bluuebunny/crossref_metadata_2025 huggingface dataset:
Suspended particulate matter along the Coastal Ocean Dynamics Experiment Central line during upwelling and relaxation events
Authors: Drake David E. , Cacchione David A.
Published: February 2008

Profiles of light transmission, temperature and salinity and analyses of suspended matter samples acquired along the Coastal Ocean Dynamics Experiment Central line in June 1981 and April‐May 1982 suggest that the development of subsurface turbid plumes and temperature inversions may be associated with the relaxation of winds favorable for upwelling. Wind relaxations and reversals appear to trigger flow field adjustments characterized by sinking of previously upwelled water over the inner and middle shelf and the rapid growth of a barotropic poleward current over the inner shelf. Complexities in the cross‐shelf current structure during relaxation may be associated with the formation of the subsurface layers of plankton‐rich water and the small temperature anomalies. Renewed upwelling produces a relatively simple, three‐layer distribution of suspended particles and the elimination of temperature inversions.
Barotropic semidiurnal tidal currents off northern California during the Coastal Ocean Dynamics Experiment (CODE)
Authors: Rosenfeld L. K. , Beardsley R. C.
Published: February 2008

Barotropic semidiurnal tidal currents measured off the coast of northern California during the Coastal Ocean Dynamics Experiment (CODE) are examined. While the pressure field is consistent with the idea that the semidiurnal surface tide is dominated by a Kelvin wave, a high degree of variability over alongshore distances of the order of 25 km is observed in the velocity field. Comparison with existing models used to predict tidal velocities from sea level measurements cannot account for this spatial structure. Perturbation analysis of a Kelvin wave propagating along a coastal boundary with bumps characterized by an alongshore length scale much less than the Rossby radius of deformation shows effects on the velocity and pressure field which decay offshore with the alongshore scale of the bumps. The effect on the velocity field exceeds that on the pressure field by a factor equal to the ratio of the Rossby radius to the alongshore scale of the bumps. We conclude that the alongshore structure observed in the measured barotropic semidiurnal tidal currents may be due in part to the local variations in the coastline geometry in the CODE region.
Modeled surface dynamic height in 1964–1984: An effort to assess how well the low frequencies in the equatorial Atlantic were sampled in 1982–1984
Authors: Reverdin Gilles , Penhoat du Yves
Published: February 2008

A wind‐forced linear model has been used to produce 21 years (1964–1984) of monthly time series of surface dynamic height in the equatorial Atlantic. The climatological seasonal cycle is subtracted, and the statistical characteristics of the residuals are analyzed. An empirical orthogonal function analysis reveals that the most significant pattern has deviations of one sign in the western equatorial Atlantic associated with near‐simultaneous deviations of the opposite sign in the eastern equatorial Atlantic. The anomalies in the last 2 years, 1983 and 1984, are particularly large. The time component of the first empirical orthogonal function peaks in July 1983, changes sign at the end of 1983, and has an extremum of the opposite sign in April 1984. At that time, the zonal slope of dynamic height had reversed with respect to normal along the equator. In 1983–1984 a large data set was collected to study the seasonal variability in the equatorial Atlantic. We do not analyze the real data here but evaluate the ability of this data set to cover correctly the time and space scales of the modeled anomalies. The model time series are sampled at the positions of the data. An optimal interpolation scheme is used with the adequate statistics extracted from the model time series, and the analysis is compared with the simulation. Our results suggest that the most noticeable features of the model anomalies for 1983–1984 are reproduced in the analysis, although the results would have been better if more data had been collected in the western equatorial Atlantic at the end of 1983. According to this study, subsets which have already been analyzed for the same period (for example, the Programme Français Ocean Climat dans l'Atlantique Equatorial conductivity‐temperature‐depth cruises) would also have retained the reversal of sign of the anomaly between the end of 1983 and early 1984, although the overall accuracy would have been reduced.
Dispersion of dyed sand tracers in an oscillatory flow field
Authors: Pizzuto James E.
Published: February 2008

A numerical model of dispersion of dyed sand tracers is developed. The model is based on a grid of cells which represent the domain of a tracer experiment. The dispersion of the tracer is simulated by specifying the trajectories (or, alternatively, the volumetric transport rates) of dyed and undyed grains between cells during a wave period. The model conserves tracer mass, and for symmetrical one‐dimensional grain oscillations, the model is equivalent to a finite‐difference approximation of the diffusion equation. By fitting the predictions of the model to the results of a field tracer experiment, the particle trajectories and sediment transport rates during the experiment may be determined. As an example, the model is used to simulate the tracer experiment of Inman and Chamberlain [1959]. The model reproduces the observed dispersion of trace if 15% of the grains move 0.71 m during 1/4 wave period, and if the remaining 85% of the grains move 0.036 m during 1/4 wave period. The rapidly moving grains presumably travel in suspension, while the slowly moving grains probably travel as bed load.
The inference of salt fingering from towed microstructure observations
Authors: Holloway Greg , Gargett Ann
Published: February 2008

Discrimination between salt fingering and turbulence‐induced microstructure has been based upon horizontal wavenumber spectra of temperature or of conductivity. Information on probability distributions is discarded in such spectral analyses. We suggest that a discriminant may be found in probability distributions, namely that salt fingering is associated with marked suppression of kurtosis. This is demonstrated in records of towed microstructure from the eastern subtropical North Pacific.
Bubbles between the wave trough and wave crest levels
Authors: Baldy S. , Bourguel M.
Published: February 2008

In order to estimate ocean‐atmosphere mass transfer fluxes controlled by aerosol generation the bubble population at the interface has to be known. This information is usually inferred from measurements at a given depth below the water surface and from broad assumptions about the variation of bubble population with depth. However, recent measurements are not consistent with the usually assumed bubble population variation, and a direct investigation in the immediate vicinity of the interface appears to be necessary. Measurements above the minimum wave trough are difficult because a sensor level is alternately in the air and in the water. We have used a laser‐based single‐particle technique to investigate this zone for different breaking wave fields generated in a wind‐water simulation facility. The main bubble population characteristics, common to the different breaking wave fields investigated, are as follows: a roughly invariant size distribution characterized by a spectrum slope of approximately −2, concentrations rapidly increasing upward, following approximately an exponential law, and clustered distributions at the different measurement levels. These results, consistent with equivalent measurements below the wave trough level, correspond to bubble generation zone characteristics suggested in a previous investigation and provide further evidence of the existence of a universal bubble distribution at the interface of breaking wave fields. Very high bubble concentrations, up to 1010 bubbles of diameter larger than 60 μ per cubic meter (nearly 10,000‐fold the value just below the trough level), are observed at the crest levels.
Feedback between ice flow, barotropic flow, and baroclinic flow in the presence of bottom topography
Authors: Hakkinen Sirpa
Published: February 2008

Coupling between externally driven barotropic flow and locally driven baroclinic flow in the presence of an ice cover and topography is studied. The topography is a necessary ingredient in this coupling. This study shows that the observed mesoscale activity of the ice edge seen in satellite imagery does not necessarily reflect the mesoscale baroclinic activity in the ocean. Besides oceanic eddies, the ice cover can trace the topographic changes via the coupling to the barotropic flow. A two‐layer ocean model coupled to an ice model is constructed to simulate an ice‐ocean system with a varying bottom topography. In the absence of wind, forcing the ice cover reflects the externally driven barotropic ocean response, especially topographically forced Taylor columns by forming ice streamers or meanders. Some of these features propagate (advected with the ocean currents) as a whole downstream, creating an image of eddy propagation even though there is no baroclinic structure underneath. When downwelling favorable winds (ice on the left from the wind direction) are turned on, in addition to this background barotropic flow, the Ekman flow in the ocean (toward the open ocean) will enhance the meandering of the ice edge due to the barotropic flow. During upwelling favorable winds, the ice edge stays rather compact, including the case when a strong baroclinic, cyclonic vortex is developing beneath an ice meander supported by the Taylor column in the ocean.
Shipboard acoustic Doppler profiler velocity observations near Point Conception: Spring 1983
Authors: Barth J. A. , Brink K. H.
Published: February 2008

During April 1983, shipboard Doppler acoustic log current profiles were collected in an effort to characterize the flow field near points Conception and Arguello, California. Subsurface velocity maps derived from these profiles have been used to describe spatial flow structures both on and off the shelf and to investigate flow variability as a function of time and of wind stress. Persistent westward flow out of the northern half of the Santa Barbara Channel and eastward flow into its southern half were observed regardless of the direction of the local wind stress. During one well‐documented upwelling‐favorable wind event, currents responded in the form of an energetic (maximum 21‐m speeds of >60 cm s−1) offshore squirt of cold water. During weak or downwelling‐favorable winds, currents continuous with the Santa Barbara Channel outflow were observed flowing to the northwest following the local isobaths before turning offshore west of Point Arguello. Evidence for wind forcing of current fluctuations nearshore between the points and north of Point Arguello was found. Lack of a thermal wind balance between directly measured velocity shear and horizontal density gradient was explained by the presence of large accelerations in the momentum equations. Lack of a consistent relation between velocity and temperature gradient illustrates the difficulty in estimating velocity from temperature information alone in this area.
Attenuation of wind waves by monomolecular sea slicks and the Marangoni Effect
Authors: Hühnerfuss Heinrich , Walter Wolfgang , Lange Philipp A. , Alpers Werner
Published: February 2008

Previous observations of wind wave damping by monomolecular surface films (“slicks”) have shown a pronounced energy detraction (“dip”) in the short gravity wave range of the wind wave spectra. In this work, wind wave tunnel experiments with mechanically generated water waves have supplied experimental evidence which clearly shows that this dip is predominantly caused by the film‐induced “Marangoni effect.”
Two‐year moored instrument results along 152°E
Authors: Schmitz William J. , Niiler Pearn P. , Koblinsky Chester J.
Published: February 2008

Results from a 2‐year (nominal) deployment of a moored array along 152°E from 28°N to 41°N are presented, with emphasis on similarities and differences between settings (approximately year‐to‐year). Ten moorings and 38 instruments were involved, from the fall of 1980 to 1982. Current‐temperature meters spanned the water column from 500‐ to 4000‐m depths, with occasional instruments in the vicinity of 300 m and near the bottom (∼6000 m). Upper level features located in the center of the array near 35°–36°N were generally stable relative to the axis of the Kuroshio Extension, varying from deployment to deployment with meanders in this flow regime. Some properties of the abyssal (∼4000 m) currents were comparatively more variable, with these changes not connected to meandering of the Kuroshio Extension in an obvious way. The vertical structure and frequency distributions of eddy kinetic energy were similar in shape and to some extent in amplitude from deployment to deployment, especially relative to meanders of the Kuroshio Extension, but translated in the opposite direction.
Wave number‐frequency domain properties of coastal sea level response to alongshore wind stress along the west coast of North America 1980–1984
Authors: Halliwell George R. , Allen J. S.
Published: February 2008

Fluctuations in alongshore wind stress τ calculated from Fleet Numerical Oceanography Center geostrophic winds along the west coast of North America are relatively energetic at alongshore wave numbers |l| ≤ 1.1 × 10−3 cpkm and frequencies 0.025 < ω < 0.5 cpd, and they effectively drive a coastal sea level (ζ) response within this (l, ω) band. Equatorward propagation (l < 0) dominates the winter τ fluctuations for ω < 0.35 cpd, and poleward propagation (l > 0) dominates the summer τ fluctuations for ω < 0.1 cpd. In contrast, poleward propagation strongly dominates the ζ fluctuations in both seasons, but more so in summer. The largest coherence between ζ and τ is observed in that part of (l, ω) space where τ is most energetic: i.e., for 0 ≤ l ≤ 1.1 × 10−3 cpkm in summer and −1.1 × 10−3 ≤ l ≤ 0 cpkm in winter. Results are compared with predictions from theoretical models for wind‐driven coastally trapped waves. The observed transfer functions show evidence for near‐resonant ζ response in both seasons, with the largest gain found along a single ridge of approximately constant poleward phase speed, along which the response is approximately in phase with τ. This behavior is consistent with a response dominated by one coastally trapped wave mode governed by a forced, first‐order wave equation with a linear friction term. The maximum gain tends to decrease along this ridge with increasing l and ω in summer, and at least with increasing ω in winter, during which we could not resolve the l dependence. This observed decrease in maximum gain is not predicted by a single wave equation. The contribution of higher wave modes to the total ζ response may explain a part of this observed decrease.
Near‐inertial current oscillations in the vicinity of the Bering Sea marginal ice zone
Authors: Lagerloef Gary S. E. , Muench Robin D.
Published: February 2008

Near‐inertial current oscillations with 10–20‐cm/s amplitudes were prevalent over the Bering Sea shelf during November 1982 and again in March and April 1983 and also evident at reduced amplitudes during the intervening winter. Spectral peak frequencies were consistently within ∼1% of the local inertial frequency ƒ, in contrast to the more superinertial (∼5% aboveƒ) frequencies commonly reported elsewhere. A superinertial secondary energy peak at 1.038ƒ was evident, corresponding to the first‐mode wave. Amplitudes decreased with distance shoreward from the shelf break, consistent with the effects of decreasing bottom depth and increasing mixed layer depth. The oscillations were highly coherent over ∼100 km distances, similar to observations reported by Thomson and Huggett (1981) for the British Columbia coast, whereas near‐inertial oscillations have been commonly reported to be uncoupled over much shorter (∼10 km) distances in other regions. Vigorous near‐inertial “ringing” was associated with rapidly passing weather systems. The decline in near‐inertial oscillation amplitudes during winter was partially due to a significant reduction in both cyclone frequency and occurrence of wind events causing clockwise wind shifts. The decline was enhanced by reduction in the vertical stratification needed to support inertio‐gravity internal waves, as the shelf waters apparently became mixed from top to bottom. The loose, mobile sea ice in the winter marginal ice zone (MIZ) did not appear to inhibit wind generation of the inertial oscillations. The presence of sea ice appears, in fact, to have contributed to the spring increase of near‐inertial current amplitudes through restratification of the water column caused by melting ice. Our observations, particularly the spatial coherency and spectral properties, were generally consistent with Kundu and Thomson's (1985) model for inertio‐gravity waves generated in the wake of a translating weather front. The half wavelength typical of these waves forced by transiting weather fronts on the Bering shelf appears to be ∼150 km, or approximately the width of the winter MIZ. The associated near‐inertial currents are 180° out of phase with those a half wavelength away in the direction of phase propagation. Thus a storm passing perpendicular to the ice edge can excite waves at near‐inertial frequencies which compress, deform, and dilate the ice pack by up to a few percent of the MIZ width. We suggest that this mechanism, in conjunction with near‐inertial interfacial shear which can increase upward heat flux, influences the width scale of the MIZ.
Inertial wave dynamics in the North Atlantic Subtropical Zone
Authors: Mied Richard P. , Lindemann Gloria J. , Trump Clifford L.
Published: February 2008

Doppler current profiler observations of an inertial wave packet are presented from a region where a cold‐core ring impinges on a front. In this intense current a drogue is deployed to mark one region of the fluid. As the drogue is advected by the current, the ship follows it, zigzagging across the drogue's trajectory. Along this ship track, vertical rotary velocity spectra indicate the presence of a downgoing intertial wave with a vertical wavelength which slowly changes from ∼50 to ∼100 m as time progresses. The wave's intrinsic frequency was measured for the first time ever. A horizontally synoptic data set is obtained at the drogue depth by correcting for frontal advection and the temporal rotation of the wave velocity. Examination of these synoptic data indicates the presence of a southgoing near‐inertial wave with horizontal wavelength ∼20 km. The wave is confined to a 25‐km region. Supplementary ray‐tracing calculations through objective maps of the ring flow field indicate that the wave is strongly influenced by Doppler shifting. This is accompanied by a slow counterclockwise turning of the horizontal wave number vector, a decrease in the intrinsic frequency, and an increase in the vertical wavelength, in qualitative agreement with the data. A companion paper (Marmorino et al., this issue) details the effect of this inertial wave upon the small‐scale temperature activity with horizontal length scales of 1–3 m.
Spectral and empirical orthogonal function analysis of four years of European Center for Medium Range Weather Forecast wind stress curl over the North Atlantic Ocean
Authors: Mac Veigh J. P. , Barnier B. , Le Provost C.
Published: February 2008

The wind stress curl is calculated from a 4‐year European Center for Medium Range Forecast (ECMWF) data set over the North Atlantic. The mean wind stress curl appears as a northern positive cell of high amplitude and a large southern negative cell of lower amplitude. The separating zero contour shows large‐scale meanders and is highly variable at the seasonal and annual cycles. The rms of the wind stress curl is zonal and mainly contained in the short‐period band (less than 10 days). The frequency spectrum is nearly white north of 35°N. In the south, because of the lack of synoptic‐scale atmospheric storms, the spectrum shows a f−0.6 dependency at frequencies higher than 1/20 cpd. Wave number spectra are white for wavelengths larger than 1200 km and decay like k−4 at shorter wavelengths. The large‐scale variability is investigated by means of the empirical orthogonal function (EOF) analysis for the nonsynoptic time scales (periods of >10 days). The most significant EOFs display basin‐size oscillations with higher amplitude north of 35°N. The associated time series present high variability at the seasonal cycle and a larger amplitude in winter. These EOFs are related to important features of the North Atlantic climatology like the seasonal variability of the position of the Icelandic low, and the annual oscillation in intensity of the subpolar low, and the subtropical high. The first 10 EOFs are above the noise level. They are combined and compared to the initial data in order to produce realistic forcings for process studies in ocean modeling.
Scatterometer wind speed bias induced by the large‐scale component of the wave field
Authors: Glazman R. E. , Pihos G. G. , Ip J.
Published: February 2008

The entire set of Seasat A satellite Scatterometer (SASS) wind speed observations, Us, colocated with the buoy measurements of the wind speed Ub and wave height H1/3 is analyzed. The “error” Ub ‐ Us is found to be influenced by the degree of wind‐wave coupling. This coupling is quantified employing the ratio of the wave‐to‐wind energy densities: X ∼ ρwg〈ζ2〉/ρaUb2. For the special case of a fetch‐limited wave growth, X is shown to coincide with the wind fetch. It is found that when the coupling is weak, i.e., at large X, the SASS tends to overestimate the wind speed, and vice versa. The magnitude of the trend is evaluated roughly as 0.5 m/s per 100 km of X. The increased radar backscatter at large X is explained by invoking the concept (due to V. Zakharov and his collaborators) of a Kolmogorov equilibrium range appearing in wave spectra of sufficiently developed seas when the wind input is concentrated at high frequencies. In this extreme case, the surface density of steep wavelet occurrence would be at its highest owing to a pronounced cascade pattern in the surface geometry. The fractal dimension DH of such an idealized surface is estimated to be about 2.333. Further, it is suggested that DH for a general case is a function of sea maturity. Finally, it is concluded that both the probability and the surface density of steep wavelet events are increasing functions of X. A major implication with respect to the electromagnetic scattering is that the so‐called spike component of the backscattering coefficient, formed from the individual radar returns caused by the steep and/or breaking wavelets, is controlled primarily by the large‐scale features of surface geometry, hence by such nonlocal factors of the wave development as the wind fetch.
The energy balance of finite depth gravity waves
Authors: Weber S. L.
Published: February 2008

The energy transfer equation, which describes the evolution of the surface wave spectrum, is solved numerically for different water depths, with an empirical expression for the bottom dissipation and explicit calculations of the resonant four‐wave interactions. The resulting growth curves for total energy, peak frequency, etc., are explained from the balance between the source terms at the various stages of growth. The equilibrium which is reached between bottom friction and the resonant interactions on the forward face of the spectrum turns out to be important. The calculated results are briefly compared with recent shallow water wave experiments (TMA, Lake Marken) and with the Coastal Engineering Research Centre growth curves. Finally the results are compared with the SWIM study.
Satellite and aircraft passive microwave observations during the Marginal Ice Zone Experiment in 1984
Authors: Gloersen Per , Campbell William J.
Published: February 2008

During the Marginal Ice Zone Experiment in the Fram Strait in June–July 1984, a number of aircraft with microwave sensors and the scanning multichannel microwave radiometer (SMMR) on board the Nimbus 7 satellite were used to acquire large‐scale and mesoscale ice‐ocean observations in conjunction with local surface measurements made by experimenters based on helicopter‐equipped ice‐strengthened vessels. An analysis of the data acquired during six flights of one such aircraft, the NASA CV‐990 airborne laboratory, is discussed in this paper. Included in the instrument complement of the CV‐990 were two passive microwave imagers operating at wavelengths of 0.33 and 1.55 cm and the airborne multichannel microwave radiometer (AMMR) operating at wavelengths of 0.81, 1.4, and 1.7 cm for both horizontal and vertical polarizations. Total and multiyear sea ice concentrations calculated from the AMMR data were found to agree with similar calculations using SMMR data. This is the first check of the performance of the SMMR Team ice algorithm for near‐melting point conditions. The temperature dependence of the multiyear sea ice concentration determination near the melting point was found to be the same for both airborne and spacecraft instrument data and to be correlated with presence or absence of clouds. Finally, it was found that a spectral gradient ratio using the data from both the 0.33‐ and 1.55‐cm radiometers provides more reliable distinctions between low total ice concentrations and open water storm effects near the ice edge than does either singly.
Modeling the near‐bottom region of the benthic boundary layer
Authors: Svensson Urban , Rahm Lars
Published: February 2008

A mathematical model of the benthic boundary layer is formulated and explored. Emphasis is placed on the near‐bottom region, where recent field measurements have revealed the existence of a viscous sublayer. Field measurements have also indicated that form drag, due to roughness elements, may be an important feature of the boundary layer. The mathematical model includes submodels for low Reynolds number effects and form drag effects due to roughness elements and is thus intended to be applicable both to the viscous part of the flow and to the drag force dominated one. Verification studies are presented both for the viscous domain and the drag force dominated regions. Data from laboratory experiments are used for this purpose. Comparisons with field measurements of the benthic boundary layer are also presented as well as some principal balances of forces of the boundary layer, as predicted by the model. The general conclusion from the study is that the mathematical model presented describes the observed features of the benthic boundary layer in a satisfactory way.
Evidence for nonlocal forcing along the southeastern United States during a transitional wind regime
Authors: Schwing Franklin B. , Oey Lie‐yauw , Blanton Jackson O.
Published: February 2008

South Atlantic Bight (SAB) winds are typically well‐correlated over large alongshore scales and closely coupled with coastal sea level (CSL) fluctuations. However, this correlation is greatly reduced when meteorological dominance is changing between the Ohio Valley High of winter and Bermuda‐Azores High of summer. During the spring 1981 transition, strong persistent wind in the northern portion of the SAB (e.g., at Charleston) was highly coherent with local CSL (coefficient of determination, R2 = 0.70). In the southern SAB, however, a weak poorly organized wind regime was decoupled with local CSL. Daytona Beach CSL was uncorrelated with local alongshore wind, contrary to factional shelf models, but was coherent with alongshore wind stress and CSL at Charleston (R2 = 0.74), lagging events in the north by ∼15 hours. The results suggest that a CSL signal forced by wind in the northern SAB propagates southward with a phase speed of ∼700 km d−1. Barotropic shelf wave theory for an exponential shelf profile representing SAB topography predicts a phase speed of ∼500 km d−1. Thus the potential importance of shelf wave activity in the SAB during mixed wind conditions should be reassessed. Analysis of SAB wind‐CSL relationships provides, for the first time, direct evidence of remote forcing on the broad shallow shelf between North Carolina and Florida. Previous observations in the SAB from other seasons have not afforded evidence of nonlocal propagations, suggesting that conditions appropriate for their observation have a strong seasonal dependence.
Measurements of surface wave modulations from internal waves during the SAR Internal Wave Signature Experiment
Authors: Gotwols B. L. , Sterner R. E.
Published: February 2008

Video images of surface waves were recorded from a research vessel to characterize the internal wave‐induced surface roughness modulations during the SAR Internal Wave Dynamics Experiment (SARSEX). These images have yielded two‐dimensional slope spectra during the vessel's traversal of two internal wave packets. By sampling the spectra along the internal wave propagation direction, spectral modulation time series were generated for surface waves of 20‐ to 100‐cm wavelength which clearly show roughness modulations correlated with the internal wave activity. Surface waves of 60‐cm wavelength or longer were found to experience the largest modulations. The maximum roughness increases and decreases occur near regions where the internal Wave surface current gradients are largest, with increased roughness occurring forward of the peak internal wave displacement.
Phytoplankton standing crops within an Antarctic ice edge assessed by satellite remote sensing
Authors: Sullivan C. W. , McClain C. R. , Comiso J. C. , Smith W. O.
Published: February 2008

Ocean color (CZCS) and passive microwave (SMMR) imageries from the Nimbus 7 satellite are combined with in situ measurements of pigments and sea ice concentration to investigate the dynamic interactions between recession of the pack ice and occurrence of ice edge blooms of phytoplankton in waters of the marginal ice zone. Those interactions were observed in situ from November 7 to December 2, 1983, during a study of the ice edge and via satellite from September 16 through December 17. The ice edge position and phytoplankton biomass obtained from SMMR and CZCS sensors were studied to obtain information on the temporal and spatial patterns of ice and pigment concentrations. A pronounced and persistent phytoplankton biomass maximum was observed in the western portion of the Weddell Sea marginal ice zone which was associated with an open ocean region known to have a reduced surface salinity. An immediately adjacent ice edge region to the east showed little evidence of ice recession, and no bloom was observed in situ or by the CZCS. The two‐dimensional relationships among light, ice distribution, and vertical stability as they affect spatial variations in phytoplankton biomass are discussed. The retreat of ice appears to provide an input of significant volumes of meltwater which creates vertical stability for a period necessary to permit growth and accumulation of phytoplankton.
Variability of the upper tropical Pacific Ocean model
Authors: Kubota Masahisa , O'Brien James J.
Published: February 2008

Variability in the tropical Pacific Ocean is investigated by using the result of a linear, reduced‐gravity transport numerical model with realistic basin geometry in spherical coordinates. Observed monthly wind stress for 1961–1984 from ships drives the model. Upper layer thickness data for 1965–1984 are analyzed after dividing it into 12‐month running mean data and residual data. The former represents interannual variability, and the latter represents higher‐frequency (mainly seasonal) variability. The standard deviation in the equatorial region is relatively small for both variabilities. The standard deviation for the interannual variability is larger in the central and western Pacific Ocean outside the equatorial region, while the variation for the higher‐frequency variability is considerably larger even in the eastern region. The large amplitude of the standard deviation about the higher‐frequency variability is largely confined to the northern hemisphere. The map of the temporal decorrelation scale shows that the temporal decorrelation scale defined as an e‐folding scale is 9–12 months about the interannual variability almost everywhere. The zonal decorrelation scale shows large changes in different regions and at different times, while the meridional decorrelation scale shows small changes. The zonal decorrelation scale decreases with increasing latitude. The zonal decorrelation scale about the interannual variability is much larger than that about the higher‐frequency variability. These data may be helpful for designing field observing programs using expendable bathythermographs and drifters.
Coastally trapped waves in the presence of a shelf edge density front
Authors: Narayanan Savithri , Webster Ian
Published: February 2008

A numerical model is developed to analyze the stability and propagation characteristics of coastally trapped waves on a shelf with a shelf edge density front. The model is applied to the Saglek Bank on the Labrador Shelf in an attempt to explain the ice edge undulations observed in NOAA 5 satellite images. It was found that the instability is suppressed by the bottom slope if the entire shelf slope is below the front. However, if the front intersects the bottom at about 1000‐m depth with an associated current speed of 50 cm s−1 (an upper limit for the Labrador Current), the front could be unstable with a wavelength of 70–90 km and phase speed of 30–45 cm s−1, in approximate agreement with the estimates from satellite images. Furthermore, the neutral propagating modes will be modified by the front. Some modes will be transformed from barotropic shelf waves to bottom‐trapped frontal waves. The presence of a density front on a continental shelf also results in either restricting or eliminating the backward propagation of energy on the shelf and hence has a significant effect on the energy propagation along the shelf.
Introduction: Studies of ocean wave spectra from the Shuttle Imaging Radar‐B Experiment
Authors: Holt Benjamin
Published: February 2008

Imagery of ocean surface waves obtained from synthetic aperture radar (SAR) provides a unique two‐dimensional fine‐resolution view of the ocean wave field which has been long thought to be of considerable value for studying air‐sea inter‐action, wave generation and propagation, and wave‐current refraction. Wave spectra from SAR have also been thought to be extremely useful for updating and verifying global wave forecast models. Such promise prompted a SAR to be placed on Seasat, an oceanographic satellite which operated in a rather glorious mode for only a little over 3 months in 1978. This imagery has been well studied and indeed has demonstrated the feasibility of acquiring useful directional wave spectra from space [e.g., Vesecky and Stewart, 1982].
Validation of a synthetic aperture radar ocean wave imaging theory by the Shuttle Imaging Radar‐B Experiment over the North Sea
Authors: Brüning Claus , Alpers Werner , Zambresky Liana F. , Tilley David G.
Published: February 2008

Synthetic aperture radar (SAR) image intensity spectra measured during the Shuttle Imaging Radar‐B (SIR‐B) mission on October 6 and 8, 1984, over the North Sea are compared with ocean wave spectra obtained from a wave prediction model. The relationship between both spectra is discussed in the light of a previously proposed SAR imaging theory of ocean waves. Most of the measured SAR image spectra of October 6 show double peaks, while the hindcast ocean wave spectra have only single peaks. It is shown that the double peaks are generated by the SAR imaging mechanism. They occur only when velocity bunching is sufficiently strong near the range direction and when enough spectral energy density is present in this spectral region. Double peaks are generated when the SAR modulation transfer function (MTF) consisting of the sum of the complex real aperture radar (RAR) MTF and the velocity bunching MTF has a strong minimum near the range direction by which the wave spectrum is cut into two, in general unequal, pieces. The azimuth angle at which this minimum occurs depends strongly on the phase of the RAR MTF. In general, the two peaks are not located symmetrically with respect to the range direction, nor do they have equal heights. We interpret the reasonably good agreement between simulated and measured SAR image spectra during the SIR‐B mission over the North Sea as further experimental evidence in support of the validity of the previously proposed SAR imaging theory of ocean waves.
Verification of a numerical ocean model of the Arabian Sea
Authors: Simmons Ray C. , Luther Mark E. , O'Brien James J. , Legler David M.
Published: February 2008

A case study evaluating the predictive capability of an upper layer circulation model of the northwest Indian Ocean is presented. The model is a nonlinear, reduced gravity model incorporating realistic boundary geometry and is forced by observed winds. Model results for the fall of 1985 are compared with and evaluated against U.S. Navy bathythermograph and NOAA satellite data collected during August–November 1985. An assessment is made of the model's ability to simulate correctly the circulation structure. Ship wind observations are converted to wind stress for model forcing by a procedure developed by Legler and Navon (1988). The model is only moderately successful in reproducing the structure of the large, rather homogeneous pool of water located off the Arabian Peninsula in September. However, the model behaves remarkably well in the dynamically active region around Socotra. Major fronts and eddies frequently observed in the region during the transition period between the southwest and the northeast monsoon appear in the 1985 model results and compare well, both temporally and spatially, with the observational data. Thus given accurate wind information, the model appears highly effective in dynamically active regions and demonstrates potential as a useful prognostic tool for evaluation of the Arabian Sea when real time winds become available.
An estimate of equatorial wave energy flux at 9‐ to 90‐day periods in the central Pacific
Authors: Eriksen Charles C. , Richman James G.
Published: February 2008

Deep fluctuations in current along the equator in the Central Pacific are dominated by coherent structures which correspond closely to narrow‐band (in wave number) propagating equatorial waves. Currents were measured roughly at 1500 and 3000 m depths at 5 moorings between 144 and 148°W from January 1981 to March 1983 as part of the Pacific Equatorial Ocean Dynamics (PEQUOD) program. In each frequency band resolved, a single complex empirical orthogonal function accounts for half to three quarters of the observed variance in either zonal or meridional current. Dispersion for equatorial first meridional Rossby and Rossby gravity waves is consistent with the observed vertical‐zonal coherence structure. The observations indicate that energy flux is westward and downward in long first meridional mode Rossby waves at periods 45 days and longer and eastward and downward in short first meridional mode Rossby waves and Rossby‐gravity waves at periods 30 days and shorter. A local minimum in energy flux occurs at periods corresponding to a maximum in upper ocean meridional current energy contributed by tropical instability waves. Total vertical flux (energy transport per unit zonal distance) across the 9‐ to 90‐day period range is 2.5 kW/m.
Thermocline ventilation of anthropogenic lead in the western North Atlantic
Authors: Shen Glen T. , Boyle Edward A.
Published: February 2008

Massive industrial aerosol emissions from North America have over the past century overwhelmed the natural distribution of lead in the western North Atlantic thermocline. The resultant features to 2000‐m depth have been mapped near Bermuda for the year 1984. Since earlier reported measurements have largely been rejected on grounds of sample contamination, the twentieth‐century evolution of anthropogenic Pb in the oceanic water column is unknown. Coupling of the 1984 water column Pb distribution to historical records in reef‐building corals and tracer‐derived thermocline ventilation rates (Jenkins, 1980) has permitted a model reconstruction of Pb penetration into the Sargasso Sea. The model is constrained by three distinct Pb distributions (Pb concentration, stable Pb isotopes, and 210Pb) with adjustable scavenging and regeneration parameters to account for nonconservative behavior. The results of the model substantiate the importance of lateral isopycnal ventilation while pointing out the necessity of dissolved‐particulate exchange (i.e., scavenging τΓ of the order of 70 years in the deep thermocline; minimum regeneration of 10% particulate Pb between surface and 1700 m). Residual discrepancies between model isotopic predictions and observations below 800 m are likely due to a combination of the following factors: (1) presence of nonradiogenic background Pb in intermediate depth waters, (2) geographic variability in North American industrial source signatures, (3) Mediterranean Pb inputs of European origin, and (4) along‐isopycnal mixing effects.
Scales of North Atlantic wind stress curl determined from the comprehensive ocean‐atmosphere data set
Authors: Ehret Laura L. , O'Brien James J.
Published: February 2008

Nineteen years of wind data over the North Atlantic are used to calculate a field of wind stress curl. An empirical orthogonal function (EOF) analysis is performed on this field, resulting in spatial patterns of wind stress curl and associated time series. A Monte Carlo technique is used to establish the statistical significance of each spatial pattern. The first four statistically significant EOF modes represent more than 50% of the curl variance. The spatial patterns of curl associated with these modes exhibit the major elements of North Atlantic climatology. The associated time series are spectrally analyzed. Most of the variance is contained in annual and semiannual frequencies. Features observed include the individual annual variation of the subtropical high and the subpolar low, the annual oscillation of intensity between the above pressure centers, the influence of localized strong sea surface temperature gradients and associated cyclogenesis regions, and the constant nature of the trades. The EOF curl patterns are in the form of basin‐sized standing waves.
Low‐frequency meandering of the Atlantic North Equatorial Countercurrent
Authors: Garzoli Silvia , Richardson Philip L.
Published: February 2008

Four 19‐month time series of indirect measurements of dynamic height were obtained in the tropical Atlantic along 28°W at 0°, 3°, 6°, and 9°N with three inverted echo sounders and one current meter mooring. The series were analyzed to study the time‐latitude variability of the North Equatorial Countercurrent (NECC). The eastward flow associated with the NECC was present at 28°W from 3° to 9°N during most of the observed period except in March‐April 1983 and April‐May 1984, periods that coincided with the onset of the wind at the equator. The amplitude of the NECC's annual cycle was maximum at 6°N and was larger in 1983 than in 1984. The analysis of the time‐latitude variability of differences in dynamic height shows a long‐period meridional shift of the NECC. The core of the current attains its northernmost location during August‐September in both years and its southernmost location during March‐April in 1983 and March in 1984. The location of the core is directly related to the position of the intertropical convergence zone. From the time series of dynamic height obtained from the indirect measurements, geostrophic velocities and transports were estimated and compared with direct observations of currents and values obtained from hydrographic casts.
Rossby‐gravity waves in the central equatorial Pacific Ocean during the NORPAX Hawaii‐to‐Tahiti Shuttle Experiment
Authors: Chiswell Stephen M. , Lukas Roger
Published: February 2008

Spectra of sea level and current taken from the central Pacific during the NORPAX experiment contain broad peaks centered around 10‐day periods. Zonal dispersion shows these peaks to be caused by Rossby‐gravity waves. An empirical orthogonal function (EOF) analysis indicates that 44% of the variance can be attributed to these Rossby‐gravity waves, and they show clear temporal modulation in amplitude. There is no evidence that the Rossby‐gravity waves are generated locally, but coherence between the EOF and a modeled response to winds from Kapingamarangi Island, allowing for dispersion, suggests that these waves are generated by meridional wind stress in the west Pacific.
Use of the geostrophic approximation to estimate time‐varying zonal currents at the equator
Authors: Picaut Joël , Hayes Stanley P. , McPhaden Michael J.
Published: February 2008

Moored thermistor chains at 2°N and 2°S and current‐temperature moorings at 0° are used to examine the accuracy of geostrophically estimated zonal velocity on the equator in the eastern (110°W) and western (165°E) Pacific. The meridionally differentiated form of the geostrophic balance is used to eliminate large errors due to wind‐balanced cross‐equatorial pressure gradients. Statistical analyses indicate that for time scales longer than 30–50 days, the observed and geostrophically estimated zonal velocities are similar (correlation coefficients of 0.6–0.9 and comparable amplitudes). Thus low‐frequency equatorial current oscillations are reasonably well represented by the geostrophic approximation. However, the mean currents are poorly resolved with the available array. In the eastern Pacific the mean zonal speed difference over the 10‐month comparison period is 25 cm s−1 at 25 m and increases to 60 cm s−1 at 125 m. At 165°E mean differences in the upper 250 m are typically 50 cm s−1 over a 4‐month record. The principal reason for these large mean differences is that the meridional scale of the mean currents is smaller than the spacing of the moorings. Comparison of observed and geostrophic velocity profiles obtained from shipboard sampling indicates that meridional spacing of about 1° latitude would be optimum for estimating the zonal velocity.
Evaluation of Geosat altimeter data with application to tropical Pacific sea level variability
Authors: Cheney Robert E. , Douglas Bruce C. , Miller Laury
Published: February 2008

Repeated Geosat altimeter measurements of sea level at ground track intersections (crossovers) and along collinear nests of profiles were used to evaluate Geosat data by (1) construction of a regional, precise surface made up of intersecting sea level profiles, (2) determination of the magnitude of the electromagnetic (EM) bias, and (3) generation of sea level time series and anomaly maps. The first procedure, after elimination of radial ephemeris error and other long‐wavelength signals, established the data's internal precision at a few centimeters. With regard to the EM bias, comparing repeated sea level profiles for different values of significant wave height (SWH) gave a value of about 1% of SWH. The final process yielded a record of sea level whose accuracy was tested by comparison with in situ measurements and wind‐driven model results. On the basis of these analyses we conclude that Geosat data can determine sea level changes with an rms accuracy of approximately 4 cm for time scales of a month or longer. For determining sea level variability, Geosat geophysical data records are a high‐quality, long‐term data set of significant value for the study of ocean dynamics.