceberg melting are reported and some of the problems involved in further investigations are considered.

On the Dynamics of Steep Gravity Waves in Deep Water

Abstract: Ocean waves on all scales play an important role in air-sea interaction, since they strongly affect the transfers of heat, momentum, water vapour, gases (O2 and CO2), salt particles and micro-organisms, between ocean and atmosphere. For the transfer of momentum, wave breaking may be crucial. Banner and Melville (1977) have presented evidence that breaking tends to induce separation in the air flow above the surface, with a consequent increase in the local momentum flux from air to water by about two orders of magnitude. Wave breaking must also transfer momentum from waves to surface currents and supply energy to mix the upper layers of the ocean, thus greatly increasing the transfers of heat and gases across the surface.

Cabbeling at thermohaline fronts

Abstract: A linear model with cabbeling dynamics is developed for a nonrotating, unstratified ocean and applied to observations of three medium- to large-scale oceanic thermohaline (density balanced) fronts. The ability of the predicted cabbeling sinking and surface convergence rates to maintain a steady front against diffusion depends critically on the assumed values of horizontal and vertical eddy viscosities. There is good theoretical evidence for the existence of small-scale (1 km), weak (surface currents 0.1 cm s−1) cabbeling fronts; however, the intensity and stability of such fronts will depend critically on the scale dependent behavior of dissipation processes.

Experiments in ocean circulation modelling

Abstract: In a laboratory model ocean, fluid in a rotating tank of varying depth is subjected to “wind-stress”, For a certain range of the parameters, Ekman number E and Rossby number R, a homogeneous fluid displays steady, westward intensified flow. For the same range of E and R, a two-layer fluid can have baroclinic instabilities. The parameter range for the various kinds of instabilities is mapped in a regime diagram. The northward transport in the western boundary current is measured as it varies with Rossby number for both homogeneous and two-layer fluid.

The earth's gravity field and ocean dynamics

Abstract: An analysis of the signal-to-noise ratio of the best gravity field available shows that a basis exists for the recovery of the dominant parameters of the quasi-stationary sea surface topography Results obtained from the analysis of GEOS-3 show that it is feasible to recover the quasi-stationary dynamic sea surface topography as a function of wavelength The gravity field models required for synoptic ocean circulation modeling are less exacting in that constituents affecting radial components of orbital position need not be known through shorter wavelengths

Winter circulation and hydrography over the continental shelf of the northwest Gulf of Alaska

Abstract: During winter 1977 temperatures and salinity were measured in the shelf region east of Kodiak Island and in the Shelikof Strait. Two subsurface cores of warm, saline water were observed; one was coincident with the shelf break and one extended northwestward from the break into the Amatuli Trough. The temperatures characteristic of these cores indicated that they were nonlocaL advective features perhaps originating in the Alaska Current and that they reflected a bifurcation of this flow upstream. Current records for Shelikof Strait showed a strong southwesterly flow with no reversals, which suggested a barotropic component driven by an axial pressure difference and resulting in hydraulic flow. The forcing by the Alaska Current was augmented at times by a weak westward baroclinic flow resulting from local freshwater input.

Oceanographic Conditions in the Coastal Waters of N. W. Italy during the Spring of 1977.

Abstract: : Two month long current and meteorological records, collected during the spring of 1977, have been used to determine the mean currents along the northwestern coast of Italy and to estimate the correlation between the variations in the flow and the large-scale winds. The overall flow was found to be northwestwards along the coast, with a speed of about 4 cm/s. This flow was directed against the mean alongshore wind and for zero wind conditions the mean flow along the coast was predicted to have a speed of 5 cm/s. This gives direct evidence of an alongshore density-driven current in the Tyrrhenian Sea. The data suggested that a significant proportion of this flow continued northwards past Elba into the Ligurian Sea. The coherence between the current and the wind fluctuations was low; on average only about 20% of the current fluctuations could be attributed to the wind. It is probable that both the local bottom topography and the dynamics of the deep basins will have influenced the response of the coastal currents. There was a uniform warming of the coastal waters during April and May, the mixed-layer temperature increasing from about 14C to 18C. Near-bottom temperatures remained constant and the warming was confined to the upper layers of the water column, suggesting that advective effects were not important.

Spatial and temporal variability of major ocean currents and mesoscale eddies

Abstract: A global picture of ocean current variability may be obtained by analyzing surface drift currents in terms of their mean and eddy kinetic energies. High values for both quantities are found in the western boundary currents and in the equatorial current system; low values are found in the interior of major gyres. However, nowhere are eddy energies less than 200 cm2 s−2, indicating that, even in the least energetic parts of the oceans, surface speeds of ~20 cm s−1 prevail. Recent experimental studies also support the widespread occurrence of mesoscale mid-oceanic eddies. Another type of eddy is abundant in the vicinity of boundary currents: examples include Gulf Stream Rings, the ‘Great Whirl’ of the Somali Current, and disturbances of the predominantly zonal equatorial flow manifested by large-scale meandering about the equator. Recent numerical models using low-viscosity and high-resolution computational grids also reveal the ubiquitous existence of mesoscale structures. The importance of eddies is that they seem to be energetic enough and sufficiently widespread so as to play some part — not yet understood — in the circulation of the world ocean. Speculative analogies to the atmosphere suggest that the mesoscale ocean eddies are ‘the storms and weather systems of the sea’. We need global statistics on their distribution, their occurrence in various oceanic regions, their dimensions, and their lifetimes. The prospect of even a single global oceanic ‘weather map’, comparable to those obtained daily for the atmosphere, is hopeless in terms ofin situ oceanographic observations. Remote sensing may provide a partial solution. In the past, sea-surface temperature observations by satellites have revealed cold and warm eddies shed by western boundary currents. Satellite observations, moreover, have shown the thermal effects of continental shelf waves and areas with pronounced upwelling. These phenomena are characterized by strong temperature gradients and relatively large differences in surface elevation. Mid-ocean eddies are far more subtle and difficult to observe since they possess smaller differences of temperature and sea-surface topography. Three representative examples, including recent experimental results in western boundary currents, the equatorial region, and a typical mid-ocean region, are discussed in detail. Typical signals of temperature and sea-level topography, as well as typical temporal and spatial scales of the observed phenomena, are given.

Report of the International Ice Patrol in the North Atlantic Ocean, Season of 1974,

Abstract: : Ice information in the North Atlantic Ocean and operations of the International Ice Patrol for the season of 1974. (Author)

Oceanographic data off northern California-southern Oregon: 40/sup 0/ to 43/sup 0/ north including the Gorda Deep Sea Fan. First edition

Abstract: This map summarizes oceanographic data and can be used for geological investigations and as a working chart on shipboard It contains the following information: ocean contours; major geographic features; offshore earthquake epicenters; bottom sediments and heat flow stations; magnetic lineations; free-air gravity anomaly; seismic reflection profiles; crustal, subcrustal, and free-air gravity profiles; water properties; monthly surface currents and sea surface temperatures; and coastal wave refraction and direction of swells 12 figures (RWR)

Environmental Conditions in Coastal Waters Near Panama City, Florida

Abstract: : This report is a concise description of coastal environmental conditions in the vicinity of Panama City, Florida. It contains information regarding the bathymetry and bottom characteristics of the nearby Gulf of Mexico and St. Andrew Bay, as well as descriptions of local weather phenomena, wave action, tides, currents, water temperature, salinity, density, sound velocity, clarity, and selected marine biological activity. Seasonal variations are emphasized.