bluuebunny/crossref_metadata_2025 huggingface dataset:
On the ridging of intact lead ice
Authors: Hopkins Mark A.
Published: February 2004

The sea ice pressure ridging process is modeled using a two‐dimensional particle simulation technique. In this model, blocks are broken from an intact sheet of relatively thin lead ice driven against a thick, multiyear floe at a constant speed. The blocks of ice rubble accumulate to form the ridge sail and keel. The energy consumed in ridge growth, including dissipation, is explicitly calculated. A series of numerical experiments are performed to establish the dependence of the energetics on the thickness of the ice sheet and the friction between blocks. The results suggest that the total energy required to create a pressure ridge is an order of magnitude greater than the potential energy in the ridge structure. A typical sea ice cover in the polar regions contains a variety of ice thicknesses that evolve in response to both dynamic and thermodynamic forcing. The variable thickness of the ice cover is created by deformation, which simultaneously causes formation of thick ice through ridge building and thin ice through lead creation. Since the energy expended in deformation is largely determined by the ridging process, an understanding of the energetics of pressure ridging is critical in the determination of ice strength on a geophysical scale.
On the effect of the alongshore pressure gradient on numerical simulations over the Northern California Continental Shelf
Authors: Zamudio Luis , López Manuel
Published: February 2004

Chen and Wang's (1990) two‐dimensional shelf circulation model has been extended to include the alongshore (the dimension absent in the model) pressure gradient. The alongshore pressure gradient, calculated independently from a linear coastal‐trapped wave model, is included as an external “forcing”. The extended model has been used to simulate the temperature and velocity fields observed during the Coastal Ocean Dynamics Experiment 2 (CODE 2) in the spring and summer of 1982 on the Northern California Continental Shelf. The results were compared to the CODE 2 observations and to the results of the purely two‐dimensional and coastal trapped wave models. Results using the extended model show some improvement in the cross‐shore and alongshore velocity fluctuations. The differences between the models are explained in terms of the opposition between the wind stress and the pressure gradient in the alongshore direction, which reduces the magnitude of the alongshore velocity. The reduced magnitude of the alongshore flow decreases the alongshore bottom stress which, in turn, reduces the offshore transport in the bottom boundary layer.
Differential sea‐state bias: A case study using TOPEX/POSEIDON data
Authors: Stewart Robert H. , Devalla Badarinath
Published: February 2004

We used selected data from the NASA altimeter on TOPEX/POSEIDON to calculate differences in range measured by the C and Ku‐band altimeters when the satellite overflew 5 to 15 m waves late at night. The range difference is due to free electrons in the ionosphere and to errors in sea‐state bias. For the selected data the ionospheric influence on Ku range is less than 2 cm. Any difference in range over short horizontal distances is due only to a small along‐track variability of the ionosphere and to errors in calculating the differential sea‐state bias. We find that there is a barely detectable error in the bias in the geophysical data records. The wave‐induced error in the ionospheric correction is less than 0.2% of significant wave height. The equivalent error in differential range is less than 1% of wave height. Errors in the differential sea‐state bias calculations appear to be small even for extreme wave heights that greatly exceed the conditions on which the bias is based. The results indicate that the influence of waves on the ionospheric correction can be ignored. The results also improved our confidence in the sea‐state bias correction used for calculating the geophysical data records. Any error in the correction must influence Ku and C‐band ranges almost equally.
A numerical study of local convection in the benthic ocean induced by episodic hydrothermal discharges
Authors: Lavelle J. W. , Baker E. T.
Published: February 2004

A nonhydrostatic primitive equation model is used to investigate motions and water column property distributions accompanying the rise of hot hydrothermal fluids into a rotating water column stratified in temperature and salinity. After preliminary model experiments used to fix the level of turbulent mixing, the model is applied to a megaplume event, the release of a large amount of hydrothermal heat into the benthic ocean over a period of several days. Events of this kind have produced water masses with anomalous temperature and salinity distributions ∼20 km in diameter, ∼800 m thick, centered vertically 700–1000 m off the seafloor. The model allows the study of the initial time development and maturation of the plume from such an event. Preliminary experiments demonstrate the sensitivity of plume rise to the level of turbulent mixing and to the ratio of turbulence viscosity to turbulence diffusivity, i.e., Prandtl number. Rise to maximum plume height occurs in 4–6 N−1, where N is buoyancy frequency. Consequences of a megaplume‐sized release of heat are examined over an initial 30‐day period. Vertical circulation accompanying a hydrothermal event leads to a slight, negative salinity anomaly below the plume's temperature anomaly core. The plume's heat (potential temperature) anomaly is shown to be a composite of hydrothermal heat and ambient heat that has been redistributed by the same vertical circulation cell. Horizontal circulation is dominated by an anticyclonic flow vortex centered just above the temperature anomaly maximum at ∼800 m above bottom and a cyclonic flow vortex at the seafloor. Azimuthal flow accounts for the largest fraction of kinetic energy within 4.5 hours (∼1.7 ƒ−1) after the start of heat release; azimuthal velocities reach maximum values of ∼70 cm s−1, 90% of which is attained within the initial 10 hours. Even as much as 4 weeks past cessation of heat release maximum azimuthal velocities are of the order of ∼10 cm s−1. The balance of vertical forces is hydrostatic by 12 hours, save for near‐bottom frictional effects. During plume formation, the radial force balance is primarily cyclostrophic near axis and geostrophic at a distance.
Heat and salt balances over the northern California shelf in winter and spring
Authors: Dever E. P. , Lentz S. J.
Published: February 2004

Heat and salt balances are estimated over the northern California shelf from early December 1988 through late February 1989 (winter) and from early March through early May 1989 (spring) from moored meteorological and oceanographic time series taken in 93 m of water 6.3 km from the coast. We find a winter mean offshore heat flux of 8.7×105 W m−1, about a factor of 5 smaller than earlier estimates of the mean summer (upwelling season) offshore heat flux on the northern California shelf. The mean offshore heat flux is predominantly in the surface boundary layer and is balanced by an along‐shelf heat flux divergence (as represented by an eddy along‐shelf temperature gradient flux) and a cooling trend making the mean winter heat balance fundamentally three dimensional. In contrast to winter, the spring mean offshore heat flux of 6.4×105 W m−1 is balanced by a positive air‐sea heat flux of 8.3×105 W m−1, which is about 80% of the mean air‐sea heat flux in summer. This makes the spring mean heat budget primarily two dimensional, like the summer mean heat budget off northern California. On timescales of days the dominant terms in the fluctuating heat budget in both winter and spring are the cross‐shelf heat flux and local changes in heat content. These are well correlated with each other and with the local along‐shelf wind stress. The along‐shelf temperature gradient flux, uncorrelated with the along‐shelf wind stress, is usually weak on timescales of days. Occurrences when it is strong are interpreted as effects of mesoscale features. Mean and fluctuating cross‐shelf salt fluxes provide essentially the same information as cross‐shelf heat fluxes. This is not surprising in light of the strong temperature‐salinity relationship on the northern California shelf.
Short‐wave length instabilities on coastal jets and fronts
Authors: Barth J. A.
Published: February 2004

The stability of a coastal jet and front is investigated using the primitive equations applied to a continuously stratified flow in geostrophic balance. A linear stability analysis successfully explains the growth of two modes of instability with distinctly different horizontal scales. A long‐wavelength mode (fastest‐growing wavelength of 0(100 km)) is found which is a modified version of a traditional baroclinic instability. A second, rapidly growing frontal instability also exists. For a realistic basic state density and flow structure, this mode has its fastest growth at short wavelengths (0(20 km)), e‐folds in less than 1.5 days and propagates rapidly in the direction of the mean flow. The frontal instability grows primarily by extracting the available potential energy of the mean flow via a baroclinic instability mechanism. A small contribution from vertical Reynolds stress is also found, but the transfer via horizontal Reynolds stress is from the eddy to the mean kinetic energy. Further evidence shows that the frontal instability is not a result of horizontal shear instability nor is it an inertial instability. The frontal mode is trapped to the surface front and its influence is confined to the upper water column (z ≲ 70 m). A significant subsurface vertical velocity maximum (20 m d−1 at 30 m) is associated with a frontal instability with a reasonable, as judged by satellite sea surface temperature observations, surface temperature perturbation of 0.35°C. The linear stability predictions are verified by and compared with results from a time‐dependent, three‐dimensional, nonlinear ocean circulation model. Finally, the frontal instability is discussed in the context of other recent stability analyses that yield high‐wavenumber modes.
Tropical Atlantic sea level variability from Geosat (1985–1989)
Authors: Arnault S. , Cheney R. E.
Published: February 2004

Geosat altimeter data between April 1985 and September 1989 are analyzed in the tropical Atlantic Ocean. First, improvements due to the use of new corrections and orbit computations are found to be effective, especially in the Gulf of Guinea, where part of the previously missing signal is recovered. Then, the variability of the ocean is examined using empirical orthogonal functions (EOFs). Only three EOFs are needed to describe 80% of the seasonal variance. The first one describes the meridional tilting of the tropical Atlantic along the mean location of the Intertropical Convergence Zone, with an annual period. The second describes a mass redistribution due to the equatorial upwelling peaking in June–July. The third function presents a clear semiannual signal. Looking at interannual variability, the first EOF reveals a mass redistribution between the equatorial region (10°N to 10°S) and the northern and southern ones (10°N to 30°N, 10°S to 30°S). In the equatorial region the upper layer volume increases from about −1.5 to 1.5×1014 m3 between 1987 and 1989. Occurring 1 year after the Pacific El Niño, this phenomenon recalls the 1984 anomaly observed during the Programme Français Océan et Climat en Atlantique Tropical/Seasonal Equatorial Atlantic experiments.
Spectroscopy of the world ocean tides from a finite element hydrodynamic model
Authors: Le Provost C. , Genco M. L. , Lyard F. , Vincent P. , Canceil P.
Published: February 2004

An atlas of the main components of the tides has been produced on the basis of a finite element hydrodynamic model, with the aim of offering the scientific community, using satellite altimetric data, a prediction of the tidal contribution to sea surface height variations under the ground tracks of the satellites that is totally independent of altimetric measurements. The geographic coverage of the simulations only excludes, temporarily, some marginal seas like the Bay of Fundy. But the design of the model, based on a nonlinear formulation of the shallow water equations, could enable the simulations to be extended to these very singular areas. On the other hand, the Arctic Basin and the Antarctic Circumpolar Basin have been fully resolved, including the under‐ice shelf areas of the Weddell Sea and the Ross Sea. Eight constituents, M2, S2, N2, K2, 2N2, K1, O1, and Q1 have been simulated. Five secondary constituents: Mu2, Nu2, L2, T2, and P1, required to insure a priori correct predictions, have been deduced by admittance. The accuracy and precision of these solutions have been estimated by reference to the harmonic constituents data set available from analysis of the entire collection of pelagic, plateau and coastal observations made to date, and archived by International Association for Physical Sciences of the Oceans and International Hydrographie Bureau. Over the deep oceans, these solutions fit the observations to within a few centimeters for the larger components: M2, S2, K1, O1, and a few millimeters for the others, in RMS maximum difference to a standard set of 78 ground truth stations. Over the shelves, the differences are larger, because of the increase in amplitude of the tidal waves, but the flexibility offered by the finite element technique to refine the discretization mesh of the model over the shallow seas enables detailed cotidal maps to be produced along the coasts. One zoom on South Georgia Island, in the South Atlantic Ocean, is presented as an illustration. Finally, the performances of the tidal predictions made on the basis of this new set of solutions was tested by looking at the residual RMS differences at the crossover points of sea level measurements supplied by the TOPEX/POSEIDON mission, when using these predictions. This test provided confirmation of most of the conclusions already drawn on the basis of the previous comparisons with in situ tide gauge data.
Photoenhancement of bioluminescence capacity in natural and laboratory populations of the autotrophic dinoflagellate Ceratium fusus (Ehrenb.) Dujardin
Authors: Sullivan James M. , Swift Elijah
Published: February 2004

Cultures of Ceratium fusus were grown at seven light intensities (5 to 400 μmol photons m−2 s−1 as photosynthetically active radiation (PAR)) in the laboratory. Measurements of bioluminescence capacity (BCAP), division rate, and cell size were made at each intensity and compared to similar data from natural populations. In cultures, BCAP increased by a factor of 5–10 with increasing light. Division rates ranged from 0 d−1 (5 μmol photons m−2 s−1) to about 0.16 d−1 (100 μmol photons m−2 s−1). In these cultures, BCAP was highly correlated with both the log of light (r2 = 0.89) and division rate (r2 = 0.69), suggesting that BCAP may be of use as an in‐situ indicator of division rate. In both cultures and natural populations, BCAP was poorly correlated with cell size (r2 ≈ 0.3 and r2 ≈ 0.1 respectively). For populations from the Gulf of Maine ( ∼42°N, 69° W) and the Marine light‐Mixed Layers (MLML) site (∼59°N, 21° W), division rates in the mixed‐layer could only be determined with statistical certainty at the Gulf of Maine station (0.04 to 0.17 d−1). At the MLML site, BCAP in C. fusus was greater in the mixed‐layer in May and below the mixed‐layer in August. The August result is opposite to what culture photoenhancement studies would predict if light was the factor controlling BCAP.
Sea surface height variations in the Atlantic Ocean: A comparison of TOPEX altimeter data with results from an ocean data assimilation system
Authors: Behringer D. W.
Published: February 2004

Estimates of sea surface height changes in the Atlantic Ocean derived from TOPEX altimeter data are compared with dynamic height estimates from an ocean general circulation model which assimilates temperature data. There is generally good, basin‐wide agreement in the annual phase and amplitude between the two data sets. In the tropics and in the subtropical gyres, spatially averaged time series of TOPEX and model dynamic height data are well correlated and have RMS differences of about 2 cm. In western boundary regions, correlations are weaker and RMS differences can be as large as 8–10 cm.
Comparison of TOPEX sea surface heights and tide gauge sea levels
Authors: Mitchum Gary T.
Published: February 2004

TOPEX sea surface height data from the first 300 days of the mission are compared to sea level data from 71 tide gauges. The initial comparison uses sea surface height data processed according to standard procedures as defined in the users handbook. It is found that the median correlations for island and for coastal tide gauges are 0.53 and 0.42, respectively. The analogous RMS differences between the two data sets are 7.9 and 10.4 cm. The comparisons improve significantly when a 60‐day harmonic is fit to the differences and removed. This period captures aliased M2 and S2 tidal energy that is not removed by the tide model. Making this correction and smoothing the sea surface height data over 25‐km along‐track segments results in median correlations of 0.58 and 0.46 for the islands and coastal stations, and median RMS differences of 5.8 and 7.7 cm, respectively. Removing once per revolution signals from the sea surface heights results in degraded comparisons with the sea levels. It is also found that a number of stations have poor comparisons due to propagating signals that introduce temporal lags between the altimeter and tide gauge time series. A final comparison is made by eliminating stations where this propagation effect is large, discarding two stations that are suspected to have problems with the sea level data, smoothing over 10‐day intervals, and restricting attention to island gauges. This results in a set of 552 data pairs that have a correlation of 0.66 and a RMS difference of 4.3 cm. The conclusion is that on timescales longer than about 10 days the RMS sea surface height errors are less than or of the order of several centimeters.
Comparison of TOPEX/POSEIDON σ0 and significant wave height distributions to Geosat
Authors: Callahan Philip S. , Morris Charles S. , Hsiao S. Vincent
Published: February 2004

Monthly Ku band σ0 and significant wave height (SWH) histograms from the NASA altimeter on the TOPEX/POSEIDON satellite are presented for January through June 1993 for three latitude bands between ±60 degrees. The data are compared to distributions from the Geosat mission for the same months in 1987–1989. Generally, the distributions agree quite well, although there are some seasonal/hemispherical differences. The σ0 comparison reveals an overall bias between the two altimeters with the TOPEX σ0 higher by about 0.7 dB, which is consistent with algorithm improvements for TOPEX. The SWH distributions show strong hemispherical/seasonal changes. The seasonal/hemispherical differences between TOPEX and Geosat are consistent for SWH and σ0. The joint distribution of σ0 and SWH is extremely stable from month to month. The typical SWH is independent of σ0 for σ0 greater than 11.3 dB. The minimum SWH grows exponentially with wind speed. This joint distribution may be useful for understanding electromagnetic bias in altimeter measurements. Finally, altimeter data are compared to buoy values from 21 overflights of the NASA verification site near Pt. Conception, California. Wave heights agree well with an RMS difference of only 0.2 m. Altimeter σ0 values are compared to buoy wind speeds. The results are consistent with the −0.7 dB σ0 offset from the histogram comparisons.
Cooling of the West Spitsbergen Current: Wintertime Observations West of Svalbard
Authors: Boyd Timothy J. , D'Asaro Eric A.
Published: February 2004

The West Spitsbergen Current (WSC) is the major source of heat and salt for the Arctic Ocean and the areas of deep convection in the Greenland Sea. The WSC current cools dramatically downstream. Hydrographic and velocity data from a 3‐week, midwinter cruise off Spitsbergen are used to investigate the heat budget of the WSC and the mechanisms of cooling. The downstream divergence of mean heat flux in the WSC produces a heat loss of at least 1000±400 Wm−2 averaged over the width of the current. Approximately 350 Wm−2 is lost to the atmosphere and 200 Wm−2 is lost to melting ice over a region somewhat wider than the current. Cooling of the WSC to the atmosphere converts the inflowing Atlantic Water (AW) to Lower Arctic Intermediate Water, which is sufficiently salty to convect. Cooling by ice converts the AW to much fresher Arctic Surface Water, which is too light to convect. The relative importance of these two conversions is primarily controlled by the rate at which the wind advects ice from the Barents Sea over the WSC. The warmest water of the WSC is often observed 100–200 m below the surface. Despite the lack of direct contact with the surface, this warm core cools at about 800 Wm−2 in our observations. This rate is too large to be caused by diapycnal diffusion. We suggest that the energetic eddy field in this area diffuses heat along the steeply sloping isopycnal surfaces that connect the warm core to the surface, renewing the surface layer several times per day. This is consistent with the very shallow surface mixed layers and high level of intrusions observed. We conclude that the surface layer of the WSC is cooled by the atmosphere and by ice from the Barents Sea and that isopycnal diffusion by mesoscale eddies continually renews this surface, thus cooling the interior of the WSC. The relative magnitude of these processes determines whether the inflowing warm, salty AW is converted to light, fresh surface water or salty, cold intermediate water.
Bioluminescent organisms and bioluminescence measurements in the North Atlantic Ocean near latitude 59.5°N, longitude 21°W
Authors: Swift Elijah , Sullivan James M. , Batchelder Harold P. , Van Keuren Jeffrey , Vaillancourt Robert D. , Bidigare Robert R.
Published: February 2004

We investigated mixed‐layer bioluminescence from early April to late September (in April 1989, May 1991, July 1983 and 1990, August 1991, September 1988 and 1989) at stations near the Marine‐Light ‐ Mixed Layers (MLML) bio‐optical moorings site. Volume‐specific bioluminescence potential (BPOT, photons per unit volume) from epipelagic organisms was estimated directly with a pump‐through bioluminescence photometer (BP) in 1983, 1988, and 1991. For all cruises, BPOT was also estimated by summing for a volume of seawater, the measurements of each species′ total stimulable bioluminescence multiplied by each species′ numerical abundance in the volume. The abundance data were taken from bottle casts, net tows, and BP effluent nets. After the onset of the spring bloom, from May through September, mixed layer BPOT was fairly constant, ∼1–4×1014 photons m−3. On one early April cruise (1989) before the spring bloom, BPOT was two orders of magnitude lower. Heterotrophic dinoflagellates in the genus Protoperidinium generally produced most (90% or more) of the mixed layer BPOT in the spring, summer, and fall. On one cruise in September (1988), the autotrophic dinoflagellate Ceratium fusus produced the bulk of the mixed layer BPOT (more than about 4×1014 photons m−3). Other autotrophic dinoflagellates in the genus Gonyaulax and mesozooplankton produced a minor part of BPOT at most stations. The relative contribution of all autotrophic dinoflagellates to BPOT increased from a few percent during the May–June–July period to ∼10% during the August–September period. In situ mechanically stimulable bioluminescence was reduced when underwater scalar irradiance (wavelengths 400–700 nm) was greater than 0.1 μmol photons m−2 s−1.
TOPEX/POSEIDON tides estimated using a global inverse model
Authors: Egbert Gary D. , Bennett Andrew F. , Foreman Michael G. G.
Published: February 2004

Altimetric data from the TOPEX/POSEIDON mission will be used for studies of global ocean circulation and marine geophysics. However, it is first necessary to remove the ocean tides, which are aliased in the raw data. The tides are constrained by two distinct types of information: the hydrodynamic equations which the tidal fields of elevations and velocities must satisfy, and direct observational data from tide gauges and satellite altimetry. Here we develop and apply a generalized inverse method, which allows us to combine rationally all of this information into global tidal fields best fitting both the data and the dynamics, in a least squares sense. The resulting inverse solution is a sum of the direct solution to the astronomically forced Laplace tidal equations and a linear combination of the representers for the data functionals. The representer functions (one for each datum) are determined by the dynamical equations, and by our prior estimates of the statistics of errors in these equations. Our major task is a direct numerical calculation of these representers. This task is computationally intensive, but well suited to massively parallel processing. By calculating the representers we reduce the full (infinite dimensional) problem to a relatively low‐dimensional problem at the outset, allowing full control over the conditioning and hence the stability of the inverse solution. With the representers calculated we can easily update our model as additional TOPEX/POSEIDON data become available. As an initial illustration we invert harmonic constants from a set of 80 open‐ocean tide gauges. We then present a practical scheme for direct inversion of TOPEX/POSEIDON crossover data. We apply this method to 38 cycles of geophysical data records (GDR) data, computing preliminary global estimates of the four principal tidal constituents, M2, S2, K1, and O1. The inverse solution yields tidal fields which are simultaneously smoother, and in better agreement with altimetric and ground truth data, than previously proposed tidal models. Relative to the “default” tidal corrections provided with the TOPEX/POSEIDON GDR, the inverse solution reduces crossover difference variances significantly (≈20–30%), even though only a small number of free parameters (≈1000) are actually fit to the crossover data.
Laser profiling of the ice surface topography during the Winter Weddell Gyre Study 1992
Authors: Dierking Wolfgang
Published: February 2004

A laser profiler mounted on a helicopter was used to measure the surface topography of sea ice in the Weddell Sea. The measurements were carried out during the cruise Antarktis X/4 of R/V Polarstern as part of the Winter Weddell Gyre Study 1992 (WWGS′92). The total length of the measured surface profiles amounts to 793 km. The observed mean ridge heights and mean ridge spacings are fairly well correlated. Therefore the ridging intensity R1, which is the ratio of ridge height and spacing, was used as a quantitative classifier in order to arrange the laser data into different groups. At a cutoff height of 0.8 m the average ridge height and spacing are 1.16 m and 160 m at the lowermost range of ridging intensities (R1<0.02), 1.2 m and 50 m at the intermediate range (0.02<R1<0.04), and 1.3 m and 26 m at the uppermost range (R1>0.04), respectively. The best fits to the observed ridge height distributions are achieved by negative exponentials, at lower ridging intensities as a function of ridge height, at the regime of highest ridging intensity as a function of the ridge height squared. The distributions of ridge spacing are well described by a lognormal distribution function. A simple model is used to estimate the average thickness hd* and the areal fraction of ridged ice from the laser data. The values of hd* range from 3.1m with an areal coverage of 5% at the lowermost range of R1 to 3.7 m with an areal coverage of 31% at the uppermost range. If the ridged ice is distributed as a uniform layer over a unit area, the corresponding effective thickness values are 0.14 m and 1.16 m, respectively. Mean ridge heights and spacings are determined for different cutoff heights in order to enable comparisons to other measurements. The effect of ridges on the surface stress over the ice is estimated using the drag partition theory, which is applicable to the regime of lowest ridging intensity. The contribution of ice ridge form drag to the total wind drag for an average ridging intensity of  = 0.007 and a cutoff height of 0.8 m is about 35 to 40% at neutral stability. If it is assumed that the aerodynamic roughness length z0 of the intervening ice surface varies between 3.3×10−4 m and 5.5×10−4 m, the drag coefficient Cdn ranges from 2.08×10−3 to 2.24×10−3 at a reference height of 10 m.
A note on seasonal cycles of temperature and salinity in the upper waters of the Greenland Sea Gyre from historical data
Authors: Pawlowicz Richard
Published: February 2004

Monthly climatologies of temperature and salinity for two regions in the Greenland Sea are created by combining historical archives of hydrographie stations with observations from recent cruises. The first region corresponds to the gyre center, where deepwater formation occurs and a large bay forms in the winter ice pack (“Nordbukta”), and the second region lies directly to the south, in the area usually covered by an ice tongue (“Odden”) in February and March. Surface temperature responds primarily to local surface heat fluxes, consistently warming in the summer to about 4°C and cooling in the fall to the freezing point. Interannual variability appears to be greater for salinity than for temperature. This, coupled with the sparse data coverage, makes it more difficult to define a seasonal salinity cycle. However, in July and August, surface salinity in both regions appears to decrease drastically, with freshening being more pronounced in the southern region. In the fall this mixed‐layer fresh anomaly is removed, probably by brine rejection due to the local formation of ice and its subsequent removal by northerly winds. Eventually, ice formation causes the surface waters to overturn and entrain the warmer water below, inhibiting further ice formation. The fresh anomaly is smaller in the gyre center than in the Odden region, so that ice formation will end there earlier, resulting in the appearance of a bay to the north of an ice tongue. Since the disappearance of ice is a necessary precursor to mixing deeper than about 100 m, this suggests that large areal changes in ice cover may be used as a proxy for identifying the strength and onset of deep convection.
Estimation of the electromagnetic bias from retracked TOPEX data
Authors: Rodríguez Ernesto , Martin Jan M.
Published: February 2004

We examine the electromagnetic (EM) bias by using retracked TOPEX altimeter data. In contrast to previous studies, we use a parameterization of the EM bias which does not make stringent assumptions about the form of the correction or its global behavior. We find that the most effective single parameter correction uses the altimeter‐estimated wind speed but that other parameterizations, using a wave age related parameter of significant wave height, may also significantly reduce the repeat pass variance. The different corrections are compared, and their improvement of the TOPEX height variance is quantified.
Warm core ring dynamics derived from satellite imagery
Authors: Hooker Stanford B. , Brown James W.
Published: February 2004

A reinterpretation of the life history of warm core ring 82‐B is constructed from drifter trajectories, hydrographie profiles, and satellite‐derived sea surface temperature fields. An analysis of the observations strongly suggests this ring is fundamentally a dipole structure for much of its existence. The dipole has unequal strength vortices, with the cyclone being the weaker component. Quantification of the dipole indicates the anticyclone is oval shaped and rotates at approximately 7.7° per day, while the cyclone revolves around the anticyclone at about 14.5° per day, yielding an orbit period of approximately 25 days for the cyclone. The elusive part of the dipole explanation is in interpreting its surface signature as a function of time, as the cyclone appears to disappear when in proximity to the steep continental slope. Vortex modeling suggests that when the weaker cyclonic eddy is placed close to a boundary, the cyclone is drawn into a filament as it is advected through the gap between the anticyclone and the boundary. This means the cyclone is either in a filamentation state or undergoing the straining associated with filamentation approximately three fourths of the time, which is in complete agreement with the satellite imagery. In addition, the 82‐B dipole configuration is sufficiently robust to survive continuous interaction with the continental slope and the onset of a Gulf Stream interaction. Although only warm core ring 82‐B is analyzed in detail (and found to be a vortex pair), dipole configurations are found in the warm core ring 81‐F time series as well.
Responses of climate and cyclones to reductions in Arctic winter sea ice
Authors: Murray Ross J. , Simmonds Ian
Published: February 2004

A perpetual January simulation of the global atmosphere has been used to study the climatology of the northern hemisphere winter, with particular reference to its synoptic characteristics and to changes induced by reductions in the concentration of Arctic sea ice. Lows were tracked using an objective scheme and were analyzed for a number measures of cyclone behavior. The qualitative features of the cyclone density and flux distributions compare well with observations, except in certain respects noted. Cyclone velocities and intensities are also presented and discussed. Decreases in sea ice concentration produced a monotonic but nonlinear warming in the lower troposphere and weakening and southward contraction of the midlatitude westerlies. Mean sea level pressure reductions were biased toward the western Arctic. There was a significant decrease in the speeds and intensities of cyclonic systems north of 45°N but little overall change in areal densities or in the arrangement of the major storm tracks. Some density maxima were displaced toward regions of opened up sea ice or in response to circulation changes. A number of aspects of the response are interpreted as being due to changes in thermal steering and baroclinicity or to nonlinear effects. Surprisingly, no significant expansion of cyclonic activity occurred in the central Arctic. The relative constancy of cyclone numbers and storm tracks is a response very different from that found in a similar study of the southern hemisphere.
Accuracy of sea ice temperature derived from the advanced very high resolution radiometer
Authors: Yu Y. , Rothrock D. A. , Lindsay R. W.
Published: February 2004

The accuracy of Arctic sea ice surface temperatures Ts derived from advanced very high resolution radiometer (AVHRR) thermal channels is evaluated in the cold seasons by comparing them with surface air temperatures Tair from drifting buoys and ice stations. We use three different estimates of satellite surface temperatures, a direct estimate from AVHRR channel 4 with only correction for the snow surface emissivity but not for the atmosphere, a single‐channel regression of Ts with Tair, and Key and Haefliger's (1992) polar multichannel algorithm. We find no measurable bias in any of these estimates and few differences in their statistics. The similar performance of all three methods indicates that an atmospheric water vapor correction is not important for the dry winter atmosphere in the central Arctic, given the other sources of error that remain in both the satellite and the comparison data. The errors are not reduced by regression with both thermal channels and the satellite scan angle. A record of drifting station data shows winter air temperature to be 1.4°C wanner than the snow surface temperature. “Correcting” air temperatures to skin temperature by subtracting this amount implies that satellite Ts estimates are biased warm with respect to skin temperature by about this amount. A case study with low‐flying aircraft data suggests that ice crystal precipitation can cause satellite estimates of Ts to be several degrees warmer than radiometric measurements taken close to the surface, presumably below the ice crystal precipitation layer. An analysis in which errors are assumed to exist in all measurements, not just the satellite measurements, gives a standard deviation in the satellite estimates of 0.9°C, about half the standard deviation of 1.7°C estimated by assigning all the variation between Ts and Tair to errors in Ts.
Introduction: The Alaska Synthetic Aperture Radar Facility special section
Authors: Carsey Frank D. , McNutt Lyn , Rothrock D. Andrew
Published: February 2004

In 1985 the National Aeronautics and Space Administration (NASA) and the University of Alaska agreed to implement, at the Geophysical Institute of the Fairbanks campus, a facility dedicated to the acquisition, processing, distribution, and archival of synthetic aperture radar (SAR) data to be downlinked from satellites. Since then, the Alaska SAR Facility (ASF) has been an active part of NASA's Mission to Planet Earth. ASF Program goals were outlined by Carsey et al. [1987].

Plans were put in place to support three satellites, and the first two, the First European Remote Sensing Satellite (ERS 1) (launched in My 1991) and the Japanese Earth Resources Satellite (JERS 1) (launched in February 1992) are presently in orbit and are being supported by ASF. The third, the Canadian RADARSAT, is scheduled for launch in the spring of 1995. Future satellite missions by U.S. or foreign agencies may well be added in time.
High‐frequency variability of western boundary currents using ERS 1 three‐day repeat altimeter data
Authors: Minster J.‐F. , Gennero M.‐C.
Published: February 2004

ERS 1 three‐day repeat altimeter Ocean Products have been analyzed from September 3 to December 9, 1991. In the high mesoscale energy areas of the world ocean the obtained height variability is comparable to that derived from 2 years of Geosat altimeter data (17‐day repeat), while it is slightly lower elsewhere. The data reveal some high‐frequency variability of western boundary currents, but not the seasonal signals, nor the low‐frequency mesoscale signal which dominates elsewhere. Isocorrelation maps show that the e‐folding time is around 10 to 15 days in strong currents. The sea height variance, integrated over all wavelengths in the frequency‐wavenumber spectrum, corresponds to less than 5% of the total 3‐month variance for periods shorter than 20 days, up to 15% of this variance for periods shorter than 34 days, which are respectively the Nyquist frequencies of the TOPEX/POSEIDON and Geosat data. This signal covers a whole range of wavelengths that cannot be obtained from current meter data. In the Gulf Stream area the total dynamic height signal is estimated by adding a climatological dynamic topography to the mesoscale variability. Near 60°W, the height variations apparently correspond to meanders with periods of 30 to 40 days and latitudinal extension about 200 km. They are consistent with westward propagation at about 10 cm/s, and their surface transport varies by about 50% on this timescale, which is in agreement with in situ observations.
Optical characteristics of suspended marine particles for short light pulses
Authors: Shifrin Kusiel S. , Zolotov Ilja G.
Published: February 2004

Oceanological problems, which need the knowledge of peculiarities of pulse propagation in the sea, are analyzed. Optical characteristics of typical particles of marine suspension at pulse irradiation are calculated. It is shown that efficiencies for backscattering for the pulse and monochromatic wave differ markedly. For efficiencies for scattering and for extinction, these differences are much less noticeable. Reasons for these differences are explained.
Scales of variability of bio‐optical properties as observed from near‐surface drifters
Authors: Abbott Mark R. , Brink Kenneth H. , Booth C. R. , Blasco Dolors , Swenson Mark S. , Davis Curtiss O. , Codispoti L. A.
Published: February 2004

A drifter equipped with bio‐optical sensors and an automated water sampler was deployed in the California Current as part of the coastal transition zone program to study the biological, chemical, and physical dynamics of the meandering filaments. During deployments in 1987 and 1988, measurements were made of fluorescence, downwelling irradiance, upwelling radiance, and beam attenuation using several bio‐optical sensors. Samples were collected by an automated sampler for later analysis of nutrients and phytoplankton species composition. Largescale spatial and temporal changes in the bio‐optical and biological properties of the region were driven by changes in phytoplankton species composition which, in turn, were associated with the meandering circulation. Variance spectra of the bio‐optical parameters revealed fluctuations on both diel and semidiurnal scales, perhaps associated with solar variations and internal tides, respectively. Offshore, inertial‐scale fluctuations were apparent in the variance spectra of temperature, fluorescence, and beam attenuation. Although calibration samples can help remove some of these variations, these results suggest that the use of bio‐optical data from unattended platforms such as moorings and drifters must be analyzed carefully. Characterization of the scales of phytoplankton variability must account for the scales of variability in the algorithms used to convert bio‐optical measurements into biological quantities.
Lagrangian mixed layer modeling of the western equatorial Pacific
Authors: Shinoda Toshiaki , Lukas Roger
Published: February 2004

Processes that control the upper ocean thermohaline structure in the western equatorial Pacific are examined using a Lagrangian mixed layer model. The one‐dimensional bulk mixed layer model of Garwood (1977) is integrated along the trajectories derived from a nonlinear 1½ layer reduced gravity model forced with actual wind fields. The Global Precipitation Climatology Project (GPCP) data are used to estimate surface freshwater fluxes for the mixed layer model. The wind stress data which forced the 1½ layer model are used for the mixed layer model. The model was run for the period 1987–1988. This simple model is able to simulate the isothermal layer below the mixed layer in the western Pacific warm pool and its variation. The subduction mechanism hypothesized by Lukas and Lindstrom (1991) is evident in the model results. During periods of strong South Equatorial Current, the warm and salty mixed layer waters in the central Pacific are subducted below the fresh shallow mixed layer in the western Pacific. However, this subduction mechanism is not evident when upwelling Rossby waves reach the western equatorial Pacific or when a prominent deepening of the mixed layer occurs in the western equatorial Pacific due to episodes of strong wind and light precipitation associated with the El Niño‐Southern Oscillation. Comparison of the results between the Lagrangian mixed layer model and a locally forced Eulerian mixed layer model indicated that horizontal advection of salty waters from the central Pacific strongly affects the upper ocean salinity variation in the western Pacific, and that this advection is necessary to maintain the upper ocean thermohaline structure in this region.
Gulf Stream structure, transport, and recirculation near 68°W
Authors: Johns W. E. , Shay T. J. , Bane J. M. , Watts D. R.
Published: February 2004

An analysis of the structure and transport of the Gulf Stream is undertaken using direct current meter observations from a 13‐mooring array deployed near 68°W from June 1988 to August 1990. The analysis is based on a “stream‐coordinate” approach, in which velocities are rotated into a local, downstream coordinate frame and averaged according to their relative cross‐stream location within the current. The picture so obtained represents the average synoptic structure of the Gulf Stream, rather than the Eulerian‐averaged structure in which the current is weakened and broadened by lateral meandering of the current and adjacent recirculations. Many familiar features of the Gulf Stream are reproduced in the analysis, including an asymmetric velocity profile with larger shear on the cyclonic (shoreward) side of the current, an offshore displacement of the velocity core with depth, and a subsurface velocity maximum on the offshore side of the current. Westward recirculations are also seen on both sides of the Gulf Stream. Maximum downstream speeds at the axis of the Gulf Stream reach approximately 2.0 m/s at the surface and 0.7 m/s at 1000 m, roughly twice the corresponding Eulerian‐averaged values. The analysis also reveals a deep extension of the Gulf Stream at 3500 m depth with a width of 130 km and average speeds of 3–4 cm/s. The transport of the Gulf Stream in the stream‐coordinate frame is 113±8 Sv, approximately 30% larger than the Eulerian‐averaged transport of 88 Sv. On the basis of these results and other recent studies the downstream transport increase of the Gulf Stream and the inflow structure to the Gulf Stream are reconsidered. It is concluded that approximately 30 Sv, or over half of the transport increase between Cape Hatteras and 68°W, is fed by inflow from the northern side of the Gulf Stream and that this inflow is concentrated near Cape Hatteras and 68°W, where the Gulf Stream flows steeply across isobaths converging from the north.
Convection beneath freezing leads: New observations compared with numerical model results
Authors: Muench Robin D. , Smith David C. , Paulson Clayton A.
Published: February 2004

Vertical distributions of temperature, salinity, and horizontal and vertical current speed were measured along the edges of a number of rapidly freezing leads in the southern central Beaufort Sea during March‐April 1992. These observations were restricted to cases having sufficiently small ice water relative speeds that brine‐driven convection was expected, based on scaling arguments, to dominate shear turbulence generated by the relative ice water motion. The observed salinity and current features were consistent with an existing conceptual model for sublead convection consequent to brine rejection from ice formation, and with the results of a numerical model which assumes two‐dimensionality in the cross‐lead direction, and uses a brine input consistent with the field observations. These models predict convection of brine‐enriched plumes beneath the lead downward to the pycnocline, where they then spread outward away from the lead. Volume continuity is satisfied by horizontal inflow of water to the lead at the surface. Observed mean downward convection speeds varied from 0.2 to 0.7 cm s−1 and had maxima up to about 2 cm s−1, consistent with the numerical model. Salinities associated with the convecting parcels were about 0.001 practical salinity units (psu) above ambient, which was an order of magnitude less than predicted by the model, while plumes of water flowing away from the lead on the pycnocline had salinities as high as 0.004 psu above ambient. These similarities and discrepancies are discussed within the context of a steady state model versus a nonsteady field situation, and it is concluded that the steady “convection cell” concept is probably valid if viewed as a time‐averaged sequence of discrete convective plumes or “thermals.”