bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of coastal lee waves along the coast of Texas observed in advanced very high resolution radiometer images
Authors: Li Xiaofeng , Zheng Quanan , Pichel William G. , Yan Xiao‐Hai , Liu W. Timothy , Clemente‐Colón Pablo
Published: February 2004

We examine a group of wave‐like cloud patterns that occurred along the coast of Texas on a National Oceanic and Atmospheric Administration satellite advanced very high resolution radiometer IR images taken on January 22, 1999. These wave‐like cloud patterns were interpreted to be signatures of a coastal lee wave packet on the basis of simultaneous field observations and theories developed by Zheng et al. [1998a]. The wave packet contains 13 waves with crest lines generally parallel to the coastline. The lengths of leading wave crest lines are longer than 500 km. The average wavelength is 9.5 km, ranging from 6.2 to 14.7 km. The width of the horizontal distribution band of the wave packet is as wide as 113 km. This case represents the most energetic coastal lee wave packet that has ever been reported.
Physical control of phytoplankton distributions in the Alboran Sea: A numerical and satellite approach
Authors: Garcia‐Gorriz Elisa , Carr Mary‐Elena
Published: February 2004

This study aims to identify the controlling processes of phytoplankton distributions in the Alboran Sea (western Mediterranean Sea). A three‐dimensional primitive equation model, the Navy Layered Ocean Model, forced by satellite‐measured winds from the European Remote Sensing satellites (ERS‐1 and 2) and the NASA scatterometer (NSCAT), is used to examine circulation from January 1996 to December 1998 and to simulate the distribution of passive tracers within the basin. We discuss the impact of the basin circulation on the observed patterns of chlorophyll observed by the Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) and the Ocean Color and Temperature Scanner (OCTS). The upper layer is fertilized with nutrients which are transported by the western anticyclonic gyre from the coastal upwelling sites in the northwest. Nutrients are supplied also by eddy‐induced upwelling in the periphery of the gyre path (found to be 20 to 60% of the supply due to advection in the present simulations). Circulation controls the supply of nutrients and the observed phytoplankton biomass in the upper layer during the nonbloom months (late spring, summer, and early fall). During the bloom regime, seasonal destratification is the dominant fertilizing process for the entire basin.
Phytoplankton chlorophyll distributions and primary production in the Southern Ocean
Authors: Moore J. Keith , Abbott Mark R.
Published: February 2004

Satellite ocean color data from the Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) were used to examine distributions of chlorophyll concentration within the Southern Ocean for the period October 1997 through September 1998. Over most of the Southern Ocean, mean chlorophyll concentrations remained quite low (< 0.3–0.4 mg m−3). Phytoplankton blooms where chlorophyll concentration exceeded 1.0 mg m−3 were observed in three general areas, which included coastal/shelf waters, areas associated with the seasonal sea ice retreat, and the vicinity of the major Southern Ocean fronts. These chlorophyll distribution patterns are consistent with an iron‐limited system. Mean chlorophyll concentrations from SeaWiFS are compared with values from the coastal zone color scanner (CZCS). The SeaWiFS global chlorophyll algorithm works better than the CZCS in Southern Ocean waters. Primary production in the Southern Ocean was estimated with the vertically generalized production model of Behrenfeld and Falkowski [1997]. Annual primary production in the Southern Ocean (>30°S) was estimated to be 14.2 Gt C yr−1, with most production (∼80%) taking place at midlatitudes from 30° to 50°S. Primary production at latitudes >50°S was estimated to be 2.9 Gt C yr−1. This is considerably higher than previous estimates based on in situ data but less than some recent estimates based on CZCS data. Our estimated primary production is sufficient to account for the observed Southern Hemisphere seasonal cycle in atmospheric O2 concentrations.
Translation, decay and splitting of Agulhas rings in the southeastern Atlantic Ocean
Authors: Schouten Mathijs W. , de Ruijter Will P. M. , van Leeuwen Peter Jan , Lutjeharms Johann R. E.
Published: February 2004

All Agulhas rings that were spawned at the Agulhas retroflection between 1993 and 1996 (a total of 21 rings) have been monitored using TOPEX/Poseidon satellite altimetry and followed as they moved through the southeastern Atlantic Ocean, decayed, interacted with bottom topography and each other, or dissipated completely. Rings preferentially crossed the Walvis Ridge at its deepest parts. After having crossed this ridge they have lower translational speeds, and their decay rate decreases markedly. Half the decay of long‐lived rings takes place in the first 5 months of their lifetimes. In addition to the strong decay of rings in the Cape Basin, about one third of the observed rings do not seem to leave this region at all but totally disintegrate here. The interaction of rings with bottom topography, in particular with the Vema Seamount, is shown frequently to cause splitting of rings. This will enhance mixing of the rings' Indian Ocean water into that of the southern Atlantic. This localized mixing may well provide a considerable source of warm and salty Indian Ocean water into the Atlantic overturning circulation.
Measured changes in ocean surface roughness due to atmospheric boundary layer rolls
Authors: Vandemark D. , Mourad P. D. , Bailey S. A. , Crawford T. L. , Vogel C. A. , Sun J. , Chapron B.
Published: February 2004

A research aircraft was recently flown over the Mid‐Atlantic Bight during a mild cold air outbreak to sample the planetary boundary layer at low levels of 15–20 m above the sea surface. Aircraft sensors measured near‐surface atmospheric turbulence and, at the same time, variations in sea surface roughness using laser and radar. The aircraft turbulence observations indicate a coherent secondary flow consistent with boundary layer roll vortices of crosswind scale 1.5–2.0 km. Modulation in measured laser and radar‐inferred sea surface slope variance occurs at similar scales. Remarkable correlation is found between the radar backscatter and near‐surface wind speed data, showing that the short wave slope variance is responsive to these large eddies. Associated small but periodic changes in wind direction do not appear to impact the short wave slope signature. Differentiation between short‐ and intermediate‐scale wave roughness using aircraft laser and radar data leads us to conclude that observed fluctuations in intermediate‐scale wave slope were not directly linked to the local wind. A synthetic aperture radar (SAR) image was acquired by the Canadian Space Agency's RADARSAT coincident with the aircraft measurements. Widespread streaking in the SAR image suggests the surface impacts of atmospheric longitudinal rolls. Our aircraft results indicate that the dominant term dictating SAR backscatter modulations at the eddy scale of 1–2 km is the fluctuation of the along‐wind velocity, nominally associated with regions of near‐surface convergence or divergence. Wind speed fluctuations of 7–10% estimated from the SAR and aircraft radar are consistent with the aircraft's measured variations in near‐surface wind speed.
Implementation of a dual variational algorithm for assimilation of synthetic altimeter data in the oceanic primitive equation model MICOM
Authors: Louvel Stéphane
Published: February 2004

Modem satellite altimetry provides an ideal tool for studying sea level variations. Simulated altimeter data are used to implement a new assimilation technique in an oceanic regional model. This variational data assimilation method is the dual formulation of the usual four‐dimensional variational algorithm. That dual formulation can take model error into account at a computational cost which is similar to the cost incurred in the exact model case. Another feature of this original technique is to minimize the dual objective function under weak constraint in the observation space [Bennett, 1992; Amodei, 1995]. The assimilation algorithm is used in the Miami Isopycnic‐Coordinate Ocean Model (MICOM). This oceanic adiabatic primitive equation model describes an idealized flow with four immiscible layers. Our purpose is twofold. First, we show the links between primal and dual methods. We implement them in academic cases and we discuss the behavior of both algorithms. Second, we examine the efficiency of the dual technique in assimilating altimeter data of the Gulf Stream circulation. This work presents the first implementation of variational assimilation methods with the MICOM model that includes an external mode. Operator splitting is used to advance that mode with larger steps than those used for internal modes. We have numerically shown the possibility to solve a weak constraint problem without additional computational cost compared with the strong constraint variational algorithm. We present experiments for different time periods to assess the ability of the assimilation scheme to transfer the surface information downward to the deep flows. Numerical results show that our variational algorithm applied with the MICOM model produces a realistic estimation from a 2‐month assimilation period.
Overview of the NOAA/NASA advanced very high resolution radiometer Pathfinder algorithm for sea surface temperature and associated matchup database
Authors: Kilpatrick K. A. , Podestá G. P. , Evans R.
Published: February 2004

The National Oceanic and Atmospheric Administration (NOAA)/NASA Oceans Pathfinder sea surface temperature (SST) data are derived from measurements made by the advanced very high resolution radiometers (AVHRRs) on board the NOAA 7, 9, 11, and 14 polar orbiting satellites. All versions of the Pathfinder SST algorithm are based on the NOAA/National Environmental Satellite Data and Information Service nonlinear SST operational algorithm (NLSST). Improvements to the NLSST operational algorithm developed by the Pathfinder program include the use of monthly calibration coefficients selected on the basis of channel brightness temperature difference (T4–T5). This channel difference is used as a proxy for water vapor regime. The latest version (version 4.2) of the Pathfinder processing includes the use of decision trees to determine objectively pixel cloud contamination and quality level (0–7) of the SST retrieval. The 1985–1998 series of AVHRR global measurements has been reprocessed using the Pathfinder version 4.2 processing protocol and is available at various temporal and spatial resolutions from NASA's Jet Propulsion Laboratory Distributed Active Archive Center. One of the highlights of the Pathfinder program is that in addition to the daily global area coverage fields, a matchup database of coincident in situ buoy and satellite SST observations also is made available for independent algorithm development and validation.
Local and regional albedo observations of arctic first‐year sea ice during melt ponding
Authors: Hanesiak J. M. , Barber D. G. , De Abreu R. A. , Yackel J. J.
Published: February 2004

The shortwave surface albedo is a critical climatological parameter for sea ice, especially during the spring melt period when the ice contains a mixture of highly reflective (snow) and absorptive (melt ponds) surfaces. Broadband and spectral albedo measurements were made over numerous surface types on first‐year sea ice during the melt period in Wellington Channel, Nunavut during the Collaborative‐Interdisciplinary Cryospheric Experiment 1997. Albedo measurements ranged from 0.75 (moist snow) to 0.21 (dark melt ponds) with many unique intermediate surfaces. Aircraft videography collected throughout Wellington Channel and Lancaster Sound was processed to reveal four main surface cover types (wet snow, mixed type, light ponds, and dark ponds). Surface albedo data were applied to the aircraft observations to upscale surface albedo measurements to regional scales. Aircraft video‐derived regional albedo (mean = 0.55±0.02) were comparable to helicopter and satellite‐derived (Advanced Very High Resolution Radiometer) albedo estimates.
Estimation of wind friction velocity and direction at the ocean surface from physical models and space‐borne radar scatterometer measurements
Authors: Lettvin Ellen E. , Vesecky John F.
Published: February 2004

This paper presents a new technique for estimating the wind friction velocity at the ocean surface from C‐band radar scatterometer measurements. This technique uses physical models of ocean surface waves and electromagnetic backscattering from a rough surface at intermediate angles of incidence to generate predictions of the normalized radar cross section (NRCS, or σ0) of the ocean surface for a given wind friction velocity and observational geometry. The ocean spectral model used in this technique has been developed specifically for this application. It combines in situ wave measurements at low wave numbers with the Phillips [1985] equilibrium spectral model. This choice of ocean wave model is supported by a set of open ocean wave measurements summarized in this paper. A suite of models, derived from both in situ and remote measurements of the sea surface, is used to characterize the directional spreading of ocean waves relative to the wind direction. The resulting two‐dimensional ocean wave spectra are used with a composite surface model to predict radar backscattering from the ocean surface at C‐band. These radar cross‐section predictions are combined with ERS‐1 scatterometer measurements in a cost function minimization scheme to yield estimates of the friction velocity vector at the ocean surface. We present examples of this technique and compare friction velocity retrievals obtained via this scheme with buoy‐based measurements under a variety of wind and wave conditions. On the basis of the analysis of a limited number of cases, this technique yielded friction velocity estimates for which the magnitude was within 22% and the direction was within ±25°. Given that scientific applications require magnitude estimates within 10–15% and directional estimates within ±20° of in situ measurements, these preliminary results suggest that this is a promising approach to wind retrieval.
Modeling the response of top‐down control exerted by gelatinous carnivores on the Black Sea pelagic food web
Authors: Oguz Temel , Ducklow Hugh W. , Purcell Jennifer E. , Malanotte‐Rizzoli Paola
Published: February 2004

Recent changes in structure and functioning of the interior Black Sea ecosystem are studied by a series of simulations using a one‐dimensional, vertically resolved, coupled physical‐biochemical model. The simulations are intended to provide a better understanding of how the pelagic food web structure responds to increasing grazing pressure by gelatinous carnivores (medusae Aurelia aurita and ctenophore Mnemiopsis leidyi) during the past 2 decades. The model is first shown to represent typical eutrophic ecosystem conditions of the late 1970s and early 1980s. This simulation reproduces reasonably well the observed planktonic food web structure at a particular location of the Black Sea for which a year‐long data set is available from 1978. Additional simulations are performed to explore the role of the Mnemiopsis‐dominated ecosystem in the late 1980s. They are also validated by extended observations from specific years. The results indicate that the population outbreaks of the gelatinous species, either Aurelia or Mnemiopsis, reduce mesozooplankton grazing and lead to increased phytoplankton blooms as observed throughout the 1980s and 1990s in the Black Sea. The peaks of phytoplankton, mesozooplankton, Noctiluca, and gelatinous predator biomass distributions march sequentially as a result of prey‐predator interactions. The late winter diatom bloom and a subsequent increase in mesozooplankton stocks are robust features common to all simulations. The autotrophs and heterotrophs, however, have different responses during the rest of the year, depending on the nature of grazing pressure exerted by the gelatinous predators. In the presence of Mnemiopsis, phytoplankton have additional distinct and pronounced bloom episodes during the spring and summer seasons. These events appear with a 2 month time shift in the ecosystem prior to introduction of Mnemiopsis.
Apparent loss of CFC‐113 in the upper ocean
Authors: Roether Wolfgang , Klein Birgit , Bulsiewicz Klaus
Published: February 2004

We report and evaluate data of the chlorofluorocarbon CFC‐113, in comparison with concurrent data for CFC‐12, from cruises into the temperate North Atlantic, the tropical western Pacific, the Eastern Mediterranean, and the Weddell Sea. We consistently find CFC‐113 deficiencies in the warmer upper waters, which we interpret as CFC‐113 depletion at rates of the order of 3% per year, with possibly accelerated rates in the mixed layer or near the surface. These results severely limit a tracer utility of CFC‐113 in the warm upper waters of the ocean. Tracer applications in the deep waters of the ocean should be much less affected, since CFC‐113 loss in such waters appears to be far slower. This also holds for the Eastern Mediterranean, despite its rather warm deep waters. For the Weddell Sea, the data indicate a CFC‐113 deficiency (∼20%) in the shelf waters, which converts into a similar deficiency in newly formed deep and bottom water. Such CFC‐113 deficiency has to be accounted for in Southern Ocean tracer work. Future work is proposed to study CFC‐113 loss in the ocean in additional detail and to elucidate the loss mechanism(s), on which our data give little clue.
Turbulence beneath sea ice and leads: A coupled sea ice/large‐eddy simulation study
Authors: Skyllingstad Eric D. , Denbo Donald W.
Published: February 2004

The importance of leads, sea ice motion, and frazil ice on the wintertime ocean boundary layer was examined by using a large‐eddy simulation turbulence model coupled to a thermodynamic slab ice model. Coupling was achieved through exchange coefficients that accounted for the differing diffusion rates of heat and salinity. Frazil ice concentrations were modeled by using an ice crystal parameterization with constant crystal size and shape. Stationary ice without leads produced cellular structures similar to atmospheric convection without winds. Ice motion caused this pattern to break down into a series of streaks aligned with the flow. Eddy fluxes were strongly affected by ice motion with relatively larger entrainment fluxes at the mixed layer base under moving ice, whereas stationary ice produced larger fluxes near the top of the boundary layer. Opening of leads caused significant changes in the turbulent structure of the boundary layer. Leads in stationary ice produced concentrated plumes of higher‐salinity water beneath the lead. Ice motion caused the lead convection to follow preexisting convective rolls, enhancing the roll circulation salinity and vertical velocity under the lead. Comparison of model time series data with observations from the Arctic Leads Experiment showed general agreement for both pack ice and lead conditions. Simulated heat flux carried by frazil ice had a prominent role in the upper boundary layer, suggesting that frazil ice is important in the heat budget of ice‐covered oceans.
Comparison of Special Sensor Microwave Imager and buoy‐measured wind speeds from 1987 to 1997
Authors: Mears C. A. , Smith Deborah K. , Wentz Frank J.
Published: February 2004

We compare wind speeds derived from microwave radiometer measurements made by the Special Sensor Microwave Imager (SSM/I) series of satellite instruments to those directly measured by buoy‐mounted anemometers. The mean difference between SSM/I and buoy winds is typically <0.4 m s−1 when averaged over all operational Tropical Atmosphere‐Ocean and National Data Buoy Center buoys for a given year, and the standard deviation is <1.4 m s−1. Mean errors for a given satellite‐buoy pair typically range from −1 to +1 m s−1, with standard deviations <1.4 m s−1. Two methods of converting buoy‐measured wind speed to a standard value measured at a height of 10 m are compared. We find that the principal difference between a simple logarithmic correction and a more detailed conversion to 10 m equivalent neutral stability wind speed is a shift of wind speed by about 0.12 m s−1 with no change in the distribution of SSM/I‐buoy wind speed differences.
Sensitivity of the thermohaline circulation to modern and glacial surface boundary conditions
Authors: Fieg Kerstin , Gerdes Rüdiger
Published: February 2004

We analyze the results from over 20 numerical experiments with a global ocean general circulation model (OGCM) under different present and last glacial maximum (LGM) surface boundary conditions. The model exhibits a large range of circulation strengths and patterns, including strong and deep overturning of North Atlantic Deep Water (NADW) under LGM boundary conditions. Parameterizations tuned for today's ocean and fixed atmospheric temperatures contribute to this failure. The experiments show a close relation between the NADW and Antarctic Bottom Water (AABW) overturning cells in the Atlantic. High transport in the NADW cell is associated with little or no transport of AABW. The strength of the AABW overturning cell depends sensitively on the treatment of sea ice in the Southern Ocean. An atmospheric energy balance model coupled with the OGCM allows a free response of the sea ice component. Because of the close link between NADW and AABW, the northern source of deep water must be relatively weak during the LGM. An ocean circulation consistent with paleoclimatic evidence only results when the surface salinity in the northern North Atlantic is reduced. The solution then shows a southward expansion of the Arctic domain and a southward shift of the deep water formation area in the North Atlantic. The glacial NADW is less dense than modern NADW, and AABW occupies a larger part of the abyssal ocean. Compared to modern distributions, there is almost no glacial Antarctic Intermediate Water causing middepth warming in the southern and tropical Atlantic.
A high‐resolution assimilating tidal model for the northeast Pacific Ocean
Authors: Foreman M. G. G. , Crawford W. R. , Cherniawsky J. Y. , Henry R. F. , Tarbotton M. R.
Published: February 2004

A high‐resolution, nonlinear, barotropic, finite element tidal model is developed for removing tidal elevations from satellite altimeter observations in the northeast Pacific Ocean. Surface elevations and currents for the constitutents M2, S2, N2, K2, K1, O1, P1, and Q1 are computed using boundary forcing from the Oregon State University global tidal model, TPXO.3, and the effects of the tidal potential, Earth tide, and ocean self‐attraction and loading. Amplitudes and phases computed from the harmonic analyses of altimeter time series at crossover locations along the tracks of the TOPEX/Poseidon satellite are assimilated into the model, and the corrected harmonics are compared with pelagic and coastal tide and pressure gauge measurements, and with the TPXO.3 and FES95.2.1 global models. Diurnal tidal currents along the British Columbia and Alaska continental shelves are shown to be strongly influenced by the presence of continental shelf waves. The surface manifestation of these waves is clearly evident in K1 coamplitude plots. K1 and M2 energy fluxes are calculated along these shelves and the potential generation of internal tides is discussed. Barotropic tidal dissipation is estimated in several key subregions, and the M2 total for the Gulf of Alaska is found to be approximately half that of previous estimates.
“Upwelling” and “cyclonic” regimes of the near‐surface circulation in the Santa Barbara Channel
Authors: Oey Lie‐Yauw , Wang Dong‐Ping , Hayward Thomas , Winant Clinton , Hendershott Myrl
Published: February 2004

The observed near‐surface circulation in the Santa Barbara Channel indicates in particular two patterns: a dominant cyclonic circulation mode and a less frequent upwelling flow mode. To explain the dynamics that may govern these two flow regimes, momentum balance from a hindcast model of currents in the channel, forced by observed hourly winds and hydrographic data, was calculated. The along‐channel balance was found to be between wind, which was eastward (i.e., equatorward), sea level tilt, which was westward (i.e., poleward), and Coriolis, which was westward if the wind was (1) intense west and east of the channel and was eastward if the wind was (2) weaker in the east. Wind condition 1 produced southward cross‐channel flow in the midchannel, connected by eastward currents upstream (downstream) along the northern (southern) coast of the channel, while wind condition 2 produced northward cross‐channel flow connected by cyclonic recirculation in the west and westward inflow in the east. It is suggested that the former corresponds to the dynamical balance that may occur in the upwelling flow mode, while the latter corresponds to the cyclonic circulation mode.
Sources of global warming in upper ocean temperature during El Niño
Authors: White Warren B. , Cayan Daniel R. , Dettinger Michael D. , Auad Guillermo
Published: February 2004

Global average sea surface temperature (SST) from 40°S to 60°N fluctuates ±0.3°C on interannual period scales, with global warming (cooling) during El Niño (La Niña). About 90% of the global warming during El Niño occurs in the tropical global ocean from 20°S to 20°N, half because of large SST anomalies in the tropical Pacific associated with El Niño and the other half because of warm SST anomalies occurring over ∼80% of the tropical global ocean. From examination of National Centers for Environmental Prediction [Kalnay et al., 1996] and Comprehensive Ocean‐Atmosphere Data Set [Woodruff et al., 1993] reanalyses, tropical global warming during El Niño is associated with higher troposphere moisture content and cloud cover, with reduced trade wind intensity occurring during the onset phase of El Niño. During this onset phase the tropical global average diabatic heat storage tendency in the layer above the main pycnocline is 1–3 W m−2 above normal. Its principal source is a reduction in the poleward Ekman heat flux out of the tropical ocean of 2–5 W m−2. Subsequently, peak tropical global warming during El Niño is dissipated by an increase in the flux of latent heat to the troposphere of 2–5 W m−2, with reduced shortwave and longwave radiative fluxes in response to increased cloud cover tending to cancel each other. In the extratropical global ocean the reduction in poleward Ekman heat flux out of the tropics during the onset of El Niño tends to be balanced by reduction in the flux of latent heat to the troposphere. Thus global warming and cooling during Earth's internal mode of interannual climate variability arise from fluctuations in the global hydrological balance, not the global radiation balance. Since it occurs in the absence of extraterrestrial and anthropogenic forcing, global warming on decadal, interdecadal, and centennial period scales may also occur in association with Earth's internal modes of climate variability on those scales.
Ice production and brine formation in Storfjorden, Svalbard
Authors: Haarpaintner Jörg , Gascard Jean‐Claude , Haugan Peter M.
Published: February 2004

Brines, which appear as salty and cold bottom water layers on Arctic shelves, form by salt rejection during sea ice formation. High ice production occurs in latent heat polynyas such as the one that appears in Storfjorden under northerly winds. Using ERS‐2 synthetic aperture radar imagery, we observed the ice cover in Storfjorden over the winter 1997/1998, revealing an area of over 6000 km2 of the open water and thin ice that are characteristic of a polynya. Changes in the polynya extent correlated well with a simple wind‐driven polynya size algorithm. Furthermore, using a frazil ice formation algorithm and the hypothesis of ice accumulation at the lee side of the polynya, we distinguished between open water, thin ice, and fast/pack ice. The average polynya width during the 6 winter months was about 30 km, with a maximum of 130 km in March; thus Storfjorden was composed of 5/6 fast and pack ice and 1/6 polynya. Open water occupied about half of the polynya; the other half was composed of brash ice and thin ice involved in ridging and rafting. A total ice volume of 40 km3 was produced in Storfjorden between November 15, 1997, and May 15, 1998. About 57% of it was formed in the open water area; 9%, in the thin ice area; and 34%, in the fast/pack ice area. This ice production released more than 1 Gt (gigaton) of salt, able to increase the salinity of the Storfjorden waters by 1.4 practical salinity units (psu). Assuming that brine‐enriched waters are 0.3 psu more saline than the parent waters, the above salt release is able to ventilate Storfjorden 4–5 times during the course of the productive season.
Tropical water vapor correction for remotely sensed sea surface temperature: Results using narrowband window radiance profiles from TOGA COARE
Authors: Hagan Denise E. , Nalli Nicholas R.
Published: February 2004

This paper describes sea surface skin temperatures (SST) derived from unique aircraft‐based measurements and a physical multispectral retrieval technique. The aircraft data were acquired under moist atmospheric conditions over the western and eastern tropical Pacific Ocean during the Tropical Ocean‐Global Atmosphere Coupled Ocean‐Atmosphere Response Experiment and the Central Equatorial Pacific Experiment. Radiometric profiles were obtained in four contiguous channels over the spectral window region 800–1000 cm−1 during aircraft ascents from 0.03 through 4.6 km altitude. These bands subdivide the “split window” of present satellite radiometers used for measurements of SST. The use of four channels in the measurement approach was motivated by theoretical studies that suggest the need for three independent pieces of information to separate atmospheric and surface components of upwelling radiance in moist atmospheres. The analyses were unusual in that the absorption path length differed for each multispectral set of nadir observations made at discrete altitudes. The mean accuracy for retrievals at all altitudes was ≲1 K and was relatively insensitive to the guess profiles used for the simple forward radiance model. Simulated four‐channel retrievals demonstrate an rms accuracy of ≃0.3 K with negligible bias for global maritime profile conditions, which include extreme moisture‐laden samples. The results demonstrate that the combination of high‐precision measurements with a robust retrieval method can provide SST (instantaneous, global, day, or night) that meet the World Climate Research Programme accuracy objectives.
Acoustic Doppler current profiler measurements of the velocity field of an ebb tidal jet
Authors: Old C. P. , Vennell R.
Published: February 2004

A broadband acoustic Doppler current profiler was used to measure the velocity field of the ebb tidal jet formed at the entrance to the Otago Harbour, South Island, New Zealand. Four separate surveys were conducted where various sets of transects were run continuously over a 13 hour period, producing time series of velocity profiles with 1 hour sampling over a grid with an across‐jet resolution of 20 m and an along‐jet resolution of 150 m. The velocity field of the ebb tidal jet is phase locked to the tidal response of the harbor, making it possible to combine the data from separate tidal cycle surveys to produce synoptic maps of the depth‐averaged velocity field. The spatial structure of the ebb tidal jet at the time of peak flow exhibits many features of a classical plane jet. There is a strong asymmetry between the ebb and flood flow structures; the ebb flow extends beyond 2 km from the entrance, while the flood flow is limited to within 600 m of the coast. The flow along the jet axis becomes pulse‐like in time with distance from the entrance. The pulse that develops propagates way from the entrance at a speed slower than the advective speed of the ebb jet. The formation of a propagating eddy observed along the eastern side of the jet suggests that this momentum pulse may be associated with the pair of separation eddies generated by the accelerating ebb tidal flow.
Data assimilation model study of wind effects in the Santa Barbara Channel
Authors: Chen Chi‐Shao , Wang Dong‐Ping
Published: February 2004

Seasonal mean circulation in the Santa Barbara Channel (SBC) consists of poleward flow on the northern shelf and equatorward flow on the southern shelf. While the equatorward flow is in the direction of the persistent, upwelling‐favorable wind, the inshore poleward flow is against the wind. The channel circulation also has a strong seasonal signal that the cyclonic circulation strengthens considerably in spring and summer. A three‐dimensional model is used to simulate the observed currents over an 8‐month period from January to August 1994. The model assimilates the moored temperature and salinity data obtained from a comprehensive circulation study in the SBC‐Santa Maria Basin (SMB). The model also incorporates surface wind forcing; the mesoscale wind stress pattern is derived from a dense network of weather buoys. The model simulation reproduces well the surface mean currents and their seasonal (monthly) variability. The transient (less than seasonal) model velocity response consists of two fundamental modes, a wind‐forced mode and an alongshore pressure gradient‐forced mode. The wind‐driven circulation is concentrated west of the channel in the SMB. The alongshore pressure gradient‐forced motion is concentrated in the channel along the northern coast. Analysis of the evolution of inshore poleward current suggests that the spring transition in this region may coincide with the end of the winter storm season.
Circulation and ventilation flux of the Pacific Ocean
Authors: Fine Rana A. , Maillet Kevin A. , Sullivan Kevin F. , Willey Debra
Published: February 2004

The flux of water from the mixed layer into the thermocline/intermediate layers of the Pacific Ocean is quantified using chlorofluorocarbon (CFC) and hydrographic data. The total ventilation flux of at least 123 Sv for the South Pacific (SP) only slightly exceeds that of at least 111 Sv for the North Pacific (NP). Although the overall ventilation flux (to 27.3 σθ) is similar in the NP and SP, the partitioning amongst the water masses is markedly different. In the NP the partitioning is equal between the wind‐driven (≤26.5 σθ) and thermohaline (>26.5–27.3 σθ) layers. While in the SP the ventilation flux of the thermohaline layers exceeds by nearly 2:1 the wind‐driven layers. The wind‐driven subtropical gyre thermocline ventilation flux for the NP (41 Sv) exceeds the SP (25 Sv), and both agree well with literature estimates of Sverdrup transports. The ventilated volumes and ages are related to the wind stress curl and surface buoyancy fluxes. In the thermocline ventilation of Shallow Salinity Minimum Water (22 m yr−1 in the NP, 15 m yr−1 in the SP) and Subtropical Mode Water is more effective in the NP than in the SP. In contrast, in the thermohaline layers direct air‐sea exchange during convective formation of Subantarctic Mode and Antarctic Intermediate Water is more effective in ventilating the SP than processes in the NP. These same differences are also used to explain the larger volume of the shadow zone in the NP. In the subpolar regions the ventilation fluxes can be used to infer formation rates of 8 Sv for the NP Intermediate Water and 9 Sv for the Subantarctic Mode Water. Into the tropical Pacific there is a substantial flux of 35 Sv of extratropical water for the wind‐driven layers and 36 Sv for the thermohaline layers. The relatively young (5–20 years increasing with increasing density) CFC‐derived ages show that a climate anomaly introduced into the subtropical thermocline could be transported into the tropics relatively quickly.
Chesapeake Bay outflow plume and coastal upwelling events: Physical and optical properties
Authors: Johnson D. R. , Weidemann A. , Arnone R. , Davis C. O.
Published: February 2004

One of a series of Chesapeake Outflow Plume Experiments, COPE‐2, was conducted in May 1997 along the coast of Virginia/North Carolina. The objective of this experiment was to describe the coastal buoyancy jet formed by the outflow of water from Chesapeake Bay, its dispersion into midshelf, and the optical property changes that accompany these events. Wind forcing scales of 3–5 days were responsible for formation of the jet (downwelling favorable winds) and its dispersion (upwelling favorable winds). During downwelling favorable events the jet established itself along the coast with speeds exceeding 0.5 m s−1, slowing and becoming more stable as it progressed. Downwelling circulation helped maintain the jet against the coast, and variations in wind strength produced wavelike variations in jet width. During upwelling favorable events, water from the jet was dispersed into midshelf in a thin near‐surface layer. Optical surrogates for dissolved organic matter (DOM), chlorophyll, and suspended particles were formed using data from a pumped optical absorption/attenuation meter (ac‐9). High loads of these materials were associated with the buoyancy jet and were subsequently dispersed into midshelf during upwelling events. During mature upwelling states, nearshore increases in chlorophyll and suspended particles mimicked the plume load, although relatively low levels of DOM made it separable from plume water by analysis of the optical signature. Upwelling relaxation fronts in these optical conditions could be seen.
Comparison of three velocity sections of the Agulhas Current and Agulhas Undercurrent
Authors: Donohue Kathleen A. , Firing Eric , Beal Lisa
Published: February 2004

Lowered acoustic Doppler current profiles (LADCP) from an early March 1995 cruise across the Agulhas Current show a swift, narrow undercurrent flowing northeast along the continental slope. Neither this Agulhas Undercurrent nor the adjacent deep extension of the Agulhas Current are evident from measurements of water properties alone, and their absence from the conventional referencing of geostrophic current estimates biases net southward transport estimates high by several sverdrups. Here we refine the original transport calculation by removing barotropic tides and by estimating instrumental and sampling errors. Two additional LADCP sections, from cruises in late March and June 1995, also show the undercurrent and the deep extension of the Agulhas. Differences in the current structure are evident. The Agulhas Current extends throughout the water column in March, but extends only to 2300 m depth in June. Additionally, the current extends further offshore in March. Of the three available LADCP sections, only those from early March and June have sufficient sampling to calculate the net southward transport of the Agulhas Current and Undercurrent. The two estimates, 78±3 and 76±2 Sv, are nearly identical. Consideration of water properties on density surfaces shows that although the undercurrent carries intermediate water with Red Sea Water influence northward, the bulk of this water mass is flowing southward, away from its source, in the Agulhas Current.
Variability of surface waterfCO2during seasonal upwelling in the equatorial Atlantic Ocean as observed by a drifting buoy
Authors: Bakker Dorothee C. E. , Etcheto Jacqueline , Boutin Jacqueline , Merlivat Liliane
Published: February 2004

The fugacity of carbon dioxide (fCO2) in tropical Atlantic surface waters was hourly monitored by a drifting carbon interface ocean atmosphere (CARIOCA) buoy from June to September 1997 during strong seasonal equatorial upwelling. The buoy drifted along the northern side of the equatorial cold tongue from 0.2°S, 7.5°W to 0.2°N, 12.5°W (June 20 to July 3). An inverse trend between temperature andfCO2reflected mixing between cold upwelled water with highfCO2and warm tropical surface water with lowerfCO2. ThefCO2maxima reflected the strength of the upwelling. Subsequently, the buoy crossed the cold tongue toward the southwest from 0.2°N, 12.5°W to 4.5°S, 20.1°W (July 3 to August 7). During this crossing, warming increased surface waterfCO2. WhilefCO2was always above 400 μatm, the air‐sea CO2flux was highest in the southern part of the cold tongue as a result of the spatial distribution of the CO2exchange coefficient. A variable diel cycle of surface‐waterfCO2with an amplitude up to 3.4 μatm was attributed to the combined effects of diel changes in temperature and stratification, biological activity, and oceanic CO2release from a shallow daytime mixing layer. At 4.5°S, 20.1°W a sharp rise of temperature, a decrease offCO2, and a maximum fluorescence marked the exit of the region with a strong upwelling signature. Finally, the buoy drifted westward from 4.5°S, 20.1°W to 2.8°S, 25.0°W (August 7 to September 15). This study has demonstrated the potential of autonomous CARIOCA buoys to monitor the evolution and high‐frequency variability of surface waterfCO2within large‐scale oceanic processes.
Investigating the carbon cycle in the Gulf of Maine using the natural tracer thorium 234
Authors: Charette Matthew A. , Moran S. Bradley , Pike Steven M. , Smith John N.
Published: February 2004

The naturally occurring radionuclide 234Th (t1/2 = 24.1 days) was used to examine the organic carbon cycle in the Gulf of Maine. A seasonal study (March, June, and September 1995) was conducted in the central Gulf of Maine in Wilkinson and Jordan Basins, and a regional survey, which included the Scotian Shelf, was conducted during August‐September 1997. Particulate organic carbon (POC) export (particulate export production) was estimated from a three‐dimensional steady state model of 234Th flux combined with measurements of the POC/234Th ratio on >53‐μm particles. The POC export for this region was seasonally variable; average values ranged from 15 to 34 mmol C m−2 d−1, between 11% and 25% of the regionally integrated primary production. The Gulf of Maine was a net source (to the Mid‐Atlantic Bight) of dissolved organic carbon (2.4 mmol C m−2 d−1) amounting to ∼2% of carbon uptake rates. Organic carbon burial in the sediments was a minor fraction of the primary production, averaging 1.6 mmol C m−2 d−1. Though only a fraction of total export production was buried in the sediments, these estimates close the budget for organic carbon in the Gulf of Maine. An implication is that off‐shelf export may not be as important as previously estimated in this shelf region.
Distribution and behavior of anthropogenic 129I in water masses ventilating the North Atlantic Ocean
Authors: Edmonds H. N. , Zhou Z. Q. , Raisbeck G. M. , Yiou F. , Kilius L. , Edmond J. M.
Published: February 2004

Iodine 129 is released by reprocessing plants in northwestern Europe in quantities greatly exceeding its natural inventory and other anthropogenic sources. Data are presented from nine profiles of 129I in the Greenland and Norwegian Seas and northern North Atlantic Ocean, collected during the Intergovernmental Oceanographic Commission's Baseline Survey of Contaminants in the North Atlantic Ocean. Anthropogenic 129I is evident throughout the data set. The distribution of 129I in the major water masses sampled provides an excellent illustration of the unique source function of 129I, which results in stronger labeling of the northern‐source overflow waters and the Deep Western Boundary Current of the North Atlantic Ocean than for many other tracers. Box models are used to explore the behavior and transport of 129I. These preliminary model simulations agree well with available measurements, pointing the way to future quantitative applications of this tracer.
Dissolved rare earth elements in the South China Sea: Geochemical characterization of the water masses
Authors: Alibo Dia Sotto , Nozaki Yoshiyuki
Published: February 2004

We have measured the vertical profiles of dissolved rare earth elements (REEs) and yttrium in the South China Sea together with conductivity‐temperature‐depth and hydrographic measurements to compare with those in the western North Pacific and the SuIu Sea. Although the South China Sea is rapidly flushed by the Pacific through the Luzon Strait with a sill depth of ∼2500 m [Broecker et al., 1986], a unique REE pattern is developed within the sea. The most striking difference exists in the dissolved Ce profiles. Dissolved Ce generally decreases from high values (6–9 pmol/kg) at the surface to a minimum of ∼3 pmol/kg at around 300–500 m where the North Pacific Intermediate Water penetrates. In deepwaters of the North Pacific and the Sulu Sea it remains at a relatively low and nearly constant concentration level of ∼5 pmol/kg throughout the water column, whereas in the South China Sea, it gradually increases with depth to a maximum of 12.9 pmol/kg at ∼2500 m, resembling the “nutrient‐like” profiles of other strictly trivalent REEs, and then sharply drops to a constant value of ∼6 pmol/kg in the bottom water below 2900 m. Some lighter REEs like Pr, Nd, and Gd, though to a much lesser extent, also show similar concentration breaks at the sill depth, but the other hydrographic properties like dissolved oxygen, nutrients, pH, and alkalinity do not. Therefore dissolved REEs may best be utilized to characterize the water masses. Two major sources for dissolved REEs in the South China Sea are fluvial and coastal input to the surface ocean and a bottom release into the deep water during the passage over the Luzon Strait. Redox chemistry including reduction of Ce(IV) to Ce(III) in the pore water of hemipelagic sediments and subsequent release of dissolved Ce(III) to the overlying deep water may be involved in the latter. The middle REE‐enriched patterns with a significant Gd depression relative to that of the North Pacific Deep Water are characteristic of the South China Sea and prevail throughout the water column by physical circulation. Since the bottom water of the basin is also fed by the North Pacific, the dissolved Ce(III) must be oxidized through bacterial mediation and removed from the bottom water presumably by scavenging near/at the sediment‐water interface along the slopes of the basin.
Ages of continental shelf waters determined from 223Ra and 224Ra
Authors: Moore Willard S.
Published: February 2004

Coastal surface waters in the South Atlantic Bight contain elevated activities of 223Ra (t1/2 = 11.4 days) and 224Ra (t1/2 = 3.66 days). These elevated dissolved activities are due to continual input of the short‐lived tracers near the coast. The presence of these tracers in an offshore water sample implies that the water is less than six half‐lives removed from the source of the tracer. The absence of the tracer implies the water is more than six half‐lives old or has been diluted substantially with old water containing little tracer. In this paper I use models based on 223Ra and 224Ra to derive ages of continental shelf waters. These models compensate for tracer dilution by normalizing the short‐lived tracers to each other or to long‐lived 228Ra. If the water on the inner shelf (0–20 km from shore) is assigned a zero age, ages for waters 80–100 km from the inner shelf are 20–30 days.