bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature—plant pigment—optical relations in a recurrent offshore mesoscale eddy near Point Conception, California
Authors: Simpson James J. , Koblinsky Chester J. , Peláez José , Haury Loren R. , Wiesenhahn David
Published: February 2008

The temperature—plant pigment—optical structure of a mesoscale anticyclonic eddy consistently found in shipboard surveys and satellite‐sensed data several hundred kilometers southwest of Point Conception, California, is described on three different time scales (100‐day mesoscale, annual, and several‐year). The satellite coastal zone color scanner (CZCS) ocean color imagery detected the near‐surface chlorophyll structure of the eddy, but in situ optical and plant pigment data suggest that such imagery does not provide a good estimate of the integrated chlorophyll field of the eddy. The temperature and plant pigment boundaries of the eddy, as determined from two‐dimensional gradients of advanced very high resolution radiometer (AVHRR) and CZCS imagery, do not coincide spatially. This and in situ temperature, plant pigment, and optical structure provide additional evidence that some eddy systems in the California Current are not isolated vortex systems but rather continuously entrain waters of nonlocal origin laterally into their upper layers. Within the California Current a ratio of AVHRR/CZCS data is useful for separating inshore from oceanic water masses and following their surface entrainment by offshore vortices. The historical 28‐year California Cooperative Oceanic Fisheries Investigations data for the Point Conception region of the California Current and remotely sensed data over this region show that the Point Conception eddy is a recurrent feature in the offshore California Current. Moreover, the available data provide evidence that a large number of warm‐core mesoscale eddies occur simultaneously in a transition zone between coastal and oceanic regimes, that these features recur at preferred locations within the transition zone, and that this family of eddies should impose a significant offshore boundary condition on the flow of the California Current.
Modeling winds and open‐water buoy drift along the eastern Beaufort Sea coast, including the effects of the Brooks Range
Authors: Kozo T. L. , Robe R. Q.
Published: February 2008

The United States Coast Guard deployed a cluster of satellite‐transmitting, surface‐drifting buoys in the Beaufort Sea north of Prudhoe Bay, Alaska on August 17, 1983. The surface currents in this coastal area are predominantly wind driven. An unusual stand of westerly winds led to eastward drift with the surviving buoys moving into Mackenzie Bay (Canada) by mid‐September. The buoy motion suggested that they were driven by the geostrophic wind modified by the orographic “umbrella” of the Brooks Range. This mesoscale effect can create changes in wind direction and regions of super and subgeostrophic speeds. It influenced an arcuate zone at least 50 km seaward of the coast from Camden Bay (Alaska) to Mackenzie Bay. A simple model was developed to predict the wind modifications and resultant wind‐driven buoy drift. The model's initial wind velocity input is a calculated geostrophic wind derived from triangular‐shaped mesoscale atmospheric pressure network data. These networks were chosen because their boundaries alternately contained the trajectories of the eastward‐moving buoys. The model then used this network velocity to generate an orographically‐modified wind field at buoy locations in offshore areas north of the Brooks Range. The actual buoy drift during the open‐water season covered approximately 650 km in 60 days with the final model‐predicted buoy drift position in error by less than 50 km. The Brooks Range influence did not appear to affect the October buoy drift which was north of Richards Island (Canada) above 70°N and east of 135°N.
Hindcasts of equatorial sea surface dynamic height in the Atlantic in 1982–1984
Authors: du Penhoat Yves , Gouriou Yves
Published: February 2008

Two different wind data sets of the years 1982–1984 are used to force a linear multimode model of the tropical Atlantic ocean. We describe the variations of the equtorial slope in both cases and investigate the differences between the two runs. The main discrepancy occurs in 1983 for the amplitude of the seasonal signal all along the equator. Model results are also compared with observations (hydrocasts and inverted echo sounders) taken during the Programme Français Océan et Climat dans l'Atlantique Equatorial/Seasonal Response of the Equatorial Atlantic (FOCAL/SEQUAL) field experiment (July 1982 through October 1984). The contrast between 1983 and 1984 is well captured by the two runs, especially the abnormal flat topography of the sea surface along the equator in the first 3 months of 1984 due to an unusual basin wide relaxation of the equatorial wind stress. The major discrepancy between model results and observations is found during the up welling periods east of 10°W, but at that time dynamic height measurements are too sparse to give a good description of these events.
On the Kuroshio Extension near the Emperor Seamounts
Authors: Hamann Ilse , Taft Bruce A.
Published: February 2008

In June–July 1982 and November 1983, studies were carried out of the vertical structure of the Kuroshio Extension along 167°E and the path of the current as it approached the Emperor Seamount chain; in addition, records from moored current meters at three locations (two at 167°E and one in the Main Gap of the Emperor Seamount chain) were obtained. The Kuroshio Extension in both 1982 and 1983 turned cyclonically (meander wave length of 450 km) as it approached the chain; the axis of the surface current was located in deep water (>3.5 km) in 1982 and in relatively shallow water (0.5 km) in 1983. In 1982 the horizontal temperature gradient decreased, and the density surfaces down to 2000 m ascended as the Kuroshio Extension flowed over the Emperor Seamounts. In neither year was there evidence of current splitting as it crossed the seamounts. In 1983, in contrast to 1982, there was no weakening of the horizontal temperature gradient, and the Kuroshio Extension went over a very shallow portion of Kinmei Seamount ( < 500 m). The current measurements made at the time of the hydrographic section show that the instantaneous Kuroshio extended to the bottom (abyssal eastward current of 2 cm s−1). The deep low‐frequency eddy kinetic energy values are intermediate between those measured at 152°E and those at 158°W, suggesting a large‐scale eastward decrease in deep eddy activity. Zonal mean flow near 3500 m at 167°E was essentially zero (0.1 cm s−1); the mean meridional components were larger (−2.1 and −0.7 cm s−1). At the southern side of the gap the deep flow was unusually steady (KE/KM < 1) and directed northeastward into the eastern basin of the North Pacific; low ratios (O(1)) were also observed in the lower thermocline compared with those at 167°E (O(10–100)). The frequency content of the gap kinetic energy differed from that measured at 167°E: the highest frequency band (2 hours < P < 2 days) was the most energetic, whereas at 167°E the mesoscale band (20 days < P < 150 days) was the most energetic. The flow in the gap resembles in many of its characteristics that observed in two other channel flows: the Vema Channel and the Charlie Gibbs Fracture Zone.
The effects of a deep channel on the wind‐induced flushing of a shallow bay or harbor
Authors: Hearn C. J. , Hunter J. R. , Heron M. L.
Published: February 2008

Wind‐driven circulation in a shallow bay or harbor is greatly influenced by bottom bathymetry. As a result, the wind‐induced flushing time of the system can be significantly reduced by a deep channel dredged along the prevailing wind direction. In Koombana Bay, on the coast of southwest Australia, there exists a navigation channel of this type. Its effective flushing of the bay is studied here by current meter and drogue deployments, the use of HF radar to measure surface transport, and simulations with idealized long‐basin models and two‐dimensional and three‐dimensional numerical models.
A comparison of methods for estimating u* from given uz and air‐sea temperature differences
Authors: Liu Paul C. , Schwab David J.
Published: February 2008

This paper presents an objective assessment of four methods for estimating sea surface friction velocity u* from wind speed at height z, uz, and air‐sea temperature difference. The methods are compared by using the computed friction velocity as the normalization factor in parametric correlations of wind‐wave parameters with the wind and wave measurements made by NOMAD buoys in the Great Lakes. The results show that (1) wind profile parameters obtained from the four methods are generally comparable, (2) parametric correlations with parameters normalized by u* lead to significantly decreased percentage deviations over correlations normalized by uz, and (3) correlations based on u* derived from the four methods show nearly identical percentage deviations. The conclusions are that (1) u* normalization acts to eliminate the effect of atmospheric stability and (2) any of the four methods can be used effectively in practical applications.
Satellite color observations of spring blooming in Bering Sea shelf waters during the ice edge retreat in 1980
Authors: Maynard Nancy G. , Clark Dennis K.
Published: February 2008

Coastal Zone Color Scanner (CZCS) images of the eastern Bering Sea between April 27 and July 22, 1980, were analyzed in a study of the biological response of the Bering Sea system to the 1000‐km retreat of the ice edge across the shelf and to the subsequent establishment of the highly stratified water column characteristic of spring and early summer. Images from the Norton Sound area showed seasonal changes both in an ice edge bloom near the sound and in the Yukon River sediment plume inside the sound. Three spring images revealed details of several stages of the classic spring bloom development over the shelf which typically begins inshore and progresses offshore. High pigment concentrations were observed over the inner shelf domain in early spring and developing across the middle shelf domain in May. A band of high chlorophyll concentration seaward of the 100‐m isobath in the approximate area of the outer domain, thought to have been caused by periodic offshore movements of shelf waters, was seen in late July. The phytoplankton pigment concentrations derived from the satellite data appeared to be much lower than those observed by the Processes and Resources of the Bering Sea Shelf group, but the spatial and temporal distributions agreed well with trends identified during that experiment. While it is clear that the ice edge and open water spring bloom events together make up the most important component of the seasonal Bering production cycle, the extraordinary spatial and temporal extent of the classic spring bloom over the shelf underscores the significance of the contribution made by this phenomenon to the annual production budget of the eastern Bering shelf.
Horizontal Reynolds stresses in the central equatorial Pacific
Authors: Lukas Roger
Published: February 2008

Seven 13‐month‐long current records from the North Pacific Experiment Hawaii‐to‐Tahiti Shuttle Experiment during 1979–1980 were analyzed to investigate eddy energetics of the upper ocean within 75 km of the equator. Profiling current meter data from the experiment were also used in an attempt to relate the eddy motions to the mean zonal flow. The current fluctuations are highly anisotropic, with zonal current dominating. After removal of a linear trend plus annual and semiannual harmonics, the residual high‐frequency current fluctuations are much more nearly isotropic. The high‐frequency eddy kinetic energy decreases by a factor of 2 over the upper 250 m and at 100 m has a relative minimum on the equator. The seasonal time scale eddy kinetic energy shows a much more dramatic decrease below the thermocline. With the exception of tidal peaks, the spectra of zonal current are red, while meridional current spectra show a flattening at the lowest resolvable frequencies. Meridional current was non‐stationary, with an energetic packet of 10‐ to 15‐day‐period oscillations occurring in early 1980. The off‐diagonal component of the Reynolds stress tensor (〈u′υ′〉) calculated from the high‐frequency residuals is everywhere positive, decreasing from north to south and with depth. The implied cross‐equatorial flux of zonal momentum is at odds with eddy viscosity parameterizations which relate 〈u′υ′〉 to the mean meridional shear of the zonal current. The observed distribution of Reynolds stresses might be explained by radiation of energy from an instability of the portion of the South Equatorial Current north of the equator. In all cases, the high‐frequency u′υ′ time series are significantly skewed toward positive values and show no evidence of periodicity, indicating that the process(es) responsible is(are) intermittent and broadband. This is consistent with the instability mechanism.
Trade wind fluctuations associated with El Niño‐Southern Oscillation events
Authors: Mitchum Gary T.
Published: February 2008

Wind fields associated with El Niño‐Southern Oscillation (ENSO) events are investigated using 20 years (1965–1984) of monthly mean wind vectors along a ship track from 30°S to 30°N in the western Pacific Ocean. The analysis shows that off‐equatorial trade wind fluctuations play a significant role in ENSO events. In particular, the meridional component is found to have strong deviations during ENSO events. Southerly deviations from the mean meridional field are noted during the ENSO events of 1965, 1972, 1976, and 1982. The trade wind deviations are consistent with atmospheric convergence into an equatorial convection region to the east of the ship track. It is hypothesized that these wind fields can cause anomalous oceanic mass convergence toward the equator.
Five‐year climatological survey of the Gulf Stream system and its associated rings
Authors: Auer Stephen J.
Published: February 2008

A 5‐year climatological survey of the Gulf Stream System's landward surface edge defines the mean, standard deviation, extreme limits, annual and interannual variabilities, and frequency distributions along 0.5° longitudinal transects from 91° to 44°W. The climatology covers the Loop Current in the Gulf of Mexico and the Gulf Stream in the northwest Atlantic Ocean. Autocorrelations and power spectra are derived for longitudinal transects between 79.5° and 57.5°W. The study also investigates the observed warm‐core ring and cold‐core ring movements and their areal extent. The observed data are compiled from the Oceanographic Analysis charts (produced by the National Oceanic and Atmospheric Administration) which utilize infrared satellite imagery and in situ observations. East of Cape Hatteras the Gulf Stream System Landward Surface Edge exhibits both interannual and annual signals. The interannual variability is equal to the annual variability. The mean monthly Gulf Stream position for the longitudinal band 70°–44°W shifts from farthest north in September to farthest south in February. The magnitude of the annual shift is largest near the Grand Banks. Frequency distributions of the Gulf Stream System position are quasi‐normal nearly everywhere. Autocorrelation plots from the 5‐year time series of Gulf Stream positions at longitudinal transects 79.5°–57.5°W exhibit three well‐defined e‐folding time regimes with a maximum time of 10 weeks at 72°W. Power spectrums from 79.5° to 57.5°W are red spectrums having dominant peaks of 1‐year period or greater. The largest total spectra energies are found at 61°W. The Loop Current sheds rings at two apparent spatial scales which are labeled major (307‐km mean) and minor (185‐km mean) warm‐core rings. Annually, the Loop Current sheds about one major warm‐core ring which translates into the western basin of the Gulf of Mexico and one minor warm‐core ring which is usually reabsorbed by the Loop Current. The major Loop Current warm‐core ring sheddings have no seasonal preference. Loop Current warm‐core rings have a mean velocity of 2.4 km/d west‐southwest. An average of 22 Gulf Stream warm‐core rings are formed and absorbed annually between 75° and 44°W. The largest frequency of warm‐core ring formations is seen near the New England Seamounts, while the largest frequency of warm‐core ring absorptions is found near Cape Hatteras. Gulf Stream warm‐core rings can absorb each other as occurred in 14% of the absorption cases with the highest frequency just upstream of the New England Seamounts. The Gulf Stream warm‐core rings have a surface diameter decay rate of − 0.026 per week (Loop Current warm‐core rings are similar). The Gulf Stream warm‐core rings have a mean velocity of 2.4 km/d west‐southwest. Cold‐core rings have a mean cool‐core surface diameter of 105 km and a mean velocity of 1 km/d southwest. More definitive conclusions on cold‐core rings are not possible, as ring identification and tracking by satellite infrared imagery is tentative.
The interaction between the undertow and the boundary layer flow on a beach
Authors: Svendsen Ib A. , Schäffer Hemming A. , Hansen J. Buhr
Published: February 2008

The theoretical result for undertow in a surf zone found by Svendsen [1984a] is combined with a boundary layer solution at the bottom, and it is shown that in this boundary layer the eddy viscosity is small relative to that produced by the breaking. The proper eddy viscosity νt between the surface and the bottom boundary layer is determined by comparison with measurements, which leads to quite accurate reproduction of the velocity profiles. The model also predicts the mean flow in the boundary layer and the mean bottom shear stress, and the results are analyzed for sensitivity to inaccuracies in the basic assumptions.
The onset of spring melt in first‐year ice regions of the Arctic as determined from scanning multichannel microwave radiometer data for 1979 and 1980
Authors: Anderson Mark R.
Published: February 2008

Sea ice ablation is an important physical process affecting the global climate system. During the Arctic melt season, rapid changes occur in both sea ice surface conditions and the extent of ice. These changes alter the albedo and vary the surface energy budget. Understanding variations in Arctic sea ice is critical for global climate studies. This paper investigates the spring onset of melt in the Arctic seasonal sea ice zone through analysis of melt signatures derived from Nimbus 7 scanning multichannel microwave radiometer data. Satellite‐derived melt signatures, determined by 18‐ and 37‐GHz vertical brightness temperatures, are associated with the initial melt of the snow pack on the sea ice surface. Sea ice melt events vary spatially and temporally. Within the arctic basin the melt signature is observed first in the Chukchi Sea and the Kara and Barents seas. As melting progresses, the melt signature moves westward from the Chukchi Sea and eastward from the Kara and Barents seas to the Laptev Sea region. The initial location of the melt signal also varies with year. In 1979 the melt signature occurs first in the Chukchi Sea; and in 1980 in the Kara Sea. The date for the initial melt varies between 1979 and 1980 by an average of 7–10 days with a maximum of 25 days in the Chukchi Sea region. Monitoring the occurrence of melt signatures can be used as an indicator of climate variability in the Arctic's seasonal sea ice zones.
Remote forcing of sea surface temperature in the El Niño region
Authors: Lagos Pablo , Mitchell Todd P. , Wallace John M.
Published: February 2008

The relationship between oceanic Kelvin waves forced over the western equatorial Pacific and seasonal and nonseasonal sea surface temperature (SST) variability at the South American coast is investigated using harmonic dial analysis and lag correlation statistics. The seasonal cycle of coastal SST is adequately described by the first two harmonics and is very regular in both El Niño and non El Niño years. In contrast, the seasonal cycle of zonal wind over the western equatorial Pacific varies from year to year and is dominated by years of large negative swings of the Southern Oscillation index. Hence it seems unlikely that the winds over the western equatorial Pacific contribute strongly to the seasonal cycle of coastal SST. For nonseasonal variability the winds with periods shorter than 15 months precede fluctuations in coastal SST by 2 to 4 months, consistent with the remote forcing hypothesis, while for the lower frequencies the SST leads the winds by 2 to 3 months, similar to El Niño composite zonal winds of Rasmusson and Carpenter (1982).
Propagation and forcing of high‐frequency sea level variability along the west coast of South America
Authors: Cornejo‐Rodriguez Maria Del Pilar , Enfield David B.
Published: February 2008

Tide and wind data from coastal and island stations from Buenaventura, Colombia (4°N), to Callao, Peru (12°S), have been analyzed for the 1979–1984 time period to determine the propagation and forcing characteristics of coastal sea level variability at periods of days to weeks, as well as how they vary either with season or between the 1982–1983 El Niño‐Southern Oscillation (ENSO) period and non‐ENSO years. During four non‐ENSO years, the ensemble averaged cross spectra between coastal sea level height (SLH) and local winds show weak evidence of local forcing during the whole year without significant differences between the austral summer and winter seasons, other than a greater energy in the wind fluctuations at Talara during summer. Cross spectra between SLH series from neighboring stations show evidence of poleward phase propagation during winter seasons at speeds of about 2.0 m s−1.between La Libertad and Talara at periods of a week or more, and about 2.7 m s−1 between Talara and Callao at periods of 5–11 days, but no propagation is found during summers. During the 1982–1983 ENSO there is a large increase in SLH energy at most frequencies at all coastal stations, but especially in the 8‐to‐11‐day band, where energies are enhanced by as much as an order of magnitude above non‐ENSO levels. The cross spectra between adjacent SLH stations indicate a nondispersive poleward propagation of events during the 1982–1983 ENSO with phase speeds of 2.2–3.5 m s−1 from La Libertad to Talara (periods of a week or more) and 3.4–3.6 m s−1 from Talara to Callao (3.5 days or more). As with the SLH energy, the coherence and phase propagation were much stronger along the Peru coast in 1982–1983 than during non‐ENSO periods, especially in the 8‐to‐11‐day band. The one‐third increase in phase speeds during the ENSO over the non‐ENSO speeds is found to be consistent with the anomalous depression of the density structure during El Niño. Comparisons between coastal SLH and the local alongshore wind suggest that locally forced SLH variability was obscured during the 1982–1983 ENSO by the noncoastally forced, but energetic propagating fluctuations, which probably originated in the equatorial waveguide.
The impact of the 1982–1983 El Niño‐Southern Oscillation on seabirds in the Galapagos Islands, Ecuador
Authors: Valle Carlos A. , Cruz Felipe , Cruz Justine B. , Merlen Godfrey , Coulter Malcolm C.
Published: February 2008

October 1982 through July 1983, the Galapagos Islands experienced the strongest El Niño‐Southern Oscillation (ENSO) event yet recorded, with heavy rains and a warm, unproductive ocean. During this period most seabirds did not breed, and many left the archipelago altogether. Dark‐rumped petrels which did breed during the event demonstrated low growth rate of chicks. Censuses and observations demonstrated substantial population decreases of other seabirds during the ENSO. Magnificent frigate birds suffered decreased nesting success, while blue‐footed boobies abandoned all nesting attempts. Total censuses of Galapagos penguins and flightless cormorants taken before and after the ENSO demonstrated declines of 77% and 49%, respectively. We discuss the seabird population declines during ENSO and their subsequent recovery.
Semidiurnal tides in the northeast Atlantic from a finite element numerical model
Authors: Vincent Patrick , Le Provost Christian
Published: February 2008

An in‐time spectral method is used to solve the complete nonlinear problem of tide propagation simultaneously over oceanic and coastal areas. For each constituent of the tidal spectrum, the corresponding elliptic modal problem is written under a variational form and solved by using a finite element technique. The model is applied to the computation of the dominant M2 wave over the northeast Atlantic. The numerous in situ data over this domain and the large extent of the European continental shelf allow analysis of the gain of accuracy obtained by different components characterizing the model. To get a mean accuracy of less than 2 cm and 2° for the amplitudes and phases of the sea surface elevation, it is found that (1) the use of a refined mesh over the shallow areas and of a quasi‐linearized version of the quadratic Chezy friction law is essential; (2) loading effects computed by means of a Green integral have to be taken into account; and (3) accurate boundary conditions need to be prescribed at the entrances of dynamically active shallow water areas if they are not included in the investigated area (or it is necessary to extend the model over the whole neighboring coastal basin if these boundary conditions are not available). From the M2 velocity field solution, bottom friction coefficients are derived for the secondary astronomical constituents of the tidal spectrum, and accurate charts of the S2 and N2 tides are produced over the modeled area.
On the parameterization of equatorial turbulence
Authors: Peters H. , Gregg M. C. , Toole J. M.
Published: February 2008

Profiles of currents, density, and microstructure were obtained in the Pacific Ocean on and near the equator at 140°W in late 1984 as part of the Tropic Heat program. During a 4½‐day time series on the equator, the shear zone above the core of the undercurrent had very low mean Richardson numbers, Ri, between ¼ and ½. Average turbulent dissipation rates, ε, were high in this zone, ≈ 10−7 W kg−1, and varied by a factor of 100 between minima in the early afternoon and maxima at night. The signal reached to 90 m, well into the stratified zone. Eddy coefficients, K, were low at high Ri, and gradually increased as Ri decreased, until they rose dramatically near Ri = ½. The observed K(Ri) relations are specific to time, location, and temporal and spatial resolution of the data.
The vertical structure of density and turbidity currents: Theory and observations
Authors: Stacey Michael W. , Bowen Anthony J.
Published: February 2008

A simple numerical model is developed that successfully simulates observations of small‐scale, laboratory, density currents flowing down inclines of constant slope. The model results suggest that laboratory determinations of the bulk Richardson number have been biased by molecular processes but that determinations of the entrainment coefficient are probably applicable to large‐scale currents, and even to turbidity currents in which the gravitational driving force is provided by suspended sediment. The entrainment coefficient is a function of the gradient Richardson number Ri above the velocity maximum in both density and turbidity currents; Ri is itself a strong function of the bottom slope but not of the sediment settling velocity or the roughness of the bottom boundary. Therefore for a given bottom slope the entrainment coefficient is uniquely defined. The bulk Richardson number Ri0, on the other hand, is additionally a function of the drag coefficient, which depends on both the Reynolds number and the bottom roughness. However, Ri0 is not a strong function of the sediment settling velocity as long as the current is energetic enough to maintain sediment in suspension.
The vertical structure of turbidity currents and a necessary condition for self‐maintenance
Authors: Stacey Michael W. , Bowen Anthony J.
Published: February 2008

A simple numerical model predicts that properties of a turbidity current can vary significantly in the vertical direction, particularly when more than one sediment size is in suspension. Each sediment size decreases in concentration with increasing distance from the bottom boundary at a rate which depends on its settling velocity, the current velocity, the entrainment coefficient, and the bottom slope. However, it is shown that the details of the vertical distribution of sediment load do not necessarily greatly influence either the vertical structure of the hydraulic properties of the flow (velocity, stress) or the bulk properties such as the entrainment coefficient, at least when only one sediment size is in suspension. The ability of a turbidity current to sustain itself is strongly dependent on the sediment load and an autosuspension criterion is obtained by taking into account the vertical structure of the currents. The model turbidity currents often cannot maintain their sediment in suspension even when the bottom stress is greater than the critical stress of deposition for low concentration flows. When this happens, the concentration near the bottom increases without limit as the turbidity current evolves with time. In real turbidity currents, grain‐grain interactions, which become important at high concentrations, may at times cause the current to quickly deposit its near‐bottom sediment load. This is suggested as a possible mechanism for the formation of the poorly sorted sediments frequently found in turbidites.
Film drop production as a function of bubble size
Authors: Blanchard Duncan C. , Syzdek Lawrence D.
Published: February 2008

Film drops from air bubbles bursting in seawater and in a 3% solution of sodium chloride in distilled water were counted with a condensation nucleus counter. Bubbles of known size were released from a capillary tip at depths from 1 to 20 cm beneath the surface of the water. Film drop production did not vary significantly with depth in seawater, but it decreased by about 3 times as the depth was increased to 10 cm in the sodium chloride solution. Drop production, however, varied markedly with bubble size. Over the range of bubble sizes studied (from about 1 to over 6 mm diameter), by far the most film drops were produced in the narrow size range of about 2–2.5 mm. About 75 film drops per bubble were found for the seawater case, and about 150 for the sodium chloride solution. On either side of this peak (bubbles of 1.5 and 2.8 mm), film drop production was less than 5 per bubble. The cause of this strong peak in drop production is not known, but it appears that bubbles of 2 to 2.5 mm diameter must play a major role in the production of film drops at sea.
The boundary currents east and north of Madagascar: 2. Direct measurements and model comparisons
Authors: Schott Friedrich , Fieux Michèle , Kindle John , Swallow John , Zantopp Rainer
Published: February 2008

Moored current measurements of 11‐month duration were carried out in the boundary currents east of Madagascar, near 12°S at Cape Amber where the mean current flows northwestward and near 23°S where the mean current flows approximately southward. Transports derived from the moored current measurements in the depth range 150–1100 m compare reasonably well with those derived from ship sections by Swallow et al. (this issue). At 12°S, very energetic boundary current transport variations occur in the 40‐ to 55‐day‐period band, contributing about 40% to the total transport variance, while at 23°S the 40‐ to 55‐day‐period band fluctuations contribute only 15% to the total transport variance. The fluctuations near 12°S do not seem to be caused by local wind forcing, which does not show an energy peak in this period band. A significant annual cycle cannot be detected in the moored current and transport time series despite significant variation of wind forcing over the subtropical Indian Ocean. A comparison of the observations is carried out with two different numerical Indian Ocean models, both forced by the seasonally varying winds of Hellerman and Rosenstein (1983). A reduced‐gravity model gives mean boundary current transports which compare well with the observations and also shows a negligible seasonal cycle. The multilayer Geophysical Fluid Dynamics Laboratory model also shows a small seasonal cycle. The observational evidence from the western subtropical Indian Ocean appears to be similar to that from the subtropical North Atlantic east of the Bahamas‐Antilles arc where also no significant seasonal boundary current response was detected, despite large annual variation of wind forcing over the ocean. The two observational situations and numerical model results for both oceans are compared.
Surface manifestations of subsurface thermal structure in the California Current
Authors: Fiedler Paul C.
Published: February 2008

Remote sensing is useful for studying certain Oceanographic problems only if the signal obtained from the sea surface contains information about subsurface structure. Historical bottle temperature data from the California Current were analyzed for surface manifestations of vertical structure and subsurface mesoscale structure. Results showed that surface temperature is useful in predicting thermocline strength over a large area south of Point Conception: the error of a regression estimate is 20–30% less than the error of the seasonal mean. However, surface temperature gives little useful information about mixed layer depth. Mesoscale patterns of temperature at the surface and at depth (caused by eddies, meanders and up welling) are coherent (r2 > 0.50) to a depth below the mixed layer only off central California and Point Conception and along the coast of Baja California. Coherence is most likely to extend below the mixed layer during summer, when the water column is strongly stratified and the mixed layer is most shallow. Thus some aspects of subsurface structure, within limited regions of the California Current, have surface manifestations potentially detectable by satellite sensors.
A shallow water spectral wave model
Authors: Young Ian R.
Published: February 2008

A shallow water spectral wave prediction model based on a numerical solution of the radiative transfer equation is presented. The model is second generation and uses a simple yet effective representation for the nonlinear source term. In addition, the model pays particular attention to the shallow water processes of refraction, shoaling, bottom friction, and wave breaking. The flexibility of the model is demonstrated by an intercomparison with field data from a number of tropical cyclones. The turning winds from such storms provide a demanding test of model physics. The comparisons are in both deep and shallow water.
Tower Ocean Wave and Radar Dependence Experiment: An overview
Authors: Shemdin O. H.
Published: February 2008

The Tower Ocean Wave and Radar Dependence Experiment (TOWARD) is a coordinated effort, involving both field experimentation and theoretical investigations, to address the divergent hypotheses on the mechanisms involved in synthetic aperture radar (SAR) imaging of the ocean surface. In the formulation of the experiment it was recognized that three distinct disciplines were to be addressed: (1) hydrodynamics, (2) radar backscatter, and (3) SAR image processing. The field operations were executed in three 6‐week segments during the period October 1984 to January 1986. The Naval Ocean Systems Center tower, located offshore of Mission Beach, San Diego, California, was used as the focal point for the field operations. The primary measurements included in situ capillary and short gravity waves, long surface waves and internal waves, ambient current and detailed meteorological measurements, stereophotography, tower‐based multifrequency radars and an L band SAR deployed on board the NASA CV‐990. The single most significant result is the determination that none of the available hypotheses on SAR imaging of long surface waves could be demonstrated to explain all the SAR observations obtained in TOWARD. Specific results are reported.
Acoustic Doppler current profiling in the equatorial Pacific in 1984
Authors: Wilson Doug , Leetmaa Ants
Published: February 2008

Hydrographic data and acoustic Doppler current profiles collected from 150°W to 85°W in the equatorial Pacific during 1984 showed significant seasonal changes in the temperature and velocity fields. On the equator, the surface current was eastward in April up to 80 cm s−1, reversing to westward at 100 cm s−1 by November. Over the same period, the Equatorial Undercurrent (EUC) transport decreased, the equatorial zonal pressure gradient (ZPG) increased, and the depth of the mixed layer and EUC core deepened. Off the equator at 150°W, the North Equatorial Countercurrent (NECC) was absent in April/May but pronounced in October/November. Superimposed on this seasonal variability were smaller‐scale (roughly 1000 km wavelength) correlated fluctuations in the upper ocean temperature and velocity fields. We identify these structures with the 20‐ to 30‐day instability waves [Legeckis, 1977]. The coincident high‐resolution velocity and temperature data allowed the calculation of Reynolds' stresses due to the waves and resultant heat and momentum flux estimates as well as details of the vertical phase structure. Barotropic instability at the northern edge of the EUC is a likely source of energy for these waves. Estimated EUC transport decreased from 50 in April to 25 × 106 m3 s−1 in November while the westward wind stress doubled and the 0‐/400‐dbar ZPG quadrupled. The data were used to estimate terms in the momentum balance in the upper 150 m, and it was found that nonlinear terms were often at least as important as the integrated ZPG in balancing the surface wind stress. East of 120°W, the eastward advection of eastward momentum, UUx, was particularly important. These momentum equation terms were used to estimate a profile of the coefficient of vertical eddy viscosity; it was similar to profiles estimated by bulk methods and by parameterization by Richardson number.
Modification of ocean eddies by air‐sea interaction
Authors: Williams Richard G.
Published: February 2008

A mixed‐layer model is developed for seasonal time scales and used to investigate the modification of ocean eddies by air‐sea interaction. An eddy is modified by the air‐sea interaction for the local envionment and the feedback from its surface temperature signal, which alters the surface heat and water fluxes. This buoyancy forcing tends to decrease the eddy temperature anomaly, and seasonal changes in mixed‐layer depth lead to the surface signal being removed in summer and reappearing in winter. The dynamical adjustment of the eddy is assessed by coupling the mixed‐layer model to a quasi‐geostrophic model: the buoyancy forcing alters the eddy velocity profile and, over several seasons, may lead to the formation of a subsurface velocity maximum. After the spring decrease in mixed‐layer depth, the eddy potential vorticity anomaly is reduced, and lateral mixing may subsequently play a role in further eroding the eddy. These modelling predictions are supported by the observations of a cold‐core eddy in the seasonal boundary layer of the northeast Atlantic.
The origin of eddy heat fluxes in the northern California upwelling regime
Authors: Send Uwe
Published: February 2008

Observed eddy heat fluxes, i.e., covariances between heat content and horizontal currents, are analyzed with moored data from the Coastal Ocean Dynamics Experiment. It is demonstrated that much of each sampled covariance arises from the separate correlations of currents and temperature with the upwelling variability, which is attributed to the particular warming and cooling processes present. Thus a large part of the observed eddy heat fluxes is wind driven. The remainder is consistent with being largely statistical noise in the observed covariance between those parts of the flow and temperature which are not correlated with the upwelling. This also suggests that the wind‐driven part alone might be a better estimate of the ensemble average eddy heat flux.
Simulated effects of barometric pressure and ozone content upon the estimate of marine phytoplankton from space
Authors: André Jean‐Michel , Morel André
Published: February 2008

Barometric pressure and total ozone content may significantly depart from their mean climatology values; these values, however, are used when processing the visible remote sensing (VRS) data with the aim of estimating the phytoplanktonic pigments concentration (chlorophyll a + phaeophytin a, in milligrams per cubic meter) within the upper ocean. The effect of ignoring such departures upon the retrieved concentration has been simulated for the broad oceanic range (0.015–20 mg/m3). The simulation is effected for typical VRS situations (geometry, aerosol) when information about the variable aerosol is not available when entering the processing (as is the case with the Coastal Zone Color Scanner (CZCS) data) or, conversely, when such information has been separately obtained (simulation of future sensors with dedicated near‐IR channels). The result is that in both these cases the use of mean climatology values leads to variable misestimates of the pigment content, by a factor of up to 2 in many common VRS situations, and above 2 for very low or high actual pigment content. After the results are discussed, the conclusion is that the actual values of the barometric pressure and of the ozone content will have to be introduced in the processing of future visible sensor data in order to preserve the expected accuracy. With regard to the exploitation of the CZCS archive, this requirement is not so essential, insofar as the pressure and ozone effects on the pigment concentration retrieval remain of the same order as the noise due to the limited radiometric accuracy of this sensor. However, at the scale of a CZCS scene, neglecting the strong structures in the pressure and ozone content fields may bias the phytoplankton concentration mapping. The use of the actual values is therefore recommended.
Mixing in the equatorial surface layer and thermocline
Authors: Moum James N. , Caldwell Douglas R. , Paulson Clayton A.
Published: February 2008

Twelve days of microstructure measurements at the equator (140°W) in November 1984 showed a surprisingly strong effect of both the daily cycle of solar heating and wind on mixing in the upper ocean. Because of limited variations in atmospheric forcing and currents during the experiment, processes in the daily mixing cycle were similar from day to day. Only the intensity of mixing varied. The lower boundary of the diurnal surface layer separated two distinct mixing regimes, the diurnal surface layer and the thermocline. Within the diurnal surface layer (which extended to 10‐ to 35‐m depth), turbulent kinetic energy dissipation rates ε varied relatively little. Although variations in surface layer depth coincided with the daily change in direction of air‐sea surface buoyancy production of turbulent kinetic energy (or simply, the surface buoyancy flux), ε was significantly greater relative to the buoyancy flux than was expected for a simple convective layer. In the thermocline below the diurnal surface layer, ε was highly intermittent; the day‐night cycle was stronger, and variability was enhanced by turbulent “bursts” of 2–3 hours duration, which may be related to internal wave breaking events. The turbulent heat flux crossing 20‐m depth was almost equal to the surface heat flux less the irradiance penetrating below 20 m. Seventy percent of the surface heat flux was transported vertically to the water below 30 m by turbulent mixing. Only a negligible amount penetrated to the core of the Equatorial Undercurrent. The gradient Richardson number Ri distinguishes between statistically different mixing environments. However, ε cannot be predicted from the value of Ri, since the intensity of mixing depends on the intensity of forcing in a way not specified by the value of Ri alone.
Sea surface inclination due to the effect of the Coriolis force on an ocean current
Authors: Rikiishi Kunio , Sato Hiroshi , Matsuo Syogo
Published: February 2008

A unique data set of simultaneous observations of the ocean current and absolute sea surface slope in the Tsugaru Strait, Japan, has been analyzed in order to examine the effect of Coriolis force on an ocean current. First, the mean surface slope across the strait (an average over the period 1972–1980) was compared dynamically with the mean ocean current along the strait (an average over the period 1953–1978). It was found that both are in good geostrophic balance. Next, time variation of the ocean current was compared with that of sea surface inclination. In the subtidal frequency range, the variation in current velocity was found to be followed by the variation in sea surface inclination such that both are generally in geostrophic balance. Although some imbalances are seen, most of them can be explained by the sea level changes caused by the storm surge or wave setup. In the tidal frequency range, the dynamical relation between the current velocity and inclination shows good agreement with the theory. The downstream component of the balance is maintained mostly by the local acceleration and pressure gradient terms, and the cross‐stream component is maintained by the Coriolis force and pressure gradient terms.
Acoustic Doppler current profiler observations of a mid‐ocean ridge hydrothermal plume
Authors: Thomson Richard E. , Gordon R. Lee , Dymond Jack
Published: February 2008

On September 10, 1987, an oceanic profiling package consisting of a Guildline conductivity‐temperature‐depth probe (CTD), SeaTec transmissometer and RD Instruments 150‐kHz acoustic Doppler current profiler (ADCP) was used to investigate the hydrothermal plume emanating from vent sites located at 2200‐m depth on the Endeavour segment of Juan de Fuca Ridge in the northeast Pacific Ocean (47°58′N; 129°06′W). The CTD‐transmissometer profiles indicate that the plume immediately downstream of the vent site consisted of two 50‐m‐thick particle‐laden effluent layers separated by a comparably thick zone of relatively particle‐free ambient fluid. The lower 50 m of the water column appeared to be dominated by smaller concentrations of resuspended particles within a benthic boundary layer. Maximum temperature, salinity, and light attenuation anomalies within the main core of the plume at 1970‐m depth were approximately +0.04°C, +0.01 ppt, and +0.05 m−1, respectively. The ADCP measurements represent the first attempt to acoustically map the current shear and backscatter amplitude associated with a mid‐ocean ridge hydrothermal plume. Repeated profiles by the ADCP revealed that the top of the plume was a region of enhanced current shear with vertical changes in speed of the order of 0.05 m s−1 over depths of approximately 100 m. The velocity measurements also indicate that the current reversed from northwest to southwest over the 1‐hour observation period, consistent with the predicted flow derived from moored current meters recovered immediately prior to the profiler survey. Contrary to expectation, acoustic backscatter signals within the particle‐laden layers of the plume were lower than background reference levels, while echo return amplitudes from the particle‐free layer were close to background levels. Time series plots of the amplitude data indicate that the basic layered structure of the plume is disrupted by billowlike features with vertical and horizontal wavelengths of 40 to 60 m and 20 to 40 m, respectively. We suggest that the weakened acoustic backscatter signals from the effluent layers is linked to a reduction in the numbers of zooplankton relative to the ambient waters.