bluuebunny/crossref_metadata_2025 huggingface dataset:
Global mapping of underwater UV irradiances and DNA‐weighted exposures using Total Ozone Mapping Spectrometer and Sea‐viewing Wide Field‐of‐view Sensor data products
Authors: Vasilkov Alexander , Krotkov Nickolay , Herman Jay , McClain Charles , Arrigo Kevin , Robinson Wayne
Published: February 2004

The global stratospheric ozone layer depletion results in an increase in biologically harmful ultraviolet (UV) radiation reaching the surface and penetrating to ecologically significant depths in natural waters. Such an increase can be estimated on a global scale by combining satellite estimates of UV irradiance at the ocean surface from the Total Ozone Mapping Spectrometer (TOMS) satellite instrument with the Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) satellite ocean color measurements in the visible spectral region. In this paper we propose a model of seawater optical properties in the UV spectral region based on the case 1 water model in the visible range. The inputs to the model are standard monthly SeaWiFS products: chlorophyll concentration and the diffuse attenuation coefficient at 490 nm. Penetration of solar UV radiation to different depths in open ocean waters is calculated using the radiative transfer quasi‐single scattering approximation (QSSA). The accuracy of the QSSA approximation in the water is tested using more accurate codes. Sensitivity studies of underwater UV irradiance to atmospheric and oceanic optical properties have shown that the main environmental parameters controlling absolute levels of UVB (280–320 nm) and DNA‐weighted irradiance underwater are solar zenith angle, cloud transmittance, water optical properties, and total ozone. Monthly maps of underwater UV irradiance and DNA‐weighted exposure are calculated using monthly mean SeaWiFS chlorophyll and diffuse attenuation coefficient, daily SeaWiFS cloud fraction data, and the TOMS‐derived surface UV irradiance daily maps. The results include global maps of monthly average UVB irradiance and DNA‐weighted daily exposures at 3 and 10 m and depths where the UVB irradiance and DNA‐weighted dose rate at local noon are equal to 10% of their surface values.
High‐salinity intermediate water of the Japan Sea in the eastern Japan Basin
Authors: Watanabe Tatsuro , Hirai Mitsuyuki , Yamada Haruya
Published: February 2004

Conductivity‐temperature‐depth data from the midwinter in 1997 are examined for the presence of the intermediate water in the eastern Japan Basin, in the northern part of the Japan Sea. Three different water masses can be detected with salinity extrema at intermediate depths between the main pycnocline and the upper portion of the Japan Sea Proper Water (UJSPW). The shallower salinity maximum and the middle salinity minimum can be identified as the Tsushima Warm Current Water (TWCW) and Japan Sea Intermediate Water, respectively. The deeper salinity maximum water, with high temperature and high dissolved oxygen, is identified as High‐Salinity Intermediate Water (HSIW) and has density similar to UJSPW (27.30–27.33 σθ). Isopycnal analyses indicate that HSIW flows southeastward from the Siberian coast, where TWCW outcrops and has an opportunity to become denser by direct cooling. We conclude that TWCW is the origin of HSIW, which in turn, is a source for UJSPW.
Heat flux and mixing efficiency in the surface mixing layer
Authors: Wolk Fabian , Lueck Rolf G.
Published: February 2004

Fluctuations of vertical velocity and temperature, w′ and T′, were measured with a horizontal profiler that was towed at night in the oceanic boundary layer between 15 and 25 m depth. Stratified and convective turbulent regimes were encountered along the tow path. A direct estimate of the turbulent heat flux F was computed from the correlation of w′ and T′. The concurrent measurement of the dissipation rate of turbulent kinetic energy ε allowed us to estimate the mixing efficiency Γ0 = F/Fε, where Fε was the heat flux estimate based on the average dissipation rate. In regions where the turbulence in the stratified boundary layer was sustained by shear instabilities 0.08 ≤ Γ0 ≤ 1.38. The average was
, a value close to the maximum mixing efficiency predicted by classical scaling arguments and laboratory results. The measurements of w′ were significantly influenced by instrument motions and the orbital velocities induced by surface waves. A motion correction algorithm made it possible to resolve overturning length scales up to 33 m and thus to capture all scales that contributed to the heat flux F. For the surface mixing layer reported here the largest flux‐supporting scales were ∼14 m. For the stably stratified regimes in particular the peak of the heat flux cospectrum was at one half of the Ozmidov wave number, 0.5ko.
GSFC00 mean sea surface, gravity anomaly, and vertical gravity gradient from satellite altimeter data
Authors: Wang Yan Ming
Published: February 2004

A mean sea surface, GSFC00, and its derivatives, the altimetry gravity anomaly and vertical gravity gradient fields, were computed using sea surface heights of TOPEX, ERS, and Geosat satellite altimeter missions provided by the NASA Ocean Altimeter Pathfinder Project [Koblinsky et al., 1998]. A new estimation method, distinct from the GSFC98 mean sea surface computation [Wang, 2000a], was explored and used to reduce ocean variability in the mean sea surface heights. The gravity anomaly and vertical gravity gradient fields were then computed from the mean sea surface height implied geoid undulations. Validation of the GSFC00 mean sea surface and gravity anomaly was also performed.
Long‐term El Niño‐Southern Oscillation (ENSO)‐like variation with special emphasis on the South Pacific
Authors: Luo Jing‐Jia , Yamagata Toshio
Published: February 2004

Mechanisms for El Niño‐Southern Oscillation (ENSO)‐like decadal (7–35 years) variability are analyzed using observational data. When a decadal positive temperature anomaly occurs in the eastern tropical Pacific, the atmospheric response excites negative wind stress curl in the western tropical South Pacific, which causes the thermocline to shoal and induce a negative temperature anomaly there. The cold anomaly moves northwestward to the western and central equatorial region and then turns eastward along the equator to reverse the original temperature anomaly in the east. The eastward propagation of the oceanic signal along the equatorial thermocline correlates with a zonal wind anomaly. The cold anomaly in the east grows through tropical air‐sea interaction and induces a positive wind stress curl in the western tropical South Pacific associated with the atmospheric teleconnection in the Southern Hemisphere. Subsequent evolution of the negative phase is similar to that of the positive phase. The complete scenario for this ENSO‐like decadal variability due to the air‐sea interaction processes within the tropics has a period of ∼14 years. We also discuss ENSO‐like variation on the interdecadal (>35 years) timescale, with possible relationship to the 1976–1977 climate regime shift.
Intense surface currents in the tropical Pacific during 1996–1998
Authors: Grodsky Semyon A. , Carton James A.
Published: February 2004

Tropical Pacific Ocean near‐surface currents and their momentum and temperature balances are investigated using several data sets, including drifting buoy velocities and TOPEX/Poseidon altimetry. The data sets are combined to produce monthly surface current estimates on a uniform grid for the 6‐year period 1993–1998, using multivariate optimal interpolation. The analysis shows dramatic changes in current from December 1996 through August 1998 in response to the recent El Niño‐Southern Oscillation event. Eastward current anomalies of ∼1 m s−1 were recorded in December 1996 in the western Pacific, generated by sporadic westerly wind bursts. By April 1997 these equatorial anomalies reached the eastern boundary, and in the summer of 1997 a band of strong eastward flow formed across the basin. This circulation pattern persisted until the beginning of 1998, when a westward equatorial jet appeared in January‐April. Interestingly, the reversal of flow occurred prior to the restoration of the trade winds. The timing of these events as well as the results of previous dynamical studies raise questions about the relative importance of terms in the zonal momentum and temperature balances. We address the first of these questions by examining the applicability of a three‐term linear zonal momentum balance on the equator. In all cases we focus on anomalies from the time mean. Our results show that local acceleration is reasonably well balanced by the difference between zonal pressure gradient anomaly and wind‐induced momentum flux. This three‐term balance displays significant basin‐wide variations and is consistent with the conclusion that the equatorial Pacific is not in equilibrium with local wind forcing due to the presence of propagating waves. Examination of the temperature balance shows that at the beginning of El Niño the warming in the central Pacific is mainly supported by horizontal temperature transport, while the vertical heat exchange and transport become important in the eastern half of the equatorial Pacific during the transition from El Niño to La Niña.
Coastal profile evolution at Duck, North Carolina: A cautionary note
Authors: Elgar Steve
Published: February 2004

The Hurst exponents of 10.8‐year‐long time series of cumulative bed level observed between the shoreline and ∼8‐m water depth on an ocean beach are shown to be consistent with bed‐level time series described by a sinusoid with a 10.8‐year period plus white noise. Thus, for these observations, Hurst exponents cannot distinguish self‐organized morphological evolution from the hypothesis that nearshore morphology on monthly to decadal timescales is a forced response to small‐scale physical processes driven by waves and currents.
A laboratory study of mean flow generation in rotating fluids by Reynolds stress gradients
Authors: McGuinness D. S. , Boyer D. L. , Fernando H. J. S.
Published: February 2004

Laboratory experiments were conducted that demonstrate that a mean azimuthal flow can be produced by introducing Reynolds stress gradients to a rotating fluid with zero initial mean flow. This mechanism may play a role in the generation of mean currents in coastal regions. The experiments entail the establishment of turbulence in a thin annular‐shaped region centered within a cylindrical test cell through the use of a vertically oscillating grid. This region rests in a horizontal plane perpendicular to the vertical axis of the tank, and the entire system is placed on a turntable to simulate background rotation. Flow visualization techniques are used to depict qualitative features of the resulting flow field. Measurements of the mean and turbulent velocity fields are performed using a two‐component laser‐Doppler velocimeter. The results show how rectified currents (mean flows) can be generated via Reynolds stress gradients induced by periodic forcing of the grid. In the absence of background rotation, rectified flow is observed in the radial and vertical directions only. The presence of background rotation tends to organize these motions in that the flow tends to move parallel to the turbulent source, i.e., in the azimuthal direction, with the source (strong turbulence) located to the right, facing downstream. The influence of rotation on the Reynolds stresses and their gradients as well as on the ensuing mean flow is evaluated, and the observations are examined by considering individual contributions of the terms in the Reynolds‐averaged momentum equations.
Remapping the thickness distribution in sea ice models
Authors: Lipscomb William H.
Published: February 2004

In sea ice models with multiple thickness categories the ice thickness distribution evolves in time. The evolution of the thickness distribution as ice grows and melts is analogous to one‐dimensional fluid transport and can be treated by similar numerical methods. One such method, remapping, is applied here. Thickness categories are represented as Lagrangian grid cells whose boundaries are projected forward in time. The thickness distribution is approximated as a linear or quadratic polynomial in each displaced category, and ice area and volume are transferred between categories so as to restore the original boundaries. In simple test problems and in a single‐column model with forcing typical of the central Arctic, remapping performs significantly better than methods previously used in sea ice models. It is less diffusive than a scheme that fixes the ice thickness in each category and behaves better numerically than a scheme that represents the thickness distribution as a set of delta functions. Also, remapping converges faster (i.e., with fewer thickness categories) than the alternative schemes. With five to seven categories the errors due to finite resolution of the thickness distribution are much smaller than the errors due to other sources. Linear remapping performs as well as the more complex quadratic version and is recommended for climate modeling. Its computational cost is minimal compared to other sea ice model components.
Shelf‐slope exchanges associated with a steep submarine canyon off Calvi (Corsica, NW Mediterranean Sea): A modeling approach
Authors: Skliris N. , Goffart A. , Hecq J. H. , Djenidi S.
Published: February 2004

A three‐dimensional, unsteady, nonlinear, high‐resolution model is used to investigate the impact of the Calvi Canyon (NW Corsica) steep topography on the shelf‐slope exchanges as well as on the circulation in the Calvi Bay in homogeneous winter and early spring conditions. A double σ coordinate system is considered in order to represent adequately the high depth gradients within the canyon. The studied region is under the influence of the West Corsica Current flowing northeastward along the NW Corsican coast (right‐bounded flow). Model results show that the circulation in the Calvi Bay is determined by flow modifications in the canyon area. The mean horizontal flow is deviated southwestward upstream of the canyon to form an anticyclonic gyre in the western part of the Calvi Bay. Within the canyon the circulation is cyclonic leading to an offshore flow downstream of the canyon. Around the canyon rim, the cross‐shelf currents become important, indicating that this region acts as a transition zone of high exchange between nearshore and offshore areas. Furthermore, the canyon topography generates high downwelling (upwelling) and downsloping (upsloping) velocities responsible for an intense vertical transport of material in the area. Numerical runs are performed for typical prevailing wind conditions. The wind is responsible for a drastic increase of cross‐shore transports between the bay and the canyon area (3–4 times larger than in the no‐wind case). SW winds induce a further enhancement of cross‐shelf exchanges, whereas the effect of N‐NE winds is to reduce exchange at the shelf break apart from the canyon head where an intense offshore flow occurs. Within the canyon, high vertical velocities are shown to be associated with high cyclonic vorticity which is enhanced (reduced) by the N‐NE (SW) wind event. A comparison between model results and measured distributions of nitrate and chlorophyll a concentrations in the area shows the role played by this specific hydrodynamics as a strong constraint on the coastal pelagic ecosystem.
Decadal upper ocean temperature variability in the tropical Pacific
Authors: Hazeleger Wilco , Visbeck Martin , Cane Mark , Karspeck Alicia , Naik Naomi
Published: February 2004

Decadal variability in upper ocean temperature in the Pacific is studied by using observations and results from model experiments. Especially propagation of upper ocean thermal anomalies from the midlatitudes to the tropics is studied as a possible source for decadal equatorial thermocline variability. In the observations, propagation along the subtropical gyre of the North Pacific is clear. However, no propagation into the equatorial region is found. Model experiments with an ocean model forced with observed monthly wind and wind stress anomalies are performed to study the apparent propagation. Distinct propagation of thermal anomalies in the subtropics is found in the model, although the amplitude of the anomalies is small. The anomalies clearly propagate into the tropics, but they do not reach the equatorial region. The small response at the equator to extratropical variability consists of a change in the mean depth of the thermocline. It appears that most variability in the subtropics and tropics is generated by local wind stress anomalies. The results are discussed by using results from a linear shallow water model in which similar features are found.
Use of conventional stability parameters during swell
Authors: Rutgersson Anna , Smedman Ann‐Sofi , Högström Ulf
Published: February 2004

The situation with swell is of climatological importance over the Baltic Sea since swell is present during as much as 40% of the time. In this study, two periods with unstable and two periods with stable stratification and wind following swell are investigated. Data are taken at a small flat island in the Baltic Sea. During unstable stratification the turbulent structure shows great resemblance to the free convective boundary layer and scales with the boundary layer height. Since surface heat flux is too small to support the high levels of turbulence present, inactive turbulence is probably the dominating source. For the stably stratified layer, there are smaller differences between data with and without swell. The turbulence is mainly transported upward into the atmosphere with the aid of pressure fluctuations induced by the waves. For most of the data with swell the gradients are smaller than for growing sea. During unstable conditions the wind gradients are negative, indicating the presence of a wave‐driven wind. The gradients increase with increasing height above the surface. The drag coefficient is smaller than is usually found for both stable and unstable stratification and varies very little with wind and stratification. There are only small variations in the heat transfer coefficients with changing stratification, but they are significantly different for stable and unstable stratification.
Velocity structure and transport of the Indonesian Throughflow in the major straits restricting flow into the Indian Ocean
Authors: Hautala Susan L. , Sprintall Janet , Potemra James T. , Chong Jackson C. , Pandoe Wahyu , Bray Nan , Ilahude A. Gani
Published: February 2004

An array of shallow pressure gauge pairs is used to determine shallow geostrophic flow relative to an unknown mean velocity in the five principal straits that separate the eastern Indian Ocean from the interior Indonesian seas (Lombok Strait, Sumba Strait, Ombai Strait, Savu/Dao Straits, and Timor Passage). Repeat transects across the straits over several tidal cycles with a 150‐kHz acoustic Doppler current profiler were made during three separate years, and provide a first look at the lateral and vertical structure of the upper throughflow in these straits as well as a means of “leveling” the pressure gauge data to determine the mean shallow velocity and provide transport estimates. We estimate a total 2‐year average transport for 1996–1997 through Lombok, Ombai, and Timor Straits as 8.4±3.4 Sv toward the Indian Ocean. The flow structure in the upper 200 m is seen to be similar in Lombok, Sumba, and Ombai Straits, with a division into two layers, governed by different dynamics, where the upper layer episodically flows away from the Indian Ocean. Laterally, flow tends to be strongest in the deepest parts of the channel, with the exception of Lombok Strait which shows a consistent intensification of flow toward the western side. Eastward flowing northern boundary currents in Sumba and Ombai Straits suggest that the South Java Current may penetrate to the Banda Sea, farther eastward than previously documented. Although additional observations are required for a conclusive comparison, the estimated transport time series suggest differences in timing of outflow into the Indian Ocean relative to inflow from the Pacific of a size that could significantly impact the Banda Sea thermocline structure.
Experiments on focusing unidirectional water waves
Authors: Brown Michael G. , Jensen Atle
Published: February 2004

Results of four groups of experiments involving transient, mechanically generated water waves in a narrow wave tank are described. The purpose of these experiments was to investigate the limitations of the validity of linear theory predictions of the spatiotemporal structure of the surface elevation in focal regions. For unidirectional surface gravity waves, focusing occurs as a result of long waves overtaking short waves. Surprisingly, in our measurements, nonlinear effects are stronger in deep water than in intermediate depth water and are stronger in nonfocusing wave trains than in focusing wave trains. These trends can be explained by the observation that the dominant source of nonlinear interaction in our measurements was the Benjamin‐Feir instability, which acts only over a limited duration in focusing wave trains, only in wave trains whose bandwidth is narrow, and only in deep water. Under conditions in which the Benjamin‐Feir instability does not act (as is expected to be the case in the ocean), predictions that take into account amplitude‐dependent dispersion but otherwise neglect nonlinear effects are in good agreement with measurements for wave trains with (ka)max slightly in excess of 0.30.
Global patterns of decadal‐scale variability observed in sea surface temperature and lower‐tropospheric circulation fields
Authors: Tomita Tomohiko , Wang Bin , Yasunari Tetsuzo , Nakamura Hisashi
Published: February 2004

The global patterns associated with decadal‐scale variability (DSV) are examined by a lag correlation technique based on local anomaly indices, using the fields of measured sea surface temperature (SST) and 850 hPa geopotential height for the last 50 years. The three dominant patterns are identified, and the variability is examined; the first spreads over the entire Pacific, which is concurrent with the decadal‐scale modulation of the El Niño/Southern Oscillation (DES variability), the second is confined to the local midlatitude North Pacific (LNP variability), and the third extends over the North Atlantic with the decadal North Atlantic Oscillation (NAO) (DNA variability). The global SST pattern of DES variability exhibits large‐scale equatorial symmetry in the Pacific, which is similar to that of the Pacific Decadal Oscillation but is distinguished by the signals in the subtropical frontal zones. These SST anomalies are accompanied by anomalous subtropical highs that appear prior to the anomalous depression around Australia. The LNP variability, which is related with the Arctic Oscillation, is characterized by the SST anomalies along the North Pacific subarctic frontal zone moving eastward accompanied by the anomalous Aleutian Low. This variability develops (decays) without (with) coherent variability in the tropics. It shows the 6‐year quadrature phase relationship with the DES variability, indicative of an interdecadal variability with a period of 24 years. The DNA variability is featured by the atmospheric NAO and by the SST anomalies in four zonal bands that spread in the North Atlantic from the tropics to high latitudes. This variability is independent of either the DES or LNP variability.
Horizontal wave number spectra of temperature in the unstably stratified oceanic surface layer
Authors: Wijesekera H. W. , Paulson C. A. , Huyer A.
Published: February 2004

Horizontal wave number spectra of temperature in the unstably stratified oceanic surface layer were determined from measurements on a bow boom at a depth of 2 m. Spectra were estimated in the wavelength band from 2 m to 2 km, normalized in accordance with Monin‐Obukhov similarity theory, and averaged in groups with similar stability parameter and fractional mixed layer depth. The shapes of the wave number‐weighted oceanic spectra agree qualitatively with observed and modeled atmospheric spectra, including the wavelength of the peaks and the variation of peak wave number with stability. However, the peak spectral levels disagree by as much as a factor of two and the variation of spectral level with stability is in the opposite sense for the oceanic and atmospheric spectra. The wave number of the peak in the near neutral oceanic spectrum is similar to the wave number of the peak in the longitudinal velocity spectrum observed in the atmospheric surface layer, which is consistent with temperature acting as a passive tracer in near neutral conditions. The wave number of the peak in the free convection oceanic spectrum is similar to the wave number of the peak in the spectrum of vertical velocity observed in the atmospheric surface layer during free convection, which reflects the dynamical role played by temperature in a freely convecting boundary layer. The difference between oceanic and modeled near‐neutral spectral levels at a wavelength of 2 m suggests that dissipation could be enhanced (up to a factor of three) by surface wave breaking.
Long‐term sea ice dynamics simulations using an elastic‐plastic constitutive law
Authors: Pritchard Robert S.
Published: February 2004

A quasi‐steady elastic‐plastic sea ice dynamics model is introduced for long‐term simulations. Tidal and inertial oscillations are removed by discarding the negligible inertia term. With this assumption the model is integrated using an implicit numerical scheme. Results are shown for a one‐dimensional case. This approach eliminates the elastic waves that typically contaminate elastic‐plastic simulations and allows the elastic‐plastic constitutive law to be integrated over longer time periods, with the potential for being used effectively for climate dynamics studies.
A numerical investigation of the 1997–1998 Ronne Polynya
Authors: Hunke Elizabeth C. , Ackley Stephen F.
Published: February 2004

The summer season of 1997–1998 marked an unprecedented extent of open water in the southern Weddell Sea, not observed since satellite observations began in the early 1970s. Wind patterns during the summer period tended to be more southerly than in years with typical summer ice coverage, leading to the hypothesis that the polynya opened due to ice advection away from the Ronne Ice Shelf and subsequent enhanced melting through the open water‐albedo feedback mechanism. A numerical model is run using a bulk forcing data set from the 1980s for model spin‐up and the control run. Initiation of the polynya by the anomalous wind pattern is investigated numerically by substituting winds from the 1997–1998 period for the control winds. While a narrow polynya is present in the control run, it opens considerably with the 1997–1998 winds, to the extent observed in the satellite images. If solar radiation flux is not allowed to heat the mixed layer, the sea ice in front of the Ronne Ice Shelf shows some opening, but the polynya does not form to the extent observed, demonstrating the important role played by open water‐albedo feedback. The mixed layer heat budget analysis shows the predominant balance in these three runs was derived from surface forcing and that the upwelling of heat from the deep ocean was not a significant driving force for the 1997–1998 Ronne Polynya. Further analysis of the fresh water budget indicates that the mixed layer salinity increased in areas of open water during the 1997–1998 season by as much as 0.5 psu.
A steady state model of particulate organic carbon flux below the mixed layer and application to the Joint Global Ocean Flux Study
Authors: Boehm Alexandria B. , Grant Stanley B.
Published: February 2004

The downward flux of particulate organic carbon (POC) through the ocean is controlled by a complex coupling of physical and biological processes. Here we analyze the equation that describes steady state coagulation, fragmentation, sedimentation, and grazing of POC below the mixed layer. The analysis yields a set of conditions under which vertical flux of POC is uncoupled from coagulation and fragmentation. When these conditions are satisfied, the model predicts that the flux of POC decays exponentially with depth down to 200–500 m, below which the flux is constant. From the magnitude of the terminal flux an estimate for the in situ clearance rate (volume swept clear of prey per grazer per unit time) for the grazer community can be obtained. This in situ clearance rate is estimated for five oceanic field sites using data collected during the Joint Global Ocean Flux Study, and the resulting values compare favorably to previously published laboratory estimates. These results suggest that, in some cases, bacterial mineralization may not be needed to explain the decline in POC flux in the mesopelagic zone of the ocean.
Computing optimum estuarine residual fluxes with a multiparameter inverse method (OERFIM): Application to the Ria de Vigo (NW Spain)
Authors: Gilcoto M. , Álvarez‐Salgado X. A. , Pérez F. F.
Published: February 2004

OERFIM is a two‐dimensional (2‐D) multiparameter inverse method for calculating estuarine residual fluxes and net ecosystem production rates in estuaries and coastal inlets. OERFIM retains the optimum solution for a weighted system of property conservation equations following the mean squares criterion. The properties involved are volume, salinity, temperature, nutrients (NH4+, NO2−, NO3−2, and PO4−3), dissolved oxygen, and inorganic carbon. Derived variables such as NO, CO, PO, NCO, and PCO are also considered. OERFIM lies between optimum multiparameter analysis and inverse general ocean circulation models. The simplicity of the method allows for derivation of analytical solutions and a clear exposition of the estuarine box models evolution: from the pioneer, just determined Knudsen method to the overdetermined models such as OERFIM. The theoretical analysis also provides a coherent presentation of analytical errors and their relation to the weights entering the equations. We validate the method with field data from the coastal upwelling system of the “Ría de Vigo”, demonstrating that OERFIM results are suitable to understand the solution structure and, therefore, the whole system itself.
Energy transport in the marginal ice zone
Authors: Dixon Tony W. , Squire Vernon A.
Published: February 2004

A novel approach to modeling ocean wave scattering in the marginal ice zone that uses the coherent potential approximation to compute the energy transport velocity is reported. The necessary theory is developed by considering sea ice floes to be thin elastic beams governed by the Euler‐Bernoulli equation, with the open water surrounding each floe subject to the same equation with its material coefficients set to be very small quantities. This mathematical stratagem facilitates the solution of the problem and yields interesting results about the speed at which wave energy propagates through a marginal ice zone, the dispersion relation for a random mixture of ice floes and water, and the mean free path or attenuation coefficient. Results from the model are compared with data reported by Wadhams et al. [1988].
A regional model of the semidiurnal internal tide on the Australian North West Shelf
Authors: Holloway Peter E.
Published: February 2004

A fully three‐dimensional nonlinear primitive equation model is applied to a study of the semidiurnal internal tide on the Australian North West Shelf, a region of strong barotropic and baroclinic tide. The model shows a significant internal tide over most of the continental slope region, predominantly between 100‐ and 1000‐m depths. Energy flux is highly variable with regions of onshore flux and regions of offshore flux, corresponding to regions of subcritical and supercritical seabed slopes. A comparison between the model and detailed observations from one region shows reasonable agreement in vertical displacement, currents, and depth‐integrated energy flux. The comparison also highlights the difficulty in obtaining appropriate observations to provide a rigorous verification of internal tide models. The M2 and S2 internal tides show similar patterns of flow with energy in the S2 internal tide about 25% of that in the M2 constituent. Estimates of the total baroclinic M2 energy are about 2.2 GW for the North West Shelf, nearly an order of magnitude larger than suggested by earlier studies. This represents about 5% of the dissipation of the M2 barotropic tide in the model domain. The seasonal variability in the baroclinic energy flux is about 20% from the mean. The baroclinic energy extracted from the tide is expected to make a significant contribution to mixing in the region.
Estimates of M2 tidal energy dissipation from TOPEX/Poseidon altimeter data
Authors: Egbert Gary D. , Ray Richard D.
Published: February 2004

Most of the tidal energy dissipation in the ocean occurs in shallow seas, as has long been recognized. However, recent work has suggested that a significant fraction of the dissipation, perhaps 1 TW or more, occurs in the deep ocean. This paper builds further evidence for that conclusion. More than 6 years of data from the TOPEX/Poseidon satellite altimeter are used to map the tidal dissipation rate throughout the world ocean. The dissipation rate is estimated as a balance between the rate of working by tidal forces and the energy flux divergence, computed using currents derived by least squares fitting of the altimeter data and the shallow water equations. Such calculations require dynamical assumptions, in particular about the nature of dissipation. To assess sensitivity of dissipation estimates to input assumptions, a large suite of tidal inversions based on a wide range of drag parameterizations and employing both real and synthetic altimeter data are compared. These experiments and Monte Carlo error fields from a generalized inverse model are used to establish error uncertainties for the dissipation estimates. Owing to the tight constraints on tidal elevation fields provided by the altimeter, area integrals of the energy balance are remarkably insensitive to required dynamical assumptions. Tidal energy dissipation is estimated for all major shallow seas (excluding individual polar seas) and compared with previous model and data‐based estimates. Dissipation in the open ocean is significantly enhanced around major bathymetric features, in a manner consistent with simple theories for the generation of baroclinic tides.
On the rate of descent of overflows
Authors: Killworth Peter D.
Published: February 2004

The path taken by dense turbulent outflows usually requires the numerical solution of along‐flow equations for mass, tracers, and momentum and cannot easily be predicted. Instead, we consider the consequences of two simple assumptions. First, there is a quadratic turbulent bottom drag. Second, the outflow is assumed to be approximately in local equilibrium so that a best fit formula from atmospheric and ocean surface layer observations plus large‐eddy simulations, used by Zilitinkevich and Mironov [1996], can be used to predict the local thickness. (No energy budget for turbulent bottom layers is known, which is a constant difficulty for numerical models of such layers.) The equilibrium solution is approximately equivalent, for most oceanic conditions, to a constant bulk Richardson or Froude number. It is shown that dense turbulent overflows follow a simple trajectory, in which the rate of depth increase is a constant, until the level of turbulence drops sufficiently that the equilibrium solution becomes invalid. This result is independent of the detailed thermodynamics, entrainment or detrainment, and the quadratic drag coefficient (but does depend on the assumption of quadratic drag). Trajectories for the major overflow regions give reasonable results when compared with the limited available data. An argument is given as to why entrainment should only occur over limited regions, with detrainment elsewhere.
North Atlantic surface circulation during the 1990's observed with satellite‐tracked drifters
Authors: Fratantoni David M.
Published: February 2004

A new compilation of Lagrangian velocity observations describes the state of the North Atlantic surface circulation during the 1990s. Gridded fields of velocity and eddy kinetic energy (EKE) are constructed from trajectories of more than 1500 15‐m drogued satellite‐tracked surface drifters in service between January 1990 and December 1999. This time period overlaps a coordinated field study of circulation and variability in the North Atlantic completed between 1996–2000 as part of the World Ocean Circulation Experiment. We describe the construction of a self‐consistent drifter climatology, present decadal‐mean quasi‐Eulerian velocity and EKE fields computed on a 1° grid, and compare these results with contemporary satellite measurements. Detailed discussion of the inferred surface circulation is focused on three regions: (1) The Gulf Stream and North Atlantic Current, (2) the Labrador Sea and subpolar gyre, and (3) the Caribbean Sea. The swiftest drifter motions were found in the equatorial region and along the tropical, subtropical, and subpolar western boundaries. The maximum instantaneous speed determined from a single (quality‐controlled and filtered) drifter observation was 273 cm s−1 in the Gulf Stream southeast of Cape Cod. The highest EKE value in the North Atlantic (2790 cm2 s−2) was found in the Gulf Stream just downstream of the New England Seamounts. Over most of the Atlantic basin, drifter‐derived EKE values were found to be O(100 cm2 s−2) higher than corresponding values derived from satellite altimetry. In the Labrador Sea a region of sharply elevated EKE appears to be geographically related to the localized ejection of drifters (and by extension, mass and kinetic energy) from the energetic West Greenland Current between 60° and 62°N. When compared to drifter measurements made in the late 1970s our results suggest (but do not statistically confirm) an enhancement and slight northward shift of the zonal Gulf Stream extension. Such a shift is consistent in sign with expectations based on observed interdecadal variations in wind stress and subtropical gyre potential energy associated with the North Atlantic Oscillation.
On the mass and salt budgets for a region of the continental shelf in the southern Mid‐Atlantic Bight
Authors: Kim Yoo Yin , Weatherly Georges L. , Pietrafesa Leonard J.
Published: February 2004

Two field studies were conducted across and along the continental shelf, one from February to May 1996 (deployment 1) and the other from July to October 1996 (deployment 2) in part to determine the mass and salt budgets of shelf water from south of Cape Henry to north of Cape Hatteras, the southernmost portion of the Mid‐Atlantic Bight. The temporal means of current meter records indicated that most of the water enters the region across its northern boundary near the shelf break as part of a southward, alongshore current and exits the southeast corner as a southeastward flowing current. Estimates of the volume transports indicated that not all the transport across the northern boundary was accounted for by transport across the southern boundary and that the remainder occurred as a broad, diffusive flow across the eastern boundary at the shelf break. Time series of volume transport across northern and southern boundaries were very similar and associated with variations in the alongshore wind stress and sea level, indicative of a geostrophic balance. Examination of the individual current meter records indicated these fluctuations were very barotropic even during deployment 2, which included the stratified summer season. Time series of the volume transport across the eastern boundary at the shelf break strongly mirrored the volume transport across the northern boundary minus that across the southern boundary, suggesting that the inferred eastern boundary transport was real and accommodated whatever the southern boundary could not. The turbulent salt flux across each boundary contributes very little to the net salt flux. The mean and time‐dependent salt fluxes show nearly identical patterns as the respective mass fluxes because the salt fluxes are almost governed by current velocity fields. The instantaneous and mean salt fluxes across each boundary were very well approximated by the instantaneous and mean volume transports across the boundary times the deployment average salinity across that boundary, respectively. The Ocean Margins Program (OMP) moored current and salinity observations appear sufficient to make estimates of the mean and time‐dependent mass and salt balance.
Okhotsk Sea intermediate water formation deduced from oxygen isotope systematics
Authors: Yamamoto Michiyo , Tanaka Noriyuki , Tsunogai Shizuo
Published: February 2004

To clarify the mechanisms of the Okhotsk Sea intermediate water formation, water samples collected in the Okhotsk Sea and neighboring western North Pacific were analyzed for δ18O as well as salinity and other routinely measured components. The δ18O‐salinity relation in the Okhotsk Sea was markedly different from that in the western subarctic Pacific feeding the Okhotsk Sea. The intermediate water of the Okhotsk Sea was less saline than that of the western subarctic water at the same density but was more saline at the same δ18O value, especially in the density range 26.5<σθ<27.0. This could be due to mixing of dense shelf water formed during sea‐ice formation with neighboring water. The amount of fresh water removed by the sea‐ice formation was estimated from the salinity anomaly of the Okhotsk Sea intermediate water. The calculated amounts of fresh water removed from the Okhotsk Sea intermediate water corresponded to the amount of sea ice formed for 0.6–3.8 years in the Okhotsk Sea. This suggests that the residence time of the Okhotsk Sea intermediate water is a few years.
Numerical study of the spatial distribution of the M2 internal tide in the Pacific Ocean
Authors: Niwa Yoshihiro , Hibiya Toshiyuki
Published: February 2004

As a first step toward numerical modeling of global internal tides, we clarify the distribution of the M2 internal tide in the Pacific Ocean using a three‐dimensional primitive equation numerical model. The numerical simulation shows that energetic internal tides are generated over the bottom topographic features in the Indonesian Archipelago, the Solomon Archipelago, the Aleutian Archipelago, and the Tuamotu Archipelago, the continental shelf slope in the East China Sea, and the mid‐oceanic ridges such as the Izu‐Ogasawara Ridge, the Hawaiian Ridge, the Norfolk Ridge, the Kermadec Ridge, and the Macquarie Ridge. The calculated spatial patterns of the M2 internal tide around the Hawaiian Ridge and the Izu‐Ogasawara Ridge agree well with the TOPEX/Poseidon altimetric observation. The conversion rate from the M2 surface to internal tide energy integrated over the whole model domain amounts to 338 GW (1 GW = 109 W), 84% of which are found to be generated over the prominent topographic features mentioned above. Reflecting the spatial distribution of the prominent topographic features in the Pacific Ocean, the energy level of the M2 internal tide in the western and central Pacific is 2–3 orders of magnitude higher than that in the eastern Pacific. This remarkable asymmetry shows that extensive microstructure measurements in the western and central Pacific are indispensable to determining the representative value of diapycnal mixing rates in the global ocean.
Hydrography of the Pontevedra Ria: Intra‐annual spatial and temporal variability in a Galician coastal system (NW Spain)
Authors: Prego Ricardo , Dale Andrew W. , deCastro Maite , Gómez‐Gesteira Moncho , Taboada Juan J. , Montero Pedro , Villareal Manuel R. , Pérez‐Villar Vicente
Published: February 2004

In order to ameliorate the dearth of existing scientific knowledge concerning the hydrography of the Pontevedra Ria, a systematic investigation was carried out between October 1997–98. Salinity variations were closely related to river discharge whereas bottom waters presented oceanic characteristics over the whole year. Current was controlled by tide, river discharge, and wind in the internal ria where the highest velocities were directed along the ria channel with a low transverse component. Favorable atmospheric conditions in spring induced coastal upwelling up the continental shelf. In May the upwelling was sufficiently strong to be detected in the inner ria and intensified in July and August, cooling the ria water to 12°–14°C. Upwelling ceased in September, and from November to March seawater transported by the poleward current (35.9; 15°C) was detected on the shelf. From January until March, unanticipated favorable upwelling conditions provoked an influx of poleward inside the ria. Ria intrusion of poleward water and association with occasional winter upwelling conditions has not been observed previously. Isopycnic three‐dimensional (3‐D) surface and 2‐D isopycnal maps show that with high river runoff or intense upwelling, lower‐salinity water leaves the ria near the northern margin in the surface layer. Under negative upwelling conditions, the water is partially dammed inside the ria and exits the ria when the wind speed falls. During upwelling events, ENACW penetrated the ria, especially near the southern shore. Arrival of ENACW at the northern entrance impedes the outward water flow through this mouth.
Sea surface velocities from sea surface temperature image sequences: 2. Application to the Brazil‐Malvinas Confluence area
Authors: Vigan Xavier , Provost Christine , Podesta Guillermo
Published: February 2004

An inverse variational model is applied to four exceptionally cloud‐free sea surface temperature image sequences of the Brazil‐Malvinas Confluence area for the purpose of estimating sea surface velocity fields. The velocity fields are constructed by minimizing a mixed layer integrated form of the heat balance equation while the horizontal divergence and vorticity of the flow field are controlled. The source terms involved in the heat balance are determined by fitting a polynomial to diurnal temperature variations as a function of temperature and longitude. A sensitivity study of the solution to perturbations of the weights imposed to the constraints on divergence and vorticity as well as of the representation of the source terms yields error fields associated with the velocity. A comparison of the estimated velocity fields with available concomitant in situ velocity measurements shows that the fields are realistic. Errors are of the order of 15–20% in magnitude and 20°–25° in direction. These errors fall within the error bars of 25–30% in magnitude and of 30°–35° in direction, except for the summer image series. Surface velocities of 0.5–0.6 m s−1 are obtained across the Malvinas Current. They are > 1 m s−1 in the frontal region, in the Brazil Current overshoot, and in warm and cold core rings and vary between 0.3 and 0.8 m s−1 in the Brazil Current. With some hypotheses on the vertical shear of the horizontal flow the transport of the Malvinas Current is estimated to be 25±5 Sv between 41° and 40°S.