bluuebunny/crossref_metadata_2025 huggingface dataset:
Persistence of a pattern of surface gravity waves
Authors: Watson Kenneth M.
Published: February 2008

The observation of ship Kelvin wakes by the Seasat synthetic aperture radar raises a question concerning the persistence of patterns of surface gravity waves. Time scales vary with wavelength and environmental conditions. The range extends from fractions of a second at the shortest wavelengths to many days for ocean swell. Several mechanisms for destroying a wave pattern are investigated here. These are viscous dissipation, direct wind‐wave interaction, and nonlinear hydrodynamic interaction with ambient surface waves. The nonlinear hydrodynamic interactions appear to be the most significant.
Spin‐down of baroclinic eddies under sea ice
Authors: Ou Hsien Wang , Gordon Arnold L.
Published: February 2008

A linear model is used to examine the spin‐down of a baroclinic eddy under the sea ice. For anti‐cyclonic eddies the ice stress, besides directly spinning down the azimuthal flow within the mixed layer, generates an Ekman divergence that raises the pycnocline near the eddy axis. For eddies of the size of the baroclinic radius of deformation (based on the unperturbed mixed layer depth H and the density jump across the pycnocline), the doming reaches a quasi‐stationary state on the frictional time scale T (defined as H/α, where α is the resistence coefficient at the ice‐water interface), which generally is of the order of days. Upward entrainment of the fluid across the pycnocline causes a flow convergence below the mixed layer that continues to spin down the deeper flow and flatten the dome. The erosion of the dome, however, occurs over a much longer time scale of (γN)−1T, where γ and N are dimensionless parameters characterizing the entrainment rate and the deep stratification. Using realistic parameter values for the polar eddies, this time scale is of the order of a year or longer. The pycnocline dome observed over the Antarctic warm cells is thus likely to survive into the following freezing season and provide a preconditioning for the deep convection in the Weddell Sea.
Strontium 90 fallout prediction
Authors: Sarmiento Jorge L. , Gwinn Elisabeth
Published: February 2008

An empirical formula is developed for predicting monthly sea level strontium 90 fallout (F) in the northern hemisphere as a function of time (t), precipitation rate (P), latitude (ϕ), longitude (λ), and the sea level concentration of strontium 90 in air (C): F(λ, ϕ, t) = C(t, ϕ)[νd(ϕ) + νw(λ, ϕ, t)], where νw(λ, ϕ, t) = a(ϕ)[P(λ, ϕ, t)/P0]b(ϕ) is the wet removal, νd(ϕ) is the dry removal and P0 is 1 cm/month. The constants νd, a, and b are determined as functions of latitude by fitting land based observations. The concentration of 90Sr in air is calculated as a function of the deseasonalized concentration at a reference latitude
, the ratio of the observations at the latitude of interest to the reference latitude (R), and a function representing the seasonal trend in the air concentration
is the month. Zonal trends in C are shown to be relatively small. This formula can be used in conjunction with precipitation observations and/or estimates to predict fallout in the northern hemisphere for any month in the years 1954 to 1974. Error estimates are given; they do not include uncertainty due to errors in precipitation data. The cumulative North Atlantic 90Sr input predicted by the model for 1.25°N to 66.25°N decay corrected to December 1972 is
, compared to an inventory estimate of
from oceanic observations. It is suggested that the discrepancy is due to a more efficient scavenging of small particles over the oceans than over land.
CTD and velocity surveys of seaward jets off northern California, July 1981 and 1982
Authors: Kosro P. Michael , Huyer Adriana
Published: February 2008

Two mesoscale surveys were conducted (in July 1981 and July 1982) near Point Arena, California, to determine the structure and circulation associated with tongues of cold surface water extending seaward from the coastal zone. Both surveys were designed at sea on the basis of available satellite IR data, and each was completed in less than a week. Sampling extended 100 km alongshore and 150 km (1981) to 250 km (1982) offshore, and included conductivity, temperature, and depth casts to 500 dbar, and continuous ocean current profiling to 150 m by means of a Doppler acoustic log. Both surveys showed that the tongues of cold water seen in the satellite images were the surface manifestation of hydrographic and current anomalies that extended to a depth of at least 100 m. In each case, strong seaward flow was observed along the northern edge of the cold tongue, which also marked a shallow water mass boundary between low‐salinity (<32.8 ppt) surface waters to the north and high‐salinity (>33.2 ppt) waters to the south. The seaward jets were very strong (up to 80 cm/s) and narrow (30 km), with strong shears (up to 10−2 s−1 in the vertical and up to 10−4 s−1 in the horizontal). They were largely geostrophic, had transports exceeding 1.5 sverdrups, and can persist for 2–3 weeks. The seaward jets seemed to be continuous with southward flowing alongshore coastal jets. There is evidence that the seaward jets are recurrent features in the vicinity of Point Arena.
Wind‐driven surface transport in stratified closed basins: Direct versus residual circulations
Authors: Strub P. Ted , Powell Thomas M.
Published: February 2008

A numerical model has been used to investigate the wind‐driven circulation in a stratified basin of moderate size, Lake Tahoe, California‐Nevada. Two types of circulation are identified: “direct” circulations, in which the current directions remain relatively constant and the mean circulation formed over several days resembles the instantaneous circulation, and “residual” circulations, in which the currents fluctuate continuously and the mean circulation is characterized by small net displacements of parcels after large oscillations. Previous studies of stratified closed basins have emphasized residual circulations caused by cyclonically propagating internal basin modes, resulting in a single cyclonic mean gyre during light to moderate winds. Observations at Lake Tahoe have shown currents which are more constant in direction, with a double gyre pattern of surface circulation, dominated by an anticyclonic northern gyre. Model experiments of Lake Tahoe demonstrate that the curl of the wind stress must be included to obtain a direct, double gyre circulation similar to the observations. Horizontally uniform winds cause a residual circulation, similar to that reported at other lakes. Use of the model to calculate the vorticity budget clarifies the role of the wind stress curl in creating the direct double gyre.
Observed and modeled mesoscale variability near the Gulf Stream and Kuroshio Extension
Authors: Schmitz William J. , Holland William R.
Published: February 2008

Our earliest intercomparisons between western North Atlantic data and eddy‐resolving two‐layer quasi‐geostrophic symmetric‐double‐gyre steady wind‐forced numerical model results focused on the amplitudes and largest horizontal scales in patterns of eddy kinetic energy, primarily abyssal. Here, intercomparisons are extended to recent eight‐layer model runs and new data which allow expansion of the investigation to the Kuroshio Extension and throughout much of the water column. Two numerical experiments are shown to have realistic zonal, vertical, and temporal eddy scales in the vicinity of the Kuroshio Extension in one case and the Gulf Stream in the other. Model zonal mean speeds are larger than observed, but vertical shears are in general agreement with the data. A longitudinal displacement between the maximum intensity in surface and abyssal eddy fields as observed for the North Atlantic is not found in the model results. The numerical simulations examined are highly idealized, notably with respect to basin shape, topography, wind‐forcing, and of course dissipation. Therefore the zero‐order agreement between modeled and observed basic characteristics of mid‐latitude jets and their associated eddy fields suggests that such properties are predominantly determined by the physical mechanisms which dominate the models, where the fluctuations are the result of instability processes. The comparatively high vertical resolution of the model is needed to compare with new higher‐resolution data as well as for dynamical reasons, although the precise number of layers required either kinematically or dynamically (or numerically) has not been determined; we estimate four to six when no attempt is made to account for bottom‐ or near‐surface‐intensified phenomena.
Classification of sea ice types with single‐band (33.6 GHz) airborne passive microwave imagery
Authors: Eppler Duane T. , Farmer L. Dennis , Lohanick Alan W. , Hoover Mervyn
Published: February 2008

During March 1983 extensive high‐quality airborne passive Ka band (33.6 GHz) microwave imagery and coincident high‐resolution aerial photography were obtained of ice along a 378‐km flight line in the Beaufort Sea. Analysis of these data suggests that four classes of winter surfaces can be distinguished solely on the basis of 33.6‐GHz brightness temperature: open water, frazil, old ice, and young/first‐year ice. New ice (excluding frazil) and nilas display brightness temperatures that overlap the range of temperatures characteristic of old ice and, to a lesser extent, young/first‐year ice. Scenes in which a new ice or nilas are present in appreciable amounts are subject to substantial errors in classification if static measures of Ka band radiometric brightness temperature alone are considered. Textural characteristics of nilas and new ice, however, differ significantly from textural features characteristic of other ice types and probably can be used with brightness temperature data to classify ice type in high‐resolution single‐band microwave images. In any case, open water is radiometrically the coldest surface observed in any scene. Lack of overlap between brightness temperatures characteristic of other surfaces indicates that estimates of the areal extent of open water based on only 33.6‐GHz brightness temperatures are accurate.
On the north and tropical Atlantic heat balance
Authors: Sarmiento Jorge L.
Published: February 2008

The heat balance deduced from a three‐dimensional, seasonally driven primitive equation model of the North Atlantic is described and compared with observations. The greatest response to the seasonal forcing occurs in the region between ∼5°N and 10°N, where the northward heat transport goes from a minimum of <0 in summer, when the North Equatorial Countercurrent dominates the surface flow and the Brazil Current is at a minimum, to a maximum of > 1.4 × 1015 W in the winter, when the Brazil Current and northward Ekman transport are at a maximum. Elsewhere in the tropics and subtropics the range in transport is smaller. In the northern hemisphere (∼12° to 32°N), there is a significant semiannual component due to the Ekman transport. The large seasonal changes in heat storage in the tropics are caused primarily by transport divergence rather than surface heat flux. In the annual mean, the equatorial region has a large surface heat flux gain associated primarily with the conversion of ∼6 × 106 m3 s−1 of northward geostrophic flow with θ < 20°C in the southern hemisphere, to a surface Ekman flow with θ ∼ 27°C in the northern hemisphere. The seasonal variation in heat storage within the subtropical and subpolar gyres is due almost entirely to the surface heat flux. However, seasonal variations in Ekman transport do lead to a relatively large annual cycle in northward heat transport (e.g., 0.5 × 1015 W to 0.9 × 1015 W at ∼35°N), with maximum transport occuring during the summer when the southward Ekman transport is at a minimum. A comparison of the model results with heat storage estimates shows that the model and data agree very well in the tropics but that at higher latitudes the model underestimates the seasonal variations because of inadequate vertical penetration of heating during periods of warming.
An objective method for computing advective surface velocities from sequential infrared satellite images
Authors: Emery W. J. , Thomas A. C. , Collins M. J. , Crawford W. R. , Mackas D. L.
Published: February 2008

Using cross correlations between sequential infrared satellite images, an objective technique is developed to compute advective sea surface velocities. Cross correlations are computed in 32 × 32 pixel search (second image) and 22 × 22 template (first image) windows from gradients of sea surface temperature computed from the satellite images. Velocity vectors, computed from sequential images of the British Columbia coastal ocean, generally appear coherent and consistent with the seasonal surface current in the region. During periods of strong wind forcing, as indicated by maps of sea level pressure, the image advective velocities are stronger and more coherent spatially and appear to cross surface temperature gradients; when winds are weaker, the advective velocities correspond better with the infrared temperature patterns, suggesting the increased contribution of the geostrophic current to the surface flow. Velocities determined from coincident, near‐surface drogued (5–10 m) buoys, positioned every half hour by internal LORAN‐C units in mid‐June, show excellent agreement with the image advective velocities. In addition, conductivity, temperature, and depth (CTD) measurements (taken during the buoy tracking) confirm the homogeneity of the upper 10 m, and CTD‐derived geostrophic currents are consistent with both buoy and sequential image displacement velocities.
Equatorial long‐wave characteristics determined from satellite sea surface temperature and in situ data
Authors: Pullen Patricia E. , Bernstein Robert L. , Halpern David
Published: February 2008

Sea surface temperature (SST) maps and imagery derived from the NOAA 6 satellite Advanced Very High Resolution Radiometer (AVHRR) for June and July 1981 in the eastern tropical Pacific portray the wavelike structure of the cool water along the equator from 93°W to 125°W. Cusped waves of approximately 1000‐km zonal wavelength and 25‐day period propagated westward with a phase speed of 40 km/day. The observed meridional extent between the crest and trough of the waves is about 300 km. Details in the imagery show cooler water at the cusps advected north and then east with the north equatorial countercurrent (NECC), consistent with the suggestion of a series of anticyclonic eddies occupying the shear zone between the NECC and the westward flowing south equatorial current. Absolute SST estimates from the AVHRR data agree to within 0.6°C with shipboard data taken along 110° W between 5°N and 5°S. The wavelike structures in the SST maps are also in agreement at the surface with a vertical expendable bathythermograph temperature section made along the equator between 93°W and 125°W, which shows the phase of the waves tilting westward with increasing depth over the upper 75 m. Such a phase shift, if it extended 100–200 km meridionally in either direction from the equator, would be associated with an equatorward flux of heat. Similar phase shifts appear in temperature time series at depths of 20 and 50 m, from a mooring at 0°33′N, 110°30′W. Near‐surface currents measured at this and a second mooring on the equator at 109°40′W indicate a regular pattern of northward advection when wave cusps pass them, followed by southwest flow during the passage of wave troughs, again consistent with an equatorward flux of heat, as well as with earlier theoretical and drift buoy findings.
The Coastal Ocean Dynamics Experiment collection: An introduction
Authors: Beardsley R. C. , Lentz S. J.
Published: February 2008

The Coastal Ocean Dynamics Experiment (CODE) was designed to identify and study those dynamical processes which govern the wind‐driven motion of water over the continental shelf. The initial effort in this multiyear, multi‐institutional research program was to obtain high‐quality data sets of all the relevant physical variables needed to construct accurate kinematic and dynamic descriptions of the response of continental shelf waters to strong wind forcing in the synoptic band covering 2‐ to 20‐day variability. Two small‐scale, densely instrumented field experiments, each approximately 4 months long, were conducted in spring and summer 1981 (CODE 1) and 1982 (CODE 2). A more sparsely instrumented, long‐term, large‐scale component was also conducted in conjunction with a separate but related Large‐Scale West Coast Shelf Experiment (informally called “SuperCODE”) to help separate the local wind‐driven response in the region of the small‐scale experiments from motions generated in some distant region along the coast and to investigate the seasonal cycles of atmospheric forcing, water structure, and coastal currents between 35° and 48°N.
Spatial and temporal variability of phytoplankton pigment off northern California during Coastal Ocean Dynamics Experiment 1
Authors: Abbott Mark R. , Zion Philip M.
Published: February 2008

The distribution of phytoplankton pigment during the 1981 Coastal Ocean Dynamics Experiment (CODE) was examined using coastal zone color scanner (CZCS) imagery. Twenty‐five CZCS images were of sufficient quality to be used for further analysis. The distribution of the data was dependent on the patterns of wind forcing, with the data set biased toward regions and periods of strong equatorward winds. The weighted mean pigment image and the coefficient of variation image showed three clearly defined regions: a coastal region approximately 100 km wide, an offshore region of low pigment and low variability, and two filaments that extended several hundred kilometers offshore. Coastline topography and longshore variations in wind forcing are important in the coastal region. The offshore filaments appear to be related to the patterns of wind stress curl and perhaps explain the large‐scale patterns of Zooplankton biomass in the California Current. Analysis of the temporal variability delineated three nearshore areas: a northern region off Cape Mendocino a central region near the CODE Central line, and a southern area off San Francisco. The width of the coastal zone seemed to vary with a 5‐ to 6‐day cycle. During two equatorward wind events, the patterns of temporal variability were consistent with the patterns of wind forcing revealed by empirical orthogonal function decomposition.
Dissipation of internal wave energy in the bottom boundary layer on the continental shelf
Authors: Sanford Lawrence P. , Grant William D.
Published: February 2008

A theoretical model is developed considering a linear mode 1 internal wave train propagating into a shallow wedge, subject only to energy dissipation in the turbulent bottom boundary layer. The model incorporates variable vertical and cross‐shelf distributions of density. Internal wave energy dissipation is calculated by extending recently developed wave‐current interaction boundary layer theories, allowing for the nonlinear interaction of a surface wave, an internal wave, and a steady current in a rough turbulent boundary layer. Enhanced dissipation estimates using the wave‐wave‐current interaction drag formulation are contrasted to dissipation estimates using common linear and quadratic drag formulaitons. Order of magnitude differences are apparent between the linear and quadratic formulaitons. The boundary layer model formulation adjusts to the particular flow environment, sometimes behaving more like the linear formulation and other times more like the quadratic formulation. Dissipation of internal wave energy in the bottom boundary layer on the continental shelf is found to be of potential first‐order importance to the internal wave energy balance on the shelf, depending in a predictable way on shelf slope, density distribution, total flow environment, and bottom roughness.
Equatorial Kelvin waves in the Atlantic
Authors: Katz Eli Joel
Published: February 2008

Long‐term inverted echo sounder records along and north of the equator in the Atlantic are analyzed to show the dominance of equatorially trapped and eastward propagating disturbances with first baroclinic mode Kelvin wave characteristics in the frequency band of 10−1 to 40−1 (cycles day−1). Propagation speed is estimated as 2.35 ± 0.22 m s−1 along the equator from 34°W to 1°W. Coherence is present to 3°N but absent at 6°N (from mooring data) and 9°N. Coherence is shown with the zonal wind stress observed in midbasin, and it is suggested that the origin of the disturbance is not far from 40°W.
Time‐space variability of the local dynamics of the Malvinas‐Brazil confluence as revealed by inverted echo sounders
Authors: Garzoli Silvia L. , Bianchi Alejandro
Published: February 2008

Two inverted echo sounders have been deployed for approximately 8 months in the region of the confluence of western boundary currents in the South Atlantic (37°58.7′S, 51°56.4′W, and 37°29.3′S, 53°49.3′S). The confluence of the subtropical Brazil Current with the sub‐Antarctic Malvinas Current creates a strong, sharp thermohaline front. From the time series obtained with the sounders, two parameters are obtained and analyzed: dynamic height from the surface relative to 800 m and the position of the front. The time series of dynamic height indicates the presence of a cold intrusion during November, the southward extension of the Brazil Current and northward extension of the Malvinas Current during January, and a simultaneous warming of the area at both moored locations (0.04 dyn m/month) from March through June. From the dynamic height time series, mean geostrophic velocities are calculated. The mean value from mid‐December through mid‐June is −14 cm/s, representative of an average southward transport of 10 × 106 m3/s. The maximum southward transport, 23 × 106 m3/s, is during January. The front oscillates around its mean position with a period of about 1 month and an amplitude that varies from 10 to 50 km. The velocity of the displacement reaches values up to 10 km/d. Atmospherically forced oscillations are detected in the records. A 21‐day oscillation in the time series, obtained with the instrument located on the slope of the continental shelf, is associated with a coastally trapped wind forced response.
Modeling the large‐scale influence of geothermal sources on abyssal flow
Authors: Joyce Terrence M. , Speer Kevin G.
Published: February 2008

An approximate temperature perturbation equation for a continuously stratified deep ocean layer on an equatorial β plane is presented. A vertically integrated flow is allowed, which in the present study is forced by uniform upwelling. Solutions with truncated vertical structure are presented which are forced by a representation of localized geothermal heat sources. Solutions exhibit a range of behavior from passive advection to β plume, depending on the ratio of barotropic flow speed to long Rossby wave phase speed. Owing to the different phase speeds of the vertical modes, the forced vertical structure is dispersed, which can result in positive and negative temperature anomalies both upstream and downstream of the source. Furthermore, it is clear that the ability of localized sources to influence “upstream” conditions is enhanced in equatorial regions compared with higher latitudes, where the background flow is better able to advect the temperature perturbations downstream. Depending on the strength of the imposed temperature anomaly at the source, there may or may not be a large‐scale reversal of the total flow field. Thus the correlations between temperature, geostrophic shear, and a passive tracer such as 3He can be positive, negative, or zero away from the geothermal source.
Regional and seasonal variations in the flux of oceanic dimethylsulfide to the atmosphere
Authors: Bates Timothy S. , Cline Joel D. , Gammon Richard H. , Kelly‐Hansen Steven R.
Published: February 2008

Dimethylsulfide (DMS) concentrations have been measured in over 1000 Pacific surface seawater samples during the past 4 years. The data have been tabulated to take into account both regional and seasonal variations in concentration. The area‐weighted summer and winter concentrations of DMS in the North Pacific Ocean are 2.2 and 1.3 nmol/L, respectively. Wind speed, surface seawater temperature, and DMS diffusivities are used to calculate air‐sea exchange coefficients. The area‐weighted summer and winter DMS piston velocities are 2.3 and 2.7 m/d, respectively. These exchange coefficients combined with the concentration data yield a net ocean to atmosphere DMS flux in the North Pacific Ocean of 0.12 Tmol/yr. Extrapolating this calculation by regional areas to the global ocean yields a net DMS flux of 0.50 Tmol/yr, less than earlier estimates of 1.2 Tmol/yr, but still consistent with excess sulfate deposition estimates and model studies of the marine atmospheric sulfur budget. The uncertainty in the flux estimate is roughly a factor of 2.
M2 tidal currents in the eastern equatorial Pacific Ocean
Authors: Weisberg R. H. , Halpern D. , Tang T. Y. , Hwang S. M.
Published: February 2008

Current meter measurements recorded over the water column at 10 depths ranging from 20 m to 3027 m using surface and subsurface moorings near 0°, 110°W are analyzed for the M2 tidal current over a 10‐month sampling interval. A kinematical description is given by month and depth, followed by a decomposition into a barotropic mode and three baroclinic modes. The barotropic tide was dominant, and its hodograph was stable over the 10 months sampled. The baroclinic tide was random, isotropic, and without mode preference.
Mesoscale eddies in the Fram Strait marginal ice zone during the 1983 and 1984 Marginal Ice Zone Experiments
Authors: Johannessen J. A. , Johannessen O. M. , Svendsen E. , Shuchman R. , Manley T. , Campbell W. J. , Josberger E. G. , Sandven S. , Gascard J. C. , Olaussen T. , Davidson K. , Van Leer J.
Published: February 2008

During the summer Marginal Ice Zone Experiment in Fram Strait in 1983 and 1984, fourteen mesoscale eddies, in both deep and shallow water, were studied between 78° and 81°N. Sampling combined satellite and aircraft remote sensing observations, conductivity‐temperature‐depth observations, drift of surface and subsurface floats and current meter measurements. Typical scales of these eddies were 20–40 km. Rotation was mainly cyclonic with a maximum speed, in several cases subsurface of up to 40 cm s−1. Observations further suggest that the eddy lifetime was at least 20 to 30 days. Five generation sources are suggested for these eddies. Several of the eddies were topographically trapped, while others, primarily formed by combined baroclinic and barotropic instability, moved as much as 10–15 km d−1 with the mean current. The vorticity balance in the nontrapped eddies is dominated by the stretching of isopycnals accompanied by a change in the radial shear. In the most completely observed eddy south of 79°N the available potential energy exceeded the kinetic energy by a factor of 2. Quantitative estimates suggest that the abundance of these eddies enhances the ice edge melt up to 1–2 km d−1.
Phytoplankton biomass and productivity in the marginal ice zone of the Fram Strait during summer 1984
Authors: Smith Walker O. , Baumann Marcus E. M. , Wilson David L. , Aletsee Ludwig
Published: February 2008

The biomass and primary productivity of phytoplankton assemblages from the marginal ice zone of the Fram Strait were investigated during June‐July 1984 as part of the 1984 Marginal Ice Zone Experiment. The entire region was characterized by strong vertical stratification and reduced nutrient concentrations near the surface. Chlorophyll a levels were elevated at the ice edge and decreased both under the ice and away from the ice edge. Chlorophyll concentrations were greatest at the top of the pycnocline and averaged 2.9 μg L−1 at 20 m. Primary productivity was also greatest at the ice edge, with daily integrated productivity averaging 426 mg C m−2 d−1. Small flagellates numerically dominated the assemblages. Growth rates, when corrected for detrital material, were close to their potential maximum for the temperatures encountered. Large differences between the water temperatures, nitrate concentrations, and chlorophyll a levels during similar periods in 1983 and 1984 were noted. These differences, in addition to the spatial and temporal variations in biological processes induced by mesoscale eddies, suggest that the interannual variability in marginal ice zones may have significant consequences to the region's food web dynamics.
The effect of observed ice conditions on the drag coefficient in the summer East Greenland Sea Marginal Ice Zone
Authors: Guest P. S. , Davidson K. L.
Published: February 2008

The summer East Greenland Sea marginal ice zone is a region characterized by extreme horizontal variations of surface roughness characteristics. The surface drag coefficient is found to be correlated with these roughness characteristics, in particular, ice concentration and ice floe roughness and size. The estimates of wind stress and wind speed yield neutral drag coefficients CDN with standard deviations of 2.3 ± 0.8 × 10−3 for areas with less than 40% ice concentration and 4.0 ± 1.1 × 10−3 for ice concentrations greater than 70%. Much of the variation in CDN for a given ice concentration is explained by differences in ice floe size and roughness. Very small, concentrated, rough floes that have been affected by wave action produce twice as much wind stress (CDN = 4.2 ± 0.7 × 10−3) as relatively large, flat floes (CDN = 2.1 ± 0.6 × 10−3) and 4 times as much as typical open ocean for a given wind speed and stability. The drag coefficients in this region are higher than other marginal ice zones, probably a result of the presence of large amounts of multiyear ice floes that extend higher above the ocean surface and create more drag than first‐year floes.
Dynamics and thermodynamics of the ice/upper ocean system in the marginal ice zone of the Greenland Sea
Authors: McPhee Miles G. , Maykut Gary A. , Morison James H.
Published: February 2008

Measurements were made of the ice/upper ocean system in the marginal ice zone of the Greenland Sea during a 4‐day storm in which wind blew the ice south across a frontal region, coinciding with the ice edge that had existed when the storm began. In response to wind stress of about 0.2 Pa, a turbulent boundary layer developed under the ice that exhibited marked Ekman rotation in both mean velocity (average surface speed about 0.17 m s−1, deflection angle about 33°) and turbulent stress profiles (typical Reynolds stress about 0.1 Pa). Ablation of the ice undersurface increased rapidly after crossing the surface temperature front, and the observed melt rate corresponded with direct heat flux measurements in the oceanic boundary layer, with maximum upward heat flux of about 200 W m−2. We discuss overall momentum and energy balances, interpret observed boundary layer measurements with a numerical model, and show that molecular effects are important for heat and mass transport at the hydraulically rough ice‐ocean interface. We also develop a simple model for predicting ice melt from interfacial stress and temperature and salinity of the mixed layer.
Seasonal current variations observed in western Hudson Bay
Authors: Prinsenberg S. J.
Published: February 2008

Yearlong current meter data from western Hudson Bay show that the annual ice cover modifies the currents. Currents observed at three depths are dominated by barotropic semidiurnal tidal currents which reach amplitudes of 28 cm s−1. During the ice‐covered season the tidal currents and tidal heights observed inshore decrease, and their arrival times are advanced. Monthly mean currents set predominantly to the south and east in accordance with the cyclonic circulation pattern of the bay. Mean current speeds are less than 4 cm s−1 and are made up of wind‐driven and density‐driven components. Their onshore‐offshore components vary in phase with the ice buildup and ice breakup seasons of the annual ice cover. Storm‐generated inertial currents are as strong as the tidal currents but rotate clockwise, opposite to the tidal current direction. They decrease with depth and are absent during the ice‐covered season. Inertial currents below the pycnocline lead those in the surface mixed layer by more than 180°, simulating an upward phase velocity. Passing weather systems also generate 5‐ to 6‐day periodic currents which slightly decrease but are coherent with depth. They reach magnitudes of up to 25 cm s−1 and occur throughout the year, regardless of the ice condition.
Two‐dimensional observations of temperature microstructure in a coastal region
Authors: Washburn Libe
Published: February 2008

Temperature microstructure is mapped in two dimensions for a section 6.7 km long and 150 m deep in water which is 200 m deep. The section is located on the continental shelf southeast of Point Conception on the southern California coast. Regions of mixing activity are composed of numerous individual events, some of which are observed to collapse onto isopycnal surfaces when plotted in a distance‐density coordinate system. Mixing regions with the temperature variance dissipation rate χ exceeding 10−6°C2 s−1 are observed to have isopycnal extents of up to 3 km. Comparison of the distributions of N and χ reveals no consistent relationship between mixing activity and the ambient stratification. Terms in the two‐dimensional budget equation for temperature variance (T′)2 are compared with χ for a volume bounded by isopycnal surfaces which is about 17 m thick and which spans the data section. The budget for (T′)2 is consistent with a balance between diapycnal production and dissipation of (T′)2 yielding an effective diapycnal diffusivity of heat of 2.0 × 10−4 m2 s−1. Water within the averaging volume is thermally stratified and the measured temperature variance dissipation rate may be used to estimate the rate at which kinetic energy is irreversibly lost to mixing of local density gradients. This rate is found to be about 3.3×10−8 W kg−1 within the averaging volume and is about a factor of 3 smaller than the kinetic energy dissipation rate ε typically found in surface mixed layers.
A numerical model of stratified circulation in Indian Arm, British Columbia
Authors: Dunbar Donald S. , Burling R. W.
Published: February 2008

A laterally integrated numerical model has been developed for the study of stratified circulation in inlets. The model is time dependent and includes advective terms, horizontal and vertical turbulent diffusion of momentum and salt, and variations in width and depth. Initial and boundary conditions based on winter measurements in Burrard Inlet and Indian Arm were used to study the inlet's response to tidal forcing. The friction term was tuned to match calculated and observed dissipation rates. Evidence for a standing wave pattern in the response of the M2 and K1 tidal constituents is discussed. A comparison of model results with cyclesonde current meter time series at two locations in Indian Arm is consistent with resonance. A modal decomposition of the calculated response shows that most of the energy is contained in the barotropic and first baroclinic modes, with the former dominating near the sill and the latter dominating in the deep basin. Second‐mode energy was significant for the K1 at some locations.
A comparison of simulated and observed fluctuations in summertime Arctic surface albedo
Authors: Ross Becky , Walsh John E.
Published: February 2008

The melt cycle during two Arctic summers is simulated with a dynamic‐thermodynamic sea ice model. The regional, seasonal and interannual variability of the surface albedo is compared directly with corresponding estimates derived by Robinson et al. (1986) from satellite imagery. Despite the large seasonal variability (∼0.8 to ∼0.2) of the observationally derived regional albedos, the largest error in the simulated albedo for any region or month is approximately 0.10. The model also captures much of the interannual variability of the regional albedos, which were observed to be lower in 1977 than in 1979 because of an earlier onset of melt. The component of the model's thermodynamic forcing that explains the most of the interannual variability of regional albedo (and ice thickness) is the air temperature. On the other hand, the various sensitivity tests show that the model is at least as sensitive to the specification of monthly snowfall as to the parameterization of the snow and ice albedos.
Gas exchange on Mono Lake and Crowley Lake, California
Authors: Wanninkhof Rik , Ledwell James R. , Broecker Wallace S. , Hamilton Mike
Published: February 2008

Gas exchange coefficients have been determined for freshwater Crowley Lake and for saline Mono Lake through the use of a man‐made purposefully injected gas, sulfur hexafluoride (SF6). The concentration decreased from an initial value of 40×10−12 mol/L to 4×10−12 mol/L for Mono Lake and from 20×10−12 mol/L to 1×10−12 mol/L for Crowley Lake over a period of 6 weeks. Wind speed records from anemometers on the shore of each lake enabled us to determine the relationship between the gas exchange coefficient k and wind speed u. The average wind speed and average exchange coefficient for the experiment were identical for the two lakes (uav=2.9 m/s, kav=2.5 cm/h), despite a large difference in size and chemical composition.

From laboratory experiments and theoretical calculations it is estimated that for wind speeds observed over Mono Lake from July until December 1984 the exchange of CO2 occurred 2–½ times faster than without chemical enhancement. This is a factor of 4 lower than needed to explain the high invasion rate of 14C produced by nuclear bomb tests.
The generation of internal waves by tidal flow over Stellwagen Bank
Authors: Hibiya Toshiyuki
Published: February 2008

The generation mechanism of internal waves by tidal flow over Stellwagen Bank in Massachusetts Bay is qualitatively clarified. First, in order to demonstrate the continuous generation process of internal waves, a numerical simulation is carried out for the hydrographic condition during a field study by Chereskin (1983). The resulting internal waveforms agree well with the acoustic images obtained at several stages of the tidal flow. Next, the generation mechanism for these internal waves is analyzed via a physical interpretation of the calculated result. This analysis is made by use of characteristics which describe the propagation of the first‐ and second‐mode internal waves. It is shown that each mode internal wave with an upstream phase propagation is efficiently amplified while being carried downstream toward the location where the maximum tidal flow becomes critical: with the decrease of the tidal flow, the internal wave thus amplified begins to propagate upstream. In previous studies, these internal waves were interpreted as quasi‐steady lee waves. The present analysis, however, provides a satisfactory explanation for the time‐dependent features that are shown in numerical simulation. This indicates that the internal waves over the bank are transient waves formed in response to a time‐varying tidal flow, and not quasi‐steady lee waves.
Comparison of dynamic height measurements from an inverted echo sounder and an island tide gauge in the central Pacific
Authors: Chiswell Stephen M. , Wimbush Mark , Lukas Roger
Published: February 2008

An inverted echo sounder (IES) and deep pressure sensor were deployed within 70 km of a shallow pressure sensor at Palmyra Island (6°N, 162°W) in the central Pacific. These instruments provided yearlong records of acoustic travel time, deep pressure and sea level. Two independent time series of dynamic height are derived from travel time and sea surface elevation, respectively. The spectra of these time series are similar, and at the spectral peaks the coherence between them exceeds 99.9% confidence levels, indicating that travel time can be used to record dynamic height fluctuations. This investigation provides a frequency dependent calibration for the IES in this region. At the energetic low frequencies (periods ∼ 1 month), this calibration agrees with a calibration by the standard method using conductivity‐temperature‐depth (CTD) casts. At higher frequencies (periods of ∼3 days), using the CTD‐derived calibration may underestimate the amplitude of some processes by as much as 30%.
Fluidization of mud in estuaries
Authors: Wolanski Eric , Chappell John , Ridd Peter , Vertessy Rob
Published: February 2008

The South Alligator River, located in the Northern Territory, Australia, is a macrotidal estuary with suspended sediment concentration values reaching 10 g 1−1In September 1986, in the dry season, the estuary was well mixed in temperature and salinity. While the vertical gradients in suspended sediment concentration were small at flood tides, for most of the ebb tide duration a lutocline separated a clear upper layer from an extremely turbid bottom layer, both layers being of comparable thickness. The tidal evolution of the suspended sediment concentration is consistent with that computed by a numerical model based on the equation of conservation of mass of suspended sediment. In this model, sediment is entrained from the bottom and mixed vertically upward by eddy diffusion, but through a Richardson number dependence, sediment‐induced buoyancy effects inhibit vertical mixing. The final depth of the turbid layer can be readily estimated analytically as a result of a balance between the rate of kinetic energy input and the buoyancy flux determined by the particle fall velocity. The presence of a lutocline helps form mud banks on the inner side of a meander.
Fundamental relationships between geoacoustic parameters and predicted bottom loss using a thin layer model
Authors: McCammon Diana F.
Published: February 2008

Bottom loss curves as a function of grazing angle for the frequency range 50–1500 Hz are obtained using a thin layer geoacoustic model of bottom interaction. A study of the model's sensitivity has revealed simple relationships between certain of the geoacoustic parameters and specific angular regions of the loss curve. Low‐angle losses are caused by losses of the transmitted ray that depend upon the sound speed ratio, gradient, and attenuation in the sediment, whereas high‐angle losses are caused by reflection from the water‐sediment interface and depend primarily on the sediment density. At low frequencies the angular position of the knee of the loss curve is dictated by the sediment thickness. Thinner sediments shift the knee toward shallower grazing angles. These relationships permit bottom losses to be estimated directly from the geoacoustic parameters without the need to exercise the thin layer model. A loss ranking scheme is demonstrated that predicts bottom losses to within ±2 dB of the full model result in over 88% of a random sample of angles and frequencies.
Diffusion by internal waves
Authors: Sanderson Brian G. , Okubo Akira
Published: February 2008

A perturbation analysis of the Lagrangian equations of motion is used to examine the diffusion induced by a random field of internal waves. At second order there is a random field of shearing motion in the horizontal plane. We calculate the single‐particle, two‐particle, and patch diffusivities that result from this motion. Patch and two‐particle diffusivity both increase as scale raised to the power of 4/3 for an internal wave field in which the spectrum of horizontal velocity varies as ω−2.
The boundary currents east and north of Madagascar: 1. Geostrophic currents and transports
Authors: Swallow John , Fieux Michèle , Schott Friedrich
Published: February 2008

Geostrophic currents and transports in the boundary currents near Madagascar are described for a section at 23°S off the east coast and at 12°S to the northeast of Cape Amber. These results are based on conductivity‐temperature‐depth and expendable bathythermograph sections made during cruises of the Marion Dufresne in 1984, 1985, and 1986, supplemented by those historical data that were sufficiently deep. The reference levels used are 1100 dbar at 12°S and 1170 dbar at 23°S, based on the results from 11 months of current meter records obtained in 1984–1985. Comparisons are made between the geostrophic current profiles and direct observations, both from moored current meters and from acoustic Doppler profiling in the Upper 200 m. The mean geostrophic transports above the chosen reference levels are 29.6 Sv northwestward off Cape Amber out to 115 km offshore and 20.6 Sv southward at 23°S out to 110 km offshore. The directly recorded currents show no detectable seasonal signal below 200 m: above that level other historical data suggest a seasonal amplitude in transport of approximately ±2 Sv at 12°S and ±0.3 Sv at 23°S.
Observations of small eddies in the Beaufort Sea
Authors: D'Asaro Eric A.
Published: February 2008

The horizontal and vertical variations of velocity, temperature, density, and turbulent kinetic energy dissipation in the central Beaufort Sea were measured with helicopter‐borne expendable current profilers and conductivity‐temperature‐depth units. Almost all velocity differences larger than 0.05 m s−1could be consistently interpreted as being due to nearly circular eddies with a diameter of 10–20km, a thickness of 50–500 m, peak velocities of 0.07–0.3 m s−1, and little expression at the top of the ocean. Four such eddies were found. Two anticyclones were found and accurately sampled. Two cyclones were found but were only poorly sampled; both were beneath and close to one of the anticyclones. Relative vorticity could be computed for two anticyclones and one cyclone. Within experimental error, the two anticyclones, and all historical Beaufort Sea anticyclones, had a relative vorticity of −ƒ and thus zero potential vorticity at the center. The cyclone had a central relative vorticity of about 0.5ƒ and thus a different value of potential vorticity than the surrounding fluid. One anticyclonic eddy (B) was sampled seven times over a period of 23 days. Its measured velocity and density fields were in approximate gradient wind balance. Its central core contained values of temperature, nitrate, and silicate that were different from those outside the core at the same density. It moved eastward at about 0.02 m s−1through the surrounding fluid. Measurements of turbulent kinetic energy dissipation were almost always less than the noise level of the instrument (about 10−9W kg−1), corresponding to a mean dissipation much less than this and a minimum decay time due to turbulence much longer than 0.3 year. The nondimensional strength (Rossby number) and shape (Burger number) of anticylcone B are very similar to those of other Beaufort Sea anticyclones and similar to those of small mid‐latitude eddies. Each of the eddies observed here was centered on a temperature maximum associated with one of the warm water masses that advect into the Arctic Ocean. The two anticyclones were centered on temperature maxima originating in the Pacific Ocean, whereas the two cyclones were centered on temperature maxima from the Atlantic Ocean. This is consistent with the hypothesis that the eddies are formed as these water masses enter the Arctic Ocean.