bluuebunny/crossref_metadata_2025 huggingface dataset:
Feasibility of sea ice typing with synthetic aperture radar (SAR): Merging of Landsat thematic mapper and ERS 1 SAR satellite imagery
Authors: Steffen Konrad , Heinrichs John
Published: February 2004

ERS 1 synthetic aperture radar (SAR) and Landsat thematic mapper (TM) images were acquired for the same area in the Beaufort Sea, April 16 and 18, 1992. The two image pairs were colocated to the same grid (25‐m resolution), and a supervised ice type classification was performed on the TM images in order to classify ice free, nilas, gray ice, gray‐white ice, thin first‐year ice, medium and thick first‐year ice, and old ice. Comparison of the collocated SAR pixels showed that ice‐free areas can only be classified under calm wind conditions (<3 m s−1) and for surface winds >10 m s−1 based on the backscattering coefficient alone. This is true for pack ice regions during the cold months of the year where ice‐free areas are spatially limited and where the capillary waves that cause SAR backscatter are dampened by entrained ice crystals. For nilas, two distinct backscatter classes were found at −17 dB and at −10 dB. The higher backscattering coefficient is attributed to the presence of frost flowers on light nilas. Gray and gray‐white ice have a backscatter signature similar to first‐year ice and therefore can not be distinguished by SAR alone. First‐year and old ice can be clearly separated based on their backscattering coefficient. The performance of the Geophysical Processor System ice classifier was tested against the Landsat derived ice products. It was found that smooth first‐year ice and rough first‐year ice were not significantly different in the backscatter domain. Ice concentration estimates based on ERS 1 C band SAR showed an error range of 5 to 8% for high ice concentration regions, mainly due to misclassified ice‐free and smooth first‐year ice areas. This error is expected to increase for areas of lower ice concentration. The combination of C band SAR and TM channels 2, 4, and 6 resulted in ice typing performance with an estimated accuracy of 90% for all seven ice classes.
Coastal ocean circulation near Barbados, West Indies, spring 1990 and 1991
Authors: Bowman M. J. , Stansfield K. L. , Fauria S. J. , Wilson T. C.
Published: February 2004

Results are presented of two oceanographic surveys of the coastal waters surrounding Barbados, West Indies, during April and May of 1990 and 1991. In both years, observations of the hydrographic structure were made with a dense grid of conductivity‐temperature‐depth stations over the upper 500 m of the water column. Acoustic Doppler current profiler (ADCP) measurements of currents in the upper 250 m were made on radial transects from the island during three short surveys in each year. One fixed mooring was deployed south of the island for the duration of each cruise. Results from both years showed the circulation to be energetic, highly variable over short timescales, and sometimes flowing contrary to historical means. Surface ADCP and geostrophic flow patterns during 1990 suggested that the Barbados Ridge, north of the island, played an important role in steering the circulation north of the island. The sudden reversal of the current south of the island between legs 1 and 2 of 1990, coupled with the presence of low‐salinity surface water, suggested we may have witnessed an encounter between the island and the northern edge of a thin (less than 35 m) mesoscale pool of Brazilian Current retroflexion region origin. On the other hand, in 1991, several eddies, both cyclonic and anticyclonic, were observed near the island, suggesting the possibility of shedding of Von Karman type eddies from the island.
Bio‐optical variability associated with phytoplankton dynamics in the North Atlantic Ocean during spring and summer of 1991
Authors: Stramska M. , Dickey T. D. , Plueddemann A. , Weller R. , Langdon C. , Marra J.
Published: February 2004

Bio‐optical data recorded from April 30 to July 19, 1991, using a mooring located in the open ocean (59°35.6°N, 20°57.9°W) are described and interpreted. Five multi‐variable moored systems (MVMS) were deployed in the upper 90 m to obtain concurrent, co‐located measurements of horizontal currents, water temperature, photosynthetically available radiation (PAR), transmission of light at 660 nm (c660), and stimulated chlorophyll fluorescence. In addition, meteorological and subsurface temperature data (12 depths from 80 to 310 m) were collected. When the mooring was deployed, surface waters were weakly stratified and there was little evidence of a phytoplankton bloom. Soon after the deployment, a marked increase in phytoplankton concentration occurred simultaneously with an increase of near‐surface water temperature. The most striking observation was a period (year days 128–140) of strong mixed layer depth variability (daily amplitude of about 40 m) during which phytoplankton standing stock reached its maximum. During this period, phytoplankton biomass was mixed down to deeper waters at nighttime. As a result, the variability of the bio‐optical parameters was extremely high, and deepwater phytoplankton concentration was much greater than would have been expected from the productivity estimates. Later, phytoplankton concentrations declined sharply in response to extremely stormy weather around year day 140. Once the storm passed (after day 143), surface waters stratified and the phytoplankton stock increased again, but the depth integrated biomass concentration did not reach as high values as before the storm. During this strong thermal stability period, fluorescence and c660 signals in near‐surface waters were much higher than at depth, and displayed a diel cycle which was well correlated with PAR.
Physical processes affecting availability of dissolved silicate for diatom production in the Arabian Sea
Authors: Young David K. , Kindle John C.
Published: February 2004

A passive tracer to represent dissolved silicate concentrations, with biologically realistic uptake kinetics, is successfully incorporated into a three‐dimensional, eddy‐resolving, ocean circulation model of the Indian Ocean. Hypotheses are tested to evaluate physical processes which potentially affect the availability of silicate for diatom production in the Arabian Sea. An alternative mechanism is offered to the idea that open ocean upwelling is primarily responsible for the high, vertical nutrient flux and consequent large‐scale phytoplankton bloom in the northwestern Arabian Sea during the southwest monsoon. Model results show that dissolved silicate in surface waters available for uptake by diatoms is primarily influenced by the intensity of nearshore upwelling from southwest monsoonal wind forcing and by the offshore advective transport of surface waters. The upwelling, which in the model occurs within 200±50 km of the coast, appears to be a result of a combination of coastal upwelling, Ekman pumping, and divergence of the coastal flow as it turns offshore. Localized intensifications of silicate concentrations appear to be hydrodynamically driven and geographically correlated to coastal topographic features. The absence of diatoms in sediments of the eastern Arabian Basin is consistent with modeled distributional patterns of dissolved silicate resulting from limited westward advection of upwelled coastal waters from the western continental margin of India and rapid uptake of available silicate by diatoms. Concentrations of modeled silicate become sufficiently low to become unavailable for diatom production in the eastern Arabian Sea, a region between 61°E and 70°E at 8°N on the south, with the east and west boundaries converging on the north at ∼67°E, 20°N.
Evaluation of the TOPEX/POSEIDON altimeter system over the Great Lakes
Authors: Morris Charles S. , Gill Stephen K.
Published: February 2004

The TOPEX/POSEIDON altimeter measurement system is evaluated for the first 46 repeat cycles (September 23, 1992–December 23, 1993) using tracks over the Great Lakes. The temporal variations in lake level are removed from the altimeter measurements using in situ lake level measurements, thus permitting the performance of the altimeter system to be assessed. For the NASA altimeter, the root‐mean‐square (RMS) scatter of the residuals is 3.95 cm using all the tracks over the lakes. However, some of the scatter in this result is probably due to lake tides or seiche, which can amount to a few centimeters amplitude near the ends of the lakes. When the seven best tracks are used, which cross the center of the lakes where tides/seiche effects are minimal, the RMS error is reduced to either 2.9 or 3.0 cm, depending on whether the Centre National d'Etudes Spatiales (CNES) or NASA orbit is used. This places an upper limit on the error budget of the altimeter system, excluding ocean tides and inverse barometer effect. There are several short‐period variations in the residuals. The most pronounced is a 55‐day period, with a 1‐cm amplitude, which we believe is (at least in part) due to orbit error. When the model‐derived wet tropospheric correction is substituted for the TOPEX microwave radiometer correction, the RMS error increases significantly, possibly resulting in an annual cycle of a few centimeters. Evaluation of the ionospheric correction indicates that the dual‐frequency correction provides an average improvement of 0.85 cm over the Doppler orbitography and radiopositioning integrated by satellite (DORIS) correction. Although there are insufficient data to directly assess the CNES altimeter, the relative bias between the altimeters is estimated to be either −14.3 or −15.6 cm (NASA altimeter measuring short), depending on whether the DORIS or dual‐frequency ionospheric correction is applied to the NASA altimeter.
Assimilation of TOPEX/POSEIDON altimeter data into a circulation model of the North Atlantic
Authors: Blayo E. , Verron J. , Molines J. M.
Published: February 2004

Assimilation experiments were conducted using the first 12 months of TOPEX/POSEIDON (T/P) altimeter measurements in a multilayered quasi‐geostrophic model of the North Atlantic between 20°N and 60°N. These experiments demonstrate the feasibility of using T/P data to control a basin‐scale circulation model by means of an assimilation procedure. Moreover, they allow us to recreate the four‐dimensional behavior of the North Atlantic Ocean during the year October 1992–September 1993 and to improve our knowledge and understanding of such circulation patterns. For this study we used a four‐layer quasigeostrophic model of high horizontal resolution (1/6° in latitude and longitude). The assimilation procedure used is an along‐track, sequential, nudging technique. The evolution of the model general circulation is described and analyzed from a deterministic and statistical point of view, with special emphasis on the Gulf Stream area. The gross features of the North Atlantic circulation in terms of mean transport and circulation are reproduced, such as the path, penetration and recirculation of the Gulf Stream, and its meandering throughout the eastern basin. The North Atlantic Drift is, however, noticeably underestimated. A northern meander of the north wall of the Gulf Stream above the New England Seamount Chain is present for most of the year, while, just downstream, the southern part of the jet is subject to a 100‐km southeastward deflection. The Azores current is shown to remain stable and to shift southward with time from the beginning of December 1992 to the end of April 1993, the amplitude of the shift being about 2°. The computation of the mean latitude of the Gulf Stream as a function of time shows an abrupt shift from a northern position to a southern position in January, and a reverse shift, from a southern position to a northern position, in July. Finally, some issues are addressed concerning the comparison of assimilation experiments using T/P data and Geosat data. The first results show that the T/P simulations are more energetic than the Geosat simulations, especially east of the Mid‐Atlantic Ridge, for every wavelength from 50 km to 500 km. This property is also verified in the deep ocean. The predicted abyssal circulation is indeed more energetic in the T/P case, which is more in accordance with what we know of the real ocean. Moreover, the good T/P altimeter coverage near the coasts greatly improves the model eddy kinetic energy levels in these areas, especially east of 25°W.
Correlated environmental corrections in TOPEX/POSEIDON, with a note on ionospheric accuracy
Authors: Zlotnicki Victor
Published: February 2004

Estimates of the effectiveness of an altimetric correction, and interpretation of sea level variability as a response to atmospheric forcing, both depend upon assuming that residual errors in altimetric corrections are uncorrelated among themselves and with residual sea level, or knowing the correlations. Not surprisingly, many corrections are highly correlated since they involve atmospheric properties and the ocean surface's response to them. The full corrections (including their geographically varying time mean values), show correlations between electromagnetic bias (mostly the height of wind waves) and either atmospheric pressure or water vapor of −40%, and between atmospheric pressure and water vapor of 28%. In the more commonly used collinear differences (after removal of the geographically varying time mean), atmospheric pressure and wave height show a −30% correlation, atmospheric pressure and water vapor a −10% correlation, both pressure and water vapor a 7% correlation with residual sea level, and a bit surprisingly, ionospheric electron content and wave height a 15% correlation. Only the ocean tide is totally uncorrelated with other corrections or residual sea level. The effectiveness of three ionospheric corrections (TOPEX dual‐frequency, a smoothed version of the TOPEX dual‐frequency, and Doppler orbitography and radiopositioning integrated by satellite (DORIS) is also evaluated in terms of their reduction in variance of residual sea level. Smooth (90–200 km along‐track) versions of the dual‐frequency altimeter ionosphere perform best both globally and within 20° in latitude from the equator. The noise variance in the 1/s TOPEX ionospheric samples is ∼(11 mm)2, about the same as noise in the DORIS‐based correction; however, the latter has its error over scales of order 103 km. Within 20° of the equator, the DORIS‐based correction adds (14 mm)2 to the residual sea level variance.
Sea level variability in the eastern tropical Pacific as observed by TOPEX and Tropical Ocean‐Global Atmosphere Tropical Atmosphere‐Ocean Experiment
Authors: Giese Benjamin S. , Carton James A. , Holl Lydia J.
Published: February 2004

Sea surface height measurements from the TOPEX altimeter and dynamic height from Tropical Ocean‐Global Atmosphere Tropical Atmosphere‐Ocean (TOGA TAO) moorings are used to explore sea level variability in the northeastern tropical Pacific Ocean. After the annual harmonic is removed, there are two distinct bands of variability: one band is centered at 5°N to 7°N and extends from 165°W to 110°W, and the other band is centered at 10°N to 12°N and extends from 120°W to the coast of Central America. The correspondence between the two independent observation data sets at 5°N is excellent with correlations of about 90%. The variability at 5°–7°N is identified as instability waves formed just south of the North Equatorial Countercurrent during the months of July through March. Wave amplitudes are largest in the range of longitudes 160°–140°W, where they can exceed 10 cm. The waves disappear when the equatorial current system weakens, during the months of March through May. The variability at 11°N in 1993 has the form of anticyclonic eddies. These eddies propagate westward at a speed of about 17 cm s−1, consistent with the dispersion characteristics of free Rossby waves. The eddies are shown to have their origin near the coast of Central America during northern fall and winter. Their formation seems to result from intense wind bursts across the Gulfs of Tehuantepec and Papagayo which generate strong anticyclonic ocean eddies. The disappearance of the eddies in the summer of 1993 coincides with the seasonal intensification of equatorial currents. Thus the variability at 11°N has very little overlap in time with the variability at 5°N.
Seasonal variations in the horizontal structure of the Amazon Plume inferred from historical hydrographic data
Authors: Lentz Steven J.
Published: February 2004

Near‐surface salinity observations from the National Oceanographic Data Center hydrographic data archive for the region 4°S–10°N, 60–40°W show that the Amazon River discharge forms a plume of low‐salinity water that extends northwestward into the western tropical North Atlantic. The average near‐surface salinity within the plume increases away from the Amazon River mouth consistent with an average entrainment of oceanic water of 2×105 m3/s every 1° of latitude. There are two notable seasonal variations. In the vicinity of the Amazon River mouth (0–2°N) the plume extends about 200–300 km eastward from June through December. However, from March to May the plume was often much wider (400–500 km) in the vicinity of the river mouth, possibly due to the combination of near‐maximum river discharge and winds with a southeastward component. North of 5°N, the Amazon Plume fans out over a broad region of the western tropical North Atlantic. During January through June, low‐salinity Amazon Plume water north of 5°N is primarily found west of 52°W, spreading northwestward toward the Caribbean. Beginning typically in May, some of the Amazon Plume water is deflected eastward in the North Brazil Current (NBC) retroflection. From August through October, surface salinities suggest ∼70% of the Amazon Plume water is carried eastward in the NBC retroflection, while the remaining ∼30% flows northwestward toward the Caribbean.
Chlorofluorocarbons in the central North Pacific and southward spreading time of North Pacific intermediate water
Authors: Watanabe Yutaka W. , Harada Koh , Ishikawa Kimitoshi
Published: February 2004

From August to October 1992, cross sections of Chlorofluorocarbons (CFCs) trichlorofluoromethane (CFC‐11) and dichlorofluoromethane (CFC‐12) were obtained between 48°N and 15°S along 175°E in the central North Pacific. On the basis of the distribution of CFCs, apparent ages of the North Pacific Intermediate Water (NPIW) along 175°E were determined for the isopycnal horizons of 26.40 to 27.40 σθ. The apparent age of NPIW was usually older toward the south and with increase of σθ along the section. The oldest NPIW on all isopycnal horizons in the North Pacific was located near 10°N. North of 20°N, NPIW on isopycnal horizons less than 26.80 σθ outcrops in winter in subpolar regions and appears to have formed after 1970. It is suggested that NPIW on isopycnal horizons less than 26.80 σθ is laterally well mixed between subpolar and subtropical regions on timescales of a few decades. NPIW on isopycnal horizons greater than 26.80 σθ near 37°N was older than its surroundings. It is suggested that new NPIW formed in the subpolar region is not transported directly southward and that the major current of NPIW is zonal in the central North Pacific, flowing eastward in the subpolar region and then turning more to the south, flowing toward 10°N near the eastern boundary. Thus we also estimated the zonal mean apparent ages of NPIW. The mean ages of NPIW suggested that the apparent southward spreading rates and the apparent southward spreading times of NPIW from the subpolar region to 10°N were approximately 80–170 km yr−1 and 20–45 years, respectively. It is concluded that the southward spreading time of NPIW is a few decades at most.
The distribution of bioluminescence and chlorophyll during the late summer in the North Atlantic: Maps and a predictive model
Authors: Ondercin Daniel G. , Atkinson Charles A. , Kiefer Dale A.
Published: February 2004

During August 1991 an instrument array (the Paravane) was towed continuously for several days over long distances in the North Atlantic and around the Marine Light‐Mixed Layer (MLML) mooring (60°N, 21°W). Among other sensors, the Paravane carried a thermistor, a fluorometer that measured the fluorescence emitted by chlorophyll a, a bathyphotometer that measured stimulable bioluminescence, and a beam transmissometer that measured the volume attenuation coefficient at 490 nm. The record of these biooptical measurements provides a detailed description of the upper 150 m of the water column as well as of diel variability. An examination of the transects, which covered a latitudinal range from 43°N to 60°N and a longitudinal range from 13°W to 54°W, indicates that in the colder and more northerly waters most of the chlorophyll a, attenuation, and bioluminescence were found within the surface mixed layer. In the warmer waters to the south, there were subsurface maxima for all three parameters. We have used the Paravane records to test a model that provides predictions of the vertical distribution of chlorophyll a, bioluminescence, and beam attenuation from oceanographie parameters that characterize the surface mixed layer: temperature, chlorophyll a concentration, irradiance incident to the sea surface, mixed layer depth, and nitrate concentration. The first three parameters can be measured from sensors aboard satellites while the last two parameters can be obtained from oceanographie databases. The model is based upon a description of the acclimation of the phytoplankton, an assumption about the vertical distribution of phytoplankton within the euphotic zone, and an empirical description of the relationship between bioluminescence, light intensity, and phytoplankton concentration.
Identification of diapycnal mixing through optimum multiparameter analysis: 1. Test of Feasibility and Sensitivity
Authors: Tomczak Matthias , Large Daniel G. B. , Nancarrow Nathan
Published: February 2004

The ability of optimum multiparameter (OMP) analysis to identify regions where diapycnal mixing is prominent is examined. OMP analysis and isopycnal analysis are applied to synthetic data sets constructed with predetermined mixing regimes and ratios. Oceanic conditions are modeled by including random noise representative of environmental variability found in the eastern Indian and Atlantic Oceans. Comparison of results from OMP and isopycnal analysis verifies that in the absence of environmental variability, OMP analysis can isolate regions with moderate diapycnal mixing. When environmental variability is included, the effects of diapycnal mixing have to be strong enough to be detected without ambiguity. It is shown that this is the case in the eastern Indian Ocean and, most probably, also in the eastern Atlantic Ocean.
Tidal corrections in the TOPEX/POSEIDON geophysical data records
Authors: Molines J. M. , Le Provost C. , Lyard F. , Ray R. D. , Shum C. K. , Eanes R. J.
Published: February 2004

The aim of this paper is to give an assessment to TOPEX/POSEIDON data users of the two available oceanic tidal corrections, which are based on the Schwiderski model (SCH) and the Cartwright and Ray model (CR), respectively. Large instantaneous differences are observed between the two corrections, and use of either model may sometimes lead to inadequate understanding of the remaining oceanic signals. In this paper we give an objective comparison of SCH and CR models and point out the major features of both models. Our methodology is applicable to the validating and testing of future tide models that will soon be appearing.
The 1992 summer circulation in the Northeast Water Polynya from acoustic Doppler current profiler measurements
Authors: Johnson Mark , Niebauer H. J.
Published: February 2004

A July–August 1992 snapshot of the circulation in the Northeast Water Polynya located off the coast of Greenland is presented using data collected with an acoustic Doppler current profiler (ADCP) during the cruise of the USCGC Polar Sea. The data reveal anticyclonic circulation with velocity and transport cores aligned with the local topographic trough. Transport through the trough is between 0.5 and 0.9 Sv. The total ADCP measured velocities are generally less than 10 cm s−1, but some regions have velocities larger than 20 cm s−1. The ratio of the average velocity of the upper 100 m to the average velocity below 100 m shows surface layer flows faster by a factor of between 1.2 and 2. This ratio in the ice‐free northwest portion of the polynya is smaller (≈1.5) than found over the adjacent continental shelf (≈2.0), indicating smaller vertical shear. The data show northward flow along the coast, supporting the idea that ice carried by this flow is blocked from entering the polynya by a persistent ice wedge to the south that extends from the coast, east over the topographic trough, to a shallow central bank. By blocking ice advecting from the south, the ice wedge enhances the polynya, supporting the idea that the Northeast Water Polynya is a latent heat polynya.
The sea state bias in altimeter estimates of sea level from collinear analysis of TOPEX data
Authors: Chelton Dudley B.
Published: February 2004

The wind speed and significant wave height (H1/3) dependencies of the sea state bias in altimeter estimates of sea level, expressed in the form ΔhSSB = bH1/3, are examined from least squares analysis of 21 cycles of collinear TOPEX data. The bias coefficient b is found to increase in magnitude with increasing wind speed up to about 12 m s−1 and decrease monotonically in magnitude with increasing H1/3. A parameterization of b as a quadratic function of wind speed only, as in the formulation used to produce the TOPEX geophysical data records (GDRs), is significantly better than a parameterization purely in terms of H1/3. However, a four‐parameter combined wind speed and wave height formulation for b (quadratic in wind speed plus linear in H1/3) significantly improves the accuracy of the sea state bias correction. The GDR formulation in terms of wind speed only should therefore be expanded to account for a wave height dependence of b. An attempt to quantify the accuracy of the sea state bias correction ΔhSSB concludes that the uncertainty is a disconcertingly large 1% of H1/3.
The Northeast Water Polynya during summer 1992: Distribution and aspects of secondary production of copepods
Authors: Ashjian Carin J. , Smith Sharon L. , Lane Peter V. Z.
Published: February 2004

Zooplankton ecology in the Northeast Water Polynya was investigated from July 15 to August 15, 1992. The initial hypotheses were that the polynya would be a site of enhanced secondary production and that the copepod community would be composed of varying proportions of North Atlantic and Arctic species advected onto the Greenland shelf through the Northern and Southern Troughs. Striking contrasts were observed between the northern and southern regions of the shelf. The southern region was dominated numerically by the North Atlantic species Calanus finmarchicus, while species of Arctic origin (C. glacialis, C. hyperboreus, Metridia longa) dominated in the northern region. The polynya itself contained few of the herbivorous Calanus species but, instead, was dominated by the omnivore M. longa. Secondary production of C. glacialis, represented by egg production rates, was high in all regions (55–88 eggs/female/day). However, because of low abundances of the large bodied Calanus species within the polynya, it is estimated that the herbivorous copepods were not significant consumers of primary production in the polynya. Fundamentally different pathways for the cycling of carbon may exist in the northern and southern regions. Copepod communities may utilize much of the primary production in the south but only a small proportion of the primary production in the polynya, where significant proportions may be unconsumed.
A method to estimate subpixel‐scale coastal polynyas with satellite passive microwave data
Authors: Markus Thorsten , Burns Barbara A.
Published: February 2004

The importance of Antarctic coastal polynyas for heat exchange between ocean and atmosphere, for high ice production, and thus, with the resultant brine rejection, for a large amount of the Antarctic bottom water is widely recognized. To obtain full understanding of their influence, continuous measurement of even small polynyas is necessary. Only passive microwave sensors, with their global coverage and their ability to penetrate cloud cover, can provide this information. However, because of their coarse resolution, a special method to estimate the area of subpixel‐scale coastal polynyas has been developed. It uses 85‐ and 37‐GHz data successively in order to take full advantage of the higher resolution at 85 GHz while compensating for its sensitivity to atmospheric effects with the 37‐GHz data. This method is based on simulating microwave images of polynya events by convolving an assumed brightness temperature distribution with the satellite antenna pattern. These images are compared with measured microwave data and the polynya area iteratively modified until best agreement is found. Application of the method to synthetic images produces a maximum error of 200 km2 but a mean error of 80 km2. The method shows distinct improvement over the more traditional, i.e., ice concentration, methods. Analysis of coincident infrared data indicate that ice with a thickness up to 0.06 m is included in the estimated open water area. Area time series derived with the method for a coastal polynya near Halley Bay show day‐to‐day changes from 50 km2 to 450 km2 during austral spring. Interpretation of these results in terms of wind forcing and ice growth in polynyas is aided by comparison with a one‐dimensional model of polynya development.
Halocline water formation in the Barents Sea
Authors: Steele Michael , Morison James H. , Curtin Thomas B.
Published: February 2004

Hydrographic data from the first phase of the Coordinated Eastern Arctic Experiment (CEAREX) are analyzed. The data consist of temperature and salinity measurements made by a ship‐based conductivity‐temperature‐depth (CTD) instrument and by a drifting SALARGOS buoy. These data were collected in the autumn and early winter of 1988–1989 in the northern Barents Sea, mostly in ice‐covered conditions and then across the marginal ice zone (MIZ). The data show that relatively warm, salty water of Atlantic origin is modified by air cooling and ice melting to produce lighter water that has properties identical to (lower) halocline water found in the Arctic Ocean. This occurs mostly at the MIZ and to a lesser degree within the ice pack itself. At the MIZ the halocline water subducts underneath the lighter meltwater that resides directly under the ice pack; geostrophic velocity calculations indicate that it then turns eastward and flows toward the Kara Sea, in keeping with previous chemical tracer analyses. A rough calculation reveals that the amount of halocline water formed in this way in the Barents Sea and Fram Strait is 30–50% of that formed by ice growth in eastern Arctic polynyas.
Topographic control of thermohaline frontal structure in the Barents Sea Polar Front on the south flank of Spitsbergen Bank
Authors: Gawarkiewicz Glen , Plueddemann Albert J.
Published: February 2004

A combination of observations and process‐oriented numerical modeling is used to investigate the thermohaline structure of the Barents Sea Polar Front on the south flank of Spitsbergen Bank. The Polar Front is the boundary between warm, saline North Atlantic Water and cool, fresh Arctic Water located over the outer edge of the bank. Observations from the Barents Sea Polar Front Experiment in August 1992 show that North Atlantic Water was present in waters of 250 m or deeper, with little vertical structure beneath the upper 50 m of the water column. The mean velocity field over the south flank of the bank shows a westward flow of roughly 0.1 m s−1 in the North Atlantic Water and weak mean velocities over the outer edge of the bank. A primitive equation model is used with idealized bathymetry to show that the inflow of North Atlantic Water into the Barents Sea via the Bear Island Trough bifurcates at the sill between Nordkapp Bank and Sentral Bank, at the eastern edge of the Bear Island Trough. One branch of the North Atlantic Water recirculates westward, out of the Barents Sea and back into the Norwegian Sea. The flow of North Atlantic Water is barotropic and linear, following the bathymetry. The recirculating branch is sheared off at the sill, such that the core of recirculating flow is concentrated between the isobath coincident with the sill depth (∼260 m) and the center of the trough (∼500 m). Both the cross‐bank structure of the model thermohaline fields, as well as the along‐bank velocity, are very similar to the observations at a depth of 80 m. Thus the frontal structure is controlled by the interaction of the barotropic inflow with the sill at the eastern edge of the Bear Island Trough and is not controlled by processes occurring over the bank.
Thermal evolution of the Greenland Sea Gyre in 1988–1989
Authors: Pawlowicz Richard , Lynch J. F. , Owens W. B. , Worcester P. F. , Morawitz W. M. L. , Sutton P. J.
Published: February 2004

Slice inverses of temperature and heat content from the 1988–1989 Greenland Sea Tomography experiment and other observations, including standard conductivity‐temperature‐depth stations, moored thermistors, surface meteorological variables, and surface ice cover are combined to better understand the thermodynamics of the Greenland Sea Gyre. Thermal evolution of the gyre center seems to divide naturally into the following three periods: a preconditioning phase (November–January), during which surface salinity is increased by brine rejection from ice formation and by entrainment but in which the mixed layer deepens only slowly to a depth of some 150–200 m; a deep mixing phase (February–March) during which the surface mixed layer deepens rapidly to approximately 1500 m in the gyre center purely under the influence of local surface cooling; and a restratification phase during which the products of deep mixing are replaced by Arctic Intermediate Water flowing in from the gyre edges. The onset of the deep mixing phase occurs after ice formation in the gyre center stops, resulting in an area of open water where large heat fluxes can occur. In surrounding regions, including the Odden region to the south, ice is still being formed. To the north and west, closer to the steep topography of the continental shelf, the inverse results show significant variability due to advection, and large temperature and heat content fluctuations with a period of about 50 days are seen.
Probing the interior of Arctic leads: Investigations using high‐frequency sound
Authors: Pinkel Robert , Merrifield Mark , Ramm Hans
Published: February 2004

In preparation for the Arctic Leads Experiment (LEADEX), two side scan Doppler sonars were deployed from the edge of Beaufort Sea leads in April 1991. The instruments, originally developed for ocean surface wave research, were used to investigate ice and water motions in the near‐lead environment, as well as to collect preliminary acoustic data required in the design of a more capable leadside sonar. The sonars could determine lead geometry with great accuracy, identifying regions of open water and young ice. Opening and closing speeds of the lead ice cover could be measured to 0.01 cm s−1 using pulse‐to‐pulse coherent techniques. The flow velocity of the water just beneath the ice, of order 1–10 cm s−1, was estimated using pulse‐to‐pulse incoherent processing. Perhaps surprisingly, the strongest acoustic returns from the lead surface came from regions of open water, not ice cover. Frazil ice was a likely source of this scattering, although temperature microstructure might also play a role. On the basis of the 1991 measurements, a 28‐beam sector scan Doppler sonar was developed for use in the LEADEX main field experiment (March–April 1992). With the fan of beams oriented in a vertical plane the sonar formed an image of the velocity field over a 45° sector, to ranges of 250 m, depths of 200 m. The instrument was deployed at LEADEX lead 3 on April 8–9. At this point a significant ice cover had developed, limiting local convective forcing. The dominant motions observed beneath the lead were near‐inertial internal waves. Significant variability in acoustic scattering was observed at the base of the mixed layer and in the upper thermocline. This presumably resulted from strong temperature and salinity fluctuations observed at these depths. The near‐inertial modulation of the ice water relative velocity affects the transit time of water parcels under a lead. Probability density functions of parcel transit time have extremely high kurtosis, for mean transit times less than an inertial day. Resultant distributions of near‐surface properties such as salt uptake or primary production will thus be extremely patchy.
Effect of the nonlinearity of the carbonate system on partial pressure of carbon dioxide in the oceans
Authors: Trela Piotr , Sathyendranath Shubha , Moore Robert M. , Kelley Dan E.
Published: February 2004

Partial pressure of CO2 is a nonlinear function of several seawater properties. Due to the nonlinearity in this relationship, the partial pressure of a uniform ocean would be different from that of a nonuniform ocean with the same bulk seawater properties. Assuming uniformity of seawater properties at some temporal and spatial scales in carbon models leads to systematic errors in partial pressure of CO2. In this paper we evaluate the magnitude of these errors. We partition the Geochemical Ocean Sections Study and Transient Tracers in the Oceans data according to the horizontal structure of several box models from the literature. Our results suggest that assumption of uniformity at large scales leads to underestimation of global surface ocean partial pressure of CO2 by at least 3–12 μatm. Nonlinear effects also introduce systematic errors in the buffer factor estimated from bulk seawater properties. We find the standard deviation of partial pressure of CO2 to be an indicator of the magnitude of the nonlinear effects. We discuss the implications of these errors for some conclusions drawn from carbon models. Biogeochemical processes, such as mixing, gas exchange, or biological activity, influence the distribution of the seawater properties. A shift in spatial or temporal patterns of these processes can modify the nonuniformity of the seawater properties and thus alter the partial pressure of the surface waters, even if the mean intensities of the processes remain constant.
Runup kinematics on a natural beach
Authors: Holland K. T. , Raubenheimer B. , Guza R. T. , Holman R. A.
Published: February 2004

Runup kinematics on a gently sloping natural beach are examined with detailed measurements from video images, resistance wires deployed at five elevations (between 5 and 25 cm) above and parallel to the beach face, and pressure sensors located in the inner surf zone. As suggested in a previous study comparing a single‐level resistance wire and manually digitized films, runup measurements are sensitive to the sensor elevation above the bed, owing to the elongated shape of the runup tongue. The measured mean runup elevation (setup) and vertical excursion increase as the sensor elevation decreases, with the video‐based runup estimates having the maximum means and variances. For the six data runs the average ratios of the videobased setup and significant runup excursion to estimates based on wires elevated 15 cm above the bed are 2.7 and 1.5, respectively. These trends, combined with the high coherence and small phase difference between the video and the lowest wire, demonstrate that the video‐based estimates correspond to a very near‐bed (less than a few centimeters elevation) wire measurement. The measured increase in runup excursion with decreasing sensor elevation and the cross‐shore variation in the amplitudes of pressure fluctuations at infragravity frequencies, are consistent with the theory for linear, in viscid, normally incident standing waves. For example, valleys in the pressure spectra occur at approximately the predicted standing wave nodal frequencies. Also in accord with small‐amplitude wave theory, observed swash excursions are nearly identical to pressure fluctuations at the location of the measured runup mean (for pressure sensors located seaward of the most offshore bed‐level rundown). However, at very low frequencies, where reflection is typically assumed complete and dissipation negligible, the observed, near‐bed swash magnitudes are overamplified relative to a best fit of the linear standing wave model based on the amplitude and phase of the seaward observations.
Breakdown of line plumes in turbulent environments
Authors: Ching C. Y. , Fernando H. J. S. , Robles A.
Published: February 2004

The results of a laboratory experiment that was designed to investigate the effects of background turbulence on turbulent line plumes are presented. This work was motivated by its potential application to winter polar leads, in which refieezing of open water induces buoyant plumes that descend through the upper ocean mixed layer. Scaling arguments are advanced to delineate different types of interactions that may occur between line plumes and background turbulence, and some of these arguments are verified using laboratory experiments. It is shown that turbulent line plumes can be completely destroyed by the background turbulence when the convective velocity of the plume w* is less than about 1.6u0, where u0, is the background turbulent intensity. Possible applications of the present laboratory results to lead‐related oceanic situations are also discussed.
Effects of dynamic interaction on sediment‐laden turbulent flows
Authors: Zhou D. , Ni J. R.
Published: February 2004

A systematic approach to explore the effects of dynamic interaction of liquid and solid phases on sediment‐laden turbulent open channel flows is proposed. The investigation is carried out based on systematic analysis of basic momentum and continuity equations. The effect of suspended sediment on the turbulent flow is taken as a perturbation to an equivalent turbulent clear water flow of the same water depth. A perturbation analysis is then developed, in an attempt to quantitatively describe the physical process of the interaction between the turbulent flow and the suspended sediment. As a result, a generalized suspended sediment concentration distribution is derived directly from the momentum equation. After conducting an analysis of the generation of the induced Reynolds stress, the mean velocity profile of the perturbed flow is also obtained. The derived concentration and mean velocity distributions agree well with experimental data. The present analysis improves our understanding of the coupling mechanism, develops a framework, and offers new analytical results for further study.
The Alaska Coastal Current: Continuity of transport and forcing
Authors: Stabeno P. J. , Reed R. K. , Schumacher J. D.
Published: February 2004

Current moorings were deployed on the continental shelf at 13 locations in the northwest Gulf of Alaska. They measured the Alaska Coastal Current at three positions along the coast during April–October 1991. The strongest currents were in the confined region of Shelikof Strait. Mean daily transport was as large as 2.5×106 m3 s−1. Mean transport over the 6‐month period ranged from 0.85×106 m3 s−1 at the easternmost line (off Gore Point) to 0.64×106 m3 s1− at the westernmost section (Shelikof Strait), indicating significant transport to the south of Kodiak Island. The transports were well correlated (r > 0.8) and in phase with each other and were also correlated with wind (r ∼ 0.6). Data suggest that in Shelikof Strait and off Gore Point, baroclinic flow is ∼75% and <40%, respectively, of total transport.
Dynamic interpretation of space shuttle photographs: Deepwater internal waves in the western equatorial Indian Ocean
Authors: Zheng Quanan , Klemas Vic , Yan Xiao‐Hai
Published: February 2004

Visible images of deep‐ocean internal waves in the western equatorial Indian Ocean taken by the space shuttle Atlantis during mission STS 44 in 1991 are interpreted and analyzed. The internal waves occurred in the form of a multisoliton packet in which there are about a dozen solitons. The average wavelength of the solitons is 1.8±0.5 km, ranging from 1.1 to 2.6 km. The crest lines are mostly straight and reach as long as 100 km. The distance between two adjacent packets is about 66 km. Using the deepwater soliton theory, we derived that the mean amplitude of the solitons is 25 m, the nonlinear phase speed is 1.7 m/s, and the average period is 18 min. The internal semidiurnal tides are the principal generating mechanism. The oblique collision of two multisoliton packets shown on photograph STS 44‐93‐103 is examined. The results show that the deep‐ocean internal waves obey the general properties of soliton collision. The leading solitons and a few followers exhibit some properties of inelastic collision characterized by a phase shift, and the rest of the solitons exhibit properties of elastic collision under resonance conditions.
On the births of jet drops from bubbles bursting on water surfaces
Authors: Spiel Donald E.
Published: February 2004

The parameters of the births of jet droplets originating from bubbles bursting on water surfaces are presented. Results are given for bubble sizes Rb from 350‐ to 1500‐μm equivalent volume radius in both sea and fresh waters. The ejection speeds of the jet droplets generated by a collapsing bubble and the height above the surface, as well as the time, at which the top drop breaks off the ascending jet have been measured. The dependence of the average droplet speed se on bubble size is shown to be an exponential for at least the top two drops. For the top drop this dependence is given by se = 10.7 exp (−0.00127 Rb) m s−1 for Rb in micrometers which is a fit to measurements between 350‐ and 1500‐μm radius. Extrapolated to small bubble size, this equation projects that the maximum droplet speed of ejection will approach 10.7 m s−1 as bubble size vanishes. Extrapolated to larger bubbles, on the other hand, this equation projects that a bubble with Rb = 3000 μm will emit a droplet with a speed of only 0.2 m s−1. The time t that the top drop separates from the rising jet is given by t = 2.45×10−5 Rb1.65, where Rb is in micrometers and t is in milliseconds.
Error‐reducing strategies for estimates of high‐resolution directional spectra using closely spaced sensors
Authors: Shyu Jinn‐Hwa
Published: February 2004

When an array of closely spaced sensors is applied, even if the number of sensors is very large, the error magnification phenomenon will render some cross spectra of wave records useless to the estimates of directional spectra because these cross spectra contain about the same information as others. Consequently, only few cospectra or quadrature (quad) spectra can provide truly useful information about the directional distribution when the ordinary spectral analysis procedures are applied. In this paper the sources of certain magnified errors are identified and several error‐reducing strategies are developed so that three more cospectra or quad spectra become useful to the estimates of directional spectra when a compact array with three closely spaced biaxial current meters plus a wave staff is utilized. While most of the strategies are directly relevant to reduction of the random errors, the influences of other data acquisition and processing errors are also fully taken into account. These error‐reducing strategies can improve the directional resolution of all estimators. Their effectiveness is illustrated through a series of model tests with the truncated Fourier series method (TFSM) and the Long and Hasselmann (1979) and Herbers and Guza (1990) minimum nastiness methods. In the TFSM analysis the additional three cospectra or quad spectra allow determination of the third and fourth angular harmonics of directional spectra, after which even the fifth and sixth harmonics can be determined approximately by a simple iterative scheme in most cases. For the modern Long and Hasselmann and Herbers and Guza techniques, the improvements by the present strategies are a bit marginal when the nonnegativity constraint of these techniques can very effectively optimize the estimates, but this may depend on the array geometry, and in some cases there is a clear improvement.