bluuebunny/crossref_metadata_2025 huggingface dataset:
Water displacements in the Pacific and the genesis of El Nino cycles
Authors: Wyrtki Klaus
Published: February 2008

Sea level observations are used to estimate the amounts of warm water exchanged during the 1982–1983 El Nino event, indicating an eastward flux of about 40×106 m3 s−1. At the end of El Nino the equatorial Pacific is depleted of warm water which is lost toward higher latitudes. The duration of a complete El Nino cycle is determined by the time required for the slow accumulation of warm water in the western Pacific. The cycle constitutes an energy relaxation of the ocean‐atmosphere system.
Observations on the propagation, growth, and predictability of Gulf Stream meanders
Authors: Vazquez Jorge , Watts D. Randolph
Published: February 2008

During a 3‐year period, Gulf Stream positions determined by satellite infrared imagery on a grid northeast of Cape Hatteras have been correlated against “inlet” path parameters (displacement from the mean position, angle, and curvature) monitored by an array of inverted echo sounders (IES). By cross‐spectral calculations between these measurements, we determined the downstream coherences, phase speeds, and spatial growth rates. The downstream path predictability from these inlet parameters was tested in a multiple input linear response model. The most energetic meanders, with periods of 33–50 days, remained highly coherent for 300 km downstream, roughly the dominant wavelength, with marginal coherence again at 500–575 km. Phase speeds are frequency dependent and decrease with distance downstream. For the 50‐(33) day meanders, phase speeds decreased from 10 (17) km/d at the inlet to 6 (8) km/d at a distance downstream of about 550 km. The average growth rate (spatial e‐folding wave number) over the entire region is 1.3×10−3 km−1. Within 300 km of the inlet, the multiple coherence accounts for 55–65% of the total path‐displacement variance, with displacement and angle being the best individual predictors in the first and last halves of this region, respectively.
Faultlike features in abyssal plain sediments: Possible dewatering structures
Authors: Buckley D. E. , Grant A. C.
Published: February 2008

Seismic reflection profiles from the Southern Nares Abyssal Plain and the Madeira Abyssal Plain show faultlike displacements of subbottom reflections in areas of thickest sediment accumulation. A remarkable aspect of these faults on the crests of basement highs is that their displacement is reverse rather than normal. We propose that these faults are primarily the result of dewatering processes and that the apparent reverse faults around basement highs reflect more extensive dewatering, hence greater compaction of the sediments overlying the basement high. Estimates of cumulative compaction with depth demonstrate that these abyssal plain sediments may have been reduced in thickness by as much as 120 m over the present 300 m. This could have been accompanied by an average rate of water explusion of 0.02 m3 m−2 yr−1. This evidence of instability of abyssal plain sediments has important implications in terms of evaluating the concept of using these sediments as a disposal medium for high‐level radioactive waste.
Sampling and aliasing during the NORPAX Hawaii‐to‐Tahiti Shuttle Experiment
Authors: Firing Eric , Lukas Roger
Published: February 2008

We examine leakage and aliasing problems in a seasonal multiple linear regression model of data taken during the NORPAX Hawaii‐to‐Tahiti Shuttle Experiment. The model includes a mean, trend, annual harmonic, and semiannual harmonic. Inclusion of the trend can exacerbate leakage, particularly for record lengths of 13 months or less. This is not a major problem for the 15‐month shuttle record. The irregularity of the shuttle shipboard time series reduces the potential aliasing of single unresolved high frequencies. Confidence limits for regression model coefficients are determined empirically from Monte Carlo subsampling experiments on moored current meter and sea level data taken during the shuttle. These limits are generally narrower than the standard regression error estimates because there is lack of fit in the regression model. Confidence limits used here pertain only to the determination of model coefficients for a given data set; they say nothing about whether the annual cycle during the shuttle period is typical of any other time interval. The shuttle sampling at each of three longitudes (150°, 153°, and 158°W) was in general not adequate to reveal significant differences in low‐frequency signals from one longitude to another. If data from the three longitudes are analyzed together without regard for longitude, the multiple linear regression parameters for temperature and zonal velocity component are fairly well determined. The meridional velocity component is so dominated by higher‐frequency variability that the model parameters do not differ significantly from zero.
Cautionary remarks on the spectral interpretation of turbulent flows
Authors: Armi Laurence , Flament Pierre
Published: February 2008

Spectral slopes are shown to be only very weak constraints for testing turbulence theories. They are primarily a consequence of applying spectral analysis to flows that are not wavelike but contain simple structures represented by a broad extension in wave number space.
Coupled ice‐ocean dynamics in the marginal ice zones: Upwelling/downwelling and eddy generation
Authors: Häkkinen Sirpa
Published: February 2008

This study is aimed at modeling mesoscale processes such as upwelling/downwelling and ice edge eddies in the marginal ice zones. A two‐dimensional coupled ice‐ocean model is used for the study. The ice model is coupled to the reduced gravity ocean model through interfacial stresses. The parameters of the ocean model were chosen so that the dynamics would be nonlinear. The model was tested by studying the dynamics of upwelling. Winds parallel to the ice edge with the ice on the right produce upwelling because the air‐ice momentum flux is much greater than air‐ocean momentum flux; thus the Ekman transport is greater under the ice than in the open water. The stability of the upwelling and downwelling jets is discussed. The downwelling jet is found to be far more unstable than the upwelling jet because the upwelling jet is stabilized by the divergence. A constant wind field exerted on a varying ice cover will generate vorticity leading to enhanced upwelling/downwelling regions, i.e., wind‐forced vortices. Steepening and strengthening of vortices are provided by the nonlinear terms. When forcing is time‐varying, the advection terms will also redistribute the vorticity. The wind reversals will separate the vortices from the ice edge, so that the upwelling enhancements are pushed to the open ocean and the downwelling enhancements are pushed underneath the ice.
Circulation in the Point Conception‐Santa Barbara Channel region
Authors: Brink K. H. , Muench R. D.
Published: February 2008

During spring and early summer 1983, fifteen current moorings were deployed around the periphery of Santa Barbara Channel and over the continental shelf to the west, off Point Conception. Data from these moorings have been used to describe the regional circulation and to address problems of wind forcing and the spatial coherency scales for current fluctuations. The mean circulation in Santa Barbara Channel was dominated by a westward jet which occupied the northwestern portion of the Channel. Current and temperature fluctuations were generally well‐correlated among all locations around the Channel, and time lags suggested cyclonic propagation of events around the Channel. The time fluctuations were dominated by a relatively few low‐frequency events. It was impossible to determine exactly either the driving mechanisms for these events or their relationships to regional flow. The flow regime was considerably different off Point Conception than in the Channel. Locally wind‐driven upwelling was observed in both the mean and fluctuating flows, and the time scales of current variability (i.e., spectral shapes) mimicked those of the local winds. A dramatic change in the regime off Point Conception occurred in late May. Before the transition, currents and sea levels had been well correlated in time with both local and remote winds. After late May the relation to fluctuating winds was less clear and the alongshore structure of sea level variability had changed radically.
Higher‐order approximations in the parabolic equation method for water waves
Authors: Kirby James T.
Published: February 2008

Application of the parabolic equation method to wave propagation problems implies that the propagation direction of all major components of the wave field must be confined to some narrow band of directions centered on a prechosen principal propagation direction. The allowed directional bandwidth is then delimited by the maximum allowed error in the principal direction wavelength when a transverse wavelength (wave turned at an angle) is imposed. In this paper we investigate higher‐order approximations which have the effect of opening the directional bandwidth to better than 45° around the principal direction and which fit within the computational framework of the lower‐order approximation. The problem is discussed within the context of the pure‐diffraction limit (constant depth), after which a higher‐order scheme is provided for waves in domains with slowly varying depth and ambient current. Several computational examples are provided to show the improvements in the higher‐order approximation relative to the existing lower‐order approximation. We then examine several forms of computational noise which arise in practical applications of either higher‐ or lower‐order approximations and suggest methods for suppressing the nonphysical, computational modes of the solutions.
Spatial variations of ocean wave directional spectra from the Seasat synthetic aperture radar
Authors: Beal R. C. , Gerling T. W. , Irvine D. E. , Monaldo F. M. , Tilley D. G.
Published: February 2008

Seasat synthetic aperture radar ocean wave spectra for a 900‐km pass are analyzed and interpreted in the context of both their probable generation sources and their surface current and bathymetric modifiers. Systematic vector wavenumber variations of several times the standard error of determination (∼1.5 % in magnitude and 0.9° in direction) occur along the entire 900‐km pass. The large‐scale spatial variation of a 200‐m swell system can be accurately accounted for as a result of dispersion from a distant storm. The more local variations are qualitatively well correlated in position with known currents and bathymetry but show systematic biases that appear partly due to an environmentally dependent instrument transfer function in the regions of high current and highest sea state. There is also substantial evidence that a large angular deviation in the center of the pass is the result of a mesoscale eddy just to the east.
Satellite remote sensing over ice
Authors: Thomas Robert H.
Published: February 2008

Satellite remote sensing provides unique opportunities for observing ice‐covered terrain. Passive microwave data give information on snow cover on land, sea ice extent and type, and zones of summer melting on the polar ice sheets, and they have the potential of estimating snow accumulation rates on these ice sheets. All‐weather, high‐resolution imagery of sea ice is obtained by using synthetic aperture radars, and ice movement vectors can be deduced by comparing sequential images of the same region. Radar altimetry data provide highly detailed information on ice sheet topography and have the potential of deducing thickening/thinning rates from repeat surveys. The coastline of Antarctica can be mapped accurately using altimetry data, and the size and spatial distribution of icebergs can be monitored. Altimetry data also distinguish open ocean from pack ice, and they give an indication of sea ice characteristics.
Wind‐driven spin‐up in eddy‐resolving ocean models formulated in isopycnic and isobaric coordinates
Authors: Bleck Rainer , Boudra Douglas
Published: February 2008

Wind‐driven spin‐up of the four‐layer, quasi‐isopycnic, eddy‐resolving primitive equation model of Bleck and Boudra (1981) is compared with that obtained with a (numerically dissimilar) “pure” isopycnic coordinate model and an isobaric (i.e., quasi‐Cartesian) coordinate model. In particular, the onset of hydrodynamic instabilities in the flow forced by a double‐gyre wind stress pattern is studied. The spin‐up processes associated with the isopycnic and quasi‐isopycnic model are found to be similar, whereas the flow pattern produced by the quasi‐Cartesian model deviates in the direction of Holland's (1978) and Holland and Lin's (1975a, b) two‐layer solutions.
On narrow‐band representation of ocean waves: 2. Simulations
Authors: Tayfun M. Aziz
Published: February 2008

In paper 1 (Tayfun, this issue) we derived two narrow‐band type representations for nonlinear waves and obtained theoretical expressions for the key statistics of the corresponding surface elevations, namely, the variance, skewness, and kurtosis. The nature of these statistics and the underlying probability structure were examined qualitatively with particular emphasis on the effects of the spectrum bandwidth. In this paper we explore the reliability of these results quantitatively. Proceeding via the Monte Carlo approach and finite Fourier transform techniques, we generate extensive samples of surface time history with preassigned spectral and statistical properties. Each sample is synthesized from a systematic superposition of the first‐order linear field and the second‐order corrections, consisting of shortwave and long‐wave modulations, respectively. This approach enables us to demonstrate explicitly the individual as well as combined effects of second‐order nonlinearities on the probability distribution and statistics of the surface elevation. In the final analysis we find that the simulated results compare favorably with the theoretical predictions and confirm the validity of various qualitative arguments put forward in paper 1.
A model for particle‐selective transport of tracers in sediments with conveyor belt deposit feeders
Authors: Robbins John A.
Published: February 2008

Conveyor belt deposit‐feeding organisms prevalent in both marine and freshwater systems have a profound effect on sediment properties and transport processes. These organisms ingest sediments over a range of depths while depositing gut contents from tails protruding above the sediment surface. This action results in particle‐selective transfer of buried materials to the sediment surface and imposes an accelerated rate of sediment and pore water burial within the feeding zone. Most previous efforts to combine sediment diagenesis with the effects of biogenic reworking characterize mixing as exclusively diffusive and ignore such major advective effects. Here a model is developed, based on fundamental diagenetic equations for transport and reaction, for the distribution of tracers in accumulating sediments subject to compaction and diffusive as well as advective redistribution by benthic organisms. Conveyor belt (CB) feeding is characterized as a first‐order process with a depth‐dependent rate constant which is either localized (Gaussian) or distributed (integrated Gaussian). Biogenic diffusivity of bulk sediments is allowed these alternative depth dependences as well. The model assumes simple linear adsorption of the tracer between solid and solution phases and uses a time‐dependent flux at (x = 0) which is a combination of that originating externally and the depth‐integrated contributions from feeding. Particle selectivity is introduced by applying mass conservation separately to transport of the tracer and bulk sediments. Properties of the model are illustrated for tracers in nondispersive systems strongly bound to sediment solids. CB recycling gives rise to transient reflections on passage of a tracer pulse through the zone of bioturbation. Reflections readily disappear in the presence of various integrative processes. The system time resolution is defined in terms of the downward propagation of dual tracer pulses and shown to be systematically degraded by intensified feeding and selective transport. A simple expression is developed for estimating the magnitude of particle‐selective changes in steady state surface concentrations in terms of the particle selectivity factor and the efficiency of sediment reworking. Unrecognized particle selectivity can lead to false inferences about changes in the rate of delivery of tracers to sediments. Selective CB recycling can cause a tracer such as 210Pb to be retained largely within the bioturbation zone, so that relatively little activity reaches the region of sediment useful for geochronological interpretation. Increased selectivity accentuates the sensitivity of the profile to details of the reworking process. The model, applied to previous studies of CB deposit feeders in tracer‐labeled freshwater microcosms, shows the need to include particle diffusion as well as advection in the treatment of CB transport.
Seasonal prediction of iceberg severity in the Labrador Sea
Authors: Walsh J. E. , Wittmann W. I. , Hester L. H. , Dehn W. S.
Published: February 2008

Statistical models for the seasonal prediction of iceberg severity in the Labrador Sea are developed from observational data for the years 1955–1984. The predictors are the monthly fields of sea level pressure and 700‐mbar geopotential height over the region north of 15°N. The primary statistical tools are gridded correlation patterns and multiple regression. Statistical significance is established by Monte Carlo simulations of the experimental procedure and by the use of a “jackknife” procedure for testing on independent data. Associations are found between iceberg severity and the circulation fields of the antecedent winter and spring. At lead times of 3–6 months, the mean absolute errors in the long‐range forecasts of severity rank are approximately 4–5 (6–7) ranks in dependent (independent) samples of 30 years. These errors are significantly smaller than the corresponding chance level value of 9.6 (± σ = 1.2). The spatial patterns depicted by the predictor fields are dominated by the North Atlantic Oscillation and are synoptically compatible with eastern Canadian iceberg conditions in both extremes of severity.
Ice pumps and their rates
Authors: Lewis E. L. , Perkin R. G.
Published: February 2008

An ice pump is a heat engine, driven by the change of freezing point with pressure, which will melt ice at depth in the ocean and deposit it at a shallower location: it is self‐starting. Calculations of the maximum magnitude of this effect are made which show good agreement with field data available for sea and lake ice. The discussion is applied to the general case of a moving pack ice sheet with a well‐mixed surface layer and to floating ice shelves. The rate of melt from an 11‐m‐deep pressure ridge keel due to ice pumping is estimated as 26 cm/year, and that from the front of the Ross Ice Shelf at McMurdo Sound, Antarctica is estimated as 5 m/year for the level of water movement noted in the authors' field observations. Far from the ice front, pumping between shelf areas of different thickness will still occur, with tidal motion providing the necessary water exchange, but its magnitude is now limited by the ability to remove the potentially stable layer of melt water out of the system. It is important to realize that the pumping does not depend on the availability of sensible heat in the water column and its effects are additional to any melting caused by the advection of warmer water to the ice‐water interface.
Wind effects on coastal zone color scanner chlorophyll patterns in the U.S. Mid‐Atlantic Bight during spring 1979
Authors: Eslinger David L. , Iverson Richard L.
Published: February 2008

Coastal zone color scanner (CZCS) chlorophyll concentration increases in the Mid‐Atlantic Bight were associated with high wind speeds in continental shelf waters during March and May 1979. Maximum spring CZCS chlorophyll concentrations occurred during April when the water column was not thermally stratified and were spatially and temporally associated with reductions in wind speed both in onshelf and in offshelf regions. Increased chlorophyll concentrations in offshelf waters were associated with high wind speeds during May when a deep chlorophyll maximum was present. Chlorophyll patchiness was observed on length scales typical of those controlled by biological processes during the April low‐wind period but not during March or May when wind speeds were greater. The spring CZCS chlorophyll maximum in the southern portion of the Mid‐Atlantic Bight occurred in response to a reduction in mixed layer depth caused by decreased wind speeds and not by increased water column stratification.
Horizontal wave number distribution of potential energy in the ocean
Authors: Dugan J. P. , Morris W. D. , Okawa B. S.
Published: February 2008

Horizontal spectra of temperature fluctuations on wavelengths from the mesoscale to the fine scale and spectra of conductivity fluctuations on the microscale are reported. These spectra are combined with intermediate‐scale isopycnal displacement data of Katz (1973), and a composite potential energy spectrum is constructed which spans scales from 2 cm to 2000 km, a range of eight decades in wave number. The overlap in energy level between scales is remarkably consistent, even though the data were acquired in different oceans and at depths from 60 to 600 m. This composite spectrum can be fit roughly by a −2 power law across these scales, and excesses above this level occur near 500 km, near 1 km, and on scales less than about 15 m. The excesses at the longest and shortest scales are apparent when energetic features, specifically mesoscale eddies and fine‐structure and microstructure patches, occur in the data. Spectral levels vary by an order of magnitude on the mesoscale and by 3 orders of magnitude on the fine scale and microscale. There appears to be a minimum in the relative variability in spectral level in the band from 1 to 50 km.
Seasonal variability of the Gulf Stream from satellite altimetry
Authors: Fu Lee‐lueng , Vazquez Jorge , Parke Michael E.
Published: February 2008

The nearly continuous 3.5 years of altimeter data in the western North Atlantic Ocean from the GEOS 3 mission (April 1975 to November 1978) have been used to study the seasonal variability of the Gulf Stream. The differences between altimetric measurements of sea surface height made at satellite ground track intersections, called crossovers, are utilized to construct time series of sea level variations. The results indicate that the Gulf Stream in the region off Cape Hatteras has a pronounced seasonal variability. The peak‐to‐peak amplitude of the seasonal cycle in terms of cross‐stream sea level difference is about 15 cm, with a maximum in April and a minimum in December. The result is in good agreement with historic hydrographic observations and recent direct measurements of the Gulf Stream. The mechanisms responsible for the observed seasonal variability are discussed.
Long waves in the equatorial Atlantic Ocean during 1983
Authors: Legeckis Richard , Reverdin Gilles
Published: February 2008

Long waves appeared at a zonally oriented sea surface temperature (SST) front in the eastern equatorial Atlantic during June and July of 1983. The low frequency, westward moving long waves (1000 km, 24 days) are monitored in the NOAA 7 satellite infrared images as meridional displacements of the front. The long waves observed in the Atlantic are similar to the waves previously seen in the eastern equatorial Pacific with several exceptions. The Atlantic long waves have a shorter duration (nearly three wave cycles at 15°W), and the wave amplitude is limited eastward of longitude 10°W. The Atlantic equatorial front appears to have a minimum north‐south displacement between longitudes 5°W and 10°W, while westward of 10°W the displacements exceed 400 km. Several buoys were launched south of the equator at longitude 4°W by the Programme Français Océan‐Climat en Atlantique Equatorial group on June 21, 1983. For the first 3 weeks, three of the buoys moved westward parallel to the equatorial SST front and measured relatively constant temperatures at 2 m. During mid‐July, changes were observed in the buoy temperatures, the buoy trajectories, and the long‐wave pattern. A comparison of the buoy temperatures at a depth of 2 m and atmospherically corrected satellite estimates of SST show a residual dependence of the satellite data on the zenith angle, even when the angle is limited to 45°. In general, the satellite SST measurements reproduce the trends observed in the buoy measurements, but small bias differences occur between buoys and between day and nighttime SST comparisons. Equatorial cross sections by ship and satellite over a 7‐day interval in June 1983 also show that SST trends are comparable in both sets of data.
Wind‐driven motion near inner shelf fronts
Authors: Chao Shenn‐Yu
Published: February 2008

The response of inner shelf fronts to wind forcing is numerically studied here by using a three‐dimensional primitive‐equation model. The front and its associated circulation are maintained by discharging light water near the surface and withdrawing heavier water from below along one vertical wall of a cyclic channel. Subsequently, a spatially uniform alongshore wind is applied. Responses to an upwelling‐favorable wind and to a downwelling‐favorable wind are highly asymmetric. Upwelling‐favorable wind forces the light‐water pool to surface and expand offshore. The pool is quickly detached from the source by the newly upwelled water. Even for a moderate plume and strong wind, it is unlikely that a downwind coastal jet can develop and force the plume to turn against its natural direction of propagation. Recent observations of Chesapeake plume support this finding. Downwelling‐favorable wind slowly narrows the plume, inside which a strong coastal jet is developed. For a density anomaly of finite alongshore extent, the jet intensifies downstream, reaches a maximum near the lead isopycnal, and decays thereafter. To compensate for the downstream acceleration, strong onshore flow develops near the upstream edge of the plume. If the wind persists, the enhanced onshore flow further narrows the plume and triggers a second intrusion. Unstable waves develop behind the second intrusion. They are, however, limited to small amplitudes by the prevailing onshore Ekman drift.
A bias in the satellite‐observed low‐level cloud motion winds over the central tropical Pacific
Authors: Mitchum Gary T.
Published: February 2008

Island wind data from the central tropical Pacific are compared with satellite‐observed low‐level cloud motion winds over the same area during 1976–1980. The purpose of the comparison is to investigate the effect of gaps in the satellite wind series. It is found that the distribution of the gaps is such that the resulting time series is biased from the complete time series because of undersampling of the strongest westerly and northerly wind anomalies. This bias is strong enough, at least in this geographical region, to cause difficulties in estimating accurate mean fields from the cloud motion winds alone. The gaps leading to this bias occur on time scales of days to weeks and are most common during the northern hemisphere winter. Further, the gaps can be attributed to the presence of heavy, high cloud cover typical of strong convective events. The bias follows from the fact that the wind anomalies are also strongest at these times.
Introduction: Summer marginal ice zone experiments during 1983 and 1984 in Fram Strait and the Greenland Sea
Authors: Johannessen O. M.
Published: February 2008

A marginal ice zone (MIZ) occurs where polar and temperate climate systems interact to form a transition between open ocean and pack ice regimes. This transition is characterized by large horizontal gradients in the properties of the ice, ocean, and atmosphere. As a geophysical boundary, the MIZ is unique in the complexity of the vertical and horizontal air‐sea‐ice interactions which take place there. Over a seasonal cycle, the ice edge can migrate hundreds of kilometers north and south to produce large variations in maximum and minimum extent.
The strait surface outflow
Authors: Wang Dong‐Ping
Published: February 2008

A three‐dimensional, primitive equation model is used to simulate the flow through a narrow strait. The flow within a strait has a simple two‐layered structure with the interface located approximately at the middepth. However, the flow experiences a sharp transition at the strait's exit: the flow jumps from a subcritical velocity inside the strait to a supercritical velocity immediately outside the strait. Correspondingly, the density interface also slopes sharply upward to the surface. After exiting the strait the surface outflow tends to form an anticyclonic gyre to the right of the strait's exit. Most of the outflow water is trapped within the gyre, although some manages to escape through a narrow coastal current. These model results compare well with observations in the Tiran Strait and in the Gibraltar Strait and Alboran Sea. The model study indicates that the flow transition at the strait's exit and the formation of an anticyclonic gyre are unique features of the nonlinear self‐advection of the density current.
The role of boundary mixing in the deep ocean
Authors: Ivey G. N.
Published: February 2008

Recent laboratory studies demonstrate that mixing at the boundaries of stratified and rotating fluids can be described by a relatively simple parameterization. These results are applied to the deep ocean, and by using available field observations, it is argued that mixing at the boundaries can lead to an apparent diapycnal diffusivity in the interior of the deep ocean whose magnitude has an upper bound of 3 × 10−5 m2 s−1.
Measurements of the wind stress, heat flux, and turbulence intensity during storm conditions over the North Sea
Authors: Geernaert G. L. , Larsen S. E. , Hansen F.
Published: February 2008

During the first two weeks of December 1985, measurements of the wind stress, the three‐component wind speed variances, and the vertical flux of sensible heat were collected from a research platform in the North Sea. Obtained using a sonic anemometer, the turbulence data represent an extensive range of wind speed conditions (5–30 m/s), and the air‐sea temperature difference was observed to span from −3° to +3°C. The data were collected from a boom extending 17 m to the west of the North Sea Platform at 33 m above the water surface. The results indicated that the 10‐m‐height neutral drag coefficient, CDN, exhibited a strong dependence on wave age, i.e., CDN was larger for growing waves than for steady state or decaying sea. The normalized turbulence statistics were found to corroborate the results of Smith (1980) and Large and Pond (1981).
Dinoflagellates as indicators of water masses during El Niño, 1982–1983
Authors: Ochoa N. , Gómez O.
Published: February 2008

The changes of the distribution patterns of some dinoflagellates considered as biological indicators showed the development of the 1982–1983 El Niño. During El Niño conditions the density of dinoflagellates was diminished, but there was a larger number of species, many of which are rarely found in this region. Protoperidinium obtusum, an indicator of cold coastal waters, disappeared almost completely during El Niño 1982–1983, but it was very abundant when the conditions returned to normal. Ceratium breve, an indicator of equatorial surface waters, during normal conditions is restricted to the northern area up to 5°S; during El Niño it was distributed up to 15°S. Several species indicators of warm waters were widely distributed during El Niño 1982–1983 but are very rare or absent during normal conditions.
Changes in the food and feeding of the sardine (Sardinops sagax sagax) during the years 1980–1984 off the Peruvian coast
Authors: Alejandro Alamo V. , Bouchon Marilu
Published: February 2008

The oceanographic changes produced by the 1982–1983 El Niño event determined qualitative and quantitative alterations of the primary and secondary trophic levels in the Peruvian littoral. These alterations produced variations in the food composition of planktivorous species such as the Peruvian sardine, Sardinops sagax sagax. In the present work, the feeding coefficient for the sardine in the zones off Paita, Callao, Pisco, and Ilo and the negative effects on the biological condition of the species (Fulton's condition factor) are described. Also shown are the qualitative variations in the diet observed before and after the 1982–1983 El Niño event throughout the study area.
A Bingham‐Plastic Model for a muddy seabed under long waves
Authors: Mei Chiang C. , Liu Ko‐Fei
Published: February 2008

The dynamics of cohesive mud under wave action is important to the geological processes along some coastlines. Because of the complex rheological properties there have been vastly different models for predicting the effect of mud on wave attenuation. This paper focuses on a non‐Newtonian behavior of highly concentrated mud, whereby shearing strain occurs only if the shear stress exceeds a certain threshold called the yield stress. The wave‐induced motion in a thin mud layer beneath a clear water layer is studied. There are circumstances in which the yield stress is dominant and acts like a Coulomb friction. Mud motion can change from continuous to intermittent as the wave attenuates. The effects of the non‐Newtonian behavior on wave damping are compared to other more common causes of dissipation.
Multiyear sea ice floe distribution in the Canadian Arctic Ocean
Authors: Hudson Rick D.
Published: February 2008

A series of aerial photographic flights, made over the polar pack ice during April 1982, from M'Clure Strait in the south to Ellef Ringnes Island in the north, shows the changes in ice floe type, size, and area as the pack moves southwest under the effect of the Polar Gyre. The area has some of the most heavily ridged and dynamically active ice in the Arctic Ocean. Floe size distributions were found to fit a negative power relationship (y = A xb, where b = −3.7), rather than the expected negative exponential function. A Prony analysis suggests that a single physical parameter controls the distribution: most likely splitting, rather than bending, shear, or crushing. The effect of proximity to the coast was investigated and showed that nearshore floes were about 20% smaller than their offshore counterparts. The ratio of maximum to minimum floe diameter was consistently 1.5–1.6. The mean floe diameter was found to be 700 m; the mean area was 0.38 km 2.Heavily hummocked and ridged floes were found to be a fairly constant fraction (1%) of the multiyear pack.
Winter currents and hydrographic conditions on the northern central Bering Sea shelf
Authors: Muench R. D. , Schumacher J. D. , Salo S. A.
Published: February 2008

Current observations obtained from the northern Bering shelf region in winter 1984–1985 indicate that midwinter circulation patterns differed from those during the rest of the year. Annual mean circulation in this region is dominated by vigorous northward currents (from 10 cm/s in Shpanberg Strait to more than 50 cm/s in Bering Strait). These northward currents are accompanied by a weak northwestward coastal flow south of St. Lawrence Island. In February–April 1985, however, flow was weakly (0–5 cm/s) southward through Shpanberg Strait and southeastward south of St. Lawrence Island while remaining northward through Anadyr and Bering straits. Comparison with current data obtained from previous years suggests that midwinter reversal of flow in Shpanberg Strait is a recurrent winter feature. It generally occurs at about the same time that the winter ice cover undergoes its major advance, and it is associated with strong northerly winds. Northward flow through Anadyr Strait persists, conversely, through the winter and is the northward extension of a western intensified northward flow over the Bering Shelf. Its source is Bering Sea water farther south, rather than water from the northern central shelf. The resultant “trapping” of shelf water on the northern central shelf, coupled with intensive regional ice formation during the same period as the flow reversal, led in 1985 to significant (about 1.5‰) brine enrichment. This salinity increase agrees qualitatively with historical data, which suggest that the northern central Bering shelf is the site both of sluggish winter circulation and of elevated salinities due to brine enrichment from ice formation.
Ice floe collisions and their relation to ice deformation in the Bering Sea during February 1983
Authors: Martin Seelye , Becker Paul
Published: February 2008

During February 1983, we carried out a field study in the Bering Sea on the nature of ice floe collisions and their relation to ice deformation. In the study we deployed on selected ice floes four radar‐tracked buoys, three of which contained triaxial accelerometers. These buoys were initially located in compact ice at a distance of about 100 km from the ice edge, with the separations between pairs of floes ranging from 300 m to 5 km. The buoys then drifted out toward the ice edge at a rate of about 0.5 km h−1, with the acceleration data being telemetered to an adjacent ship. The ice motion divided into two parts: an initial solid body translation with no relative buoy displacement, followed by a rapid transition to a period in which the buoy separations underwent large excursions. Examination of the accelerometer records shows two major collisions which were correlated with the large‐scale ice deformation and hundreds of small collisions which recurred at the ocean swell period. The first major collision occurred at the onset of ice deformation; the second occurred when two floes which had been diverging started to converge. The periodic collisions began following the major collisions; their magnitude depended on the local ice compactness and the size of the ocean swell amplitude.
Island wakes in shallow waters
Authors: Wolanski Eric
Published: February 2008

Field, laboratory, and numerical results suggest that the free shear layer behind flow separation points and the internal circulation generated by rotation in the eddy are important processes in island wakes in shallow coastal waters.
Principal component analysis of satellite passive microwave data over sea ice
Authors: Rothrock D. A. , Thomas Donald R. , Thorndke Alan S.
Published: February 2008

The 10 channels of scanning multichannel microwave radiometer data for the Arctic are examined by correlation, multiple regression, and principal component analyses. Data from April, August, and December 1979 are analyzed separately. Correlations are greater than 0.8 for all pairs of channels except some of those involving the 37‐GHz channels. Multiple regression shows a high degree of redundancy in the data; three channels can explain between 94.0 and 99.6% of the total variance. A principal component analysis of the covariance matrix shows that the first two eigenvalues contain 99.7% of the variance. Only the first two principal components contain variance due to the mixture of surface types. Three component mixtures (water, first‐year ice, and multiyear ice) can be resolved in two dimensions. The presence of other ice types, such as second‐year ice or wet ice, makes determination of ice age ambiguous in some geographic regions. Winds and surface temperature variations cause variations in the first three principal components. The confounding of these variables with mixture of surface types is a major source of error in resolving the mixture. The variance in principal components 3 through 10 is small and entirely due to variability in the pure type signatures. Determination of winds and surface temperature, as well as other variables, from this information is limited by instrument noise and presently unknown large‐scale variability in the emissivity of sea ice.
A naive zero‐dimensional sea ice model
Authors: Thorndike A. S.
Published: February 2008

A single observation of the microwave brightness temperature over sea ice cannot determine the composition of the ice surface in terms of the three constituents open water, first‐year ice, and multiyear ice. The ambiguity can be removed by interpreting the time series of brightness temperatures at a fixed location in the context of a model of how the composition evolves in time. A model is discussed which includes the effects of ice growth, melting, deformation, and aging. The aging process accounts for the change of first‐year ice into multiyear ice at the beginning of the cold season. The model reproduces the annual cycle of brightness temperature. A procedure, based on Kalman filtering, is presented for estimating the fractional areas of the three surface types. The procedure combines the model of ice evolution with the time series of brightness temperatures. The estimation errors are in the range 2–12%. These methods can be used with existing passive microwave data to construct a climatology of sea ice based on the three‐type classification. It is also possible to use the observations to improve model parameters such as the rate of melting and the rate of creation of open water by mechanical processes.
Modelling meter‐scale acoustic intensity fluctuations from oceanic fine structure and microstructure
Authors: Duda Timothy F. , Flatté Stanley M. , Creamer Dennis B.
Published: February 2008

Using model spectra of sound speed fluctuations, we have calculated the intensity variance and the wave number spectrum of intensity for acoustic propagation from a point source. We consider solutions in the unsaturated (Rytov) approximation, which is accurate when the intensity variance, normalized to unity mean intensity, is less than about 0.3. Our model medium spectra are consistent with observed vertical profiles of sound speed. Model fine‐scale sound speed inhomogeneities are characterized by the Garrett‐Munk (GM) internal wave spectrum or a simpler anisotropic (A) inverse power law spectrum. Microscale sound speed structure is modelled by a band‐limited isotropic Kolmogorov inertial subrange spectrum. With the GM model medium, the Rytov approximation is typically valid when the combination σR2 of frequency σ and range R is less than that given by 90 kHz and 1.1 km. Experiments within this window can determine characteristics of the fine scale medium spectra. In order to probe microstructure effects, frequencies near the high limit are necessary so that the Fresnel radius is 4 m or less. Previously published unsaturated vertical wave number intensity spectra recorded in the Kane Basin northwest of Greenland are compared with theory. The intensity spectral shapes from the GM and A fine structure models correspond well with those from the experiment. GM models give spectra low in level, by up to a factor of 20. Predictions from A type models can match the experimental spectral level if they are given an anisotropy ratio of sound speed inhomogeneities of 0.15, compared with the GM value of ƒ/N ≈ 0.02. Calculations show that microstructure may have intermittently influenced the Kane Basin transmission at small Fresnel radius Rƒ and that high intensity variance at large Rf must result from fine‐structure variability.
Gulf Stream bimodality and variability downstream of the Charleston bump
Authors: Bane John M. , Dewar William K.
Published: February 2008

Gulf Stream mean flow and variability have been studied in the Gulf Stream Deflection and Meander Energetics Experiment (DAMEX). This study was conducted between September 1981 and April 1982 in the area of the Charleston bump, off the coast of the southeastern United States. Using data from an array of current meters and satellite imagery, it has been shown that the seaward deflection of the Gulf Stream by the bump has a bimodal character and that the Gulf Stream meander field downstream of the bump differs between the two states of deflection. The two deflection conditions have been termed the weakly deflected state and the strongly deflected state in this paper. A weakly deflected Gulf Stream flows past the Charleston bump and close enough to the edge of the continental shelf that its shoreward sea surface temperature (SST) front remains inshore of the 600‐m isobath between Charleston and Cape Hatteras. A strongly deflected Gulf Stream turns sharply eastward at the bump and flows seaward far enough to have its shoreward SST front offshore of the 600‐m isobath for several tens of kilometers along the continental slope downstream of the bump. The transitions between deflection states may occur very rapidly, and once in a strongly deflected state the Gulf Stream may remain so for up to several months. Two transitions were observed during DAMEX, one from a weakly to a strongly deflected state and one in the other direction. The transition from weakly to strongly deflected state took only a few days at a given site, while the signatures of the other transition were not as definite in the data records. The strongly deflected state occurred during the fall and winter in DAMEX (October through January), and satellite observations from earlier years suggest that it is this time of year in which the strongly deflected state preferentially occurs. It was not clear from the DAMEX data alone how the transition from a weakly deflected to a strongly deflected state may be induced, but path or transport changes in the Gulf Stream as it approaches the bump and interactions between the current and rings or eddies are candidate mechanisms. The bimodal character of the stream's path affects the low‐frequency variability of the current between the Charleston bump and Cape Hatteras in the following manner. Typical meander/frontal eddy patterns dominate the mesoscale fluctuation field during times of weak deflection, while larger‐amplitude meanders of the Gulf Stream jet, which can have very sharp curvature and strong anticyclonic circulations in their crests, exist during times of strong deflection. Furthermore, these larger‐amplitude meanders, which we call the DAMEX biweekly meanders, have generally slower phase propagation speeds than do the typical meander/frontal eddy events (about 20–25 km/day compared with 35–60 km/day) as well as longer periods (about 16 days compared to 1 week).
Nonresonant and resonant reflection of long waves in varying channels
Authors: Kirby James T. , Vengayil Padmaraj
Published: February 2008

One of the principal drawbacks associated with the use of equations of Korteweg‐deVries (KdV) or Kadomtsev‐Petviashvili (K‐P) form to model wave propagation in a varying channel is the implicit neglect of reflection in those equations. This study formulates pairs of KdV or K‐P equations which are coupled through inhomogeneity in bottom slope or channel width, and applies these equations to several propagation problems involving aperiodic and periodic wave motion. The formulation eliminates the neglect of reflection effects in the single KdV or K‐P equation approach. Forms of the KdV equations are given which totally account for mass flux balance between the incident and reflected wave. We then examine several cases involving waves propagating in variable channels and compare model results to previously available data.