bluuebunny/crossref_metadata_2025 huggingface dataset:
On the seasonal variability of the Alaska Coastal Current
Authors: Johnson Walter R. , Royer Thomas C. , Luick John L.
Published: February 2008

Current measurements of the Alaska Coastal Current were analyzed for their mean structures and seasonal cycles. The current is westward (alongshore) at the surface, 25 to 175 cm S−1, with a baroclinic shear of 30 cm s−1 in the upper 70 m. The amplitude of the seasonal variation of the flow decreases with depth, and its maximum phase delay of 3 months occurs at 175 m relative to the surface. The amplitude of the seasonal cycle of the north‐south (cross‐shore) flow is a minimum at mid‐depth. The phase of this seasonal cycle is also delayed at deeper depths, but the maximum shift relative to the surface occurs at 110 m rather than at the bottom (175 m). Empirical orthogonal function analysis indicates that the first mode of the alongshore flow has nearly constant amplitude with depth (barotropic variations) and is related to the east–west wind. The second mode explains significant variance of the surface current and the freshwater discharge. The cross‐shore flow analysis shows that the first mode is again nearly barotropic and is principally related to the east‐west wind, with increased southward flow when the winds are increased westward. The second mode of the cross‐shore flow fluctuates with runoff such that the offshore flow at the surface and the onshore flow near to the bottom coincide with increased freshwater discharge.
Comparison of measured and predicted sea surface spectra of short waves
Authors: Shemdin O. H. , Hwang P. A.
Published: February 2008

Reliable sea surface slope time series, using a laseroptical receiver system deployed on a wave follower, are analyzed to yield slope frequency spectra of the ocean surface up to 300 Hz. The results show significant differences when compared with the Pierson and Stacy (1973) model. An empirical model is proposed in this paper that is consistent with the observed slope spectra. The newly proposed model is compared with other more recently advanced shortwave spectral models.
A new method for estimating the turbulent heat flux at the bottom of the daily mixed layer
Authors: Imawaki Shiro , Niiler Pearn P. , Gautier Catherine H. , Halpern David , Knox Robert A. , Large William G. , Luther Douglas S. , McWilliams James C. , Moum James N. , Paulson Clayton A.
Published: February 2008

A new method is presented for estimating the vertical turbulent heat flux at the bottom of the daily mixed layer from the temperature data in the mixed layer and net solar irradiance data at the sea surface. We assume that fluctuations in the divergence of advective heat flux have longer than daily time scales. The method is applied to data from the eastern tropical Pacific, where the daily cycle in the temperature field is confined to the upper 10–25 m. The night‐to‐day difference of the turbulent heat flux calculated from the data obtained during nine daily cycles in November 1984 agrees well on average with the same quantity estimated from microstructure observations. The night‐to‐day difference of the turbulent heat flux, estimated at several mooring stations near the equator (an average over 100 to 300 daily cycles), varies from 120 to 220 W/m2 with larger values on the equator. Equatorial turbulence measurements show that the turbulent heat flux is much larger during nighttime than daytime. Therefore the present estimates give approximately the nighttime average, which is the major part of the turbulent heat flux. From the daytime heat budget we obtain divergence of the low‐frequency horizontal heat advection at 1°30′S, 140°W; it is governed by equatorial mesoscale fluctuations having a predominant period of 15–20 days.
Surface heat flux in the northern Gulf of California
Authors: Lavin M. F. , Organista S.
Published: February 2008

Recent coastal meteorological data (1979–1986) are used to evaluate the seasonal cycle of surface heat fluxes in the northern Gulf of California. Although net heat loss occurs from October to January, the annual mean of the net surface heat flux was found to be into the sea (69 W m−2 near the coast and 83 W m−2 offshore), with a mean evaporation rate ≃0.9 m yr−1. These results require an oceanic export of heat and salt out of the northern gulf to achieve a balance, and imply that the annual mean thermohaline circulation must have an inflowing component at depth, thus enriching the central and northern parts of the gulf. These results differ from previous meteorological estimates, which suggested a net surface heat loss, but confirm those based on hydrographic data.
Transports through Bering Strait: Annual and interannual variability
Authors: Coachman L. K. , Aagaard K.
Published: February 2008

Reanalysis of the 1976–1977 mean monthly transport estimates for Bering Strait of Coachman and Aagaard (1981) shows a considerably stronger wind dependence than was calculated by Aagaard et al. (1985). We find (1) a long‐term mean transport of 0.8 Sv, (2) an annual transport cycle of amplitude 0.6 Sv, with the maximum in June, the minimum in February, and a secondary maximum in January probably associated with North Pacific blocking‐ridge activity, and (3) an interannual variability marked by a number of low‐flow years in the past two decades, including three of the four lowest‐transport winter periods during this century. In a new current time series from 1984 to 1985 we find anomalously strong and persistent northerly flow during a 2‐month period in which the current/wind correlation breaks down. This occurred during a prolonged period with southerly winds, and we believe the data point to an asymmetry in the dynamical response of the Bering Strait flow to major changes in wind direction.
Loop Current boundary variations
Authors: Vukovich Fred M.
Published: February 2008

The periodicity of warm ring separation from the Loop Current and the characteristics of cold perturbations found along the Loop Current boundary were studied using a long‐term data set made up of NOAA satellite infrared images. The results showed that the period between separation of warm rings from the Loop Current was highly variable. The average period was about 10.9 months. The minimum period was 6 months, and the maximum period was 17 months. For the data set used, ring separations occurred most often in the winter. The study of the cold perturbations indicated that these perturbations were most pronounced along the northern and eastern portions of the Loop Current boundary and were less pronounced south of 27°N along the western boundary. The data suggested that the perturbations either formed or intensified in the northwestern portions of the boundary. The large effects along the eastern boundary of the Loop Current were thought to be associated with the movement of the intense perturbations that are initially found along the northwestern portions of the boundary.
Surface waves on vertically sheared flows: Approximate dispersion relations
Authors: Kirby James T. , Chen Tsung‐Muh
Published: February 2008

Assuming linear wave theory for waves riding on a weak current of 0(ε) compared to the wave phase speed, an approximate dispersion relation is developed to 0(ε2) for arbitrary current U(z) in water of finite depth. The 0(ε2) approximation is shown to be a significant improvement over the 0(ε) result, in comparison with numerical and analytic results for the full problem. Various current profiles in the full range of water depths are considered. Comments on approximate action conservation and application to depth‐averaged wave models are included.
Evidence for wind‐driven current fluctuations in the western North Atlantic
Authors: Brink K. H.
Published: February 2008

Two subsurface current meter moorings were deployed for 20 months along 70°W in a low‐energy portion of the western North Atlantic. The resulting data were compared with estimates of the wind stress curl in an attempt to seek a relationship between currents below the mixed layer and meteorological forcing at subinertial frequencies. Currents and temperature tend to be significantly coherent with the curl and are most coherent with the curl at remote locations, usually more than 500 km away from the mooring and generally to the east. Coherences generally decrease with increasing frequency. The current response is surface intensified. A linear stratified model for stochastically wind‐forced Rossby waves in a flat‐bottomed ocean is presented as an attempt to rationalize the results. The effort was not entirely successful, so that it appears that a more realistic model, perhaps including bottom topography and mean currents, will be needed to rationalize these observations fully.
Statistical geometry of a small surface patch in a developed sea
Authors: Glazman Roman E. , Weichman Peter B.
Published: February 2008

Based on short‐range asymptotics for the structure function, D(r) = L2μ(μ)r2−2μ − B(μ)r2, the fractal (μ>0) and the marginal fractal (μ = 0) regimes in surface geometry are studied. The analysis is self‐contained in that it provides a brief exposition of basic notions of fractal geometry (for a monofractal case) as applied to a small surface patch corresponding to the equilibrium wave number spectrum of the form αk−4+2μϒ(θ). Effects of the fractal codimension μ and of the inner and outer scales on the steepness of small‐scale wavelets are examined, and the cascade pattern in the geometry of an essentially fractal surface (i.e., when μ≥1/4) is shown to be solely responsible for the observed rms wave slope. On the contrary, the slope of a marginally fractal sea is influenced by the dominant wavelength. The inner scale of the equilibrium range, h, is evaluated for the case of the intermediate degrees of wave development (i.e., when the nondimensional fetch x∼104) by employing a geometrical‐statistical theory of breaking waves. The resulting theoretical predictions of whitecap and foam coverage are in good agreement with field observations at h≈0.5 m. Finally, a “fractal decomposition” for a surface patch is developed based on the Karhunen‐Loeve expansion. The resulting series formalizes the cascade process of constructing realizations of a Gaussian random patch. The influence of the sea maturity on surface geometry is highlighted by showing it as the main factor of L and μ. The work is aimed at improving the present understanding of microwave remote sensing signatures.
Ocean acoustic tomography from ships
Authors: Cornuelle B. , Munk W. , Worcester P.
Published: February 2008

Mesoscale mapping of the ocean sound speed field in a 1000×1000 km area by means of ocean acoustic tomography is greatly enhanced by augmenting a few acoustic moorings with a movable ship‐based receiver. Computer simulations based on realistic noise levels in the measured acoustic travel times give 5% (1%) residual variance in ΔC(x;y,z) for four (six) acoustic source moorings in an ocean perturbed in the gravest baroclinic mode. For comparison, objective mapping based on traditional vertical profiles requires 3 times the steaming distance to yield equivalent residual error. Detailed results depend on many parameters: the assumed mesoscale spectrum and vertical mode structure, the number of observed multipaths, the mooring configuration, the number of ship stations and the travel time signal level (due to mesoscale eddies) and noise level (due to internal waves and position‐keeping errors). These parameters have critical values, below which there is distinct deterioration and beyond which there is little gain. We believe that the critical values can be attained in practice so the ultimate limit on mesoscale mapping is imposed by the internal wave‐induced travel time error. This assumes that position keeping of the submerged acoustic sources and receiver by a combination of satellite navigation and high‐frequency acoustics can be achieved with ±10‐m accuracy. The present study assumes a stationary ocean; a second paper will deal with reciprocal transmissions yielding currents and hence the barotropic mode. This is required in a dynamic ocean model for estimating ΔC(x,y,z;t). All this is preparatory to a tomography experiment in the Greenland Sea in 1988–1989.
Estimates of equatorial upwelling between 140° and 110°W during 1984
Authors: Halpern David , Knox Robert A. , Luther Douglas S. , Philander S. George H.
Published: February 2008

The equation of continuity is used to estimate profiles of vertical velocity between 25 and 120 m from moored current measurements in arrays nested within the triangle with vertices located at 1°30′S, 140°W and along the equator at 140° and 110°W during December 1983 through March 1984 and May‐September 1984. All directions of the 4‐ to 5‐month mean values were upward. The ensemble averaged mean vertical velocity was 2.2 × 10−5 m s−1. Upwelling speeds decreased eastward.
Producing accurate maps of the Gulf Stream thermal front using objective analysis
Authors: Watts D. Randolph , Tracey Karen L. , Friedlander Amy I.
Published: February 2008

The objective analysis (OA) method is adapted in order to map the Gulf Stream thermal front, and resulting output maps are verified against independent data. This extension of the OA method involves removing the mean field and normalizing the variance prior to performing the objective analysis; both of these fields are restored afterward. In this way, the mapped field decays to an appropriate mean field far away from the measurement sites, and the statistics of the normalized perturbation field are homogeneous, as is required by the OA method. We test the sensitivity of the adapted OA method to variations in four control parameters: mean field, correlation function, standard deviation field, and input sampling interval. Of these, specification of the mean field has the most influence upon the mapped fields, whereas the correlation function has more influence upon the estimated error fields. Using a time‐averaged mean field produces the best maps of the thermal field. The space‐time correlation function is determined empirically from 5 years of inverted echo sounder data collected in the Gulf Stream. Interestingly, even in this frontal region the observed correlations do not differ significantly in the cross‐stream and downstream directions. An input sampling interval δt = 1 day (with input data only accepted within T = ±1 day) proved to be best, as power spectra confirm that all significant variance is preserved. Within a reasonable variation of the control parameters, this adapted OA method is robust, and accurate maps of the thermal field are obtained. The OA maps of the Gulf Stream thermal field are verified against nearly 500 independent measurements from expendable bathythermographs and air‐dropped expendable bathythermographs. The rms difference is determined to be 47 m, which is less than the contour interval of 50 m, and which represents less than 7% of the dynamic range (>700 m) found across the Gulf Stream. Thus the adapted OA method can be applied to frontal regions, such as the Gulf Stream, where the traditional method cannot be used.
Subtidal salinity and velocity variations in the St. Lawrence Estuary
Authors: Tee Kim‐Tai
Published: February 2008

Between April and September 1982, fourteen current meters were moored at six stations along the St. Lawrence Estuary: two stations each in the lower, middle, and upper estuaries. The experimental data reveal a complex structure in the subtidal salinity and velocity variations, caused by a combination of tidal, atmospheric and density forcing. The results provide an important data base for modeling baroclinic variations in coastal estuaries. The salinity data indicate that the atmospheric forcing induced an 11.5‐day oscillation which propagated as an internal Kelvin wave. However, the velocity data provide a different picture of wave propagation. The atmospheric forcing also induced salinity variations with a time scale of 40 to 50 days. The oscillation occurs initially in the middle estuary and then propagates toward upstream and downstream regions. Tidally rectified salinity and velocity oscillations at monthly and fortnightly periods were observed at two stations. From the results of an optimum multiple regression model, it was found that the tidally rectified component dominated the other components in the analyzed currents at these two stations. The freshwater pulse, characterized by a salinity minimum, has two time scales of variation: a long time scale of 73 days and a short time scale of 10–15 days. The long‐period pulse was induced by the seasonal runoff. The short‐period pulse was induced by two forcing mechanisms: vertical mixing by unusually strong tidal currents, and the advection of low‐salinity water by wind‐induced currents. The seasonal runoff also induced strong oscillations in the along‐channel current in the lower estuary. This forcing of the current oscillation does not agree with a previously suggested forcing by atmospheric pressure.
Genetic tracers of zooplankton transport in coastal filaments off northern California
Authors: Bucklin Ann , Rienecker Michele M. , Mooers Christopher N. K.
Published: February 2008

Genetic markers were used to describe the transport of the calanoid copepod Metridia pacifica in a cool filament off Point Arena, California, in July 1986. The markers used were genetic variants of enzymes (allozymes); individual copepods were assayed for allozymic variability at nine enzyme‐encoding genes (loci) by polyacrylamide gel electrophoresis. Zooplankton samples were collected in a 300 km by 170 km domain. Maps of surface dynamic height in this domain showed an offshore jet, with strong cross‐shore transport, in the presence of a cool anomaly comprising multiple fronts and filaments. The genetic data sorted the samples into two heterogeneous groups (according to maximum likelihood analysis): one comprising samples near the coast and at the head of the filament, and the other comprising offshore samples. The groups themselves were heterogeneous, revealing smaller‐scale patterns of transport and mixing. The genetic spatial structure of the calanoid copepod, Metridia pacifica, collected in the flow field was used to infer patterns of transport in the filament flow field. Patterns of transport inferred from genetic differences between zooplankton samples were compared with expected particle transport based on models which consider physical (geostrophic advection, Ekman drift, and mixing) transport plus vertical migration behavior. According to both the flow models and the genetic data, transport of zooplankton occurred primarily along paths of geostrophic flow. There was little cross‐jet exchange and almost no exchange between samples in the filament and samples in a cyclonic eddy to the south of the jet. The genetic data further indicated that copepod populations at the coastal source of the filament were genetically heterogeneous. Advection in the filament thus resulted in the juxtaposition of genetically distinct zooplankton populations in the jet axis. The genetic structure of zooplankton in the filament resulted from advection of previous distant populations, not (because of the time scales of the processes) from changes in the genetic character of samples during transport. The presence of multiple fronts and filaments within the cool anomaly prevented homogenization of the plankton assemblages during transport. Thus samples collected less than 10 km apart across the jet axis were genetically different. These findings indicated that plankton populations in complex flow fields may show patchiness in biological, biochemical and/or genetic character at small time/space scales.
The subantarctic and polar fronts in relation to deep water masses through the southwestern Atlantic
Authors: Peterson Ray G. , Whitworth Thomas
Published: February 2008

The two principal fronts within the Antarctic Circumpolar Current (ACC), the Subantarctic Front (SAF) and the Polar Front (PF), are investigated with respect to their spatial patterns and relations to deep water masses from the northern Drake Passage to the western and southern Argentine Basin. Observations from four recent cruises in adjoining and overlapping regions are supplemented with satellite infrared imagery and trajectories from surface drifters. East of Drake Passage, the width of the Polar Frontal Zone (PFZ) increases rapidly when the SAF turns sharply northward as a part of the Falkland (Malvinas) Current, while the PF remains oriented mainly toward the northeast. Found within this region of the PFZ are mesoscale eddies, the upper layers of which consist of Subantarctic Mode Water from the Pacific. The contrasts in upper layer water properties that identify the SAF can be traced the entire length of the Falkland Current to the Brazil‐Falkland confluence zone and then southward to the southern Argentine Basin. There the SAF turns eastward and later, but perhaps not always, merges with the PF north of Ewing Bank to form a single, intense current core strongly influenced by bottom topography. At times this eastward current loops southward through a gap in the Falkland Ridge into the Georgia Basin, thereby supplying relatively warm and salty Subantarctic water to the Antarctic Zone. East of the gap, the two fronts become separated and are once again distinct features in the vicinity of the Islas Orcadas Rise. At depth, within Drake Passage and the western Scotia Sea, the SAF and PF are not lateral boundaries between distinct water masses, but are instead identified by enhanced vertical displacements of property isopleths. With the northward turn of the SAF east of Drake Passage, a thick layer of Circumpolar Deep Water (CDW) is advected over the Falkland Plateau into the Argentine Basin. There it is joined by waters entering the Argentine Basin via a deep spreading route through the Georgia Basin: denser CDW, deep water from the Weddell Sea, and episodically, deep water from the southeastern Pacific Ocean. Together, these waters form a northward flow off the Patagonian shelf that extends from the sea surface to the bottom, most of which turns back toward the south with the Falkland Current return. Also flowing south, along the seaward side of the Falkland Current return well away from the western boundary, is the main core of North Atlantic Deep Water (NADW). Detatched masses of NADW are observed within the CDW at the western boundary as well as within the ACC south of the SAF in the south central Argentine Basin.
Stability of a coastal upwelling front: 1. Model development and a stability theorem
Authors: Barth J. A.
Published: February 2008

A two‐layer shallow water equation model is used to investigate the linear stability of a coastal upwelling front. The model features a surface front parallel to a coastal boundary and bottom topography which is an arbitrary function of the cross‐shelf coordinate. Global conservation statements for energy, momentum and potential vorticity are examined to help elucidate the instability mechanism. By combining these conservation statements, a general stability theorem is established which allows the a priori determination of the stability of a coastal upwelling front. The necessary conditions for instability derived for these ageostrophic flows differ from traditional quasi‐geostrophic criteria. The stability theorem suggests that a coastal upwelling front may be unstable no matter what the basic state flow configuration is. Confirmation of the existence of these unstable waves, a description of their characteristics and a comparison of their properties to observations are presented in a companion paper.
Empirical orthogonal function analysis of cloud‐containing coastal zone color scanner images of northeastern North American coastal waters
Authors: Eslinger David L. , O'Brien James J. , Iverson Richard L.
Published: February 2008

Empirical orthogonal function (EOF) analyses were performed on 36 coastal zone color scanner (CZCS) images of the Mid‐Atlantic Bight and Gulf of Maine taken from February 28, 1979, through July 9, 1979. The EOF procedure was modified to allow images with significant portions of data missing because of clouds to be included in the analysis. Analyses performed both with the temporal and with the spatial means removed from the data produced similar results. A strong gradient existed in the temporal mean from high pigment concentrations nearshore to much lower pigment concentrations offshore. The first mode of the temporally averaged analysis explained 21.5% of the variance and showed a south‐to‐north pattern corresponding to an April Mid‐Atlantic Bight bloom and a June bloom over Nantucket Shoals and Platts Bank. The second temporally averaged mode explained 18.3% of the variance and corresponded to a shelf‐wide phytoplankton bloom that resulted in increased pigment concentrations through the spring. The first mode of the spatially averaged analysis explained 59.1% of the variance and had a pattern similar to the temporal mean. The second mode explained an additional 13.2% of the variance and was almost identical to the first mode in the temporally averaged analysis. The inclusion of cloud‐containing images introduced some small‐scale spatial noise into the EOF analyses. However, the inclusion of these images in the EOF analysis allowed postanalysis image reconstruction that provided estimates of pigment concentrations beneath the clouds.
The size and height to which jet drops are ejected from bursting bubbles in seawater
Authors: Blanchard Duncan C.
Published: February 2008

The oft‐quoted 1‐to‐10 rule, that the diameter of the top jet drop is about one‐tenth that of a bubble bursting in seawater, holds for bubbles of <500 μm diameter at about room temperature. The diameter of the second jet drop is about 8% larger than that of the top drop. Some of the lower drops are larger and some are smaller than the top drop. Both drop size and ejection height decrease with decreasing water temperature. Jet drops are produced from bubbles estimated to be as small as 10 μm in diameter.
Mesoscale eddies, jets, and fronts off Point Arena, California, July 1986
Authors: Rienecker Michele M. , Mooers Christopher N. K.
Published: February 2008

A broad (about 40 km wide) cold filament observed off Point Arena in advanced very high resolution radiometer images at the end of June 1986 evolved into a narrow (10–20 km wide) cold filament embedded in a large‐scale (about 200 km alongshore) cool anomaly by mid July. The cool anomaly was part of a much larger‐scale anomaly, stretching from north of Cape Mendocino to south of San Francisco, in which several cold filaments were embedded. The filament off Point Arena, surveyed by ship from July 7 to 19, 1986, extended offshore around the edge of a cyclonic center. The horizontal temperature gradient was sharpest (up to 1.5°C/2.2 km) across the southern edge of the filament, and a salinity front was located within the cold filament; temperature and salinity fronts were not coincident. The surface salinity was high (33.2 psu (practical salinity unit)) in the cyclonic center and decreased across the cold filament to about 32.6 psu. The entire cool anomaly was denser than surrounding water, and there was a sharp density front (1 sigma‐t unit/10 km) at its northern edge. At the inner (cyclonic) edge of the filament the temperature and salinity variations were density compensating. The cold filament was advected offshore by a jet which was symmetric about its axis, located about 10 km north of the cold filament core. The surface manifestation of the cold filament was highly variable in space and time: the location of the filament core changed by about 5 km in 14 hours along one transect; the velocity field was less variable. Several narrow (10 km wide) water mass anomalies were evident, including a salinity subduction zone in the northern segment of the cold filament. Thermohaline intrusions 50–100 m thick may have been caused by complex frontal interactions upstream of the anomaly and offshore in a region of jet confluence. From a second survey (July 27 to August 5, 1986) the offshore jet had reoriented to alongshore, possibly related to an observed increase in the poleward flow over the continental slope. Prior to the second survey there were changes in the nearshore wind stress and the large‐scale wind stress curl.
Some mesoscale features of flow in Shelikof Strait, Alaska
Authors: Reed R. K. , Schumacher J. D.
Published: February 2008

Moored current observations were obtained from a small region of Shelikof Strait during 1986–1987. Results from two sites <4 km apart revealed very similar energy spectra and highly correlated alongstream component flow. At separations >11 km, however, correlations were quite weak. A new feature, intense 13‐day spectral peaks of narrow horizontal and vertical scale, was also revealed. The feature appears to be a baroclinic, residual flow linked to tidal currents.
On estuarine cohesive sediment suspension behavior
Authors: Mehta Ashish J.
Published: February 2008

Several transport processes must be considered in any evaluation of the behavior of cohesive sediments in estuaries influenced by currents and waves. Focusing on the need to understand the evolution of the suspension concentration profiles to hydrodynamic forcing, it is shown that a physical framework identifying the various mass transport components which govern suspension profile dynamics is beginning to emerge. Unfortunately, our knowledge of these components, including those associated with the generation, transport, and dewatering of fluid muds, remains incomplete. A combination of field and laboratory based research is essential for providing data bases free of significant lacunae and for resolving major interpretative ambiguities which arise from laboratory to prototype scaling and from practical limits to field measurements.
Suspended sediment transport processes in Cumberland Basin, Bay of Fundy
Authors: Amos Carl L. , Tee Kim T.
Published: February 2008

Cumberland Basin, located at the head of Chignecto Bay, Bay of Fundy, exhibits a seaward (exponential) decreasing, time‐dependent, surface sediment concentration. There is a strong correlation between suspended sediment concentration and longitudinal concentration gradient. A similar correlation was found in Shepody Bay, Chignecto Bay, and Minas Basin, suggesting that an equilibrium condition exists between the two variables. Total suspended mass in Cumberland Basin was constant over 2 years of observation (1011 g) despite changes in sediment concentration and concentration gradient. Temporal controls on suspended sediment concentration are river influx, ice melting, dispersion, settling on the intertidal mud flats, and water mass exchange at the mouth of the basin. This exchange is due to cross‐channel velocity variations; exchanges due to tidal current asymmetry and settling lag are small. A simple box model was developed to study the temporal variation of total suspended sediment in the basin. The results show that the water mass exchange at the basin mouth varies with time and is the dominant factor controlling suspended mass due to efficient dampening of temporal fluctuations in suspended mass.
A numerical investigation of sea surface temperature variability in the Arabian Sea
Authors: McCreary Julian P. , Kundu Pijush K.
Published: February 2008

A numerical model is developed to study the thermodynamics of the Arabian Sea. The model consists of a surface mixed layer of thickness hm and temperature Tm, embedded in a dynamic layer of thickness h≥hm. Entrainment and detrainment in the mixed layer are determined by wind stirring and cooling at the oceanic surface, as in the Kraus and Turner (1967) model. The dynamic layer is a 1½‐layer model which allows entrainment due to shear instability at the base of the layer, similar to the Pollard et al. (1973) model. Monthly climatological data, along with the model sea surface temperature (SST), are used to determine the wind stress and heat fluxes forcing the model. The model is very successful in simulating the observed SST patterns, generally differing by no more than 0.5°C. During the Southwest Monsoon (June‐September), Tm decreases markedly near Somalia and the Arabian peninsula owing to the entrainment of cool subsurface water at the coast and its subsequent advection offshore; farther offshore in the central Arabian Sea it decreases owing to increased evaporative cooling. During the Northeast Monsoon (December‐March), the decrease in Tm is caused in part by reduced solar radiation and by increased evaporative cooling, with additional cooling by entrainment in the northern Arabian Sea. An interesting observed feature is that there is a net annual surface heat flux into the Arabian Sea. In the western Arabian Sea this flux is a direct result of coastal upwelling during the Southwest Monsoon, the cold water reducing the latent heat flux out of the ocean. In the central and eastern Arabian Sea it is caused by the southward advection of this upwelled water toward the equator. The annual heat and mass budgets are closed by equatorial currents: a westward undercurrent is the source of cool subsurface water that is entrained in the Arabian Sea, and a warm eastward surface current removes the excess heat and entrained water from the upper layer.
Laboratory studies of wave‐current interaction: Kinematics of the strong interaction
Authors: Lai Ronald J. , Long Steven R. , Huang Norden E.
Published: February 2008

Controlled laboratory experiments have been conducted to study the kinematics of wave‐current interactions. The results confirm the conservation of waves under the steady state condition. The data also show that the kinematic effect of the current on waves can be treated as a simple Doppler shift. After the Doppler correction, the kinematics of the waves (either breaking or nonbreaking) follows the linear theory very well. The experiments also confirm the blockage of the waves by currents when the ratio ū/C0 approaches −1/4.
Lead isotopes in trade wind aerosols at Barbados: The influence of European emissions over the North Atlantic
Authors: Hamelin B. , Grousset F. E. , Biscaye P. E. , Zindler A. , Prospero J. M.
Published: February 2008

Previous studies have shown that Pb can be used as a transient tracer in the atmosphere and the ocean because of strong time‐variability of industrial inputs and because Pb isotopic composition can be used to identify contributions from different sources. We present Pb isotopic measurements on aerosols collected from the North Atlantic Ocean in the trade wind belt. Aerosols sampled at Barbados during the 1969–1985 period have a Pb isotopic composition different from that observed by previous investigators in Bermuda corals and Sargasso Sea waters. Barbados aerosols appear to contain significant amounts of relatively unradiogenic industrial and automotive Pb that is derived from Europe and carried to Barbados by the trade winds. In contrast, Bermuda corals and Sargasso sea waters are influenced mainly by U.S.‐derived emissions, which contain more radiogenic Pb originating from Missouri‐type ores. This difference generates a strong latitudinal Europe‐U.S.A. isotopic gradient, thus allowing study of trans‐Atlantic atmospheric transport and ocean mixing processes.
Seasonal variability in global sea level observed with Geosat altimetry
Authors: Zlotnicki V. , Fu L.‐L. , Patzert W.
Published: February 2008

Time changes in global mesoscale sea level variances were observed with satellite altimetry between November 1986 and March 1988, showing significant, geographically coherent seasonal patterns. The NE Pacific and NE Atlantic variances show the most reliable patterns, higher than their yearly averages in both the fall and winter. The response to wind forcing appears as the major contributor to the NE Pacific and Atlantic signals; errors in the estimated inverse barometer response due to errors in atmospheric pressure, residual orbit errors, and errors in sea state bias are evaluated and found to be negligible contributors to this particular signal. The equatorial regions also show significant seasonal patterns, but the uncertainties in the wet tropospheric correction prevent definitive conclusions. The western boundary current changes are very large but not statistically significant. Estimates of the regression coefficient between sea level and significant wave height, an estimate of the sea state bias correction, range between 2.3% and 2.9% and vary with the type of orbit correction applied.
Sampling of oceanic rings by satellite radar altimeter
Authors: Tournadre Jean
Published: February 2008

In the present paper, the probability for a mesoscale oceanic rings to be seen by a perfect satellite altimeter is investigated. First, the motion of a ring center is determined using a stochastic differential equation. The problem of radar altimeter sampling is then investigated, first in the one‐dimensional case, then for two dimensions. The probability of a ring to be seen by a satellite is then computed and is shown to depend on the satellite period and fundamental interval, the mean and standard deviation of the ring speed, and the distance between the ring center and the nearest track when the ring appears. The maximum of this probability and the time at which the maximum arises give an estimate of the satellite ability to sense the rings. The observation of Gulf Stream (GS) warm and cold core rings (WCR/CCR) by the Topex‐Poseidon and Geosat altimeters are then presented as examples. For both satellites and ring events, the probability for the ring center to lie on a satellite track (i.e., the entire ring signal is seen) is very low (less than 5%). However, more than 90% of the GS WCRs and 65% of the GS CCRs are seen at least once (i.e., the distance between the ring center and a satellite track is less than the ring radius) with a probability over 80%. The mean probability for the satellite to see a significant part of the ring signal (the distance between the ring center and a satellite track is less than half the ring radius) drops to about 50%. Aliasing between ring motion and satellite sampling should be taken into account during the definition of altimetric data assimilation methods for numerical models. On the other hand, the probability of view is high enough to indicate that altimetric data could improve climatological and statistical studies of mesoscale eddies.
A comparison of surface and satellite‐derived aerosol measurements in the western Mediterranean
Authors: Haggerty J. A. , Durkee P. A. , Wattle B. J.
Published: February 2008

Meteorological and aerosol measurements taken during the Western Mediterranean Circulation Experiment are described, and a 4‐day period during the experiment is analyzed in detail. Aerosol measurements are found to correlate well with meteorological conditions during this time. The Navy Aerosol Model is used to derive meteorological range from surface meteorological data. A model called SATVIS is used to derive aerosol optical depth from satellite radiance data and to give a crude estimate of meteorological range. Comparisons with surface measurements show that both models performed reasonably well for this data set.
The surface circulation of the Balearic Sea
Authors: La Violette Paul E. , Tintoré Joaquín , Font Jordi
Published: February 2008

Until recently, the surface circulation of the Balearic Sea has been viewed as largely cyclonic with a fairly quiescent central dome. However, recent studies involving ship data, tracked drifters, current meter moorings, and satellite imagery indicate that this sea has strong mesoscale variability and a more complex general circulation. These studies, together with an examination of registered satellite imagery collected during the Western Mediterranean Circulation Experiment (WMCE), indicate that the surface circulation is strong year‐round, and characterized by two permanent density fronts located on the continental shelf slope (the Catalan Front) and the Balearic Islands shelf slope (the Balearic Front). The Catalan Front is the more active of the two fronts. In the northern area, a plume of cold water is frequently observed moving southward along the continental slope region, shedding dipole eddies along the leading edge of the plume. In addition, the Catalan Front continuously spawns energetic filaments that appear to be associated with the plume of cool water. The likely mechanism of formation of these filaments is the deflection of the cold water by the regional submarine canyons.
Eddies and thermohaline intrusions of the shelf/slope front off the northeast Spanish coast
Authors: Tintoré Joaquín , Wang Dong‐Ping , La Violette Paul E.
Published: February 2008

A low‐salinity anticyclonic eddy was found during a field study of the shelf/slope front off the northeast Spanish coast in July 1983. The eddy was associated with a tongue of low‐salinity, cold water that originated in the Gulf of Lions. Hydrographic stations indicated the presence of multiple salinity‐inversion layers. In particular, a relative salinity maximum layer was found at the base of the eddy, which can be traced through the study area along the same isopycnal surface. This suggests the thermohaline intrusion of near‐surface, warm, high‐salinity, open‐ocean water along the frontal boundary. The anticyclonic eddy also induced a strong up welling and, consequently, a high biological production at the coast. Subduction along the coastal front seems to provide major transport of particulate material into the open sea.
On the sensitivity of Sverdrup transport estimates to the specification of wind stress forcing in the tropical Pacific
Authors: Landsteiner Mary C. , Mcphaden Michael J. , Picaut Joël
Published: February 2008

We use Sverdrup dynamics to estimate geostrophic transports between 20°N and 20°S in the tropical Pacific Ocean averaged over the period 1979–1981. Three wind stress products are used to force the model. Results are compared to geostrophic transports computed along expendable bathythermograph transects in the western, central, and eastern Pacific for the same period. Depending on the choice of wind stress, modeled transports may differ from the observations by a factor of 2 and, in some cases, flow is opposite to that observed. Possible limitations of the Sverdrup theory are discussed; however, we conclude that detailed and accurate simulation of the general circulation in the tropical Pacific is limited more by the uncertainties in presently available estimates of the surface wind stresses than by deviations from Sverdrup balance.
Ionospheric effects on Geosat altimeter observations
Authors: Musman Steven , Drew Alice , Douglas Bruce
Published: February 2008

The presence of free electrons and ions modifies the propagation speed of electromagnetic waves. Thus the apparent sea height measured by a radar altimeter such as that on board Geosat is influenced by passage through the ionosphere. We explore ionospheric effects using several methods. A model ionosphere for Westford, Massachusetts, is constructed from two frequency observations of Global Positioning System satellites. This model is compared with a theoretical calculation, Faraday rotation observations, and the ionospheric correction furnished with the Geosat geophysical data records. We discuss the influence of the solar cycle, which is important at the moment as a particularly active maximum is approached. Some general remarks on the ionospheric influence on the oceanographic signal observed by a satellite altimeter are also included.
Excitation of intermediate‐frequency equatorial waves at a western ocean boundary: With application to observations from the Indian Ocean
Authors: Moore Dennis W. , McCreary Julian P.
Published: February 2008

A linear, continuously stratified model is used to study the equatorial waves that are generated at the western boundary of the ocean by wind fields oscillating at periods of 30 and 60 days. Solutions are found in ocean basins with a western boundary oriented meridionally or slanted at a 45° angle, like the one in the Indian Ocean. They are evaluated analytically when the boundary is meridional but must be found numerically when the boundary is slanted. The possible equatorial waves are Kelvin and Yanai waves, and at the 60‐day period there are a few Rossby waves. Because Yanai and Rossby waves typically have short wavelengths, they are not directly forced by the wind; however, they can be strongly excited at the western boundary and in that case are highly visible in the interior ocean. When the western boundary is slanted, zonal winds also excite antisymmetric equatorial waves, resulting in considerable meridional flow on the equator. At the 30‐day period, energy associated with Kelvin and Yanai waves propagates eastward and downward from the western boundary along ray paths, producing an equatorial shadow zone in the western ocean. At the 60‐day period the presence of Rossby waves complicates the radiation pattern. Solutions compare favorably with several aspects of the observed equatorial wave field in the western Indian Ocean.
The northeast Pacific Ocean response to the 1982–1983 El Niño
Authors: Johnson Mark A. , O'Brien James J.
Published: February 2008

The ocean's response to atmospheric forcing and to forcing along the coast by Kelvin waves is examined in light of nearshore seasonal variability and the major 1982–1983 El Niño. In addition to driving the northeast Pacific gyre and local currents, the wind modifies the depth to the main thermocline, changing the apparent westward phase speed of Rossby waves excited by passing Kelvin waves. The amplitude of the passing Kelvin wave determines whether the Rossby wave depresses or raises the thermocline while propagating westward. Along the northeast Pacific coast from Oregon to Washington, model results suggest that the wind raises the main thermocline during the 1982–1983 El Niño. Generally, the coastal response off Oregon and Washington appears to be strongly driven by the large‐scale atmosphere, while along the California coast and south to the equator, the dominant El Niño signal has an oceanic origin. That signal, with periods between 2 and 5 years, originates in the western equatorial Pacific Ocean and is tracked eastward through the equatorial waveguide and then poleward along the coast to 50°N using data from two reduced gravity, primitive equation models coupled at 18°N. At shorter, seasonal time scales, the acceleration of the wind appears to be an important mechanism in driving coastal currents.
Climatology comparison and long‐term variations of sea surface temperature over the tropical Atlantic Ocean
Authors: Servain Jacques , Séva Marc , Rual Pierre
Published: February 2008

The primary aim of the present study is to compare two sea surface temperature (SST) climatologies produced from merchant ship observations over the tropical Atlantic Ocean. The first climatology uses measurements taken between 1911 and 1972. The second uses 1964–1984 data. The second climatology is generally warmer by a few tenths of degrees. Part of the difference is due to changes in the temperature measurement techniques with time. The difference also shows, especially along shipping routes, some spatial discrepancies which are not due to instrument changes. It is demonstrated the difference is mostly caused by inhomogeneity in the spatial and temporal density of the available observations used to construct the first climatology. Using a simple technique to eliminate spurious bias, the analysis allows isolation of the long‐term trend of SST anomalies in the tropical Atlantic Ocean during this century. South of the thermal equator, a warming trend occurs principally during boreal summers and extends to the present with an increasing range when calculated over the past 26‐year period. In the north, such a warming is more questionable between the 1940s and 1970s. It is more evident during the past 26‐year period but with a temperature range less than half of that for the southern basin. Thus large abnormal patterns have a tendency to straddle the thermal equator, including a north‐south climate dipole. Three spatially limited areas with a cooling trend are suggested. The reliability of SST anomalies along the tropical section of the Europe‐South America shipping track in recent years is also discussed.