bluuebunny/crossref_metadata_2025 huggingface dataset:
Spring distributions of density, nutrients, and phytoplankton biomass in the ice edge zone of the Weddell‐Scotia Sea
Authors: Nelson David M. , Smith Walker O. , Gordon Louis I. , Huber Bruce A.
Published: February 2008

We collected data on temperature, salinity, nutrient concentrations (nitrate, nitrite, phosphate, and silicic acid), and phytoplankton biomass (chlorophyll a, particulate carbon, nitrogen, and biogenic silica) in the upper 150 m in the marginal ice zone of the eastern Scotia Sea and northwestern Weddell Sea during November and early December of 1983. A distinct hydrographic front separating Drake Passage water from Weddell and Scotia sea surface waters was located at approximately 59°S and was the site of a consistent maximum in phytoplankton biomass. In addition, there was a pronounced phytoplankton biomass maximum associated with a surface salinity minimum near the northern limit of pack ice in the waters of the Weddell‐Scotia confluence that characterized the western portion of the study area. In the eastern half of the study area, characterized by largely unmodified Weddell Sea surface water, the phytoplankton biomass near the ice edge was 2–5 times lower than that in the Weddell‐Scotia confluence but was increasing with time. The water column structure, nutrient fields, and phytoplankton biomass distribution all suggest that the high phytoplankton biomass in the ice edge zone of the Weddell‐Scotia confluence and the lower but temporally increasing biomass near the ice edge in unmodified Weddell Sea water reflect ice edge phytoplankton blooms in different stages of their seasonal development. A bloom had become well established in the waters of the Weddell‐Scotia confluence by mid‐November, but the ice‐free, vertically stable near‐surface water column necessary for enhanced phytoplankton growth had apparently not been present long enough for high biomass levels to develop within the Weddell Sea proper.
Evolution of dissolved oxygen in the Arctic mixed layer
Authors: Top Zafer
Published: February 2008

Various observations of dissolved oxygen in the Arctic mixed layer show that the concentrations vary from a few percent undersaturation to about 10 percent supersaturation. In this work, a balance calculation is attempted based on seasonal sources and sinks of dissolved oxygen. The average calculated concentration was found to vary from about 1 percent undersaturation to about 10 percent supersaturation depending on the boundary conditions.
Coastally trapped waves in the presence of a barotropic shelf edge jet
Authors: Narayanan Savithri , Webster Ian
Published: February 2008

The structures and propagation characteristics of coastally trapped waves on a continental shelf with a barotropic coastal current are analyzed. When the current located on the shelf edge has a velocity in the direction of the phase propagation of the topographic shelf waves and when the topography stabilizes the shear instability, the linearized perturbations on the mean flow consist of propagating shelf and shear wave modes and the evanescent shelf‐shelf and shelf‐shear coalescence modes at complex wave numbers. At low Rossby numbers the shear waves and backward propagating shelf waves coalesce at low frequencies. As the Rossby number is increased, the coalescence occurs at higher and higher frequencies and lower wave numbers. For sufficiently high Rossby numbers, the coalescence may occur directly between the forward propagating shelf wave and the shear wave, the backward propagating shelf wave being eliminated entirely. Hence the manner in which energy is transported along a continental shelf can be fundamentally altered by the presence of a mean current.
Changing transport and curvature bias: A new type of meandering in the Florida Straits
Authors: Chew Frank , Bushnell Mark H.
Published: February 2008

Meanders in strong, inertial flows are generally asymmetric. Florida Current meanders with periods of 7–10 days and flows that tend to meander offshore when strong and onshore when weak, which we call type A, have been widely documented. We find a countertrend in the Florida Current data collected under the aegis of Subtropical Atlantic Climate Studies: a type B meandering where flows tend to meander offshore when weak and onshore when strong. On time scales of several months and depending on the strength of the flow, the tendency displays a largely one‐sided preference for either the onshore or the offshore component of the meander. In particular, the data reveal a negative curvature bias during the generally higher transports in spring and summer when most of the speed cores were inshore, and a positive curvature bias during lower transports in fall and winter when most speed cores were offshore. The data show that any use of cross‐channel sea level slope to estimate the transport would generally overestimate the weaker, but underestimate the stronger flows. Type B meander is interpreted as one of three types embodied in a meandering equation in which curvature changes are controlled primarily by the Coriolis effect of downstream acceleration and hence by that of changing transport. In this light the bimodal paths of the Kuroshio south of Japan is a type B meander.
Instability of concentrated free surface flows
Authors: Trowbridge J. H.
Published: February 2008

Unexpected surface level and discharge oscillations have been reported in tributaries of the Yellow River in China. The oscillations typically occur during the declining part of long‐period flood waves, when the flows carry extremely high concentrations of very fine sediment. The oscillations reportedly cannot be explained by analysis techniques developed for flows of clear water. An analysis is presented in which the flowing material is modeled as a Bingham plastic. The analysis is based on the depth‐integrated mass and momentum equations, with a simplified representation of boundary friction. With reasonable values of the parameters involved, the analysis indicates that the existing qualitative observations of surface and discharge oscillations can be explained by a linear instability to surface waves. Although based on a Bingham plastic model, the qualitative conclusions can be extended to more general types of constitutive behavior.
Measurement of the diffusion coefficients of sparingly soluble gases in water
Authors: Jähne Bernd , Heinz Gerhard , Dietrich Wolfgang
Published: February 2008

The diffusion coefficients D of important gas tracers dissolved in water and seawater were measured with a modified Barrer method. The measurements include the gases He, Ne, Kr, Xe, H2, CH4, and CO2 dissolved in distilled water in the temperature range from 5 to 35°C, and He and H2 dissolved in seawater in the same temperature range. The maximum systematic error is estimated to be well below 5%. The isotopic fractionation in the diffusion coefficient, ∈D, was determined to be (−0.87 ± 0.05)‰ for 13CO2/12CO2 and (15 ± 3)% for 3He/4He.
Interannual variability in the tropical Pacific for the period 1979–1982
Authors: Inoue Masamichi , O'Brien James J. , White Warren B. , Pazan Stephen E.
Published: February 2008

The linear wind‐driven numerical model of Busalacchi and O'Brien (1980, 1981) and the temperature‐depth observations based on the expendable bathythermograph (XBT) data collected by the volunteer observing ships were used to study the interannual variability of the model upper layer thickness and of the observed dynamic height (0/400 dbar) in the tropical Pacific (10°S–16°N and 140°E–90°W) for the period 1979–1982 leading to the onset of the 1982–1983 El Niño‐Southern Oscillation (ENSO) event. Maps of mean and of interannual rms differences for the model and observation show many common features. Maximum interannual variability is found off‐equator in the northwest and southwest tropical Pacific and in the equatorial eastern Pacific. However, there are some notable differences, the major one of which is the model's inability to reproduce the countercurrent ridge. A single eigenvector, which is associated with the ENSO signal, dominates both the model and observation, accounting for nearly 50% of the total interannual variance. This eigenvector represents an east‐west oscillation of the tropical Pacific Ocean, and it is nearly identical in its spatial structure and time amplitude for the model and observation. As for other basin‐wide oscillations with variability of smaller spatial and temporal scales, the model output does not compare well with the XBT data collected by the existing XBT network. Model‐observation cross‐correlation is high in the western and eastern Pacific but not in the central Pacific, pointing to the difficulties in identifying interannual signals where the signals are small with the existing sparse data coverage.
High spatial resolution in vertical slice ocean acoustic tomography
Authors: Cornuelle Bruce , Howe Bruce M.
Published: February 2008

Most studies of ocean acoustic tomography have assumed that little horizontal information is available from the many acoustic multipath travel times observed in a single vertical plane (slice) between source and receiver moorings. There is in fact significant small‐scale information present in such data sets. We examine single vertical slice tomography in spectral terms, and show that the acoustic measurements resemble a high‐pass filter, which is more sensitive to small scales (shorter than 100 km) than to longer scales, with the exception of the mean, which is well measured. The sensitivity extends to scales smaller than 10 km, in theory, although the level of the ocean energy spectrum is so low at these scales that even small data errors limit the measurement. We use analytical calculations supplemented by numerical simulations with realistic data sets to show that accurate reconstructions of the high wave number features are possible out to the limits of the parameterization (9.2‐km wavelength) when the power spectrum of the ocean features is white or red, the total measurement error is 1 ms, and multiple receivers are used. The ultimate limit of spatial resolution may be smaller still, depending on array configuration, measurement errors, and the shape of the power spectrum.
The California Current system: The seasonal variability of its physical characteristics
Authors: Lynn Ronald J. , Simpson James J.
Published: February 2008

The seasonal variation of the physical characteristics and of large‐scale current patterns of the California Current system is examined using harmonic analysis applied to the 23 years of California Cooperative Oceanic Fisheries Investigations data collected between 1950 and 1978. The amplitude and phasing of seasonal variation in dynamic height and the overall standard deviation of dynamic height define three domains: oceanic, coastal, and an intervening transition zone. The transition zone is a broad band centered approximately 200–300 km offshore and parallel to the coast in which the seasonal range of dynamic height is a relative minimum and the standard deviation is a maximum. It is hypothesized that recurrent mesoscale eddies and energetic meanders create this zone. Such eddies and meanders would contribute heavily to the standard deviation of dynamic height but not its seasonal variation. The transition zone is coincident with the core of flow of the California Current. A strong interaction between the core of the California Current and the mesoscale eddy field is evident. Seasonal variation in the fields of temperature, salinity, σt, and oxygen is related to variations in the California Current, the Inshore Countercurrent and the California Undercurrent through vertical adjustments in the density field and through changes in transport. In the undercurrent there is an especially strong relation between seasonal variations in strength of flow and the extreme values of water mass characteristics.
Introduction
Authors: Enfield David B.
Published: February 2008

The scientific papers collected in this volume were presented at the Chapman Conference on El Niño: An International Symposium, held on October 27‐31, 1986 in Guayaquil, Ecuador. The conference was organized by the American Geophysical Union (AGU) under a grant from the National Science Foundation (NSF), who also funded the travel for many of the U.S. participants. Travel for most of the participants from other countries was supported by the Intergovernmental Oceanographic Commission (IOC) and the South Pacific Permanent Commission (Comisión Permanente del Pacífico Sur, or CPPS). Local arrangements for the conference were provided for by the Instituto Nacional de Pesca del Ecuador (INPE) with funds provided by the IOC and AGU.
An investigation of the El Niño‐Southern Oscillation cycle With statistical models: 2. Model results
Authors: Graham Nicholas E. , Michaelsen Joel , Barnett Tim P.
Published: February 2008

We have constructed two sets of linear statistical models for predicting equatorial Pacific sea surfaces temperatures (SSTs) from the tropical wind field and from the near‐global sea level pressure (SLP) field. The wind models were constructed to encompass the domains relevant to the forcing of trapped equatorial waves associated with the El Niño. Thus they provide a measure against which the performance of some simple physical models may be compared. The SLP models were constructed to better define the roles of the observed motion of SLP features and changes in the Southern Oscillation as they relate to subsequent equatorial SSTs. The wind models were designed to provide forecasts at lead times of 1 to 5 months, and the SLP models were designed to provide forecasts at lead times of 7 to 16 months. The models were constructed using a combination of extended empirical orthogonal functions and canonical correlation analysis, a technique we found well suited to the handling of large data sets and the analysis of model structures. Forecast skills were estimated by cross validation. The results show that the wind field models do well at predicting eastern and central Pacific SSTs during much of the year, and their structure is in general agreement with the idea that Kelvin/Rossby waves initiated by remote wind forcing are responsible for much of the observed SST signal. However, the models do not track the onset of warm and cold events well, particularly in the eastern Pacific. This suggests that well‐organized, consistent wind anomalies are not responsible for the initial temperature anomalies. The SLP models did not do well in least squares sense but performed skillfully when applied with a simple El Niño‐no El Niño decision rule at lead times of up to 16 months.
Effects of El Niño on new, regenerated, and total production in eastern boundary upwelling systems
Authors: Wilkerson F. P. , Dugdale R. C. , Barber R. T.
Published: February 2008

The station C‐3 near the upwelling center at 15°S off the Peruvian coast was studied during cruises from March to May during the El Niño year 1976 and the non‐El Niño year 1977. Mean nutrient concentrations, integrated to the base of the euphotic zone, were lower in 1976 than in 1977 (86% for nitrate and 41% for silicate), although the mean surface temperatures in the two years were similar. The 1% light penetration depth was shallower in 1976. Estimates of mean in situ nitrate and ammonium uptake were lower for the El Niño year by about 25% and 69%, respectively, than for the non‐El Niño year. The proportion of new production, ƒ, was higher in 1976, owing to lower integrated ammonium uptake, than in 1977. Mean integrated values for carbon fixation were similar for both years. New carbon production was calculated from carbon fixation values multiplied by ƒ and from the product of nitrate uptake and the Redfield ratio. The values agreed well, except in 1976 when the Redfield ratio calculation yielded a low value due to a distorted C/N uptake ratio, about 15 in 1976 compared to 7 in 1977. The mean of all calculated values of new carbon production was 7.74 mg‐at. C m−2 h−1. The high C/N uptake ratio in the El Niño year suggests a greater than normal interception of up welled CO2 by new production with possible effects on the pCO2 gradient between the ocean and atmosphere. A compilation of the maximum values observed during comparable cruises to three upwelling areas showed maximum values of euphotic zone nitrate concentration and specific nitrate uptake to be reduced considerably during El Niño years, while silicate concentrations remained relatively unchanged.
The El Niño event and its influence on the zooplankton off Peru
Authors: Carrasco S. , Santander H.
Published: February 2008

The Zooplankton groups in general, and the copepoda group in particular, were determined and quantified. Changes were observed in their latitudinal distribution in the area between 6°00′ and 12°38'S and up to 270 n. mi (513 km) off the coast during January and February 1983. The biomass fluctuated between 3 and 18 mL m−2, where the highest values are given by organisms typical of subtropical surface waters such as giltheads, appendicularians, and oceanic copepods. Because of the tropicalizing effect of the study area, a density decrease of larval stages of Zooplankton typical for the area was observed, while prawn larval stages, unusual for the area, were found. Furthermore, there is a significant increase of carnivorous and omnivorous genera of the Copepoda group, such as Centropages, Candacia, Euchaeta, and Labidocera, all identified as predators of anchovy and sardine larvae.
Simultaneity of response of Atlantic Ocean tropical cyclones and Indian monsoons
Authors: Handler Paul , O'Neill Bridget
Published: February 2008

To demonstrate global simultaneity in climatic response to volcanic aerosols, we have picked climate events from two regions separated by ∼180° longitude. These events are the Indian monsoon and the frequency of tropical cyclones in the North Atlantic Ocean, both of which occur during the summer season in the northern hemisphere. The simultaneity of these two regions is shown through several different methods. As a first step, we show there is a strong linear correlation between the deviations from the local averages of these two widely separated climate events. From 1900 to 1986 the correlation is above the 99.75% significance level. In the case of the Indian monsoon, a decrease in solar radiation results in a nonlinear decrease in precipitation. In the case of North Atlantic tropical cyclones, decreased radiation results in decreased occurrence. We divide the Indian monsoon and tropical cyclone seasons, each, into two classes, above or below the local average. We examine the association of this seasonal classification in a χ2analysis using a two by two contingency table, where we find χ2= 13.74 for the period 1900–1986. The probability of achieving this degree of association by chance is less than two parts in ten thousand. Finally, the causal element of the observed simultaneity is hypothesized to be the presence of low‐latitude volcanic aerosols. Over the period 1900–1986 there are 19 seasons in which a known, reported low‐latitude aerosol could have affected the climate anomalies without interference from preexisting, or concurrent, high‐latitude aerosols. Of the 19 seasons, 94% had below normal frequency of tropical cyclones, and in 73% the seasons the precipitation of the Indian monsoon was below normal. A similar analysis is performed for high‐latitude aerosols (≥30° latitude), where opposite results are expected. In this case there are 13 seasons, 46% of which have above normal frequency of tropical cyclones and 77% with above normal Indian monsoons. The Indian monsoon shows a significant response to high‐latitude aerosols, while the tropical cyclone frequency does not. Data prior to 1900 (1871–1899) are shown for completeness. We conclude that there is a significant correlation between the frequency of tropical cyclones in the North Atlantic Ocean and the Indian monsoon and there is little chance that this correlation is due to random events. From the Atlantic to the Indian subcontinent there are simultaneous climatic anomalies in conjunction with the presence of low‐latitude aerosols. While it is possible to conceive of a complex set of internal teleconnections to bring about this climate pattern, the simplest and most economical hypothesis is to assume that global forcing through the reduction of solar radiation resulting from the presence of stratospheric volcanic aerosols may play a major role in producing the observed climate anomalies.
The effect of nonsphericity of marine particles on light attenuation
Authors: Jonasz Miroslaw
Published: February 2008

The assumption that the projected area of marine particles equals the projected area of spheres with volumes equal to those of the particles can result in a significant underestimation of calculated attenuation of light by the particles. This underestimation can reach 300%, depending on the refractive index and size distribution of the particles.
A generalization of the concept of maximal exchange in a strait
Authors: Armi Laurence , Farmer David
Published: February 2008

The concept of maximal exchange through a strait applies to all such flows for which an exchange control region is bounded by supercritical flows at both ends. This includes flows subject to frictional and time dependent effects
An inverse solution for the depth and frequency dependent sediment attenuation of low‐frequency (20–320 Hz) compressional waves
Authors: Mell W. E. , Mercer J. A.
Published: February 2008

The mechanisms that control low‐frequency acoustic propagation and that are unique to the shallow water environment are resident in the seabed. A method of determining the sediment attenuation of low‐frequency compressional waves as a function of frequency and sediment depth is examined. The method utilizes the Backus‐Gilbert geophysical inverse theory, and the emphasis is placed on assessing the resolution and error associated with the inferred structure and the experimental geometry, rather than merely obtaining a solution that fits the simulated data. A laterally homogeneous geoacoustic test model is used to generate artificial data for input to the inverse procedures. The results provide insights regarding resolution and error for generically similar sediments and experimental geometries.
Spectral analysis of ocean profiles from unequally spaced data
Authors: Moore M. I. , Thomson P. J. , Shirtcliffe T. G. L.
Published: February 2008

The spectral analysis of unequally spaced data is discussed with reference to two examples of vertical profiles of internal wave displacement. For our examples, a Conductivity, Temperature, Depth probe was used to record temperature from which the wave displacements were determined. Ship heave, among other causes, resulted in the data being recorded at unequal intervals of depth. Spectral analysis is complicated by unequal data spacing, but the necessity of using an appropriate method is demonstrated by the comparison of results from two such methods with those from two analyses based on equispaced techniques. The equispaced analyses produce results consistent with the currently accepted picture of internal wave spectra but not with the results from the analyses which take account of the unequal spacing. This has important ramifications for Oceanographic spectral analysis procedure. It is clear from our examples that the variability inherent in the unequal spacing has a much greater effect than one might at first imagine. In particular, our examples suggest that important structure at higher wave numbers may be totally lost if inappropriate methods of analysis are used.
Expected differences between buoy and radar altimeter estimates of wind speed and significant wave height and their implications on buoy‐altimeter comparisons
Authors: Monaldo Frank
Published: February 2008

The validation and specification of the capacity of spaceborne radar altimeters to estimate marine wind speed and ocean significant wave height are dependent upon comparisons of these quantities as estimated by radar altimeters and conventional in situ sensors mounted aboard surface buoys. Two important questions are associated with these comparisons. First, what are the expected differences between buoy and altimeter estimates of wind speed and significant wave height? Second, given a knowledge of these expected differences and a finite number of buoy‐altimeter comparisons, what conclusions can be reasonably drawn about the capacity of an altimeter to estimate wind speed and significant wave height? In this paper we outline and quantify the expected differences between buoy and altimeter estimates of wind speed and significant wave height. These differences are categorized as those associated purely with the buoy, purely with the altimeter, or the disparate manner in which buoys and altimeters sample the spatially and temporally varying wind and wave field. Based on these expected differences, statistical tests are given to validate and specify altimeter performance. In addition, statistical approaches to discriminating between candidate algorithms for converting the return pulse characteristics of a radar altimeter into wind speed estimates are discussed.
A note on the mean seasonal transport on the Argentinian shelf
Authors: Forbes M. C. , Garraffo Z. D.
Published: February 2008

A one dimensional model estimation of the winter and summer mean circulation on the Argentinian continental shelf is presented. The model forcing mechanisms are surface wind stress and horizontal density gradients assuming basic Ekman dynamics. The density and wind stress field were obtained from historical data sets. The calculation predicts a northward transport of 1×106 m3/s forced mainly by the wind stress, with largest values in winter. The primary density contribution is found to be from the barotropic density field. The surface velocities obtained were between 10 cm/s in summer and 17 cm/s in winter, toward the NNE. The results are consistent with both observations and other model calculations.
The origin of Norwegian Sea Deep Water
Authors: Swift James H. , Koltermann Klaus Peter
Published: February 2008

A nearly homogeneous water mass, the Norwegian Sea Deep Water, is found below 2000‐m depth in the Norwegian and Lofoten basins of the Norwegian Sea. Recent observations indicate that this water is a mixture of relatively cold and fresh Greenland Sea Deep Water with warmer, saltier Eurasian Basin Deep Water from the Arctic Ocean. We have found this mixture along the western and southern periphery of the Greenland Sea, near the level where the pressure‐compensated densities of the parent water masses are equal. The along‐isopycnal mixing produces a remarkably uniform water mass, which can be traced only a short distance away from its entry into the Norwegian Sea through gaps in the mid‐ocean ridge north of Jan Mayen Island. Direct measurements of flow through these gaps confirm motion in the proper sense to accomplish this connection.
The scaling of turbulence in the presence of stable stratification
Authors: Gargett Ann E.
Published: February 2008

The force of gravity singles out the vertical direction in a stably stratified fluid. Since buoyancy forces remove energy preferentially from the vertical component of velocity, there is a pervasive belief that turbulence in such systems may be significantly anisotropic, with horizontal length and velocity scales greatly exceeding their vertical counterparts. This paper examines the scaling of the equations of motion of a stratified fluid, assuming that the energy‐containing scales of the motion are significantly anisotropic and that nonlinear terms are important in the equations of motion (an assumption of the existence of “turbulence”). Relevant nondimensional parameters are found to be the vertical Reynolds number Rew ≡ wh/v, where w and h are vertical velocity and length scales respectively, and the turbulence Froude number Fr ≡ u/Nl, where u and l are the horizontal velocity and length scales, respectively, and N is the buoyancy frequency. Two determinate scalings are found. The first case, termed buoyancy‐affected high Rew turbulence and characterized by Rew ≫ 1 and Fr ∼ 1, is necessarily isotropic. This scaling has its roots in the work of Dougherty (1961); its use is widespread in recent literature. It is important to recognize this as the appropriate scaling for isotropic turbulence in which the importance of buoyancy forces is in limiting the vertical (hence through isotropy, also the horizontal) scale of the energy‐containing eddies which irreversibly transfer energy to smaller scales, while noting that in a stratified fluid there are other possible modes of motion which can transfer energy reversibly (linear waves) or to larger scales (vortical modes). The second, termed buoyancy‐affected low Rew turbulence and characterized by Rew ∼ 1 and Fr ∼ 1, is truly anisotropic, with the possibility of u ≫ w and h ≪ 1. The field observations of Gargett et al. (1984) and the laboratory observations of Stillinger et al. (1983) and Itsweire et al. (1986) are examined in the context of these scalings. It is concluded that the field observations are characteristic of the buoyancy‐affected high Rew regime, while the laboratory regime may be buoyancy‐affected low Rew throughout its reported evolution. A critical test for the existence of the latter regime is suggested.
Baroclinic instability of buoyancy‐driven coastal density currents
Authors: Qiu Bo , Imasato Norihisa , Awaji Toshiyuki
Published: February 2008

Coastal density currents induced by buoyancy supply along an upper coast are studied in a three‐dimensional numerical model. Scaling analysis of the governing equations reveals that when the vertical eddy diffusivity is small, the horizontal Ekman number Eh = Ahƒ/(g'Qe)2/3 is the crucial parameter determining the structures of the current, where Ah is the horizontal eddy viscosity, Qe is the discharge rate per unit length along the coast, g' is the reduced gravity constant, and ƒ is the Coriolis parameter. Based on numerical experiments with Ah and Qe varied as external parameters, a critical Eh (Ehc) is found between 0.354 and 0.566. The density current develops unstably below this value. In cases where Eh < Ehc, excessive accumulation of fresh water causes sudden density changes near the coast, which eventually breaks down the quasi‐steady balance of the current and triggers small‐scale disturbances in the long‐shore direction. The large‐scale unstable waves induced by these disturbances have length scales of the order of 100 km and an e‐folding time of several days. Study of the energetics revealed that the unstable waves grow via the baroclinic process, and as they develop into the finite‐amplitude stage, an energy transfer from the eddy field to the mean field accelerates the density current near the coast and induces an oppositely flowing mean flow offshore. These induced flows are important in the detachment process of the fully developed unstable eddies.
Recent current observations in the eastern Yellow Sea
Authors: Hsueh Y.
Published: February 2008

Observations of current velocity, pressure, and temperature in the eastern Yellow Sea from January 10 through April 12, 1986, together with geostrophic winds calculated from surface atmospheric pressure distributions, are analyzed for a study of the synoptic band response of the Yellow Sea to the wintertime winds. North wind pulses in the winter monsoon are found to give rise to northward flow bursts in the Yellow Sea trough, which appear to peak just as the wind relaxes and to be driven by a synoptic band north‐to‐south rise in bottom pressure, synchronous with the north‐wind pulses. The existence of a similar rise in coastal sea level indicates that the observed southward pressure rise is but an offshore extension of a setup along the west coast of South Korea forced by the north wind pulses. The advection, by northward flow bursts, of warm water from the south apparently causes the measured temperature to be substantially higher in the trough than in coastal waters at the same latitude and the observed rate of cooling in the trough to be less than half of that in coastal waters to the east. A winter‐to‐spring transition is also found in the bottom pressure records obtained in the trough, in which the mean north‐to‐south gradient in winter reverses suddenly in early March. A similar reversal also appears in sea level records along the west coast of South Korea. The reversal appears to be triggered by the weakening of the north winds at the arrival of spring.
Satellite observations of tidal upwelling and mixing in the St. Lawrence estuary
Authors: Gratton Yves , Mertz Gordon , Gagné Jacques A.
Published: February 2008

Satellite thermal images (NOAA 9) of the St. Lawrence estuary are used to confirm the existence of a persistent cold spot due to tidal upwelling at the head of the lower St. Lawrence estuary and to show that cold water may be found episodically up to 100 km downstream of the head. This extended cold anomaly may exist in two spatial configurations: one confined to near the south shore, the other being centered over mid‐estuary. We discuss the various physical agencies likely to contribute to the growth of this anomaly and conclude that wind, internal tides, and advection of cold water from the head region are the most significant.
Subharmonic edge waves on a large, shallow island
Authors: Foda Mostafa A.
Published: February 2008

Subharmonic resonance of edge waves by incident and reflected waves has been studied thus far for the case of a plane infinite beach. The analysis will be extended here to the case of a curved coastline, with a large radius of curvature and slowly varying beach slope in the longshore direction. It will be shown that the effects of such slow beach slope changes on a propagating edge wave are similar to the familiar shoaling effects on incident waves. The case of subharmonic edge wave generation on large shallow islands will be discussed in detail. The nonlinear analysis will show that within a certain range of island sizes, the generation mechanism can produce a stable standing edge wave around the island. For larger islands the solution disintegrates into two out‐of‐phase envelopes of opposite‐going edge waves. For still larger islands, the generated progressive edge waves become unstable to sideband modulations.
Identification of Savannah River water on the South Atlantic Bight shelf using tritium
Authors: Bush Kathryn A.
Published: February 2008

Tritium and salinity data were used in an investigation of the transport and fate of freshwater on the South Atlantic Bight (SAB) shelf. Simultaneous tritium and salinity samples were collected at selected locations as part of the April 1985 Spring Removal Experiment (SPREX). A three‐source mixing model was used with tritium and salinity as tracers to determine if fresh water from the Savannah River could be distinguished from other freshwater sources on the SAB inner shelf. Variations in tritium concentration, integrated freshwater fraction, and model results were related to hydrographic and meteorological conditions. Results suggest that salinity and tritium concentration can be used to identify Savannah River water on the shelf and that Savannah River water maintains a distinct tritium‐salinity relationship at least as far north as Charleston, South Carolina. Thus tritium may be a convenient and useful tool for studying nearshore mixing and transport processes in the SAB.
Notes on the cluster method for interpreting relative motions
Authors: Kirwan A. D.
Published: February 2008

It is shown that the so‐called cluster method for determining the horizontal gradients of the horizontal velocity has some basic limitations caused by restrictive physical assumptions. For large‐area clusters there is aliasing of these estimates by large‐scale shear, while for small‐area clusters, the displacement of the statistical cluster center from a physically significant flow center can produce seriously aliased cluster model parameter estimates. These effects are independent of typical experimental problems such as measurement error and statistical reliability. An alternative to the cluster paradigm is proposed. This, however, requires solving a nonlinear inverse problem to recover estimates of the horizontal velocity gradients.
The dependence of turbulent dissipation on stratification in a diffusively stable thermocline
Authors: Gregg M. C. , Sanford T. B.
Published: February 2008

To relate the viscous dissipation rate ϵ in the thermocline to internal waves, we operated the multiscale profiler (MSP) in the eastern North Pacific. The location is well removed from fronts and strong currents, and below 0.6 MPa the water column is diffusively stable. Hence internal wave breakdown is the only known source of turbulence. We found that shear levels were in close agreement with the Garrett and Munk model of internal waves and that dissipation rates were low,
. This is the first report of
> (previous observations indicated
) and agrees with predictions by McComas and Müller (1981a) and by Henyey et al. (1986), both based on calculations of energy transfer within the internal wave spectrum.
Tritium and helium 3 in the northeastern Atlantic Ocean during the 1983 TOPOGULF cruise
Authors: Andrié Chantal , Jean‐baptiste Philippe , Merlivat Liliane
Published: February 2008

This study is part of the TOPOGULF program, in which tracer measurements were closely associated with the hydrological data. The sampled area was located near the Azores Islands on the both sides of the Mid‐Atlantic Ridge. The tritium content of the surface waters reveals a strong front along the Azores current. The 3He distributions are used to identify some areas where ventilation processes are active. At depth, the spatial distribution of tritium is studied along isopycnals. In the thermocline it is essentially the anticyclonic gyre which is responsible for the northeast‐southwest gradient in tritium concentrations. The respective influences of the Labrador Sea Water and the Mediterranean Water are noticeable through the tritium data. The Mediterranean Water seems to be an end member responsible for a decrease of the tritium contents in the north and for an increase in the south, by mixing. A quantitative approach using a mixing model is used to check the validity of the 3He‐3H “age.” The model leads to two extreme values of the time scales for the middepth circulation in the studied area: 35 years for the ventilation time of the Labrador Sea Water and around 200 years for the residence time of the oldest waters in the southeastern area.
Atmospheric conditions during the spring and fall transitions in the coastal ocean off western United States
Authors: Strub P. Ted , James Corinne
Published: February 2008

We examine large‐scale atmospheric behavior around the time of the spring and fall transitions in the coastal ocean off the west coast of North America. Records of adjusted sea level (ASL), coastal wind stress, sea level atmospheric pressure (SLP), and 500‐mbar heights for the years 1971–1975 and 1980–1983 are analyzed. The records cover periods of 91 days, centered on the dates of the spring and fall transitions as determined from coastal adjusted sea level data. Empirical orthogonal functions are obtained from the ASL, coastal wind stress, and SLP records. The two dominant modes of the ASL and coastal wind stress are similar around the times of both the spring and fall transitions, and the time series for these modes are highly correlated with one another. Transitionlike behavior is evident in the time series of the first modes in both spring and fall, but the spring transition is more pronounced. Principal estimator patterns, formed from the dominant empirical orthogonal functions show the spatial patterns of SLP which force the ASL and coastal wind stress during the transitions. The SLP pattern which coincides with the spring transition is the formation of a high‐pressure system centered at 45°N and 140°W along with the development of a low‐pressure cell over the southwest continental United States. Inspection of the 500‐mbar height composites for 91 days surrounding the spring transition for the 9 years reveals the formation of a ridging pattern and diffluent flow over the western United States at the time of the transition; following the transition, the ridging relaxes but the diffluent flow over the continent remains for the duration of the 45 days examined here. The fall transition is characterized by a rise in ASL, particularly north of 40°N, and a change from southward to northward wind stress. The SLP pattern which coincides with the fall transition involves the appearance of a low‐pressure system off western North America centered at 50°N and 140°W, representing the passage of synoptic storms through the region. Prior to the fall transition, the 500‐mbar heights are somewhat diffluent and show a trough over the southwestern United States; after the transition the 500‐mbar flow over the northeast Pacific and North America is nearly zonal.
Tower‐based measurements of the ocean C band radar backscattering cross section
Authors: Keller William C. , Wismann Volkmar , Alpers Werner
Published: February 2008

Continuous measurements of the C band normalized radar cross section (NRCS) at vertical/vertical polarization as a function of wind speed and direction were carried out from a research platform in the North Sea during a period of 11 months in 1984. The NRCSs have been correlated with other environmental data routinely collected at the platform, like air‐water temperature difference, water temperature, and ocean wave slope. The wind speed exponent of the C band NRCS at 45° incidence angle was determined as 1.50, valid in the wind speed range 2–19 m/s. Our data set shows that the C band NRCS depends strongly on the air‐sea temperature difference. For example, when the air‐sea temperature difference decreases from +5°C to −5°C, the NRCS increases by 6 dB at a wind speed of 8–9 m/s and an incidence angle of 45°. For stable air‐sea interfaces and low wind speeds the NRCS increases with increasing root‐mean‐square wave slope. However, no systematic dependence on water temperature was observed.
The seasonal and interannual variability of the California Current system: A numerical model
Authors: Pares‐Sierra Alejandro , O'Brien James J.
Published: February 2008

A reduced gravity model that incorporates the geometry of western North America has been used to study the dynamics of the California Current system. Three experiments were performed: first the model was run using 19 years of wind stress from the Comprehensive Ocean‐Atmosphere Data Set (local model); a second experiment (remote model) consisted of forcing the model through its southern boundary using the results of a similar reduced gravity equatorial model; in a third experiment, both forcings were used simultaneously (local plus remote model). The main objective of this work was to analyze the low‐frequency variability on the California Current system in terms of its contributions from remote and local forcing. Away from the coast, the basic (steady) state of the model is determined by the predominantly negative wind curl through a Sverdrup balance. The general seasonal cycle is in agreement with what has been described by other authors. Through cross‐correlation and cross‐spectral analysis between the model results and observed sea level data, it was established that most of the interannual variability in sea level height at the coast is due to disturbances of equatorial origin that propagate into the region in the form of coastally trapped Kelvin waves. For the annual frequency variability, on the other hand, it was found that both local and remotely forced variability contribute to the total variance.
Some observations of the Azores Current and the North Equatorial Current
Authors: Stramma Lothar , Müller Thomas J.
Published: February 2008

The regions containing the two zonal currents of the subtropical gyre in the eastern North Atlantic, the Azores Current and the North Equatorial Current (NEC), have quite different physical characteristics. Associated with the Azores Current are strong horizontal thermohaline gradients that can be located easily both at the surface and at depth with temperature data alone, thus making satellite IR imagery and expendable bathythermograph profiles suitable for observing it. During winter, the surface expression of the Azores Current is often found to the north of the strongest subsurface gradients. In contrast to the Azores Current and to the central water mass boundary just to the south, the NEC has relatively weak horizontal temperature and salinity gradients, requiring density information in order to identify it. There is no clear surface manifestation found with the NEC. Common to both currents, though, is that each transports O(8 Sv) in the upper 800 m of the ocean near 27°W, with the largest velocities being in the upper 400 m.
Dynamical regimes of a fully nonlinear stratified model of the Atlantic equatorial undercurrent
Authors: Wacongne Sophie
Published: February 2008

The dynamical regimes governing various regions of a nonlinear stratified mean equatorial undercurrent are investigated by computing zonal momentum balances in Philander and Pacanowski's (1984) numerical simulation of the equatorial Atlantic. Only in a narrow region of the simulation next to the western boundary does a subsurface regime exist where the positive zonal pressure gradient force overcomes the negative zonal frictional forces, resulting in a net inertial acceleration to the east and in the formation of the eastward undercurrent below westward surface flow. Elsewhere, the net force is westward and the undercurrent, experiencing a net loss of eastward momentum, weakens from west to east. For the parameterizations of frictional processes adopted in the model, zonal momentum is dissipated mostly by vertical friction in the upper thermocline and above, and by lateral friction below. Because the net retarding effect of vertical friction on the upper layers of the undercurrent is larger than that of lateral friction on the lower layers, there is on average an apparent migration of the location of the undercurrent core velocity from above the thermocline in the west of the Atlantic basin to below in the east. The bulk of the mean midbasin model undercurrent can be described as terminating in the overlying westward flow; only a small fraction (the deeper more inertial layers) terminates at the eastern coast. It is argued that the mechanisms at work in the model are plausible ones to explain the zonal evolution of the observed undercurrent, which should motivate a reexamination of existing data. Better agreement between simulated and observed eastern undercurrent speeds might be obtained by reducing the eddy coefficient of lateral mixing used in the simulation.