bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical boundary layers and spurious residual flows
Authors: Jamart Bruno M. , Ozer José
Published: February 2008

On the basis of a simple example, it is shown that unrealistic “numerical” boundary layers can develop along solid boundaries in models using a certain type of staggered computational grid. In this particular case the artifact can be ascribed to the discretization of the Coriolis term along the boundary combined with the inadequacy of the boundary condition. As a consequence of that error, the solution of a three‐dimensional numerical model is found to converge toward an incorrect steady state (the residual mean flow does not vanish as it should). A straightforward correction, called the “wet‐points‐only” method, is proposed. The procedure consists of eliminating the boundary points from the evaluation of the Coriolis term. The wet‐points‐only method is shown to also affect the results obtained with a two‐dimensional (vertically integrated) model. In this case, however, the implementation of the procedure usually downgrades rather than improves the numerical solution. For schemes wherein the velocity components are not calculated at the same locations, care must be taken in the evaluation of any term that couples the two components of the momentum equation.
Fine‐scale variability at 140°W in the equatorial Pacific
Authors: Chereskin T. K. , Moum J. N. , Stabeno P. J. , Caldwell D. R. , Paulson C. A. , Regier L. A. , Halpern D.
Published: February 2008

In November‐December 1984 we carried out an intensive 12‐day upper ocean sampling program on the equator at 140°W as part of the Tropic Heat Experiment. From our observations we constructed hourly averaged profiles of temperature, salinity, σt, turbulent kinetic energy dissipation rate, and horizontal velocity. These data were used to examine the correspondence between hydrographic and velocity fields and to compare the measured turbulent dissipations with the calculated Richardson numbers. We found that the core of the Equatorial Undercurrent tracked a density surface (σt = 25.25) on times as short as 1 hour. The variability in both hydrographic and velocity fields was greatest at the semidiurnal frequency. The supertidal energy was not significantly different from the Garrett‐Munk mid‐latitude level once latitudinal scaling was removed from the Garrett‐Munk model parameters. Horizontal velocity spectra were found to be contaminated by displacement of the background shear. Turbulent dissipation was dominated by a diurnal cycle, with high values of dissipation occurring at night above the undercurrent core. Shear and buoyancy frequency, calculated over 12‐m vertical scales, were observed to track each other above the core and were dominated by a diurnal period above 40 m and by a semidiurnal period below 40 m. When shear and buoyancy frequency were combined to form a Richardson number, neither diurnal nor semidiurnal cycles were present. Above the undercurrent core, the Richardson numbers were uniformly small (0.3 to 0.6).
The vertical eddy viscosity in the presence of baroclinic flow in coastal waters
Authors: Hopkins Tom Sawyer , Slatest Leonard A.
Published: February 2008

The vertical dependence of the eddy viscosity A(z) is explored using a simple analytical model and data from a closely spaced set of moorings off Long Island. Two different situations are examined, one with fairly steady flow, and the other with fairly steady wind forcing. In both cases the results differed from previous expressions for A(z), for example, in that A(z) increased instead of decreased toward the bottom boundary. This difference is a consequence of treating a baroclinic instead of a non‐stratified situation. The omission of baroclinicity also leads to larger column‐averaged values of A(z), a fact that becomes more obvious when the full velocity vector is modeled instead of just the main component. Low values (0(10) cm2/s) with an interior minimum were obtained for the steady flow, strongly baroclinic situation; and higher values (0(100) cm2/s) were required for the more strongly wind‐forced situation. Comparisons are made with the Munk and Anderson [1948] Richardson number dependency for A(z). Other aspects of the solution and its applicability to the observed flow are also discussed.
Large‐scale structure of the spring transition in the coastal ocean off western North America
Authors: Strub P. Ted , Allen J. S. , Huyer A. , Smith R. L.
Published: February 2008

Past measurements off the coast of central Oregon and Washington have shown that the rapid change from northward monthly mean winter winds to southward summer winds forces a “spring transition” of the coastal ocean: sea levels and temperatures drop, and mean surface currents shift from northward to southward. Current and water temperature data from 35°N to 48°N from 1981 and 1982, and sea level and wind stress data from 1971–1975 and 1980–1983, show the transition to have a large alongshore scale, typically 500 to 2000 km; the large‐scale wind stress appears to be the forcing mechanism at latitudes north of approximately 37°N. South of 37°N, sea level usually falls more gradually before the northern transition event. Both wind and sea level events generally progress from south to north over a 3‐ to 10‐day period, but this is not always true. Several aspects of the spring transition reflect coastal trapped wave dynamics. Previous studies at 45°N found persistent vertical shear of the southward summer current, associated with a cross‐shelf density gradient. During 1982 the shear and the density front develop over the shelf break immediately after the transition at 43°N and to the south, but they are much less persistent than at 48°N. The stronger winds between 38°N and 42°N and the narrower shelf result in an offshore displacement of the density front and vertical shear past the shelf break, leaving the water over the shelf less stratified and more subject to barotropic reversals of the current than that farther north, where the front stays closer to the coast.
Yes, some of the Mediterranean outflow does come from great depth
Authors: Kinder Thomas H. , Parrilla Gregorio
Published: February 2008

In 1973 Stommel et al. predicted that the Western Mediterranean Deep Water (WMDW) contributes directly to the Mediterranean outflow through the Strait of Gibraltar (Strommel et al., 1973). Hydrographic data obtained in November 1985 showed unambiguous evidence of WMDW west of the major Gibraltar sill, thus confirming the prediction.
Effects of sub‐ice mesoscale features within the marginal ice zone of Fram Strait
Authors: Manley T. O.
Published: February 2008

Four distinct sub‐ice mesoscale features were observed during the 1983 Marginal Ice Zone Experiment in Fram Strait. The first one was an anticyclonic eddy located over the Yermak Plateau and strongly correlated with bottom topography, however, it appears not to have been topographically generated. The remaining features were observed along the ice edge of the East Greenland Current. Two were closely related in that one was a filament of Atlantic Water that was apparently entrained by a warm core cyclonic eddy located northwest of the Molloy Deep. The last one could not be shown conclusively as a westward extension of a branch of Atlantic Water or an isolated cyclonic eddy. Simplified estimates show that, on average, each of the three features had enough available heat energy residing within the first 30 m of their cores to melt over 600 km2 of 2‐m‐thick ice. Other estimates of potential melting and retreat rates of the marginal ice zone are calculated on the basis of various utilization depths from which available heat energy can be drawn. Further consideration is also given to the possibility that these types of features may also act as “destructive preconditioners” of sea ice since it is unlikely that complete melting would occur because of their relative movements. Eddies and intrusions significantly increase the amount of available temperature‐salinity (T‐S) space within which mixing can be accomplished. These admixtures produced by direct interaction of Atlantic Water or Atlantic Intermediate Water and the Polar Waters of the East Greenland Current further provide a very effective mechanism which transports salt to deeper levels through salt fingering and double diffusion. Calculations of heat, mass, and salt fluxes for the observed features show that the heat transported by the ice edge eddies was significant in comparison with a depth comparable flux of the East Greenland Current, while mass and salt fluxes were roughly 7 times less.
Upwelling filaments and motion of a satellite‐tracked drifter along the west coast of North America
Authors: Thomson Richard E. , Papadakis John E.
Published: February 2008

An Argos‐tracked surface buoy deployed off Vancouver Island in July 1984 reached Hawaii in July 1985. We present an analysis of the drifter track with particular emphasis on the equatorward leg seaward of the North American coast for the period July–December 1984. A low‐pass filter is used to separate motions into mean and fluctuating components. The mean track was consistently to the right of the direction expected according to the climatological geopotential topography relative to 1000 dbar, and the average southward drift speed of 0.20 m s−1 exceeded the mean geopotential flow speed by a factor of 2–3. On the basis of 1 year of drifter positions we estimate that surface waters complete one circuit of the North Pacific Gyre in 4–5 years. The amplitudes of the mesoscale buoy displacements about the mean path were approximately 43 ± 10 km, and the root‐mean‐square drift speed was 0.32 ± 0.18 m s−1. Motions at tidal and near‐inertial frequencies were negligible. From August to October the buoy paralleled a major upwelling regime centered off northern California. During this period the track underwent five sinuous zonal perturbations with characteristic amplitudes of approximately 50 km. Two of the perturbations were associated with abrupt temperature drops of 3°C and maximum seaward currents of 0.70 m s−1. National Oceanic and Atmospheric Administration advanced very high resolution radiometer thermal imagery for these times reveals that the buoy had encountered seaward protruding cold water filaments (“squirts”) associated with 100‐km‐length upwelling zones that constitute the large‐scale upwelling regime. Southward of the upwelling regime the equatorward drift speed of the buoy was only slightly greater than the equatorward advance of the surface isotherms, suggesting that advection rather than winter cooling might be mainly responsible for the shift in the temperature pattern.
Sidewall effects in a double diffusive system
Authors: Schladow S. Geoffrey , Imberger Jörg
Published: February 2008

The stability of a double diffusive system comprising of continuous gradients in temperature and salinity has been examined with respect to finite amplitude disturbances. On the basis of existing experimental data it is shown that for the particular case where salinity provides the stabilizing gradient (the “diffusive” mode) such instability will occur when the system is still stable to infinitesimal disturbances. A numerical model that incorporates the effects of the double diffusive instability together with other mixing processes that occur in natural and man‐made water bodies has been developed. Data from two salt gradient solar ponds, where the finite disturbance is provided by the differential heating that occurs at the shallow sidewalls are shown to agree well with the model results. While the exact details of the instability may eventually be shown to differ from those assumed in the model, it appears beyond question that in the presence of finite amplitude disturbances, the accepted infinitesimal stability criterion is of no real significance.
Physical properties of summer sea ice in the Fram Strait
Authors: Tucker Walter B. , Gow Anthony J. , Weeks Wilford F.
Published: February 2008

The physical properties of sea ice in the Fram Strait region of the Greenland Sea were examined during June and July 1984 in conjunction with the Marginal Ice Zone Experiment field program. Most of the ice sampled within Fram Strait during this period was multiyear. Thicknesses and other properties indicated that none of the multiyear ice was older than 4 to 5 years. Snow cover on the multiyear ice averaged 29 cm, while that on first‐year ice averaged only 8 cm deep. This difference may be related to enhanced sublimation of the snow on the thinner first‐year ice. The salinity profiles of first‐year ice clearly show the effects of ongoing brine drainage in that profiles from cores drilled later in the experiment are substantially less saline than earlier cores. Thin section examinations of crystal structure indicate that about 75% of the ice consisted of congelation ice with typically columnar type crystal structure. The remaining 25% consisted of granular ice with only a few occurrences of snow ice. The granular ice consisted primarily of frazil, found in small amounts at the top of floes but mainly observed in multiyear ridges. The horizontally oriented crystal c axes showed various degrees of alignment, ranging from no alignment to strong alignments in which the alignment direction changed with depth, implying a change in floe orientation with respect to the ocean current at the ice‐water interface during ice growth. Evidence of crystal retexturing was observed in the upper meter of nearly every multiyear core. This retexturing, consisting of grain boundary smoothing and nearly complete obliteration of the ice platelet‐brine layer substructure, is attributed to summer warming.
An instability theory of ice‐air interaction for the formation of ice edge bands
Authors: Chu P. C.
Published: February 2008

Ice edge bands are well‐observed phenomena at the ice edge of the world ocean at times when winds are blowing off the ice. Differing from the wave radiation theory, water wave theory, wind wave theory, and ice‐water coupling theory, we propose an ice‐air feedback mechanism to generate the ice edge bands. To eliminate ocean effects, the water is set motionless. Thermally generated surface winds, blowing from ice to water (ice breeze) with some deflection due to the earth's rotation, force the drift of ice floes in the marginal ice zone (MIZ). By changing the surface temperature gradient, the ice motion feeds back on the surface winds. A coupled ice‐air model similar to the author's earlier paper is employed to discuss the instability properties of such a feedback mechanism. The linearized governing equations are then solved as an eigenvalue problem with two model parameters: mean ice thickness Hi (0.5 m < Hi < 2.5 m) and a characteristic surface temperature difference over ice and water DT0 (4°C < DT0 < 20°C). The model results show alternating ice divergence and convergence zones and demonstrate a great number of e‐folding acceleration modes excited by the coupled ice‐air system. Ice floes are transported from the divergence area to the convergence zone and are eventually rearranged into a band structure. The e‐folding acceleration rate of ice motion depends on the width of two adjacent convergence zones l. It increases with L/l (where L is the length of twice the MIZ width, i.e., 200 km) for 10 km < l < 200 km, and then remains high for 2 km < l < 10 km. The length scale (2–10 km) of the high acceleration modes agrees well with the observed ice edge bandwidth (1–10 km). The e‐folding acceleration rate increases with an increase in DT0 and with a decrease in Hi.
The size of wind‐driven coastal polynyas
Authors: Pease Carol H.
Published: February 2008

The sizes of wind‐generated coastal polynyas have been observed to be nearly constant for steady atmospheric conditions owing to the balance between the advection of sea ice away from the coast and the area‐averaged production rate of new ice. A simple model is used to explore the relationship of several environmental parameters to the maximum size attained by the polynya and the speed at which the maximum is reached for a given atmospheric event. The model results suggest that size is strongly a function of air temperature, such that colder air produces a smaller polynya for a given offshore wind velocity. However, size is only moderately a function of wind speed, especially for winds greater than 10 m s−1, since increasing the speed increases both the advection rate and the ice production rate. The model results are compared to observations made around a coastal polynya during February 1982 and 1983 along the southern coast of St. Lawrence Island in the northern Bering Sea and during February 1985 along the southern coast of the Seward Peninsula. The model correctly predicts the general maximum dimensions of these winter polynyas, although the atmospheric stationarity assumptions limit the usefulness of the predictions of the speed at which the maximum is reached. The results of this study suggest that the contribution of heat from the coastal ocean to the high‐latitude winter atmosphere is a self‐limiting process proportional to the amount of time the wind‐driven ice drift has a component normal to the coast. This has important implications for the interpretation of satellite imagery for ice‐covered oceans and for understanding high‐latitude climate dynamics.
Mesoscale sea ice deformation in the East Greenland marginal ice zone
Authors: Leppäranta M. , Hibler W. D.
Published: February 2008

In this paper, mesoscale (10 km) ice kinematics data obtained during the drift phase of the 1983 Marginal Ice Zone Experiment are analyzed. The measurements were made with a microwave transponder system accurate to better than 1 m. From the point of view of granular media theory, the ice pack was close to ideal. Over the scale of the array the pack was quite regular, with floes of relatively uniform size closely packed together. The main external driving force for the ice was the ocean current. Simultaneous current measurements were made at three of the strain array sites. The ice behaved in a relatively rigid manner, with more shear than dilatation occurring. Least squares fits of the strain rate tensor showed the deformation field to be quite homogeneous. Superimposed on the rigid motion were smaller fluctuations with a spectrum falling off proportional to frequency to the power of −3/2 to −2. Close examination of individual strain lines showed rather discontinuous distance changes more representative of plastic slip rather than floe bumping. Although a substantial signal at the inertial period was present in the absolute drift, no clear peaks at this period occurred in the spectra of the strain rate tensor invariants. Analysis of the spatial variation of the underlying ocean currents revealed quite a different picture from that of the ice kinematics. In particular, the current field exhibited a much greater spatial variability than the ice motion, with considerable variance at the inertial period. Coherence between the ice and ocean differential velocity was small for all frequencies. Overall, the rigid interactive character of the compact ice cover prevented most of the differential ocean currents from being transferred to the differential ice motion.
Imaging by X band radar of subsurface features: A nonlinear phenomenon
Authors: van Gastel Klaartje
Published: February 2008

A hydrodynamic theory is presented for the imaging of bottom topography and internal waves by X and K band radar. Central to this imaging is the energy spectrum of short surface waves. Here modulations of spectra by bottom topography or internal waves are calculated. A one‐dimensional spectrum is used where wave numbers range from 50 to 1300 m−1. The effect of bottom topography or internal waves is described by a slowly varying surface current. Refraction, wind, nonlinear interactions, and dissipation are taken to govern the spectrum. For the first three effects, expressions are used which are derived from first principles. These already exist in the literature. Of the dissipation, little is known. By using two completely different parameterizations for the dissipation, it is shown here that this term is not essential to the modulation mechanism. In both cases it is found that for low wind speeds and k ≧ 260 m−1 a small current change of about 20% can generate a change in energy level of a factor of 1000. The modulation is in antiphase with the current. Both magnitude and phase of the modulation agree qualitatively with measurements. This agreement is due to the inclusion in the present theory of nonlinear interactions between short surface waves.
The influence of a narrow transverse canyon on initially geostrophic flow
Authors: Klinck John M.
Published: February 2008

The interaction of a geostrophic current with a transverse submarine canyon is considered with an analytical, two‐level model of a homogeneous fluid on an f plane. The dynamical hypothesis is that the flow in the canyon is forced by the pressure gradient due to a sloping free surface. The interaction of flow in the canyon with the overlying fluid is through the vertical velocity forced by divergence in the canyon. The mathematical problem considers a flat‐bottom ocean with an infinitely long canyon having a rectangular cross section and uniform depth. The dynamics are rotationally modified, shallow‐water equations for each level. The initial time behavior of the model is considered with a power series solution which shows that flow in the canyon responds quickly, in about 0.1 of the inertia period, to an imposed surface pressure gradient. The time‐dependent model is solved by means of a Laplace transform in time in three spatial domains: over the canyon and on either side. For a canyon of arbitrary width, the flow over the canyon is composed of standing waves, while radiating waves exist on either side of the canyon. In the absence of friction, the oscillations continue indefinitely, since there are standing gravity modes in the canyon. In steady state, there is no net flow of water across the canyon, so such submarine features should act as barriers to barotropic geostrophic flow. The limit of a narrow canyon is considered. Arguments are presented to show that a canyon is narrow if its width is less than half of the smaller of the radius of deformation or the width scale of the overlying current. For a forcing current with a width about equal to the radius of deformation, the oscillations in the canyon have periods of about 0.1 up to 1. times the inertia period. Such oscillations have been observed in most canyons for which current meter observations exist.
On the ice and heat balance in Fram Strait
Authors: Untersteiner N.
Published: February 2008

The sea ice margin northwest of Spitsbergen is schematically represented by a stationary wedge maintained by opposing ice and warm Atlantic water advection. Ice melt and cooling of the surface water generate a mixed layer with properties approximating those found elsewhere in the Arctic basin. The heat energy required to melt the advancing ice is roughly comparable to the rate of heat loss of the West Spitsbergen Current and suggests that direct heat exchange with the atmosphere is less important. Only a small fraction of the nearly fresh water from ice melt exits through eastern Fram Strait, and most of it appears to return to the Arctic basin. Whether or not it contributes to the formation and maintenance of the Arctic mixed layer depends on the largely unknown circulation pattern north of Fram Strait. An example of the large interannual variation of the mean wind stress field is shown to illustrate the likelihood of an equally large variance of the ice and surface water circulation.
Remote sensing of shelf sea currents using a high‐frequency ocean surface current radar system
Authors: Matthews J. P. , Simpson J. H. , Brown J.
Published: February 2008

In a deployment of an ocean surface current radar system made during May 1985, currents were measured in a region of sea to the northeast of Anglesey, Wales, and compared with data obtained from three current meters. The uppermost current meter was fixed at 5 m from the surface, in a water column of 40‐m depth with tidal range of 9 m. In the east–west direction, close to the orientation of the major axis of the tidal ellipse, the radar and top current meter show good agreement to within an rms value of 0.16 m s−1, consistent with earlier comparative studies. For the weaker north–south components of the flow, however, differences between the radar results and those from the current meters are apparent. A larger‐amplitude north‐south signal is recorded by the radar. In terms of the M2 rotary (clockwise and anticlockwise) components of the flow, the radar data contain amplitude and phase anomalies with respect to a predicted surface behavior deduced from the current meter records and theory. In particular, anticlockwise phase at the surface is advanced considerably (by ≃ 20°). Further analysis shows that the flow field recorded by the radar has two components: the predicted tidal response, and an additional elliptical term of lower eccentricity than the main east–west tidal signal and with major axis directed close to north. Hourly synoptic maps of tidal circulation patterns derived from the radar show a smooth transition from near‐westward flows on the ebb to near‐eastward flows on the flood. The variation of north–south residual currents with height can be interpreted in terms of a “mean state” consistent with geostrophic shear and associated with the roughly east–west density gradient.
On the determination of breaking surface wave distributions using ambient sound
Authors: Farmer David M. , Vagle Svein
Published: February 2008

When surface gravity waves break, they generate an acoustic signal which can be used to derive information about their properties and distribution. Observations of sound formed in this way have been obtained at 1, 10, and 40 m below the surface in the fetch limited environment of Georgia Strait, British Columbia. Interpretation of the results is aided by a model of randomly distributed sound sources on the ocean surface. It is shown that the signal variability is governed by the number density, or mean spacing of the breakers, by the tendency for breakers to repeat at half the wave frequency, and by the group structure of the wave field. Calculated wave field properties reveal several features which can be related to changes in the wind, including variations in wave period, mean breaker spacing, and the average acoustic strength of individual breakers. Bubble clouds caused by the breaking waves can also be detected, and there is evidence that they contribute to the trapping of sound in a shallow layer close to the surface.
Effects of El Nino‐Southern Oscillation and North Pacific weather patterns on interannual variability in the subarctic Bering Sea
Authors: Niebauer H. J.
Published: February 2008

Extraordinary interannual variability in ice cover, air and sea surface temperatures (SST), and surface winds in the eastern Bering Sea have been observed over recent years. To investigate the causes of this interannual variability, long‐term (20–30 years) time series of air, ocean, and ice parameters from the Bering Sea were cross‐correlated with the southern oscillation index (SOI), an index of El Nino‐Southern Oscillation (ENSO) events in the tropical southern hemisphere, as well as with an index of Pacific/North American (PNA) events in the north Pacific. Five to thirty percent of the interannual variability (linear regression with various smoothing) in the Bering Sea data sets, with the exception of surface winds, is explained by the SOI when the Bering Sea data lags the SOI. For comparison, 29–52% of the variability in the SST off South America can be explained by the SOI. The signs of the correlations all suggest that warming in the Bering Sea follows negative anomalies in the SOI, that is, ENSO events. Positive anomalies in the SOI, which tend to precede El Nino events, were found to precede cooling in the Bering Sea. Significant correlation persists for 18–20 months. Higher‐order polynomial regressions between the SOI and Bering Sea data can explain up to 40% of the Bering Sea variability. The mechanism for the connection between ENSO events and Bering Sea interannual variability appears to be of atmospheric nature and is associated with the winter position and intensity of the Aleutian low. The Aleutian low is intensified and eastward of normal in association with El Nino, i.e., warm events but is weaker and westward of normal during cool events. It is the regional winds associated with the variable position of the Aleutian low that cause the regional warming and cooling events. This seesaw in the Aleutian low is also used to explain the out‐of‐phase ice conditions between the Bering Sea and the Sea of Okhotsk. PNA events are also associated with an intensified Aleutian low as well as 700 mbar ridging over northwestern North America causing southerly flow over Alaska. However, while correlation between ENSO events and PNA was significant, the correlation between the Bering Sea and PNA was marginal except for surface winds. Here surface winds from the north were significantly correlated with the PNA. This apparent inconsistency, as well as the lack of correlation of surface winds with the SOI, is explained by the lack of preferred site of the Aleutian low during ENSO events. This lack of preferred site helps explain why the major El Nino event of 1982–1983 had little apparent effect on the Bering Sea.
Generation of submesoscale vortices: A new mechanism
Authors: D'Asaro Eric A.
Published: February 2008

Small‐scale, intense vortices composed of water with anomalous values of quasi‐conservative tracers have been observed in many oceans. They are particularly numerous in the Beaufort Gyre of the Arctic Ocean. Possible mechanisms responsible for the generation of these features are examined. Conservation of temperature, salinity, and nutrients requires that Beaufort Sea vortices be created from water that flows into the Arctic Ocean from the Pacific Ocean across the broad, shallow Chukchi Sea. Much of this water passes through Barrow Canyon, near Point Barrow, Alaska. Observations in the canyon show the generation of vortices of approximately the same size as those observed in the Beaufort Sea. Barrow Canyon is therefore a likely site for the generation of Beaufort Sea vortices. Most observed Beaufort Sea vortices have a central potential vorticity near zero because of a relative vorticity close to −ƒ. Their Chukchi Sea source water is typically stratified with little relative vorticity, so that its potential vorticity is nonzero. A key step in the generation of the vortices is therefore the reduction of the potential vorticity of Chukchi Sea water to nearly zero. It is proposed that this occurs through the action of frictional torques occurring as the Chukchi Sea water flows through Barrow Canyon, rather than througji the action of vertical mixing. Because this flow is driven by a downstream pressure gradient, it is concentrated on the right‐hand wall of the canyon by the Coriolis force. The frictional torques thus preferentially reduce the potential vorticity of the fluid. Anticyclonic vortices are therefore preferentially generated. It is suggested that a similar scenario may play a role in the generation of submesoscale vortices containing water from the Mediterranean and Labrador seas.
A modeling study of the effects of baroclinicity on the structure of the interacting atmospheric and oceanic boundary layers
Authors: Ly Le Ngoc , Takle Eugene S.
Published: February 2008

The effects of baroclinicity on the air and ocean boundary layers under conditions for strong dynamical (compared to thermodynamic) forcing are studied by use of a numerical model of air‐sea interaction, which consists of a closed system of equations including equations of motion, turbulent kinetic energy, turbulent exchange coefficient, local turbulent length scale, and assumptions of fixed stratification and aroclinicity in both the atmosphere and ocean. Baroclinicity is incorporated into the equations of motion by specifying horizontal gradients of air temperature in the atmosphere and seawater density in the ocean. Experiments were conducted to determine the effects of different magnitudes and directions of baroclinicity and of atmospheric stratification on the dynamical and turbulent structure of the interacting boundary layers. The results of the simulations demonstrate that certain levels of baroclinicity produce double maxima in the K profiles in the atmosphere and ocean. Baroclinic effects change the dominant components of the turbulent kinetic energy in both air and sea boundary layers from shear production and dissipation for dimensionless heights and depths of less than 0.1 (about 20% of the height or depth of the boundary layer at zero surface heat flux) to shear production and buoyant destruction for dimensionless heights and depths greater than 0.1. The results show that the most significant effects of baroclinicity in the air and sea boundary layers are the increases in turbulent exchange coefficient, turbulent kinetic energy budget, shear stresses, and dimensionless wind and wind‐induced current in the regions of the boundary layers far from the interface. The results of the simulations also show that for fixed stratification and baroclinicity, surface quantities (e.g., friction velocity, drag coefficient, and geostrophic drag coefficient) are affected more by surface heat flux than by baroclinicity, whereas the opposite is true for characteristics of the whole boundary layer (e.g., boundary layer height and angle between the geostrophic wind and surface stress). Our results show good agreement with the few observations that have been taken where baroclinicity has been reported.
Joint Canada‐U.S. Ocean Wave Investigation Project: An overview of the Georgia Strait Experiment
Authors: Hughes B. A. , Dawson T. W.
Published: February 2008

An overview of the Georgia Strait Experiment ( Joint Canada‐U.S. Ocean Wave Investigation Project, or JOWIP), 1983, is presented containing a list of participants, objectives, procedures, and main results. JOWIP was designed to provide quantitative comparisons between surface measurements and remote SAR imagery of internal waves and narrow V surface ship wakes. First‐order Bragg modeling gives factor of 3 accuracy for L band internal wave modulation; the composite model and possibly nonlinear surface wave‐internal wave interaction theory are required at X band. Narrow V wakes were imaged in Dabob Bay, Washington, under low‐wind conditions at L band. Surface slopes in the Kelvin wakes are not large enough to produce specular reflections even at a radar incidence angle of 23°. Modulations along the V arms are strongly evident and have the same wavelength as the transverse Kelvin wake component. These results and others are described in detail in other papers in this same issue.
Full‐spectrum modeling of synthetic aperture radar internal wave signatures
Authors: Lyzenga David R. , Bennett John R.
Published: February 2008

An integrated hydrodynamic‐electromagnetic model which combines a full‐spectrum numerical solution of the wave action equation with a two‐scale composite radar backscatter model is described, and results are presented for several internal wave cases observed during recent synthetic aperture radar experiments. The combined model predicts radar backscatter modulations significantly larger than those predicted by a simple Bragg scattering model under relatively high wind speeds ( > 5 m/s), particularly at short wavelengths (X band) and for horizontal polarization. Furthermore, these predictions are in general agreement with observations in some cases where the simple Bragg model fails. Under other conditions, particularly at lower wind speeds and for vertical polarization, the predictions of the composite model are not significantly different from those of the Bragg model. In some of these cases, both models appear to underpredict the observed radar modulations, indicating that additional hydrodynamic and/or electromagnetic effects are present which are not included in either model.
Wave‐following measurements in the water beneath an air‐water interface
Authors: Cheung Tak Kee , Street Robert L.
Published: February 2008

Eulerian velocity fields beneath an air‐water interface in a laboratory facility have been determined for the case of wind‐ruffled mechanically generated waves of 22‐mm amplitude and 1‐Hz frequency, with wind speeds ranging from 1.7 to 6.2 m s−1, and in a wave‐following coordinate system. The velocity was measured with a two‐component wave‐following laser Doppler anemometer. The wave‐following data are compared with non‐wave‐following data under similar flow conditions. The results demonstrate that the waves affect the mean flow, even though the mean profiles remain essentially logarithmic. The wave‐following results appear as extensions of fixed‐frame results to shallower depths
A tide‐generated internal waveform in the western approaches to the Strait of Gibraltar
Authors: La Violette Paul E. , Arnone Robert A.
Published: February 2008

Aircraft expendable bathythermograph, radar, infrared scanner, and visual data collected in October 1982, 1984, and 1985, as well as space shuttle photographs, indicate that an internal waveform (depending on flow conditions, either an internal hydraulic jump or a lee wave) is a semipermanent feature over the Camarinal Sill in the western approaches to the Strait of Gibraltar. Comparison of these data with both historic and recent current meter mooring data indicates that the waveform, generated at the interface between the Atlantic and Mediterranean waters, undergoes periodic changes wrought by interaction of the tidal current and the flow of the Atlantic and Mediterranean waters. We believe that the waveform is a major mixing mechanism between the two water masses.
The role of vertical chemical fractionation in controlling late Quaternary atmospheric carbon dioxide
Authors: Boyle Edward A.
Published: February 2008

The 30% decrease in atmospheric carbon dioxide during glacial maxima must be driven by some change in the chemical circulation of the ocean. Here, a new model for late Quaternary CO2 variability is presented which resolves some problems occurring in previous models (including the timing of carbon dioxide response and changes in the oxygen content of the deep ocean). The primary driving factor in this model is a rearrangement of chemical distributions in the ocean whereby labile nutrients and metabolic CO2 are concentrated in deep waters rather than in intermediate waters as observed in the modern ocean. This new “bottom‐heavy” chemical structure does not affect atmospheric carbon dioxide directly. Instead, CO2‐induced acidity lowers the deep ocean carbonate ion concentration and temporarily increases carbonate dissolution rates. Oceanic alkalinity then rises until the deep ocean carbonate ion is restored to its steady state value. The resulting increase in oceanic alkalinity draws CO2 out of the atmosphere into the ocean. Alkalinity and atmospheric CO2 lag several thousand years behind the change in oceanic chemical structure; this delayed response is determined by the limited rate of continental weathering and deep ocean carbonate dissolution relative to the oceanic alkalinity inventory. It is proposed that characteristic deglacial and preglacial states of the ocean are leading factors driving glacial‐interglacial climate changes. This concept reinterprets the carbon isotope contrast between surface water and deep waters [Δδ13C(P‐B)] as due to a shift of light metabolic carbon from intermediate waters into deep waters. The process is illustrated here by a simple equilibrium five box ocean model. The observed intermediate‐depth nutrient depletion is not sufficient in itself to determine which of several possible mechanisms are operating, and some mechanisms are not as effective in changing atmospheric CO2 as others. The largest response is seen from deepening the regeneration cycle of organic carbon; the least response is seen from converting North Atlantic Deep Water into intermediate water.
Geosat crossover analysis in the tropical Pacific: 2. Verification analysis of altimetric sea level maps with expendable bathythermograph and island sea level data
Authors: Tai Chang‐Kou , White Warren B. , Pazan Stephen E.
Published: February 2008

Altimetric sea level map time series of the tropical Pacific have been produced from the crossover differences generated in the first 17 months of the Geosat mission. To verify the validity of altimetric sea level so produced, they are compared with the dynamic height field derived by expendable bathythermograph (XBT) and island sea level data. Overall, the three fields show statistically significant correlation with each other. At island sea level stations, altimetric sea level, in general, has better correlation with island sea level than the XBT‐derived dynamic height. Complex empirical orthogonal function (CEOF) analysis (which is used to discern coherent structures from data contaminated by random errors) has been conducted on the altimetric sea level and XBT‐derived dynamic height field. The first CEOF modes (which each explain 70% of the variance of the respective field) correlate significantly better with each other than the original fields. The relatively short record is clearly dominated by the annual signal. Major features away from the equator are also observed to propagate to the west.
A model of biogeochemical cycling of phosphorus, nitrogen, oxygen, and sulphur in the ocean: One step toward a global climate model
Authors: Shaffer Gary
Published: February 2008

An ocean model has been developed which, for prescribed physics, deals with interrelationships between chemical distributions, biogeochemical sinks and sources, chemical reactions at redox fronts, and transports across the air‐sea and sediment‐water interfaces. In its first application here, the model focuses on biogeochemical cycling of phosphorus, nitrogen, oxygen, and sulphur in an ocean forced by river input of nutrients. This is a natural starting point for a global climate model since ocean circulation and biology determine atmospheric CO2 concentrations for a given inventory of inorganic C and oceanic production is controlled mainly by the availability of inorganic P and/or N. A general approach is taken to look at oxic versus anoxic conditions, P versus N limitation of primary production, with or without inorganic removal of phosphate to the sediments. As demanded by this approach, the model is nonlinear and continuous in a vertical coordinate. To focus on the biogeochemical aspects, ocean physics are kept as simple as possible. Cold, oxygen‐rich water sinks at high latitudes and is upwelled with a constant velocity. Turbulent mixing is parameterized with a constant, vertical diffusion coefficient. The biogeochemical processes considered are new production, burial, nitrogen fixation, phosphorite formation, and three types of organic decomposition: oxidation with O2, denitrification, and sulphate reduction. Organic matter is taken to consist of a high‐ and a low‐reactive fraction. The chemical species considered explicitly are PO43−‐P, NO3−‐N, O2, NH4+‐N and H2S‐S. Results indicate that a change from oxic to weakly anoxic conditions at middepths in a P‐limited ocean would lead to strong local denitrification and low nitrate concentrations throughout the water column. New production would also become dominated by nitrogen fixers. Geological evidence implies that anoxic conditions in the water column have been rare in the Phanerozoic ocean. Both phosphorite formation (for P limitation) and denitrification (for N limitation) can strongly constrain primary production and the development of anoxia. N limitation, i.e., negligable nitrogen fixation, practically precludes anoxia but is unlikely for very long times scales. For P limitation and no phosphorite formation the model indicates that the redox state of the ocean may be most sensitive to changes in ocean biology followed by changes in ocean circulation and mixing and finally by changes in ocean temperature.
Coupled circulation and ice floe movement model for partially ice‐covered continental shelves
Authors: Bruno Michael S. , Madsen Ole S.
Published: February 2008

A coupled ice‐ocean model has been developed for use in the short‐term (order of days) prediction of the ice and water movement on the shallow Arctic continental shelf. Our interest in partially ice‐covered conditions allows the neglect of ice‐ice interactions. Thermodynamic effects are also assumed negligible over the short time scale of interest. The intended application to shallow‐water regions permits the use of the vertically integrated water momentum equations but necessitates the inclusion of finite depth effects. Model comparison with actual measurements of ice floe movement in the Beaufort Sea are extremely encouraging, especially when compared with predictions afforded by uncoupled or ice‐only formulations. The use of the depth‐averaged circulation model has been found to weaken the algorithm's ability to simulate ice floe movement in a wind field rapidly varying in time. Recommendations for future improvements include refinement of wind forecasting methods for inclusion in a coupled air‐ice‐ocean model.
Resonant seiche motion in the Chesapeake Bay
Authors: Chuang Wen‐Ssn , Boicourt William C.
Published: February 2008

Chesapeake Bay is a long and narrow estuary in which seiche motions are common phenomena. These motions are generally driven by the longitudinal (N‐S) wind at 2‐ to 3‐day time scales and are characterized by a node at the mouth and an antinode at the head of the bay. Recent observations revealed a burst of seiche activity which was, however, related to the lateral (E‐W) wind. The amplitude of current fluctuations was about 50 cm s−1 and was not simply related to the winds. The period was about 1.6 days, which was less than the natural period of the whole bay. Since the optimum wind was aligned with only a small portion of the bay (the lower reaches of the bay, about 40 km long), the primary wind effect may be active only at the entrance region. Nevertheless, it appeared that the wind‐driven current was able to trigger a resonant seiche motion in the rest of the bay. The coupled response was modeled through a two‐section conceptual model, and the results compare well with the observations.
New estimates of the available potential energy in the world ocean
Authors: Oort Abraham H. , Ascher Stephen C. , Levitus Sydney , Peixóto José P.
Published: February 2008

On the basis of extensive global data sets the total amounts of internal, potential, latent, and kinetic energy in the world oceans and atmosphere are estimated and compared for annual mean and seasonal conditions. Next, an expression for the available gravitational potential energy in the oceans is derived. The computed amounts of zonal mean and transient eddy available potential energy and the amount of kinetic energy present in the oceans are found to be much smaller (at least 1 order of magnitude) than those in the atmosphere. Because of the sparseness of directly measured subsurface values, the estimates of the kinetic energy and the transient eddy available potential energy were obtained by extrapolation from the corresponding values measured at the ocean surface. The fact that relatively large density variations are found only in the upper few hundred meters of the oceans and the greater stability of the oceans are the basic reasons for the generally small values of the potential and kinetic energy in the oceans compared with those in the atmosphere.