bluuebunny/crossref_metadata_2025 huggingface dataset:
Evidence for phase coupling between edge wave modes
Authors: Huntley D. A.
Published: February 2008

Assuming a nearshore wave field made up of linear combinations of several phase‐coupled edge wave modes at each frequency, we have calculated the form of the cospectra between two alongshore‐separated horizontal velocity components. Cospectra between two measurements of alongshore velocity are shown to be very insensitive to the presence or absence of phase coupling between the modes, while cospectra between two cross‐shore velocities are sensitive to a wide range of mode coupling. Cospectra between alongshore and cross‐shore velocities are particularly sensitive to coupling between a low‐mode edge wave, dominating the alongshore velocity, and higher mode edge waves dominating the cross‐shore velocity. Measured cospectra between alongshore and cross‐shore velocities from the alongshore arrays at the Nearshore Sediment Transport Study experiments on Torrey Pines Beach and Leadbetter Beach have been examined for evidence of mode coupling in the low‐frequency (0.005–0.027Hz) surf beat band. Clear evidence for mode coupling is found at both sites. The influence of the mode coupling on the cospectra varies with frequency in qualitative agreement with the simulated cospectra. Although phase locking between the edge waves can be shown not to be complete, it is not possible directly from the cospectra to quantify the degree of phase coupling, primarily because the number of modes involved is not known. Although the approach taken in this paper is essentially descriptive, it clearly indicates that coupling between edge wave modes must be seriously considered when modelling the nearshore wave field. This is important since previous theoretical work has shown that phase‐coupling is a necessary requirement for the development, by edge waves, of nearshore topography with alongshore structure.
The response of Delaware's inland bays to ocean forcing
Authors: Wong Kuo‐chuin , DiLorenzo Joseph
Published: February 2008

Sea level and current observations made during a 2‐month summer period in Delaware's inland bays are used for the examination of the tidal and subtidal variability in the bays. To first order, the coupled inland bays are found to be forced primarily by coastal sea level fluctuations at both tidal and subtidal frequencies. The observations suggest that the systems behave as low‐pass filters in response to coastal forcing. Overall, tidal variance decreases sharply inside the bays, with the semidiurnal tides suffering significantly higher attenuation than the diurnal tides. The subtidal variability, however, experiences no appreciable attenuation within the bays. The systems are also found to be only weakly nonlinear in nature. A linearized frequency‐dependent pumping mode model is developed, and results indicate that the model adequately describes the first‐order response of the inland bays to coastal sea level forcing.
Directional measurement of short ocean waves with stereophotography
Authors: Shemdin Omar H. , Tran H. Minh , Wu S. C.
Published: February 2008

Stereophotographs of the sea surface, acquired during the Tower Ocean Wave and Radar Dependence experiment (TOWARD), are analyzed to yield directional wave height spectra of short surface waves in the 6‐ to 80‐cm range. The omnidirectional wave height spectra are found to deviate from the k−4 distribution, where k is the wave number. The stereo data processing errors are found to be within ±5%. The omnidirectional spectra yield 514 degrees of freedom for 30‐cm‐long waves. The directional distribution of short waves is processed with a directional resolution of 30°, so as to yield 72 degrees of freedom for 30‐cm‐long waves. The directional distributions show peaks that are aligned with the wind and swell directions. It is found that dynamically relevant measurements can be obtained with Stereophotography, after removal of the mean surface associated with long waves.
The dependence of sea surface slope on atmospheric stability and swell conditions
Authors: Hwang Paul A. , Shemdin Omar H.
Published: February 2008

A tower‐mounted optical device is used to measure the two orthogonal components of the sea surface slope. The results indicate that an unstable stratification at the air‐sea interface tends to enhance the surface roughness. The presence of a long ocean swell system steers the primary direction of shortwave propagation away from wind direction, and may increase or reduce the mean square slope of the sea surface.
Wind stress measurements during the Tower Ocean Wave and Radar Dependence Experiment
Authors: Geernaert G. L. , Davidson K. L. , Larsen S. E. , Mikkelsen T.
Published: February 2008

During the Tower Ocean Wave and Radar Dependence Experiment (TOWARD), near‐continuous measurements of the wind drag were conducted using the dissipation technique. An intercomparison between these measurements and direct stress magnitudes using a sonic anemometer was performed over 3 days of the experiment. The results indicated that the dissipation technique compared well to the directly determined values when conditions were steady and neutral; otherwise, the dissipation method performed poorly. When neutrally stratified data were used, the drag coefficient exhibited a systematic dependence on both surface tension and wave age.
Observing the seasonal variability in the tropical Atlantic from altimetry
Authors: Menard Yves
Published: February 2008

The tropical Atlantic circulation is dominated by a strong wind‐driven seasonal cycle which is here described by means of the sea level heights measured by GEOS 3 and Seasat altimeters. Seasat worked for just 3 months, and GEOS 3 yielded an inhomogeneous space‐time coverage during its 3.5 years of operation. To remedy this coverage shortfall, all GEOS 3 and Seasat data were merged together on a monthly basis without regard to year, thereby ignoring the weak interannual perturbations of the tropical Atlantic. In this way, a complete time series was produced for 1 year. Along each profile, altirnetric heights were referenced to a global mean sea surface and then filtered to remove high‐ and low‐frequency noise. The residual heights were objectively analyzed to produce monthly maps of sea level anomaly between 10°S and 20°N. These maps show a large annual signal in the western side of the basin, between the equator and 10°N, where the North Equatorial Countercurrent and South Equatorial Current are predominant. The signal has an amplitude of 8 cm from a minimum in April–May to a maximum in October–November. In the east the signal is weaker and depicts a semiannual cycle. These results have been compared to similar maps obtained from historical hydrographic data (Merle and Arnault, 1985). The two sets of maps are in good agreement, especially north of the equator where the largest seasonal variability occurs. The major difference comes from underestimation of the altimetric signal amplitude due to the strong filtering and uneven distribution of the data.
The Nantucket Shoals Flux Experiment: 3. The alongshelf transport of volume, heat, salt, and nitrogen
Authors: Ramp Steven R. , Brown Wendell S. , Beardsley Robert C.
Published: February 2008

The alongshelf transport of volume, heat, salt, and nitrogen through a section across the continental shelf south of Nantucket Island was examined using moored current and bottom pressure measurements in conjunction with data from 15 hydrographic cruises along the mooring transect. The mean “observed” transport of shelf water, estimated from the moored current observations in the traditional way for the Summer time period (March to September 1979), was westward at 38.9 ± 8.2 × 104 m3 s−1. The “geostrophic” transport was inferred from differences between measured bottom pressures whose mean and trend were geostrophically levelled using the observed currents between each station. The mean geostrophic transports for the Summer and Annual (March 1979 to April 1980) time periods were westward at 31.9 ± 10.0 × 104 m3 s−1, and 29.0 ± 9.1 × 104 m3 s−1, respectively, with no significant seasonal variation. There was excellent agreement between the two methods in estimating transport fluctuations in the wind‐driven (4–20 day) band. The best estimates of the mean advective transport of heat, salt, and dissolved inorganic nitrogen were westward 3.16 ±1.42 × 109 kcal s−1, 1.18 ± 0.53 × 107 kg s−1, and 1.22 ± 3.03 × 109 μg ‐ at N s−1, respectively. Eddy transports were estimated where possible and found to be insignificant relative to advective transports in the alongshelf direction. This new value of mean salt transport is consistent with recently observed values of volume and salt transport into the Gulf of Maine through the Northeast Channel and the overall regional salt budget as computed by the Brown and Beardsley [1979] box model. The observed nitrogen transport can potentially supply between 39 and 53% of the nitrogen demand in the Middle Atlantic Bight.
Ocean wave spectra derived from Shuttle Imaging Radar‐B imagery and surface measurements
Authors: Iguchi Toshio , Inomata Hideyuki , Masuko Harunobu , Fugono Nobuyoshi
Published: February 2008

During the Shuttle Imaging Radar‐B (SIR‐B) mission in October 1984, synthetic aperture radar (SAR) images were taken off the coast of Japan. Wave spectra derived from SIR‐B imagery were compared with simultaneous wave buoy observations. Waves at the time of flight were nearly perpendicular to the SAR flight direction and were composed of two major systems: a swell of about 200‐m wavelength and wind waves with 70‐m wavelength. Both the swell and wind wave peaks were identifiable in the SAR image spectrum after stationary response correction. Peak frequencies derived from SIR‐B images and from the wave gauge agreed satisfactorily. However, the relative magnitudes of the peaks are not in accordance with the surface measurements. Possible reasons for the disagreement are discussed.
Comparison of Shuttle Imaging Radar‐B ocean wave image spectra with linear model predictions based on aircraft measurements
Authors: Monaldo Frank M. , Lyzenga David R.
Published: February 2008

During October 1984, coincident shuttle imaging radar‐B synthetic aperture radar (SAR) imagery and wave measurements from airborne instrumentation were acquired. The two‐dimensional wave spectrum was measured by both a radar ocean wave spectrometer and a surface contour radar aboard the aircraft. In this paper we compare two‐dimensional SAR image intensity variance spectra with these independent measures of ocean wave spectra to verify previously proposed models of the relationship between such SAR image spectra and ocean wave spectra. The results illustrate both the functional relationship between SAR image spectra and ocean wave spectra and the limitations imposed on the imaging of short‐wavelength, azimuth‐traveling waves.
Ocean wave directional spectra and wave‐current interaction in the Agulhas from the Shuttle Imaging Radar‐B synthetic aperture radar
Authors: Irvine D. E. , Tilley D. G.
Published: February 2008

SIR‐B synthetic aperture radar ocean‐wave spectra for a 200‐km pass crossing the Agulhas current off the coast of Africa are analyzed. A significant enhancement of one spectral peak along the northern edge of the current is attributed both to amplification of the waves by refraction‐dominated wave‐current interaction and to transient specular backscatter contributions spatially correlated to the waves.
Marine data sets and the shift of shipping routes
Authors: Cadet Daniel L. , Pafadnam Yarcé
Published: February 2008

Shipping routes of merchant ships have been changing since 1854, when the first observations over the ocean were organized. In certain areas where longitudinal and/or latitudinal gradients of surface parameters exist, spurious climatic signals due to the shift in the shipping routes can appear even when space averaging is made over a large domain. This problem is documented, and two methods to correct the time series are presented. Fields resulting from an objective analysis of the observations take into account the shift of shipping routes.
Wave setup: A field study
Authors: Nielsen Peter
Published: February 2008

A new and efficient method is described for obtaining field measurements of surf zone mean water levels. The method applies manometer tubes rather than the traditional pressure transducers, and hence makes it unnecessary to survey the vertical positions of the “sensors.” A substantial data base is obtained which, apart from quantitative data for the field site and similar beaches, gives clear, general indications of where previous wave setup models need to be amended. It is clear from the data that while traditional setup models work reasonably well seaward of the still water line the most landward part of the mean water surface (on fairly steep beaches at least) requires radically different models. It is still possible, however, to obtain reasonable estimates of the shoreline setup by tying together the concepts of setup and runup and utilizing presently available empirical formulae for the maximum runup level.
Influence of wind‐generated spray on evaporation
Authors: Resch François
Published: February 2008

When wind speed increases and ultimately exceeds a critical value, whitecaps and subsequently sea droplets appear. This is the source of an important increase in the rate of evaporation. Experiments reported here were performed in a large air‐sea interaction simulating facility which allow us to quantify this increased rate. Various wind (10, 12, and 14 m/s) and wave (wind‐generated and mechanically generated) conditions were studied to check this evolution. Profiles of mean wind velocity and humidity are determined at about 35–50 data points across the boundary layer and as close to the air‐water interface as possible. Using the profile method, momentum and water vapor fluxes were evaluated and represented by their dimensionless expressions as friction coefficients Cf and Sherwood number Sh, respectively. When plotted in the conventional manner, i.e., versus Reynolds number based on fetch and free stream velocity, Sherwood numbers show a clear deviation from available results, indicating a large increase of evaporation with increasing Reynolds number. Results were then plotted as a function of a modified Reynolds number based on friction velocity and significant wave height. From this an empirical correlation is proposed.
Vertical wave number spectra of velocity and shear at small internal wave scales
Authors: Duda Timothy F. , Cox Charles S.
Published: February 2008

We analyze spectra from five sets of hourly vertical profiles of upper‐ocean horizontal velocity collected with the Cartesian Diver velocity recorder. Each set consists of 11 to 27 profiles over depth ranges of 25–220 m to 25–340 m. The vertical wave number (m) power spectra of velocity and shear have no reproducible power law form in the band [0.02–0.1] cpm. Shear spectra tend to rise then fall with increasing wave number, with the transition wave number mc varying within the above band. For shear spectra, steepness at m near 0.1 cpm ranges from m−1/2 to m−2. The data sets fall into two categories. For one group, inverse Richardson functions Ri−1(mc) have values near 2. Despite variability of velocity variance, these sets have Ri−1(0.1 cpm) ≈ 3, suggesting that shear is near saturation. Low variability of Ri−1(0.l), despite high kinetic energy variability for this group, suggests that energy at high wave number (and thus shear) is suppressed. This suggests that instability mechanisms attenuate spectra at high wave number, with attenuation becoming more broadband and influencing progressively lower vertical wave numbers (in addition to consistently influenced high wave numbers) at higher energy. For the other group, Ri−1(0.1) ≈ 1, shear spectra are less steep, and shear is concentrated at high wave number, suggesting less attenuation at the small‐scale end of our measurement band. For both groups, predicted wave numbers of spectral steepening, estimated from the data using two techniques, are related approximately inversely with horizontal kinetic energy in the band [0.005–0.01] cpm, quantifying the shear spectral roll‐off.
The impact of atmospheric aerosols on trace metal chemistry in open ocean surface seawater: 2. Copper
Authors: Maring H. B. , Duce R. A.
Published: February 2008

Atmospheric deposition contributes copper to the surface ocean. The biogeochemical importance and fate of this copper is poorly understood for open ocean regions. Atmospheric aerosols collected at Enewetak Atoll, in the tropical North Pacific, were exposed to seawater and artificial rainwater in laboratory experiments. Aerosol copper during the high‐dust season at Enewetak Atoll is made up of aluminosilicate, oceanic, and possibly soil organic matter components. During the low‐dust season, aerosol copper appears to be essentially all of oceanic origin. Virtually all nonaluminosilicate copper in marine aerosols collected at Enewetak is soluble in seawater. Dissolved organic matter and possibly cations in seawater increase the dissolution of aerosol copper. The net atmospheric flux of soluble copper to the tropical North Pacific near Enewetak is approximately 0.13 nmol cm−2 yr−1 out of a total net atmospheric copper flux of 0.14 nmol cm−2 yr−1. Atmospheric deposition supplies roughly the same quantity of soluble copper to tropical open North Pacific surface waters as does upwelling to eastern North Pacific surface waters. Atmospheric copper deposition, which appears to be primarily of natural origin, may be the most important input of copper to the surface waters of the central gyre of the North Pacific.
Estimation of wave radiation stresses from slope array data
Authors: Herbers T. H. C. , Guza R. T.
Published: February 2008

A compact array of four bottom‐mounted pressure sensors arranged in a square, a slope array, is frequently used to obtain estimates of the wave radiation stresses in shallow water. For wavelengths long in comparison with the array dimension (L), existing processing methods (Higgins et al., 1981) have bias errors of O(kL)2, with k the wavenumber. An estimator for wave radiation stresses and energy fluxes is derived here that reduces the bias to O(kL)4, thus considerably extending the frequency range of accurate estimates of a slope array. The stability of the new estimator to statistical fluctuations in the cross spectra is similar to the method of Higgins et al. [1981].
A test of geostrophy in the Gulf Stream
Authors: Johns Elizabeth , Watts D. Randolph , Rossby H. Thomas
Published: February 2008

July In 1982 two detailed sections of density and absolute velocity were taken across the Gulf Stream northeast of Cape Hatteras to conduct an accurate test of geostrophy in a strong current. The sections, which were taken about 4 days apart, were each completed within 48 hours, using one ship to make closely spaced (12 km) conductivity‐temperature‐depth measurements to 2000 m, and a second ship to simultaneously take Pegasus absolute velocity profiles to the ocean bottom. The Gulf Stream path and curvature were also surveyed. The dynamically inferred velocity profiles were made absolute by matching their velocities to the Pegasus profiles at 2000 m. The geostrophic method (properly referenced) underestimated the observed velocities by 10–25 cm s−1 in the core of the current above 500 m where speeds exceeded 150 cm s−1. The difference is a factor of 2 larger than the sampling and measurement errors in corresponding parts of the current, estimated to be 5–10 cm s−1 in the strong current and 2–5 cm s−1 elsewhere. We can account for the supergeostrophic currents quite effectively by including the centripetal acceleration (from the path curvature) in the momentum equation. In this case the differences in the current core decrease to less than 5–10 cm s−1, well within the uncertainties of the method. The transport above 2000 m is less sensitive to curvature effects; it agrees to within 3 Sv before and 1 Sv after correcting for curvature, or approximately 2% of the total 93‐Sv transport. The deep velocity field below 1000 m had significant changes (10–20 cm s−1) in structure, and even reversals, in the 4 days between the sections, with cross‐stream scales of 50–100 km. This deep variability, attributed to topographic Rossby waves, introduces more than 10 Sv uncertainty in defining the total volume transport of the Gulf Stream.
Greenland Sea convection in the winter of 1987–1988
Authors: Rudels Bert , Quadfasel Detlef , Friedrich Hans , Houssais Marie‐Noelle
Published: February 2008

During February 1988 a layer of almost uniform temperature and salinity between 100 and 1250 m depth was observed in the central Greenland Sea. This feature, indicative of previous deep convection, is explained in terms of a conceptual penetrative convection model.
Wet tropospheric range corrections for satellite altimeter‐derived dynamic topographies in the western North Atlantic
Authors: Bisagni James J.
Published: February 2008

Radiosonde data and surface meteorological data collected from moorings and ships on both the warm and cold sides of the North Atlantic subtropical front were analyzed for the January to June 1986 time period. These data were used to investigate the magnitude and the spatial‐temporal scales associated with the variation of the wet tropospheric range correction for the U.S. Navy's Geosat radar altimeter. Analysis consisted of both numerical integration of high‐resolution radiosonde data and use of an atmospheric model to calculate the wet tropospheric range correction for the study region during the January‐June 1986 period. Results showed that the wet tropospheric range correction varied by about 15 cm overall, i.e., ranging from approximately 10 to 25 cm. This variation however, occurred over length scales which were large and time scales which were short compared with those from the subtropical front. Based on these results, the wet tropospheric range correction represented a synoptic scale variation in the lower atmosphere which would have little effect on the mesoscale dynamic signal associated with the subtropical front or the mesoscale eddy field as measured by the Geosat altimeter.
Sea ice ridging in the Ross Sea, Antarctica, as compared with sites in the Arctic
Authors: Weeks W. F. , Ackley S. F. , Govoni J.
Published: February 2008

At the end of the 1980 austral winter, surface roughness measurements were made by laser profilometer during a series of flights over the Ross Sea pack ice. The total track length was 2696 km, and 4365 ridges were counted. The frequency distribution of individual ridge heights was found to be well described by a negative exponential distribution. No clear‐cut regional variation was noted in ridge heights. The distribution of ridge frequencies per kilometer showed a strong positive skew with a modal value of 1.88; the most frequent ridging occurred off the east coast of Victoria Land. Comparisons with similar data sets from the Arctic indicate that large ridges are significantly more likely in the Arctic Ocean than in the Ross Sea. Utilizing a reasonable model for the geometry of ridges, estimates are made of the average thickness of a hypothetical continuous layer composed only of the deformed ice from ridges. The noncoastal Ross Sea value of 0.09 m is less than half of the lowest comparable value from the Arctic (0.20 m, central Beaufort Sea) where values in excess of 1.0 m have been observed in the shear zones north of Greenland.
Bed roughness produced by saltating sediment
Authors: Wiberg Patricia L. , Rubin David M.
Published: February 2008

Several expressions for characterizing bed roughness produced by a layer of saltating sediment have previously been proposed, and another is presented herein. These expressions relate the magnitude of the bottom roughness to the thickness of the near‐bed layer of saltating particles. In two previous studies, the empirically set constant of proportionality was determined using data for which the roughness associated with bed forms had to be calculated and subtracted from the total observed roughness, the remaining roughness being attributed to bed load. In this paper the expressions for bottom roughness are tested against values observed in upper plane bed flows where the transport is high and the bed is nearly flat. The results indicate that the two expressions in which the coefficient of proportionality was set using data requiring removal of bed form roughness overpredict the observed roughness by roughly 2 orders of magnitude, whereas the other two equations show good agreement with the measurements. The equations that overpredict the roughness may have attributed the roughness of small bed forms to bed load.
On the slope of the equilibrium range in the frequency spectrum of wind waves
Authors: Liu Paul C.
Published: February 2008

An effort to empirically assess the slope of the equilibrium range in a wind wave frequency spectrum with a large number of data recorded in the Great Lakes did not serve to clarify the uncertainty between a −4 or a −5 frequency exponent representation. The uncertainty is further compounded by indications that the slope is not necessarily unique, but tends to vary with wave momentum. For sufficiently well developed wind waves the exponent appears to cluster between −3 and −4. For practical applications the f−4 equilibrium range is perhaps an effective approximation. What the correct slope is for the equilibrium range, or even whether or not a unique slope exists, remains elusive and has yet to be satisfactorily substantiated.
A study of oceanic surface heat fluxes in the Greenland, Norwegian, and Barents Seas
Authors: Häkkinen Sirpa , Cavalieri Donald J.
Published: February 2008

This study examines oceanic surface heat fluxes in the Norwegian, Greenland, and Barents seas using the gridded Navy Fleet Numerical Oceanography Central surface analysis and the First GARP Global Experiment (FGGE) IIc cloudiness data bases. Monthly and annual means of net and turbulent heat fluxes are computed for the FGGE year 1979. The FGGE IIb data base consisting of individual observations provides particularly good data coverage in this region for a comparison with the gridded Navy winds and air temperatures. The standard errors of estimate between the Navy and FGGE IIb winds and air temperatures are 3.6 m/s and 2.5°C, respectively. The computations for the latent and sensible heat fluxes are based on bulk formulas with the same constant heat exchange coefficient of 1.5×10−3. The results show extremely strong wintertime heat fluxes in the northern Greenland Sea and especially in the Barents Sea in contrast to previous studies. The highest monthly average net fluxes are well over 400 W m−2 in these two regions in January and February 1979. The estimated uncertainty for the higher heat fluxes based on the comparison between the FGGE IIb and the Navy data sets is about ±30%.
Shallow water application of the third‐generation WAM wave model
Authors: Cavaleri Luigi , Bertotti Luciana , Lionello Piero
Published: February 2008

We present the results of detailed tests of the third‐generation WAM wave model. The tests are carried out under well‐known conditions, and they are chosen so as to check different aspects of the model. The test area is the Adriatic Sea, east of Italy, which is very shallow in its northern part. As expected from the basic physical approach of WAM to the problem, the results show the model's capability of responding equally well to different meteorological situations. Some discrepancies present at short nondimensional fetch and in shallow water are addressed with different formulations for breaking and bottom friction.
Development and properties of sea ice in the coastal regime of the southeastern Weddell Sea
Authors: Eicken Hajo , Lange Manfred A.
Published: February 2008

From October to December 1986 a program consisting of sea ice core analysis in combination with sea ice observations was carried out from the icebreaker R/V Polarstern as part of the Winter Weddell Sea Project. The ship operated in the central and southeastern Weddell Sea with interests focusing on the ice shelf front between 70°S and 77°S where a system of coastal polynyas extended for several tens to hundreds of kilometers, opened and maintained despite temperatures well below freezing by offshore wind forcing. Three wind‐controlled ice‐formation regimes may be distinguished: (1) For wind speeds <3 m/s, a continuous sheet of columnar ice with little deformation (<10% rafted) develops. (2) For wind speeds of 3–10 m/s, the ice cover is more highly rafted and ridged (25–50%) and shows an intermediate columnar/granular texture with features common to both these ice types. (3) For wind speed >10 m/s, the ice cover is heavily ridged and rafted (>50%) and formation of granular ice predominates. Of the total length of cores sampled in the coastal regime, 32% consisted of columnar and 35% of granular ice. In addition, we observed two unique ice classes along the coast. Platelet ice, formed through consolidation of underwater ice platelets underneath the solid ice cover, contributed 11% to our core samples. Another 22% consisted of intermediate columnar/granular ice, which originates under the dynamic hydrographic conditions of the near‐ice‐shelf region.
A mixing length interpretation of fluctuations in passive scalar concentration in homogeneous turbulence
Authors: Garrett Chris
Published: February 2008

The root‐mean‐square concentration fluctuation for a passive scalar in a turbulent flow, obtained by integrating the spectrum of Batchelor (1959), can be interpreted in terms of a mixing length times the mean scalar concentration gradient. One contribution to the mixing length is just the length scale of the dominant eddies. For very large Prandtl number there is another contribution which may be interpreted as the distance that a fluid element can be dispersed, according to Taylor's (1921) theory, in the time taken to reduce the minimum scale of the element from the viscous cutoff scale to the diffusive cutoff scale.
Shipboard acoustic Doppler current profiling in the eastern Caribbean Sea, 1985–1986
Authors: Smith Orson P. , Morrison John M.
Published: February 2008

Procedures to collect and reduce shipboard acoustic doppler current profiles (ADCP) for application to quantitative estimates of transport variation on a synoptic scale are described. Transport estimates based on data from five consecutive cruises across the eastern Caribbean are discussed in terms of ensemble averaging and vertical smoothing of ADCP records and satellite navigation procedures. Comparison of smoothed ADCP with Pegasus dropsonde current profiles indicates an error of 4 cm s−1 for Earth‐referenced ADCP eastward velocities. Comparisons with geostrophic current estimates in an area of significant and irregular ageostrophic effects indicate shipboard ADCP as a more accurate and reliable method for establishing seasonal and spatial variability of transport within instrument specific depth limitations.
Extracting ocean surface information from altimeter returns: The deconvolution method
Authors: Rodríguez Ernesto , Chapman Bruce
Published: February 2008

We present an evaluation of the deconvolution method for estimating ocean surface parameters from ocean altimeter waveforms. We show that this method presents a fast, accurate way of determining the ocean surface parameters from noisy altimeter data. Three parameters may be estimated by using this method: the altimeter height error, the ocean surface standard deviation, and the ocean surface skewness. By means of a Monte Carlo experiment, we determine an “optimum” deconvolution algorithm and the accuracies with which the above parameters may be estimated using this algorithm. We then examine the influence of instrument effects, such as errors in calibration and pointing angle estimation, on the estimated parameters. Finally, we use the deconvolution algorithm to estimate height and ocean surface parameters from Seasat data.
Wintertime air‐sea interaction processes across the Gulf Stream
Authors: Bane John M. , Osgood Kenric E.
Published: February 2008

Aircraft, buoy and satellite measurements have been used to study the wintertime air‐sea interaction processes across the Gulf Stream during January 25–30, 1986. The turbulent flux regime in the marine atmospheric boundary layer exhibited considerable spatial and temporal variability during this 6‐day period, which was related to both the evolution of the synoptic scale atmospheric conditions and the sea surface temperature (SST) field. During the pre‐storm conditions prior to January 25, the spatial structure of the SST field played an important role in generating a shallow atmospheric frontal zone along the Gulf Stream front by causing differential heating of the marine atmospheric boundary layer over the stream versus over the cooler shelf waters. As this front moved shoreward on January 25, the warm, moist, maritime air flowing northwestward behind the front induced moderate ocean‐to‐atmosphere heat fluxes (∼300 W m−2 total heat flux measured over the core of the Gulf Stream). The subsequent outbreak of eastward flowing cold, dry, continental air over the ocean on January 27 and 28 generated high total heat fluxes (∼1060 W m−2 over the core of the Stream), as did a second, somewhat weaker outbreak which followed on January 30 (∼680 W2 over the core of the Stream). During each of these outbreaks, with air flowing from land out over the continental shelf, Gulf Stream and Sargasso Sea waters, the SST field again affected the spatial structure of the flux fields. The near‐surface fluxes of both sensible and latent heat were found to be relatively low over the cool continental shelf waters, while higher fluxes were seen over the Gulf Stream and Sargasso Sea. Similar spatial structure was seen in the near‐surface momentum flux values, but relative changes were typically smaller from one location to another on a particular day. The most noticeable responses of the Gulf Stream to these surface fluxes were the deepening of its mixed layer and a loss of upper layer heat; however, no direct current observations were made in the stream, so velocity changes may not be assessed. An average mixed layer deepening of about 35 m was observed in the stream, and the upper layer heat loss was estimated to be 3.2×1013 J m−1 alongstream, an amount sufficient to decrease the average mixed layer temperature by 0.62°C. No path changes in the stream could be attributed to the atmospheric forcing of this period, since there was a large offshore movement of the stream in the region of the Charleston bump at this time due to other processes. Any path changes that may have been associated with the atmospheric forcing would have been masked by that offshore movement.
Velocity and hydrographic structure of subsurface shelf water at the Gulf Stream's edge
Authors: Churchill James H. , Cornillon Peter C. , Hamilton Peter
Published: February 2008

Relatively cool and fresh water, originating from the Middle Atlantic Bight continental shelf, has often been found along the northwestern margin of the Gulf Stream. In this paper we present measurements of temperature, salinity, and velocity within subsurface filaments of entrained shelf water adjacent to the Gulf Stream. The data indicate that vertical mixing within and near these filaments is effected by double‐diffusive processes and shear‐induced turbulence. The measurements also reveal a complex velocity and hydrographic structure within the filaments and show that the character of individual filaments differed considerably. For example, the measured mean flow within two filaments was much slower than the current in the adjacent Gulf Stream, whereas a third filament appeared to be incorporated within the high‐velocity region of the Gulf Stream. The most thoroughly sampled band of entrained shelf water exhibited temperature inversions and contained a slowly moving intrusion of warm water, presumably detached from the Gulf Stream. The estimated transport of shelf water within this band was roughly 7.2×104 m3 s−1, comparable with the rate at which water is transported over the southern Middle Atlantic Bight continental shelf as estimated by a previous study. However, the transport of individual entrained shelf water filaments may vary considerably because of the significant variation in their currents and hydrographic composition.
Hurricane‐generated currents on the outer continental shelf: 1. Model formulation and verification
Authors: Cooper Cortis , Thompson J. Dana
Published: February 2008

A numerical model is developed to simulate currents generated by hurricanes on the outer continental shelf and slope. Emphasis is on the mixed‐layer response within a few hours of storm passage; however, some attention is given to the lower layer and shelf wave responses. The model is based on a layered, explicit, finite difference formulation using the nonlinear primitive equations including conservation of heat. The problem of topography intersecting the model layer is resolved by introducing artificial steps of the order of 100 m where the layer intersects the slope. Model comparisons are presented for three Gulf of Mexico hurricanes using a 0.2° grid. For two of the storms, the model reproduces better than 80% of the observed velocity variance with correlation coefficients of greater than 0.8 for the mixed layer. Discrepancies in the comparisons are traced to unresolved local topography and nonstorm forcing such as warm‐core rings. Further model simulations reveal that (1) substantial shelf waves were generated with phase speeds of 4 to 10 m s−1, (2) the response is primarily baroclinic even in water as shallow as 200 m, (3) an entrainment law which scales with the velocity difference between the mixed layer and upper thermocline yields markedly better comparisons than one which scales with the wind stress, and (4) deviations from a straight‐line storm path can significantly alter the response.
A simple three‐dimensional model of the circulation off Newfoundland
Authors: Hukuda H. , Greatbatch R. J. , Hay A. E.
Published: February 2008

A simple numerical model is developed to study the three‐dimensional structure of the steady circulation off Newfoundland. The model uses linear dynamics, a vertical eddy viscosity to parameterize the vertical mixing, and a linear parameterization of bottom friction in which the bottom stress is related to the bottom velocity. Realistic geometry and bottom topography are included. The results presented here are for an ocean of uniform density. The model is driven by specifying the sea level along the northern boundary, the inflow corresponding to the inshore and offshore branches of the Labrador Current. The model can reproduce the circulation pattern found by Greenberg and Petrie (1988), who used a vertically integrated nonlinear primitive equation model. It also enables dynamical interpretation to be given in terms of flow along f/h contours and frictional “diffusion” across these contours. In this connection, we investigate the dependence on the friction parameters of the transport through several sections. We also examine the onshore‐offshore mass exchange over the southeastern edge of the Grand Banks. We find that the model Labrador Current flowing southward along the shelf break leads to an onshelf flux in the upper part of the water column and an offshelf flux in the bottom Ekman layer. This is caused by the frictional torque and leads to an along‐slope decay of the current amplitude. Finally the limitations of the model and plans for its further development are discussed.
Transport processes of suspended matter derived from time series in a tidal estuary
Authors: Grabemann I. , Krause G.
Published: February 2008

Optical beam transmittance meters integrated into Aanderaa current meters were used to measure long time series of suspended matter concentration simultaneously with current velocity and salinity in the turbidity maximum of the Weser estuary (shallow coastal plain estuary of the North Sea). They cover the spectrum from 10 min to several months. The time histories of concentrations and fluxes are discussed for characteristic locations within the turbidity maximum. The analyses demonstrate that the tidal dynamics of deposition into and resuspension of particles from temporally and spatially limited material sources at the bottom is the dominant process in the turbidity maximum while the nontidal gravitational circulation acts as a long‐term source and sink. There is a remarkable repeatability of concentration patterns during similar discharge conditions.
Measurements of the magnetic fluctuations associated with ocean swell compared with Weaver's Theory
Authors: Ochadlick Andrew R.
Published: February 2008

Fluctuations in the Earth's magnetic field caused by ocean swell have been measured above the ocean's surface with total field magnetometers. The magnetic field measurements were made both from an oceanographic research tower and from a dual magnetometer system on an aircraft. The results are consistent with the theory of magnetic fields associated with ocean waves and swell as developed by Weaver (1965). Aeromagnetic measurements give a good estimate of the period of the dominant ocean swell and its direction of propagation.
Upper ocean temperature variability in the northeast Pacific Ocean: Is it an indicator of global warming?
Authors: Royer Thomas C.
Published: February 2008

The upper waters of the Northeast Pacific Ocean contain very low frequency temperature fluctuations which have amplitudes of more than 1°C. Hydrographic measurements at 60°N, 149°W, and sea surface temperatures (SST) on a 5° grid over the Northeast Pacific are used to examine these variations. The very low frequency (VLF) 20‐ to 30‐year fluctuation in SST found at and north of 55°N is not evident at lower latitudes. This VLF fluctuation exists throughout the water column on the shelf of the northern Gulf of Alaska. Contained within the hydrographic data on the shelf are responses to El Niño‐Southern Oscillation (ENSO) forcing. However, ENSO responses are not evident in the SST data. The propagation characteristics of SST anomalies through the region are not consistent from one event to another. One SST anomaly moved eastward through the region over a 3‐year period (1956–1959), whereas the 1983 anomaly appeared simultaneously throughout the Gulf of Alaska. Correlations with local wind stress and wind stress curl are very poor, implying that the temperature variability is not wind forced. The causes for these temperature anomalies are uncertain. Though climate changes due to increases in greenhouse gases might be amplified at high latitudes, heating due to global warming is discounted. Coupling of the temperature fluctuations with solar activity and lunar tides is possible especially at high latitudes and the periods of the temperatures, tides, and solar activity are well matched. In any case, the recent upper ocean warming is probably not a result of large‐scale global change but is, rather, part of the VLF zonal signal. Below normal water and air temperatures should occur over the next 5–15 years. This VLF signal must be considered and understood before we will be able to measure the effects of high‐latitude climate changes.
Corections for the effects of significant wave height and attitude on Geosat radar altimeter measurements
Authors: Hayne G. S. , Hancock D. W.
Published: February 2008

Range estimates from a radar altimeter have biases which are a function of the significant wave height (SWH) and the satellite attitude angle. Based on results of pre‐launch Geosat modeling and simulation by the Johns Hopkins Applied Physics Laboratory, a correction for SWH and attitude was already applied to the sea surface height estimates from Geosat's production data processing. By fitting a detailed model radar return waveform to Geosat waveform sampler data, we can provide an independent estimate of the height bias due to SWH and attitude angle. The waveform fitting also produces independent estimates of the SWH and of the attitude angle. The waveform fitting has been carried out for 10‐s averages of Geosat waveform sampler data over a wide range of SWH and attitude values. Our results confirm that Geosat sea surface height correction is good to well within the original decimeter‐level specification but that an additional height correction can be made at the several centimeter level. Our results are expressed as additive corrections to the NOAA‐distributed Geosat estimates of sea surface height, SWH, and attitude, and we provide coefficients for the polynomial expressions for these corrections.
Determination of the major semidiurnal tides of the northwest European Continental Shelf from Geosat altimetry
Authors: Woodworth P. L. , Thomas J. P.
Published: February 2008

Geosat radar altimeter data from repeat cycles 1–38 of the Exact Repeat Mission (ERM) over the period November 1986 to August 1988 have been employed to derive the parameters of the semidiurnal ocean tides of the northwest European continental shelf using a modified form of response analysis. Values for M2 and S2 have been found to be compatible with those of previous empirical tidal maps and are estimated to be accurate to approximately 6 cm. This is an accuracy comparable to, or better than, that provided by current numerical models of the area. The results imply that altimetric models of the major tidal constituents in most coastal areas should be derivable from Geosat and subsequent altimetry to an accuracy, averaged over the whole coastal area, not previously possible from conventional tide gauge measurement programs or from numerical modeling.
The global distribution of f/H and the barotropic response of the ocean
Authors: Koblinsky C. J.
Published: February 2008

The barotropic response of the ocean over smoothly varying topography is directly related to the potential vorticity gradient ∇f/H. A global estimate of f/H and ∇f/H have been constructed from a high‐resolution digital topographic data base. Four different regimes of the barotropic response of the ocean are suggested by these maps: (1) In the tropical latitudes from 20°S to 20°N, ∇f/H ∼ β/H. The response will be similar to a flat‐bottom Sverdrup regime. (2) In mid‐latitudes (20° to 70°) north of 30°S, ∇f/H ≫ β/H. The response will be quasi‐stationary, weak, and dominated by nonlocal forcing (flow along isolines of f/H). (3) In a number of small regions throughout the mid‐latitudes in both hemispheres, ∇f/H ≪ β/H. In these regions the local response (flow across isolines of f/H) should be amplified, and wavelike motions may occur over a broader bandwidth of frequencies. (4) South of 30°S, the mid‐ocean ridge system becomes zonal and isolates several large regions within closed lines of f/H. In these regions, principally the abyssal plains of the southern ocean, the low‐frequency barotropic response of the ocean may be wavelike in character and much stronger than the Sverdrup response. Consequently, this analysis suggests that the southern ocean may have a stronger barotropic response to wind forcing than the other five major ocean basins.