bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial variations in the chlorophyll‐specific absorption coefficients of phytoplankton and photosynthetically active pigments in the equatorial Pacific
Authors: Allali Karima , Bricaud Annick , Claustre Hervé
Published: February 2004

Chlorophyll‐specific absorption coefficients of particles, a*p(λ), and of phytoplankton, a*ph(λ), were determined using the glass‐fiber filter technique along 150°W in the equatorial Pacific (13°S–1°N). A site‐specific algorithm for correcting the path length amplification effect was derived from field measurements. Then a decomposition technique using the high‐performance liquid chromatography pigment information and taking into account the package effect was used to partition a*ph into the contributions of photosynthetic pigments (a*ps) and nonphotosynthetic pigments (a*nps). Both a*ph and a*nps values were observed to decrease from the oligotrophic waters of the subequatorial area (13°–1°S) to the mesotrophic waters of the equatorial area (1°S‐1°N) and from the surface to deep waters. The a*ph variations were primarily, but not exclusively, caused by changes in the concentrations of nonphotosynthetic pigments. The level of pigment packaging was also variable both horizontally and vertically, as a result of changes in populations and photoacclimation. In comparison with a*ph, a*ps exhibited a reduced range of variation with depth and along the latitudinal gradient. The variations in a*ps originating from the package effect were partly compensated by variations in the concentrations of photosynthetic pigments. We extended this analysis to include data collected in other areas with different trophic states. The a*ps values varied over a factor of 4 at 440 nm, instead of 8 for a*ph, for chlorophyll a concentrations covering 2 orders of magnitude (0.02–2 mg m−3). In agreement with a previous study performed off California with a different method [Sosik and Mitchell, 1995], we conclude that a*ps is less dependent on environmental parameters than a*ph. In addition, our results provide evidence that the variability in a*ps cannot be neglected. The use of a*ps instead of a*ph in light‐photosynthesis models (in conjunction with a quantum yield for carbon fixation defined with respect to the photosynthetically active absorbed amount of quanta) presents the advantage of removing the variability associated with nonphotosynthetic pigments.
Moored observations of the current and temperature structure over the continental slope off central California: 1. A basic description of the variability
Authors: Ramp Steven R. , Rosenfeld Leslie K. , Tisch Timothy D. , Hicks Michael R.
Published: February 2004

Current meter data have been analyzed from seven moorings on the continental slope along the central California coast, from Point Piedras Blancas to Point Reyes. The goal was to examine the subtidal variability in the 100 m to 1000 m depth range, particularly with regard to alongshore propagating events and interactions with eddies and meanders of the California Current offshore. The 2‐year time series available off Point Sur were first analyzed in conjunction with the local and remote surface wind stress and coastal synthetic subsurface pressure, and then correlated with shorter coincident current records moored at similar depths to the north and south. The poleward flowing California Undercurrent was the most prominent feature at all the moorings except at one site located well into the Monterey Submarine Canyon. The strongest poleward flows over the slope occurred in 3‐ to 4‐month bursts, not phase locked with the seasons, with vector speeds exceeding 40 cm s−1. South of the canyon, an approximately monthly signal was identified which propagated poleward, upward, and offshore. The behavior of this signal was consistent with that of an internal coastal Kelvin wave generated at the surface by remote wind stress to the south and was likely not of equatorial origin. The wave was apparently scattered by the abrupt topography of the canyon, since its energy persisted to the north of the canyon but with unstable phase. At least three eddy‐meander interaction events were observed. These warm, deep (>1000 m), anticyclonic features reversed the flow over the slope to equatorward when they moved onshore and interrupted the flow of the undercurrent. One event forced anomalously strong (>15 cm s−1) onshore flows off Monterey Bay and offshore flows off Point Sur. While quantitative transport estimates could not be made with this sparse data set, it seems apparent that such events play a significant role in the exchange of water properties between the shelf and the deep ocean.
ERS 1 radar and field‐observed characteristics of autumn freeze‐up in the Weddell Sea
Authors: Drinkwater Mark R. , Lytle Victoria I.
Published: February 2004

ERS 1 satellite microwave radar data are analyzed to investigate changes in sea ice characteristics during a period when a drifting ice camp was deployed in the Weddell Sea, Antarctica. Synthetic aperture radar and scatterometer data are calibrated and geolocated to derive a time series of C band backscatter coefficient (σ°) corresponding with simultaneous surface measurements during the austral autumn freeze‐up. Thermistor strings were implanted in the snow and ice at a number of local and regional sites. Surface measurements at these sites indicate that up to 50% of the surface of ice floes surviving the summer were flooded, with an unconsolidated, saline slush layer at the snow/ice interface consisting of approximately half seawater and half ice of meteoric origin. The slush was typically 5–30 cm thick and covered by a 20‐ to 50‐cm‐thick dry snow layer. Results show that the microwave radar backscatter characteristics of this perennial ice region responded sensitively to changes in air temperature and corresponding changes in turbulent flux of heat at the surface of the sea ice. At ice concentrations exceeding 95%, the modulation of the regional backscatter coefficient by wind speed and direction was negligible. Warm summer conditions persisted for around 2 weeks after ice camp deployment on February 7 (day 38), with air temperatures of around −3° to −5°C prior to the onset of autumn freeze‐up. From February 26 (day 57) onward, cooling began and snow ice growth proceeded as air temperatures fell to below −20°C. Altogether, between February 7 (day 38) and March 15, 1992 (day 75), the backscatter coefficient time series measured by each radar indicated that σ° fell by several decibels during the freezing and transformation of the layer of saturated, saline basal snow into snow ice. This change is caused by a reduction in the permittivity and thus the scattering intensity of the basal snow as a function of the disappearance, by freezing, of the saltwater saturated layer. These results suggest the possibility of monitoring the timing and autumn freeze‐up transition of regional ice signatures as a means of quantifying the proportion of flooded perennial sea ice.
A real‐time oceanographic nowcast/forecast system for the Mediterranean Sea
Authors: Horton Charles , Clifford Melody , Schmitz Joyce , Kantha Lakshmi H.
Published: February 2004

We describe here a nowcast/forecast system for the entire Mediterranean Sea, designed for real‐time forecasts and closely resembling operational numerical weather prediction systems. The core of the system is a high‐resolution (10 km) three‐dimensional primitive equation‐based, sigma‐coordinate numerical circulation model, assimilating remotely sensed multi‐channel sea surface temperature and in situ expendable bathythermograph/conductivity‐temperature‐depth observational data, using an optimal‐interpolational scheme. We present results for 1993 and 1994 from this data‐assimilation model, focusing principally on the mesoscale features prevalent in the western and eastern Mediterranean Sea. We show that the model exhibits considerable skill in simulating both the permanent and transient mesoscale features in the Mediterranean. In particular, hitherto less well‐known and less well‐studied circulation features in the Adriatic and Aegean Seas are carefully examined and presented. Particular care is given to discussing the circulation in the entire Mediterranean, with particular attention to flows through various straits and their variability.
Observations of seamount‐attached eddies in the North Pacific
Authors: Bograd Steven J. , Rabinovich Alexander B. , LeBlond Paul H. , Shore Jennifer A.
Published: February 2004

Satellite‐tracked drifters were used to examine eddy activity in the vicinity of the Emperor Seamount Chain (ESC) in the North Pacific during 1991–1993. The trajectories of two drifters drogued at a depth of 120 m revealed a pair of counterrotating mesoscale eddies attached to the leeside of Ojin/Jingu Seamount in the summer of 1992. The eddies had diameters of 75–100 km and rotational speeds of 20–40 cm/s at 120 m. Sea surface height anomalies derived from blended TOPEX/ERS‐1 satellite altimetry revealed that the eddies had a surface manifestation as well. One of the drifters made five loops within the cyclonic eddy over a period of 62 days, during which time the eddy translated westward, toward the seamount, at 2.9 cm/s. This is one of the first observations demonstrating an extended attachment of a topographically generated eddy to a seamount. Drifters drogued at a depth of 15 m which crossed the ESC in the summer of 1991 and winter of 1993 revealed no eddy activity, most likely because of a decoupling of the topographic influence to the 15 m flow at their crossing latitude over the Nintoku Seamount (summit depth at 1000 m). The implication is that eddy formation within the mixed layer near the ESC is confined to the region around the taller Ojin/Jingu and Kinmei Seamounts (summit depths at 800 m and 100 m, respectively). It is suggested that long‐lived eddies attached to the leeside of the ESC can profoundly influence local biological production and water exchange between the western and eastern basins of the North Pacific.
The relation between ice deformation, oceanic heat flux, and the ice thickness distribution in the Arctic Ocean
Authors: Björk Göran
Published: February 2004

A one‐dimensional ocean model, coupled with an ice model where the ice cover is partitioned into a number of thickness categories, is used to investigate how the ice thickness distribution in the Arctic Ocean depends on the two deformation processes, export (net divergence) and ridging. The model standard case generates vertical profiles of temperature, salinity and an ice thickness distribution similar to the observations. The standard case oceanic heat flux agrees well with recently deduced heat fluxes from Arctic Ice Dynamics Joint Experiment (AIDJEX) data. The oceanic heat flux is about 18 W m−2 during summer and about 1 W m−2, during winter. It is found that the mean ice thickness decreases with increasing ice export in close agreement with other investigations. However, the dependence of the mean ice thickness on ridging activity is found to be very weak. The change of the mean ice thickness is only 12 cm when increasing the ridging activity in the model from 0 to 0.4 yr−1; where the larger value represents an estimate of the actual ridging activity in the Arctic Ocean. In a sensitivity study, different types of ridging and albedo parameterizations are tested, and this weak dependence is found to be very robust. Other properties of the model ice cover are sensitive to ridging though: The equilibrium thickness of undeformed ice decreases with both export and ridging activity. The annual maximum open water fraction and the amplitude of the seasonal thickness variation increases with export and ridging.
Ocean surface currents obtained from microwave sea‐echo Doppler spectra
Authors: McGregor John A. , Poulter E. Murray , Smith Murray J.
Published: February 2004

Ocean currents may be determined from the positions of Bragg peaks in Doppler spectra of radar echoes from the sea surface. In this paper the applicability of this technique at microwave frequencies is investigated. Advantages of high range resolution and sensitivity to currents within centimeters of the ocean surface ensue from the short Bragg wavelength at microwave frequencies. A disadvantage is that the technique is restricted to low wind speed, fetch‐limited sea conditions for which individual Bragg peaks are resolvable in the Doppler spectra. Experiments at low grazing angles with an S band (3 GHz) Frequency‐modulated interrupted continuous wave radar show that in these conditions surface drift currents can be measured to better than ±2 cm s−1 accuracy over a large range of azimuth angles with respect to the wind direction. In conditions under which the Bragg peaks are not resolvable, currents may be measured by using local wind direction measurements to correct the mean Doppler velocity for the relative contributions of the advancing and receding Bragg peaks. Experiments revealed that the accuracy of current measurements obtained in this manner was better than ±5 cm s−1. The technique was applied to the mapping of tidal currents in an inlet, demonstrating the significant potential of the radar measurements for nearshore and coastal dynamics studies.
Simulations of the Atlantic Ocean with a free surface sigma coordinate ocean model
Authors: Ezer Tal , Mellor George L.
Published: February 2004

A sigma coordinate, free surface numerical model with turbulence dynamics has been implemented for the Atlantic Ocean and the Greenland Sea, from 80°S to 80°N. It is driven at the surface by monthly mean sea surface temperature and wind stress climatologies and is executed for 30 years. This is the first time that a model of this type, previously used mostly for coastal and regional simulations, has been implemented for the entire Atlantic Ocean and run for a long period of time. The model horizontal circulation, thermohaline overturning circulation, and meridional heat fluxes are described; the results are compared with observations and the results of other models. The model produces intense deep western boundary currents and complicated gyre structures associated with small‐scale topographic variations. The meridional overturning circulation consists of about 14 Sv (1 Sv=106 m3 s−1) of southward flowing deep water mass crossing the equator and a northward heat flux with a maximum value of more than 1 PW (1015 W). Although the maximum meridional heat flux is comparable to estimates obtained from observations, the amplitude of the seasonal variations of northward heat flux across 26°N is underestimated in comparison with observations; it is similar to that obtained by other models.
Low‐frequency current variability at the Straits of Crete, eastern Mediterranean
Authors: Tsimplis M. N. , Velegrakis A. F. , Theocharis A. , Collins M. B.
Published: February 2004

Current meter data from six moorings are analyzed to study current variability at the straits of the Cretan Arc which connect the south Aegean Sea with the eastern Mediterranean. The three layers in which the current meters were deployed show different current characteristics. The upper layer shows evidence of the Asia Minor current in the Rhodes Strait and a clockwise eddy in the Karpathos Strait. Water in the middle layer moves slowly into the south Aegean. The bottom current meters in Kassos and Antikithira Straits recorded currents, steady in amplitude and direction, with speeds equal to or higher than those observed in the upper layer. The observations suggest a significant outflow (0.5 Sv) of Cretan Dense Water (CDW) to the Levantine and Ionian Seas. Rotary empirical orthogonal functions are used to extract and describe the coherent part of the variability. Forty‐four percent of the total variability is described by the first three empirical orthogonal functions. Less than 20% of the current variability of the western strait is coherent with variability of the eastern straits. The coherent part of the variability refers mainly to periods longer than 20 days. The current meter data are compared with atmospheric pressure, showing good correlation during the first period of the measurements, when a major atmospheric pressure low passed over the Aegean.
Correlation of oceanographic signatures appearing in synthetic aperture radar and interferometric synthetic aperture radar imagery with in situ measurements
Authors: Marmorino G. O. , Thompson D. R. , Graber H. C. , Trump C. L.
Published: February 2004

Synthetic aperture radar (SAR) imagery collected over the continental shelf near Cape Hatteras, N. C., is analyzed in conjunction with shipboard hydrographic and current measurements. The SAR measurements were made over a 2‐hour period on June 20, 1993, in both standard mapping mode and interferometric synthetic aperture radar (INSAR) mode from a NASA DC‐8 aircraft as part of the High‐Resolution Remote Sensing Experiment. In situ currents were measured using a surface‐towed acoustic Doppler current profiler (ADCP). The measurements were made near the end of a period of Gulf Stream incursion onto the shelf as detected using a shore‐based HF radar. Winds were southwesterly at 4–6 m s−1. Long, curvilinear SAR signatures, resembling earlier SEASAT observations made in the same area, are shown to correspond to narrow, shallow fronts separating water masses that increase in surface density with distance offshore. Across‐front changes in surface current inferred from the INSAR data are consistent with 2‐m‐depth currents measured by the ADCP over scales of tens of meters. Thus frontal current gradients measured by INSAR reflect real changes in surface current and are not due to biases induced by changes in the surface‐wave spectrum. This lends support to the detailed INSAR surface maps derived by Graber et al. [1996]. An east‐west salinity front having the largest observed surface density and current gradient is corrugated on length scales up to the local Rossby radius of deformation and translates southward between successive images. In data from the longer radar wavelengths the salinity front appears as a dark band downwind of a bright signature, and this is interpreted as a region where Bragg‐scale waves regenerate following their dissipation in the frontal region. In addition to the fronts the imagery shows closely spaced packets of southward propagating ocean internal waves occurring in the strongly stratified inshore water mass. This case study further serves to emphasize the potential of SAR imagery for study of a wide range of shelf processes.
Observations of low‐frequency circulation and amplified subinertial tidal currents at Cobb Seamount
Authors: Codiga Daniel L. , Eriksen Charles C.
Published: February 2004

We present acoustic Doppler current profiler (ADCP) survey results resolving three‐dimensional current structure in thermocline stratification atop Cobb Seamount (130.8°W, 46.8°N). Mean flow includes clockwise circulation near the bottom and an east‐northeastward background current. Clockwise flow is not strong enough to isolate fluid from the background current as in a Taylor cap unless this occurs in the deepest 50 m, outside ADCP coverage. Diurnal currents (subinertial, 0.69ƒ) are amplified within a few kilometers radially and about 100 m vertically of the seamount by up to 5.3 times ambient K1 tidal currents. Their diagnostics include clockwise propagation around the seamount with first azimuthal wavenumber, clockwise rotation in time, narrow current ellipses oriented nearly along bathymetric contours with positively correlated radial and azimuthal components, counterclockwise turning with depth, and downward propagation. They are compared to the stratified seamount‐trapped wave of first azimuthal wavenumber and third‐highest subinertial resonant frequency (0.70ƒ) calculated numerically using measured bathymetric and stratification profiles. Inviscid free wave currents exhibit symmetric patterns not consistent with the measurements; in a forced damped wave maintained by ambient tidal currents against parameterized friction of 2 day timescale, as appropriate to dissipation timescales estimated from microstructure measurements, symmetries are broken such that each observed current diagnostic is matched. When the wave is linearized about a steady, baroclinic, clockwise current representing the measured mean flow, its frequency and structure are very weakly modified.
Splitting of a free jet flowing over a saddle sill
Authors: Stern Melvin E.
Published: February 2004

If a steady jet with two free streamlines ascends a sill while entirely remaining on one sloping side, then the rising motions must be compensated by transverse sinking motions in order that the cross‐stream integral of relative vorticity vanishes at all downstream sections. The maximum sill height which allows such a flow is computed assuming slow downstream changes in a quasi‐geostrophic barotropic model; a 1½ layer baroclinic model is also considered. If the critical sill height is exceeded, it is suggested that the jet will split with only part of it crossing the sill on the original side. This might explain why the Antarctic Circumpolar Current bifurcates at the Falkland Plateau, where one branch forms the Malvinas Current and the other branch turns eastward across the Atlantic. The theory is related to previous laboratory observations in which bifurcation occurs.
Source‐transport inversion: An application of geophysical inverse theory to sediment transport in Monterey Bay, California
Authors: Tait James F. , Revenaugh Justin
Published: February 2004

Application of forward coastal sediment transport models in situations involving large temporal and spatial scales or topographically complex environments can be highly problematic since the distribution of hydrodynamic parameters is rarely adequately known. Where rocky topography is present, flow patterns may be altered and sediments trapped by topographic barriers. A frequently employed approach to these problems is the application of the statistical technique known as empirical orthogonal function (EOF) analysis. One limitation of EOF analysis of grain size and mineralogical data is that EOF is a purely geometric technique which does not allow incorporation of a priori knowledge we may have regarding the physical environment. In fact, there is no guarantee that a meaningful physical interpretation of the results of an EOF analysis actually exists. This is not true of geophysical inverse theory, which is capable of incorporating diverse forms of information and is not limited to purely geometric manipulations of data. We have formulated an inverse theoretical approach to study sediment transport which we call STI, short for source‐transport inversion. STI relaxes the nonphysical assumption of orthogonal endmembers and can handle many forms of a priori information. STI has been developed initially in the context of modeling the sediment supply and dispersal system of Monterey Bay, California. Using the geographical distribution of heavy mineralogy data, significant sources are identified and sediments traced from those sources along transport pathways. Model results are encouraging both in terms of goodness of fit between model and data and in terms of the agreement of model results with the sediment sourcing and dispersal patterns inferred in previous studies. Model results indicate that beach sediments are primarily derived from the open coast north of the bay, that a littoral cell boundary exists in the center of the bay at Moss Landing, and that beach deposits produced by paleolittoral drift during a sea level low stand lie along the 100‐m isobath.
Deep tracer and dynamical plumes in the tropical Pacific Ocean
Authors: Johnson Gregory C. , Talley Lynne D.
Published: February 2004

Anomalous middepth plumes in potential temperature‐salinity, θ‐S, and buoyancy frequency squared, N2, originate east of the East Pacific Rise Crest and decay toward the west. Conductivity‐temperature‐depth (CTD) data from recent hydrographic sections at 15°S and 10°N are used together with meridional sections at 110°, 135°, and 151°W to map these structures. Warm salty plumes west of the rise crest have maxima centered at 2700 m, 10°S and 8°N, and are interrupted by a cold, fresh tongue centered at 2900 m, 2°S. The θ‐S anomalies decay to half their peak strength 2800 km to the west of the rise crest, ±300 km in the meridional, and ±0.4 km in the vertical. Vertical N2 minima occur within the plumes, regions of reduced vertical gradients in θ and S. These minima are underlain by maxima near the depth of the rise crest, about 3200 m. The N2 plumes decay more rapidly to the west of the rise crest than do the θ‐S plumes. The N2 structure is consistent with a pair of stacked gyres in each hemisphere. There are at least three possible mechanisms consistent with some aspects of these features. First, a deep maximum in upwelling somewhere below 2700 m would result in equatorward and westward interior flow at 2700 m, advecting these plumes along with it. Second, rapid upwelling of warm, salty, unstratified water in the eastern basins could result in westward overflows over the rise crest. Third, upwelling and associated entrainment processes owing to hydrothermal venting could result in stacked counter‐rotating gyres west of the rise crest.
Modeling tsunamis from earthquake sources near Gorringe Bank southwest of Portugal
Authors: Gjevik B. , Pedersen G. , Dybesland E. , Harbitz C. B. , Miranda P. M. A. , Baptista M. A. , Mendes‐Victor L. , Heinrich P. , Roche R. , Guesmia M.
Published: February 2004

The Azores‐Gibraltar fracture zone with the huge bathymetric reliefs in the area southwest of Portugal is believed to have been the source of large historic tsunami events. This report describes simulations of tsunami generation and propagation from sources near the Gorringe Bank. The well‐documented 1969 tsunami event is examined both with a ray‐tracing technique and with finite difference models based on various shallow water equations. Both methods show that the most likely source location is southeast of the Gorringe Bank near the epicenter location determined from seismic data. The tsunami source is calculated by formulas given by Okada [1985] for surface deformation of an elastic half‐space caused by faulting. Observed wave amplitude and travel time and values computed from an initial wave field according to Okada [1985] formulas show acceptable agreement for most stations along the coast of Portugal and Spain. However, in order to explain a large primary wave with downward displacement observed on the coast of Morocco, an alternative source model with a larger area of downward displacement has been introduced. This also leads to a better overall fit with observed travel time. Implications for disastrous events, as the one in 1755, are also discussed. Linear hydrostatic shallow water models are used for most of the simulations, but the importance of nonlinearity and dispersion is examined with the Boussinesq equations. The sensitivity of the solution to changes in the location and the strength of the source is discussed, and a series of grid refinement studies are performed in order to assess the accuracy of the simulations.
Evolution of mixed Rossby gravity waves
Authors: Moore Dennis W. , Kloosterziel R. C. , Kessler William S.
Published: February 2004

A Green's function is derived, which can be used to study and predict the evolution of the velocity and pressure fields associated with the mixed Rossby gravity wave component of the totality of motions due to forcing on an equatorial β plane. Initial value problems can also be solved with the aid of the Green's function. Since energy associated with the Rossby gravity mode always travels east, the Green's function can be employed to predict what signal should arrive to the east of a given location if the time history of the fields are known at that position. Various simple analytical examples are discussed. A numerical ocean general circulation model is used to demonstrate the usefulness of the Green's function formalism.
On deep western boundary currents
Authors: Cember Richard P.
Published: February 2004

The Stommel and Arons [1960a, b] theory of the deep circulation of the world ocean does not directly address the physics of deep boundary currents. In the present paper a maximally simple steady state physics for deep western boundary currents is developed and integrated into the Stommel‐Arons model. This is accomplished by modifying the assumptions of the latter to include effective horizontal eddy viscous terms everywhere in the deep water, including in the interior. The resulting solution for the meridional velocity in a rectangular ocean on a beta plane is mathematically analogous to that of Munk [1950] for the wind‐driven circulation. In the interior the meridional velocity reduces identically to that of Stommel and Arons. Among other benefits, the solution eliminates the theoretical difficulties associated with the crossing of the equator by the deep western boundary current. As an initial test of the theory's consistency with observation, theoretical plots of pressure and meridional velocity as a function of longitude are qualitatively compared with hydrographic sections and inferred meridional velocity fields in the eastern and western basins of the abyssal North Atlantic. Also, the theoretical profile for the meridional velocity as a function of longitude is qualitatively compared with observations of longshore velocity as a function of offshore distance in the deep western boundary current of the North Atlantic Deep Water.
Temperature evolution of the upper ocean in the Greenland Sea January to March 1989
Authors: Sutton Philip J. , Morawitz Werner M. L. , Worcester Peter F. , Cornuelle Bruce D.
Published: February 2004

Tomographic data obtained during early 1989 in the Greenland Sea have been analyzed at 4–8 hour resolution to give the range‐averaged vertical temperature evolution in the upper 500m for a 106km path. The tomographic inversions used both ray travel time data and normal mode group velocity data in order to maximize near‐surface resolution. Two major events are apparent in the results. The first is the warming of a cold (−1.9°C) 100m thick surface layer, and the second, 10 days later, is the cooling of a relatively warm (−0.9°C) subsurface layer between 300m and 500m depth. This warm subsurface layer is a critical source of salinity and buoyancy for deep convection. The surface layer warming is consistent with a mixed layer deepening over a portion of the path, bringing up water from below. Special Sensor Microwave Imager (SSM/I) ice data indicate that the local ice field disappears 3–4 days after the surface warming. The cooling of the warm 300m to 500m layer is also consistent with a vertical process. There is no ice cover at this time, and so surface heat fluxes are large. A northerly wind event occurs at the onset of the cooling of the 300–500 m layer, suggesting that wind‐induced mixing may have played a role in initiating the process. There is evidence of southward flow advecting warm water into the area both before and after the two events studied in detail here.
Effects of instability waves in the mixed layer of the equatorial Pacific
Authors: Baturin N. G. , Niiler P. P.
Published: February 2004

Data from more than 1900 Lagrangian drifters in the equatorial Pacific Ocean from 1980 to 1994 together with velocity records from two Tropical Ocean‐Global Atmosphere ‐ Tropical Atmosphere Ocean (TOGA‐TAO) equatorial moorings at 11° and 140°W, advanced very high resolution radiometer (AVHRR) sea surface temperature (SST) product, and European Centre for Medium‐Range Weather Forecasts (ECMWF) winds were used to investigate the effects and energetics of currents associated with the tropical instability waves (TIWs). Adaptive multitaper spectral analysis was used to estimate how spectral energy varied in the 15‐to‐30‐day period TIW band. The drifter data was analyzed separately for high and low values of the TIW energy in regions of 20° longitude by 20° latitude centered at 0°N, 110°W and 0°N, 140°W to construct meridional profiles of energetics of the TIW region. High TIW energy values typically occurred around October when the South Equatorial Current (SEC) and the North Equatorial Countercurrent (NECC) both became stronger and the eddy kinetic and potential energy production at 140°W was noticeably larger. At 110°W the eddy kinetic and potential energy production existed all the time without large differences between the periods of high and low TIW activity. The meridional kinetic energy was enhanced in the region between the equator and 10°N from 150° to 100°W, with the largest values occurring between 110° and 140°W in longitude and around 5°N in latitude. The largest terms in the horizontal kinetic energy production equation were
and
with maxima in the region of anticyclonic shear between SEC and NECC, from 2° to 6°N. The temperature variance, or the potential energy production, peaked closer to the equator at 3°N. The linear growth timescale of the instability was about 10 days.

The time‐variable wind supplied energy to the current fluctuations during the TIW off period, but for the TIW on period the wind energy input was reduced (at 110W) or even reversed (at 140°W, between 1°S and 7°N), suggesting that air‐sea interaction was important in the total energy balance of the waves. The effect of instability was to reduce the shear of the mean current and to warm the equatorial cold tongue. These calculations suggest that there exists a balance between energy production and dissipation in the TIWs.
Improved techniques for the derivation of sea surface temperatures from ATSR data
Authors: Barton Ian J.
Published: February 2004

A new technique is developed for the analysis of satellite data to provide accurate measurements of seasurface temperature (SST). Satellite data sets are partitioned into subsets depending on the value of a selected parameter (for example, latitude, total water vapor, and water vapor content of an atmospheric layer) to provide a suite of algorithm coefficients that reduces the errors associated with the derivation of SST. For data sets obtained with the along‐track scanning radiometer (ATSR) the data themselves can be used to modify the coefficients used in the SST algorithm, but for other instruments it may be necessary to use additional data sets to select a correct set of algorithm coefficients. A simulated set of ATSR data is used to develop algorithm coefficients for different atmospheric conditions, and the improvement in SST derivation is demonstrated. For ATSR, when all the data for three infrared channels in both the nadir and forward views are available, the improvement is marginal, but for situations when there are limited data the improvement is considerable. The analysis suggests that in the future the best SST analyses will be obtained by developing an interactive system, where the satellite data are ingested into a numerical weather forecast model so that algorithms can be selected and applied with a forecast or analysis of the atmospheric state. The new techniques are tested by application to a large global data set of ATSR brightness temperatures. This analysis highlights the future need for large SST validation data sets that include coincident satellite and surface‐based measurements.
Removing wave effects from the wind stress vector
Authors: Rieder Karl F. , Smith Jerome A.
Published: February 2004

The presence of ocean surface waves has been observed to affect both the magnitude and direction of the wind stress. Here concurrent wind and wave data are employed to study their relationship. To help isolate the influence of the waves, the wind stress is broken into three frequency bands: “low” (frequencies below 0.06 Hz), corresponding to large‐scale motions in the boundary layer at frequencies below any significant wave energy; “middle” (frequencies between 0.06 and 0.16 Hz), corresponding to the frequencies of the dominant swell and wind waves; and “high” (frequencies above 0.16 Hz), corresponding to waves too short to influence coherently the wind fluctuations at the anemometer site 8 m above the surface. Most often, the low band holds the most stress. The magnitude of the wind stress within the low band increases roughly with the square of the mean wind speed, the high band appears to increase with the wind speed to the fourth power, and the middle band exhibits varied dependence. The direction of the wind stress in the low band is closely tied to the mean wind direction. In contrast, the directions in the middle and high bands are influenced by the waves and can be significantly off the mean wind direction. The middle band is biased toward the direction of long‐period swell, while the high band is biased toward the direction of shortperiod seas, which is closer to the wind direction. Thus it is mainly within the middle band that large deviations in stress versus wind magnitude and direction are found. To further isolate the influence of waves, a wave‐correlated fraction of the wind stress is estimated using direct correlations between the surface elevation and wind fluctuations. Removing this wavecorrelated stress from the total results in a residual stress that is better behaved: the magnitude of the residual stress in the middle band is modeled by a simple wind speed dependent drag coefficient, and the direction is very nearly aligned with the wind in both the middle and high bands. These results indicate that waves are indeed closely associated with the observed deviations from “bulk formula” stress estimates. They also suggest a new method by which to estimate the wind stress; namely, partitioning the stress into three separately modeled parts: a low‐frequency stress, a high‐frequency wave‐correlated stress, and a high‐frequency residual stress.
Seasonal variability in distribution and fluxes of methane in the Arabian Sea
Authors: Patra Prabir K. , Lal Shyam , Venkataramani S. , Gauns Mangesh , Sarma V. V. S. S.
Published: February 2004

Methane, a biogeochemically important gas in Earth/s atmosphere was measured in the water column and air in the Arabian Sea in different seasons, viz., northeast monsoon, intermonsoon, and southwest monsoon, as part of the Joint Global Ocean Flux Study (India). These observations record its distributions in the water column as well as its fluxes and their seasonal variations. Methane is mainly produced in subsurface water, and its supersaturation occurs in the upper 400 m. The CH4 peak concentration and its location vary with latitude and season. Below about 400 m, seawater CH4 concentrations, in general, are observed to be undersaturated, suggesting its consumption. Production of CH4 in oxygenated water appears to be under biological control; however, the peak in deep anoxic water does not show any particular relation with any single chemical, biological, or physical variable and rather suggests it to be maintained by the quasi‐horizontal transport. The average surface supersaturations are found to be 140 ± 37, 173 ± 54, and 200 ± 74 in the northeast monsoon, intermonsoon, and southwest monsoon, respectively. Wind speed dependent flux estimation reveals the coastal region of the Arabian Sea to be a stronger source of methane compared to the open oceanic region, although a zonal transect along 10°N also shows higher flux of methane. The effects of the Findlater Jet induced downwelling on the distributions of CH4 in the near surface water as well as on its emissions have been discussed. Its annual emission rate of 0.03–0.05 Tg CH4 yr−1 from the Arabian Sea is nearly the same as that observed from the global oceans.
Bifurcation of the Kuroshio Extension at the Shatsky Rise
Authors: Hurlburt Harley E. , Metzger E. Joseph
Published: February 2004

A 1/16° six‐layer Pacific Ocean model north of 20°S is used to investigate the bifurcation of the Kuroshio Extension at the main Shatsky Rise and the pathway of the northern branch from the bifurcation to the subarctic front. Upper ocean‐topographic coupling via a mixed barotropic‐baroclinic instability is essential to this bifurcation and to the formation and mean pathway of the northern branch as are several aspects of the Shatsky Rise complex of topography and the latitude of the Kuroshio Extension in relation to the topography. The flow instabilities transfer energy to the abyssal layer where it is constrained by geostrophic contours of the bottom topography. The topographically constrained abyssal currents in turn steer upper ocean currents, which do not directly impinge on the bottom topography. This includes steering of mean pathways. Obtaining sufficient coupling requires very fine resolution of mesoscale variability and sufficient eastward penetration of the Kuroshio as an unstable inertial jet. Resolution of 1/8° for each variable was not sufficient in this case. The latitudinal extent of the main Shatsky Rise (31°N–36°N) and the shape of the downward slope on the north side are crucial to the bifurcation at the main Shatsky Rise, with both branches passing north of the peak. The well‐defined, relatively steep and straight eastern edge of the Shatsky Rise topographic complex (30°N–42°N) and the southwestward abyssal flow along it play a critical role in forming the rest of the Kuroshio northern branch which flows in the opposite direction. A deep pass between the main Shatsky Rise and the rest of the ridge to the northeast helps to link the northern fork of the bifurcation at the main rise to the rest of the northern branch. Two 1/16° “identical twin” interannual simulations forced by daily winds 1981–1995 show that the variability in this region is mostly nondeterministic on all timescales that could be examined (up to 7 years in these 15‐year simulations). A comparison of climatologically forced and interannual simulations over the region 150°E–180°E, 29°N–47°N showed greatly enhanced abyssal and upper ocean eddy kinetic energy and much stronger mean abyssal currents east of the Emperor Seamount Chain (about 170°E) in the interannual simulations but little difference west of 170°E. This greatly enhanced the upper ocean‐topographic coupling in the interannual simulations east of 170°E. This coupling affected the latitudinal positioning of the eastward branches of the Kuroshio Extension and tended to reduce latitudinal movement compared to the climatologically forced simulation, including a particularly noticeable impact from the Hess Rise. Especially in the interannual simulations, effects of almost all topographic features in the region could be seen in the mean upper ocean currents (more so than in instantaneous currents), including meanders and bifurcations of major and minor currents, closed circulations, and impacts from depressions and rises of large and small amplitudes.
Assimilation of ERS SAR wave spectra in an operational wave model
Authors: Breivik Lars‐Anders , Reistad Magnar , Schyberg Harald , Sunde Jens , Krogstad Harald E. , Johnsen Harald
Published: February 2004

Inverted wave spectra from ERS‐1 synthetic aperture radar (SAR) image and wave mode products have been assimilated in the operational wave model for the ocean wave forecast service at the Norwegian Meteorological Institute. Elements of the operational system are explained briefly, and the impact of including the SAR wave data in the operational wave model runs is shown both for individual cases and as overall statistics. Although individual cases clearly show that the satellite observations are able to influence the forecast in a generally positive way, the average improvement is minor for the areas covered by the wave model. Reasons for this are the intermittency of the data, on the average small differences between inverted SAR and model first‐guess wave spectra, and to some extent, limitations in the analysis method.
Biologically active insolation over Antarctic waters: Effect of a highly reflecting coastline
Authors: Podgorny Igor , Lubin Dan
Published: February 2004

Near an Antarctic coastline or sea ice edge, multiple reflection of photons between the high‐albedo surface and a cloud will increase the downwelling surface insolation not only over the high‐albedo surface itself but also out over the adjacent open water. This insolation enhancement is examined with a Monte Carlo radiative transfer model. The insolation enhancement extends to a typical distance of 4 km out to sea, with the most important effects being within 2 km of the coastline. The strength of the multiple reflection effect depends primarily on cloud base height and cloud optical depth and only slightly on cloud geometrical thickness. The insolation enhancement is also a function of wavelength, being larger for ultraviolet wavelengths than for the visible. This is due to a slightly greater contribution from Rayleigh scattering at the shorter wavelengths, although at ultraviolet wavelengths where ozone absorption is strong, tropospheric ozone absorption can offset the Rayleigh scattering contribution at larger cloud optical depths. On the basis of the limited range of the multiple reflection effect (2–4 km out to sea) the insolation enhancement due to the high‐albedo coastline is unlikely to be a major influence on the primary productivity of all Antarctic waters; however, it may influence phytoplankton blooms near the coast and photobiological experiments carried out at coastal research stations. Also, the insolation enhancement may have significance in sea ice leads and polynyas.
Space‐time variation of mixed‐layer properties, heat and salt fluxes, and ice melt in the Newfoundland marginal ice zone
Authors: Tang C. L. , DeTracey B. M.
Published: February 2004

Oceanographic data collected in the Newfoundland marginal ice zone in March 1992 are analyzed to study the variation of mixed‐layer properties across the ice zone. The mixed‐layer depth decreases from 80 m in the interior of the pack ice to 25 m at the eastern ice edge over a distance of 120 km. In the open ocean without ice cover, the depth is considerably greater, 150∼200 m. The temperature under the pack ice is near freezing. A sharp increase in both the temperature and salinity occurs across the ice edge. The variation of the mixed‐layer properties is simulated by integrating a one‐dimensional bulk mixed‐layer model coupled to sea ice, from November 1991 to March 1992. The initial ocean conditions are obtained from an objective analysis of archived data of November 1991. The forcings are 6‐hourly meteorological data from the European Centre for Medium‐Range Weather Forecasts. Ice concentration and thickness are treated as prescribed functions of time extracted from daily ice maps since ice in the area is not locally formed. The model simulation is in good agreement with the observations. From the model results, a detailed analysis of the roles of wind stress, ice melt, surface cooling, and shortwave radiation in the water mass transformation of the upper ocean is carried out. There are large differences in the melt rate and water‐ice heat flux between the times when ice enters the shelf and after the water has been cooled by the ice to near freezing: 15∼20 cm d−1 and 500∼700 Wm−2, and 0∼2 cm a−1 and 20∼50 Wm−2 respectively. A large portion of the heat in the water column is expended for ice melting from January to March. Calculations that use surface data such as surface wind and sea surface temperature without considering ice melt can underestimate the net ocean‐to‐air heat flux, especially at the eastern ice edge in March.