bluuebunny/crossref_metadata_2025 huggingface dataset:
Indirect wind observations in the southwestern Atlantic
Authors: Garzoli Silvia L. , Clements Miguel E.
Published: February 2008

Two time series of wind speed have been inferred from ambient noise measurements obtained with bottom‐deployed inverted echo sounders in the southwestern Atlantic. Comparison between inferred winds and winds from the National Meteorological Center Tropical Strip Surface Analysis product establishes that there is a good agreement between the two observations. The wind records from the two instruments, deployed 181 km apart, show significant differences at low frequencies. The mean speed for the recorded period is 10 m/s. The energy density spectra of the inferred wind records show a decrease in energy with frequency with a slope of −1.7 for frequencies between 0.22 and 20 cpd. The analysis of the spectra from the time series at the two moored locations shows differences in the band 2–10 days. An increase in the variance is detected in the offshore location at discrete periods corresponding to atmospheric oscillations. These oscillations are considerably less energetic in the continental shelf‐slope regime but are coherent in both locations.
The seasonal variations of surface currents in the tropical Atlantic Ocean: A comparison of ship drift data with results from a general circulation model
Authors: Richardson P. L. , Philander S. G. H.
Published: February 2008

Historical ship drifts from the tropical Atlantic Ocean are compared with surface currents from a general circulation model forced with monthly mean climatological winds. The model accurately reproduces the spatial structure of the currents and its time dependence, which varies considerably from the eastern side of the basin, where a semiannual harmonic is prominent, to the western side, where an annual harmonic is dominant. However, the amplitude of the simulated surface currents in the western side of the basin is too large. Mixing processes in the model appear to be too weak, especially when the winds are weak in regions where the thermocline is deep. High‐frequency fluctuations of the winds need to be taken into account, and parameterization of the mixing needs to be improved, especially when the Richardson number is small.
Possible role of gravity currents in northern California's coastal summer wind reversals
Authors: Dorman Clive E.
Published: February 2008

North winds along the northern California coast in the summer of 1982 were interrupted by six events with southerly winds. Four of these events occurred under similar circumstances. One of these four events is presented in detail. At the start of this event the marine layer is thickened in the southern California bight. A couple of days later the marine layer thickens from Point Conception to Monterey. Then the marine layer thickness increase surges to the north along the coast to Point Arena, where progression stopped and an eddy formed. In this surging stage, winds switched to southerlies as the leading edge of the event passed. A day later, the leading edge surged further to the north. Inshore winds were southerly, and the lifted marine layer extended to Cape Blanco in Oregon. This event is interpreted as a gravity current surging up the coast. The basic reservoir is the thickened marine layer in the southern California bight. Northerly progression is interrupted by a blocking wave near Point Arena where an eddy forms. It is hypothesized that most of the major wind reversals along the northern California coast during the summer are gravity currents or Kelvin waves in the marine layer that are formed to the south.
Observations of subtidal currents over the northern California continental slope and adjacent basin: Some evidence for local wind forcing
Authors: Noble Marlene , Beardsley Robert C. , Gardner James V. , Smith Robert L.
Published: February 2008

Currents at several depths were monitored on the upper slope, on the midslope and over an adjacent deep‐sea basin off northern California for nearly simultaneous periods from 4 to 14 months. In 1980 and 1981, subtidal current fluctuations with periods shorter than 32 days were oriented parallel to the topography over the slope but had no consistent orientation over the basin. Mean currents flowed northwestward over the slope and southward in the basin. The subtidal current fluctuations in the three regions were generally incoherent with each other and were weakly coherent with wind stress and coastal sea level. Observations of wind‐driven flow over the slope are consistent with a nonresonant model for wind‐forced shelf and slope currents, but the observations are too limited to define specific model parameters. Over the basin, the wind‐forced currents have characteristics similar to those predicted by stochastic models for wind‐forced flow in the open ocean.
Application of wind‐forced, long, coastal‐trapped wave theory along the California coast
Authors: Chapman David C.
Published: February 2008

The theory of wind‐forced, frictional, long, coastal‐trapped waves is applied along the California coast (1) to examine the sensitivity of the model to the numerous arbitrary and subjective choices which must be made during the application procedure and (2) to hindcast observable quantities in the region of the Coastal Ocean Dynamics Experiment (CODE) in an attempt to understand the dynamics of the region. Results of the model sensitivity study show that the model predictions are highly sensitive to the choice of wind stress used to force the model. Along the California coast, measured coastal and buoy winds are far superior to the calculated (Bakun) winds. The model predictions are relatively insensitive to uncertainties in the other model inputs. Hindcast results show that bottom pressure and alongshelf currents over the shelf are primarily wind forced throughout the year with most of the forcing located between Pigeon Point (∼200 km south of CODE) and the CODE site. While the time variability is hindcast quite well, the model systematically underpredicts the bottom pressure and alongshelf currents by a factor of 1.2–2.5 and fails to predict the observed midshelf vertical structure of the alongshelf currents. Cross‐shelf velocities and temperatures are poorly hindcast throughout.
The three‐parameter model of the submarine light field: Radiant energy absorption and trapping in nepheloid layers recalculated
Authors: Stavn Robert Hans
Published: February 2008

The use of the three‐parameter model of the submarine light field for determining the absorption and trapping of radiant energy in nepheloid layers is revised and clarified. Predictions of the relative amount of energy trapping in a nepheloid layer are compared with the detailed energy budget of that layer. The predictions are confirmed by the radiant energy budget. This model cannot be used to estimate the scattered component of radiant energy flux in the submarine light field. However, with the proper light field measurements, the three‐parameter model can be extended to a four‐parameter version consisting of the scalar irradiance (E0), downwelling vector irradiance (Ez), average cosine of the downwelling radiant flux , and the average cosine of the upwelling radiant flux
. This extended model is mathematically equivalent to the Preisendorfer irradiance quartet model and can be applied in similar ways to study the scattered radiant flux.
Least squares multiple tracer analysis of water mass composition
Authors: Mackas David L. , Denman Kenneth L. , Bennett Andrew F.
Published: February 2008

We present an inverse method that uses measurements of the concentration of several tracer variables to find the mixture of source water types that best describes (in a weighted least squares sense) the composition of the water sample. The solution includes two physically realistic constraints: first, that all sources together must sum to 100% and, second, that no source is present in negative amounts. These constraints improve the statistical stability of the solution. The method is particularly valuable in regions involving strong mixing among a relatively large number of source water types. In contrast to conventional TS analysis, more water types can be considered, the assumption of mixing along isopycnals is unnecessary, and sensitivity to errors in individual tracer measurements is reduced by averaging the influence of a larger number of tracers. We demonstrate the method using data from two oceanographic regions. Analysis of summer data from the continental margin off Vancouver Island (British Columbia, Canada) confirms and quantifies the importance of deep upwelling of California Undercurrent water onto the continental shelf. It also identifies localized outer shelf filaments of low‐salinity water originating from the Vancouver Island Coastal Current. Finally, we reanalyze the North African data of Tomczak and confirm his interpretation of diapycnal mixing at the frontal boundary between North Atlantic Central Water and South Atlantic Central Water masses.
The distribution of nutrients in the southeastern Beaufort Sea: Implications for water circulation and primary production
Authors: Macdonald R. W. , Wong C. S. , Erickson P. E.
Published: February 2008

Hydrographic data collected above the shelf and slope in the southeastern Beaufort Sea show marked contrast in surface properties of nutrients, temperature, salinity and oxygen between August 1974, a year when ice remained close to shore, and August 1975, a year with much open water. The near‐surface properties are dominated by river inputs, biological activity, and the ice regime. Below the winter mixed zone (40–50 m), properties are similar to those observed elsewhere in the Arctic Ocean. Bering sea water is detected at 50–60 m as a very weak signal in temperature, nutrients and oxygen. Upwelling in both years was observed at the eastern side of Mackenzie Canyon; this upwelling likely results from the interaction of coastal circulation with topography. Estimates of new productivity based on nutrient budgets are low (20 g C m−2 yr−1) compared to temperate coastal waters, but fall in the range expected for the Arctic. In 1974, the heavy ice year, turbid water and ice cover appear to have reduced new production by about 30%. Calculations show that this production over the shelf could potentially supply a significant portion of the nutrients found in the upper halocline over a wide region of the Arctic Ocean by regeneration at the shelf bottom and transport off the shelf in brine drainage.
Distribution of chemical tracers in the eastern equatorial Pacific during and after the 1982–1983 El Niño/Southern Oscillation event
Authors: Feely Richard A. , Gammon Richard H. , Taft Bruce A. , Pullen Patricia E. , Waterman Lee S. , Conway Thomas J. , Gendron James F. , Wisegarver David P.
Published: February 2008

During April 1983 and March‐April 1984, two cruises were conducted in the central equatorial Pacific to determine the effects of the El Niño/Southern Oscillation (ENSO) event on the sea‐air exchange of CO2. Measurements of total carbon dioxide, pCO2, total alkalinity, freon‐11, salinity, temperature, oxygen, nutrients, and wind and current velocities were made along three meridional transects (158°W, April 1983; 150°W, March 1984; 170°W, April 1984). The cessation of upwelling during the ENSO event caused pCO2 concentrations in surface waters to decrease to near‐saturation levels along the equator. The calculated net flux of CO2 across the sea‐air interface was essentially negligible in the eastern equatorial Pacific during this period. However, when normal trade winds and consequent upwelling returned in late 1983 and early 1984, the equatorial region returned to a pCO2 condition of highly supersaturated surface waters in the region between 8°N and 8°S along the 150° and 170°W transects. The calculated post‐ENSO sea‐air flux of CO2 exceeded 6.0 mmol CO2 m−2d−1 The mean annual CO2 flux in the equatorial Pacific was estimated to be 0.02 Gt of carbon during the 1982–1983 ENSO event as compared with 0.6 Gt during 1984.
Circulation and water masses of the East Greenland shelf
Authors: Bourke Robert H. , Newton John L. , Paquette Robert G. , Tunnicliffe Mark D.
Published: February 2008

The water masses and circulation over the northern Greenland continental shelf are described based on two cruises to the region during the summers of 1979 and 1984. The cold Polar Water over the shelf was found to increase notably in salinity toward the shelf break and the East Greenland Polar Front. A colder, more saline, and relatively isolated fraction of the Polar Water was identified just above the Atlantic Intermediate Water of the front. A middepth layer, stable in time, indicates little vertical heat exchange. Warm Atlantic Intermediate Water was found to intrude close to the coast via a newly defined system of troughs in the shelf. The Polar Water was found to circulate over the shelf in a clockwise gyre. Baroclinic transports, northward near the coast with 0.58‐Sv mean flow and southward elsewhere with 1.47‐Sv mean flow, yielded a net southward transport in the East Greenland Current of 0.89 Sv.
Use of synthetic aperture radar‐derived kinematics in mapping mesoscale ocean structure within the interior marginal ice zone
Authors: Manley T. O. , Shuchman R. A. , Burns B. A.
Published: February 2008

Synthetic aperture radar (SAR) imagery of the marginal ice zone over the western sector of the Yermak Plateau defined a region of anomalous ice motion that could not be accounted for by simple free‐drift movement of the sea ice based on daily averaged winds over the same time period from June 29 to July 6, 1984. Sea ice trajectories within this anomalous region are, however, consistent with oceanic forcing of the pack ice by a mesoscale eddy that had recently formed off the Polar Front. Although the use of such imagery has already been shown to be a diagnostic tool in mapping ocean features at the ice edge, the observed correlation 50 to 70 km behind the local ice edge indicates that SAR imagery has the potential to define energetic mesoscale and larger oceanic features well within the polar pack ice.
Aerosol size distributions in the marginal ice zone during the 1983 Marginal Ice Zone Experiment
Authors: Borrmann S. H. , Davidson K. L. , Miller M. E.
Published: February 2008

Measurements of the surface aerosol were performed by means of two laser optical particle counters during the East Greenland Sea Marginal Ice Zone Experiment. The number size distributions and total concentrations obtained for particles with radii between 0.09 μm and 12.5 μm were close to the global background level. Number size distributions decreased by a fraction of 100 with a frontal passage for particles with radii greater than 0.9 μm, while the size distribution for smaller particles remained fairly constant. The size distributions for wind speeds above and below the threshold for whitecap formation on the sea surface were compared. The number size distributions for particles above 1‐μm radius for wind speeds of 5 m s−1 were less by a factor of 100 than those for 7 m s−1.
Observations and geologic significance of marine snow in a shallow‐water, partially enclosed marine embayment
Authors: Wells J. T. , Shanks A. L.
Published: February 2008

Because of their fragile nature, marine snow‐sized aggregates (aggregates >0.5 mm in longest dimension) have been generally overlooked in shallow‐water environments. We report in situ observations and measurements in Cape Lookout Bight, North Carolina, that indicate that marine snow is probably always present and usually abundant. Underwater photographs show that over a period of hours, marine snow varies in size from 8 to 71 × 10−5 mL and in abundance from 291 to 489 L−1, but that such variations in size and abundance are not obviously related to tide, total suspended sediment concentration, or current speeds in the 10 to 20 cm s−1 range. Photographs and concurrent transmissometer records suggest that variations in size, shape, and abundance of marine snow may be sufficiently great that particulates do not remain optically constant and thus affect beam transmission, irrespective of total suspended‐sediment concentration levels. Marine snow is significant geologically in that it has high settling rates (50 to 200 m per day) and may be the package in which much of the vertical mass flux occurs. If so, it offers an explanation for the high accumulation rates observed in coastal and estuarine fluid mud deposits.
The Mediterranean Outflow as an example of a deep buoyancy‐driven flow
Authors: Tziperman Eli
Published: February 2008

Motivated by the Mediterranean outflow into the North Atlantic, a simple diffusive layer model of a deep buoyancy‐driven circulation driven by a middepth inflow from the eastern boundary is developed. Cross‐interfacial velocities are allowed and are related to the stratification through a density equation. The horizontal circulation, cross‐interfacial (vertical) velocities, and density stratification are all coupled and are determined by the model as part of the solution. The importance of water masses injected into the ocean interior in driving the deep circulation is demonstrated. The inflow from the eastern boundary turns northward before reaching the western boundary current region and flows along the eastern boundary. The westward distance traveled by the inflow before turning northward can be derived by considering the dissipation of long westward traveling Rossby waves by the vertical density diffusion. Layers above and below the inflow are also set in motion, and their circulation is southward along the eastern boundary, opposite to the direction of the circulation in the inflow layer. The vertically integrated circulation of the model is similar to that in a Stommel‐Arons model with the mass source on the eastern boundary: Most of the inflow flows to the western boundary current region, spreads there along the boundary, and reenters the interior as a broad northward current.
The influence of bays on adjusted sea level over adjacent shelves with application to the Labrador Shelf
Authors: Wright Daniel G. , Greenberg David A. , Majaess Fouad G.
Published: February 2008

We examine how low‐frequency variations in adjusted sea level over a continental shelf are influenced by an inland sea connected to the shelf through a strait. An analytical model shows that free continental shelf waves propagating by the mouth of the strait are strongly modified at a period corresponding to a Helmholtz‐like resonance of the inland sea and strait. Also, near this period atmospheric pressure variations over the inland sea result in relatively strong flow through the strait, and the resulting cross‐isobath flow over the exterior shelf efficiently generates continental shelf waves in the region forward of the strait. Calculations using a fully nonlinear numerical model with more realistic, although still idealized topography verify the predictions of the simpler analytical model. We apply this theory to the Hudson Bay‐Labrador Shelf system where we find that this mechanism of shelf wave generation strongly influences the shelf response in the energetic meteorological band ( ∼ 2–6 days). Data from Nain, Labrador are analyzed using multiple linear regression models and lend further support to the theory.
Near‐surface particle size distribution profiles over the North Sea
Authors: de Leeuw G.
Published: February 2008

Profiles of particle size distributions near the air‐sea interface were measured over the North Sea as part of the Humidity Exchange Over the Sea pilot experiment in 1984. Minima and maxima in the concentration profiles were observed, in agreement with results obtained previously in the North Atlantic. Differences are ascribed to the improved vertical resolution in the present measurements, while the shorter wave period in the North Sea has an influence, too. The results are qualitatively explained in terms of a wave‐rotor model.
A model of the tropical Pacific sea surface temperature climatology
Authors: Seager Richard , Zebiak Stephen E. , Cane Mark A.
Published: February 2008

A model for the climatological mean sea surface temperature (SST) of the tropical Pacific Ocean is developed. The upper ocean response is computed using a time dependent, linear, reduced gravity model, with the addition of a constant depth frictional surface layer. The full three‐dimensional temperature equation and a surface heat flux parameterization that requires specification of only wind speed and total cloud cover are used to evaluate the SST. Specification of atmospheric parameters, such as air temperature and humidity, over which the ocean has direct influence is avoided. The model simulates the major features of the observed tropical Pacific SST. The seasonal evolution of these features is generally captured by the model. Analysis of the results demonstrates the control the ocean has over the surface heat flux from ocean to atmosphere and the crucial role that dynamics play in determining the mean SST in the equatorial Pacific. The sensitivity of the model to perturbations in the surface heat flux, cloud cover specification, diffusivity, and mixed layer depth is discussed.
Observations of the internal structure of sea ice by X ray computed tomography
Authors: Kawamura Toshiyuki
Published: February 2008

X ray computed tomography CT was used to observe nondestructively the internal structure of sea ice grown in the laboratory. The CT images were compared with photographs taken by the conventional method. Both brine layers and brine drainage channels, which are characteristic sea ice features, were clearly recognizable on the CT images. The CT scanner is an extremely useful tool for examinations of sea ice structure and can possibly be applied to three‐dimensional measurements of ice core density.
A model study of wind‐ and buoyancy‐driven coastal circulation
Authors: Ikeda Motoyoshi
Published: February 2008

A two‐level model with a flat bottom on a β‐plane is employed to examine wind‐ and buoyancy‐driven coastal circulation on the western boundary of the ocean. The model of the ocean interior receives wind stress through the surface Ekman layer, which is purely determined from wind stress. Buoyancy flux is given to the upper level. Momentum equations are linear, and geostrophy in cross‐shore momentum is assumed. Density equations retain horizontal and vertical advection terms as well as horizontal diffusion. This cost‐effective three‐dimensional model is capable of a case study of a seasonal time‐scale simulation with various parameters varied. Oceanic responses to wind stress and buoyancy flux occur only along the coast to right of the forcing area facing offshore. A barotropic component merging to the western boundary is responsible for elimination of the undercurrent in the wind‐driven flow in most cases. The widths of the barotropic and baroclinic components are proportional to (horizontal viscosity)1/3 and (horizontal diffusion)1/2, respectively. Thus the undercurrent exists with a small diffusion coefficient. A wind‐driven current in a stratified system is insensitive to bottom friction, while a homogeneous system is sensitive to the friction. A buoyancy flux produces a baroclinic eddylike feature in the forcing area plus a baroclinic coastal flow. A significant barotropic component is produced by bottom friction in the buoyancy‐driven case, increasing (reducing) the upper (lower) level flow. Model sensitivity to assumed interactions between the Ekman layer and upper level and vertical finite‐difference scheme is examined. The flow field is insensitive to the assumptions and scheme, while vertical stratification is sensitive.
The attenuation rates of ocean waves in the marginal ice zone
Authors: Wadhams Peter , Squire Vernon A. , Goodman Dougal J. , Cowan Andrew M. , Moore Stuart C.
Published: February 2008

During field operations in the Greenland and Bering Seas in 1978, 1979 and 1983, a number of experiments were carried out in which wave energy was measured along a line of stations running from the open sea deep into an icefield. Wave buoys in the water and accelerometer packages on floes were the instruments employed, with airborne vertical photography to supply information on floe size distribution. It was found that the decay of waves is exponential, with a decay coefficient which generally increases with frequency except for a roll‐over at the highest frequencies. The observations can be fitted reasonably well to a theory of one‐dimensional scattering.
Observations and wind‐forced model simulations of the mean seasonal cycle in tropical Pacific sea surface topography
Authors: McPhaden Michael J. , Busalacchi Antonio J. , Picaut Joël
Published: February 2008

We examine simulations of the mean seasonal cycle in the tropical Pacific using a multiple vertical mode linear numerical model forced with three different surface wind stress products averaged over the period 1979–1981. The model is run to equilibrium for each of four vertical modes, and results are summed. Simulated mean seasonal cycles in dynamic height and sea level are then compared with observed variations based on expendable bathythermograph and island tide gauge data averaged over the same 1979–1981 period. All simulations show characteristic features of the mean meridional ridge‐trough structure in surface topography. However, north and south equatorial ridges at 20°N and 20°S are much higher than those observed, only weak equatorial ridges are generated near 4°N, and none of the simulations exhibits a significant equatorial trough. These discrepancies are due principally to limitations in model physics and in the wind forcing. Observed and modeled mean seasonal variations in surface height are of the order of a few centimeters. Coherence estimates of 0.5–0.7 are found between the model simulations and the observations for the 1 cycle per year harmonic, which dominates the seasonal cycle over most of the tropical Pacific. This suggests that about 25–50% of the variance in the observed annual surface height is accounted for by the linear model, given current estimates of the surface wind field. Harmonics higher than the annual are less well modeled because of their weaker signal levels. Regional patterns are observed in coherence levels between modeled and observed variability; i.e., longitudinally, the eastern Pacific is most poorly modeled, while latitudinally, the equatorial band (5°N to 5°S) is best modeled. However, no wind stress product is clearly superior to the others for simulating the mean seasonal cycle. Thus uncertainty in the surface stress field remains a fundamental obstacle to more accurate modeling of the variability in tropical Pacific sea surface topography.
Calculations of unbiased estimates of the magnitude of residual velocities from a small number of drogue trajectories
Authors: Sanderson Brian G. , Pal Badal K. , Goulding Allan
Published: February 2008

The linear regression method of Okubo and Ebbesmeyer (1976) has been commonly used to compute velocity gradients and residual motion. However, Okubo and Ebbesmeyer did not properly address the question of how estimates of velocity gradients and residual velocities are biased by using a cluster consisting of a small number of drogues. Since this problem has caused some confusion in the oceanographic literature, we will address it here.
A note on chimney formation in ice edge regions
Authors: Häkkinen Sirpa
Published: February 2008

Wind‐driven ice‐ocean interaction in the marginal ice zone has been shown to contribute to enhanced entrainment when the winds are favorable for upwelling at the ice edge. If a strong surface heat loss is present, formation of a deep convective region is possible resulting from an ever decreasing buoyancy and a rapid deepening of the mixed layer, i.e., a “chimney”. This chimney does not extend to the bottom, but loss of buoyancy would indicate eventual overturning to the bottom in the studied two‐layer ocean model where initially a “fresh” and cold (freezing) mixed layer lies above a stagnant, warm, and saline lower layer. A catalyst for the convection is the ice (and especially the existence of the ice edge), which has both a dynamic and thermodynamic interaction with the ocean in the coupled ice‐ocean model. The entrainment between the mixed layer and the lower layer consists of both the wind mixing component (involving the frictional velocity at the ocean surface, a Kraus‐Turner parameterization) and the convectively induced entrainment (no dissipation of convective turbulence). The latter is necessary in producing the chimney. The results are an extension to the earlier model results (Häkkinen, 1987) which did not include the convective component of entrainment.
The spectral irradiance field at the surface and in the interior of the ocean: A model for applications in oceanography and remote sensing
Authors: Sathyendranath Shubha , Platt Trevor
Published: February 2008

A spectral model of irradiance is presented for the computation of light energy available at the surface and at various depths in the ocean for the wavelength range from 400 to 700 nm. For any latitude, irradiances are computed as a function of geographic location, date, and time. Application of the model is demonstrated through computation of the profiles of vertical attenuation coefficient and of the effective specific absorption of phytoplankton. The model results are compared with those from conventional procedures, which disregard spectral and angular distributions of the underwater light field, for calculation of the effective specific absorption. The magnitude of the errors incurred by such simplifications is estimated and is shown to be nonnegligible and variable with solar elevation, depth, and the phytoplank‐on pigment concentration in the water.
A numerical study of the nonlinear stability of the eastern ocean circulation
Authors: Lee Dong‐Kyu
Published: February 2008

Nonlinear unstable waves in the eastern ocean basin are analyzed using a three‐layer quasi‐geostrophic numerical model. The upper two layers are forced to maintain a mean circulation in the absence of mesoscale motion. The waves are produced by initial small perturbations added to the mean flow. Two experiments, focused on the eastern ocean basin and differing only by mean flow strength, are performed. A region of high eddy kinetic energy is formed in the southern region, but the eastern and northern regions are vacant of eddies because of the energy efflux by westward and southwestward propagating unstable waves. Regional energetics are calculated to highlight the differences between the eastern and southern regions. Two dominant waves are found in the southern region. Waves with a period of 120 days propagate to the west and form several wave trains parallel to the southern boundary. Longer‐period waves with a period of 200 days propagate to the southwest. Comparisons with observed eddies in the northeast Pacific are discussed. Besides baroclinic instability, it is found that the energy flux by propagating waves is very important in the finite amplitude stability of the eastern ocean general circulation.
Long shelf waves generated by a coastal flux
Authors: Middleton John F.
Published: February 2008

Solutions are presented for the shelf response of barotropic and stratified oceans to an oscillatory coastal flux through a strait. The flux is modeled as the return interior flow due to an Ekman transport that arises from a fictitious square‐wave longshore wind stress. The width 2 d, of the square‐wave stress is taken to be that of the strait and the response due to the coastal flux determined from longwave wind forced solutions that exist in the literature. The net longshore energy flux for the nth strait forced shelf wave mode, wave number kn, is shown to be proportional to
[bnsin(knd)( knd)]2, where
is the coastal flux spectrum and bn the modal “wind” coupling coefficients. Results compare favorably with existing barotropic theories and estimates of net longshore energy flux obtained for the Australian Coastal Experiment region are shown to be in reasonable agreement with observations at periods of 9 days, when forcing by Bass Strait is assumed greatest.
A three‐dimensional coupled ice‐ocean model of coastal circulation
Authors: Ikeda Motoyoshi
Published: February 2008

A coupled ice‐ocean model is employed to examine roles of ocean circulation on sea ice formation and distribution along the east coasts of North America and Greenland. The model has a flat bottom and a rectangular domain with a coastal boundary to the west, an artificial solid boundary to the north, and open eastern and southern boundaries. The model is driven by idealized alongshore wind stress and atmospheric cooling; the wind stress decays northward and southward with a maximum amplitude at the middle. The open water heat flux is locally specified with both seaward and southward decay, and the heat flux through ice is taken to be inversely proportional to the ice thickness. Ice internal stresses are simplified under the assumption that the major strain is cross‐shore shear deformation. The ocean model has three levels: the surface mixed layer and two levels in the lower ocean. Linear momentum equations are used, and a geostrophic cross‐shore momentum balance is assumed. Vertical viscosity is represented only by the surface and bottom Ekman flow. Equations for temperature and salinity retain advection and diffusion terms in both vertical and horizontal directions. The model reveals the following important roles of the ocean: northerly wind induces shoreward Ekman flow and southward barotropic flow, which develops only to the southern (downstream in the sense of long coastal‐trapped wave propagation) side of wind forcing region and merges westward owing to the β‐effect. Coastal downwelling produces additional baroclinic alongshore flow, intensifying (weakening) the southward flow in the upper (lower) ocean. Cyclonic circulation is generated by differences in Ekman flow between the ice‐covered onshore area and open‐water offshore area. Ice, which occupies the coastal area, is narrowed dynamically by the shoreward Ekman flow and thermodynamically by the warm offshore water in the Ekman flow. Ice is also advected southward by the alongshore current, associated with the coastal flow and the cyclonic circulation, as well as direct wind stress. When a lower ocean is warmer than the freezing point, convective overturning carries heat upward and reduces ice formation. Ice grows faster over downwelled and southward advected cold anomalies in the lower ocean.
Altimetry for non‐Gaussian oceans: Height biases and estimation of parameters
Authors: Rodríguez Ernesto
Published: February 2008

The effects of a non‐Gaussian ocean on satellite altimetry parameter estimation are discussed. The first part of this paper shows how non‐Gaussian ocean parameters affect height estimation for satellites of the Seasat/Geosat/TOPEX type. In the second part, the estimation of the altimeter tracker bias and the non‐Gaussian ocean parameters from the altimeter return signal is studied. A new convolution model that facilitates the deconvolution of the ocean surface specular point probability density function is introduced. Next, it is argued that it is not feasible in practice to estimate the electromagnetic bias from noisy altimeter returns. It is then shown that the least squares estimation of the surface parameters in the log‐frequency domain has several advantages over estimating parameters in the time domain. The maximum likelihood estimation equations for the estimation of the waveform parameters are derived, and their solution is discussed.
Satellite sea surface temperature at the North Atlantic Polar Front related to high‐resolution towed conductivity‐temperature‐depth data
Authors: Viehoff T. , Fischer J.
Published: February 2008

A meander structure of the North Atlantic Polar Front has been observed by satellite and towed undulating conductivity‐temperature‐depth probe (CTD) during the summer 1981. The high resolution of the CTD data allowed a comparison at the resolution of the satellite images (1.2 km). The average surface temperature differences of the independently calibrated CTD and satellite data were less than 0.2 K for those mixed‐layer CTD data measured within 1 day of the satellite images. A strong decline of the temporal cross correlations between mixed‐layer temperatures and sea surface temperature (SST) was observed shortly after the transition of an atmospheric front. A comparison of the SST with the isopycnic temperature distribution revealed the longer persistence of the structures in the stably stratified layers just beneath the mixed layer. The slow decline of the cross correlation between SST maps and the isopycnic temperature showed that the towed‐fish survey was a synotpic measurement of the thermohaline field in the seasonal thermocline.
Quantification of sand bar morphology: A video technique based on wave dissipation
Authors: Lippmann T. C. , Holman R. A.
Published: February 2008

A technique is presented to remotely measure the scales and morphology of natural sand bars based on the preferential dissipation of wind waves and swell over the crests of the bar. Photographic or video images are recorded and statistical uncertainties associated with incident wave height modulations removed by averaging (time exposures). Ground truth testing of the technique was carried out as part of the SUPERDUCK experiment in October 1986. The time exposures generally provided a good mapping of underlying morphology, allowing detection of the bar and determination of cross‐shore and longshore length scales. However, during high waves, persistent surface foam obscures the relationship of image intensity to local dissipation (modeled theoretically by dissipation of a random wave field), and an enhancement technique of image differencing must be done to remove the bias. Errors in the estimate of bar crest distance from the shoreline are generally less than 35%, but this value depends on the geometry of the particular bar. Logistic simplicity and quantitative capabilities make this technique very attractive.
Incoherent like‐ and cross‐polarized backscatter cross sections of an anisotropic rough sea surface with swell
Authors: Bahar Ezekiel , Herzinger Craig M. , Fitzwater Mary Ann
Published: February 2008

Using the full wave approach, it is shown that for normal incidence the like‐polarized backscatter radar cross sections of anisotropic rough seas depend on the direction of the electric field with respect to the orientation of the remotely generated swell. For normal incidence the full wave cross‐polarized backscatter radar cross sections are also dependent on the surface height parameters and the orientation of the swell. These results suggest a method for the remote sensing of the surface height parameters of the swell and its orientation as well as the velocity of the local wind at the sea surface.
Wind estimates from wave slopes
Authors: Marsden R. F. , Juszko B.‐A.
Published: February 2008

Wave slopes, from a pitch and roll buoy, and wind velocity components, from a platform‐mounted anemometer, was sampled simultaneously during a 1984 study on the Grand Banks of Newfoundland. The principal direction of wave slope was highly correlated with the 10‐m wind direction. Residual errors in direction were large only for wind speeds less than 5.0 m/s. When these estimates were removed from the record, there was an 8.0° rms error in the estimated wind direction. The upwind slope variance correlated at 0.90 with the 10‐m wind speed. A quadratic regression of wind speed to upwind slope variance resulted in an rms error of 1.9 m/s. A rotary spectral analysis showed an extremely high coherence between the slope estimated wind components and the directly measured surface wind components for periods greater than 18.0 hours. It is suggested that the technique could be applied to surface following pitch and roll buoys to estimate surface wind speeds.
Hydrographic variability of southeastern United States shelf and slope waters during the Genesis of Atlantic Lows Experiment: Winter 1986
Authors: Atkinson Larry P. , Oka Eiichi , Wu Sunny Y. , Berger Thomas J. , Blanton Jackson O. , Lee Thomas N.
Published: February 2008

Continental shelf waters are particularly responsive to winter storm events mainly because of their shallow depths. Those of the southeastern United States (the South Atlantic Bight (SAB)) are especially responsive because they are broad and shallow. Also, the Gulf Stream serves as a continual source of warm water at the outer boundary. Thus the SAB receives strong meteorological (wind stress and heat loss) and oceanographic (advective) forcing. During the Genesis of Atlantic Lows Experiment (GALE) the response of shelf waters to winter storm events and Gulf Stream forcing was observed. The mean conditions showed a mixed water column with areas of stratification near the coast and at the shelf break. The nearshore area was stratified only during weak offshore winds, and the shelf break area was stratified during southward winds with accompanying onshore Ekman flow. On the inner shelf, advective buoyancy flux was similar in value to heat flux buoyancy and the buoyancy equivalent of wind mixing. Over the shelf break the advective buoyancy flux was 4 times the other forms of buoyancy flux and controlled the observed potential energy variability. A simple box model heat budget used to separate the effect of Gulf Stream eddies and meanders, and Ekman flow and air‐sea heat exchange on the shelf heat content showed that the observed heat content variability was caused by intrusion of Gulf Stream water. The intrusions may be caused either by onshore Ekman flow during southward winds or Gulf Stream meander events.
A two‐dimensional coupled ice‐ocean model of the Bering Sea marginal ice zone
Authors: Kantha Lakshmi H. , Mellor George L.
Published: February 2008

A two‐dimensional coupled ice‐ocean model has been formulated and applied to the wintertime Bering Sea marginal ice zone. The oceanic component is a multilevel model that incorporates second‐moment closure for turbulent mixing in the water column. The ice cover is modeled as a viscous‐plastic continuum. Melting at the ice‐ocean interface is computed using well‐known law‐of‐the‐wall concepts in a turbulent boundary layer, with particular attention to the disparate momentum and scalar transfer resistance coefficients over rough walls. The thermodynamic and dynamical interactions between the ocean and the ice cover and the energy balances at the air‐ice and air‐sea interfaces are modeled according to the companion paper (Mellor and Kantha, this issue). The model incorporates barotropic tides, both diurnal and semidiurnal, for application to the Bering Shelf. Double‐diffusive fluxes across the interface between the colder, fresher layer beneath the melting ice and the warmer, more saline water underneath are prescribed from laboratory data on double‐diffusive convection. During winter, sea ice in the central Bering Sea is transported toward the shelf break by off‐ice winds, where it encounters northward flowing warmer north Pacific waters and melts. It is this situation to which the two‐dimensional model has been applied by neglecting all variations in the along‐ice‐edge direction. The water conditions downstream of the ice edge, the ice conditions upstream, and the wind stress are the primary inputs to the model. The model simulates transition from ice‐covered to open ocean conditions and the associated ice edge front and the two‐layer circulation underneath the ice cover. Sensitivity studies indicate that the density structure and the circulation beneath the ice and the position of the ice edge are rather sensitive to the parameters affecting the dynamics and the thermodynamics of the coupled ice‐ocean system. Even small changes in the relevant parameters can cause a substantial retreat or advance of the ice edge, which may help explain why marginal ice zones are such dynamically active regions.
Seasonal variations in sea ice motion and effects on sea ice concentration in the Canada Basin
Authors: Serreze Mark C. , Barry Roger G. , McLaren Alfred S.
Published: February 2008

Drifting buoy data, surface pressure, and geostrophic wind analyses from the Arctic Ocean Buoy Program are used to examine seasonal features of the sea ice motion in the Canada Basin for 1979–1985. Although the 7‐year annual mean motion in this region is clockwise, the month‐to‐month motion is highly variable. In late summer to early autumn, the circulation can become net anticlockwise for periods lasting at least 30 days. Results from a linear model demonstrate that these “reversals” of ice motion in the Beaufort Gyre are a wind‐driven response to persistent cyclonic activity that contrasts sharply with the predominantly anticyclonic regimes of spring, late autumn, and winter. Model‐predicted ice divergences of 0.5% or more per day which can occur during periods of anticlockwise ice motion are in good agreement with values calculated from optimally interpolated velocity gradient fields. Visible band imagery and passive microwave data confirm associated large areal reductions in ice concentration of approximately 20%. Data from under‐ice submarine sonar transects and surface pressure records prior to the study period point to frequent recurrences of these late summer to early autumn ice conditions.
Sensitivity of a multilayered oceanic general circulation model to the sea surface thermal boundary condition
Authors: Huang Rui Xin
Published: February 2008

Experiments with a low resolution, multilayered model of the oceanic general circulation with wind and thermal forcing were carried out in order to identify processes controlling important aspects of the general circulation. Emphasis was placed on the sensitivity of the model's solution to the sea surface thermal boundary condition. For long restoring time scale, wind‐driven circulation dominated the solution, resembling the circulation in the North Pacific. For short restoring time scale, strong thermohaline circulation driven by deep water formed at high latitude dominated the solution, resembling the circulation in the North Atlantic. Accordingly, other aspects of the circulation, such as the baroclinic structure of the currents and the meridional mass flux partition, changed with the restoring time scale.
An analytical study of the frictional response of coastal currents and upwelling to wind stress
Authors: Dalu Gianni A. , Pielke Roger A.
Published: February 2008

In this paper we present several theoretical results concerning currents forced by the wind in coastal regions, for a shallow sea and for a very deep sea. We investigate the time behavior and the spatial structure of the stream function and the momentum components, i.e., the onset, the transient, the asymptotic, and the periodic behavior of the currents and of the upwelling, forced by winds of different spatial and time structures. Results show that the intensity of the along coast jet initially grows linearly under a δ in time wind impulse, quadratically under a Heaviside in time wind impulse, and cubically under a linearly growing wind impulse. The asymptotic state is such that the intensity of the current vanishes if the wind impulse has a finite duration, while the intensity of the sea current has a final finite amplitude if the wind intensity goes to some finite value. If the wind stress is periodic in time, there is upwelling only when the period of the forcing is longer than a characteristic time scale, which is the sum of the inertial period and the friction e‐folding time. Otherwise there are waves which propagate away from the region where the wind stress is acting. The spatial structure is such that the upwelling occurs in a horizontal region of the order of the Rossby deformation radius, corrected by the effect of friction (and by the effect of periodicity, when the wind stress is periodic in time). However, the horizontal gradient of the wind stress can be more important than the Rossby deformation radius in determining the horizontal extent of the upwelling region.