bluuebunny/crossref_metadata_2025 huggingface dataset:
Open ocean surface wave measurement using Doppler sonar
Authors: Pinkel R. , Smith J. A.
Published: February 2008

In October–November 1983, Doppler sonars mounted on the research platform Flip were used to scatter 75‐kHz sound from the underside of the sea surface at low angle, as well as from the interior of the mixed layer. Surface gravity waves were seen in velocity estimates from the surface scattering sonar, even though the wave conditions were unusually calm. Valid measurements of sea surface motion were obtained over the range interval 600 to 1400 m from Flip. A second sonar which transmitted horizontally and scattered from the interior of the mixed layer also sensed surface waves, although with amplitude reduced in proportion to the decay of the motions with depth. Wave number‐frequency spectra of the observed motions are consistent with linear theory. The existence (emergence) of this technology enables the synthesis of kilometer‐long surface wave arrays in the open sea, without the cost and logistical support usually associated with large‐aperture arrays. In addition, the Doppler acoustic approach can provide information on lower‐frequency surface currents and on the spatial variations in these low‐frequency currents, such as Langmuir cells, which might affect wave propagation.
Multiple dipole eddies in the Alaska Coastal Current detected with Landsat thematic mapper data
Authors: Ahlnäs Kristina , Royer Thomas C. , George Thomas H.
Published: February 2008

Seventeen dipole eddies, including five large, well‐formed ones, three second‐generation eddies, and two double eddies, were observed in the Alaska Coastal Current near Kayak Island in one single scene of the Landsat thematic mapper (TM) on April 22, 1985. The digital Landsat TM satellite data were computer analyzed to extract details in the near coastal circulation in the northern Gulf of Alaska. Enhancement techniques were applied to the visible and thermal IR bands. The features are evident only in the visible bands because of the ability of these bands to detect the distribution of sediments in the near surface. These eddies did not have a significant thermal signature. The sources of these sediments are the glacial streams found throughout the Gulf of Alaska coast. Eddies of this configuration and frequency have never been observed here previously. However, the oceanographic and meteorological conditions are typical for this time of year. These eddies should be important to the cross‐shelf mixing processes in the Alaska Coastal Current and are an indicator that the flow here can be unstable at certain times of the year.
Fine‐scale temperature variability: The influence of near‐inertial waves
Authors: Marmorino G. O. , Rosenblum L. J. , Trump C. L.
Published: February 2008

Measurements made with a towed thermistor chain and acoustic doppler current profiler in the seasonal thermocline of the Sargasso Sea are examined for relationships among small‐scale temperature “activity,” shear, and internal wave variability. Patches of intense activity measuring 5–10 m high and several kilometers in length are found to persist within a near‐inertial wave packet. The packet was tagged with a drogue and followed for about 16 hours as it was advected along an edge of a cold‐core ring. The patches occur along surfaces of high vertical shear, where the Richardson number (7‐m vertical resolution) falls to values less than one. Within the patches are groups of small‐scale internal waves and fluid overturns. The overturns are 1–3 m high and are associated with wave‐breaking events. Away from the wave packet, activity levels are less, and the active fraction of the water column appears to be linked to variability in the internal wave field. It is conjectured that the near‐inertial wave patches are the same species as persistent mixing patches observed by Gregg et al. (1986), which were also associated with a near‐inertial wave.
Sea surface temperature, low‐level moisture, and convection in the tropical Pacific, 1982–1985
Authors: Steiner Ellen J. , Khalsa Siri Jodha Singh
Published: February 2008

Sea surface temperature (SST), lower tropospheric moisture, and deep convection in the tropical Pacific are described and compared for the period January 1982 through December 1985. All the data used were wholly or partially satellite derived, enabling the examination of continuous fields over large areas. SST data were from the blended analysis produced by the Climate Analysis Center, low‐level precipitable water (LLPW) in the 1000‐ to 700‐mbar layer was derived from the TIROS‐N operational vertical sounder aboard the NOAA polar‐orbiting satellites, and deep convection was estimated from the presence of highly reflective clouds (HRC) visible on NOAA satellite picture mosaics. Monthly means of LLPW and HRC were computed from daily data to correspond to the averaging period of SST. Maxima and minima of the three variables were found to be offset in both time and space, demonstrating that high SST does not always result in enhanced local convection. In the eastern equatorial Pacific, increases of SST and LLPW were found to precede rises of HRC by 1 or more months. Variability of all three parameters in the eastern Pacific was dominated by the 1982–83 El Niño‐Southern Oscillation and the seasonal cycle, whereas the seasonal cycle of all parameters in the western and central Pacific was weak. The strong signals in the eastern equatorial Pacific were in part responsible for the higher correlation coefficients between all pairs of variables there. Recent modeling studies are beginning to take into account the complexity of atmospheric response to surface heating.
El Niño occurrences over the past four and a half centuries
Authors: Quinn William H. , Neal Victor T. , Antunez De Mayolo Santiago E.
Published: February 2008

Applicable publications, involving five languages, have been reviewed to obtain information on El Niños that occurred over the past four and a half centuries. Since this information refers strictly to El Niño occurrences, a regional manifestation of the large‐scale (El Niño‐Southern Oscillation (ENSO)) event, it is based primarily on evidence obtained from the west coast region of northern South America and its adjacent Pacific Ocean waters. Authored lists of events were not acceptable without referenced valid information sources. It was desirable to have cross‐correlated reports from independent sources. Relative strengths of events are based on such considerations as wind and current effects on travel times of ancient sailing ships, degree of physical damage and destruction, amounts of rainfall and flooding, mass mortality of endemic marine organisms and guano birds, extent of invasion by tropical nekton, rises in sea temperatures and sea levels, affects on coastal fisheries and fish meal production, etc. Emphasis is placed on strong and very strong events. For example, the 1940–1941, 1957–1958, and 1972–1973 events fall into the strong category, whereas the 1891, 1925–1926 and 1982–1983 events are considered very strong. Over our period of study, 47 El Niño events were placed in the strong or very strong categories. Over the period 1800‐present, we noted 32 El Niño events of moderate or near moderate intensity. Weak events are not included here. The approach used here caused us to revise many of our earlier evaluations concerning event occurrences and intensities. Our tropical Pacific thickness analyses and cumulative plots of Southern Oscillation index anomalies over the southeast Pacific trade wind zone showed additional evidence as to the unusual strength of the 1982–1983 event. Also, in our investigation we noted several periods of long‐term (near decadal or longer) climatic change.
Downward longwave irradiance at the ocean surface from satellite data: Methodology and in situ validation
Authors: Frouin Robert , Gautier Catherine , Morcrette Jean‐Jacques
Published: February 2008

A methodology is presented for estimating downward longwave irradiance at the ocean surface from satellite radiance data. The downward longwave irradiance is computed with a fast and accurate radiative transfer model as a function of temperature, water vapor, ozone and carbon dioxide mixing ratios, fractional cloud coverage, emissivity of clouds, and cloud top and cloud base altitudes. A sensitivity study is performed to assess the relative importance of the model input parameters and devise strategies regarding their retrieval. Ozone and carbon dioxide mixing ratios are consequently fixed at their climatological values, whereas the other parameters, highly variable in space and time, are determined from satellite data. Temperature and water vapor mixing ratio are obtained from NOAA Tiros operational vertical sounder data, and cloud parameters are retrieved from GOES visible and infrared spin scan radiometer data. Several methods are investigated to retrieve the cloud parameters. In the most refined method, cloud base altitude is deduced from cloud top altitude and liquid water path, assuming a vertical liquid water distribution within the clouds. In the other methods, simplifying assumptions are introduced, which include directly relating liquid water path to cloud geometrical thickness, fixing the cloud geometrical thickness to its climatological value, and, finally, parameterizing the cloud effects only as a function of fractional cloud coverage. Satellite‐derived irradiances are compared to those measured in situ during the Mixed Layer Dynamic Experiment, conducted in October–November 1983 off the central California coast. The results indicate that the satellite methods perform similarly, with standard errors of estimate ranging from 21 to 27 W m−2 on a half‐hourly time scale and from 16 to 22 W m−2 on a daily time scale. These errors correspond to 6 to 8% and 4 to 6% of the average measured values, respectively. When compared with techniques based on empirical formulas that employ conventional surface data, the satellite methods also exhibit similar standard errors of estimate. The satellite methods, however, are favored, since they are generally less biased and globally applicable.
Fitting dynamics to data
Authors: Thacker William Carlisle , Long Robert Bryan
Published: February 2008

A formalism is presented for fitting dynamic forecast models to asynoptic data. Because of the importance of wind stress forcing in oceanic models and of the inadequacies of wind stress observations, the formalism allows an oceanic model to be fit to both Oceanographic and meteorological data. Within the context of this formalism the important question of whether an asynoptic data set contains sufficient information to determine the model state completely and unambiguously is discussed. Because the information travels along wave characteristics, it is clear that for the data to be sufficient to determine the model state, they must be distributed so that every feature of the flow is seen at some time or another. Such widespread coverage of the oceans requires a data collection system that relies heavily on satellites. The formalism is illustrated using a highly truncated model of the wind‐driven equatorial ocean and computational examples demonstrate how surface elevation and wind stress observations might be used to recover the model state.
The formation of longitudinal fronts in a coastal plain estuary
Authors: Huzzey Linda M. , Brubaker John M.
Published: February 2008

Longitudinal estuarine fronts, aligned parallel to the axis of the estuary, are characteristic of the York River. Their time scale for genesis and decay is of the order of hours; they are usually located at the inner edge of the shoals or over the main channel. Field measurements have shown marked intratidal differences in density and current speeds across this estuary. These can be correlated with changes in depth and the strength of the advective processes. Differential advection between the channel and shoal regions, when acting upon a constant longitudinal density gradient, is shown to be of sufficient magnitude to generate strong lateral density gradients, and thus fronts, at particular times within the tidal cycle.
Anomalous southward intrusion of the Oyashio east of Japan: 1. Influence of the seasonal and interannual variations in the wind stress over the North Pacific
Authors: Sekine Yoshihiko
Published: February 2008

The Oyashio is a western boundary current of the subarctic circulation in the North Pacific. In recent years an anomalous southward intrusion of the Oyashio has been observed frequently from winter to late spring that is closely associated with the atmospheric temperature and other climatic elements of the eastern part of Japan. The anomalous southward intrusion of the Oyashio east of Japan was observed in 1963, 1974, 1981, and 1984. The average southward limit of the Oyashio water in the northern area of the Kuroshio Extension is approximately 39°–39.5°N in spring, but the Oyashio intrudes south to about 36°N in these anomalous years. The relationship between the southward intrusion of the Oyashio and the variation in wind stress over the North Pacific is examined by use of wind stress data. It has been demonstrated that prior to occurrences of the anomalous southward intrusion of the Oyashio in late spring, the southward shift of the latitude with no wind stress curl was commonly observed in the North Pacific by the development of the prominent Aleutian low. If a Sverdrup balance is assumed, the subarctic circulation shifts southward about 300–500 km from its annual mean latitude. During the Oyashio intrusion periods, stronger southeastward wind stress by the Siberian high were observed in the western region of the North Pacific, which suggests that the occurrence of the Oyashio intrusion is associated with the global change in the atmospheric circulation. However, analysis of historical data shows that if the southward shift of the wind system occurs, a warm eddy detached from the Kuroshio Extension and a large eastward expansion of the Tsugaru warm current suppress the development of the anomalous southward intrusion of the Oyashio east of Japan. A simple method to predict the anomalous intrusion of the Oyashio in late spring is proposed on the basis of these results.
On wind forcing and observed oceanic wave number spectra
Authors: Eriksen Charles C.
Published: February 2008

When oceanic internal waves are forced by rapidly translating winds and wind stress is applied as a body force which is uniform within and vanishes outside a surface layer, their spectrum has a vertical wave number shape indistinguishable from the Garrett and Munk observational synthesis. Bandwidth and high‐wave number dependence are functions of the stress gradient layer thickness and vertical structure. The close correspondence between the predicted spectrum of forced waves and observed spectra suggests that the wave number shape of the near‐inertial part of the oceanic internal wave spectrum is a consequence of wind forcing. The same mechanism is consistent with observed equatorial wave number spectra. Conversely, if mid‐latitude near‐inertial internal waves and equatorial waves are directly wind forced, then their observed wave number spectra imply that the vertical gradient of stress due to wind is nearly a step function which cuts off sharply at a depth comparable to observed seasonal pycnocline depths.
Thermohaline circulation in the Gulf of California
Authors: Bray N. A.
Published: February 2008

The Gulf of California, a narrow, semienclosed sea, is the only evaporative basin of the Pacific Ocean. As a result of evaporative forcing, salinities in the gulf are 1 to 2 ‰ higher than in the adjacent Pacific at the same latitude. This paper examines the thermohaline structure of the gulf and the means by which thermohaline exchange between the Pacific and the gulf occurs, over time scales of months to years. In addition to evaporative forcing, air‐sea heat fluxes and momentum fluxes are important to thermohaline circulation in the gulf. From observations presented here, it appears that the gulf gains heat from the atmosphere on an annual average, unlike the Mediterranean and Red seas, which have comparable evaporative forcing. As a result, outflow from the gulf tends to be less dense than inflow from the Pacific. Winds over the gulf change direction with season, blowing northward in summer and southward in winter. This same seasonal pattern appears in near‐surface transports averaged across the gulf. The thermohaline circulation, then, consists of outflow mostly between about 50 m and 250 m, inflow mostly between 250 m and 500 m, and a surface layer in which the direction of transport changes with seasonal changes in the large‐scale winds. Using hydrographic observations from a section across the central gulf, total transport in or out of the northern gulf is estimated to be 0.9 Sv, heat gain from the atmosphere is estimated to be 20 to 50 W m−2, and evaporation is estimated to be 0.95 m yr−1. These estimates are annual averages, based on cruises from several years. Seasonal variations in thermohaline structure in the gulf are also examined and found to dominate the variance in temperature and density in the top 500 m of the water column. Salinity has little seasonal variability but does exhibit more horizontal variablility than temperature or density. Major year‐to‐year variations in thermohaline structure may be attributable to El Niño‐Southern Oscillation events.
On bore collapse
Authors: Yeh Harry H. , Ghazali A.
Published: February 2008

Using the laser‐induced fluorescent method, the transition process from bore to runup mode, i.e., “bore collapse,” is investigated experimentally. The observed process appears to be different from both previous analytical and numerical predictions. The results indicate that momentum exchange takes place between the incident bore and the quiescent water body along the shoreline. Turbulence generated in a bore nearshore is highly three‐dimensional and sporadic. Very close to the shore, turbulence is advected with the bore front, and consequently, the bore collapse process involves strong turbulent action onto the dry beach bed.
A model study of potential sampling errors due to data scatter around expendable bathythermograph transects in the tropical Pacific
Authors: McPhaden Michael J. , Busalacchi Antonio J. , Picaut Joël , Raymond Gary
Published: February 2008

We describe a series of sampling sensitivity experiments to examine potential errors due to data scatter around expendable bathythermograph (XBT) transects in the tropical Pacific. We use a linear, multiple vertical mode model forced with three different monthly mean wind stress sets for the period 1979–1983. The model is sampled along approximately straight lines of grid points corresponding to the mean positions of XBT tracks in the eastern, central, and western Pacific and then sampled again at the dates and locations of actual XBT casts for 1979–1983. Model dynamic heights are calculated with a resolution of 1° of latitude and 1 month, then processed to a monthly mean seasonal cycle and anomalies associated with the 1982–1983 El Niño. When results are compared for the two methods of sampling, the model indicates that data scattered zonally around XBT transects in general can lead to about 2 dyn cm error in dynamic height (equivalent to a 10‐m error in model pycnocline displacement) in composite sections of XBT data. This magnitude of error generally does not obscure anomalies associated with the 1982–1983 El Niño or the annual and semiannual harmonics of the mean seasonal cycle in the model, though frequencies higher than the semiannual can be adversely affected. Errors larger than 2 dyn cm occur in regions where XBT sample spacing in the zonal direction is insufficient to resolve Rossby wave variations in the model (for example, from 16°N to 20°N in the central Pacific and from 8°S to 20°S in the eastern Pacific). These conclusions are insensitive to the choice of monthly mean wind stress used to force the model.
Thermodynamic‐biological‐optical coupling in the oceanic mixed layer
Authors: Simonot Jean‐yves , Dollinger Eric , Le Treut Hervé
Published: February 2008

In order to quantitatively investigate the role of phytoplanktonic blooms in the open ocean on sea surface temperature (SST) prediction, the mixed layer model of Gaspar (1985, 1988) is coupled to a primary production model adapted from Agoumi (1985), allowing an interactive prediction of the upper ocean turbidity, over two seasonal cycles at Ocean Weather Station (OWS) R (Romeo). (In this paper we use “turbidity” for total optical content, thus including mineral and phytoplanktpnic content.) The validity of Gaspar's model, originally tested at OWS P (Papa), is first demonstrated for OWS R in its only thermodynamic version. Agoumi's (1985) model, developed for multiyear simulations over the English Channel, is then adapted to the case of the open ocean upper layers. It is shown how turbulent mixing is an important factor regulating primary production and nutrient fluxes, in order to obtain spring and autumn phytoplanktonic blooms and winter decay. Finally, it is shown how the typical spring and autumn errors in SST prediction from the mixed‐layer model can be changed in sign in the thermodynamic‐biological‐optical coupled version of the model. These results confirm that the phytoplanktonic seasonal cycle has a significant impact on sea surface temperature simulation. It is therefore reasonable to consider taking this factor into account in future upper ocean simulation experiments, and some recommendations are suggested for further studies.
Studies of the location of azimuth modulation minima for Ku band ocean radar backscatter
Authors: Li F. , Neumann G. , Shaffer S. , Durden S. L.
Published: February 2008

An extensive data set of radar backscatter measurements at 14 GHz was used to evaluate the locations of the azimuthal modulation minima relative to the cross‐wind directions. It was found that the minima were significantly offset from the cross‐wind directions toward the downwind direction for the horizontal polarization data. These offsets were substantially smaller for the vertical polarization data. Simple scattering model calculations, based on the two‐scale scattering approach, also show similar offsets. Implications of these results for the geophysical model function are discussed.
Deuterium in interstitial water from deep‐sea cores
Authors: Friedman Irving , Hardcastle Kenneth
Published: February 2008

As part of the Joint Oceanographic Institutions Deep Earth Sampling project, the interstitial waters of cores from 69 holes were sampled for deuterium analysis. Sixteen of the cores penetrated sediments as old as Eocene, and several sampled Cretaceous sediments, which allowed us to examine changes in the deuterium content of the oceans with time. Deuterium is shown to be a conservative constituent of the pore water. Its abundance in the pore fluids can be changed by diffusion, but the rate is slow, and corrections for this effect have been made. Changes in the abundance of deuterium can be related to changes in the amount of ice stored in continental glaciers, inasmuch as precipitation in the form of snow is highly depleted in deuterium compared with the oceans. Many of the cores show a change in isotopic composition of samples from early to late Miocene that can be ascribed to the buildup of the Antarctic ice sheets. After correcting for the role of diffusion in reducing the isotopic contrast between samples from a single core, we estimate an increase of 10 per mil (‰) δD (corresponding to a° δ18O change of about 1.2‰) between the early and late Miocene. A similiar analysis of Pleistocene to Holocene changes indicates a δD rise of 8‰ during the time of maximum continental ice, which corresponds to a δ18O increase of about 1.0‰. On the basis of limited data, we find no δD change in the oceans from Cretaceous to Miocene.
Evaluation of counting methods for oceanic radium‐228
Authors: Orr James C.
Published: February 2008

Measurement of open ocean 228Ra is difficult, typically requiring at least 200 L of seawater. The burden of collecting and processing these large‐volume samples severely limits the widespread use of this promising tracer. To use smaller‐volume samples, a more sensitive means of analysis is required. To seek out new and improved counting method(s), conventional 228Ra counting methods have been compared with some promising techniques which are currently used for other radionuclides. Of the conventional methods, α spectrometry possesses the highest efficiency (3–9%) and lowest background (0.0015 cpm), but it suffers from the need for complex chemical processing after sampling and the need to allow about 1 year for adequate ingrowth of 228Th granddaughter. The other two conventional counting methods measure the short‐lived 228Ac daughter while it remains supported by 228Ra, thereby avoiding the complex sample processing and the long delay before counting. The first of these, high‐resolution γ spectrometry, offers the simplest processing and an efficiency (4.8%) comparable to α spectrometry; yet its high background (0.16 cpm) and substantial equipment cost (∼$30,000) limit its widespread use. The second no‐wait method, β‐γ coincidence spectrometry, also offers comparable efficiency (5.3%), but it possesses both lower background (0.0054 cpm) and lower initial cost (∼$12,000). Three new (i.e., untried for 228Ra) techniques all seem to promise about a fivefold increase in efficiency over conventional methods. By employing liquid scintillation methods, both α spectrometry and β‐γ coincidence spectrometry can improve their counter efficiency while retaining low background. The third new 228Ra counting method could be adapted from a technique which measures 224Ra by 220Rn emanation. After allowing for ingrowth and then counting for the 224Ra great‐granddaughter, 228Ra could be back calculated, thereby yielding a method with high efficiency, where no sample processing is required. The efficiency and background of each of the three new methods have been estimated and are compared with those of the three methods currently employed to measure oceanic 228Ra. From efficiency and background, the relative figure of merit and the detection limit have been determined for each of the six counters. These data suggest that the new counting methods have the potential to measure most 228Ra samples with just 30 L of seawater, to better than 5% precision. Not only would this reduce the time, effort, and expense involved in sample collection, but 228Ra could then be measured on many small‐volume samples (20–30 L) previously collected with only 226Ra in mind. By measuring 228Ra quantitatively on such small‐volume samples, three analyses (large‐volume 228Ra, large‐volume 226Ra, and small‐volume 226Ra) could be reduced to one, thereby dramatically improving analytical precision.
Water mass formation in the Gulf of California
Authors: Bray N. A.
Published: February 2008

The Gulf of California is a long, narrow marginal sea lying between the Baja California peninsula and the mainland of Mexico. Air‐sea fluxes of heat and moisture in the gulf are enhanced because of geographical isolation from the Pacific provided by the mountainous Baja California peninsula. In the northern gulf, annual evaporation rates are about 1 m y−1. Unlike most evaporative basins, however, the gulf gains heat from the atmosphere at an annual average rate of 20 to 80 W m−2 (Bray, 1988). Given the unusual air‐sea forcing of the gulf, what form or forms should water mass formation take? The annual moisture loss and heat gain require that high‐salinity surface water be transported downward to an intermediate depth and that cold, fresh inflow be transported upward to an intermediate depth. This is accomplished through several mechanisms. (1) Winter convection: this occurs only in a limited geographical region, the Wagner Basin of the far northern gulf, except in El Niño–Southern Oscillation years, when convection appears to be more widespread. (2) Dispersion of convected water in small eddylike features: this occurs within a large‐scale southward transport possibly driven by the large‐scale density gradient associated with atmospheric fluxes. (3) An anticyclonic circulation in the northern gulf: this is found south of the convection region and transports high‐salinity water off the shallow shelves and to substantial depths, where it may mix with water of central gulf origin. (4) Tidal mixing: most of the energy available for mixing in the northern gulf derives from the tides. In particular, tidal mixing over the sill in the island region is responsible for the substantial reduction in salinity of northern gulf waters as they enter the central gulf.
Eulerian measurements of horizontal accelerations in shoaling gravity waves
Authors: Elgar Steve , Guza R. T. , Freilich M. H.
Published: February 2008

Laboratory and field measurements of suspended sediment in the nearshore suggest that fluid accelerations are an important factor in sediment transport by oscillatory waves. Here, Eulerian accelerations of the cross‐shore velocity are calculated from measurements of velocity obtained by an array of bottom‐mounted electromagnetic flow meters spanning a natural surf zone. Large shoreward accelerations of brief duration are associated with the steep front faces of both near‐breaking and breaking waves. Weaker offshore accelerations of longer duration occur during passage of the more gently sloped rear faces. The acceleration field is thus strongly skewed in the shoreward direction. Power spectra and bispectra indicate, as expected, that statistics of the acceleration field are significantly influenced by high‐frequency motions but are rather insensitive to surf beat.
Variations in the Arctic, Antarctic, and global sea ice covers during 1978–1987 as observed with the Nimbus 7 scanning multichannel microwave radiometer
Authors: Gloersen Per , Campbell William J.
Published: February 2008

The extent and area of sea ice and the amount of open water within the ice boundaries have been computed for the Arctic, Antarctic, and global ice covers every 2 days from November 1978 to August 1987 utilizing the Nimbus 7 scanning multichannel microwave radiometer (SMMR) observations. During this 9‐year period, no significant trends were found in the ice areas of the Arctic and Antarctic packs or in their sum, the global ice area. Also, no significant trends were found in the maxima and minima of the annual ice extents for either polar pack. However, during these 9 years, significant negative trends were found in the annual global ice extent maxima (5%) and in the annual maxima of the global open water area within the sea ice boundaries (7–14%). Significant negative trends were also found in the annual open water maxima in the Antarctic (5–10%) and the annual open water minima in the Arctic (13–23%). The open water within the ice boundaries averaged approximately 14% in the Arctic and 18% in the Antarctic, at the time of their maximum extents. This negative trend in the global ice extent maxima during 1978–1987 also occurred during 1973–1976, found by an analysis of the monochromatic microwave observations obtained by the Nimbus 5 satellite. The combined 15‐year negative trend is 6%. A significant change between the 1973–1976 and the 1978–1987 periods in the Antarctic ice pack is that the very large polynya that formed and persisted in the Weddell Sea during three out of four of the austral winters in the earlier period did not form in any of the 9 years of the latter period. This study, in conjunction with recent studies of global temperature change, lends support to the thesis that climatic changes in the global average temperature might be detectable by observing variations in global sea ice extent.
Modeling the nutrient and carbon cycles of the North Atlantic: 1. Circulation, mixing coefficients, and heat fluxes
Authors: Schlitzer Reiner
Published: February 2008

A model of the nutrient and carbon cycles in the North Atlantic is formulated, and water flow rates, eddy mixing coefficients, particle fluxes and CO2 gas exchange rates are calculated. The model incorporates geostrophy, wind‐driven Ekman fluxes and budget equations for a suite of seven tracers. Geostrophic transports are based on Levitus' (1982) climatological data, and nutrient distributions are obtained from historical station data. The model is solved by linear programming. Budgets of mass, heat, salt, oxygen, phosphate, nitrate, silicate, CO2, and alkalinity can be satisfied simultaneously in the North Atlantic. Water transports in the model depend largely on the geostrophic flows derived from the climatological data and agree quantitatively with independent transport calculations in the northern North Atlantic but seem to underestimate the shallow circulation and the upwelling in the tropical Atlantic. Meridional heat fluxes are northward in the whole model domain, and the pattern of air‐sea heat fluxes agrees with bulk formula estimates. Nutrient budgets in the tropical and subtropical Atlantic place strong constraints on shallow diapycnal mixing coefficients where the values are small and well determined (between 0 and 0.2 cm2/s). They are poorly determined in the deep water.
An overview of the SAR Internal Wave Signature Experiment
Authors: Gasparovic R. F. , Apel J. R. , Kasischke E. S.
Published: February 2008

The SAR Internal Wave Signature Experiment (SARSEX) was conducted in the New York Bight in late summer 1984 to investigate synthetic aperture radar (SAR) imaging of oceanic internal waves. The experiment was designed to acquire adequate in situ data to test hydrodynamic theories for the interaction of surface waves and currents, as well as theories for radar imaging of internal wave surface manisfestations. This paper provides an overview of the experiment and highlights from results obtained to date. Excellent agreement has been found between measured and calculated surface wave modulations at wavelengths from 20 to 100 cm. Internal wave signatures in SAR images at X and L band were found to have comparable magnitudes. Calculated SAR intensity modulations were in reasonable agreement with observed modulations at both radar frequencies.
Synthetic aperture radar imaging of ocean waves from an airborne platform: Focus and tracking issues
Authors: Raney R. K. , Vachon P. W.
Published: February 2008

There has been a controversial issue of many years standing in airborne Synthetic Aperture Radar (SAR) ocean imaging which this paper addresses and resolves. Investigators have been strongly divided on the reasons for apparent improvement in wave contrast in response to processor focus adjustment. The dispute has centered on two parameters of wave dynamics: orbital velocity and phase velocity. This paper shows that both orbital velocity and phase velocity are of fundamental importance in the SAR wave imaging problem. The first affects the phase of the received signal, leads to velocity bunching, and is scaled by the ratio of sensor altitude to sensor velocity. The second affects the magnitude of the received signal, leads to translation of wave features during image formation (observed as blurring in the image), and is scaled by the ratio of wave phase velocity to sensor velocity, thus becoming significant for airborne radars. This treatment of the phase velocity parameter is new. It is shown that focus adjustment, as a side effect, shifts image position. This explains why experiments have appeared to “prove” that focus adjustment may be optimised for wave movement. The paper shows that better performance is obtained by compensating individual looks for wave movement before look summation, while using nominal perfect focus just as for static scatterers. The work is applicable to a full ocean wave spectrum and does not depend on the details of the scattering mechanism itself.
Theory for synthetic aperture radar imaging of the ocean surface: With application to the Tower Ocean Wave and Radar Dependence Experiment on focus, resolution, and wave height spectra
Authors: Kasilingam Dayalan P. , Shemdin Omar H.
Published: February 2008

A one‐dimensional model is developed to simulate azimuthal synthetic aperture radar (SAR) imaging of the ocean surface. The model developed here is general and can admit both the “distributed surface” and the “velocity bunching” approaches. Computer simulations are performed to test the validity of this model. The simulations show that the time‐dependent modulation patterns due to the radar cross section variation and the velocity bunching effects give optimum focusing around half the phase velocity of the long wave. It is shown that the focus dependence is due to an incoherent integration process and not due to motion induced phase errors. It is argued that the radar reflectivity is correlated over distances small in comparison with the SAR resolution. In the simulations the radar reflectivity is assumed to be spatially decorrelated. Also given are the relative importance of the various effects that degrade the azimuthal resolution. It is shown that the limited radar temporal coherence due to the velocity spread of short waves degrades the azimuthal resolution of the SAR. This coherence time depends on sea state and radar wavelength. It is shown that the orbital acceleration effects are small in comparison with the smearing due to the velocity spread. It is found that the degraded azimuthal resolution of the radar minimizes the nonlinear effects of velocity bunching. The simulations show that in the Tower Ocean Wave and Radar Dependence Experiment (TOWARD), SAR imaging at L band is reasonably linear.
On the global flux of atmospheric sea salt
Authors: Erickson David J. , Duce Robert A.
Published: February 2008

The calculated global wet and dry deposition fields of atmospheric sea‐salt to the ocean surface, obtained using a sea‐salt mass size distribution appropriate for an elevation of 15 m above mean sea level (AMSL), are examined on a monthly basis with 5° × 5° latitude‐longitude spatial resolution. A monthly Gaussian frequency distribution of wind speeds is computed for each 5° × 5° area. This global wind speed climatology is coupled with equations relating atmospheric sea‐salt removal processes to wind speed. This allows us to estimate various global properties of atmospheric sea salt, such as the mass median radius of a log‐normal sea‐salt mass distribution, the deposition velocities of both wet and dry atmospheric sea‐salt deposition and the global deposition field of atmospheric sea‐salt. The global dry depositional flux of atmospheric sea salt through a plane 15 m AMSL is 0.8–2.2 × 1016 g yr−1. The global wet depositional flux of atmospheric sea‐salt is 0.15–0.45 × 1016 g yr−1. The global flux of atmospheric sea salt is thus approximately 1–3 × 1016 g yr−1. The largest atmospheric sea‐salt deposition is found in the high‐latitude regions of both hemispheres. While the dry deposition of atmospheric sea salt dominates wet deposition removal on a global scale, over areas associated with the Intertropical Convergence Zone atmospheric sea salt is removed with comparable efficiency by wet and dry deposition.
The mean barotropic circulation on the Newfoundland shelf and slope
Authors: Greenberg David A. , Petrie Brian D.
Published: February 2008

We present results of a numerical model calculation of the barotropic mean circulation in the Grand Banks region of the continental shelf off eastern Canada. The modeled circulation is compared with available current data and shows qualitative and some quantitative agreement. The model accounts for the general flow of the Labrador Current along the shelf edge, its splitting into two branches north of Flemish Pass and south of Cabot Strait, and the circulation over the Grand Banks. On the other hand, it underestimates the strength of the clockwise circulation over Flemish Cap and the width of the Labrador Current. It is also possible that neglect of the influence of the Gulf Stream and North Atlantic Current gives rise to local discrepancies between observed and modeled flows.
The morphology of shelfbreak eddies
Authors: Garvine R. W. , Wong K.‐C. , Gawarkiewicz G. G. , McCarthy R. K. , Houghton R. W. , Aikman F.
Published: February 2008

We used a combination of buoy tracking, intensive hydrography, satellite thermal imagery, and moored current meters to resolve the structure of eddies at the shelfbreak front in the Middle Atlantic Bight south of New England. Eddylike features were always present at the front in our study area throughout the 15‐day period of observations in June 1984. We found that hydrographic features in our across‐shelf hydrographic transects that appeared to represent the detached parcels of shelf water often reported in the literature were, in fact, part of the three‐dimensional structure of shelfbreak eddies. Adequate alongshelf resolution, in particular, enabled us to determine that no detached parcels were present. The two prominent features of the eddy groups we found were plumes of lighter shelf water that protruded into slope water, curling “backward” opposite the direction of mean shelf flow, and neighboring cyclones with warmer, saltier slope water in their cores, partly or wholly encircled by the plumes. The plumes have the potential especially for producing vigorous across‐front exchange of heat, salt, and nutrients and may play roles analogous to the “squirts” found on the California shelf.
Application of a model of upper‐ocean physics for studying seasonal cycles of oxygen
Authors: Musgrave David L. , Chou James , Jenkins William J.
Published: February 2008

We couple a model of oxygen which includes surface gas exchange and net biological production with an extant model for upper‐ocean physics that responds to surface inputs of seasonal buoyancy flux and wind stress. This model predicts the time‐dependent depth of the mixed layer and vertical fluxes due to turbulent mixing below the mixed layer. Using this model, we simulate the seasonal thermal and oxygen cycles at a site in the subtropical North Atlantic and compare the simulation results with a composite year of temperature and oxygen created by averaging observations of temperature and oxygen from 1961 to 1970. The magnitude of diffusive vertical mixing is constrained to a narrow range by the thermal cycle. We then use this model diagnostically to estimate the biological new production by adjusting the levels of annual production of oxygen in the model until the simulation results match the composite year. The estimate of production is sensitive to the magnitude of turbulent vertical mixing (presumed known from the seasonal thermal cycle), the amount of near‐surface production, and the surface gas exchange rate. In consideration of the role of air injection due to bubbles and the lack of nitrate in the surface waters, we conclude that production in the surface waters is negligible. The major uncertainty in the estimate of the production is due to the poorly constrained relationship between the gas exchange rate and the wind speed. Within the bounds provided by the laboratory and field experiments of gas exchange, we estimate that the vertically integrated, annual oxygen production is in the range of 3–4 mol m−2, which is slightly less than that estimated by Jenkins and Goldman (1985).
The vertical thermohaline structure in the Argentine basin
Authors: Roden Gunnar I.
Published: February 2008

The vertical thermohaline structure in the central Argentine basin is investigated on the basis of high‐resolution hydrographic data. Emphasis is placed on fronts, their horizontal gradients, vertical stability and associated fine structure. Horizontal thermohaline gradients vary strongly with depth, regions of strong gradients alternating with those of weak gradients. The strongest gradients occur often at depths below the upper mixed layer. The salinity gradient maximum occurs above the temperature gradient maximum. Enhanced gradients are found where warm, salty water moves over cooler, fresher water such as between the subtropical water (STW) and antarctic intermediate water (AAIW) and between the North Atlantic deep water (NADW) and the antarctic bottom water (AABW). Temperature, salinity, and density fronts do not always coexist. Density‐compensating temperature and salinity fronts occur in the surface layer of the subantarctic and at abyssal depth below 3500 m. Vertical profiles of the Väisälä frequency indicate much reduced hydrostatic stabilities in the Brazil current and subantarctic frontal zones. Potential vorticity minima indicate the formation of subantarctic mode water just north of the subantarctic front and its subsequent northward and upward spread across isopycnals. The thermohaline fine structure is vertically intermittent. The amplitude variances between the enhanced and quiet regions vary by almost 2 orders of magnitude. Enhanced fine structure amplitudes are found near the STW‐AAIW and NADW‐AABW interfaces, where large horizontal thermohaline gradients occur and the hydrostatic stability is low. The temperature and salinity fine structures are largely density compensating. The coherence between the temperature and salinity fine structure is strongly depth dependent and is highest in regions where warm, salty water moves over cooler, fresher water.
The response of drifting buoys to currents and wind
Authors: Krauss W. , Dengg J. , Hinrichsen H.‐H.
Published: February 2008

Two buoy types have been tested with respect to their drift performance under drogued and undrogued conditions. Additionally, forces acting on the buoys were measured directly. Quadratic drag laws have been confirmed for the drag in water and the combined drag of wind and waves. Stokes drift contributes about one half to the wind factor of 0.023, which is obtained for undrogued buoys in the Atlantic. The forces on a windowshade drogue are given by a linear relation between force and water velocity for speeds exceeding 10 cm/s. They have been extrapolated to speeds of less than 10 cm/s by both a linear and a quadratic relationship. Correlations between drift and wind speed in the Atlantic suggest that the linear law is a better approximation under realistic conditions. According to these measurements in the Atlantic the described buoy‐drogue system with a windowshade drogue in 100‐m depth is a good current‐measuring device. Slippage is negligible for wind speeds of less than 15 m/s and is less than 2 cm/s under gale conditions. Undrogued buoys are strongly affected by wind and cannot be used for the analysis of currents without correction, even under light winds.
The underwater noise of rain
Authors: Prosperetti A. , Crum L. A. , Pumphrey H. C.
Published: February 2008

Numerous data on the spectra of underwater noise due to natural as well as artificial rain show a prominent and characteristic peak at a frequency around 14 kHz. It is argued that this acoustic emission is due to bubbles entrained in the liquid by the impact of raindrops. The mechanics of the entrainment is such that only drops in a narrowly defined size range have a high probability of entraining bubbles. The narrowness of this size range may explain why the 14‐kHz peak is so ubiquitous and well defined.