bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of the East India Coastal Current: 2. Numerical solutions
Authors: McCreary J. P. , Han W. , Shankar D. , Shetye S. R.
Published: February 2004

A linear, continuously stratified model is used to investigate the dynamics of the East India Coastal Current (EICC). Solutions are found numerically in a basin that resembles the Indian Ocean basin north of 29°S, and they are forced by Hellerman and Rosenstein [1983] winds. Effects due to the following four forcing mechanisms are isolated: local alongshore winds adjacent to the east coasts of India and Sri Lanka, remote alongshore winds adjacent to the northern and eastern boundaries of the Bay, remotely forced signals propagating from the equator, and interior Ekman pumping. Each process contributes significantly to the EICC surface flow at some locations and at some times during the year. Along the Indian coast (north of 10°N), the surface EICC flows northeastward from February until September, with a strong peak in March–April and weaker flow from June to September; interior Ekman pumping, remote alongshore winds and equatorial forcing all contribute to the springtime peak, whereas local alongshore winds are the primary driving force of the weaker summertime flow. Along Sri Lanka (south of 10°N), the surface EICC flows northward only during March and April; the absence of northward flow at other times is due to interior Ekman pumping, which drives a strong southward current for much of the year (April to December). Along both coasts there is southward flow from October to January that is driven by interior Ekman pumping and local alongshore winds. The EICC also has significant subsurface flow on several occasions. Along the Indian coast, there is southwestward flow extending to depths greater than 1000 m from May to July that is driven primarily by equatorial forcing. From July to September, the southwestward flow forms a shallow subsurface counterflow (a Coastal Undercurrent); its cause is primarily equatorial forcing and interior Ekman pumping, not the local alongshore winds, as might be expected.
Flux of surface‐active organic complexes of copper to the air‐sea interface in coastal marine waters
Authors: Shine James P. , Wallace Gordon T.
Published: February 2004

Concentrations of surface‐active organic complexes of copper in coastal seawater were used to estimate their transport from the water column to the air‐sea interface by molecular diffusion and bubble scavenging. Under average wind conditions observed in Massachusetts Bay, molecular diffusion to the air‐sea interface was the primary transport mechanism. Estimated diffusion flux rates ranged from 3.8 to 210 × 10−17 mol Cu cm−2 s−1, with a mean value of 62 × 10−17 mol Cu cm−2 s−1. Temporal variability in the flux rates was directly related to estimated rates of primary production, presumably due to the biological production of surface‐active organic matter within the bulk water. Flux rates due to bubble scavenging were generally 3 orders of magnitude less than those observed for diffusion, with a mean value of 2.3 × 10−19 mol cm−2 s−1 for particulate Cu and 3.7 × 10−19 mol cm−2 s−1 for dissolved Cu. Temporal variability of the estimated bubble‐mediated fluxes reflected sensitivity to changes in wind stress, as well as the variablility in concentration of the surface‐active forms of copper. Residence times of copper in the sea‐surface microlayer, based on a comprehensive estimate of the flux of copper from bulk water and atmospheric sources, ranged from 2 min during a phytoplankton bloom period to 21 min during the winter months. Estimates of the flux of surface active forms of copper from the water column to the air‐sea interface suggest that the entire inventory of copper within the surface mixed layer of Massachusetts Bay can be cycled through the microlayer within approximately 50 days. This is of the same timescale as the residence time of copper within the surface mixed layer of Massachusetts Bay, indicating that a major portion of copper within the surface mixed layer will be transported to the microlayer before removal from the mixed layer. The formation and transport of surface‐active forms of copper may significantly influence the biogeochemical behavior of copper, and, perhaps, other metals within the surface mixed layer.
Intratidal variations in stratification and mixing in the Hudson estuary
Authors: Nepf H. M. , Geyer W. R.
Published: February 2004

This study represents a detailed examination of intratidal variations in boundary‐layer structure in a relatively narrow, straight section of the Hudson river estuary during high river discharge. The presence of active mixing is inferred from estimates of the Richardson number. The maximum height above bed to which mixing occurs is comparable during flood and ebb; however, the regions of mixing differ in density structure. During the flood, active mixing is confined to a well‐mixed near‐bed layer, whereas during the ebb, active mixing occurs throughout regions of significant stratification. Tidal straining maintains stratification during the ebb, while it promotes the growth of a uniform bottom, mixed layer during the flood. In general, maximum and minimum near‐bed stratification occur during late ebb and flood, respectively, reflecting the dominant role played by tidal straining in determining intratidal variation. Vertical stretching was also found to be an important term in the stratification balance during the ebb.
Global remnant cloud contamination in the along‐track scanning radiometer data: Source and removal
Authors: Jones Matthew S. , Saunders Mark A. , Guymer Trevor H.
Published: February 2004

Validation studies indicate that, in cloud‐free conditions, the along‐track scanning radiometer (ATSR) on the ERS 1 satellite is measuring global sea surface temperature (SST) to a point relative precision of better than 0.3°C. However, recent reports show that the presence of nighttime remnant cloud contamination is affecting ATSR SST precision in certain geographical areas. We modify the filtering scheme described by Jones et al. [1996] for removing remnant cloudiness in ATSR 0.5° spatially averaged sea surface temperature (ASST) data from the South Atlantic and apply this scheme to global ASST data (version 500) for the whole of 1992, 1993, and 1994. We find that globally 4.65% of the ASST data is cloud contaminated and that remnant cloud removal substantially reduces differences between day and night SST signals. The cloud contamination is seasonal and is linked to the occurrence of marine stratiform (fog, stratus, and stratocumulus) cloud types. Such cloud is low‐lying and uniform and thus difficult to detect with conventional cloud‐clearing techniques. Our effective global removal of remnant cloudiness will improve the accuracy of the ASST data and thus benefit the use of the ATSR in the early detection of climate change.
Direct numerical simulation of the roll‐off range of internal wave shear spectra in the ocean
Authors: Hibiya Toshiyuki , Niwa Yoshihiro , Nakajima Kensuke , Suginohara Nobuo
Published: February 2004

Oceanic internal gravity waves play an important role in the dynamics of the ocean, providing a link in the overall energy cascade from large forcing scales to small dissipation scales. Quantifying the cascade of energy available for mixing processes in the ocean interior, for example, is essential to accurate modeling of the oceanic general circulation. In the present study, based on an extensive numerical model that resolves most of the internal wave spectrum, the dynamics of the process by which internal waves dissipate their energy in the deep ocean are investigated. Putting all the calculated results together, we propose here a model for the dynamic balance of the internal wave spectrum wherein a downscale energy flux into the high vertical wavenumber near‐inertial portion of the spectrum is balanced by energy dissipation at critical layers formed by high vertical wavenumber near‐inertial flows.
A comparison of oceanic skin effect parameterizations using shipborne radiometer data
Authors: Kent Elizabeth C. , Forrester Thomas N. , Taylor Peter K.
Published: February 2004

Sea surface temperature data from a shipborne radiometer were used to assess the thermal skin effect parameterization schemes of Saunders [1967], Hasse [1971], Schlüssel et al. [1990], and Soloviev and Schlüssel [1994]. Under low‐wind, high‐insolation conditions, the presence of a near surface thermocline resulted in an apparent skin effect which depended on the history of the surface heating. Neglecting these cases, the Saunders [1967] and other schemes which omit solar radiation were the most effective. The observed variation with wind speed of the adjustable coefficient, λs, in the Saunders formulae was similar to that predicted by Soloviev and Schlüssel [1994], but the values were significantly higher, resulting in a greater magnitude of the observed skin effect. For the conditions occurring in this data set the better formulae predicted the skin effect with a standard deviation of ±0.16°C compared to a variation of the observed skin effect of nearly ±0.3°C.
Winter upwelling off Luzon in the northeastern South China Sea
Authors: Shaw Ping‐Tung , Chao Shenn‐Yu , Liu Kon‐Kee , Pai Su‐Cheng , Liu Cho‐Teng
Published: February 2004

A major upwelling region centered about 100 km offshore between 16° and 19°N off northwest Luzon in the South China Sea is revealed in the distributions of temperature, salinity, and dissolved oxygen concentration during a cruise in December 1990. Upward movement of water low in dissolved oxygen can be identified to a depth of 300 m. Climatological distributions of temperature and upper ocean heat content and tracer distribution obtained from a recent numerical experiment lend support to the existence of this upwelling region. Results from a general circulation model of the South China Sea further show that upwelling off Luzon occurs between October and January, in agreement with the climatological data. Current structures obtained from a simple two‐layer model and the general circulation model both suggest that this upwelling is not driven by local winds but contains a large, remotely forced component arising from the basin circulation. The upwelling is sustained by offshore Ekman drift from above and a converging northward undercurrent from below. The would‐be downwind coastal jet in the surface layer is largely offset by currents associated with the winter circulation gyre. Upwelled water with high nutrient content spreads southwestward in January and could be an important nutrient source for the surface water in the interior South China Sea in spring.
North Atlantic ocean circulation during the last glacial maximum and subsequent meltwater event: A numerical model
Authors: Seidov D. , Sarnthein M. , Stattegger K. , Prien R. , Weinelt M.
Published: February 2004

A numerical model that was forced with reconstructed sea surface temperature and sea surface salinity values of the North Atlantic was used to investigate three major states of the North Atlantic ocean circulation since the last glaciation: the modern state, the last glacial maximum (LGM), and an important meltwater event (MWE) near 14,200–13,200 14C yr B.P. Preliminary results of numerical experiments show significant differences of the three outlined modes in the northern North Atlantic and especially in the Norwegian Greenland Seas (NGS). The overturning strength of the North Atlantic salinity conveyor belt and northward heat transport decreased somewhat in the LGM and drastically in the MWE case. Accordingly, the North Atlantic Deep Water production decreased by 30% during the LGM and almost ceased at the MWE. The climatologically most important changes occurred during the MWE and are characterized by a reversal in the circulation of the surface water in the northeastern part of the NGS, implying that the North Atlantic Current did not reach the Norwegian Sea anymore.
The influence of canyons on shelf currents: A theoretical study
Authors: Chen Xiaoyang , Allen Susan E.
Published: February 2004

The influence of submarine canyons on shelf currents is studied using the Rossby adjustment method for a homogeneous, inviscid fluid on an f plane. The canyon in the model is assumed to have vertical edges and constant width. The geostrophic flow around a canyon is found to be dependent upon two geometric parameters: the ratio of the depth of the canyon to the depth of the shelf and the ratio of the width of the canyon to the Rossby radius over the canyon. Moreover, a single parameter determines most of the properties of the geostrophic state. This parameter is called the canyon number and is a combination of the two basic geometric parameters. In the geostrophic state an infinitely long flat‐bottom canyon will act as a complete barrier to an approaching shelf flow. The approaching flow is asymmetrically diverted along the canyon, and a net flux is generated to the left of the flow in the northern hemisphere. If the canyon cuts a shelf between the shelf break and the coast and connects to a strait (the geometry of Juan de Fuca Canyon) an in‐canyon (out‐canyon) current will be generated when the shelf break current flows keeping the shelf at its left (right) in the northern hemisphere. If the canyon has a stepped or sloped bottom, the geostrophic flow has a singularity where the step or slope meets the left canyon edge (looking upcanyon) in the northern hemisphere. Flow can cross the canyon edge through the singularity, so the canyon is no longer a complete barrier to the approaching shelf flow. In this case, as above, a net flux is generated to the left of the approaching shelf flow.
Bromoperoxidase and iodoperoxidase enzymes and production of halogenated methanes in marine diatom cultures
Authors: Moore R. M. , Webb M. , Tokarczyk R. , Wever R.
Published: February 2004

Halogenated methanes produced in the oceans are important as carriers of chlorine, bromine, and iodine into the atmosphere. There they play roles in the regulation of ozone in the stratosphere and perhaps in the Arctic troposphere at polar sunrise. While the mechanisms for the production of some polyhalogenated compounds by marine macrophytes have previously been substantially elucidated, the same has not been true in the case of marine phytoplankton. We describe laboratory experiments on the production of various brominated and iodinated compounds in cultures of marine diatoms, obtained from the Provasoli‐Guillard Center for Culture of Marine Phytoplankton collections (Bigelow Laboratory for Ocean Sciences, Maine, USA; CCMP). Species examined included Nitzschia sp. (CCMP 580), Nitzschia arctica, Porosira glacialis, and two Navicula sp. (CCMP 545 and 546). A suite of brominated compounds, notably bromoform and dibromomethane, is produced by the Nitzschia and Porosira species. Nitzschia sp.(CCMP 580) was grown in sufficient quantities to allow the identification of a bromoperoxidase enzyme, which is assumed to be responsible not only for the CHBr3 and CH2Br2 production but also for CH2I2 which was measured in those cultures. Chloroiodomethane was produced, either directly by the algae or by a photochemical reaction of CH2I2. One Navicula species (CCMP 545), found to produce CH2I2 and CH2ClI, was shown to possess an iodoperoxidase. Bromoform and dibromomethane were not detected in cultures of this species. Other compounds produced in certain of these non axenic cultures included methyl and ethyl iodide, and bromoiodomethane.
Satellite retrieval of inherent optical properties by linear matrix inversion of oceanic radiance models: An analysis of model and radiance measurement errors
Authors: Hoge Frank E. , Lyon Paul E.
Published: February 2004

The linear summability of inherent optical properties (IOPs) is exploited to provide matrix equations for retrieval of phytoplankton absorption, dissolved organic matter, and constituent backscatter. Spectral models for the phytoplankton pigment absorption coefficient, chromophoric dissolved organic matter (CDOM) absorption coefficient, and total constituent backscatter (TCB) coefficient are first used to calculate 5 × 105 water‐leaving spectral radiances for a wide range of normally distributed IOP values at 410, 490, and 555 nm. Then, the spectral radiances are inverted to simultaneously provide phytoplankton pigment absorption coefficient, CDOM absorption coefficient, and total constituent backscatter coefficient on a pixel‐by‐pixel basis to demonstrate that (1) matrix inversion is very rapid and well conditioned, (2) the IOPs are exactly determined when the water‐leaving radiances and IOP spectral models are error free, (3) for equal radiance errors sequentially occurring in one of three sensor bands, phytoplankton pigment retrieval errors are generally higher than CDOM and TCB coefficient errors, (4) retrieval errors for all the IOPs are strongly dependent on phytoplankton pigment spectral model Gaussian width errors, (5) phytoplankton pigment absorption and CDOM absorption retrieval errors are more sensitive to CDOM spectral slope errors than the TCB coefficient retrievals, and (6) TCB wavelength‐ratio‐exponent errors produce less impact on the phytoplankton absorption coefficient retrieval than upon the CDOM absorption or the TCB coefficient retrievals.
Numerical simulation of the dynamics of sea spray over the waves
Authors: Mestayer P. G. , Van Eijk A. M. J. , De Leeuw G. , Tranchant B.
Published: February 2004

SeaCluse is a code describing and quantifying the nonlinear interactions between spray droplet concentrations and the scalar fields of water vapor concentration and temperature in the marine atmospheric surface layer as a function of the basic micrometeorological parameters. It is currently developed to simulate most of the dynamics of the evaporating sea spray droplets, their transformations, and their influence on the structure of the marine lower atmosphere. It includes two parts, a “preprocessor” computing the air flow structure and droplet trajectories over the waves in the absence of turbulence and evaporation, and a “main program” computing along the vertical the horizontally averaged budgets of droplet and water vapor concentrations, and sensible heat, including the dynamic and thermodynamic air‐droplet interactions. This paper presents the first simulations, without evaporation, which reveal several characteristic features of the spray droplet dynamics over the waves. The mean air flow induced by the wave motion generates an efficient transport of many droplets up to the wave crest level or slightly higher, where they accumulate. In contrast, turbulence appears to be a rather inefficient process to elevate further the droplets that have nonnegligible weight and inertia (and an efficient process for very small droplets). The residence times in the air Tfly of droplets larger than 90 μm in radius do not increase much, compared to their values in still air or over a flat surface, and they increase with increasing wind speed much less rapidly than the wave height Ho: Tfly ∼ U0.3 while Ho ∼ U2. Above the wave crest, the droplet concentrations are several orders of magnitude smaller than between wave troughs and crests. The precision of the turbulent diffusivity model for droplets therefore appears crucial to correctly infer the spray surface source function from concentration measurements in the atmosphere.
A nested primitive equation model of the Iceland‐Faeroe front
Authors: Fox Alan D. , Maskell Stephen J.
Published: February 2004

A fully two‐way interactive nested primitive equation model of the Iceland‐Faeroe region is described. The model consists of a fine grid (approximately 3 km resolution) model nested 3:1 within a coarse grid (approximately 9 km resolution) larger area model. The fine grid model has increased resolution in both the horizontal and vertical directions. This allows better representation of coastlines and bottom topography, as well as of the ocean fields and dynamics. The model nesting technique used is suitable for relatively short‐term applications, for example, ocean forecasting or studies of mesoscale ocean processes. The nesting technique is found to be robust, with little noise or distortion produced at the interfaces between the model regions. Results from the nested model are compared with those from a coarse grid only model. Introduction of the nested fine grid model is seen to produce benefits in the form of tightened frontal gradients, increased meandering, and increased eddy activity; greater overflow of cold bottom water southward over the Iceland‐Faeroe ridge is also observed in the nested model. Calculations of the heat and volume transports through the Iceland‐Faeroe‐Shetland region show significant differences between the nested model and the coarse grid reference model. When the nested model is run in one‐way interactive mode, with no feedback from the fine grid model to the coarse grid model, increased noise is generated at the boundaries of the fine grid model.
The buildup of the ice sheet in central Greenland
Authors: Souchez R.
Published: February 2004

A study of the isotopic and gas composition of the basal silty ice recovered by the Greenland Ice Core Project (GRIP) core indicates that local ice formed in the absence of the Greenland Ice Sheet is still preserved at Summit. Such ice developed most probably within a peat deposit in a permafrost environment. This local ice was subsequently intimately mixed with glacier ice from an advancing ice sheet progressing on the site. This is in agreement with the “highland origin and windward growth” hypothesis for ice sheet development, not for an in situ or regional growth from snowbanks. The basal ice from the GRIP core possibly dates back to the original buildup of the Greenland Ice Sheet 2.4 million years ago.
A simple model study of the Arctic Ocean freshwater balance, 1979–1985
Authors: Steele Michael , Thomas Don , Rothrock Drew , Martin Seelye
Published: February 2004

The freshwater budget of the Arctic Ocean from autumn 1979 to autumn 1985 is examined using a simple ice‐ocean model. The ice model, described in detail by Thomas et al. [this issue], uses data from drifting buoys to determine the velocity field and data from passive microwave satellites to determine the concentration field. The resulting fluxes of momentum and salt are then used to drive the ocean model. The model “grid” consists of seven broad regional cells in which we compute average quantities such as salinity profiles. The domain extends down to 200 m depth. The results indicate that the interannual variability of mixed layer salinity (MLS) is greater in the western Arctic than in the eastern Arctic. The interannual variability of MLS in the Arctic Ocean as a whole is quite small in this simulation but is still as large or larger than the trend predicted by Manabe et al. [1991] due to increasing atmospheric CO2. The results of our freshwater analysis indicate that there was an increase of 45% above the mean in the freshwater export through Fram Strait during 1982. This increase occurred in both the sea ice and ocean components, although mostly in the former. A decrease in the freshwater outflow through the Canadian Archipelago (which generally constitutes about 34% of the total) occurred at about the same time. Finally, a simple experiment was run in which river and precipitation fluxes were increased to the level predicted by Manabe et al. [1991] by the end of a 100‐year increased CO2 simulation. The resulting increase in oceanic freshwater flux through the Canadian Archipelago is about 60% more than that through the Fram Strait, which might have an influence on the preferred location for deep water formation in a warmer climate.
A quantitative description of sea ice inclusions
Authors: Perovich Donald K. , Gow Anthony J.
Published: February 2004

Structurally, sea ice consists of an ice matrix with inclusions of brine and air. A quantitative description of the size of these inclusions is critical for both interpreting and modeling the electromagnetic properties of sea ice. Photomicrographs of ice thin sections were analyzed using a personal computer‐based image‐processing system to determine the number of inclusions, the inclusion size distributions, and statistics for brine pockets in young ice and first‐year ice and for air bubbles in a multiyear hummock. Inclusions ranging in size from thousandths of square millimeters to a few square millimeters were measured. In all cases a two‐parameter lognormal distribution fits the cumulative inclusion size distributions well (correlation coefficient greater than 0.99). This includes brine pockets in both granular and columnar ice and a range of brine volumes from 2% to 40%. As ice warms, and its brine volume increases, the size distribution shifts toward larger brine pockets. This increase in brine pocket size is particularly pronounced for brine volumes greater than 10% as individual brine pockets coalesce. Air bubbles are much larger than brine pockets, with mean major axis lengths of the order of millimeters for air bubbles and tenths of a millimeter for brine pockets. Observations of inclusion shape factors indicate that, in general, brine pockets are more elongated than air bubbles.
Assimilating satellite concentration data into an Arctic sea ice mass balance model, 1979–1985
Authors: Thomas D. , Martin S. , Rothrock D. , Steele M.
Published: February 2004

Using satellite ice concentration data, observed buoy velocities, and a thermodynamic ice growth model, we compute the time histories of the thickness distributions of four ice types: level and ridged first‐year ice, and level and ridged multiyear ice. These histories are computed for seven regions covering the Arctic Ocean with a 10‐day time step for 1979 through 1985. A blend of observed buoy motions and wind‐driven, free‐drift velocities drives the advective and ridging parts of the model, while climatological growth and melt rates determine the ice thickness. The model adjusts the thickness distributions so that the modeled concentrations of open water, first‐year ice, and multiyear ice match the concentrations derived by Kalman filtering of satellite passive microwave observations. The major adjustment is to reduce modeled ice concentrations in summer and particularly in the peripheral seas to account for unmodeled melt. The model includes an ice salinity parameterization which, along with changes in ice volume, gives the salt or freshwater flux from the ice. Our results show that the Arctic ice cover consists primarily of multiyear ice, 60% by area and 82% by volume, and that most of this ice is ridged. The average ice thickness is 2.7 m with a seasonal variation of 30% and an interannual variation of 10%. The study also shows that for each cell and the Arctic as a whole, the changes in ice volume caused by growth minus melt approximately balance the changes caused by import minus export. The annual ice export through Fram Strait varies from 1100 to 3000 km3, primarily because of variations in ice velocity. All regions except the Chukchi Sea have a net ice growth, a net export, and a net salt input to the ocean surface. The annual mean salt flux to the ocean surface from net ice production is 7.3 kg m−2downward. Fluxes along the transpolar drift stream are larger than elsewhere; the largest downward flux of 33 kg m−2yr−1in the Nansen Basin can be attributed to the strong divergence near Fram Strait. A companion paper [Steele et al., this issue] uses these fluxes and ice velocities to derive the Arctic Ocean freshwater balance.
A well‐calibrated ocean algorithm for special sensor microwave / imager
Authors: Wentz Frank J.
Published: February 2004

I describe an algorithm for retrieving geophysical parameters over the ocean from special sensor microwave / imager (SSM/I) observations. This algorithm is based on a model for the brightness temperature TB of the ocean and intervening atmosphere. The retrieved parameters are the near‐surface wind speed W, the columnar water vapor V, the columnar cloud liquid water L, and the line‐of‐sight wind WLS. I restrict my analysis to ocean scenes free of rain, and when the algorithm detects rain, the retrievals are discarded. The model and algorithm are precisely calibrated using a very large in situ database containing 37,650 SSM/I overpasses of buoys and 35,108 overpasses of radiosonde sites. A detailed error analysis indicates that the TB model rms accuracy is between 0.5 and 1 K and that the rms retrieval accuracies for wind, vapor, and cloud are 0.9 ms−1, 1.2 mm, and 0.025 mm, respectively. The error in specifying the cloud temperature will introduce an additional 10% error in the cloud water retrieval. The spatial resolution for these accuracies is 50 km. The systematic errors in the retrievals are smaller than the rms errors, being about 0.3 ms−1, 0.6 mm, and 0.005 mm for W, V, and L, respectively. The one exception is the systematic error in wind speed of −1.0 ms−1 that occurs for observations within ±20° of upwind. The inclusion of the line‐of‐sight wind WLS in the retrieval significantly reduces the error in wind speed due to wind direction variations. The wind error for upwind observations is reduced from −3.0 to −1.0 ms−1. Finally, I find a small signal in the 19‐GHz, horizontal polarization (hpol) TB residual ΔTBH that is related to the effective air pressure of the water vapor profile. This information may be of some use in specifying the vertical distribution of water vapor.
Seasonal and interannual variations of the oceanic heat flux under a landfast Antarctic sea ice cover
Authors: Heil Petra , Allison Ian , Lytle Victoria I.
Published: February 2004

A multilayer thermodynamic model is used to simulate sea ice growth for 12 years between 1958 and 1986 in the vicinity of the Australian station Mawson on the coast of East Antarctica. The atmospheric forcing data for the model are derived from radiosonde profiles and from surface measurements. Global radiation data are available for 4 years, and we use these measurements for comparison with the results of a Zillman‐type model for global radiation. Combining the thermodynamic model with sea ice thickness measurements for 12 years, we solve the energy balance equation for the oceanic heat flux. The oceanic heat flux is not constant but changes with time within the year and from year to year. The oceanic heat flux averages 7.9 W/m2, and the yearly means vary between 5 and 12 W/m2. Seasonal values of the oceanic heat flux range from 0 to 18 W/m2. From the yearly averaged values a decadal trend is evident: During the first years that were analyzed the yearly average lies well above 10 W/m2; then in the mid‐1970s a decrease to 9 W/m2 occurs, while for all later years the values are ∼6–8 W/m2. In general, the oceanic heat flux increases from the start of the fast ice formation season in early April until it breaks out in December or January. To compare the calculated oceanic heat fluxes for different years, we divide the total ice season into three characteristic time regimes of the sea ice growth and calculate the averaged oceanic heat fluxes for each regime. For the first regime (through August) the mean flux is 2.7 W/m2, for the middle regime (September) it is 8.4 W/m2, and for the final regime (October–January) it is 17 W/m2. We discuss the results of our model calculations in conjunction with current meter observations, which give evidence of seasonally varying intrusions of relatively warm Circumpolar Deep Water into Prydz Bay. Comparison of passive microwave data of sea ice extent and concentration (from the scanning multichannel microwave radiometer sensor) with the model results reveals a correlation between the magnitude of the oceanic heat flux and local features such as polynyas.
Correlation scales, objective mapping, and absolute geostrophic flow in the California Current
Authors: Chereskin T. K. , Trunnell M.
Published: February 2004

The spatial covariances of the time‐dependent density and geostrophic velocity fields off southern California are determined from a unique set of repeated hydrographic observations (44 cruises) made by the California Cooperative Oceanic Fisheries Investigations from 1984 to 1994. The covariances and objective analysis are used to combine direct velocity observations, from shipboard acoustic Doppler current profiler (ADCP) measurements made on a recent survey (October 1993), with hydrographic observations. The analysis reduces ageostrophic noise in the ADCP velocities by smoothing and enforcing horizontal nondivergence; additionally, the velocities are mapped over scales that are dynamically consistent with the hydrography. Maximum surface geostrophic flow in the California Current in October 1993 is about 35 cm s−1, 50% larger than that estimated assuming a 500‐m level of no motion. Absolute flow at 500 m is O(10 cm s−1) and indicates that the surface eddy field penetrates through the thermocline. Uncertainty in the geostrophic reference calculated from the ADCP measurements is of O(4 cm s−1). The velocity residual (objectively analyzed minus raw ADCP estimates) exhibits smaller correlation scales than the geostrophic flow.
Statistical analysis of the surface circulation of the California Current
Authors: Swenson Mark S. , Niiler Pearn P.
Published: February 2004

We use a set of mixed‐layer drifting buoy trajectories from the California Current (20°N–40°N) during 1985–1990 to obtain statistically reliable estimates of the mean currents, the mean variance field, and the geographically varying diffusivity, integral timescales, and integral space scales. Typical values for the diffusivity are 1.1–8.7 × 107 cm2 s−1, while the timescales and space scales are 2.1–7.1 days and 16–59 km, respectively. The variance field displays a strong westward gradient out to 125°W, and diffusivity shows a tendency to decrease toward the southwest part of the domain. Significant anisotropy is found in the variance field near the coastal boundary and at 30°N, 130°W, which is the region where the subarctic and northern subtropical fronts approach the California Current. The antisymmetric component of the diffusivity tensor indicates that cyclonic eddies dominate the mesoscale signature of drifters in this region. We seek simple parameterizations to relate the scales of motion of the random velocity field to the diffusivity by testing least squares fits to κ∞ ∝ u02T and κ∞ ∝ u0L, where u02 is the velocity variance. We found no cases for which these two hypotheses could be distinguished. For the meridional component the linear regressions are not successful, which suggests that the meridional departure velocities result from a flow regime that is significantly organized by, for example, waves or coherent structures. A subset of the drifters measured temperature along their tracks, and we use the resultant data to produce the first direct estimates of the horizontal eddy heat flux divergence based on Lagrangian estimates. In addition, we separately compute the “eddy diffusivity” parameterization of the eddy heat flux divergence, ∇ · 〈u′θ′〉 = ∇(κ∇Θ), using our diffusivity estimates and a sea surface temperature climatology. The two independent terms agree well, which provides a measure of reassurance about the diffusivity estimates. The eddy heat flux divergence in the California Current is very small (<5 W m−2) and does not appear to be significant in the long‐term heat budget of the upper ocean in this region.
Determination of surface turbulent fluxes for the Tropical Ocean‐Global Atmosphere Coupled Ocean‐Atmosphere Response Experiment: Comparison of satellite retrievals and in situ measurements
Authors: Clayson C. A. , Curry J. A.
Published: February 2004

A new approach is introduced for determining from satellite the turbulent fluxes of heat, moisture, and momentum at higher frequencies and spatial resolution than have been reported previously. Values of “skin” sea surface temperature, surface wind speed, surface air temperature, and surface water vapor mixing ratio are required inputs for a bulk turbulence flux model based on surface renewal theory. Each of these input variables is determined from satellite. Multiple satellite sensors, model results, and diagnostic studies of in situ and satellite observations are used to determine the optimal manner in which to determine the input parameters. The diurnal cycle of SST is determined to vary with peak solar insolation, daily‐average precipitation, and daily‐average wind speed. The static stability of the atmospheric surface layer is hypothesized to be reflected in the cloud characteristics and thus is determined to depend on cloud top temperature and whether or not it is raining. The validity of the satellite‐derived surface fluxes and input parameters are examined using in situ measurements in the western equatorial Pacific Ocean made during the Tropical Ocean‐‐Global Atmosphere Coupled Ocean‐‐Atmosphere Response Experiment. Pixel‐scale comparisons of the satellite fluxes with the ship fluxes show biases that are within the accuracy of the ship measurements. An attempt is made to determine daily‐averaged fluxes from satellite, which is complicated by the fact that some of the satellite‐derived input variables are obtained from polar‐orbiting satellites with at best twice daily coverage in the tropics. Judicious interpolation allows reasonable daily‐averaged fluxes to be obtained from satellite on a spatial scale of 50 km.
A simple model of mixing in stratified tidal flows
Authors: Monismith Stephen G. , Fong Derek A.
Published: February 2004

We use a simple model of vertical mixing in a stratified tidal flow to study flows that might be observed in shallow estuaries. In the model, flow is driven by a specified surface pressure gradient due to barotropic tidal motions. The model incorporates two means for accomplishing vertical mixing: (1) shear instability and (2) bottom mixed‐layer deepening by turbulence produced at the estuary bottom and in the shear layer at the top of the mixed layer. We discuss model results that show how the combined action of shear instability and tidal “stirring” accomplishes vertical mixing. The interaction between the instabilities that develop because of the substantial tidal timescale velocity shear caused by stratification is the key feature of mixing. Shear instability weakens the stability of the mixed layer, allowing stirring to efficiently entrain lighter fluid into the mixed layer. The importance of shear is found to depend on the stability of the water column and on the relative importance of frictional forces.
Sources of variability in the column photosynthetic cross section for Antarctic coastal waters
Authors: Claustre Hervé , Moline Mark A. , Prézelin Barbara B.
Published: February 2004

Using a highly resolved Long Term Ecological Research (LTER) database collected near Palmer Station, Antarctica, from 1991 to 1994, the variability in the column photosynthetic cross section (Ψ*, m2 g Chl α−1) was analyzed. The relationship between the daily integrated primary production rates versus the product of surface irradiance (QPAR(0+)) and the integrated chlorophyll content (down to 0.1% QPAR(0+)) gave a Ψ* value of 0.0695 m2 g Chl α−1 (r2=0.85, p<0.001, n=151) which is similar to those determined for temperate and tropical seas. However, the average value of single Ψ* estimates is higher (0.109±0.075 m2 g Chl α−1) with extreme values extending over a fiftyfold range (0.009–0.488 m2 g Chl α−1). The possible drivers of this variability are analyzed in detail, considering variables which are presently used in biooptical models (e.g., surface irradiance and chlorophyll content) and those which are not (taxonomic composition). A sixfold variation in Ψ* was observed with time of year and strongly associated with the high seasonality in incident irradiance characteristic of these polar sampling sites. Variability in daily incident irradiance as influenced by cloudiness and variation in chlorophyll content were responsible for an additional twofold variation in Ψ*. Finally, the taxonomic dependency of Ψ* was demonstrated for the first time. For identical chlorophyll content and surface irradiance, mean Ψ* values of 0.114±0.051 m2 g Chl α−1 were recorded for diatom blooms and 0.053±0.011 m2 g Chl α−1 for cryptophyte‐dominated populations. Results illustrate the validity of Ψ*‐based approaches for estimating primary production for the Southern Ocean but emphasize the need to address taxonspecific photophysiology to better estimate primary production on smaller spatio‐temporal scales.
A modeling study of tidally driven estuarine exchange through a narrow inlet onto a sloping shelf
Authors: Wheless Glen H. , Valle‐Levinson Arnoldo
Published: February 2004

The circulation and particle transport through a narrow inlet (Kelvin number < 0.5) and onto a sloping shelf are numerically examined using a three‐dimensional hydrodynamic model. The model domain consists of an estuarine basin with vertical density stratification separated from a well‐mixed sloping shelf by a narrow inlet. Forcing is supplied by semidiurnal tides and buoyancy differential. Strong ebb flows resulting from this combined forcing transport estuarine water seaward through the inlet to form a radially spreading buoyant surface plume over the shelf. A series of radial density fronts corresponding with the ebbing tidal outflow are found on the seaward side of the inlet mouth and are convergence zones for floating particles. Strong anticyclonic frontal flow advects particles around the boundary of the outflow plume. Particles released nearest the seaward side of the inlet mouth are able to enter the inlet at depth and remain, while those particles released farther offshore rarely enter the inlet. This result has clear implications for the shelf‐to‐estuary transport of pollutants or the larval phase of marine species. Asymmetric tidally induced eddies which appear on both sides of the inlet also contribute to the near‐field circulation. Calculations of gradient Richardson number in the inlet show that regions susceptible to enhanced mixing occur during periods of maximum tidal velocities due to increased shear.
The tides in the Arctic Ocean from a finite element model
Authors: Lyard Florent H.
Published: February 2004

The two main diurnal (i.e., K1 and O1) and semidiurnal (i.e., M2 and S2) tidal waves have been computed from a hydrodynamic, finite element, spectral model. The spatial resolution of the model varies from a few kilometers at the coastline to 100 km in the deepest regions. An optimization of the open boundary conditions has been performed to improve the solution accuracy. The bottom topography used in this model has been originally extracted from the Earth Topography 5‐minutes Grid (ETOPO5) and corrected from various sources of data. The impact of the input parameters like the friction coefficient, the loading effects, and the parameterisation of the additional friction due to the Arctic ice cover is investigated. The tidal elevations are compared to a set of in situ observations and validated. They also are compared to the Kowalik and Proshutinsky [1993] model. These comparisons mainly show good agreement between the two models. Nevertheless, significant differences are observed where small wavelength structures are produced by the topographic trapping of the tidal energy. The velocities associated with the elevations are also presented. The potential rate of work, the dissipation, and the energy fluxes are computed from these elevations and velocities. Because of the uncertainties of the velocities at the open boundaries, we are restricted to a qualitative analysis of the energy equation terms, which appears to be consistent with the previous studies on Arctic tides.
The thickness distribution of sea ice and snow cover during late winter in the Bellingshausen and Amundsen Seas, Antarctica
Authors: Worby A. P. , Jeffries M. O. , Weeks W. F. , Morris K. , Jaña R.
Published: February 2004

Data collected from a voyage of RV Nathaniel B. Palmer to the Bellingshausen and Amundsen Seas during August–September 1993 are used to investigate the thickness distribution of sea ice and snow cover and the processes that influence the development of the first‐year pack ice. The data are a combination of in situ and ship‐based measurements and show that the process of floe thickening is highly dependent on ice deformation; in particular, rafting and ridging play important roles at different stages of floe development. Rafting is the major mechanism in the early stages of development, and core structure data show the mean thickness of individual layers of crystals to be only 0.12 m. Most ice <0.3 m is not ridged but is usually rafted before attaining this thickness, well before thermodynamic growth has ceased. In thicker floes, ridging is more common, with most floes >0.6 m having some surface deformation. Blocks within ridge sails are typically in the range 0.3–0.6 m thick, and ship‐based observations estimate approximately 25% of the pack exhibits surface ridging. When corrected for biases in the observational methods, the data show that the dominant ice and snow thickness categories are >0.7 m and 0.2–0.5 m, respectively, and account for 40% and 36% of the surface area of the pack ice. Approximately 8% of the pack is open water. An estimate of the effects of ridging on the distribution of ice mass within the pack suggests that between 50 and 75% of the total mass is contained within the 25% of the pack that exhibits surface ridging.
Hydrostatic, quasi‐hydrostatic, and nonhydrostatic ocean modeling
Authors: Marshall John , Hill Chris , Perelman Lev , Adcroft Alistair
Published: February 2004

Ocean models based on consistent hydrostatic, quasi‐hydrostatic, and nonhydrostatic equation sets are formulated and discussed. The quasi‐hydrostatic and nonhydrostatic sets are more accurate than the widely used hydrostatic primitive equations. Quasi‐hydrostatic models relax the precise balance between gravity and pressure gradient forces by including in a consistent manner cosine‐of‐latitude Coriolis terms which are neglected in primitive equation models. Nonhydrostatic models employ the full incompressible Navier Stokes equations; they are required in the study of small‐scale phenomena in the ocean which are not in hydrostatic balance. We outline a solution strategy for the Navier Stokes model on the sphere that performs efficiently across the whole range of scales in the ocean, from the convective scale to the global scale, and so leads to a model of great versatility. In the hydrostatic limit the Navier Stokes model involves no more computational effort than those models which assume strict hydrostatic balance on all scales. The strategy is illustrated in simulations of laboratory experiments in rotating convection on scales of a few centimeters, simulations of convective and baroclinic instability of the mixed layer on the 1‐ to 10‐km scale, and simulations of the global circulation of the ocean.