bluuebunny/crossref_metadata_2025 huggingface dataset:
Observations of a poleward surface current off the coasts of Portugal and Spain during winter
Authors: Frouin Robert , Fiúza Armando F. G. , Ambar Isabel , Boyd Timothy J.
Published: February 2008

Evidence of a warm, salty surface current flowing poleward along the Iberian Peninsula is presented using a sequence of satellite infrared images and concomitant in situ hydrographic data obtained during the winter of 1983–1984. The current, which flows over 1500 km along the upper continental slope‐shelf break zone off western Portugal, northwest and northern Spain, and southwest France, is 25–40 km wide, about 200 m deep, and characterized by velocities of 0.2–0.3 m s−1. According to the hydrographic data acquired during late November and early December 1983, the current's salinity signal off Portugal is about 0.2 practical salinity units, and its waters are ∼0.5°C warmer than the surrounding ones. The satellite observations, however, which span a longer time period and cover a much larger area, indicate that the current's typical thermal signature is 1°–1.5°C. The current's associated geostrophic volume transports show an increase from about 300×103 m3 s−1 near 38°3′N to 500–700×103 m3 s−1 at 41°–42°N. The origin of this poleward flow and the causes for its increasing transport off western Iberia are investigated. Onshore Ekman convergence induced by southerly winds along the Portuguese west coast provides about one fifth of the computed transports in the correct direction. A mechanism giving better quantitative agreement with the observations is the geostrophic adjustment of the eastward oceanic flow driven by the large‐scale meridional baroclinic pressure gradient in the eastern North Atlantic as the flow reaches the continental slope of the western Iberian Peninsula. Topographic trapping by the bathymetric step existing along the shelf break explains both the width and the path of the observed current. The role of “dam break” type mechanisms is discarded owing to strong discrepancies between the available models and the present observations. Since satellite images reveal that similar situations occurred during many winters, the flow identified here appears as a characteristic feature of the winter circulation off southwest Europe. Furthermore, the occurrence of analogous poleward flows in eastern boundary layers of the subtropical and mid‐latitude oceans suggests that these currents are typical features of those regions' winter circulation.
Opening and closing of sea ice leads: Digital measurements from synthetic aperture radar
Authors: Fily M. , Rothrock D. A.
Published: February 2008

The coming opportunity to extract quantitative sea ice data from routine synthetic aperture radar imagery requires the development of automated image processing techniques. An algorithm is described for measuring the opening and the closing of leads by comparing two sequential synthetic aperture radar (SAR) digital images. The pair of images is classified into leads and ice, correcting for variation in brightness with range. Displacements are determined automatically on a regular 2‐km grid (on a 100‐km square scene) by cross‐correlation. An algorithm groups together cells which cover a lead “event.” The lead area change is estimated for each cell group by counting lead pixels before and after deformation. All positive changes are summed to obtain the amount of opening, and all negative changes give closing. Errors are estimated by comparison with area changes determined from manually digitized lead boundaries and are about 0.2% of the area of the scene. For comparison, the measured opening and closing are in the range of 1 to 3% of the scene area. In ice models the openings and closings of leads are parameterized in terms of the large‐scale deformation. SAR allows us to study these parametric relations by giving us access both to direct observations of opening and closing and to detailed kinematic data from which to estimate the mean deformation. In this image pair for which the deformation is nearly pure shear, we find relatively small amounts of opening and closing, consistent with previous observations, and with parameterizations in most models. The large values of opening and closing predicted by the Poisson‐Gauss kinematic model are not in evidence.
Satellite‐derived water vapor corrections for Geosat altimetry
Authors: Emery William J. , Born George H. , Baldwin Dan G. , Norris Charles L.
Published: February 2008

The absence of a radiometer on Geosat to provide simultaneous measurements of tropospheric water vapor makes it necessary to have the best possible estimates of coincident water vapor corrections from other satellite‐borne sensor systems. In this study, tropospheric water vapor contents are computed from two different satellite sensor systems. These water vapor estimates are intercompared and are compared with other coincident estimates of tropospheric water vapor from radiosondes and from the standard weather analyses of the Fleet Numerical Oceanography Center (FNOC). Statistical comparisons are also made with a climatological water vapor data base computed from the scanning multichannel microwave radiometer (SMMR). The primary data sources for this study are the TIROS operational vertical sounder (TOVS) flying on the NOAA series of polar orbiter weather satellites and the special sensor microwave imager (SSM/I) flying since July 1987 on Defense Meteorological Satellite Program (DMSP) satellite number 8. A period of overlapping TOVS and SSM/I data from the summer of 1987 is used for statistical comparisons to determine the utility and reliability of altimetric path length corrections computed from these data. Because of its all weather sensing capability the SSM/I is shown to be capable of providing reliable global water vapor maps over periods as short as 4 days, while the TOVS system can be reliably used only for compositing periods of a week or more because of cloud contamination. In terms of magnitudes, both systems provide water vapor estimates consistent with a global set of island‐ship radiosonde to within 0.5–0.9 g/cm2. The SSM/I provides the most detailed global water vapor maps, closely approximated by the 8‐day TOVS composites. The larger spatial resolution of the FNOC analysis and the SMMR climatology fails to properly resolve many of the important spatial details of the global water vapor distribution. The FNOC analysis systematically underestimates tropical water vapor contents. Seasonal means and standard deviations of both the TOVS and SSM/I global water vapor maps clearly demonstrate the importance of the annual cycle in atmospheric water vapor. The relative success of the SMMR climatology in matching some of the statistics emphasizes the importance of the annual cycle. Converted to altimetric path‐length corrections for typical satellite tracks in the North Atlantic and North Pacific, the water vapor errors are maximum just north of the equator in both oceans. SSM/I‐ and TOVS‐derived path length corrections are both significantly higher in the equatorial zone than those derived from the other water vapor maps.
Mean sea surface and variability of the Gulf of Mexico using Geosat altimetry data
Authors: Leben Robert R. , Born George H. , Thompson J. Dana , Fox Chad A.
Published: February 2008

Geosat Exact Repeat Mission (ERM) altimetric measurements of the sea surface height, in the Gulf of Mexico are used to determine the mean sea surface height with respect to the ellipsoid and mesoscale variability along Geosat ground tracks in the gulf for the time period from November 8, 1986, to November 25, 1988. The alongtrack mean sea surface is determined using a regional crossover adjustment procedure, in which the tilt and bias of mean arcs are estimated using a least squares technique to minimize the height differences at crossovers points. A mean surface generated using the Geosat ERM alongtrack mean is calculated and contrasted with a previously derived mean surface determined using GEOS 3 and Seasat crossover differences. This provides a first look at the variability in the mean between the time periods of 1987–1988 and 1975–1978. In addition, the alongtrack mesoscale variability time series has been produced from the Geosat ERM data set by using a robust orbit error removal algorithm to determine the variability of the sea surface height with respect to the alongtrack mean. A surface generated using the rms of this alongtrack time series shows good qualitative and quantitative agreement with previous in situ observations in the region. This study demonstrates the potential of satellite altimetry for oceanographic studies of the Gulf of Mexico.
Oceanic tides from Geosat altimetry
Authors: Cartwright D. E. , Ray R. D.
Published: February 2008

Direct tidal analysis of the altimetry from the Geosat Exact Repeat Mission's first year is used to derive estimates of the diurnal and semidiurnal oceanic tides. The geoid is removed by collinear differences at 34.1‐day separation, and the orbit error is reduced by subtracting a slowly modulated 1 cycle/revolution term. A sequence of independent analyses at grid areas of 1° latitude×1.5° longitude using “orthotide” functions ensures complete definition of the diurnal and semidiurnal species. Global admittance maps for M2and S2within the latitudes 58°N and 59°S compare well with ground truth at 66 open‐ocean sites. Maps of differences between Geosat and the Naval Surface Weapons Center model show important areas of the order of 10–15 cm. The integral for the global power input from the moon gives 2.51 TW (M2), 0.44 TW (S2), lower than many previous estimates, but in agreement with figures deduced from a recent analysis of satellite orbits.
Estimates of the zonal slope and seasonal transport of the Atlantic North Equatorial Countercurrent
Authors: Carton James A. , Katz Eli J.
Published: February 2008

We use data from six inverted echo sounder moorings and the Geosat satellite altimeter to examine the seasonal variability of sea surface elevation. Monthly sea level maps are constructed using a contemporaneous subsurface temperature survey to provide a reference sea level field. The maps are then used to describe the origin and structure of the western tropical Atlantic North Equatorial Countercurrent (NECC) during a 2‐year period beginning in November 1987. The data reveal a zonal current which is confined between 3°N and 9°N with a typical width of 300 km. The NECC flows strongly eastward during November and December 1986 and May 1987 through January 1988. The reappearance of the current is then delayed until August, but the current flows strongly from August until the end of our record in October 1988. Volume transport is estimated for the 2‐year period from surface elevation by approximating the vertical structure of the ocean as a two‐layer fluid. We find that the NECC has a maximum transport of 40×106 m3 s−1 at 38°W. This water has its origin in the retroflection of the North Brazil Current. Eastward of 38°W the NECC loses strength as water exits the current to join the currents further south.
Agulhas eddies invade the south Atlantic: Evidence From Geosat altimeter and shipboard conductivity‐temperature‐depth survey
Authors: Gordon Arnold L. , Haxby William F.
Published: February 2008

There is mounting evidence that Indian Ocean water penetrates into the South Atlantic. A sequence of Geosat altimeter data from November 1986 to November 1987 discloses numerous transient anticyclonic mesoscale features within the South Atlantic subtropical gyre. They migrate from the Agulhas Retroflection towards the northwest, then after stalling, cross the Walvis Ridge, to continue drifting to the west, at 5 to 8 cm s−1. The “family” of these features can be traced to the western South Atlantic in the latitude range of 20°–30°S. The 1987 population of eddies in the South Atlantic and their mean drift velocity suggests a production rate of about five eddies per year. As much as 15×106 m3 s−1 of Indian Ocean water may pass into the subtropical South Atlantic by this process. One of the larger eddies disclosed by the Geosat altimeter was crossed by the Discovery during a conductivity‐temperature‐depth survey of the Benguela Current in May 1987. The dynamic height of the sea surface relative to 3000 dbar reveals a 30 dyn cm crest, in excellent agreement with the Geosat data. The eddy displays a distinct sign of Indian Ocean stratification: an isohaline layer in the 15°–19°C interval. The colder South Atlantic water cannot achieve these characteristics by local interaction with the atmosphere. However, there is evidence for some surface modification: surface salinity values are higher than those found within the Agulhas Current. This is explained by enhanced evaporation driven by the warm temperatures of the eddy below the colder atmosphere. This process would eventually remove the Indian Ocean signature, converting the water within the eddy to typical South Atlantic thermocline water.
The impact of atmospheric aerosols on trace metal chemistry in open ocean surface seawater: 3. Lead
Authors: Maring H. B. , Duce R. A.
Published: February 2008

Atmospheric aerosols collected at Enewetak Atoll in the tropical North Pacific were exposed to seawater in laboratory experiments to assess the impact of atmospheric aerosols on lead chemistry in surface seawater. The net atmospheric flux of soluble lead to the ocean is between 16 and 32 pmol cm−2 yr−1 at Enewetak. The stable lead isotopic composition of soluble aerosol lead indicates that it is of anthropogenic origin. Anthropogenic aerosol lead from Central and North America appears to be less soluble and/or to dissolve less rapidly than that from Asia. Dissolved organic matter and possibly lower pH appear to increase the nonaluminosilicate aerosol lead solubility and/or dissolution rate. The isotopic composition of lead in air, seawater and dry deposition suggests that after deposition in the ocean, nonaluminosilicate paniculate lead can be reinjected into the atmosphere during sea salt aerosol production.
The Newfoundland ice extent and the solar cycle from 1860 to 1988
Authors: Hill Brian T. , Jones Stephen J.
Published: February 2008

Sea ice conditions off the east coast of Newfoundland for the last 130 years are presented, forming what is believed to be the longest ice record for the northwestern Atlantic. Because of differences in how these data were originally collected, the series is divided into two sets, before and after 1920. Time series for solar activity and air temperature at St. John's have also been compiled and correlation coefficients between the various data sets determined. The relationships between the sea ice extent and solar activity are discussed in the context of the Iceland ice index and recent findings in the atmosphere‐ocean‐ice system in the northern hemisphere. The association with the quasi‐biennial oscillation (QBO) and the similarity with the fluctuating trends of sea levels, sea surface temperatures, and storms in the North Atlantic are noted. Predictions for the sea ice extent are made for the next few years based on the relationship with solar activity.
Sea level oscillations observed with Geosat along the two shear fronts of the Pacific North Equatorial Countercurrent
Authors: Périgaud Claire
Published: February 2008

Geosat data are processed and analyzed into sea level variations over the tropical Pacific Ocean during the first 26 months of the Exact Repeat Mission from November 15 1986 to January 15 1989. The resolution is 1° latitude and longitude and 10 days. The frequency and wave number spectra of these sea level variations show much more energy in the northeastern than in the western or southern Pacific. Energy highs of 8000 cm2 per (cycle per day) per (cycle per degree of longitude) are clearly identified along 5°N for periods of 28–40 days and wavelengths of 1000–2200 km (band 1), and along 12°N for periods of 50–90 days and wavelengths of 630–950 km (band 2). Filtered in energy band 1, the sea level anomalies show a maximum amplitude of 8 cm between 4° and 7°N and no symmetry nor antisymmetry with respect to the equator, a zonal westward phase velocity of 35 km/day and an eastward group velocity of 30 km/day. As a function of longitude, the filtered signal presents three different regimes separated by the Line and Marshall islands. The amplitude is strongest east of 160°W (2.5 cm time averaged), weak west of the date line (1.0 cm), and intermittent and weak (1.1 cm) along 2000 km in the central Pacific. In the eastern region, amplitude is seasonally modulated with a minimum in April–May and a maximum in December–January corresponding in time with the variation of the zonal shear flow between the North Equatorial Countercurrent (NECC) and the South Equatorial Current as derived from the altimeter meridional gradient. Filtered in energy band 2, the sea level anomalies show a maximum amplitude of 6 cm between 10°N and 13°N, a westward phase propagation of 12 km/day, and an eastward group velocity of 10 km/day. The amplitude of the waves is strongest east of 120°W between February and July 1987 and between November 1987 and March 1988. These wave packets are well correlated both in time and space with the increase of the zonal shear between the NECC and the North Equatorial Current.
Tracer dating and ocean ventilation
Authors: Thiele G. , Sarmiento J. L.
Published: February 2008

The interpretation of transient tracer observations depends on difficult to obtain information on the evolution in time of the tracer boundary conditions and interior distributions. Recent studies have attempted to circumvent this problem by making use of a derived quantity, age, based on the simultaneous distribution of two complementary tracers, such as tritium and its daughter, helium 3. The age is defined with reference to the surface such that the boundary condition takes on a constant value of zero. We use a two‐dimensional model to explore the circumstances under which such a combination of conservation equations for two complementary tracers can lead to a cancellation of the time derivative terms. An interesting aspect of this approach is that mixing can serve as a source or sink of tracer based age. We define an idealized “ventilation age tracer” that is conservative with respect to mixing, and we explore how its behavior compares with that of the tracer‐based ages over a range of advective and diffusive parameters.
Circulation in the Canary Basin: A model/data analysis
Authors: Spall Michael A.
Published: February 2008

The Canary Basin region of an eddy‐resolving, primitive equation model of the North Atlantic is studied in terms of its time mean fields, eddy variability, and role in three fundamental oceanic processes. The model calculation was carried out by Bryan and Holland as the first Community Modeling Effort of the World Ocean Circulation Experiment. Each of the major currents in the region is represented in the model fields. Several aspects of the large‐scale climatological density field which was used for initialization were improved by the dynamical model while other aspects were degraded. The major deficiencies in the model are the representation of the Mediterranean salt tongue and low values of the eddy kinetic energy. The difference in the model salt tongue is believed to be at least partially due to an insufficient treatment of the Mediterranean outflow. Several numerical parameterizations which may be partially responsible for the low eddy kinetic energy are suggested as topics for future study. The role of this region in the ventilation of the thermocline, meridional flux of temperature, and formation of the Mediterranean salt tongue is studied. In general, the model results compare well with the available data and, in some instances, suggest mechanisms for previously observed flow characteristics and possibly important phenomena which have not yet been observed. Final recommendations are made to both the modeling and observational communities for future activities in this region.
Measurements of sea spikes in microwave backscatter at moderate incidence
Authors: Jessup A. T. , Keller W. C. , Melville W. K.
Published: February 2008

Previous authors have associated large events, or “sea spikes”, in the radar cross section of the sea surface with steep or breaking waves. Here we present a method based on an intensity threshold and the mean Doppler frequency to identify and quantify sea spikes likely to be associated with large‐scale wave breaking. This method is applied to microwave measurements of Ku band made with a dual‐polarized Doppler scatterometer at a moderate incidence angle (45°) from a fixed platform in the North Sea. For VV and HH polarization the mean normalized radar cross section σ0, the frequency of sea spike occurrence N, and the sea spike contribution to the mean normalized radar cross section, σSS0, are correlated with direct measurements of the friction velocity, u*, in the range 13 ≤ u* ≤ 49 cm s−1. The friction velocity exponents for both N and σSS0 indicate an approximately cubic dependence, while the residual radar cross section σres0 = σ0 ‐ σSS is approximately proportional to friction velocity for u* greater than approximately 20 cm s−1. At high friction velocities, (u* ≈ 40–50 cm s−1) these data show that the contribution of large sea spikes to the mean radar cross section for measurements between 25° and 45° relative to the wind is in the range of 5–10% for VV polarization and 10–20% for HH polarization.
Barotropic motions and the exchange of angular momentum between the oceans and solid Earth
Authors: Ponte Rui M.
Published: February 2008

The role of the ocean in transferring angular momentum between the atmosphere and the solid Earth is examined for periods longer than a day. Changes in the total angular momentum of the ocean can occur through the action of external torques such as surface wind stresses and continental torques (i.e., body forces acting on lateral boundaries), which represent momentum exchange with the atmosphere and the solid earth respectively. Analysis of these external torques suggests that in general, the related angular momentum exchanges are mostly associated with barotropic variability in the ocean. Solutions for a mid‐latitude basin, obtained with a shallow water numerical model forced by simple periodic zonal winds, illustrate how the momentum exchanged with the atmosphere is quickly transmitted to the solid Earth through the continental torque, with the bottom friction torque being negligible. For wind forcing confined to the middle of the ocean basin, both free waves and forced variability with large horizontal decay scales can participate in the interaction with the boundaries. The fast time scales involved in oceanic barotropic adjustment permit a rapid equilibration between the forcing regions and the coastal boundaries. The angular momentum transfer mechanism between the ocean and the solid Earth is consistent with the observed coherence at no discernible time lag between atmospheric and solid Earth angular momentum variations.
Acoustic scattering from ocean microstructure
Authors: Goodman L.
Published: February 2008

An examination is made of the scattering cross section per unit volume per unit solid angle, σ, for the case of acoustic scattering from ocean microstructure. Both monostatic and bistatic source/receiver geometries are considered. Diffraction is explicitly included in the formulation, resulting in an expression for σ which accounts for finite scattering volume effects associated with vertically anisotropic microstructure. Vertically anisotropic microstructure results in σ a maximum at reflection with respect to the horizontal plane, where σ = σr, with an angular bandwidth of order the maximum of β0, α, where β0 is the beamwidth angle of the scattering volume, and α is the anisotropy slope angle. For the stratified part of the ocean column, neglecting doubly diffusive effects, under typical open ocean conditions, temperature induced microstructure scattering dominates that of fluid velocity scattering by several orders of magnitude. Two models of temperature microstructure, termed the classical turbulence model and the empirical microstructure model, the latter based on field observations, are used as input into the acoustic formulation. Specific functional forms are obtained for σr in terms of environmental microstructure parameters. For frequencies of the order of 100 kHz and greater, scattering is principally the result of microstructure in the wave number regimes corresponding to the classical inertial or Batchelor subranges. Typical open ocean microstructure modeled as isotropic classical turbulence results in volume backscattering strengths Sv = 10 log (σr) ≈ −110 dB. However, for very narrow beamwidth sonar systems, Sv scales as −20 log α, which for anisotropy slope angles of order that of internal waves would result in a 37‐dB increase in scattering strength. Intense turbulence associated with high vertical shear zones such as that present in Stellwagen bank in Massachusetts Bay or at Knight Inlet, British Columbia, can result in volume backscattering strengths of the order of −60 dB. Bistatic scattering at the reflection angle, particularly at near‐forward directions, results in general, in greatly enhanced scattering strength over that associated with backscattering.
The flow of the undercurrent over the continental borderland off southern California
Authors: Lynn Ronald J. , Simpson James J.
Published: February 2008

Complex bathymetric features offshore of southern California have a pronounced effect upon the flow of the California Undercurrent Geostrophic dynamics and water mass characteristics are used to reveal the various paths of flow and spread of undercurrent waters for a July 1985 survey. Undercurrent waters are identified by relatively high spiciness and low dissolved oxygen at densities between σt = 26.4 and 26.9 (∼200 to 400 m). A jetlike core of flow follows the continental slope within the California Bight and exits the bight through a gap in the Santa Rosa‐Cortes Ridge. Mixtures that include undercurrent waters exit the bight through other gaps in the bathymetric ridge and about the southern end of the ridge. As evidenced by patterns in the fields of geostrophic currents and water mass characteristics, baroclinic instabilities develop about the ridge which result in the diversion of undercurrent waters offshore beneath the California Current and into the offshore mesoscale eddy field. The offshore subsurface diversion of undercurrent waters and their inclusion in the offshore mesoscale eddy field are also found in the long‐term mean distributions for July.
Variability in the eastern equatorial Pacific Ocean during 1986–1988
Authors: McPhaden Michael J. , Hayes Stanley P.
Published: February 2008

We examine variability in the eastern equatorial Pacific during 1986–1988 using conductivity‐temperature‐depth data, velocity and temperature data from equatorial moorings between 110°W and 140°W, and wind data from a basin scale zonal array of islands and moorings between 110°W and 165°E. The period studied coincides with the El Niño/Southern Oscillation (ENSO) event of 1986–1987 and a subsequent cold event in 1988. Weak warm sea surface temperature anomalies first appeared in the eastern equatorial Pacific in mid‐1986 and increased to >1°C in September–November 1986 in association with a 30 cm s−1 weakening of the South Equatorial Current and a 20‐ to 40‐m depression of the thermocline. These warm anomalies lasted until early 1988, after which a large‐scale shoaling of the thermocline led to sea surface temperatures more than 3°C colder than climatology. Year‐to‐year fluctuations in the eastern Pacific were related primarily to zonal wind variations in the central and western Pacific. Westerly wind stress anomalies of 0.02–0.05 N m−2 were observed between 140°W and 165°E from the latter half of 1986 until the end of 1987; these were replaced by easterly wind anomalies of similar magnitude between 157°W and 165°E in 1988. Energetic intraseasonal fluctuations with periods of 2–3 months were also prominent in zonal current, temperature, and dynamic height time series. These fluctuations propagate eastward at approximately first baroclinic mode Kelvin wave phase speeds and are forced west of the date line by episodes of westerly winds. Extrema in several oceanic variables occurred in association with these waves, though their precise dynamical link to the ENSO cycle is unclear from our data. Sea surface temperature and thermocline depth anomalies at 0°, 110°W were less pronounced during the 1986–87 ENSO than during the 1982–1983 ENSO; the Equatorial Undercurrent, though weaker than normal in early 1987, did not disappear as it did in early 1983.
Effects of initial conditions and Ekman suction on tidal outflows from inlets
Authors: Van Senden David C. , Imberger Jörg
Published: February 2008

The processes of vortex formation and spin‐down due to secondary (Ekman) motions have been studied in the field near an inlet and in the laboratory. The nonbuoyant tidal discharge issuing from an estuary into the coastal ocean was investigated during spring tides in January 1984. Surface drogue tracks showed that after an initial phase of development the outflow structure consisted of a pair of vortices propagating away from the inlet ahead of a jet region. The vortex velocity structure was well represented by a Rankine vortex with a small Ekman‐suction‐induced radial velocity. To investigate the effect of the initial conditions on the flow development, a series of laboratory experiments was conducted in which the source flow acceleration was varied while other parameters were held constant. Vortex spin‐up due to shear layer roll‐up is compensated by spin‐down due to Ekman suction, and eventually the outflow structure becomes independent of the initial conditions. It is shown that during the initial phase the vortex radius and the azimuthal and radial velocities within the vortex depend on source flow acceleration.
The exchange of Kuroshio and East China Sea shelf water
Authors: Chern Ching‐Sheng , Wang Joe , Wang Dong‐Ping
Published: February 2008

A detailed hydrographic study of the East China Sea shelf edge north of Taiwan revealed an intense cold eddy on the shelf break and a large low‐salinity filament at the slope. The cold eddy which is induced by the upwelling of the subsurface Kuroshio water has been repeatedly documented in previous studies. The filament which is made of the mixed shelf and subsurface Kuroshio water, on the other hand, has not been recognized before. The shelf edge upwelling appears to be associated with the sharp bending of the Kuroshio north of Taiwan, while the outpouring of shelf water appears to be associated with the northeasterly storms. Both the eddy and the filament consist of large fractions of the subsurface Kuroshio water, and they may be important to the salt and nutrient budget on the East China Sea shelf.
A study of wave‐turbulence interaction by use of a nonlinear water wave decomposition technique
Authors: Jiang Jih‐Yih , Street Robert L. , Klotz Stephen P.
Published: February 2008

Wave‐turbulence interaction may contribute to momentum and energy transfer in the near‐surface region beneath water waves. However, the nature and extent of this mechanism have not been well understood. A wave separation technique was developed to study quantitatively the momentum and energy transport due to wave‐turbulence interaction. In this technique a nonlinear stream function representation of the wave motion was determined so as to satisfy the kinematic and dynamic boundary conditions at the water surface. Wave‐induced velocities were then deduced from the stream function and subtracted from measured velocity components to obtain the turbulent flow field. This technique was applied to laboratory data taken beneath wind‐generated water waves. Coherence spectra indicate high correlation between turbulence and wave‐induced motions at some frequencies. Time‐averaged correlations between wave and turbulent velocities increase with wind speed and decrease with increasing distance away from the interface. Although there is no significant momentum transfer due to wave‐turbulence interaction, this mechanism results in significant energy transfer among the mean, wave‐induced, and turbulent flow fields.
Model‐data comparisons of moments of nonbreaking shoaling surface gravity waves
Authors: Elgar Steve , Freilich M. H. , Guza R. T.
Published: February 2008

The predictions of linear and nonlinear (Boussinesq) shoaling wave models for nonbreaking unidirectional surface gravity waves are compared to field observations, with particular emphasis on quantities that may be important for cross‐shore sediment transport. The extensive data sets were obtained on two natural beaches, span water depths between 1 and 10 m, and include incident wave power spectra with narrow, broad, and bimodal shapes. Significant wave heights varied between approximately 30 and 100 cm, and peak periods between approximately 8 and 18 s. The evolution of total variances of sea surface elevation, cross‐shore velocity, and horizontal acceleration is modeled at least qualitatively well by both linear and nonlinear theories. Only the nonlinear theory predicts the increasingly asymmetric sea surface elevations and horizontal velocities (pitched‐forward wave shapes) and the weaker variation of skewness (difference between crest and trough profiles) which are observed to occur during shoaling. The nonlinear theory also models qualitatively well the large skewed accelerations which occur during the passage of asymmetric waves.
Withdrawal of shelf water into an estuary: A barotropic model
Authors: Masse Ann K.
Published: February 2008

Coupled circulation between an estuary and the adjacent shelf is a new area of study. At low frequencies estuarine gravitational circulation requires landward flow of lower layer shelf water to balance the seaward flow of brackish estuarine water over the shelf. Here a clearer description of the low frequency physical coupling between the estuary and shelf waters is developed through the use of a steady, linear, barotropic model. Complex bottom topography for the shelf is treated. The shelf adjacent to Delaware Bay, located on the east coast of the United States, is used as an example. The results show that the landward flow field driven only by withdrawal of flow through the estuary's entrance is independent of the flow field otherwise present over the shelf. In the northern hemisphere this landward flow passes along the coast to the right of the estuary entrance, when viewed facing offshore, before it enters the estuary. Model results are supported by near bottom current observations collected on the shelf adjacent to the mouth of Delaware Bay.
Synthetic aperture radar imaging of ship wakes in the Gulf of Alaska
Authors: Shemdin Omar H.
Published: February 2008

The Gulf of Alaska SAR experiment was conducted during March 9–14, 1984 to investigate SAR imaging of narrow‐V wakes in a deep mixed layer environment so that surface manifestations of ship‐generated internal waves would be made small. Five SAR flights were executed over large ships of opportunity in deep water where the mixed layer depth exceeded 100 m in all cases. SAR images were obtained in sea states 1–4. Range and azimuthally traveling ships were imaged. The incidence angles of azimuthally traveling ships ranged from 24° to 53°. The following results are reported: (1) The half angles associated with narrow‐V wakes are consistent with first‐order Bragg surface wave theory described by Case et al. (1984). (2) The decay rate along the bright arms of the narrow‐V wake is consistent with the combined viscous and radiation decay of short surface waves with first‐order Bragg wavelengths. (3) Narrow‐V wakes are observed in sea states 1–3 at incidence angles less than 45°, with the longest narrow‐V wakes bright‐arm observed being 3.3 km. (4) Turbulent wakes (dark band between the bright arms) are observed in sea states 1–4 at incidence angles less than 53°, with the longest turbulent wake length observed being 41 km. (5) Bright boundaries along one side of the turbulent wake are observed.
Synthetic temperature profiles derived from Geosat altimetry: Comparison with air‐dropped expendable bathythermograph profiles
Authors: Carnes Michael R. , Mitchell Jim L. , de Witt P. Webb
Published: February 2008

Synthetic temperature profiles are computed from altimeter‐derived sea surface heights in the Gulf Stream region. The required relationships between surface height (dynamic height at the surface relative to 1000 dbar) and subsurface temperature are provided from regression relationships between dynamic height and amplitudes of empirical orthogonal functions (EOFs) of the vertical structure of temperature derived by de Witt (1987). Relationships were derived for each month of the year from historical temperature and salinity profiles from the region surrounding the Gulf Stream northeast of Cape Hatteras. Sea surface heights are derived using two different geoid estimates, the feature‐modeled geoid and the air‐dropped expendable bathythermograph (AXBT) geoid, both described by Carnes et al. (1990). The accuracy of the synthetic profiles is assessed by comparison to 21 AXBT profile sections which were taken during three surveys along 12 Geosat ERM ground tracks nearly contemporaneously with Geosat overflights. The primary error statistic considered is the root‐mean‐square (rms) difference between AXBT and synthetic isotherm depths. The two sources of error are the EOF relationship and the altimeter‐derived surface heights. EOF‐related and surface height‐related errors in synthetic temperature isotherm depth are of comparable magnitude; each translates into about a 60‐m rms isotherm depth error, or a combined 80 m to 90 m error for isotherms in the permanent thermocline. EOF‐related errors are responsible for the absence of the near‐surface warm core of the Gulf Stream and for the reduced volume of Eighteen Degree Water in the upper few hundred meters of (apparently older) cold‐core rings in the synthetic profiles. The overall rms difference between surface heights derived from the altimeter and those computed from AXBT profiles is 0.15 dyn m when the feature‐modeled geoid is used and 0.19 dyn m when the AXBT geoid is used; the portion attributable to altimeter‐derived surface height errors alone is 0.03 dyn m less for each. In most cases, the deeper structure of the Gulf Stream and eddies is reproduced well by vertical sections of synthetic temperature, with largest errors typically in regions of high horizontal gradient such as across rings and the Gulf Stream front.
Bubble‐mediated aerosol production as a consequence of wave breaking in supersaturated (hyperoxic) seawater
Authors: Stramska Małgorzata , Marks Roman , Monahan Edward C.
Published: February 2008

The influence of changes in the degree of saturation of the surface waters, with respect to the major atmospheric gases, on the aerosol productivity of an individual whitecap has now been inferred from results recently obtained using the University of Connecticut's Whitecap Simulation Tank IV. As the level of dissolved oxygen increased from 100% saturation to 130%, i.e., to a significant degree of supersaturation, the production of aerosol droplets by the whitecap generated by a standard laboratory breaking wave was found to increase by a factor of 2.4 in the case of submicron radius droplets, while the generation of larger droplets (r > 2.5 μm) was observed to increase by at least a factor of 4.0. As a consequence of these findings, a multiplier, defined in terms of the degree of gas saturation, has been introduced as a term in the various sea surface aerosol generation models.
Wind wave directionality effects on the radar imaging of ocean swell
Authors: Ocampo‐Torres F. J. , Robinson I. S.
Published: February 2008

The effect of short wave directionality on the tilt modulation transfer function (TMTF) is investigated in detail through numerical simulations. Under the assumption of Bragg resonance as the appropriate mechanism to explain microwave backscattering from the sea surface, and the imaging process as linear mapping, the possibility is demonstrated of a near‐azimuth wave capable of being imaged by real aperture radars. It is proven that at least for the radar and ambient conditions adopted, the TMTF is more important than the hydrodynamic modulation transfer function (HMTF). It is through the TMTF that short wave directionality emerges as important, allowing long azimuth waves to modulate the radar cross section. The inversion of the radar image field to recover accurate wave measurements requires a knowledge of local wind direction and a suitable description of the directionality of the short radar‐interacting waves, since the radar response is found to be strongly dependent on them. It is shown that the combined response of the TMTF and the HMTF, the predicted image spectrum, can differ from the long wave spectrum from which it has been derived, for some directions of radar look, long waves and wind. Some distortion is observed, as shifting, and in some cases splitting, of the spectral peak.
Observations of wave‐induced set‐up on a natural beach
Authors: King B. A. , Blackley M. W. L. , Carr A. P. , Hardcastle P. J.
Published: February 2008

A new technique has been used to make field measurements of wave‐induced set‐up. The technique is reliable and accurate, and the results presented show the variation of mean set‐up at the shoreline with incident wave height. The amount of set‐up is well predicted by a linear function of incident wave height and is found to be in good agreement with theoretical predictions based on the observed decay of wave height across the surf zone. The maximum set‐up observed was about 40 cm.
The effect of clouds on photolysis rates and ozone formation in the unpolluted troposphere
Authors: Thompson Anne Mee
Published: February 2008

The photochemistry of the lower atmosphere is sensitive to short‐ and long‐term meteorological effects; accurate modeling therefore requires photolysis rates for trace gases which reflect this variability. As an example, the influence of clouds on the production of tropospheric ozone has been investigated, using a modification of Luther's two‐stream radiation scheme to calculate cloud‐perturbed photolysis rates in a one‐dimensional photochemical transport model. In the unpolluted troposphere, where stratospheric inputs of odd nitrogen appear to represent the photochemical source of O3, strong cloud reflectance increases the concentration of NO in the upper troposphere, leading to greatly enhanced rates of ozone formation. Although the rate of these processes is too slow to verify by observation, the calculation is useful in distinguishing some features of the chemistry of regions of differing mean cloudiness.
Hydrocarbon and carbon monoxide emissions from biomass burning in Brazil
Authors: Greenberg J. P. , Zimmerman P. R. , Heidt L. , Pollock W.
Published: February 2008

Field measurements of hydrocarbon emissions from biomass burning in the cerrado (grasslands) and selva (tropical forest) regions of Brazil in 1979 and 1980 are characterized and quantified here. Regional consequences of burning activities include increased background mixing ratios of carbon monoxide and ozone, as well as reduced visibility, over extensive areas. Global extrapolation of the emission rate of hydrocarbons from these fires indicates that 6×1013 g C of gas phase hydrocarbons and 8×1014 g CO may be released annually from biomass burning. These emissions contribute significantly to the global budgets of hydrocarbons and carbon monoxide.
Trace metals in Bermuda rainwater
Authors: Jickells T. D. , Knap A. H. , Church T. M.
Published: February 2008

The concentrations of Cd, Cu, Fe, Mn, Ni, Pb, and Zn have been measured in Bermuda rainwater. Factor analysis indicates that Fe, Mn, and Pb have similar origins to acidic components derived from North America. The other metals all behave similarly but differently to the acids. Sea salt, even after allowances for fractionation, apparently contributes minor amounts of Cu, Pb, and Zn and uncertain amounts of Fe, Mn, and Cd to Atlantic Ocean precipitation. Wash‐out ratios, calculated from this data along with earlier measurements of atmospheric trace metal concentrations on Bermuda, are of the same order as those reported from other remote ocean areas. The wet depositional fluxes of Cu, Ni, Pb, and Zn to the western Atlantic Ocean are significant compared to measured oceanic flux rates. However, the wet depositional fluxes of Fe and Mn to this area are relatively small, suggesting additional inputs, while an excess wet depositional flux of Cd suggests large‐scale atmospheric recycling of this element.
Possible solar signature on a well‐established weather phenomenon
Authors: Tritakis Vasilis P.
Published: February 2008

Analysis of 4963 Etesian cases that took place over 90 years (1892–1981) reveals a possible solar signature in the troposphere. The signature consists of a characteristic tendency of the Etesian cases to build predominant peaks on the 7th–8th solar rotation days (Bartel days). Further analysis of the data in various solar activity levels showed the possible solar control on the Etesians' occurrences to be significant in the epoch of the solar maximum but weak in the intermediate years and insignificant in the epoch of solar minimum, of solar cycles 13–21. Keeping in mind that in most cases of solar‐weather events the coupling was detected mainly in winter, a possible solar signature on the Etesians appears to be a rare case where a summer weather effect would be affected by the sun.
Changes in atmospheric CO2: Influence of the marine biota at high latitude
Authors: Knox Fanny , McElroy Michael B.
Published: February 2008

Approximately half of the nitrogen and phosphorus entering deep waters of the contemporary ocean are transported from the surface in inorganic form as preformed nutrients. A simple model for ocean chemistry is presented and shown to account for the present level of atmospheric CO2. Fluctuations in preformed nutrients, modulated by changes in insolation and circulation at high latitudes, can result in significant variations in CO2. It is suggested that these changes may account for the apparent control on climate exercised by secular variations in the orbital parameters of the earth.
Measurements of stratospheric bromine
Authors: Sedlacek W. A. , Lazrus A. L. , Gandrud B. W.
Published: February 2008

From 1974 to 1977, molecules containing acidic bromine were sampled in the stratosphere by using tetrabutyl ammonium hydroxide impregnated filters. Sampling was accomplished by WB‐57F aircraft and high‐altitude balloons, spanning latitudes from the equator to 75°N and altitudes up to 36.6 km. Analytical results are reported for 4 years of measurements and for laboratory simulations that determined the filter collection efficiencies for a number of brominated species. Mass mixing ratios for the collected bromine species in air average about 27 pptm in the stratosphere. Seasonal variability seems to be small.
Periodic (18.6‐year) and cyclic (11‐year) induced drought and flood in western North America
Authors: Currie Robert Guinn
Published: February 2008

Analysis of 102 recent tree‐ring chronologies confirms earlier evidence for 18.6‐year tidal drought/flood induction (Currie, 1981d, 1984b) and led to discovery of 11‐year solar cycle induced drought/flood for western North America. Bistable phasing in terms of geography is found with epochs of maximum in lunar nodal 18.6‐year drought in western Canada out of phase with those in the western United States and northern Mexico the past two centuries. Solar drought/flood induction provides one mechanism that appears to have modulated the intensity of nodal drought/flood induction in the latter region, most recently at epoch 1936.1. The above results were confirmed by analysis of yet more voluminous data, and they led to discovery of an example of bistable phasing with respect to time in western Canada during the 17th century. The implications for agriculture of such phenomena, which occur world‐wide (Currie, 1984c), are surveyed.