bluuebunny/crossref_metadata_2025 huggingface dataset:
Jakobshavns Glacier drainage basin: A balance assessment
Authors: Bindschadler Robert A.
Published: February 2008

Maximum and minimum estimates are made of the drainage basin feeding the Jakobshavns Glacier by using surface elevation maps derived from Seasat altimetry. Benson's (1962) net balance measurements are used to calculate the balance flow within the basin. Comparisons of the balance flux at the terminus with estimates of actual flux suggest the basin is in overall equilibrium or slightly thickening. This agrees with measurements along the nearby EGIG traverse. Balance velocities accelerate rapidly within 100 km of the coast. Farther upstream, balance velocities are consistent with both measured velocities along the EGIG traverse and calculated deformation velocities. It is estimated that Jakobshavns Glacier discharges between 4.8 and 7.6% of the annual net balance over Greenland and drains between 3.7 and 5.8% of the ice sheet area.
Seasonal variability in meanders of the California Current System off Vancouver Island
Authors: Ikeda M. , Emery W. J. , Mysak L. A.
Published: February 2008

Satellite infrared images taken over the past few years reveal seasonal variations in the meanders of the California Current System (CCS) off Vancouver Island. The CCS exhibits meanders with wavelength between 120 and 150 km in both winter and spring, when the upper ocean current all flows northwestward or southeastward, respectively. In summer, the CCS includes the California Undercurrent, which flows northwestward beneath the southeastward surface current and has shorter wavelength (75–80 km) meanders. Around the end of August, these shorter scale meanders are engulfed by the longer 150 km meanders. Finally, in the fall, eddies are detached from the offshore extensions of the longer meanders. A linear stability theory using a four‐layer model of the CCS successfully predicts the wavelengths in the winter and spring, but not in the summer and fall. The meander evolution observed in summer and fall is instead simulated by using a nonlinear numerical model in a domain with topographic obstacles selected to match the alongshore variations in the continental slope. The topographic features with a spatial periodicity of 75 km act as a trigger to initiate the short wavelength (75 km) meanders; following this, these 75 km meanders grow because of baroclinic instability. The 75‐km meanders, which have grown to large amplitudes, are replaced by longer (150 km) meanders because of nonlinear interactions between these two scales of meanders. Cyclonic eddies are finally shed from the longer meanders.
A model function for ocean radar cross sections at 14.6 GHz
Authors: Wentz F. J. , Peteherych S. , Thomas L. A.
Published: February 2008

The relationship between the ocean's normalized radar cross section (NRCS) at 14.6 GHz and the surface wind vector is derived using the 3 months of Seasat microwave scatterometer (SASS) measurements. The derivation is based on the statistics of the SASS observations, and no in situ measurements are required, other than a mean global wind speed, which comes from climatology. The frequency distribution of the global wind vectors observed by SASS is assumed to be a bivariate normal probability function. A NRCS model function is found that maps the assumed wind vector statistics into the observed SASS NRCS statistics. This function is compared with a NRCS model coming from the Joint Air Sea Interaction Experiment (JASIN) and with aircraft scatterometer measurements. The results indicate that the statistically derived NRCS model is an improvement over the JASIN model, which was based on a limited number of in situ anemometer measurements.
Observations of Gulf Stream‐induced and wind‐driven upwelling in the Georgia Bight using ocean color and infrared imagery
Authors: Mcclain Charles R. , Pietrafesa Leonard J. , Yoder James A.
Published: February 2008

Ocean color and infrared imagery from aircraft and satellite sensors are combined with in situ measurements of currents, chlorophyll, temperature, salinity, coastal winds, and sea level to study upwelling events in the Georgia Bight where the Gulf Stream and continental shelf waters strongly interact. These interactions were observed over an 8 day period in April 1980 during which five independent upwellings occurred. The upwellings included a nearshore wind‐driven upwelling enhanced by topographic effects, three Gulf Stream filament‐induced upwellings, and what appears to have been a Gulf Stream meander‐induced event. The chlorophyll distributions as inferred from the imagery are found to be reliable tracers which indicate filamentary circulation and propagation and advective routes by which nearshore water moves offshore. The propagation of two of the filaments and the meander are studied in detail using the imagery and mooring array temperature time series. Both techniques yield nearly identical results for the phase speeds of each event. There is evidence that one of the filaments accelerated as it entered into the Charleston Bump area where the Gulf Stream deflects offshore. The other filament exhibited a steady deceleration as it moved past Cape Canaveral and eventually lost any semblance of wave motion. Also included are data from April 1979 which offer corroborating evidence of filamentary structure and circulation. Intercomparisons of field measurements and the Nimbus 7/coastal zone color scanner estimates of surface pigment concentrations show excellent agreement over the range of 0.1–7.0 mg/m3.
The seasonal variation of the mixed layer and the pycnocline under polar sea ice
Authors: Lemke P. , Manley T. O.
Published: February 2008

A model of the seasonal variation of the mixed layer and the pycnocline under polar sea ice is compared with observations during the Arctic Ice Dynamics Joint Experiment (AIDJEX) 1975–1976. The model is of the Kraus‐Turner type, extended to include mixed layer and pycnocline. The forcing mechanisms are the mechanical mixing due to ice keel stirring and the surface buoyancy flux due to melting and freezing of sea ice. The model is designed to be used for climate studies in conjunction with atmospheric and oceanic general circulation models and with sea ice models.
Fluctuations of monthly sea level as related to the intensity of the Gulf Stream from Key West to Norfolk
Authors: Blaha John P.
Published: February 2008

Tide gauge data from Key West to Norfolk were used to identify a monthly signal in sea level that is uncorrelated with local shelf‐trapped processes. Time series (1955–1975) of local winds, sea level slope, and river runoff were used in a regression model of sea level to separate a local response and a residual signal. The monthly means of the residual contribution were investigated for their relationship to the seasonal fluctuations of the Gulf Stream. In the Florida Channel, lower sea level is found to correspond to increased flow of the Florida Current. During July and August a marked fall in residual sea level, unrelated to the coastal winds, is found from Key West to Charleston, suggesting that the transport of the Gulf Stream increases both in and north of the Florida Channel during this time. Measured long‐term monthly surface currents at Diamond Shoals, Cape Hatteras, which markedly increase in summer to high velocities, tend to substantiate this claim. An additional wintertime low in residual sea level occurs north of the Florida Channel. The wintertime low does not result from steric heating within the upper 100–150 m of water, nor does it, in contrast to the summertime low, appear to coincide with increased northward surface flow. Monthly mean Sverdrup transport was computed across the North Atlantic between 15°N and 35°N. When compared at the same latitude, residual sea level and Sverdrup transport, both interpreted as indices of Gulf Stream transport, generally disagree in phase during summer. However, north of the Florida Channel they are consistent during winter, assuming that lower sea level at this time reflects increased flow in the stream.
Genesis and effects of long waves in the equatorial Pacific
Authors: Hansen Donald V. , Paul Carl A.
Published: February 2008

Data from 20 satellite‐tracked drifting buoys deployed in the eastern equatorial Pacific Ocean during the summer of 1979 were used to investigate the nature, effects, and energetics of currents associated with cusp‐shaped long waves observed in satellite IR imagery of the sea surface during all except El Nino years. It is shown that the long waves are associated with a vigorous pattern of mesoscale eddies lying primarily between the equator and 7°N. The spatial structure of the eddy kinetic energy closely resembles the eigenfunctions obtained from Philander's (1978) investigation of barotropic instability of that part of the South Equatorial Current lying north of the equator. Computation of the energy exchange between the eddies and the mean field suggests an e folding time of about two weeks for the eddies and a braking effect on the mean flow comparable to a change of surface wind stress of a few tenths of a dyne per square centimeter. The eddies also effect an equatorward transport of heat that amounts to about two thirds of the poleward heat transport of the divergent Ekman transport in the near‐surface waters.
The vertical structure of the zonal pressure gradient in the eastern equatorial Pacific
Authors: Mangum L. J. , Hayes S. P.
Published: February 2008

CTD data from the EPOCS and NORPAX experiments were used to construct a mean zonal pressure gradient profile between 110°W and 150°W for the 1979 to 1981 pre‐El Niño time period. The mean zonal pressure gradient referenced to 100 dbar had a value of −4.5 × 10−7 m s−2 at the surface and decreased to within two standard errors of zero at 200 dbar. Below this depth the mean was not significantly different from zero. Deviations from this mean were not related to fluctuations of the zonally averaged zonal wind stress between 150°W and 110°W. Rather, the largest deviations, in the boreal springs of 1979 and 1980, appeared to be associated first with vertical‐mode Kelvin wave pulses propagating eastward along the equator. The 1979–81 mean profile was also used as a reference to examine variations in zonal pressure gradient during the 1982/83 ENSO event. The sea surface was more sharply sloped upward from the east to west in April and September 1982 before arid near the beginning of the event. The surface slope was below normal in April and October 1983. Vertical profiles of the zonal pressure gradient deviations showed large high vertical‐mode contributions during the vent than in the prevent samples.
Resolution, bias, and variance in tomographic estimates of sound speed and currents
Authors: Eisler Thomas J. , Porter David L. , New Ronald , Calderone Denise
Published: February 2008

The Backus‐Gilbert method is used to evaluate the quality of estimates of sound speed anomaly and (two) current components obtained from acoustic travel time data in a horizontal ocean slice. The approach is more flexible than previous ones in that reciprocal transmissions are not required and, if present, are not rigidly coupled by addition and subtraction. Nine categories of bias error are identified. They are associated with imperfect resolution of the three unknowns and with cross contamination between them. Measures of these errors are developed that are system properties, as are stochastic error and resolution length. Bias error is calculated in numerical experiments and is combined with stochastic error to obtain mean error. The various quantities contributing to the mean error can be selectively reduced and brought into balance by trading off resolution. It is shown that it is possible in principle to estimate currents from one‐way transmission data, and results suggest that further study is merited. It is shown that array design can incorporate a mixture of reciprocal and nonreciprocal transmissions and that equal weights for reciprocal data pairs are not always optimal.
Evidence for wind‐pumping of air‐sea gas exchange based on direct measurements of CO2 fluxes
Authors: Smith Stuart D. , Jones E. Peter
Published: February 2008

In a series of measurements of CO2 flux over the sea the mean flux was near zero, even though the surface water had substantially higher partial pressure of CO2 than the air. Hourly variations in wind speed were well correlated with the flux, suggesting that a wind‐driven process, such as wave breaking and downward mixing of bubbles, may drive additional CO2 into the water as the wind speed increases. The traditional model of air‐sea gas flux as a function of sea‐air partial pressure difference was modified to include downward pumping by wind. We conclude that the flux of nonatmospheric gases such as radon does not serve as a complete model for the two‐way surface flux of atmospheric constituents such as CO2.
Abyssal eddies near the Gulf Stream
Authors: Kelley E. A. , Weatherly G. L.
Published: February 2008

A comparison is made of long (8–12 months) records of three near‐bottom current meters with satellite‐derived frontal positions of Gulf Stream meanders and rings. Energetic fluctuations with time scales 0(30–90 days) coincide with, and most probably result from, the movement of Gulf Stream meanders and rings.
Gulf Stream and wind‐induced current variability on the Georgia continental shelf, winter 1978
Authors: Li Li , Wimbush Mark , Watts D. Randolph , Brincko Alex J. , Lee Thomas N.
Published: February 2008

Low‐frequency longshore current fluctuations on the continental shelf off Georgia and their relationships with local atmospheric forcing and Gulf Stream displacement were examined for a 3‐month period from January to April 1978. (Acoustic travel time and bottom pressure measurements at a station on the continental slope were used to determine the depth of the main thermocline, as an indicator of Gulf Stream displacement.) On the middle shelf, current variability was dominated by local wind forcing at periods longer than 2 days, with very little Gulf Stream influence. Longshore wind stress was the main driving force at periods longer than 4 days, while cross‐shore wind contributed at shorter periods. In contrast, on the outer shelf, current fluctuations in the upper layer were highly coherent with Gulf Stream displacement at a 12‐day period, and marginally coherent with longshore wind at a 6‐day period. Linear regression analysis showed that Gulf Stream and local wind forcing accounted for most of the fluctuations in the upper layer over the shelf break for time scales greater than 5 days and at around 2 days. A low multiple coherence window at 2.8–5 days was probably due to Gulf Stream frontal eddies. In the lower layer over the shelf break the current fluctuations had a character intermediate between the upper layer currents (Gulf Stream dominated) and mid‐shelf currents (wind dominated).
Lagrangian observations of surface circulation at the Emperor Seamount Chain
Authors: Vastano Andrew C. , Hagan Denise E. , McNally Gerard J.
Published: February 2008

In a Kuroshio tracking experiment initiated in February 1977, two satellite‐reporting buoys, drogued to 100‐m depth, were released southeast of Kuyshu Island, Japan. These drifters crossed the Shatskiy Rise in the Kuroshio Extension during May and October and then traversed the Emperor Seamount Chain. Although they reached the chain 117 days apart, their movements near the seamounts display remarkably similar patterns, demonstrating upstream meanders in the surface flow; cyclonic eddy activity immediately west of the chain; passage through the same gap associated with the Jingu and Nintoku seamounts; and a wavelike pattern present over the Hess Rise east of the chain. One drifter exhibited cyclonic eddy motion east of the chain in the lee of the Kinmei Seamount.
The East Greenland Polar Front in autumn
Authors: Paquette Robert G. , Bourke Robert H. , Newton John F. , Perdue William F.
Published: February 2008

Closely spaced salinity and temperature measurements in the region of the East Greenland Polar Front from 75°N to 79°N in October–November 1981 are presented. The Return Atlantic Current (RAC), having a core of relatively warm and saline Atlantic Intermediate Water (AIW) (T = 0.5° to 3.0°C, S = 34.9 to 35.0), was found everywhere along a steep front separating it from the colder, fresher Polar Water. A narrow frontal jet was found to have velocities greater than 0.80 m/s where the station density was great enough to resolve its concentrated character. Notable fine structure was present, especially in the warm AIW just east of the front. A cold, saline water, forming a knee in the temperature‐salinity correlation, was present in the upper margins of the RAC. The knee is formed primarily by warm AIW or Atlantic water flowing under the upper layers of water flowing from the Arctic Ocean. Calculations are presented to show that an initially isothermal underflow could be modified to a thick thermocline by double diffusion. Calculations of the rate of cooling of fine‐structure elements by double diffusion indicate that the fine structure would have a limited lifetime (about 12 days) if its waters were not continually replenished.
Mesoscale eddies of the Arctic Ocean
Authors: Manley T. O. , Hunkins Kenneth
Published: February 2008

Subsurface baroclinic eddies in the Arctic Ocean have a diameter of 10–20 km and are confined in depth between 50 and 300m. During the Arctic Ice Dynamics Joint Experiment (AIDJEX) in the central Beaufort Sea between March 1975 and May 1976, extensive information on eddy characteristics, statistics, and behavior was collected from four manned drifting ice camps. During this 14‐month period, 146 eddies were encountered, of which 19 were found to be repeated crossings, making a total of 127 separate eddies observed during this period. On the basis of the 1975–1976 AIDJEX data set, it is concluded that eddies are (1) prevalent in the Amerasia Basin of the Arctic Ocean and, in particular, the Beaufort Sea where they may occupy up to a quarter of the available surface area, (2) located in the depth range of 50–300 m (although a few deeper eddies are also present), (3) the second largest producers (32%) of kinetic energy found within the upper 200 m of the Beaufort Sea, and (4) predominantly anticyclonic in rotational tendency. These eddies apparently originate north of Point Barrow, Alaska, as a result of instability in the eastward flowing Alaskan Coastal Current and transfer seasonally varying water properties from the Chukchi Sea and Alaskan Shelf into the Arctic Ocean. They appear to translate in response to barotropic forcing over short time scales and, over longer time periods, move with the mean geostrophic field. The season of formation for an eddy may be identified by the anomalous thermal properties still residing in its core.
Large horizontal surface velocity shears in the ocean obtained from images of refracting swell and in situ moored current data
Authors: Sheres David , Kenyon Kern E. , Bernstein Robert L. , Beardsley Robert C.
Published: February 2008

Aerial photographs showing strong refraction of swell near the northern California coastline were obtained on September 8, 1982. The possibility that this refraction is due to a large horizontal current shear is discussed; a maximum shear value of the order of 10−3 s−1, with the velocity directed along a linear slick‐like front, is calculated from the wave data in the photo. In situ current data obtained at 90 m depth at a nearby midshelf site on two surface moorings separated by 390 m also show occasional periods of large horizontal velocity shear. On January 4, 1982, a maximum horizontal shear of order 10−3 s−1 was observed for several hours. These separate observations taken together indicate that large horizontal surface velocity shears of order 10−3 s−1 occur over the northern California continental shelf, and that large surface current shear can be usefully detected and measured by high flying high resolution sensors.
A synoptic description of the flow at Drake Passage from year‐long measurements
Authors: Hofmann Eileen E. , Whitworth Thomas
Published: February 2008

The fronts and water mass zones comprising the Antarctic Circumpolar Current at Drake Passage have associated with them characteristic temperature structures. This property is used to construct maps that depict changes in the location of the fronts at 500 m. The zonation maps are based on temperature and velocity data obtained from 15 moorings deployed in the northern and central Drake Passage as part of the International Southern Ocean Studies experiment DRAKE 79. They provide a description of the flow of the Antarctic Circumpolar Current through Drake Passage at weekly intervals for a period of 1 year: January 1979 to January 1980. Mesoscale activity in central Drake Passage was dominated by the migration of three cold‐core rings and one warm‐core ring. The cold‐core rings formed from northward extending meanders of the Polar Front; the warm‐core ring from a southward extending meander of the Subantarctic Front. All four rings appeared to form within Drake Passage and to follow similar trajectories, which were influenced by local bathymetry. Variations in the location of the Subantarctic and Polar fronts were caused by meanders. In the narrowest portion of Drake Passage, when rings are present in the Polar Frontal Zone, the Polar Front is found farther south than when rings are absent.
Profiles of low‐frequency subsurface current fluctuations in the Strait of Georgia during 1981 and 1982
Authors: Yao T. , Pond S. , Mysak L. A.
Published: February 2008

A description of the statistical character of subsurface current fluctuations at subtidal frequencies in the Strait of Georgia, British Columbia, is given. The description is based on cyclesonde profiles taken during spring 1981, fall 1981, and spring 1982. The fluctuations are most intense in the upper part of the water column (above approximately 180 m in about 300‐m depth). The dominant period is between 10 and 25 days. Cross correlations between currents separated in the horizontal indicate a zero crossing at about 10 km. A comparison is made between the fall 1981 observations and a simple model of linear baroclinic instability. During this time period, there is evidence for upward phase propagation in agreement with the baroclinic instability model. The vertical structure of the current fluctuations can be explained well by three uncorrelated, empirical orthogonal modes. The first mode can be associated with the energy in the upper water column. The second and third modes account for the major part of the current variance at depth. The second and third modes appear dependent on topography; however, they do not show the alongshore phase propagation predicted for topographic waves. There are pronounced differences in the record mean estimates between the 1981 and 1982 observation periods. This result suggests that there may be important interannual variations in the subsurface currents in the central part of the Strait of Georgia.
Nonlinear internal waves on the California continental shelf
Authors: Howell Thomas L. , Brown Wendell S.
Published: February 2008

A series of intermittent interval wave events were observed at a single site in 133 m of water on the northern California continental shelf during the Coastal Ocean Dynamics Experiment 1981. Simultaneous time‐series observations of temperature and conductivity were used to infer isotherm and isopycnal depths which were combined with current observations to develop a kinematic description of an average internal wave event. The event described consists of a downward displacement of the middepth isopycnals and a corresponding increase of upper‐layer minus lower‐layer velocity in the ratio R = 105 ± 33 s. The observed value of R is in excellent agreement with the prediction of the two‐layer internal soliton theory for which the theoretical value of R, given the hydrographic conditions of the observation site, is 105 s. Predicted values of upper‐layer onshore velocity (0.15 m s−1), lower‐layer offshore velocity (0.12 m s−1), and time scale (24.6 min) compare well with corresponding observations of 0.14±0.02 m s−1, 0.14±0.02 m s−1, and 28±4 min, respectively, for a 29‐m internal wave of depression. Based on these results and similar observations of others, we conclude that internal solitary waves, generated in the region of the continental slope, evolve into packets of solitons as they propagate shoreward before dissipating their energy of about 8.23×105 J per meter of wave crest.
Validation of an equatorial Atlantic simulation model using inverted echo sounder data
Authors: Garzoli Silvia L. , Philander S. G. H.
Published: February 2008

Changes in the vertically averaged temperature of the water column, observed over a 12‐month period at eight locations in the tropical Atlantic with inverted echo sounders, are described in terms of empirical orthogonal functions. These modes are compared with those from a similar analysis for data from a general circulation model of the tropical Atlantic. The method proves to be useful for the validation of models.
Ocean acoustic tomography with moving sources or receivers
Authors: Gaillard Fabienne
Published: February 2008

Simultaneous determination of the sound speed field and of the position of the acoustic elements is an important possible development in ocean acoustical tomography. The problem is examined here in the range independent case, with axial transmitters and receivers. After showing that moving the receiver by a few kilometers does not compromise the ray identification, an inversion is performed for both a fixed and a moving receiver. Allowing receiver displacements does not reduce the resolution significantly in the upper part of the ocean but does increase the sensitivity to noise. This sensitivity implies that for such experiments the measurement of the travel times must be very accurate. More efficient use of a priori knowledge of the ocean reduces this sensitivity by decreasing the number of degrees of freedom.
Investigation of seasonal variability of the wind stress curl over the North Atlantic Ocean by means of empirical orthogonal function analysis
Authors: Barnier Bernard
Published: February 2008

The seasonal variability of the wind stress curl over the North Atlantic is investigated by means of empirical orthogonal function (EOF) analysis. The curl field is calculated from 1 year of First Global GARP Experiment wind data. It was found that 44% of the variability is contained in four significant eigenvectors. Their spatial patterns are characterized by basin‐sized oscillations with larger amplitude to the north of 40°N. Their associated time series coefficients have the highest amplitude during the winter and show a tendency toward a white frequency spectrum which nevertheless exhibits noticeable peaks or gaps at certain frequencies. Physically, the first EOF is seen as the seasonal fluctuations of the mean wind stress curl pattern. Five other eigenvectors are also found to be above the noise level, but they account for only a smaller percentage of variability (19%). They are characterized by smaller spatial scales than the basin size. Their time series coefficients show a whiter frequency spectrum.
Measurement of the ocean wave‐radar modulation transfer function at 4.3 GHz
Authors: Schröter J. , Feindt F. , Alpers W. , Keller W. C.
Published: February 2008

Measurements of the ocean wave‐radar modulation transfer function M at 4.3 GHz (C band) carried out in the North Sea are presented here. It was found that the values for M for C band lie within the same range as for X, L, and Ka bands. The measurements were made at incidence angles of 54° (HH and VV polarization) and 40° (VV polarization only). It was found that M decreases with increasing wind speed U and ocean wave frequency ƒ. The phase of M was such that maximum backscatter occurs at the forward (leeward) face of the long ocean waves. For small dimensionless frequencies, ƒ* = (ƒU)/g, the modulus of M reaches values of up to 30. This indicates that there is a source of strong hydrodynamic modulation, most probably wind induced, that is as yet unexplained by existing theories.
Dynamic transfer of simulated altimeter data into subsurface information by a numerical ocean model
Authors: Hurlburt Harley E.
Published: February 2008

A global, eddy‐resolving capability to predict the ocean circulation is technologically feasible within the next decade. For this purpose, the satellite altimeter is the most promising operational source of oceanic data with global coverage, but only at the surface. A comparable source of subsurface data is not on the horizon. This investigation demonstrates the ability of a numerical ocean model to dynamically transfer simulated altimeter data into subsurface information. This was done for a variety of dynamical regimes with (1) barotropic, baroclinic, mixed, and episodic instabilities, (2) flat bottoms or large‐amplitude topography, (3) relatively vigorous or gentle exchange of energy between the layers, and (4) major time scales that are short (∼60 days), long (∼1 year), or both. In all cases the pattern of the deep pressure field is much different from the one for the current‐related variations in the sea surface elevation, and sometimes not obviously related to it. The model was able to reconstruct the deep pressure field even in situations with energetic shallow and deep circulations, baroclinic instability, and a vigorous vertical exchange of energy. However, in such experiments the frequency of updating for the free surface elevation was critical. In this study the maximum update interval that allowed successful dynamic surface to subsurface transfer was about half the shortest major time scale (SMTS, e.g., 50–60 days in the experiments with baroclinic instability). Without knowledge of the deep pressure field, numerical predictions of the surface pressure field and the depth of the pycnocline typically were better than climatology for 1/4 to 1/2 the SMTS, but with successful dynamic surface to subsurface transfer, forecasts without updating were better than climatology for the SMTS or more. The time scale for predictive skill can be substantially longer than the maximum update interval permitted because the update interval must be short enough to allow decreasing error in the deep pressure field from one free surface update to the next until the error asymptotes at some acceptable level, approximately 30–50% in these results. Forecasts of nondispersive isolated eddies with beta Rossby number O(1) demonstrated predictive skill for 3 months or more even when the subsurface initial state was unknown. A serendipitous result of the study is some progress in understanding the generation of cyclonic eddies associated with the Loop Current in the eastern Gulf of Mexico (section 5.5).
Sea surface description requirements for electromagnetic scattering calculations
Authors: Guissard A. , Baufays C. , Sobieski P.
Published: February 2008

Several fundamental and unsolved questions should be answered or clarified before new and substantial progress can be made toward a more rigorous and complete solution of the general problem of electromagnetic scattering, and of the related problem of emission, by the ocean surface. Successively discussed are the limitations of the linear surface waves theory, the assumptions implied by and the inadequacies of the method used to obtain the spatial spectrum of the sea surface from the temporal spectrum, and the poor knowledge of the spectrum angular behavior. It is stressed that the sea surface is not uniquely determined by the wind speed and that it should be depicted by a more complete set of internal parameters. Relationships between some usual sea state parameters, such as H1/3, σ, u*a, and U(z) are discussed. On the other hand the available methods for solving the electromagnetic scattering problem are briefly discussed, and it is shown that the assumptions implied by Brown's (1978) two‐scale model, based on the boundary perturbation method, are roughly satisfied when applied to the sea surface. The contribution that particular scattering mechanisms could provide to the scattered power is estimated. The azimuthal behavior of the backscattering coefficient is taken as an illustration.
Applications of airborne remote sensing in atmospheric sciences research
Authors: Serafin Robert J. , Szejwach Gerard , Phillips Byron B.
Published: February 2008

The potential for airborne remote sensing for atmospheric sciences research and in particular for research over the oceans is explored. Passive and active techniques from the microwave to visible bands are discussed. It is concluded that technology has progressed sufficiently in several areas that the time is right to develop and operate new remote sensing instruments for use by the community of atmospheric scientists as general purpose tools. There exists promising candidates of both active and passive types in the electromagnetic spectrum from microwave to visible wavelengths. Short‐range, rapid response measurements of temperature, water vapor, winds, and turbulence are all possible using infrared radiometry and Doppler lidar velocimetry. Pulsed Doppler radar for measurements of the three‐dimensional structures of winds and hydrometeors in precipitating systems has been clearly established. Pulsed Doppler lidar is less well developed in comparison to Doppler radar but promises to be an important complement to radar observations by providing wind measurements in the nonprecipitating and cloud free atmosphere. It is possible now to equip a single aircraft or several aircraft with a variety of remote sensing instruments that together form a powerful, highly mobile atmospheric observing system for measurement of fundamental meteorological variables in three dimensions on a variety of spatial scales. This capability is of major importance to the study of mesoscale systems, particularly to those over the ocean, where the deployment of surface based sensors is exceedingly difficult, if not impossible, and costly.
On the generation of deep mean flows: Some numerical experiments
Authors: Harrison D. E. , Semtner A. J.
Published: February 2008

There is renewed interest in the processes responsible for the formation of the oceanic main thermocline and deep circulation, but analytical techniques remain inadequate for the study of even idealized thermocline systems in closed basins because of their nonlinear boundary currents, mixing, and dissipation. Most closed basin work has been done with quasi‐geostrophic (QG) model physics, but the QG system has limitations, particularly for studies of the deep circulation. It is subject to several lower layer vorticity‐forcing and dissipation constraints that have no clear primitive equation counterparts. These constraints are likely to introduce both special deep flow characteristics and considerable sensitivity to the type and magnitude of lower layer friction assumed. As a first look at some of the effects of these constraints, we have carried out (1) a series of QG experiments that can be compared with otherwise identical primitive equation (PE) experiments and (2) a second set of QG experiments in which the lower layer friction is changed in form. In every otherwise identical PE/QG comparison, significant quantitative and/or qualitative changes are found in the deep circulation. Nontrivial upper layer flow changes are sometimes also found. Deep layer friction changes in the QG systems also induce substantial deep flow changes. These results suggest that the limitations and sensitivity of QG physics make it less than ideal for model studies of deep mean circulation physics and hence for detailed tuning against deep ocean data. It is important that the behavior of PE systems be examined with new calculations if our understanding of the deep circulation is to advance.
The North Atlantic Current
Authors: Krauss W.
Published: February 2008

Based on trajectories of satellite‐tracked buoys and hydrographic sections, both Dietrich's and Worthington's schemes of the North Atlantic Current are reconsidered. Ninety satellite‐tracked buoys have been analyzed in order to distinguish between these schemes. Neither could be confirmed. The North Atlantic Current appears as a superposition of a broad west wind drift and a frontal jet in the western part of the North Atlantic north of 40°N, which becomes independent from the subtropical gyre. Neither a permanent branching, suggested by Dietrich, nor a confinement of the subpolar gyre to the east of Newfoundland (per Worthington) can be found. The North Atlantic Current extends over the entire North Atlantic, carrying more than 20 sverdrups (Sv) toward the north. This northward transport is mainly due to the northward flow around Flemish Cap and a sudden turn of the North Atlantic Current east of the Mid‐Atlantic Ridge. The buoy tracks have been used to determine speed and direction in the upper layers (≤ 100 m). We combine these results with hydrographic data in order to obtain an estimate of the mass transport. Transport across the Mid‐Atlantic Ridge is based on recent sections (Fahrbach et al., 1985), while transport in the northeastern North Atlantic has been derived from the Erika Dan sections at 53.5°N and 59.5°N. According to these two sections, the return flow occurs mainly below 1000 m after water mass conversion in the northern areas. The results imply that about 7 Sv of Atlantic water are transformed into deep water in the area between 53.5°N and 60°N.
Synoptic Gulf Stream velocity profiles through simultaneous inversion of hydrographic and acoustic Doppler data
Authors: Joyce T. M. , Wunsch C. , Pierce S. D.
Published: February 2008

Data from a shipborne acoustic profiling device have been combined with conductivity, temperature, depth/O2 sections across the Gulf Stream to form estimates of the absolute flow fields. The procedure for the combination was a form of inverse method. The results suggest that at the time of the observations (June 1982) the net Gulf Stream transport off Hatteras was 107 ± 11 Sv and that across a section near 72.5°W it had increased to 125 ± 6 Sv (subject to further uncertainty from the definition of the stream). The transport of the deep western boundary current was 9 ± 3 Sv. These and other transport estimates are plausibly close to previous calculations, but we do not claim that they represent the temporal mean. For comparison purposes we have done an inversion using the hydrographic/O2 data alone as in previously published results and obtained qualitative agreement with the combined inversion. Inversion of the acoustic measurements alone, when corrected for instrument biases, leaves unacceptably large mass transport residuals in the deep water. Our conclusion is that the inversion of the combined data sets produces results much improved over those from using either acoustic or hydrographic/chemical constraints in isolation. The procedures are close analogues to those which can be used with satellite altimeters and are a procedure for obtaining very accurate geoid slope measurements.
Estimating ice thickness and internal pressure and stress forces in pack ice using Lagrangian data
Authors: Lewis James K. , Crissman Randy D. , Denner Warren W.
Published: February 2008

A methodology is presented which allows one to calculate an ice thickness term using observed ice motion and wind data. Since the wind data can come from atmospheric pressure fields or numerical models, the methodology is in fact a remote‐sensing capability which relies on ice motion data from satellite imagery, buoys drifting on the ice, etc. The thickness term is shown to be an effective ice thickness which reflects the strength of the ice as a result of the true ice thickness plus the added mass effect of the horizontal gradients of pressure and internal ice stresses. The method for estimating the actual ice thickness and then calculating the forces due to pressure and internal stresses is also outlined. Examples of the temporal variations of the effective ice thickness in the Beaufort Sea are presented. These variations are explained in terms of the compactness of the ice field as the motion is toward or away from the ice pack.
Satellite microwave and in situ observations of the Weddell Sea ice cover and its marginal ice zone
Authors: Comiso J. C. , Sullivan C. W.
Published: February 2008

The radiative and physical characteristics of the Weddell Sea ice cover and its marginal ice zone are studied using multichannel satellite passive microwave data in conjunction with in situ observations during the 1983 Antarctic Marine Ecosystem Research at the Ice Edge Zone Experiment. Time series studies from winter through spring, using every other day observations from the Nimbus 7 scanning multichannel microwave radiometer, reveal significant spatial variability of the brightness temperatures of consolidated ice in winter and a recurring temporal and oftentimes larger spatial variability in spring. The recurring effect in spring was found to be strongly correlated with observed surface air temperatures and is apparently associated with the cyclic changes in wetness of the snow cover of the ice while experiencing the freeze‐thaw cycle. Analysis of scatter plots of observed brightness temperatures from selected study regions using two or three frequencies and/or polarizations shows that to effectively discriminate ice from open water within the ice pack, a minimum of two channels at different frequencies, preferably 18 GHz and 37 GHz, is required. Serious problems associated with using only one frequency, even at two polarizations, (i.e., 37 GHz, and perhaps higher frequencies) have been observed. Ice concentrations derived from the sensor are compared with helicopter and ship observations, and results show consistency but a relatively low correlation coefficient partly due to the quasi‐qualitative nature of the in situ observations and uncertainties in ice emissivity in spring. The character and the northernmost extent of the ice margin are quantified using radial plots of ice concentration across the ice pack and into ice free ocean. Temporal changes in the ice margin structure are compared with ship data of physical temperature, ice characteristics, wind, and weather. Studies of the mass balance of fresh water and of biological features of the marginal ice zone are shown to benefit from time series information concerning the position of the ice edge as derived from satellite remote sensing.
Nonlinear data assimilation for shallow water equations in branched channels
Authors: Budgell W. P.
Published: February 2008

A framework has been developed for the optimal combination of a network of time series observations with a numerical model of nonlinear shallow water wave propagation in branched channels. The model results and observations are weighted according to their reliability to produce estimates of surface elevation and transport. Two filtering techniques are adopted to perform the dynamic‐stochastic modeling. For weakly nonlinear conditions a modified incremental covariance Chandrasekhar‐type algorithm is employed, whereas for more strongly nonlinear dynamics a Bierman square root form of the extended Kalman filter is used. Numerical experiments performed using parameters from the Great Bay estuary in New Hampshire demonstrate that both filters successfully estimate the time‐ and space‐dependent elevation and transport distributions under conditions of stochastic forcing (model error) and measurement noise. Although the Chandrasekhar algorithm underestimates the covariances of the filter estimates, it performs nearly as well as the fully nonlinear algorithm, even for the significantly nonlinear test case. It is shown that the Chandrasekhar filter performance does not degrade when the algorithm is applied to systems in which the process noise and measurement noise structures are purely sinusoidal, thus violating the assumption of white noise under which the filter algorithm is derived.
Automated extraction of pack ice motion from advanced very high resolution radiometer imagery
Authors: Ninnis R. M. , Emery W. J. , Collins M. J.
Published: February 2008

Multiple subarea cross correlations have been computed from visible, advanced very high resolution radiometer images of the Beaufort Sea in an automated technique to detect pack ice motion. The computational method is an application of the well‐known matched filter and consists of subdividing the first image into a set of subareas and correlating each reference subarea against the appropriate region of the second image. The correlation functions are processed to determine a set of local maxima which define end point vectors of ice displacements from the subarea centers. Resulting velocities agree well with estimates of ice movement obtained by manually measuring invariant ice feature displacements. The velocity fields show the spatial structures of ice motion over scales of 100–500 km with a high degree of pattern consistency and agreement with simple surface wind driving.
Sea slope changes associated with westward propagating equatorial temperature fluctuations
Authors: Musman Steven
Published: February 2008

At five locations in the eastern equatorial Pacific between 113°W and 130°W, both sea height and temperature fluctuations were observed during the repeated ground track phase of the Seasat mission. A fluctuation of 1.6 ± 0.6 cm/deg latitude in the smoothed sea slope between 2°N and 4°N is associated with the passage of two temperature disturbances. The corresponding sea height fluctuation of 1.0 ± 0.9 cm is not statistically significant. The sea slope estimate, together with kinematic assumptions about velocities, provides an approximate evaluation of the principal contributions to the meridional momentum balance in the propagating wave.
Physical oceanography near the North Pole
Authors: Pounder E. R.
Published: February 2008

As part of LOREX 79, observations of current, conductivity, temperature and depth were made for 40 days from an ice floe which drifted in the area within 1.5° of the north pole. Daily profiles were taken to a maximum depth of 1400 m. Observations were analyzed to give profiles of S, T and σT and of water speed and true direction. The water column was stable at all stations; density increased with depth. Observations of the under‐ice mixed layer showed it to become both thinner and warmer during northward drift of the floe. Downward motion and cooling of Atlantic water advected southward were observed. Near the middle of the drift period the surface salinity dropped abruptly by 1‰, indicating passage into a different water mass. A rough calculation showed only small water transport over the Lomonosov Ridge where the drift track crossed it.