bluuebunny/crossref_metadata_2025 huggingface dataset:
Ice flow between the Greenland Ice Core Project and Greenland Ice Sheet Project 2 boreholes in central Greenland
Authors: Hvidberg C. Schøtt , Dahl‐Jensen D. , Waddington E. D.
Published: February 2004

The ice flow between the Greenland Ice Core Project (GRIP) and Greenland Ice Sheet Project 2 (GISP2) boreholes in the Summit region of central Greenland is modeled with a steady state finite element model. The model calculates the free ice sheet surface and the coupled ice flow and temperature fields along the flow line between the boreholes. Three‐dimensional effects are expressed in terms of the divergence of the flow and included in the coupled stress and temperature fields. In addition to ice‐core data, several geophysical surface programs have provided data that are used to constrain the model. The modeled isochrones resemble the bedrock structure along the flow line but rise at the divide. The rise at the divide is not seen in internal layers found by surface radio echo sounding. An ice particle, originally deposited at the surface, moves through different stress and temperature regimes. A set of trajectory lines are followed from the surface to the boreholes, in order to follow the variation of stress deviators, temperature, and deformation along with the ice movement. These variations along a trajectory line constitute a history of the corresponding ice layer. The difference between the history of ice layers found in the GRIP and GISP2 boreholes is mainly due to the shear stress, which is 3–4 times higher for GISP2 ice than for GRIP ice. Furthermore, the GRIP ice experiences a nonzero longitudinal stress deviator much longer than the GISP2 ice.
Spatial and temporal structure of the barotropic response of the Scotian Shelf and Gulf of Maine to surface wind stress: A model‐based study
Authors: Greenberg David A. , Loder John W. , Shen Yingshuo , Lynch Daniel R. , Naimie Christopher E.
Published: February 2004

The barotropic current and pressure field responses of the Scotian Shelf and Gulf of Maine region to spatially uniform wind stress are examined using a three‐dimensional finite‐element numerical model. The model is linear and harmonic with spatially varying eddy viscosity and bottom friction coefficients obtained from a nonlinear M2 tidal solution. The solutions for low‐frequency (20‐day period) wind stress and upstream boundary forcing are generally consistent with previous depth‐averaged model results, showing a substantially stronger response for along‐shelf (compared to cross‐shelf) stress and strong topographic shaping of the associated “arrested topographic waves.” With their expanded domain and dimensionality, the present solutions reveal important additional features of the responses, such as the Northeast Channel being the primary conduit for cross‐shelf subsurface flow compensating the cross‐shelf Ekman transport over the Scotian Shelf, widespread areas of near‐bottom upwelling and downwelling along the coast and shelf break, and leakage of the response across the shelf break. Model solutions for stress forcing with periods in the “storm band” (2–5 days) show similar structures and elevation/current gains to those in the low‐frequency solutions, with the primary exception that the large Northeast Channel transport for along‐shelf stress excites a topographic wave over the continental slope south of Georges Bank. The strength of bottom stress, dependent on the magnitudes of both the bottom friction coefficient and near‐bottom viscosity in the model, has a significant quantitative influence on the inner‐shelf response (coastal elevation amplitudes and cross‐shelf decay scales) in particular. The implications of the model solutions for the interpretation of various observational features of the region's response to wind stress are discussed, including coastal elevations, offshore bottom pressures, currents, transports, upwelling zones, frequency dependences, and seasonal and frictional influences.
Aircraft observations of sea surface temperature variability in the tropical Pacific
Authors: Hagan Denise , Rogers David , Friehe Carl , Weller Robert , Walsh Edward
Published: February 2004

During the southern summer of 1992–1993, a series of aircraft observations of sea surface temperature (SST) were obtained over the tropical western Pacific ocean as part of the Tropical Ocean Global Atmosphere Coupled Ocean‐Atmosphere Response Experiment (TOGA COARE). Down‐looking thermal infrared (10–11 μm) observations of the sea surface, coincident with uplooking infrared observations (9–11 μm) and meteorological measurements from the same aircraft platform are described. The data are compared with buoy and ship‐based measurements of SST, and show good agreement. The radiometric measurements, corrected for surface emissivity effects, show diurnal warming which precedes warming measured by sub‐surface buoy sensors. Mesoscale surface features are also seen which have spatial dimensions similar to those of tropical cloud clusters in the wavelength range of 1–100 km. Significant horizontal temperature gradients of 1°C occur in less than 10 km. On some days, the gradients can be directly related to precipitation. Clouds appear to create ‘imprints’ of their structure on the ocean surface by shielding incoming solar radiation, consistent with calculations of such a process using a one‐dimensional ocean mixed layer model. Measurements of the height of the well‐mixed region of the boundary layer and air potential temperature show a positive relation with increasing SST. An increase in buoyancy flux with increasing SST is identified with mesoscale sub‐cloud processes in fair weather conditions, and suggests that SST maxima on scales of 10–50 km enhance the transfer of moisture in the boundary layer by natural convection processes.
Resuspension and transport of fine sediments by waves
Authors: Mei Chiang C. , Fan She‐jun , Jin Kang‐ren
Published: February 2004

Although waves are the primary cause of sediment resuspension in the nearshore zone, in existing theoretical models, long‐scale currents induced by the mean wind are often taken to be the only agent for the diffusion and convection of resuspended sediments. We present here theoretical examples where waves play a direct role in all aspects of sediment transport. Details are given for the simple case where only waves are present; the wave‐induced current and diffusivity are shown to be no less important than similar factors in the wind‐driven current. Hence, in a comprehensive model, one should include not only the current forced directly by the mean wind, but also the current forced by waves which may or may not be forced by the local wind.
Nonlinear processes of energy transfer from traveling hurricanes to the deep ocean internal wave field
Authors: Niwa Yoshihiro , Hibiya Toshiyuki
Published: February 2004

Generation of large‐scale internal waves by a hurricane traveling over the ocean with a uniform velocity is investigated by using a three‐dimensional, multilevel numerical model. It is found that two distinctive kinds of internal waves are excited in the wake of the hurricane, namely, near‐inertial waves, which can be explained based on the linear theory, and superinertial waves with frequencies 2ƒ0 and 3ƒ0(ƒ0 is the inertial frequency at the latitude of the hurricane track), which are generated through nonlinear effects. Our special attention is directed to the superinertial waves with frequencies 2ƒ0 and 3ƒ0 because these internal waves are considered to be efficient energy sources for small‐scale mixing in the deep ocean. These superinertial waves predominantly have low‐vertical‐mode structures and satisfy the dispersion relation for lee waves. In areas away from the hurricane track, in particular, the double‐inertial frequency waves become larger than the near‐inertial waves. The nonlinear resonant triads causing the generation of such superinertial waves are examined by calculating the bispectrum, which clearly shows that the lowest‐vertical‐mode double‐inertial frequency wave is generated efficiently through the nonlinear interaction between the high‐vertical‐mode near‐inertial waves.
Evidence for quasi‐biennial oscillations in zooplankton biomass in the subarctic Pacific
Authors: Conversi Alessandra , Hameed Sultan
Published: February 2004

To investigate the possibility of climatic influence on the marine biosphere, we analyzed the decadal time series of Zooplankton biomass and sea surface temperature (SST) measured at station P, Gulf of Alaska, during the period 1957–1980. A relationship between the two series is not apparent in the raw data. However, Fourier analysis revealed peaks at 28.8 months in both Zooplankton and SST spectra. This period belongs to the range of the quasi biennial oscillation (QBO). Such a signal has been found originally in atmospheric and later in physical oceanographic variables. However, it has not been reported previously in biological variables. Cross‐spectral and band‐pass filter analyses indicate that temperature and Zooplankton variations at this frequency may be related. Possible mechanisms are discussed. These results are important because they indicate that a climatic signal, the QBO, is present in the oceanic biota.
Mineralogy of atmospheric microparticles deposited along the Greenland Ice Core Project ice core
Authors: Maggi V.
Published: February 2004

The mineralogical composition of atmospheric dust particles changes along the Greenland Ice Core Project (GRIP) ice core in phase with other paleoatmospheric records, showing that climatic changes affect the location, the relative extent, and the surface characteristics of the dust source areas. Fifty GRIP ice samples from the Eemian to the last glacial maximum were analyzed using a scanning electron microscope coupled with X ray energy dispersive system microprobe. More than 20 mineral types or groups were identified and their relative abundance was evaluated. A different mineralogical composition was systematically observed in cold and warm time periods. Quartz, illite, chlorite, micas, and feldspars prevail in the mineral assemblage associated with cold stages or phases (marine isotope stage (MIS) 4, MIS 2, cold part of MIS 3 fast variations), while kaolinite and Fe (hydr)oxides dominate in warm episodes (MIS 5e5, warm parts of fast variations). The first dust mineral assemblage is related mainly to the mechanical weathering prevailing in arid and cold mid‐high‐latitude areas, while the second dust mineral assemblage is related mainly to deep chemical weathering in warm and humid low‐latitude areas. K/C and O/Q ratios may be assumed as indicative of the relative importance of low‐latitude versus arid and mid‐high‐latitude source areas. It is worthwhile to mention that the first warmer part of Eemian (5e5) differs in dust mineralogy from the second part (5e4–5e1) and that also the fast variations are accompanied by clear mineralogical changes of the dust microparticles. The changes of the atmospheric dust mineral background are possibly related to changes of the atmosphere dynamics (meridian pressure gradient, polar front shift, storm track changes, etc.) and or to changes in the relative extent of the deflation source areas.
South China Sea warm pool detected in spring from the Navy's Master Oceanographic Observational Data Set (MOODS)
Authors: Chu Peter C. , Tseng Hsing‐Chia , Chang C. P. , Chen J. M.
Published: February 2004

A South China Sea warm pool with sea surface temperature (SST) higher than 29.5°C, recently reported by Chu and Chang [1995a, b] and Chu et al. [1997], appears in the central South China Sea (west of the Luzon Island) in boreal spring, strengthens until the onset of the summer monsoon (mid‐May), and then weakens and disappears at the end of May. The transient features and interannual variabilities of the warm pool have not yet been studied. Here we use a subset of the U.S. Navy's Master Oceanographic Observation Data Set (MOODS) to investigate the surface thermal features. First, we employed an optimal interpolation scheme to build up a 10‐day interval synoptic data set for December 1963 to November 1984 on a 0.5°×1° grids (finer resolution in zonal direction) from the MOODS SST data. An ensemble mean SST field
was established with a rather weak horizontal gradient (28.5°C near the Palawan Island to 26°C near the southeast China coast). Second, we performed a composite analysis to obtain the averaged SST anomaly field
deviating from the ensemble mean for the winter and spring seasons (December–May). During December–March,
is negative almost everywhere throughout the whole South China Sea. In early April, positive
with closed isoline (warm pool) was evident west of Luzon Island. In May, the central SCS warm anomaly becomes stronger. On May 11–20, the central SCS warm pool (114°–119°E, 14°–19°N) has
. The size of the warm pool is around 200,000 km2. Third, we performed an empirical orthogonal function (EOF) analysis on the residue data
, deviating from
, for the winter and spring seasons, in order to obtain transient and interannual variations of the SST fields. EOFl accounts for 35.5% of the variance and resembles the ensemble mean pattern of nearly parallel contours with a maximum value in the southeast and a minimum value in the northwest. EOF2 accounts for 21.4% of the variance and is characterized by a warm/cool pool (116°–118°E, 16°–18°N) west of the Luzon Island. The corresponding principal component (PC2) has strong interannual variability with a maximum value of 10 on February 11–20, 1965 and a minimum of −12 on March 21–31, 1964. This indicates the appearance of either a warm pool with a maximum strength of 1.2°C or a cool pool with a maximum strength of −1°C. Combination of
and PC2×EOF2 leads to an occurrence of a central SCS warm pool from April to May with a warm anomaly varying between 0.8° and 3°C.
An interlaboratory comparison of techniques for extracting and analyzing trapped gases in ice cores
Authors: Sowers Todd , Brook Ed , Etheridge David , Blunier Thomas , Fuchs Andreas , Leuenberger Markus , Chappellaz Jerome , Barnola Jean Marc , Wahlen Martin , Deck Bruce , Weyhenmeyer Connie
Published: February 2004

We undertook an interlaboratory comparison of techniques used to extract and analyze trapped gases in ice cores. The intercomparison included analyses of standard reference gases and samples of ice from the Greenland Ice Sheet Project 2 (GISP2) site. Concentrations of CO2, CH4, the δ;18O of O2, the δ15N of N2, and the O2/N2, and Ar/N2 ratios were measured in air standards and ice core samples. The standard reference scales for CO2 and CH4 were consistent at the ±2% level. The δO2/N2 and δ18O of O2 measurements showed substantial deviations between the two laboratories able to measure these ratios. The deviations are probably related to errors associated with calibration of the working standards. The δArN2 and δ15N of N2 measurements were consistent. Five laboratories analyzed the CH4 concentration in a 4.2‐m section of the GISP2 ice core. The average of 20 discrete CH4 measurements was 748±10 parts per billion by volume (ppbv). The standard deviation of these measurements was close to the total analytical uncertainty associated with the measurements. In all cases, those laboratories employing a dry extraction technique determined higher CH4 values than laboratories using a wet extraction technique. The origin of this difference is unclear but may involve uncertainties associated with blank corrections. Analyses of the CO2 concentration of trapped gases showed extreme variations which cannot be explained by analytical uncertainties alone. Three laboratories measured the [CO2] on 21 discrete depths yielding an average value of 283±13 parts per million by volume (ppmv). In this case, the standard deviation was roughly a factor of 2 greater than the analytical uncertainties. We believe the variability in the measured [CO2] results from impurities in the ice which may have compromised the [CO2] of trapped gases in Greenland ice.
Flow dynamics of a wide Arctic canyon
Authors: Signorini S. R. , Münchow A. , Haidvogel D.
Published: February 2004

We extend and interpret acoustic Doppler current profiler and conductivity‐temperature‐depth data collected in the summer of 1993 over Barrow Canyon in order to implement a high resolution (1.5 to 5 km) model of the Beaufort and Chukchi Seas. This paper addresses physical processes relevant to the Barrow Canyon region using common dynamical analyses of both field data and numerical results. The field data reveal the dominant physical processes that guide the design of our numerical experiments. The observed velocity field shows an intense and variable down canyon flow with transports ranging from 0.5 to 1.4 Sv. A momentum analysis reveals that the cross‐canyon dynamic balance for the barotropic component is primarily geostrophic. Conversely, the baroclinic cross‐canyon momentum balance is ageostrophic and secondary flow results from a local imbalance between the vertically varying Coriolis acceleration and the cross‐canyon pressure gradient. In addition to the moderate influence of stratification (Froude number of 0.4 and Burger number of 0.06), the barotropic pressure gradient component across the canyon (inferred from the large magnitude and little vertical variability of the residuals) is dynamically important for both upcanyon and downcanyon flows that occur at different locations concurrently. The along‐canyon dynamic balance is ageostrophic since the time derivative and the Coriolis term are of the same order of magnitude (temporal Rossby number is approximately 1). An analysis of the longitudinal density and velocity fields from the model reveals that the main driving mechanism for generating the observed upcanyon flow is the nonlinear interaction of the variable barotropic flow with the steep topography. Stratification is maintained by the downcanyon advection of fresh and warm water from the Bering and Chukchi Seas and the upcanyon advection of saltier and colder water from the Arctic.
Observations of near‐surface currents and hydrography in the Connecticut River plume with the surface current and density array
Authors: O'Donnell James
Published: February 2004

It has been well established that the Connecticut River forms a large plume in the vicinity of its mouth during periods of high river discharge. The plume is bounded on the offshore side by a distinct front where the water color and turbidity changes rapidly and foam and detritus accumulate. Though there have been many observations of similar fronts throughout the world, the details of the density and velocity structure in the vicinity of a plume front and the propagation velocity of the feature have not been adequately resolved. To better observe the properties of these phenomena, we have constructed a ship‐mounted array of instruments to measure the near‐surface currents and density (SCUD) distribution in plumes and fronts. SCUD provides current velocity components at four levels and conductivity and temperature at five levels in the upper 3 m of the water column. By using the global positioning system in differential mode to obtain position, the system has a horizontal resolution of 5 m at a ship speed of 1–2 ms−1. Estimates of the ground referenced water velocity components have an uncertainty of approximately 0.1 ms−1. To demonstrate the performance of the SCUD array, we report the preliminary results of an observation program to examine the variability of the front of the Connecticut River plume. In the spring of 1994, several 200 m across‐front SCUD transects separated by 200 m were obtained during the mid ebb in Long Island Sound. During this period the front advanced to the west with a velocity of the order of 0.1 ms−1 in opposition to an eastward tidal current of 1.0 ms−1. A practical salinity increase of 20 in less than 10 m was observed at the front on crossing into the plume. In concert, the front normal velocity component decreased by 0.5 (±0.1) ms−1 over 10 m, and the vertical shear in the front parallel component decreased dramatically. The performance and potential of the instrumentation and the implication of the observations for the development theories of river plume fronts are discussed.
The turbulence regime of a very stable marine airflow with quasi‐frictional decoupling
Authors: Smedman Ann‐Sofi , Högström Ulf , Bergström Hans
Published: February 2004

Data from an air/sea interaction experiment over the Baltic Sea during conditions with very large land ‐ sea surface temperature contrast have been analyzed. It is found that the measured shearing stress and sensible heat flux were strongly suppressed compared to what would be expected from current theory. Analysis of spectral behavior shows that a strong wind gradient imposed by the presence of a low‐level jet at or below 100 m height during about 80% of the time is exerting strong influence on the turbulence regime by suppressing low‐frequency fluctuations. The dissipation length scale was found to equal a new length scale LUT which has the vertical velocity standard deviation in the numerator and the sum of the wind gradient and the Brunt‐Väisälä frequency in the denominator. It was also found that the 10 m drag coefficient CD10 was a strong function of this scale, with small values of LUT giving almost zero CD10 values. Integrating the locally found wind gradient down to the surface resulted in roughness length values several orders of magnitude less than that valid for a dynamically smooth flow. With turbulence measurements at only one height, 10 m, no conclusive explanation of this anomaly could be given. Observed significant wave height during the experiment was, however, found to be a factor of 2.5 lower on the average than predicted by current theory.
Atmospheric boundary layer over the central and western equatorial Pacific Ocean observed during COARE and CEPEX
Authors: Serra Yolande L. , Rogers David P. , Hagan Denise E. , Friehe Carl A. , Grossman Robert L. , Weller Robert A. , Anderson Steven
Published: February 2004

The present study is based on aircraft data collected in the western and central equatorial Pacific as a part of the Coupled Ocean‐Atmosphere Response Experiment (COARE) and the Central Equatorial Pacific Experiment (CEPEX). The purpose of this discussion is to provide some insight into the coupling of the atmosphere to the ocean in regions of light winds and high humidity, as well as near deep organized convection, and to compare and contrast these climatically important tropical regions. The results presented use both the aerial extent of cold cloud top temperatures and surface layer similarity to highlight the variation of the surface fluxes as a function of convective regimes. A wide range of convective conditions were encountered during the 5 months of COARE and CEPEX, ranging from deep, towering anvils to shallow trade cumuli. The variety of conditions sampled has provided a unique set of turbulence data over open ocean, which are compared to fundamental spectral forms. Results suggest that assumptions regarding surface layer processes based on a large‐scale assessment of the convective conditions are likely to be inaccurate. For example, during free convective conditions, where buoyancy production dominates over mechanical production of turbulence in the boundary layer, surface heat and buoyancy fluxes are enhanced for the given wind conditions, compared to those observed for forced convection, due to transport by buoyant plumes. This highlights the importance of considering the effect of the buoyancy flux on the vertical velocity variance in light winds in the parameterization of the surface fluxes. For forced convective conditions, where cloud circulations cause enhanced mechanical turbulence and reduced buoyancy in the boundary layer, surface fluxes are enhanced, as are the scales of turbulent eddies, drawing surface heat and moisture away from the surface. As with buoyant plumes, this process needs to be considered by surface flux parameterizations early enough in the convective process in order to accurately represent the role of the surface in the development of convection. While the temperature of the warm pool region in COARE is found to be largely independent of local conditions measured by the aircraft, we observe that the warmest temperatures (>30°C) coincide exclusively with the lightest winds, which highlights the importance of wind‐driven mixing in determining the thermal structure of the upper ocean.
Trapped‐wave modification and critical surface formation by mean flow at a seamount with application at Fieberling Guyot
Authors: Codiga Daniel L.
Published: February 2004

Effects of radially and vertically sheared mean azimuthal flow on trapped waves at a seamount are shown to include changes to resonance frequency and spatial structure and the formation of two types of critical surface. In waves calculated using bathymetry, stratification strength, and frequency (0.66ƒ) appropriate to amplified diurnal currents observed at Cobb Seamount (46.8°N), mean flow based on measurements there does not cause critical surfaces. Even though clockwise mean flow vorticity is a significant fraction of ƒ, effects on the wave are limited to weakly reduced spatial scales and an increase in resonance frequency much weaker than estimates of the Doppler shift. The Doppler shift is opposed by variations in mean horizontal shear that cause a downslope potential vorticity gradient opposite that of the bottom slope supporting the wave; mean vertical shear is unimportant. In the general case, mean flow can cause (1) a stratified seamount‐trapped wave critical surface where the intrinsic frequency vanishes, causing both horizontal and vertical scales of the wave to diminish and (2) an internal wave critical surface where the intrinsic frequency rises to the effective Coriolis frequency, or low‐frequency bound for superinertial internal waves. An internal wave critical surface bounds a “superinertial cap” within which subinertial currents are effectively superinertial. Mean flow at Fieberling Guyot (32.4°N) reduces the effective Coriolis frequency by 0.43ƒ and causes a superinertial cap having an internal wave critical surface for diurnal currents (0.93ƒ) that coincides with measured turbulence maxima extending several kilometers away laterally above the seamount.
Complementarity of ERS 1 and TOPEX/POSEIDON altimeter data in estimating the ocean circulation: Assimilation into a model of the North Atlantic
Authors: Blayo E. , Mailly T. , Barnier B. , Brasseur P. , Le Provost C. , Molines J. M. , Verron J.
Published: February 2004

This study examines the possibility of improving ocean circulation estimates by using TOPEX/POSEIDON (T/P) altimetric measurements in conjunction with those obtained from ERS 1. An evaluation is carried out by assimilating these data sets into a circulation model of the North Atlantic. Experiments with simulated data show that the simultaneous use of both data sets results in clearly enhanced results, even for the estimate of the deep circulation, which is a key issue in ocean circulation modelling. However, the benefit is less clear when using real altimeter data, which could result from the fact that the spectral structure of the orbit error is not taken into account in the assimilation procedure. Comparisons of the model results with the altimeter measurements and with numerous independent in situ velocity measurements demonstrate that the estimates of the surface and subsurface circulations are still improved with a dual assimilation. However, this gain seems weaker than could be expected from experiments with simulated data. Moreover, comparisons with deep velocity measurements show no improvement at all, which probably indicates that measurement errors and nonmodelled physics are not well taken into account in the assimilation procedure. It is also observed that the combined use of the two data sets may help in limiting some systematic shortcomings of the numerical tools in exploiting the data. Finally, it is worth noting that the ERS 1 orbit characteristics almost systematically lead to better results than T/P ones for the range of temporal and spatial scales addressed in these experiments.
Beryllium 10 concentrations in the Greenland Ice Sheet Project 2 ice core from 3–40 ka
Authors: Finkel R. C. , Nishiizumi K.
Published: February 2004

A nearly continuous record of 10Be (half‐life of 1.5×106 years) concentrations is reported in the Greenland Ice Sheet Project 2 (GISP2) ice core for the time period between 3288 and 40,055 years B.P. The resolution is between 20 and 50 years in the Holocene. During the Pleistocene, sampling was coarser, with the resolution ranging between 50 and 200 years. Both concentrations and fluxes are reported. Concentrations of 10Be are observed to correlate strongly with δ18O and more weakly with snow accumulation rates. Beryllium 10 fluxes show less dependence than do concentrations on climate‐related parameters. A good correlation exists between Δ14C and 10Be for centennial scale variations, which are most likely due to heliomagnetic modulation of the 10Be production rate in the atmosphere. There is no evidence of a long‐term geomagnetic effect on the 10Be flux at GISP2. The interpretation of the record depends strongly on the model one uses to infer atmospheric 10Be concentrations from the measured concentrations in snow.
Modeling the thermodynamics of a sea ice thickness distribution: 2. Sea ice/ocean interactions
Authors: Holland M. M. , Curry J. A. , Schramm J. L.
Published: February 2004

In this paper we examine the coupling of an ice thickness distribution model with an ocean mixed layer model. The annual cycle of the modeled mixed layer temperature, salinity, and depth are compared to observations from the drifting ice stations of the Arctic Ice Dynamics Joint Experiment (AIDJEX). The role of the ice thickness distribution in determining the ice/ocean coupling is examined. We find that the ice thickness distribution is important for the exchange of heat, salt, and fresh water between the ice and the ocean, especially with regard to the effects of thin, first‐year ice. Several different parameterizations of the ice/ocean turbulent heat exchange are compared. The results indicate that the storage of heat in the ocean mixed layer is an important physical process for determining the annual average ice thickness. Double diffusion and the stabilizing effects of meltwater also impact the exchange of heat between the ocean and ice cover. Questions remain as to the relative importance of these processes and their accurate parameterization in ice/ocean coupled models.
Methanesulfonate in the Greenland Ice Sheet Project 2 Ice Core
Authors: Saltzman E. S. , Whung P.‐Y. , Mayewski P. A.
Published: February 2004

In this paper we present measurements of methanesulfonate in the Greenland Ice Sheet Project 2 (GISP2) ice core. Methanesulfonate is an atmospheric oxidation product of dimethylsulfide. The GISP2 methanesulfonate record contains information about the atmospheric loading of biogenic sulfur over the past 110 kyr and its relationship to climate change. The GISP2 data set supports the inferences made from the Renland ice core from Greenland that the glacial atmosphere over Greenland had reduced concentrations of biogenic sulfur compared with the present day [Hansson and Saltzman, 1993]. We conclude that the flux of biogenic sulfur from the North Atlantic Ocean must have been lower during glacial times and speculate that this decrease may have been related to differences in phytoplankton speciation. The data suggest that changes in direct radiative forcing from biogenic sulfur aerosols would act as negative feedback to the glacial/interglacial climate cycles in this region.
Toward realism in modeling ocean wave behavior in marginal ice zones
Authors: Meylan Michael H. , Squire Vernon A. , Fox Colin
Published: February 2004

The model of Meylan and Squire [1996], which treats solitary ice floes as floating, flexible circular disks, is incorporated into the equation of transport for the propagation of waves through a scattering medium, assumed to represent open ice pack in a marginal ice zone. The time‐independent form of the equation is then solved for homogeneous ice conditions allowing for dissipation due to scattering, together with extra absorption from interactions between floes, losses in the water column, and losses arising from the inelastic character of the sea ice including local brash. The spatial evolution of wave spectra as they progress through the pack is investigated with the aim of explaining the field data of Wadhams et al. [1986]. Specifically, the change toward directional isotropy experienced by waves as they travel into the ice interior is of interest. In accord with observations, directional spread is found to widen with penetration until eventually becoming isotropic, the process being sensitive to wave period. The effect of absorption on the solution is investigated.
Analysis of ERS‐1/2 synthetic aperture radar wave mode imagettes
Authors: Kerbaol Vincent , Chapron Bertrand , Vachon Paris W.
Published: February 2004

The European Space Agency (ESA) ERS‐1 and ERS‐2 C band VV polarization active microwave instrument (AMI) offers the unique ability to combine interlaced wind scatterometer and high‐resolution synthetic aperture radar (SAR) wave mode imagettes. In this study, more than 2000 imagettes were considered. Eadi imagette has been statistically analyzed in comparison with normalized radar cross‐section (NRCS) measurements from the scatterometer mode. During the ERS‐1 AMI wave mode mission the incidence angle of the imagette center was modified from roughly 19.9° to 23.5°. Using ERS‐1 and ERS‐2 NRCS, calibration has thus been completed for both configurations, which allows a better characterization of some signal data saturation effects. However, since a SAR relies on platform displacement to achieve fine resolution, surface motions reduce its nominal resolution. As the wind speed increases, scatterer motion occurring during the SAR integration time also increases, causing the characteristic large azimuth cutoff wavelength. Acknowledging the strong dependence between sea state conditions and azimuth smearing effects, our results are highlighted by the global comparison with wind estimates derived from the scatterometer. The results demonstrate the ability to define a SAR wind algorithm from a kinematic point of view. Finally, a higher‐order statistical analysis shows evidence of deviation from standard Rayleigh statistics, leading to a balance between K law and lognormal distributions. This deviation is mainly due to the SAR's high‐resolution properties.
Reduced space optimal analysis for historical data sets: 136 years of Atlantic sea surface temperatures
Authors: Kaplan Alexey , Kushnir Yochanan , Cane Mark A. , Blumenthal M. Benno
Published: February 2004

A computationally efficient method for analyzing meteorological and oceanographic historical data sets has been developed. The method combines data reduction and least squares optimal estimation. The data reduction involves computing empirical orthogonal functions (EOFs) of the data based on their recent, high‐quality portion and using a leading EOF subset as a basis for the analyzed solution and for fitting a first‐order linear model of time transitions. We then formulate optimal estimation problems in terms of the EOF projection of the analyzed field to obtain reduced space analogues of the optimal smoother, the Kalman filter, and optimal interpolation techniques. All reduced space algorithms are far cheaper computationally than their full grid prototypes, while their solutions are not necessarily inferior since the sparsity and error in available data often make estimation of small‐scale features meaningless. Where covariance patterns can be estimated from the available data, the analysis methods fill gaps, correct sampling errors, and produce spatially and temporally coherent analyzed data sets. As with classical least squares estimation, the reduced space versions also provide theoretical error estimates for analyzed values. The methods are demonstrated on Atlantic monthly sea surface temperature (SST) anomalies for 1856–1991 from the United Kingdom Meteorological Office historical sea surface temperature data set (version MOHSST5). Choice of a reduced space dimension of 30 is shown to be adequate. The analyses are tested by withholding a significant part of the data and prove to be robust and in agreement with their own error estimates; they are also consistent with a partially independent optimal interpolation (OI) analysis by Reynolds and Smith [1994] produced in the National Centers for Environmental Prediction (NCEP)(known as the NCEP OI analysis). A simple statistical model is used to depict the month‐to‐month SST evolution in the optimal smoother algorithm. Results are somewhat superior to both the Kalman filter, which relies less on the model, and the optimal interpolation, which does not use it at all. The method generalizes a few recent works on using a reduced space for data set analyses. Difficulties of methods which simply fit EOF patterns to observed data are pointed out, and the more complete analysis procedures developed here are suggested as a remedy.
Relationship between anomalies in sea surface temperature and air‐sea heat flux in a simple coupled ocean‐atmosphere model
Authors: Zhang Sheng , Greatbatch Richard J.
Published: February 2004

Observational studies have shown that sea surface temperature (SST) anomalies are often generated by changes in air‐sea heat flux from the atmosphere. By contrast, ocean‐only climate models usually assume that SST anomalies are strongly damped by the air‐sea heat flux. In this paper we use regression analysis to show that anomalies in air‐sea heat flux can systematically drive anomalies in SST even in a very simple coupled ocean‐atmosphere model. The atmosphere model is an energy balance model in which atmospheric heat transport is parameterized as a downgradient, diffusive transfer, whereas the ocean model is a three‐dimensional circulation model. Anomalies in atmospheric temperature are generated by variability in the ocean model. The region in which the air‐sea heat flux anomalies systematically enhance, rather than damp, SST anomalies lies along the periphery of the region of high variance in SST. It exists because the atmosphere model is much more efficient than the ocean model at dispersing heat anomalies from the region of high SST variance, allowing heat anomalies to be partially reabsorbed by the ocean, where the SST variance is less. The regression analysis also shows that the damping time for SST anomalies in other parts of the model domain is typically several hundred days.
Observations of sea surface salinity in the western Pacific fresh pool: Large‐scale changes in 1992–1995
Authors: Hénin Christian , du Penhoat Yves , Ioualalen Mansour
Published: February 2004

This paper investigates the variability of sea surface salinity (SSS) in the western equatorial Pacific fresh pool. For this purpose, we processed data collected from thermosalinographs embarked on merchant ships. Two main cross‐equatorial shipping lines that are representative of the oceanic conditions in the western tropical Pacific were selected: the Japan‐Tarawa‐Fiji line that crosses the equator near 173°E (eastern track) and the New‐Caledonia‐Japan line that crosses the equator near 156°E (western track). We show that there is a strong SSS variability in the region at monthly as well as interannual timescales. This high variability is attributed to the successive passages of a zonal salinity front, trapped in the (5°N–5°S) equatorial band and migrating in phase with the southern oscillation index. We also found the eastern track to be more variable in SSS because it is more exposed to these SSS front incursions. We carried out a detailed study of the mechanisms responsible for this variability; it revealed that the rainfall input acts as a source of freshwater responsible for the existence of a contrasted distribution of SSS (mainly high‐salinity waters in the central Pacific and low‐salinity waters in the western Pacific). However, the main mechanism responsible for the SSS variability is zonal advection that makes the two distinct masses of water converge, resulting in a salinity front which shifts back and forth in the equatorial band.
Sea surface cooling caused by typhoons in the Tohoku area in August 1989
Authors: Sakaida Futoki , Kawamura Hiroshi , Toba Yoshiaki
Published: February 2004

A remarkable sea surface cooling event was observed in the north western Pacific off Japan coast, which is known as the Tohoku Area, by using well‐calibrated satellite sea surface temperature images, when typhoons T8914 and T8915 passed over the Tohoku Area in August 1989. The sea surface cooling maximum reached up to 9°C, which is much larger than that reported in the previous studies. The corresponding hydrographic data show that the sea surface cooling state is closely related with the ocean structure in the Tohoku Area; the larger sea surface cooling occurs in the Oyashio area. The numerical experiments taking account of the ocean structure show that the surface cooling maximum is 3–4 times larger in case of the Oyashio profile than that of the Kuroshio profile and clarify the mechanism of the sea surface cooling.
Eulerian and Lagrangian aspects of the longshore drift in the surf and swash zones
Authors: Brocchini M.
Published: February 2004

A theoretical study of the mean longshore mass flux and longshore drift velocities due to waves obliquely incident on a uniform sloping beach is presented. Analysis is performed using both Eulerian and Lagrangian representations of the flow. A number of results based on inviscid solutions are obtained concerning the mean longshore mass flux 〈My〉 inside the swash zone. Thus 〈My〉 depends on the parameters (wave amplitude, wave frequency, and wave number) of waves incident at a shoreline in a similar fashion to the dependence of the mass flux occurring between the crests and troughs of propagating waves on the same wave parameters. The mass flux depends on the square of the local wave amplitude, even for very steep waves which break before reaching the shoreline. A Lagrangian approach shows that particle paths are not closed even offshore of the breaking point and that “zigzag transport” is characteristic of Lagrangian particle paths in the two‐dimensional horizontal flow seaward of the swash zone. The cross‐shore profile of the longshore drift velocity is analyzed. Very weak longshore drift velocity characterizes the nonbreaking waves up to the swash zone. Onshore of the breaking point we find that the longshore drift velocity has a quasi‐linear profile up to the maximum velocity reached near the shoreline. Effects of seabed friction are included in the computation of cross‐shore profiles of the longshore drift velocity. A sensitivity analysis reveals that even for relatively small friction parameters (ƒ≈0.1), velocities inside the swash zone are greatly reduced. The reduction in longshore drift velocity is greater for the Lagrangian profile than for the Eulerian one, and for larger friction parameters (ƒ≥0.1) the maximum longshore velocity moves toward the breaking point, where the friction effects are smaller. Finally, steady state profiles of the longshore drift velocities (Eulerian and Lagrangian) are computed.
Corrections for detector nonlinearities and calibration inconsistencies of the infrared channels of the advanced very high resolution radiometer
Authors: Walton C. C. , Sullivan J. T. , Rao C. R. N. , Weinreb M. P.
Published: February 2004

The data received from the thermal infrared channel 4 (∼10.3–11.3 μm) and channel 5 (∼11.5–12.5 μm) of the advanced very high resolution radiometer (AVHRR) flown on the National Oceanic and Atmospheric Administration (NOAA) Polar‐Orbiting Operational Environmental Satellites provide only a linear estimate of the actual radiance. We describe here a simple procedure, which incorporates data from prelaunch calibration tests, to correct the linear estimates for the nonlinear response of the channels 4 and 5 Mercury‐Cadmium‐Telluride (Hg‐Cd‐Te) sensors. The procedure applies a “nonzero radiance of space” concept to specify the form of the linear radiance estimate. This linear radiance is nearly independent of the operating temperature of the AVHRR and is the sole input to the correction algorithm. Additionally, it is demonstrated with NOAA 14 data that this calibration procedure resolves discrepancies found in the prelaunch data which can affect the calibration accuracy of channel 3 (∼3.55–3.95 μm), which possesses a linear response, as well as channels 4 and 5. When applied to independent sets of prelaunch calibration data, this procedure reproduces the laboratory‐measured temperature data to within an accuracy of 0.1°–0.2°K. Comparison with nonlinearity corrections based on different procedures points to the superior applicability of the present results over the entire range of Earth‐scene temperatures measured by the AVHRR in orbit. This accuracy is particularly important when these three infrared channels are used in multichannel algorithms to generate environmental parameters such as sea surface temperature. The algorithm coefficients and values of the nonzero radiance of space required to calculate the nonlinearity radiance corrections are given for the AVHRRs on NOAA 7, 9, 10, 11, 12, and 14 spacecraft.
Synthesis of particulate and extracellular carbon by phytoplankton at the marginal ice zone in the Barents Sea
Authors: Vernet María , Matrai Patricia A. , Andreassen Inger
Published: February 2004

Large phytoplankton biomass accumulates during ice‐edge blooms in Arctic waters, where taxa such as diatoms or the prymnesiophytePhaeocystis pouchetiiusually dominate. Based on characteristics from temperate phytoplankton, we hypothesized that in Barents Sea waters, a larger fraction of primary production would be extracellular (for synthesis of colonial mucilage) during periods of dominance byP.pouchetiias opposed to periods when diatoms dominated. This alternation ofP.pouchetiiand diatoms would affect the relationship between the particulate and dissolved carbon pools in the upper water column of the marginal ice zone (MIZ). Results presented in this paper do not support this hypothesis. AlthoughP.pouchetiicontributed strongly to the extracellular carbon pool (mucilage and dissolved organic carbon, DOC) during an ice‐edge bloom in May 1993, arctic diatoms contributed an equal amount of exuded carbon. Three process stations visited along a north‐south transect in the MIZ in the Barents Sea, presented between 36% and 55% of the primary production as extracellular carbon, defined as labeled organic matter which passes through a Whatman GF/C filter. No difference in the carbon allocation between diatom‐ andP. pouchetii‐rich phytoplankton was observed in these stations. In contrast, the station located in ice‐free waters had 18% of primary production in the extracellular fraction. These results (1) highlight similar carbon allocation for diatom‐ andP. pouchetii‐dominated phytoplankton in surface waters of the Barents Sea during the spring and/or ice‐edge bloom at the MIZ and (2) suggest that polar phytoplankton may be stronger producers of extracellular carbon, and possibly DOC, than previously thought.