bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermocline of the Flores and Banda seas
Authors: Gordon Arnold L. , Ffield Amy , Ilahude A. Gani
Published: February 2004

In December 1991, 30 conductivity‐temperature‐depth (CTD) stations to 1000 dbar were obtained from the R/V Baruna Jaya I in the Flores Sea, Banda Sea, and Alor‐Wetar passage of the Indonesian sea. A salinity maximum within the interval 100–150 dbar and a salinity minimum within the interval 300–350 dbar mark water mass core layers derived from the North Pacific. They are drawn into the Flores Sea from the Makassar Strait, with subsequent flow into the Banda Sea, and are weakened en route by strong vertical mixing characteristic of the Indonesian seas. In the Flores Sea, water below 300 dbar becomes saltier with increased distance from the Makassar Strait, suggesting that an advective process may be drawing relatively salty water into the Flores Sea lower thermocline from the Banda Sea. The Banda‐to‐Flores Sea flow may be a consequence of vertical transfer of horizontal momentum produced by the same turbulent processes that are responsible for enhanced vertical mixing. The interocean transport profile may not correspond exactly with the Pacific‐to‐Indian Ocean pressure gradient profile, as deeper water is carried along with the through flow by the effects of eddy viscosity. The 550‐m sill at the southern end of the Makassar Strait creates a situation where downward flux of momentum entrains deeper water that must be compensated by lower thermocline water drawn from the Banda Sea. Geostrophic transport relative to 1000 dbar in the Banda Sea shows not only a strong through flow transport in the upper 300 dbar (6.3×106 m3 s−1) but also a deeper flow toward the Flores Sea (1.5×106 m3 s−1 from 300 to 500 dbar and an additional 2.4×106 m3 s−1 from 500 to 1000 dbar). A simple model suggests that the magnitude of the deeper westward flow is proportional to the vertical eddy viscosity coefficient. Water mass analysis shows that either the South Pacific or Indian Ocean can provide the lower thermocline Banda Sea water.
Temporal variability in the vertical structure of bioluminescence in the North Atlantic Ocean
Authors: Neilson Douglas J. , Latz Michael I. , Case James F.
Published: February 2004

The temporal and depth variability of stimulated bioluminescence at 59°N, 21°W in the North Atlantic during 1991 was measured by two bathyphotometers (BP's). A moored BP (MOORDEX) obtained a 106‐day time series of bioluminescence at 50 m between May 1 and August 15. A profiling BP (high‐intake, defined excitation, HIDEX) measured bioluminescence in the upper water column during cruises in May and August. MOORDEX‐measured bioluminescence intensity cycled with an approximate 20‐day periodicity. In May, bioluminescence was correlated with chlorophyll fluorescence with similar vertical distributions in the water column. From May to August, the mean intensity and duration of individual flash events increased, and integrated water column bioluminescence increased by a factor of 4, to 1.2×1015 quanta m−2. In August, chlorophyll fluorescence distributions and mixed layer depths were shallower than in May. Despite this, the vertical distribution of bioluminescence remained unchanged from May. The following results, potentially caused by typical seasonal changes superimposed upon short‐term high variability during each cruise, suggest a change in organism assemblage between May and August: (1) increase in the intensity of flash events, (2) shift to a broader distribution of flash kinetics, and (3) loss of correlation between fluorescence and bioluminescence.
Gulf Stream surface convergence imaged by synthetic aperture radar
Authors: Marmorino G. O. , Jansen R. W. , Valenzuela G. R. , Trump C. L. , Lee J. S. , Kaiser J. A. C.
Published: February 2004

On July 20, 1990, the north edge of the Gulf Stream (36.7°N, 72.0°W) was sampled by the R/V Cape Henlopen and simultaneously imaged by the Jet Propulsion Laboratory's airborne synthetic aperture radar (SAR). Hydrographic measurements show an abrupt surface front separating warm, salty Gulf Stream water in the south from a filament of cool, fresh (<33 practical salinity unit (psu)) water to the north. The filament lies within the stream and is likely water entrained from the continental shelf. The southern boundary of the filament is marked by increased surface wave breaking in a 100‐ to 200‐m‐wide zone, accumulations of Sargassum, and an orthogonal velocity change of 20 cm/s. The front is manifested in a sequence of SAR images as a narrow line having returns 1–2 dB higher than background. (A second, transient SAR line occurs near the northern filament boundary.) The observations are compared with model calculations of the surface wave hydrodynamics and radar scattering. The ocean waves are driven by southwesterly 8‐m/s winds and interact with the front to produce primarily an enhancement of 2‐ to 3‐m waves over a ≲200‐m‐wide region centered downwind of the front. Using a composite scattering radar model along with measured breaking‐wave statistics, we show that the observed modulations in the radar backscatter can be accounted for through breaking‐wave and tilted Bragg wave scattering effects. These results further show that SAR images of the ocean surface can be exploited for detailed study of particular ocean processes.
Momentum fluxes through sheared oceanic thermohaline steps
Authors: Padman Laurie
Published: February 2004

Measurements of microscale velocity shear in an oceanic, diffusive‐convective staircase in an environment with a large applied mean shear are presented. The observed enhancement of shear at high‐gradient interfaces separating the homogeneous convecting layers is consistent with stress continuity, where the effective viscosity of the convecting layers is much greater than the viscosity in the interfaces. For the staircase described, the effective mean viscosity is O(10−4) m2s−1, which is at least an order of magnitude larger than would be expected in the absence of the double‐diffusive convection. The dynamic stability of the interfaces, as parameterized by the gradient Richardson number, is reduced significantly by the addition of the enhanced mean shear to the time‐dependent interfacial shear that is due to convective eddies in the adjacent layers. Hence, not only the momentum flux but also the scalar (heat and salt) fluxes are increased by the interaction of mean shear with diffusive convection. For the present study, the effective Prandtl number for the staircase is between 1 and 3.
Accuracy assessment of the large‐scale dynamic ocean topography from TOPEX/POSEIDON altimetry
Authors: Tapley B. D. , Chambers D. P. , Shum C. K. , Eanes R. J. , Ries J. C. , Stewart R. H.
Published: February 2004

The quality of TOPEX/POSEIDON determinations of the global scale dynamic ocean topography have been assessed by determining mean topography solutions for successive 10‐day repeat cycles and by examining the temporal changes in the sea surface topography to identify known features. The assessment is based on the analysis of TOPEX altimeter data for cycles 1 through 36. Important errors in the tide model used to correct the altimeter data have been identified. The errors were reduced significantly by use of a new tide model derived with the TOPEX/POSEIDON measurements. Maps of the global 1‐year mean topography, produced using four of the most accurate models of the marine geoid, show that the largest error in the dynamic ocean topography is now the uncertainty in the geoid. Temporal variations in the spatially smoothed maps of the annual sea surface topography show expected features, such as the known annual hemispherical sea surface rise and fall and the seasonal variability due to monsoon influence in the Indian Ocean. Changes in the sequence of 10‐day topography maps show the development and propagation of an equatorial Kelvin wave in the Pacific beginning in December 1992 with a propagation velocity of approximately 3 m/s. The observations are consistent with observed changes in the equatorial trade winds, and with tide gauge and other in situ observations of the strengthening of the 1992 El Niño. Comparison of TOPEX‐determined sea surface height at points near oceanic tide gauges shows agreement at the 4 cm RMS level over the tropical Pacific. The results show that the TOPEX altimeter data set can be used to map the ocean surface with a temporal resolution of 10 days and an accuracy which is consistent with traditional in situ methods for the determination of sea level variations.
Spray droplet modeling: 1. Lagrangian model simulation of the turbulent transport of evaporating droplets
Authors: Edson J. B. , Fairall C. W.
Published: February 2004

The investigation of aerosol production and transport over the world's oceans is of importance in studies concerning cloud physics, air pollution, atmospheric optics, and air‐sea interaction in general. However, the contribution of sea spray droplets to the transfer of moisture and latent heat from the sea to the atmosphere is not well known. In light of this, the Humidity Exchange Over the Sea Experiment in Simulation Tunnel and Couche Limite Unidimensionelle Stationnaire d'Embrums (one dimensional stationary droplet boundary layer) programs were designed to investigate the generation, turbulent transport, and evaporation of droplets ejected by bursting bubbles within the air‐sea simulation tunnel at Institut de Mecanique Statistique de la Turbulence (IMST), Luminy, France. This first part describes the Lagrangian model developed as part of these programs to simulate the turbulent transport of evaporating droplets. The model relies on a form of the Langevin equation, which has been modified to account for the effects of gravity and the inertia of the droplets. The comparisons between the model and measurements show good agreement, particularly within the surface layer at IMST. Part 2 will describe the coupling of the model with an Eulerian k‐ε model, which allows for improved simulation of the velocity and scaler fields, as well as a means for interaction between the droplets and these fields. The model is designed to provide a better understanding of the influence of these droplets on the near surface energy budget.
A significant wave height dependent function for TOPEX/POSEIDON wind speed retrieval
Authors: Lefevre J. M. , Barckicke J. , Ménard Y.
Published: February 2004

The ocean surface roughness affects the radar cross section measured by altimeters. The wind speed is responsible for this roughness and most of present algorithms use the radar cross section (RCS) to infer it. A few authors (Monaldo and Dobson, 1989; Glazman and Greysukh, 1993) emphasized the influence of the sea maturity on satellite measurements. They found a marginal improvement in wind speed retrieval by including significant wave height in their algorithm. In this paper several previously established algorithms relating altimeter radar cross section to ocean surface wind speed are first analyzed. The shapes of the RCS versus wind speed curves are shown to depend mainly on the minimization methods used to generate the model functions. An empirical wind speed algorithm is then derived from the two altimeters (ALT and SSALT) on board TOPEX/POSEIDON (T/P) satellite using a quality controlled data set in which North Atlantic operational surface wind and wave analyses are collocated with altimeter ALT measurements. Unlike usual algorithms, this new function depends on both the radar cross section and the significant wave height. The improvement in the T/P wind speed estimate seems significant at the 99.9% level. The accuracy of the derived function is evaluated using an independent collocated SSALT and numerical weather prediction models data set. Here again the improvement is significant, but at the 90% level because of the smaller amount of data available. The T/P wind speed estimates are furthermore compared to collocated estimates from National Oceanic and Atmospheric Administration data buoys: the new algorithm retrieves wind speed from Geosat measurements with an accuracy compatible with usual algorithms.
Inertial (non‐Darcian) channeled seepage flow
Authors: Foda Mostafa A.
Published: February 2004

A slow wave solution is identified for an infinite elastic medium intersected by a two‐dimensional fluid channel. Because the wave speed is much slower than the medium's elastic shear wave, the response in the elastic medium is governed by elastostatics. The inertia of the wave is essentially focused in the fluid channel. Furthermore, wave damping is caused by fluid viscous friction on the channel's elastic walls. The solution is extended to the case of a distribution of fluid channels in an elastic solid. It is proposed that these solutions may also be used in the case of a granular porous medium. The seepage channels would then represent a network of preferential flow paths. Therefore we would allow, in this case, the channel porosity to be different from the average granular porosity. For a strongly channeled seepage flow or for a low channel porosity the solution is shown to approach that of a single‐channel solution, giving rise to a slow propagating wave mode. On the other hand, for weak channeling or nearly “homogeneous” seepage flow the solution is shown to reproduce Biot's (1956) critically damped wave of the second kind. It is proposed that the resonances observed by Foda and Tzang (this issue) are in the form of these strongly channeled wave modes.
Hemispheric asymmetry of deep water transport modes in the western Atlantic
Authors: Friedrichs Marjorie A. M. , McCartney Michael S. , Hall Melinda M.
Published: February 2004

Subtropical studies of the Atlantic meridional cold water flow show a hemispheric contrast in the dominant southward transport mode below 2000 m; in the North Atlantic, lower deep water (LDW) (1.8° ≤ θ ≤ 2.4°C) dominates with small transport of middle deep water (MDW) (2.4° ≤ θ ≤ 3.2°C), while in the South Atlantic, the opposite is observed. We use numerous observations in the western basins of the tropics to show that the transition occurs rapidly near the equator in the western Atlantic. A meridional section in the central Brazil Basin suggests zonal flows are responsible for the transition. LDW transport from the Guiana Basin (north of the equator) flows eastward in the northern Brazil Basin and is inferred to continue on through the Romanche Fracture Zone into the eastern Atlantic. An opposing flow of MDW from the eastern tropical Atlantic flows toward the western boundary, where it bifurcates to supply MDW to the Deep Western Boundary Current (DWBC) of the Brazil Basin, as well as to feed the northward flow of MDW in the Guiana Basin offshore of the DWBC. The magnitude of each of these oppositely directed flows is roughly 7 Sv. We furthermore speculate that they are connected predominantly by upwelling from LDW to MDW within the low‐latitude eastern basin. The overall deep water transport system below 2000 m in the western basins of the mid‐ and low‐latitude Atlantic is thus found to comprise the following three distinct components. (1) A strong DWBC transport of LDW with associated recirculation dominates the Guiana Basin north of the equator. (2) In the northern Brazil Basin (just south of the equator) a narrow eastward flow absorbs the LDW and carries it eastward, while a somewhat broader westward flow imports MDW into the western basin. (3) This MDW flow then bifurcates, with the southward branch causing the MDW dominance in the Brazil Basin, where the MDW dominated DWBC and associated recirculations are the third component of the deepwater transport system.
Cross calibration of TOPEX, ERS‐I, and Geosat wave heights
Authors: Cotton P. D. , Carter D. J. T.
Published: February 2004

A method of calibrating estimates of significant wave height (Hs) from satellite altimeters against buoy data is proposed, which compares monthly means in 2° latitude × 2° longitude bins obtained from the satellite data with mean values obtained from hourly buoy measurements. The method is applied to Geosat data, ERS‐1 fast‐delivery and off‐line products and to TOPEX Ku band data. Results for Geosat data are in good agreement with those from earlier work in which individual altimeter and buoy values were compared, lending support to the proposed method. Based upon these results, linear functions are derived for estimating buoy measurements of Hs from ERS‐1 and TOPEX altimeter data. Significant differences are found between the ERS‐I fast delivery and off‐line values. Regression, from 60°S to 60°N, of corresponding 2°×2° mean wave heights for individual months from ERS‐1 and TOPEX confirm that there are significant differences between the data from these satellites. Comparisons of means from ERS‐1 and from TOPEX with those from Geosat for the same calendar month but 5 years apart show wider scatter about the regression line, indicating the between‐year variability in individual 2°×2° bins.
Statistical characterization of the geophysical and electrical properties of snow on Landfast first‐year sea ice
Authors: Barber D. G. , Reddan S. P. , LeDrew E. F.
Published: February 2004

In this work we quantify the vertical geophysical and electrical properties of a snow cover on landfast first‐year sea ice observed during the Seasonal Sea Ice Monitoring and Modelling Site (SIMMS'92) experiment. Snow grain morphology, density, salinity, temperature and wetness were measured; the volume fractions of air, ice, brine, and the complex dielectric constant of the snow were modeled over a 3‐cm vertical resolution spanning a seasonal period from April to June. Our results show that over the vertical dimension the snow grain morphology, salinity, density, and fractional volumes of brine, ice, and air covary. The statistical characterization of the vertical grain morphology indicates that two distinct layers occurred under cold (−20°C) and three layers under warm (−5°C) atmospheric temperatures. Over the seasonal period it was shown that new snow was deposited at about 250 kg·m−3 and quickly compacted to 375 kg·m−3 Snow grains grew at different rates within the snow cover because of differing metamorphic conditions. Dielectrically, the snow volume followed closely the seasonal and vertical patterns of grain morphology, salinity, temperature, density and the phase proportions of water within the snow volume. As the season evolved, the increasing brine volumes and presence of water in liquid phase caused the dielectric properties to increase over several factors (ε′mix) and orders of magnitude (ε″mix).
On the relationship between energy fluxes, dielectric properties, and microwave scattering over snow covered first‐year sea ice during the spring transition period
Authors: Barber D. G. , Papakyriakou T. N. , LeDrew E. F.
Published: February 2004

In this research we investigate the seasonal nature of the co‐variability in surface energy balance variables, volume dielectrics, and microwave scattering (ERS 1) of a snow‐covered first‐year sea ice surface during a spring transitional period. Variables required to derive the components of the energy balance and dielectric properties were measured during the Seasonal Sea Ice Monitoring and Modeling site in the Canadian Arctic Archipelago in 1992. We observed that both the energy terms and dielectric properties followed a pattern similar to the total relative scattering cross section (σ°) over the seasonal transition from winter to spring. We explain this relationship through the impact of surface fluxes on dielectric and geophysical properties of the snow‐covered first‐year sea ice. We speculate that ice surface scattering dominated the total scattering cross section σ° prior to Julian day 120 and that the snow volume contributed an increasing amount of scattering to σ° over the remainder of the season. From a multivariate statistical analysis we find that the surface temperature Ts and the net shortwave energy flux K* explained a statistically significant amount of the variation observed in the seasonal evolution of σ°. An inverse relationship existed between both Ts and K* relative to σ,° and the influence of Ts was approximately twice that of K* in explaining the observed variation in σ°.
Nutrients, oxygen, and inferred new production in the Northeast Water Polynya, 1992
Authors: Wallace D. W. R. , Minnett P. J. , Hopkins T. S.
Published: February 2004

Nutrient and oxygen distributions were measured during a hydrographic survey of the Northeast Water Polynya off the northeast coast of Greenland (77–81°N, 6–17°W) during July–August 1992 and were interpreted in the context of satellite imagery of the region. Satellite imagery revealed a convoluted plume of cold water flowing along isobaths from underneath fast ice in the southwestern portion of the polynya toward the northeast. This plume carried relatively high nutrient and low oxygen inventories. Nitrate to phosphate ratios were low in the polar water, consistent with an ultimate source of this water mass in the Pacific sector of the Arctic Ocean. It is hypothesized that the low N:P Arctic outflow might be the cause of nitrate limitation along the east coast of America as far as Cape Hatteras. Gradients of both nutrients and oxygen inventories in the euphotic zone were observed along and across the axis of mean flow within the polynya and are shown to be due to net production of organic matter. On the basis of these spatial gradients of nitrate and oxygen, an assumed along‐axis current velocity of 10 cm s−1, and the observed relationships of biologically removed inorganic carbon with nitrate and oxygen, the net organic matter production was estimated to be 40–60 mmol(C) m−2 d−1. This represents the organic carbon available for export from the polynya euphotic zone. Nutrient‐deficient and oxygen‐rich waters were observed merging with the southward flowing East Greenland Current, suggestive of possible export, however, the ultimate fate of organic carbon produced within the polynya requires further study.
A note on the bimodal directional spreading of fetch‐limited wind waves
Authors: Young I. R. , Verhagen L. A. , Banner M. L.
Published: February 2004

Measurements of the directional spectra of fetch‐limited wind waves are presented. The directional spreading functions for these spectra are unimodal and narrowest in the region of the spectral peak frequency. Consistent with previous measurements, the spreading broadens for frequencies just above and below the spectral peak frequency. At frequencies of approximately twice the peak frequency, however, the unimodal spreading becomes bimodal, and more wave energy propagates at an angle to the wind than in the wind direction. The bimodal sidelobes continue to separate with increasing frequency and become larger in magnitude. Results obtained with a numerical model with a full solution to the nonlinear terms indicate that the bimodal structure is maintained by directional transfer of energy through nonlinear wave‐wave interactions.
Measurements of the summer surface heat budget of the Northeast Water Polynya in 1992
Authors: Minnett P. J.
Published: February 2004

A research cruise of the United States Coast Guard Cutter Polar Sea to the Northeast Water Polynya (NEWP), off the eastern coast of Greenland (77–81°N, 6–17°W), was made from mid‐July to mid‐August of 1992 (NEWP '92) as the first field component of the multidisciplinary study of a high‐Arctic polynya. Instruments to measure the components of the surface heat budget of the polynya were installed on a foremast at the bow of the ship. Measurements of apparent wind speed and direction, air temperature and humidity, long‐ and short‐wave downwelling radiation were made, together with sea surface temperature. The surface heat budget of the polynya derived from these measurements is presented and is shown to be dominated by the net radiation, with a mean value of 133 W m−2, when calculated over the duration of the cruise. The short‐wave insolation was high during the days with clear skies, reaching over 500 W m−2 at noon and dropping to about 75 W m−2 during the sunlit, polar night, with a mean value of 197 W m−2. In comparison, the mean value of the incident long‐wave radiation is 267 W m−2. In general, the turbulent fluxes were negligible. The measured heat budget is compatible with the observed thermal structure in the surface layers of the polynya and the presumed ice melt during the summer season.
Summer mean circulation of the northwestern Atlantic Ocean
Authors: Reynaud Thierry H. , Weaver Andrew J. , Greatbatch Richard J.
Published: February 2004

The Mellor et al. (1982) method is applied to a new high‐resolution analysis of the temperature and salinity fields in order to determine the summer transport and circulation of the northwestern Atlantic Ocean. This high‐resolution analysis is carried out using an objective analysis scheme which is a modification of that used by Levitus (1982). In view of the strong topographic control exhibited by the circulation features in the area (i.e., the shelf break Labrador and Greenland currents), the scheme preferentially searches for data along, rather than across, isobaths. The horizontal resolution is 1/3° by 1/3°, with 37 vertical levels. The data were obtained from the Marine Environment Data Service archived data and was supplemented by a subset of the National Oceanographic Data Center data from J. Reid and by additional data for the 1980s from Fukumori and Wunsch (1991). Summer mean transports of 49 and 46 Sv are found in the Labrador Sea and the Irminger Sea, respectively. Most of the transport through the region is determined by the transport through the eastern boundary, emphasizing the importance of the eastern Atlantic for determining the circulation in the west. The local wind stress forcing plays a relatively unimportant role in driving the transport in the northwestern Atlantic Ocean. The current structure is obtained by combining the results from the Mellor et al. (1982) method together with a level of no motion (at the bottom) calculation. Using these two methods, the bottom currents are evaluated, and hence the current structure for the whole domain is determined. The results show that the bottom currents follow the planetary potential vorticity (ƒ/H) lines closely. The strongest currents are found along the shelf breaks, offshore from the coasts of Greenland and Labrador. The results also indicate the presence of cross‐shelf flow on the western side of the Labrador Sea. The cross‐shelf transport (∼5 Sv) of fresh shelf waters may well be important in modifying the salinity characteristics, and hence convective properties, of the central Labrador Sea.
Measurements of the evolution of ocean wave spectra due to bottom friction
Authors: Young I. R. , Gorman R. M.
Published: February 2004

Data from a field experiment in which seven wave measurement instruments were placed in a linear transect across the Great Australian Bight are analyzed to determine the spectral decay which can be attributed to bottom friction. Since other processes such as atmospheric input, nonlinear interactions, “whitecap” dissipation, refraction, and shoaling will also be active, the spectral wave model WAM is used as an analysis tool, explicitly taking these additional processes into account in the analysis. The data show marked spectral decay across the shelf. Analysis reveals that the bottom friction coefficient Cƒ is not constant as often assumed in operational wave models. The bottom friction coefficient varies approximately inversely with the wave‐induced bed velocity, consistent with the predictions of previous laboratory data and eddy viscosity models. It is possible that percolation may also be important in the region, but the available data do not allow the relative contributions of bottom friction and percolation to be determined.
Measurements of electromagnetic bias at Ku and C bands
Authors: Arnold D. V. , Melville W. K. , Stewart R. H. , Kong J. A. , Keller W. C. , Lamarre E.
Published: February 2004

The electromagnetic (EM) bias ε is an error present in radar altimetry of the ocean surface due to nonuniform reflection with surface displacement. The electromagnetic bias is defined as the difference in height between the mean reflecting surface and the mean sea surface. A knowledge of the electromagnetic bias is required for reducing errors in mean sea level measurements by satellite radar altimeters. Direct measurements of the EM bias at 14 GHz (Ku band) and 5 GHz (C band) were made from an oil production platform in the Gulf of Mexico over a 6‐month period during 1989 and 1990. A total of 1280 hours of usable data was collected. During the experiment the significant wave height (SWH) varied from 0.6 to 3.2 m; the wind speed at 25 m above the surface varied from 0.1 to 14.3 m s−1; the Ku band bias varied from −1.0 to −13.8 cm, or from −1.6% to −5.3% of the SWH; and the C band bias varied from −0.4 to −19.9 cm, or from −0.6% to −6.3% of the SWH. The biases had mean values of −3.7% and −3.6% of SWH with standard deviations of the variability about the mean of 0.7% and 1.0% of SWH for Ku and C bands, respectively. We found a nonlinear relationship between dimensionless bias (bias/SWH) and wind speed at both low and high wind speeds. For wind speeds less than 3–4 m s−1, both biases were found to be approximately constant. For wind speeds greater than 3–4 m s−1 but less than 10 m s−1, both biases were found to increase linearly with wind speed. For wind speeds greater than 11–12 m s−1, the C band bias reaches a maximum. The Ku band bias reaches a maximum and then begins to decrease for wind speeds greater than 9–10 m s−1.
A triple decomposition of the fluctuating motion below laboratory wind water waves
Authors: Thais Laurent , Magnaudet Jacques
Published: February 2004

Understanding of the dynamics of the top meters of the ocean requires an improvement of present knowledge about interactions between wind waves, mean sheared current, and turbulence. To achieve this goal, a key point lies in relevant definitions and evaluations of orbital and turbulent motions. The aim of this paper is to build and validate a separation technique allowing one to distinguish all three crucial contributions of the fluctuating motion, namely the potential and rotational parts of the orbital motion, as well as turbulent fluctuations. The whole method is first developed and tested for periodic rotational waves. The first step of this technique consists of a determination of the instantaneous stream function associated with the potential motion induced by the waves in presence of a linear sheared current. The second step consists of a linear filtration of the remaining motion from which the orbital rotational motion is extracted. The strong hypotheses involved in the technique are then carefully checked and shown to be relevant in the case of laboratory wind waves. The method is finally applied to experimental data obtained by laser Doppler velocimetry measurements in a wind‐water laboratory facility. Influence of the mean sheared current on the prediction of orbital velocities is pointed out, and the orbital rotational contribution is found to have a significant magnitude.
Primary productivity and new production in the Northeast Water (Greenland) Polynya during summer 1992
Authors: Smith Walker O.
Published: February 2004

The primary productivity and rates of new production were assessed in the Northeast Water Polynya during July–August 1992 by using 14C and 15N tracer techniques. The average rate of primary production for the entire region, including an approximate correction for the effects of ice cover, was 0.21 g C m−2 d−1, with the maximum observed rate being slightly over 1.1 g C m−2 d−1. Rates of new production (uncorrected for effects of ice cover) averaged 3.08 mmol N m−2 d−1. Surface f ratios (the ratio between nitrate uptake and the total inorganic nitrate uptake) averaged 0.63, and depth‐integrated f ratios equaled 0.69. It appeared that the water column in general was bilayered, in that f ratios were reduced near the surface in low (less than 2 μM) nitrate waters and increased deeper in the euphotic zone. Ammonium concentrations and uptake were consistently low throughout the region. Growth rates were modest, with surface growth rates averaging 0.33 per day. A simple relationship among the attenuation of solar radiation by sea ice (and its associated snow cover and microbial community), the percentage of open water, ice thickness, water column attenuation, and phytoplankton photosynthesis is described. The relationship is nonlinear, but, in general, nutrient‐replete water column photosynthesis are largely a function of the percentage of open water rather than ice thickness. Both irradiance and nutrient fields exert strong influences on phytoplankton productivity and ultimately result in a mosaic of biomass within the polynya.
Calculated quantum yield of photosynthesis of phytoplankton in the Marine Light‐Mixed Layers (59°N, 21°W)
Authors: Carder K. L. , Lee Z. P. , Marra J. , Steward R. G. , Perry M. J.
Published: February 2004

The quantum yield ø of photosynthesis (mol C (mol photons)−1) was calculated at six depths for the waters of the Marine Light‐Mixed Layer (MLML) cruise of May 1991. As there were photosynthetically available radiation (PAR) but no spectral irradiance measurements for the primary production incubations, three ways are presented here for the calculation of the absorbed photons (AP) by phytoplankton for the purpose of calculating ø. The first is based on a simple, nonspectral model; the second is based on a nonlinear regression using measured PAR values with depth; and the third is derived through remote sensing measurements. We show that the results of ø calculated using the nonlinear regression method and those using remote sensing are in good agreement with each other, and are consistent with the reported values of other studies. In deep waters, however, the simple nonspectral model may cause quantum yield values much higher than theoretically possible.
Florida Current meanders and gyre formation in the southern Straits of Florida
Authors: Lee Thomas N. , Leaman Kevin , Williams Elizabeth , Berger Thomas , Atkinson Larry
Published: February 2004

Moored current measurements, shipboard hydrography, and a time sequence of satellite‐derived surface thermal images are used to show the formation and evolution of cold, cyclonic gyres coupled to large offshore meanders of the Florida Current in the southern Straits of Florida (SSF). Gyre formation is dependent upon the orientation of the Loop Current as it enters the SSF. With a well‐developed Loop Current the flow overshoots the entry to the SSF causing the formation of a cold recirculation off the Dry Tortugas, approximately 200 km in size, that persists over timescales of about 100 days. The demise of the gyre occurs as it moves to the east at about 5 km d−1, reducing to half its original size off Big Pine and Marathon Keys and unobservable off the northern Keys. Previously observed local gyres between Key West and Islamorada, Florida (Lee et al., 1992), are identified as a latter stage in the downstream evolution of the gyres formed off the Tortugas. When the Loop Current is not developed, flow from the Yucatan Channel turns anticyclonically into the SSF, causing strong eastward flow over the slope off the Dry Tortugas and lower Florida Keys, and gyre formation does not occur.
Structure of an eddy measured with drifters
Authors: Sanderson Brian G.
Published: February 2004

Drifters are used to measure the structure of an eddy on Western Bank, Scotian Shelf over a 5 day period. A regression method that uses both the temporal and spatial structure of flow field observations is presented and used to analyze this eddy. The eddy has vorticity −1.9×10−5 s−1 with divergence, stretching deformation and shearing deformation smaller by more than an order of magnitude. The eddy is centered on the crest of Western Bank. The motion residual to the eddy had a slab like part that moved all points on a plane in a circle without rotation. This latter type of motion can cause substantial error when vorticity and other eddy properties are estimated using methods that operate on a single drifter track. The Eulerian statistics of residual motion show correlations greater than 0.5 are restricted to spatial separations less than 2 km and temporal lags less than 3 h, but motion directed along the vector separating two velocity measurements has a significant Eulerian correlation for timescales of more than 40 hours and length scales of order 5 km. Transverse motion is positively correlated over lesser scales. Much cluster distortion results from subtidal frequency motion that has spatial scales that are seldom coherent over drifter separation scales greater than 2–3 km. The long Lagrangian timescale is inconsistent with a description of horizontal mixing in terms of an eddy diffusion coefficient. Rather, we might picture drifters being dispersed by slowly evolving, narrow streams of current that have larger spatial scales along their axis than across their axis.
Direct inversion method to measure the concentration profile of suspended particles using backscattered sound
Authors: Lee Tae Hwan , Hanes Daniel M.
Published: February 2004

Acoustic backscatter using a single‐frequency transducer can be used for field measurement of irregularly shaped, suspended sediment with a given size distribution. It is assumed that the size distribution of the suspended sediment does not change significantly along the sound path. A newly found explicit solution to acoustic backscatter equation is derived. This explicit solution reduces the computation time significantly during the inversion process. The near‐field effect can be included in the inverted quantities by calculating the initial condition with the far‐field acoustic backscatter equation and under the assumption of uniform near‐field concentration. This method proved successful in the laboratory with initial concentrations of sand up to 3.5 g/L. The errors in estimation of concentration that result from errors in the attenuation coefficients or near‐field concentration are significantly amplified with range in a uniform concentration field. However, with an exponential concentration profile, which is commonly found in sediment suspension phenomena, the inversion is only weakly sensitive to attenuation coefficients associated with sound absorption by water and sound scattering by suspended particles. Near‐field concentration errors result in commensurate errors throughout the range in the exponential profile.
Solar radiation, phytoplankton pigments and the radiant heating of the equatorial Pacific warm pool
Authors: Siegel David A. , Ohlmann J. Carter , Washburn Libe , Bidigare Robert R. , Nosse Craig T. , Fields Erik , Zhou Yimei
Published: February 2004

Recent optical, physical, and biological oceanographic observations are used to assess the magnitude and variability of the penetrating flux of solar radiation through the mixed layer of the warm water pool (WWP) of the western equatorial Pacific Ocean. Typical values for the penetrative solar flux at the climatological mean mixed layer depth for the WWP (30 m) are ∼23 W m−2 and are a large fraction of the climatological mean net air‐sea heat flux (∼40 W m−2). The penetrating solar flux can vary significantly on synoptic timescales. Following a sustained westerly wind burst, in situ solar fluxes were reduced in response to a near tripling of mixed layer phytoplankton pigment concentrations. This results in a reduction in the penetrative flux at depth (5.6 W m−2 at 30 m) and corresponds to a biogeochemically mediated increase in the mixed layer radiant heating rate of 0.13°C per month. These observations demonstrate a significant role of biogeochemical processes on WWP thermal climate. We speculate that this biogeochemically mediated feedback process may play an important role in enhancing the rate at which the WWP climate system returns to normal conditions following a westerly wind burst event.
Deep water formation in the western Mediterranean
Authors: Rhein Monika
Published: February 2004

Wintertime deep convection was studied in the Gulf of Lions (northwestern Mediterranean) using the chlorofiuoromethane (CFM) distributions (components F11 and F12), from December 1991 and February–March 1992. Convection occurred on small spatial and temporal scales and it was not complete: only convection to 1900 m depth was observed. The vertical mixing of the water column above the convection depth turned out to be of major influence regarding the characteristic of newly formed deep water and regarding the boundary conditions for CFMs in modeling deep water formation. Air‐sea gas exchange and entrainment were found to be negligible. These findings are important in estimating deep water formation rates for all water masses renewed by convection (e.g., Greenland Sea Deep Water, Labrador Sea Water) and in evaluating the spreading of deep water masses along the western boundary current. A box model is presented which uses CFM and tritium distributions to estimate formation of Western Mediterranean Deep Water below 1000 m. The model starts with zero tracer concentrations in 1945, the integration step is 1 year, and the deep water formation rate is assumed to be constant from 1945 to 1992. The best fit between CFM model concentrations and measurements were obtained at a mean deep water renewal time of 5–7 years, equivalent to a conversion of 0.46 Sv Modified Atlantic Water (0‐ to 150‐m depth) and 0.76 Sv Levantine Intermediate Water (150‐ to 400‐m depth) into deep water. However, the tritium measurements are only partly matched by the model, by assuming that convection stopped in the years 1964–1968.
An ocean large‐eddy simulation of Langmuir circulations and convection in the surface mixed layer
Authors: Skyllingstad Eric D. , Denbo Donald W.
Published: February 2004

Numerical experiments were performed using a three‐dimensional large‐eddy simulation model of the ocean surface mixed layer that includes the Craik‐Leibovich vortex force [Craik 1977; Leibovich 1977] to parameterize the interaction of surface waves with mean currents. Results from the experiments show that the vortex force generates Langmuir circulations that can dominate vertical mixing. The simulated vertical velocity fields show linear, small‐scale, coherent structures near the surface that extend downwind across the model domain. In the interior of the mixed layer, scales of motion increase to eddy sizes that are roughly equivalent to the mixed‐layer depth. Cases with the vortex force have stronger circulations near the surface in contrast to cases with only heat flux and wind stress, particularly when the heat flux is positive. Calculations of the velocity variance and turbulence dissipation rates for cases with and without the vortex force, surface cooling, and wind stress indicate that wave‐current interactions are a dominant mixing process in the upper mixed layer. Heat flux calculations show that the entrainment rate at the mixed‐layer base can be up to two times greater when the vortex force is included. In a case with reduced wind stress, turbulence dissipation rates remained high near the surface because of the vortex force interaction with preexisting inertial currents. In deep mixed layers (∼250 m) the simulations show that Langmuir circulations can vertically transport water 145 m during conditions of surface heating. Observations of turbulence dissipation rates and the vertical temperature structure support the model results.
Turbulence variability at the equator in the central Pacific at the beginning of the 1991–1993 El Niño
Authors: Lien R.‐C. , Caldwell D. R. , Gregg M. C. , Moum J. N.
Published: February 2004

A 38‐day, 5990‐cast microstructure study on the equator performed during the onset of the 1991–1993 El Niño shows the effect on small‐scale activity at 140°W of an equatorial Kelvin wave. By using two ships, data were taken continuously from November 4 to December 12, 1991, near the National Oceanic and Atmospheric Administration Pacific Marine Environmental Laboratory mooring at O°N, 140°W. The ships occupied the station sequentially with a 3.5‐day overlap for intercalibration. Variability in currents was observed on tidal periods, and periods of 4 days (presumably equatorially trapped internal gravity waves), 8 days (cause unknown), 20 days (tropical instability waves), and longer (Kelvin waves). Variation in water structure occurred most prominently on the timescale of Kelvin waves. The diurnal cycle typical of that location was observed: nocturnal deepening of the surface mixed layer was accompanied by a “deep cycle,” bursts of turbulence penetrating into the stratified region below the nighttime mixed layer. During the observational period, one Kelvin wave trough and one crest passed through the site. Changes accompanying the phase change in the Kelvin wave included a reversal of the near‐surface current, a deepening of the thermocline, and a change of water mass. Changes in small‐scale activity included a tenfold decrease of the thermal dissipation rate and a fourfold decrease of the rate of heat transport downward from the mixed layer. The nighttime mixed layer deepened from 30 to 60 m. The thickness of the stratified region in which nocturnal turbulence bursts occurred, the deep cycle region, thinned from 40 to 20 m because it was confined between the bottom of the nighttime mixed layer and the low‐shear region near the core of the undercurrent. The decrease in downward heat flux observed at this passage of the downwelling Kelvin wave front could explain the rapid sea surface temperature (SST) increase seen at El Nino onsets. The magnitude of the change in vertical flux is similar to the magnitude of the change in horizontal advection. This process would produce a warmer SST much more quickly than could the advection of warm waters eastward.
A note on the evolution equations for the area fraction and the thickness of a floating ice cover
Authors: Schulkes R. M. S. M.
Published: February 2004

In this paper, two sets of evolution equations for the area fraction and the ice thickness are investigated. First of all, a simplified alternative derivation of the evolution equations as presented by Gray and Morland (1994) is given. In addition, it is shown that with proper identification of ridging functions, there is a close connection between the derived equations and the thickness distribution model introduced by Thorndike et al. (1975).