bluuebunny/crossref_metadata_2025 huggingface dataset:
A numerical study of the roles of subgyre‐scale mixing and the western boundary current on homogenization of a passive tracer
Authors: Musgrave David L.
Published: February 2008

A numerical model integrated the steady advection‐diffusion equation by using a kinematic circulation with characteristics of a subtropical gyre, i.e., closed streamlines and western intensification. Homogenization of the interior concentration increased, and the gradients were forced to the boundaries as mixing, parameterized as eddy diffusion, decreased. As the western boundary current intensified, the value of the homogenized interior became closer to the southern boundary value. This indicated that cross‐stream mixing was enhanced within the western boundary current. Tongues of high and low tracer concentration spiraled across streamlines toward the center of the gyre. These simulations will be helpful in the interpretation of lateral distributions of geochemical tracers, which are being generated by programs such as TTO.
The large‐scale horizontal structure of the Antarctic Circumpolar Current from FGGE drifters
Authors: Hofmann Eileen E.
Published: February 2008

The last decade of research in the Southern Ocean has shown that the Antarctic Circumpolar Current (ACC) is a complex system composed of narrow, high‐speed currents separated by broad, quiescent zones. The circumpolar nature of this structure was examined using position and velocity data obtained from approximately 300 surface‐drifting buoys deployed in the Southern Ocean during the First GARP Global Experiment (FGGE). The distribution of buoys on 1°×1° squares shows that in some regions, most notably south of Australia, the buoys form three coherent bands of high buoy density which are separated by regions of low buoy density. The latitudes of these bands coincide with those of the Subtropical Front, Subantarctic Front, and Polar Front. To further examine the relationship between these fronts and buoy distribution, locations of the three fronts, determined from historical hydrographic data, were used to partition the buoys into zonal bands corresponding to front and nonfront regions. A mean buoy density and mean near‐surface speed were then computed for each zonal band. High buoy densities were associated with all three fronts in the region south of Australia. Other regions also showed a tendency, although not as pronounced, for buoys to accumulate in fronts. The mean near‐surface speeds suggest that the Subantarctic and Polar Fronts are circumpolar. Moreover, the mean near‐surface speeds associated with the three frontal regions differ. Speeds within the Subantarctic and Polar Front regions are approximately twice that associated with the Subtropical Front.
Dispersion of sea ice in the Bering Sea
Authors: Martin Seelye , Thorndike Alan S.
Published: February 2008

The dispersion of sea ice in the Bering Sea is analyzed in terms of the changes in separation between pairs of ice floes. The statistics of these changes depend on the separation itself and on the time interval over which the changes are measured. Rather than being constant, as in the case of molecular or Fickian diffusion, the diffusivity increases according to the 1.8 power of the separation. For short times the diffusivity is proportional to time. For times greater than 3 days the diffusivity appears to approach a constant value for any particular separation. Comparison with other data shows that the ice floe diffusivity is about an order of magnitude smaller than the diffusivity at the surface of the temperate ocean and about an order greater than the diffusivity of sea ice in the Beaufort Sea.
Wind‐induced stratified ocean response in the ice edge region: An analytical approach
Authors: Sjøberg Bjørn , Mork Martin
Published: February 2008

The response of a continuously stratified ocean to a moving ice edge is considered in terms of an analytical model. It is assumed that the principal cause for the generation of such phenomena as upwelling near the edge is due to divergence in the across‐edge Ekman transports. The semi‐infinite ice cover is considered to act only as a modifier of an applied wind stress. Thus the ice edge is simulated by a discontinuity in the ocean surface stress distribution. The results show that a stationary state relative to the moving edge develops. The amplitude of the response is finite, and it includes a system of standing waves relative to the edge. These results parallel the generation of lee waves in a rotating wave regime. How prominent the waves will be depends on the ratio U0/cn, where U0 is the edge velocity and Cn an eigenvalue corresponding to a vertical mode of the solution. As the stationary solution builds up, an along‐edge jet is established. It is pointed out that this jet could cause divergence in the surface layer, which could explain the generation of ice bands if the ice edge consists of broken ice.
Nutrients and alkalinity in the Labrador Sea
Authors: Anderson L. G. , Coote A. R. , Jones E. P.
Published: February 2008

Levels of nutrients, alkalinity, and total carbonate are related to the different water masses in the Laborador Sea, which include winter Labrador Sea Upper Water, Labrador Sea Water, North Atlantic Deep Water, and Northwest Atlantic Bottom Water. Alkalinity values in the Northwest Atlantic Bottom Water are consistent with a cyclonic flow around the periphery of the Labrador Sea and near‐stagnant conditions in the center. Nitrate and oxygen concentrations, combined to form the conservative tracer NO and taken together with potential temperatures, suggest that North Atlantic Deep Water and Northwest Atlantic Bottom Water in the Labrador Sea are part of a continuum of overflows at different densities from the Norwegian‐Greenland Sea region. NO values also suggest that neither of these water masses contains significant amounts of Mediterranean Sea Water or Antarctic Bottom Water.
A mixed‐layer bulk parameterization of surface fluxes tested with aircraft data
Authors: Khalsa Siri‐Jodha Singh
Published: February 2008

A bulk parameterization of surface fluxes is tested with aircraft data from a series of flights in the central equatorial Pacific. The parameterization used relates the fluxes of momentum, heat, and moisture at the surface to parameters in the well‐mixed region above the surface layer. Derived transfer coefficients for momentum and moisture agree well with those estimated from theoretical work. Sensible heat flux was too small at flight level to parameterize effectively.
Oscillations and rotations of elliptical warm‐core rings
Authors: Cushman‐Roisin Benoit , Heil Wolfgang H. , Nof Doron
Published: February 2008

Exact analytical solutions are found to describe ƒ plane time‐dependent, elliptical warm‐core rings where the interface intersects the surface along the periphery. The space variables can be eliminated to reduce the problem to a system of differential equations in time. The motion of the center of mass is resolved and subtracted. Small departures from circular shape have three intrinsic frequencies: two are inertial and superinertial, while the third is a low‐frequency mode that corresponds to a slow rotation of the elliptical eddy without change in shape. An exact solution for steadily rotating elliptical eddies of finite eccentricity (named Rodons) is also found and discussed. Comparison with elliptical warm‐core Gulf Stream rings shows that this low‐frequency mode may explain their clockwise rotation. The solution also shows the existence of a periodically reversing deformation field that, combined with a reasonable amount of mixing, would result in an efficient homogenization of the water contained in the ring. An exact solution that corresponds to the pulsation of a circular eddy has also been found.
A numerical study of the frequency and the energetics of nonlinear internal gravity waves
Authors: Shen Colin Y. , Holloway Greg
Published: February 2008

Internal gravity wave motions in a two‐dimensional vertical plane of fluid having constant mean Brunt‐Vaisala frequency are numerically simulated. The waves are integrated to statistical equilibrium under forcing and dissipation with forcing applied to low wave number modes. The model is used to study the variation of the internal wave energy dissipation rate with the Richardson number Ri, the effect of nonlinear wave interaction on the wave frequency, the wave number spectrum of the buoyancy flux, and the balance of the spectral energy flux. The energy dissipation rate is shown by our simulations to vary strongly near Ri ≈ 1 and to increase proportionally to Ri−1. The rms frequency fluctuation is found to increase approximately linearly with Ri−1/2 and with the wave number magnitude. The simulations show that the buoyancy flux varies nonuniformly with wave numbers, kinetic to potential energy conversion occurs mostly at low wave numbers, and an opposite conversion occurs in the rest of the wave number space. The mean spectral energy balance in the region where negative conversion occurs is marked by positive (gain) potential energy transfer and negative (loss) kinetic energy transfer in the intermediate wave number range and positive transfer for both kinetic and potential energy in the high wave number range; the latter is balanced by dissipation. The spectra of kinetic and potential energy are presented. The similarity in the slope of the kinetic energy spectra between the stratified turbulence from our simulation and the two‐dimensional unstratified, homogeneous turbulence is noted.
Altimeter height measurement error introduced by the presence of variable cloud and rain attenuation
Authors: Monaldo Frank M. , Goldhirsh Julius , Walsh Edward J.
Published: February 2008

It has recently been recognized that spatially inhomogeneous cloud and rain attenuation can substantially affect the precision of height measurements by a space‐borne radar altimeter system (Walsh et al., 1984). Through computer simulation, it was found that typical levels of cloud and rain attenuation and associated spatial variabilities may degrade altimeter precision at 13.5 GHz and may cause severe degradation at 35 GHz. This degradation in precision is a result of radar signature distortion induced by variable attenuation over the beam‐limited altimeter footprint. Because attenuation effects increase with frequency, range imprecision caused by them will significantly impact on the frequency selection of future space‐borne altimeter systems. In this paper, altimeter precision degradation from highly idealized cloud and rain models is reviewed and extended to include degradation resulting from the rain attenuation structure as measured by a ground‐based radar system.
Estimating open pack ice parameters using wind field and remotely sensed data
Authors: Feldman Uri
Published: February 2008

Real time data on thickness and surface and subsurface drag coefficients of drifting open pack ice, vital for predicting its motions, are not routinely available from measurements. Hence a method for estimating these parameters, in near real time, was developed and tested in the southeast Beaufort Sea. To this end, a reduced form of the general equation of motion for drifting pack ice was employed, assuming wind stress, water drag, and Coriolis force to be at equilibrium. Data were derived from satellite images, surface weather charts, and previously observed minimum and maximum of the three parameters. Among the four data series tested, three were acceptable. Routine application of the method depends on the availability of near real time remotely sensed data from microwave systems, producing at least 3‐day sequences of sidelapping images.
High‐resolution observations of low contrast phenomena from an advanced geosynchronous platform
Authors: Maxwell Marvin S.
Published: February 2008

Present technology allows radiometric monitoring of the earth, ocean, and atmosphere from a geosynchronous platform with good spatial, spectral, and temporal resolution. A new system is proposed that could provide a capability for multispectral remote sensing with a 50‐m nadir spatial resolution in the visible bands, 250 m in the 4‐μm band, and 1 km in the 11‐μm thermal infrared band. The diffraction‐limited telescope has a 1‐m aperture, a 10‐m focal length (with a shorter focal length in the infrared), and linear and area arrays of detectors. The diffraction‐limited resolution applies to scenes of any brightness, but for a dark, low contrast scene, the good signal‐to‐noise ratio of the system contributes to the observation capability. The capabilities of the advanced geosynchronous platform system are assessed for quantitative observations of ocean scenes. Instrument and ground system configurations are presented, and projected sensor capabilities are analyzed.
On the temporal variability of the surface Gulf Stream and near‐bottom flows
Authors: Ionov Victor V. , Weatherly Georges L. , Harkema Reinard
Published: February 2008

Long (3–4 years) time series of the surface Gulf Stream position and near‐bottom flow south of Nova Scotia support earlier findings of a barotropic semimonthly periodicity in the region, a bimodal Gulf Stream path downstream of the New England Seamount Chain, and a seasonal shift in the Gulf Stream position. New results are (1) a marked reduction of the meridional shifts of the surface Gulf Stream when it is in its north position mode, (2) the semimonthly periodicity seeming to be related at times to the Mf tide (the most energetic long‐period tide), and (3) an energetic, highly coherent (but out of phase) motion with a near‐40‐day period in the surface Gulf Stream position and near‐bottom flow.
Dynamic roughness and the transition between wind wave regimes
Authors: Gulliver John S. , Song Charles C. S.
Published: February 2008

A variational principle applicable to a closed and dissipative mechanical system is applied to wind waves. The result of this principle is that the water surface will take the form that provides the greatest surface drag and maximizes surface drag coefficient, or dynamic roughness. Therefore the normal train of logic is reversed: a maximum dynamic roughness is the criterion for gravity waves, capillary waves, or a hydraulically smooth water surface. Equations are assembled for the dynamic roughness of the water surface, and the variational principle is applied to find the transition between gravity and capillary waves and between capillary waves and a smooth water surface. It is found that wind fetch has no effect upon the point of transition from capillary to gravity waves. The transition between a smooth water surface and capillary waves, however, was found to depend upon both wind shear and fetch. The shear velocity of the transition increases with increasing fetch.
How radial orbit errors are mapped in altimetric surfaces
Authors: Mazzega Pierre
Published: February 2008

In the radar altimeter measurement of the satellite height above the instantaneous sea surface, radial orbit errors are “mapped” on the earth with the spacecraft motion. In many geophysical and oceanographical applications of satellite altimetry, a precise knowledge of the mapped error features is necessary to estimate sea (or ice sheet) surface topographies and to assess their absolute accuracies. So we derive a general formulation to infer from any a priori time spectrum of orbit errors the characteristic wavelengths of the mapped error biasing the recovery of a sea surface topography. Because of commensurability between the satellite motion and earth rotation, radial orbit errors at the nodal or orbital periods and their harmonics are mapped into smooth long‐wavelength surfaces and fully aliased in the steady surface topography. As this phenomenon presents a close relationship with the resonance of the orbit perturbations, we suggest naming it the mapped orbit error resonance. Our formulation also provides an explicit account of both time and space sampling effects on the correlation of the mean sea surface, oceanic tides, and orbit errors. For instance, the typical wavelength of a resonant mapped error is scattered by the land gaps in all the near wavelengths of an oceanic surface. The derived mapping function also seems to indicate that the statistics of the crossover differences are unable to estimate the absolute precision of altimetric surfaces because a nonnegligible portion of radial orbit errors falls into the steady component of the sea surface.
Sediment‐size distributions of the beach and nearshore environs along the central west coast of India: An analysis using EOF
Authors: Murty T. V. Ramana , Veerayya M. , Murty C. S.
Published: February 2008

EOF analysis of the data on grain‐size distributions of sediments in the Ø‐size class from the beach foreshore, backshore, dune, and nearshore environments of Colva and Calangute revealed that the first three Ø‐dependent eigenfunctions c1(Ø), c2(Ø), and c3(Ø) account for more than 97% to 99% of variation in the data set, the largest variation being represented by the first Ø‐dependent function c1(Ø) alone. This function showed significant differences in the concentration of grain‐size particles across the shore covering various physiographic units of Colva, i.e., dominance of very fine sands in the dunes and backshore, fine sands in the foreshore, and silt and clays in the offshore areas beyond 5‐m water depths, reflecting the impact of the changing character of the transportational and depositional processes affecting the sediments, thus implying different energy environments. This analysis also showed marked alongshore variations in the sediment distribution pattern in different sectors of the subaerial beach of Colva and suggests transportation of sediments from either ends to the central region. The three energetic eigenfunctions used to obtain the predictable or information rich part of the original signal are comparable with normalized input data and indicate the efficacy of this method.
Sensitivity studies of a simple inverse method applied to the Cox and Bryan model
Authors: Bigg Grant R.
Published: February 2008

The inverse method of Wunsch (1978) for determining steady state ocean circulation patterns is examined using a numerical model as the source of both data and observations. A simple, but commonly used, formulation of the technique is tested. The studies carried out have relevance to other descriptions, as they focus on features common to all formulations. The theme of the paper is a study of present methods rather than a comprehensive survey of parameter space. It is found that an optimizing principle of least perturbation from an initial velocity field can produce flows that are highly correlated with the observed fields. This is when station spacing is of the order of 1° – 2° and the number of layers is not greater than the number of vertical observations. Allowing flow through all faces of the boxes gives significantly more realistic velocities than merely having horizontal flow. However, three major problems arise with the box method. These are the inability to handle significant shears with moderate sampling, the lack of a uniformly successful way to decide on an initial state, and the necessity of using boxes of limited size. In particular, when the method uses boxes straddling an entire basin, the results are poor.
Turbulent heat and mass transfers across a thermally stratified air‐water interface
Authors: Papadimitrakis Y. A. , Hsu Y.‐H. L. , Wu J.
Published: February 2008

Rates of heat and mass transfers across an air‐water interface were measured in a wind‐wave research facility, under various wind and thermal stability conditions (unless otherwise noted, mass refers to water vapor). Heat fluxes were obtained from both the eddy correlation and the profile method, under unstable, neutral, and stable conditions. Mass fluxes were obtained only under unstable stratification from the profile and global method. Under unstable conditions the turbulent Prandtl and Schmidt numbers remain fairly constant and equal to 0.74, whereas the rate of mass transfer varies linearly with bulk Richardson number Rib. Under stable conditions the turbulent Prandtl number rises steadily to a value of 1.4 for a bulk Richardson number of Rib ≈ 0.016. Results of heat and mass transfers, expressed in the form of bulk aerodynamic coefficients with friction velocity as a parameter, are also compared with field data.
Seasonal ice extent on the northeast Newfoundland shelf
Authors: Symonds G.
Published: February 2008

Over the Northeast Newfoundland Shelf the main source of ice is advection from the north by winds and currents. Using historical ice charts, it is shown that the advance of ice is limited by ice melt throughout the winter months when the ocean provides the only source of heat, part of which is lost to the atmosphere and part of which goes to melting ice. Following techniques developed by Maykut (1978, 1982), the vertical growth of sea ice south of 55°N is examined in terms of the net heat loss from the ocean (Fw) and the conductive heat flux (Fc) through the ice to the atmosphere. Fc is estimated by assuming a linear temperature gradient through the ice from the freezing point of seawater at the underside of the ice to the surface temperature, calculated by solving the radiation balance at the ice surface using monthly climatological data. The flux Fw is estimated from monthly averaged temperature profiles from station 27 off St. John's, Newfoundland, in the south and from historical data from the Labrador Shelf in the north. The results suggest that in the north, over bare ice, growth of approximately 1 cm/d might be sustained off Hopedale (55°N) for December through March, while in the south off St. John's an estimated melt rate of 5 cm/d can be sustained throughout the winter months. Growth rates are strongly dependent on the depth of snow cover and the fraction of open water. The flux Fw reaches 250 W m−2 at station 27 in January, and it is suggested that much of this heat is derived from summertime heating when the whole of the Northeast Newfoundland Shelf is ice free.
Electromagnetic bias of airborne off‐nadir laser backscatter from the ocean
Authors: Dudis Joseph J.
Published: February 2008

Two recent theoretical models for the joint probability density function of wave slope and wave height are applied to the problem of using measured electromagnetic radiation of near‐vertical incidence backscattered from the ocean's surface to determine the mean sea level. For each of the models, expressions for the electromagnetic bias (the difference between the mean of the electromagnetic response distribution and that of the true mean sea level) and the conditional backscatter cross section, as functions of significant wave slope and specular incidence angle, are derived. The predictions from both models are qualitatively the same as those observed during the off‐nadir airborne laser experiments of Hoge et al. (1984): a positive electromagnetic bias and greater backscatter cross section from regions above mean sea level under low‐wind conditions and a negative electromagnetic bias and greater backscatter cross section from regions below mean sea level under moderate‐wind conditions. More quantitative comparisons appear limited by the ability to measure the mean square wave slope and determine the spectral nature of the sea.
Space and time variability of the surface color field in the northern Adriatic Sea
Authors: Barale Vittorio , McClain Charles R. , Malanotte‐Rizzoli Paola
Published: February 2008

A time series of coastal zone color scanner images for the years 1979 and 1980 was used to observe the spatial and temporal variability of bio‐optical processes and circulation patterns of the northern Adriatic Sea on monthly, seasonal, and interannual scales. The chlorophyll‐like pigment concentrations derived from satellite data exhibited a high correlation with sea truth measurements performed during seven surveys in the summer of both years. Comparison of the mean pigment fields indicates a general increase in concentration values and larger scales of coastal features from 1979 to 1980. This variability may be linked to the different patterns of nutrient influx due to coastal runoff in the 2 years. The distribution of surface features is consistent with the general cyclonic circulation pattern. The pigment heterogeneity appears to be governed by fluctuations of freshwater discharge, while the dominant wind fields do not appear to have important direct effects. The Po River presents a plume spreading predominantly in a southeastern direction, with scales positively correlated with its outflow. The spatial scales of the western coastal layer, in contrast, are negatively correlated with this outflow and the plume scales. Both results are consistent with, and may be rationalized by, recent theoretical and experimental results involving a dynamical balance between nonlinear advection and bottom friction, with alternate predominance of one of the two effects.
On the structure of artificially generated water wave trains
Authors: Papadimitrakis Yiannis A.
Published: February 2008

The structure of an artificially generated sinusoidal, water wave train of fixed frequency is examined under the influence of wind. The characteristics of this wave train were obtained with the aid of capacitance‐type wave height gauges in a wind wave research facility at Stanford University. Experimental results are given for seven wind speeds in the range 140–400 cm/s and 1‐Hz, 2.54‐cm (nominal) amplitude, artificially‐generated waves. The amplitude and phase of the various wave components were deduced by a simple method utilizing their traveling wave property and their characteristic dependence upon the streamwise position in the channel. The dispersion relation and component phase speeds were also examined. It was found that (1) the amplitude of the forced and free‐traveling second harmonics compares favorably with existing theories and (2) the nonlinearities of the primary wave, the interaction between short gravity waves and the primary wave, and the advection effects of wind drift are mainly responsible for the deviation of the measured phase speeds from the linear theory. The latter results are consistent with the field measurements of Ramamonjiarisoa and Giovanangeli (1978), indicating that the apparent phase speeds at high frequencies are independent of the frequency. The measured phase speeds were also found to increase with wind speed, at a given frequency, in accord with previous laboratory measurements and theoretical computations.
Recurring polynyas over the Cosmonaut Sea and the Maud Rise
Authors: Comiso J. C. , Gordon A. L.
Published: February 2008

Two polynyas over the deep ocean were observed in the Antarctic region during the winter of 1980: one near 43°E, 66°S (Cosmonaut polynya) and another near 2°E, 64°S (Maud Rise polynya). The time history of these two polynyas was examined on an alternate day basis using ice concentration maps from the Nimbus 7 scanning multichannel microwave radiometer (SMMR). A quantitative analysis of a study area around it shows that the totally enclosed Cosmonaut polynya attained a maximum size on July 25, 1980, with an open water area of as much as 137,700 km2. This polynya lasted for a few weeks, disappeared on August 16, 1980, and was not observed for the rest of the winter. Similar polynyas in the same region have occurred for several years, including 1973, 1975, 1979, 1982, and 1986. The Maud Rise polynya, on the other hand, was observed as a reduction in ice concentration to about 37% within the SMMR resolution of about 900 km2. However, the open water area in the region amounted to 92,800 km2 on July 20, and the polynya recurred several times during the same winter period. It is proposed that both polynyas are products of deep‐reaching convection which introduces warmer deep water into the surface layer. In this way, they are viewed as sensible heat polynyas in that they are maintained by oceanic heat. The oceanographic settings of these two polynyas are similar. The hydrographic data at both sites indicate the existence of localized doming of the pycnocline. This brings warmer, saltier deep water closer to the sea surface, which has been demonstrated to be an effective preconditioner for deep‐reaching convection. It is probable that the polynyas are terminated by “invasion” of sea ice from the sides, which attenuates convection. The capability of a polynya to survive an entire winter period may be related to its size; the larger polynyas are better protected from convergence of the surrounding sea ice. For example, a simple model shows that a polynya with a diameter of about 100 km or greater is much more likely to survive a winter season than a smaller one.
A microwave radiometer weather‐correcting sea ice algorithm
Authors: Walters J. M. , Ruf C. , Swift C. T.
Published: February 2008

An algorithm is developed which uses six channels of the Scanning Multichannel Microwave Radiometer to estimate fractions of multiyear and first‐year sea ice types under variable atmospheric and sea surface conditions. Previously published sea ice algorithms have used a minimal number of channels and have therefore avoided most problems associated with noisy data as well as detailed atmospheric correction. Algorithms used for retrieval of atmospheric parameters concentrate on a statistical approach utilizing as many channels as possible. The present work attempts to synthesize these two classes of algorithms by using several radiometer data channels. This algorithm is specifically tuned to derive sea ice parameters while accepting error in the auxiliary parameters of surface temperature, ocean surface wind speed, atmospheric water vapor, and cloud liquid water content. The four additional environmental parameters are derived only for the purpose of correcting the sea ice parameters at the expense of accepting absolute errors in the derivation of the secondary parameters. These large errors propagate small errors in the resultant sea ice fractions. This weather‐correcting algorithm performs at least as well, if not better, than the first‐generation algorithms over consolidated ice and appears to perform very well when the sea ice concentration is less than 20%. To this end, the results are compared with the results of two algorithms that appear in the published literature. Unlike one of the algorithms that employs a weather filter, this new algorithm utilizes the radiative transfer equation to correct for these effects and thus eliminates false retrievals of sea ice without discarding data. The penalty that is paid is that more computer resources are required.
Large‐scale oceanography in Fram Strait during the 1984 Marginal Ice Zone Experiment
Authors: Quadfasel Detlef , Gascard Jean‐Claude , Koltermann Klaus‐Peter
Published: February 2008

The pattern of large‐scale circulation in Fram Strait during summer 1984 is inferred from hydrographic data and water mass analysis and direct current observations by use of surface and subsurface floats. The West Spitsbergen Current carrying warm and salty Atlantic water splits into several branches, two flowing northward into the Arctic Ocean and two turning westward, causing a recirculation across the main axis of Fram Strait. The individual flow paths are topographically controlled, suggesting a strong barotropic component of the circulation.
Evolution of microwave sea ice signatures during early summer and midsummer in the marginal ice zone
Authors: Onstott R. G. , Grenfell T. C. , Matzler C. , Luther C. A. , Svendsen E. A.
Published: February 2008

Emissivities at frequencies from 5 to 94 GHz and backscatter at frequencies from 1 to 17 GHz were measured from sea ice in Fram Strait during the Marginal Ice Zone Experiment in June and July of 1983 and 1984. The ice observed was primarily multiyear; the remainder, first‐year ice, was often deformed. Results from this active and passive microwave study include the description of the evolution of the sea ice during early summer and midsummer; the absorption properties of summer snow; the interrelationship between ice thickness and the state and thickness of snow; and the modulation of the microwave signature, especially at the highest frequencies, by the freezing of the upper few centimeters of the ice.
Results from the 1984 Marginal Ice Zone Experiment preliminary tomography transmissions: Implications for marginal ice zone, Arctic, and surface wave tomography
Authors: Lynch James F. , Spindel Robert C. , Chiu Ching‐Sang , Miller James H. , Birdsall Theodore G.
Published: February 2008

During the 1984 Marginal Ice Zone Experiment (MIZEX '84), a 224‐Hz center frequency acoustic tomography sound source was deployed off Spitsbergen, Norway, in 1200 m of water. Over the course of 10 days it transmitted hourly signals that were recorded by receivers at two locations, one moving with the ice pack and the other stationary. The main purpose of the transmissions was to answer the following questions which are important to the feasibility of acoustic tomography in marginal ice zone (MIZ) and Arctic regions: (1) Can the signals be coherently averaged to improve the signal‐to‐noise ratio of the multipath arrival peaks, (2) are the surface‐scattering and bottom reflection losses acceptably low, (3) are the arrivals identifiable, (4) are the arrivals stable, and (5) are the arrivals resolvable? Our data analysis provides generally positive answers, indicating that ocean acoustic tomography is feasible in MIZ regions. However, the shallow bathymetry in the MIZEX '84 area increases the difficulty of the problem, consistent with the observations of Palmer et al. (1985) and DeFerrari and Nguyen (1985) in the shallow water of the Straits of Florida. In analyzing the data, it was noticed that the phase (or travel time) fluctuation spectra of surface interacting rays exhibited a shape similar to that of the surface wave frequency spectrum. This suggested that tomography could also measure the surface wave field, a previously unexplored possibility. Theoretical expressions are derived in this paper which relate the acoustic fluctuations to standard surface wave descriptors, e.g., the frequency‐directional spectrum. These expressions are then used to compute the surface wave frequency spectra for 2 days of data. Though these spectra are uncorroborated by other wave spectrum measurements (e.g., wave rider buoys), the rms wave heights predicted by the acoustics agree well with rms wave heights estimated by wind force data.
Photogrammetric observations of the lateral melt of sea ice floes
Authors: Hall Richard T. , Rothrock D. A.
Published: February 2008

Melting of the sidewalls of ice floes affects the ice concentration and subsequently the heat and mass balance of the ice cover. Lateral melt was measured photogrammetrically during Marginal Ice Zone Experiments in the Greenland Sea in June and July 1983 and 1984. A medium format metric camera was used in the second year; geometric control was established by surveying a set of targets on each measured floe. Floe perimeters were measured from sequential photographs, and mean lateral melt was estimated to an accuracy of about 6 cm. In 1984, melt rates increased from 3 cm d−1 on day 179 to 10 cm d−1 on day 193. The increase precedes the increase of water temperature noted by others on day 191.
Sea ice drift near Bering Strait during 1982
Authors: Pease Carol H. , Salo Sigrid A.
Published: February 2008

Six Argos ice stations were deployed in the northeastern Bering Sea in January and February 1982. Four moved north through Bering Strait and made between one and five passes through the strait before they sank or were crushed by the ice, and two remained in western Norton Sound and Shpanberg Strait. Net winds in the region were directed toward the southwest and were relatively uniform geographically. Net currents were northward, and both mean velocity and mean speed were greater at Bering Strait than at Shpanberg Strait. Norton Sound contributed ice northward through Bering Strait in the mean during winter and spring. There was also a net divergence of ice near Cap Lisburne. A theory for open‐shelf shallow water ice drift is developed that adds terms for bottom drag and stress feedback from the water column. A stress analysis for a station that remained in western Norton Sound and Shpanberg Strait showed that bottom drag did not contribute significantly but that stress feedback from the accelerated shallow water current can be of the same order as the Coriolis force. However, the analysis contained a residual, possibly associated with internal ice stress, coastal setup, or unknown measurement error, which was of roughly the same order as the wind and current stress.
Edge waves on the Sydney coast
Authors: Middleton Jason H. , Cahill Madeleine L. , Hsieh William W.
Published: February 2008

Pressure and current oscillations at periods of 40 s to 17 min observed during storm conditions at two locations separated by 560 m in the alongshore direction in the coastal ocean near Sydney, Australia, indicate the existence of infragravity waves having amplitudes of ∼20 cm and velocities of ∼10 cm s−1. The observed infragravity waves appear to be locally forced by the wind wave envelope through radiation stress, yet the observed alongshore phase differences of the infragravity waves are consistent with those predicted from free edge wave theory for low‐mode edge waves travelling northward and the relationship of pressure to velocity at each location is also consistent with free edge wave theory. As a function of time, the infragravity wave spectral energy grows and decays in step with the longer‐period wind waves, suggesting a continuous transfer of energy. The infragravity waves appear to contain energy in both directly forced and freely propagating (edge wave) oscillations. The edge waves may be generated either by radiation stress as outlined above, by a resonant triad mechanism, or by a combination of the two.
Recognition of spatial structures and ensemble averages in the benthic boundary layer
Authors: Abdelrhman Mohamed A. , Bedford Keith W.
Published: February 2008

Simultaneous high‐frequency spatial and temporal measurements of benthic boundary layer (BBL) velocity and sediment concentration generate complex data sets. In order to investigate the various spatial and temporal structures, a pattern recognition method is, for the first time, adapted and used to investigate different and similar structures (patterns) of velocity and acoustically measured suspended sediment concentration profiles in the lowest 2 m of the BBL at Tiana Beach, Long Island. This layer is subject to interactions between differently scaled forcing fields which result in structures difficult to predict using existing time average or boundary layer methods. Under the assumption of no a priori knowledge about either the spatial or temporal structures in the BBL, a deterministic mathematical methodology is implemented to recognize spatial structures in the data and classify them in an optimum number of classes. The spatial pattern analysis in this paper indicates that ∼ 70% of the above mentioned data are represented by only 5–20% of its size. Spatial patterns different from those predicted from theory or experience are recognized.
Vertical velocities and dynamical balances in Gulf Stream meanders
Authors: Osgood Kenric E. , Bane John M. , Dewar William K.
Published: February 2008

A triangular array of current meter moorings was deployed within the cyclonic flank of the Gulf Stream in the South Atlantic Bight from September 1981 to April 1982. Using velocity and temperature data and the nondiffusive heat equation, a time series of vertical velocity was derived. A mean vertical velocity of −0.013 cm s−1 and standard deviation of 0.078 cm s−1 were obtained. To better understand the subsurface structure of Gulf Stream meanders, the time series of horizontal and vertical velocities and temperature were examined at times when events were passing through the array. The flow along the trailing edge of a Gulf Stream meander and within the leading portion of a cold core frontal eddy was found to have an upward component (positive w), while that within the trailing portion of the frontal eddy and along the leading edge of a meander had a downward component (negative w). Using the horizontal and vertical velocity time series, cross‐stream and along stream momentum balances were calculated. The downstream flow was found to be in geostrophic balance. In contrast, the Coriolis and nonlinear terms were found to contribute equally to the determination of the cross‐stream flow.
Lateral and vertical variations in the wind‐driven circulation in long, shallow lakes
Authors: Hunter J. R. , Hearn C. J.
Published: February 2008

Solutions are derived for the steady state lateral and vertical variations of horizontal velocity in a long, shallow, wind‐driven basin, using both linear viscous and mixing length assumptions. The bathymetry is represented by a depth distribution function which describes the occurrence of different depths over a cross‐section of the basin. It is shown that the relative importance of the lateral (depth‐integrated) and overturning (vertically varying) circulations is dependent mainly on the bottom roughness and on the shape of the depth distribution. For natural bathymetries, the lateral circulation is generally dominant and becomes increasingly so as the bottom roughness decreases or as the depth distribution becomes broader. It is found that natural bathymetries can be characterized, in this context, by a single dimensionless number, related to the moments of the depth distribution.
Skewness in the nearshore zone: A comparison of estimates from Marsh‐McBirney current meters and colocated pressure sensors
Authors: Doering John C. , Bowen Anthony J.
Published: February 2008

Many of the field studies that have undertaken an investigation of surf zone dynamics (e.g., Nearshore Sediment Transport Study, Canadian Coastal Sediment Study) have relied on Marsh‐McBirney electromagnetic current meters to measure the velocity field. Data from these instruments have been used to compute higher order moments of the velocity field, which are used as an input in many sediment transport models. However, recent laboratory measurements by Aubrey and Trowbridge (1985) have raised questions regarding the suitability of Marsh‐McBirney current meters for surf zone studies and the accuracy of higher order velocity moments. Fortunately, colocated pressure and velocity measurements were made during field programs. In effect, this provides a calibration check in the field of the performance of these instruments. A cross‐spectral analysis indicates that colocated Marsh‐McBirney current meter measurements are highly coherent; this is true for measurements from inside and outside the surf zone. As a result, normalized skewness estimates computed (with the aid of the bispectrum) from these colocated current meter measurements differ by only a few percent. A cross‐spectral analysis between colocated pressure and velocity measurements show a similar distribution of variance for wind wave frequencies. Observed differences between normalized skewness estimates from colocated pressure and velocity measurements are shown to be consistent with the theoretical expectation that pressure has a nonlinear dependence on velocity. These results suggest that the Marsh‐McBirney current meter is suitable for the estimation of nondimensional velocity moments, even in breaking wave conditions.
Remote sensing of water vapor convergence, deep convection, and precipitation over the tropical Pacific Ocean during the 1982–1983 El Niño
Authors: Ardanuy Philip E. , Cuddapah Prabhakara , Kyle H. Lee
Published: February 2008

Deep tropospheric warming and mass flux, produced by the convection associated with organized tropical precipitation, is responsible on monthly and seasonal time scales for the presence of the Hadley and Walker circulations. In El Niño‐Southern Oscillation (ENSO) event years such as 1982–1983, in response to a perturbed sea surface temperature (SST) field in the equatorial Pacific Ocean, a major displacement in the ascending branch of these thermally direct, planetary‐scale cells occurs. As the northern winter monsoonal rainfall develops over the tropical Pacific Ocean near the date line, normal precipitation over Indonesia and the Amazon and Congo river valleys is suppressed. Later, as the SST maximum approaches the coast of South America, flooding occurs over Ecuador. As a direct result of the induced anomalies in the general circulation, droughts are caused not only in Indonesia but also in northern Australia and in the northern subtropical Pacific Ocean along an axis from the Phillipines to Hawaii. The scanning multichannel microwave radiometer (SMMR) on board the Nimbus 7 spacecraft has been used to derive estimates of atmospheric water vapor. The correlation between the satellite and verifying radiosonde data is better than 0.83 at all stations considered. The Earth radiation budget experiment flown on the same satellite observes the terrestrial net radiation, albedo, and outgoing longwave radiation (OLR). The OLR fields have been related to the 200‐mbar divergence fields in the tropics during the First GARP Global Experiment with a correlation of 0.8. The derived relationship has been successfully extended to realistically map the irrotational flow and divergent circulation present in the troposphere both prior to and during the 1982–1983 ENSO event. Together, the two data sets yield a joint estimate of the convergent flux of water vapor, a critical controlling parameter for organized convection. The derived water vapor flux convergences are analyzed during the recent El Niño episode to map the evolution of the parameter, inferred deep convection, and estimated rainfall over regions impacted by the event. The inferred monthly rainfall amounts are compared with observations for 14 island and coastal stations in the Pacific Ocean. For the stations, linear models are developed that explain up to 71% of the variance of the signal. For a rainfall model developed using the ensemble of stations, skill is demonstrated in describing the temporal and spatial evolution of the drought and flood anomalies present during 1982 and 1983. Over an equatorial belt extending from Indonesia to the coast of South America, positive rainfall anomalies reaching 40 cm month −1 are present. Due to changes in the Hadley and Walker circulations, these flood regions are bordered on all sides by rainfall deficits which are in excess of −20 cm month−1.