bluuebunny/crossref_metadata_2025 huggingface dataset:
Biogeochemical cycling in the global ocean: 1. A new, analytical model with continuous vertical resolution and high‐latitude dynamics
Authors: Shaffer Gary , Sarmiento Jorge L.
Published: February 2004

A new, simple analytical model of ocean chemistry is presented which includes continuous vertical resolution, high‐latitude dynamics, air‐sea exchange and sea ice cover. In this high‐latitude exchange/interior diffusion‐advection (HILDA) model, ocean physics are represented by four parameters: k and w, an eddy diffusion coefficient and a deep upwelling velocity in the stratified interior; q, a rate of lateral exchange between the interior and a well‐mixed, deep polar ocean; and u, an exchange velocity between surface and deep layers in the polar ocean. First, estimates are made of ice‐free and ice‐covered areas at high latitudes, surface temperatures, and air‐sea exchange velocities from available data. Then values of the physical parameters are estimated from simultaneous, least mean square fits of model solutions for temperature (T) and “abiotic” carbon 14 (Δ14C) to interior profiles of T and Δ14C and surface layer Δ14C values all derived from available data. Best fit values for k, w, q, and u are 3.2×10−5 m2 s−1, 2.0×10−8 m s−1, 7.5×10−11 s−1 and 1.9×10−6 m s−1 respectively. These results are interpreted in terms of modes of ocean circulation and mixing and compared with results from other simplier and more complex models. In parts 2 and 3 of this series, these values for k, w, q and u are taken as inputs for studying phosphorus, oxygen, and carbon cycling in the global ocean with the HILDA model.
A census of mesoscale eddies in Shelikof Strait, Alaska, during 1989
Authors: Bograd Steven J. , Stabeno Phyllis J. , Schumacher James D.
Published: February 2004

Over a 5‐month period in the spring and summer of 1989, 12 mesoscale eddies were identified crossing a section of moored current meters in the Shelikof sea valley. This represents the first census of mesoscale eddies on the northwestern Gulf of Alaska continental shelf. The majority of eddies (7) were observed in May and June. Anticyclonic eddies outnumbered cyclonic eddies two to one, but all had characteristics similar to eddies previously observed in the region. Analysis of the current meter time series revealed that the mean speeds, volume transport, and the structure of the flow at the present location were similar to current meter and hydrographic measurements during other years in the sea valley. We suggest that 1989 was a typical year in terms of eddy formation as well. The proliferation of mesoscale eddies in this region in spring has an impact on the larval dispersal and eventual recruitment of walleye pollock.
Ocean‐ice interaction in the marginal ice zone using synthetic aperture radar imagery
Authors: Liu Antony K. , Peng Chich Y. , Weingartner Thomas J.
Published: February 2004

Ocean‐ice interaction processes in the marginal ice zone (MIZ) by wind, waves, and mesoscale features, such as up/downwelling and eddies are studied using ERS 1 synthetic aperture radar (SAR) images and an ocean‐ice interaction model. A sequence of seven SAR images of the MIZ in the Chukchi Sea with 3 or 6 days interval are investigated for ice edge advance/retreat. Simultaneous current measurements from the northeast Chukchi Sea, as well as the Barrow wind record, are used to interpret the MIZ dynamics. SAR spectra of waves in ice and ocean waves in the Bering and Chukchi Sea are compared for the study of wave propagation and dominant SAR imaging mechanism. By using the SAR‐observed ice edge configuration and wind and wave field in the Chukchi Sea as inputs, a numerical simulation has been performed with the ocean‐ice interaction model. After 3 days of wind and wave forcing the resulting ice edge configuration, eddy formation, and flow velocity field are shown to be consistent with SAR observations.
An ERS 1 synthetic aperture radar image of atmospheric lee waves
Authors: Vachon P. W. , Johannessen O. M. , Johannessen J. A.
Published: February 2004

An ERS 1 synthetic aperture radar (SAR) image of the island Hopen shows a distinct 7.6‐km wavelength wave phenomenon near the island. This wave phenomenon is interpreted as the surface imprint on open water of atmospheric lee waves. The pattern is visible in the SAR image, since the lee waves modulate the horizontal wind speed near the ocean surface which, in turn, modulates the surface roughness and the radar cross section. The physical setting for the observation is presented and discussed. The lower bound on horizontal wind speed modulation is estimated to range from 3±2 ms−1(for the wind speed minima) to 12±2 ms−1(for the wind speed maxima) based upon the observed radar cross‐section modulation and the ERS 1 scatterometer wind retrieval model CMOD4. The wavelength and wind speed modulation are consistent with linear lee wave model predications. The model uses an atmosphere with an exponential profile of the Scorer parameter (ratio of buoyancy frequency to wind speed) to represent a shallow, ground‐based inversion layer observed at Bear Island and a bell‐shaped barrier to represent the forcing effects of Hopen.
Arctic sea ice concentrations from special sensor microwave imager and advanced very high resolution radiometer satellite data
Authors: Emery W. J. , Fowler C. , Maslanik J.
Published: February 2004

Nearly coincident data from the special sensor microwave imager (SSM/I) and the advanced very high resolution radiometer (AVHRR) are used to compute and compare Arctic sea ice concentrations for different regions and times of the year. To help determine overall accuracies and to highlight sources of differences between passive microwave, optical wavelength, and thermal wavelength data, ice concentrations are estimated using two operational SSM/I ice concentration algorithms and with visible‐ and thermal‐infrared wavelength AVHRR data. All algorithms capture the seasonal patterns of ice growth and melt. The ranges of differences fall within the general levels of uncertainty expected for each method and are similar to previous accuracy estimates. The estimated ice concentrations are all highly correlated, with uniform biases, although differences between individual pairs of observations can be large. On average, the NASA Team algorithm yielded 5% higher ice concentrations than the Bootstrap algorithm, while during nonmelt periods the two SSM/I algorithms agree to within 0.5%. These seasonal differences are consistent with the ways that the 19‐GHz and 37‐GHz microwave channels are used in the algorithms. When compared to the AVHRR‐derived ice concentrations, the Team‐algorithm results are more similar on average in terms of correlation and mean differences. However, the Team algorithm underestimates concentrations relative to the AVHRR output by 6% during cold months and overestimates by 3% during summer. Little seasonal difference exists between the Bootstrap and AVHRR results, with a mean difference of about 5%. Although the mean differences are less between the SSM/I‐derived concentrations and concentrations estimated using AVHRR channel 1, the correlations appear substantially better between the SSM/I data and concentrations derived from AVHRR channel 4, particularly for the Team algorithm output.
A preliminary evaluation of ocean topography from the TOPEX/POSEIDON mission
Authors: Nerem R. S. , Schrama E. J. , Koblinsky C. J. , Beckley B. D.
Published: February 2004

We have analyzed 50 ten‐day cycles of TOPEX/POSEIDON (T/P) altimeter data to evaluate the ocean dynamic topography and its temporal variations. We have employed data from both the U.S. and French altimeters along with the NASA precision orbits in this analysis. Errors in the diurnal and semidiurnal components of the Cartwright‐Ray tide model have been significantly reduced using a correction developed from T/P altimeter data by Schrama and Ray (this issue). A hybrid geoid model formed from a combination of JGM‐2 and OSU91A was employed, as well as a geoid model based solely on OSU91 A. The long wavelengths of the mean dynamic topography show considerable improvement over previous missions based on comparisons to historical hydrographic data, although geoid error still corrupts the dynamic topography for wavelengths shorter than 2500 km. The RMS variability is similar to previous results from Geosat, with background “noise” approaching 3 cm RMS. The computed annual and semiannual variations are also similar to previous Geosat results, although the hemispheric distribution of the annual heating cycle is much better represented in the T/P results. They also compare reasonably well with the Levitus hydrographic compilation in the northern hemisphere, although the T/P variations generally have larger amplitudes. Ten‐day average maps of variations in sea level compare well with simultaneous measurements at ocean tide gauges, with RMS differences of less than 4 cm and correlations greater than 0.6 for most of the island gauges. Time‐longitude plots of these sea level variations at different latitudes in the Pacific clearly show the presence of equatorial Kelvin waves and Rossby waves, with the wave speeds agreeing well with theoretical and observed values. Measurement of variations in global sea level over cycles 2–51 have an RMS variability of 6.3 mm and a rate of change of −3.5±8 mm/yr, the uncertainty primarily due to insufficient averaging of the interannual and periodic sea level variations. With several more years of data and accurate monitoring of the altimeter drift at the calibration sites, T/P has the potential for providing a precise (±1 mm/yr) estimate of the rate of global sea level rise. These results show that the accuracy of the T/P measurements of sea level has dramatically improved over previous missions, with estimated time variable errors of 4 cm or less (1σ). Although geographically correlated orbit errors have also been reduced to the few centimeter level, further improvement in determinations of the mean dynamic topography will be difficult to obtain until a more accurate model of the marine geoid is available.
Ocean tides in the northern North Atlantic and adjacent seas from ERS 1 altimetry
Authors: Andersen Ole Baltazar
Published: February 2004

Twenty months of ERS 1 35‐day repeat altimeter data containing 18 repeat cycles have been used to estimate the major diurnal and semidiurnal ocean tide signals in the northern parts of the North Atlantic and adjacent seas. ERS 1 provides valuable information when investigating ocean tides, owing to the repeated dense spatial sampling. However, several tidal constituents are extremely difficult to resolve using conventional harmonic analysis with the chosen sun syncronous orbit. Instead, temporal analysis at each crossover location is applied using a modified form of the orthotide formulation, which simultaneously solves for the diurnal and semidiurnal species as well as for the annual signal. The use of the response formalism ensures that the sun syncronous component S2can be resolved, although this component is “frozen” in the orbit. Maps of the M2, S2and K1tidal amplitudes and phases in 0.5°×0.5° grids are presented and are seen to compare favorably with measurements at 68 pelagic tide gauges provided by the International Association for Physical Sciences of the Ocean. The major tidal constituents of the ERS 1 derived model are also in close agreement with the improved Flather (1981) ocean tide model for the northwest European continental shelf area, as well as a numerical model for the Arctic and Nordic Seas by Gjevik and Straume (1989).
Observations of a street of cyclonic eddies in the Indian Ocean sector of the Antarctic Divergence
Authors: Wakatsuchi Masaaki , Ohshima Kay I. , Hishida Masataka , Naganobu Mikio
Published: February 2004

Hydrographic and drifting buoy data from Japanese cruises show that the Antarctic Divergence in the Indian Ocean sector is composed of a street of cyclonic eddies. These eddies measure about 500 km in the zonal direction and 200 km in the meridional. Part of the eastward flowing Antarctic Circumpolar Current (ACC) meanders southward in the regions between the eddies. In the eddy regions, warm, saline Circumpolar Deep Water is upwelled into the shallow layers, while cold, dense coastal water advects into the deep layers; the advection occurs along the isobaths of ridges which extend north from the coast. The combination of the advection with the upwelling produces a water column denser than the surrounding water and leads to the formation and maintenance of the cyclonic eddies. Presence of the northward extending ridges approximately governs the location of eddy formation. The eddy formation recurs year after year, although eddy locations can vary somewhat. A polynya was observed to persistently occur and corresponded with one of the eddies in location, size, and form. The oceanographic observations also suggest that the primary meridional exchanges of heat and salt in the Antarctic are caused through the eddies and ACC meanders within the Antarctic Divergence.
Structural and stratigraphie features and ERS 1 synthetic aperture radar backscatter characteristics of ice growing on shallow lakes in NW Alaska, winter 1991–1992
Authors: Jeffries M. O. , Morris K. , Weeks W. F. , Wakabayashi H.
Published: February 2004

Changes in ERS 1 C band synthetic aperture radar (SAR) backscatter intensity (σ°) from ice growing on shallow tundra lakes at three locations in NW Alaska are described. Ice core analysis shows that at all lakes on the coast at Barrow the ice, whether floating or frozen to the bottom, includes an inclusion‐free layer overlying a layer of ice with tubular bubbles oriented parallel to the direction of growth. The clear ice may also be overlain by a discontinuous layer of bubbly snow ice. Backscatter is low (‐16 to −22 dB) at the time of initial ice formation, probably due to the specular nature of the upper and lower ice surfaces causing the radar pulse to be reflected away from the radar. As the ice thickens during the autumn, backscatter rises steadily. Once the ice freezes to the lake bottom, regardless of the presence of forward scattering tubular bubbles, low backscatter values of‐17 to −18 dB are caused by absorption of the radar signal in the lake bed. For ice that remains afloat all winter the ice‐water interface and the tubular bubbles combine, presumably via an incoherent double‐bounce mechanism, to cause maximum backscatter values of the order of −6 to −7 dB. The σ° saturates at −6 to −7 dB before maximum ice thickness and tubular bubble content are attained. A simple ice growth model suggests that the layer of ice with tubular bubbles need be only a few centimeters thick midway through the growth season to cause maximum backscatter from floating ice. During the spring thaw a previously unreported backscatter reversal is observed on the floating and grounded portions of the coastal lakes but not on the lakes farther inland. This reversal may be related to the ice surface topography and wetness plus the effects of a longer, cooler melt period by the coast. Time series of backscatter variations from shallow tundra lakes are a record of (1) the development of tubular bubbles in the ice and, by association, changes in the gas content of the underlying water and (2) the freezing of ice to the bottoms of the lakes and therefore lake bathymetry and water availability. SAR is also able to detect the onset of lake ice growth in autumn and the initiation of the spring thaw and thus has potential for monitoring high‐latitude lake ice growth and decay processes in relation to climate variability.
Determining the response of sea level to atmospheric pressure forcing using TOPEX/POSEIDON data
Authors: Fu Lee‐Lueng , Pihos Greg
Published: February 2004

The static response of sea level to the forcing of atmospheric pressure, the so‐called inverted barometer (IB) effect, is investigated using TOPEX/POSEIDON data. This response, characterized by the rise and fall of sea level to compensate for the change of atmospheric pressure at a rate of −1 cm/mbar, is not associated with any ocean currents and hence is normally treated as an error to be removed from sea level observation. Linear regression and spectral transfer function analyses are applied to sea level and pressure to examine the validity of the IB effect. In regions outside the tropics, the regression coefficient is found to be consistently close to the theoretical value except for the regions of western boundary currents, where the mesoscale variability interferes with the IB effect. The spectral transfer function shows near IB response at periods from 20 to 300 days. The regression coefficient averaged over the regions poleward of 30 degrees is −0.84±0.29 cm/mbar (1 standard deviation). The deviation from −1 cm/mbar is shown to be caused primarily by the effect of wind forcing on sea level, based on a multivariate linear regression model involving both pressure and wind forcing. The regression coefficient for pressure resulting from the multivariate analysis is −0.96±0.32 cm/mbar. In the tropics the multivariate analysis fails because sea level in the tropics is primarily responding to remote wind forcing. However, after removing from the data the wind‐forced sea level estimated by a dynamic model of the tropical Pacific, the pressure regression coefficient improves from −1.22±0.69 cm/mbar to −0.99±0.46 cm/mbar, clearly revealing an IB response. The result of the study suggests that with a proper removal of the effect of wind forcing the IB effect is valid in most of the open ocean at periods longer than 20 days and spatial scales larger than 500 km.
Slow El Niño‐Southern Oscillation boundary waves
Authors: White Warren B.
Published: February 2004

Anomalies of sea surface temperature (SST) and heat storage in the upper 400 m of ocean (HS400) for 13 years from 1979 to 1991 are mapped onto a 2° latitude by 5° longitude grid each month over most of the global ocean from 30°S to 60°N. Time sequences at every grid location are band pass filtered to reveal El Niño‐Southern Oscillation (ENSO) signals on period scales ranging from 2 to 7 years. Time‐distance diagrams are constructed along the equator and eastern boundary of the North Pacific, North Atlantic, and South Indian Oceans. These time‐distance diagrams display slow poleward propagation of equatorial ENSO signals, consistently in HS400 and intermittently in SST. In the North Pacific Ocean, ENSO signals in HS400 take 9–18 months to propagate from the equator northward along the west coast of North America to the Gulf of Alaska. In the North Atlantic Ocean, ENSO signals in HS400 take 6–12 months to propagate from the equator along the west coast of Africa to the Strait of Gibraltar. In the South Indian Ocean, ENSO signals in HS400 take 9–18 months to propagate poleward from the equator along the west coasts of Indonesia and Australia to Perth. Speeds of poleward propagation of ENSO waves in both HS400 and SST along these eastern boundaries range from 5 to 30 cm s−1. These ENSO boundary waves propagate in the same direction as Kelvin waves, but with speeds an order of magnitude smaller. They provide a remote and delayed influence upon ENSO activity in the middle‐latitude eastern boundary in each ocean. Time‐distance diagrams are also constructed along the western boundary and equator of the North Pacific, North Atlantic, and South Pacific Oceans. These time‐distance diagrams display slow propagation of ENSO signals in SST and HS400 in both directions depending on the ocean. In the North Pacific Ocean, ENSO signals in both SST and HS400 propagate equatorward from Taiwan to New Guinea, taking 6–18 months to make this transit. Moreover, they arrive on the equator in phase with zonally propagating equatorial ENSO waves. This indicates that ENSO activity in the western subtropical North Pacific Ocean influences ENSO activity in the western equatorial Pacific Ocean through slow equatorward propagation. Speeds of equatorward propagation of ENSO waves in both HS400 and SST along this western boundary range from 5 to 20 cm s−1. In the North Atlantic and South Pacific Oceans this off‐equatorial influence is not possible, since slow ENSO waves in HS400 propagate poleward along these western boundaries.
A numerical study of dense water formation and transport on a shallow, sloping continental shelf
Authors: Gawarkiewicz Glen , Chapman David C.
Published: February 2004

The circulation and transport of dense water generated by an idealized coastal polynya is studied using a three‐dimensional primitive equation model. Starting with a homogeneous, quiescent ocean, a constant negative buoyancy flux is imposed at the surface over a half‐elliptical region adjacent to the coastal boundary on a gently sloping continental shelf. The flow response can be divided into the following three phases: geostrophic adjustment, instability, and offshore eddy transport. During geostrophic adjustment the fluid within the forcing region becomes denser and the flow at the edge of the forcing region accelerates in response to the strong density gradient there. Eventually, the flow at the leading edge of the forcing region (relative to Kelvin wave propagation) becomes unstable and a train of counterrotating eddies develops. These eddies then form a complex three‐dimensional flow field and rapidly transport dense water offshore, across isobaths. The density within the forcing region reaches a maximum which remains fairly constant after the eddies begin to transport the dense fluid offshore. The results are qualitatively insensitive to weakening of the negative buoyancy forcing and to changing the bottom slope. Eddy scales and velocities are consistent with observations in the Arctic. The results suggest that instability processes and eddy fluxes are important in transporting dense water off continental shelves and into marginal seas.
The long‐lived mollusc Arctica islandica: A new paleoceanographic tool for the reconstruction of bottom temperatures for the continental shelves of the northern North Atlantic Ocean
Authors: Weidman Christopher R. , Jones Glenn A. , Kyger
Published: February 2004

The carbonate shell of the bivalve Arctica islandica has been recognized, for more than a decade, as a potentially important marine geochemical biorecorder owing to this species' great longevity (200+ years) and wide geographic distribution throughout the northern North Atlantic Ocean, a region vital to global climate and ocean circulation. However, until now this potential has not been realized owing to the difficulty of precisely sampling the shell of this slow growing species. Using newly available automated microsampling techniques combined with micromass stable isotope mass spectrometry, a stable oxygen isotope record (1956–1957 and 1961–1970) has been obtained from a live‐captured, 38‐year‐old A. islandica specimen collected near the former position of the Nantucket Shoals Lightship (41°N. 69°W). The shell's δ18O signal is compared with an expected signal derived from ambient bottom temperature and salinity data recorded at the lightship for the same period. The results show that A islandica's δ18O record (1) is in phase with its growth banding, confirming the annual periodicity of this species' growth bands, (2) is in oxygen isotopic equilibrium with the ambient seawater, (3) shows a consistent shell growth shutdown temperature of ∼6°C. which translates into an ∼8‐month (May–December) shell growth period at this location, and (4) records the ambient bottom temperature with a precision of ∼±1.2°C. These results add important information on the life history of this commercially important shellfish species and demonstrate that A. islandica shells can be used to reconstruct inter‐ and intra‐annual records of the continental shelf bottom temperature.
Tests of a two‐grid world ocean model
Authors: Coward Andrew C. , Killworth Peter D. , Blundell Jeffrey R.
Published: February 2004

A numerical method for a global ocean model which does not need artificial islands or Fourier filtering at high northern latitudes is described. The method uses two grid schemes: one, for most of the ocean, is regular latitude‐longitude; the other uses a rotated pseudo‐latitude and pseudo‐longitude scheme with the poles in the equatorial Pacific and Indian Oceans. The two grids defined by these coordinates communicate in the equatorial Atlantic. A method for communicating information between these is described briefly, and a test of the method is made using equatorial Kelvin and Rossby waves. The two‐grid method is found to perform excellently (when compared with a similar problem using a simple latitude‐longitude grid), so that the method may be considered validated for future use in a global model.
Sea ice type maps from Alaska Synthetic Aperture Radar Facility imagery: An assessment
Authors: Fetterer Florence M. , Gineris Denise , Kwok Ronald
Published: February 2004

Synthetic aperture radar (SAR) imagery received at the Alaska SAR Facility is routinely and automatically classified on the Geophysical Processor System (GPS) to create ice type maps. We evaluated the wintertime performance of the GPS classification algorithm by comparing ice type percentages from supervised classification with percentages from the algorithm. The RMS difference for multiyear ice is about 6%, while the inconsistency in supervised classification is about 3%. The algorithm separates first‐year from multiyear ice well, although it sometimes fails to correctly classify new ice and open water owing to the wide distribution of backscatter for these classes. Our results imply a high degree of accuracy and consistency in the growing archive of multiyear and first‐year ice distribution maps. These results have implications for heat and mass balance studies which are furthered by the ability to accurately characterize ice type distributions over a large part of the Arctic.
A new approach for determining fully empirical altimeter wind speed model functions
Authors: Freilich Michael H. , Challenor Peter G.
Published: February 2004

A statistical technique is developed for determining fully empirical model functions relating altimeter radar backscatter (σ0) measurements to near‐surface neutral stability wind speed. By assuming that σ0 varies monotonically and uniquely with wind speed, the method requires knowledge only of the separate, rather than joint, distribution functions of σ0 and wind speed. Analytic simplifications result from using a Weibull distribution to approximate the global ocean wind speed distribution; several different wind data sets are used to demonstrate the validity of the Weibull approximation. The technique has been applied to 1 year of Geosat data. Validation of the new and historical model functions using an independent buoy data set demonstrates that the present model function not only has small overall bias and RMS errors, but yields smaller systematic error trends with wind speed and pseudowave age than previously published models. The present analysis suggests that generally accurate altimeter model functions can be derived without the use of collocated measurements, nor is additional significant wave height information measured by the altimeter necessary.
Air‐ice drag coefficients in the western Weddell Sea: 1. Values deduced from profile measurements
Authors: Andreas Edgar L. , Claffey Kerry J.
Published: February 2004

From 197 hourly averaged, four‐level wind speed profiles collected on Ice Station Weddell (ISW) in February and March 1992, we compute the neutral stability, 10‐m, air‐ice drag coefficient, CDN10. Values range from 1.3×10−3 to 2.5×10−3 for the multiyear ice floe that was ISW. Individual CDN10 values depend critically on how well the mean wind is aligned with the dominant snowdrift patterns. On ISW, 20% of the time, we experienced drifting or blowing snow; when the wind speed at 5 m exceeded 8 m s−1, such wind‐driven snow was a virtual certainty. Consequently, the surface was continually changing, drifts were building, drifts were eroding. As the wind continued from a constant direction and the building drifts streamlined the surface, CDN10 could decrease by as much as 30% in 12 hours. If the wind direction then shifted by as little as 20°, CDN10 would immediately increase significantly. The implications are that snow‐covered sea ice does not present an isotropic surface; it has a preferred direction dictated by the wind's history. Consequently, computing surface stress using an average value for CDN10 will produce errors of up to 30%.
On the hydrography of the Northeast Water Polynya
Authors: Budéus Gereon , Schneider Wolfgang
Published: February 2004

The water masses and circulation in the area of the Northeast Water Polynya, located on the East Greenland Shelf north of 79°N, are described on the basis of an R/V Polarstern cruise during spring and summer 1993. The baroclinic flow shows northward components close to the East Greenland coast and eastward components at the northern limit of the polynya. An anticyclonic half circle is formed by this and the southward flowing East Greenland Current. In the south the circle is not closed. The upper water column, occupied by Polar Water, is affected by this circulation pattern, while deeper waters in the trough system of the area seem to spread independently. Different types of deep waters are found in different troughs, all being of Atlantic origin, though they seem not to be directly connected to Return Atlantic Water. It is shown that what is called Polar Water must be formed, at least partly, on the Greenland Shelf and that deepwater formation does not occur in the investigated area.
The western equatorial Pacific: A water mass crossroads
Authors: Fine Rana A. , Lukas Roger , Bingham Frederick M. , Warner Mark J. , Gammon Richard H.
Published: February 2004

The western equatorial Pacific is a crossroads for thermocline and intermediate waters formed at higher latitudes. The role of the equatorward flowing, low‐latitude western boundary currents (LLWBCs) in advecting well‐ventilated (with respect to atmospheric gases), higher‐latitude waters varies with density. At densities <26.5 σθ the Mindanao Current (MC) (Wyrtki, 1961; Masuzawa, 1969) advects recently ventilated water observed as tracer maxima predominantly from the North Pacific subtropical gyre (tropical water is <3 years old and the remnant subtropical mode water is <5 years); it branches into the southern Celebes Sea feeding the Indonesian throughflow and toward the east north of the equator. Between 26.5 and 26.8 σθ the MC advects predominantly North Pacific Intermediate Water (having a component that is <20 years old) mainly into the southern Celebes Sea; there is also some indication of a tracer maximum extending eastward north of the equator. However, below 26.8 σθ, South Pacific water masses appear to be stronger, so that they are the major ventilation source for the western equatorial region, including the Celebes Sea. At 27.2 σθ the New Guinea Coastal Undercurrent advects Antarctic Intermediate Water (having a component that is <25 years) into a background of older water. The presence of subtropical mode water in the western tropical North Pacific and Celebes Sea is attributed to an equatorward LLWBC in the North Pacific (and suggests a reason for the absence of 18° water in the tropical North Atlantic). The absence of a LLWBC in the North Atlantic highlights a basic difference between the circulation of the two oceans, which may be due to the different ways they import and export water. At the western boundary in the North Atlantic, warm water is imported and cold water is exported as part of the global thermohaline circulation, whereas at the western boundary in the North Pacific, warm water (above 26.8 σθ) is mainly exported to the Indian Ocean via the Indonesian throughflow and cold water is imported.
The abundance of benthic calcareous foraminifera and other meiofauna at a time series station in the Northeast Water Polynya, Greenland
Authors: Newton Adrian C. , Rowe Gilbert T.
Published: February 2004

Abundance and vertical distribution of living calcareous Foraminifera and associated meiofauna have been estimated during the ice‐free period in 1992 and 1993 at a time series station in the Northeast Water Polynya off eastern Greenland. Calcareous forams (>150 μm) represented on average 28–39% of the meiofaunal size class. The mean abundance for both years was 574 individuals/100 cm2, and the variability of the estimates (Standard deviation = ±140) was relatively modest for benthic samples (Standard error=8.7% of the mean, number of samples=8). The abundance in 1992 was lower than in 1993 (probability <0.05), reflecting a smaller polynya, with less surface water productivity. While 41% of the variation in abundance in 1993 could be explained as a function of time (the estimated mean doubled between May 30 (387 ind/100 cm2) and July 24 (734 ind/100 cm2)), supporting earlier observations elsewhere that Foraminifera respond rapidly to seasonal or pulsed food inputs, the relationship was not statistically significant. The number of species present was low, a characteristic observed in other foram biofacies associated with open water shelf regions of the Arctic. This assemblage was dominated by a few calcareous forms: Elphidium excavatum, Melonis barleeanum, Nonionella labradorica, and Bucella frigida. Green and brown material, which we suspect was freshly settled phytodetritus, was found in numerous individuals of the dominant calcareous species located as deep as 6 cm within the sediment. The dominant species, including those containing “pigments,” were encountered at specific, fairly narrow depth ranges within the sediment, with maximum abundances being common below, rather than at the sediment surface. Other meiofauna (nematodes, agglutinated forams, and ostracods) occurred to depths as great as 10 cm in all cores, but their greatest densities were generally confined to surface sediments.
On the origin of the Tsushima Warm Current
Authors: Lie Heung‐Jae , Cho Cheol‐Ho
Published: February 2004

The origin of the Tsushima Warm Current (referred to as TWC) was investigated by surface drifter experiments and conductivity, temperature, and depth (CTD) surveys in the northeastern East China Sea (ECS) at three different times: July 1991, and April and November 1992. Trajectories of 10 satellite‐tracked drifters provide direct information for the first time on the surface flow patterns in each season, and CTD observations allow identification of warm and saline TWC waters. The results of the experiments argue against two historical concepts of TWC origins, i.e., (1) a northward flow transporting warm and saline water through the deep trough southwest of Kyushu toward the Korea Strait after separation from the Kuroshio and (2) a northeastward continuation of the Taiwan Current (TC) on the shelf of ECS after passing through the Taiwan Strait. A persistent northward current was found to exist both on the shelf west of the trough and on the western flank of the trough. The northward flow seems to bifurcate around the northwestern corner of the trough, splitting into a northward continuing flow on the shelf of 100–150 m and an eastward flow along the northern wall of the trough. The northward flow on the shelf, which might be the shore fringe of the Kuroshio, corresponds to the origin of TWC entering the Korea Strait. The eastward flow on the northern slope turned back to the south along the west coast of Kyushu and eventually joined the Kuroshio. This structure was accompanied by an anticyclonic eddy in the northern trough. The second concept, that of TWC originating from TC, contradicts the observed differences in physical properties between TWC and TC waters. The saline water in the Taiwan Strait flows out intermittently only during late winter‐early spring, and its salinity during other seasons is lower than that of the TWC water in the Korea Strait. Experiments also indicated a seasonal shift of drifter paths in the northeastern ECS and coexistence of cyclonic and anticyclonic eddies in the trough during the cold season.
Wave‐driven flow over shallow reefs
Authors: Symonds Graham , Black Kerry P. , Young Ian R.
Published: February 2004

Long‐term (1 month) observations of waves and currents over a natural reef are presented which show a strong correlation between offshore rms incident wave height and cross‐reef currents at subtidal frequencies. The energy spectrum of the cross‐reef currents shows a significant peak at twice the semidiurnal tidal frequency, while the spectrum of sea surface elevation over the reef flat shows no corresponding peak. Furthermore, experimental results reported by Gourlay (1993) show setup over the reef occurs in the absence of a beach, and the cross‐reef transport decreases with an increase in the sea surface slope across the reef flat due to an increase in setup at the top of the reef face. Analytic solutions for flow forced by wave breaking over an idealized reef explain the above features of cross‐reef flows in the absence of a beach. Through the surf zone on the reef face the cross‐reef gradient in the radiation stress due to wave breaking is partitioned between balancing an offshore pressure gradient associated with setup over the reef and forcing a mean flow across the reef. Over the reef flat, where the depth is constant, there is no forcing due to wave breaking and the flow is driven by a pressure gradient which results from the setup through the surf zone. The magnitude of the setup through the surf zone is such that the transport across the reef flat matches the transport through the surf zone which is forced by the gradient in the radiation stress. Solutions are presented for general reef geometry, defined by the reef width and slope of the seaward reef face, and incident wave forcing, defined by the depth at the breakpoint and the depth of water over the reef. As the depth over the reef goes to zero, the solutions converge to the plane beach solutions described by Longuet‐Higgins and Stewart (1964), wave setup is maximized, and the cross‐reef transport is zero. In other cases the relative magnitudes of the setup and the cross‐reef transport depend on the geometry of the reef and the incident wave forcing.
X band microwave backscattering from ocean waves
Authors: Lee P. H. Y. , Barter J. D. , Beach K. L. , Hindman C. L. , Lake B. M. , Rungaldier H. , Shelton J. C. , Williams A. B. , Yee R. , Yuen H. C.
Published: February 2004

Backscattering experiments at microwave frequencies were conducted off the west coast of Scotland in the summer of 1991. Using a dual‐polarization, eight‐frequency, X band, coherent scatterometer mounted on the bow of a boat, we measured time‐resolved backscattering from ocean waves at a range of grazing angles from 10° to 70°. From the grazing‐angle‐dependent signals and their Doppler spectra, we are able to differentiate Bragg scattering from non‐Bragg scattering and resolve “peak separation” between the vertical and horizontal polarizations. We observe instances of “super” events, i.e., instances when the horizontal polarization return power equals or exceeds the vertical polarization power at particular frequencies. We find that “super” events occur not only at low grazing angles but at any grazing angle for upwind viewing directions and obtain statistics for such occurrences as a function of grazing angle. We study the coherence properties of scatterers and find strong evidence that at low grazing angles, lifetime‐dominated, non‐Bragg scattering contributes noticeably to returns of both polarizations, but is dominant in providing returns for the horizontal polarization. We examine “spiking” events and find that they can be related to, but need not be limited to, breaking wave events. By comparing the data of upwind runs with cross‐wind and circle runs, we obtain wind direction dependence of Doppler spectra, which further assists in the identification of scattering mechanisms.
Introduction to special section on Physical Oceanography of the Amazon Shelf
Authors: Geyer W. Rockwell , Beardsley Robert C.
Published: February 2004

The Amazon shelf is an unusual oceanographic environment. In addition to the large input of fresh water from the Amazon River, unusually large tidal currents, vigorous wind‐driven currents, and an impinging western boundary current contribute to one of the most energetic continental shelf environments in the world. Much of the shelf is very shallow; the 20‐m isobath extends as far as 200 km from the river mouth. The proximity of the Amazon shelf to the equator means that rotational effects are much weaker than at midlatitudes.
Lagrangian flow observations of the Amazon River discharge into the North Atlantic
Authors: Limeburner Richard , Beardsley Robert C. , Soares Ivan D. , Lentz Steven J. , Candela Julio
Published: February 2004

Nine satellite‐tracked drifters with near‐surface drogues were launched in or near the mouth of the Amazon River on the north Brazil shelf during 1989–1991 at four different stages of river discharge. The drifters initially moved along shelf toward the northwest over the north Brazil shelf with mean speeds varying from 41 to 128 cm/s and a maximum along‐shelf velocity of 197 cm/s. Many drifters experienced strong acceleration near 2°N between the 5‐m and 20‐m isobaths, caused in part by the sharp reduction in cross‐shelf cross‐sectional area near the shore‐perpendicular Cabo Norte shoal. The drifter trajectories showed strong cross‐shelf tidal variability in the flow field near the Amazon River mouth, and the largest low‐frequency, along‐shelf variability was located over the open shelf just north of Cabo Norte. Good visual correlation between drifter along‐shelf velocity and along‐shelf wind stress supports the dynamical model of Lentz (this issue) that subtidal fluctuations in near‐surface along‐shelf currents in the Amazon River Plume are strongly wind driven. Drifters left the north Brazil shelf after about 5 to 30 days. Three drifters moved northwestward parallel to the northeast coast of South America, crossed the shelf break near 8°N, and moved into deeper North Atlantic water where they began looping in anticyclonic eddies (often called retroflection eddies or loopers) with periods of approximately 11 days as they moved northwestward to the Caribbean Sea. Four drifters initially moved along shelf toward the northwest and then offshore between 3°N and 7°N, where they followed the retroflection of the North Brazil Current. Only one drifter entered the zonal current system that characterizes the equatorial Atlantic circulation.
Modeling the formation and deposition of frazil ice beneath Filchner‐Ronne Ice Shelf
Authors: Bombosch Andreas , Jenkins Adrian
Published: February 2004

Large areas of the Filchner‐Ronne Ice Shelf are underlain by layers of marine ice, which form when supercooled seawater circulating beneath the ice shelf freezes. The freezing process initially produces a suspension of disc‐shaped frazil ice crystals, and these are subs quently deposited onto the ice shelf base in areas where the flow of water is slack enough. This has been modeled assuming that the freezing takes place within buoyant plumes of Ice Shelf Water ascending the ice shelf base from source regions near the grounding lines of the major inlet glaciers. The deposition of the majority of the suspended frazil ice is found to occur in spatially discrete bursts, where peak rates of accumulation at the ice shelf base exceed 1 m yr−1 of solid ice. There is a good correlation between the location of the zones of crystal deposition and the position of the upstream limits of the marine ice layers. The high rates of localized accumulation account for the rapid buildup observed in the layer thickness, which then gradually declines as the marine ice is carried downstream with the flow of the ice shelf. Model results also suggest an origin for the ice platelets observed at depth in the water column near the Filchner Ice Shelf.
Variations of atmospheric angular momentum associated with intraseasonal oscillations forced by zonally moving prescribed heating
Authors: Itoh Hisanori
Published: February 2004

Intraseasonal variations of atmospheric angular momentum (AAM) are numerically studied. With prescribed 40‐day‐period external heating which moves eastward from 60°E to the dateline in the tropics, intraseasonal oscillations are forced in a numerical model. In accordance with the oscillations, the variations of AAM also show 40‐day periods. The phase relationship between the model intraseasonal oscillations and AAM variations is similar to that observed. Further, AAM exhibits the largest variation in the equatorial region, and a phase propagation from equatorial regions to the subtropics, and from high latitudes to the subtropics, as found in the real atmosphere. After careful inspection of these features, it was clarified that the source region for intraseasonal variations of AAM is not the equatorial region, but the subtropics. Also, the equatorial region is an apparent or superficial source region, since AAM is transported from the subtropics, in accordance with the propagation of Rossby wave trains to the subtropics. The phase propagation of AAM from high latitudes to the subtropics can also be explained from the behavior of Rossby wave trains in the midlatitudes radiating from the equatorial region. Thus, Rossby wave trains associated with intraseasonal oscillations play an important role in intraseasonal variations of AAM.
A two‐dimensional modeling study of the volcanic eruption of Mount Pinatubo
Authors: Bekki S. , Pyle J. A.
Published: February 2004

The formation and temporal evolution of the sulphate aerosol cloud generated by the volcanic eruption of Mount Pinatubo in June 1991 is simulated using a two‐dimensional sulphate aerosol model. Results are compared to time series of SO2 and aerosol data (aerosol mass, optical depth, and surface area density). The modeled SO2 decay appears to be broadly consistent with observations. The absence of homogeneous nucleation in the model seems to lead to significant discrepancies in the timing of the peak in aerosol loading and the magnitude of the surface area density. This suggests that homogeneous nucleation plays an important role during the early stages of a volcanic eruption in determining the average size of volcanic sulphate particles and hence their residence time in the atmosphere. By including the heterogeneous hydrolysis of N2O5 to HNO3, the model predicts subtantial decreases in NO2 column, enhancements in ClO column and a small reduction in global O3. The modeled aerosol layer is still far from having recovered its background level 2 years after the eruption.
A new numerical model of the middle atmosphere: 2. Ozone and related species
Authors: Garcia Rolando R. , Solomon Susan
Published: February 2004

A new two‐dimensional model with detailed photochemistry is presented. The model includes descriptions of planetary wave and gravity wave propagation and dissipation to characterize the wave forcing and associated mixing in the stratosphere and mesosphere. Such a representation allows for explicit calculation of the regions of strong mixing in the middle atmosphere required for accurate simulation of trace gas transport. The new model also includes a detailed description of photochemical processes in the stratosphere and mesosphere. The downward transport of H2, H2O, and NOy from the mesosphere to the stratosphere is examined, and it is shown that mesospheric processes can influence the distributions of these chemical species in polar regions. For HNO3 we also find that small concentrations of liquid aerosols above 30 km could play a major role in determining the abundance in polar winter at high latitudes. The model is also used to examine the chemical budget of ozone in the midlatitude stratosphere and to set constraints on the effectiveness of bromine relative to chlorine for ozone loss and the role of the HO2 + BrO reaction. Recent laboratory data used in this modeling study suggest that this process greatly enhances the effectiveness of bromine for ozone destruction, making bromine‐catalyzed chemistry second only to HOx‐catalyzed ozone destruction in the contemporary stratosphere at midlatitudes below about 18 km. The calculated vertical distribution of ozone in the lower stratosphere agrees well with observations, as does the total column ozone during most seasons and latitudes, with the important exception of southern hemisphere winter and spring.