bluuebunny/crossref_metadata_2025 huggingface dataset:
Atmospheric and oceanic forcing of Weddell Sea ice motion
Authors: Kottmeier C. , Sellmann Lutz
Published: February 2004

The data from sea ice buoys, which were deployed during the Winter Weddell Sea Project 1986, the Winter Weddell Gyre Studies 1989 and 1992, the Ice Station Weddell in 1992, the Antarctic Zone Flux Experiment in 1994, and several ship cruises in Austral summers, are uniformly reanalyzed by the same objective methods. Geostrophic winds are derived after matching of the buoy pressure data with the surface pressure fields of the European Centre for Medium Range Weather Forecasts. The ratio between ice drift and geostrophic wind speeds is reduced when winds and currents oppose each other, when the atmospheric surface layer is stably stratified, and when the ice is under pressure near coasts. Over the continental shelves, the spatial inhomogeneity of tidal and inertial motion effectively controls the variability of divergence for periods below 36 hours. Far from coasts, speed ratios, which presumably reflect internal stress variations in the ice cover, are independent of drift divergence on the spatial scale of 100 km. To study basin‐scale ice dynamics, all ice drift data are related to the geostrophic winds based on the complex linear model [Thorndike and Colony, 1982] for daily averaged data. The composite patterns of mean ice motion, geostrophic winds, and geostrophic surface currents document cyclonic basin‐wide circulations. Geostrophic ocean currents are generally small in the Weddell Sea. Significant features are the coastal current near the southeastern coasts and the bands of larger velocities of ≈6 cm s−1 following the northward and eastward orientation of the continental shelf breaks in the western and northwestern Weddell Sea. In the southwestern Weddell Sea the mean ice drift speed is reduced to less than 0.5% of the geostrophic wind speed and increases rather continuously to 1.5% in the northern, central, and eastern Weddell Sea. The linear model accounts for less than 50% of the total variance of drift speeds in the southwestern Weddell Sea and up to 80% in the northern and eastern Weddell Sea.
Generation of intermediate water vortices in a rotating stratified fluid: Laboratory model
Authors: Afanasyev Y. D. , Filippov I. A.
Published: February 2004

We hypothesize that a formation mechanism of anticyclonic eddies (lenses) is the outflow of intermediate waters down the canyons of the continental shelf. We reproduced in the laboratory the horizontal injection of fluid into the rotating stratified surroundings at the equilibrium density level. The experiments demonstrate that such an injection forms an anticyclonic eddy. Measurements of the velocity field show that the core of the eddy is almost axisymmetric and is in solid body rotation. The periphery of the eddy is formed by the jet flow. Cyclonic satellites were also observed at the periphery of the eddy. The main features of the laboratory flow are consistent with those of the “young” eddy observed recently in the Gulf of Cadiz.
A robust method for diagnosing regional shelf circulation from scattered density profiles
Authors: Sheng Jinyu , Thompson Keith R.
Published: February 2004

We present a straightforward method for estimating surface circulation on an f plane from a set of irregularly spaced vertical density profiles. The first step is to express bottom density ρh as the sum of a mean
for a given water depth h and an anomaly,
. Sea level η can then be decomposed into a dynamic height
relative to a deep reference level and a correction term,
. The dynamic height is estimated using a generalization of the method of Helland‐Hansen [1934] for diagnosing flow through a cross‐shelf section under the assumption of zero bottom geostrophic flow. The correction η′ satisfies a two‐dimensional elliptic partial differential equation forced by the bottom density anomaly, wind stress and the open boundary conditions. Before calculating the density‐driven component of η′ we first test if the ρ′h are statistically different from uncorrelated noise. If they are not, the correction associated with the bottom density anomaly is set to zero. Thus the method has a degree of robustness to errors in the density observations. If the ρ′h have well‐defined spatial structure the elliptic equation is solved for η′ and sea level is equated to
. Note that even if this last step is required the only gridding of the density data is two‐dimensional. This makes the proposed method simpler to use than many of the existing diagnostic models which require a three‐dimensional gridding of the observed density profiles. To test the method, we use it to diagnose the flow from an idealized density field overlying an isolated topographic feature. The predicted sea level and flow fields are then compared, and shown to be in good agreement, with results from the Princeton Ocean Model. The method is then used to diagnose the winter surface circulation on the Scotian Shelf from observed density profiles. The reliability of the diagnosed flow pattern is assessed by comparing it against all available near‐surface current measurements. The differences between the observed and diagnosed currents are used to estimate the remotely forced circulation on the Scotian Shelf. It is shown that the main features of the circulation can be explained by gradients in the density field. Remote forcing is important near the coast and the shelf break. The effect of local wind is relatively weak.
A synoptic atmospheric surface forcing data set and physical upper ocean model for the U.S. JGOFS Bermuda Atlantic Time‐Series Study site
Authors: Doney Scott C.
Published: February 2004

An atmospheric surface forcing data set with synoptic temporal resolution is constructed for the U.S. Joint Global Ocean Flux Study (JGOFS) Bermuda Atlantic Time Series (BATS) site for 1988–1992. The forcing data set is based primarily on the 6‐hourly European Centre for Medium Range Weather Forecasts (ECMWF) operational analysis, daily cloud fraction and surface insolation estimates from the International Satellite Cloud Climatology Project, and monthly derived satellite precipitation estimates from the microwave sounding unit. Good agreement is found between the ECMWF surface properties (e.g., wind speed, air temperature) and synoptic meteorological data from the Bermuda airport and Comprehensive Ocean‐Atmosphere Data Set (COADS) ship reports, though the analysis tends to damp the amplitude of extreme weather events. Monthly air‐sea heat and freshwater flux estimates are generally consistent with climatological estimates for the BATS region. The diagnosed net heat and freshwater fluxes from the BATS conductivity‐temperature‐depth data show significant additional month to month variability that is not related to local atmospheric forcing but appears to arise from mesoscale advection. The surface forcing data set is then coupled to a one‐dimensional upper ocean boundary layer model, and the resulting simulations quantitatively reproduce much of the observed behavior of sea surface temperature, heat content, and mixed layer depth for the BATS site for the period October 1988 through September 1992. The induced variability in the ocean model on diurnal and storm timescales is analyzed, and the impact of using the ECMWF analysis data rather than synoptic ship or mooring observations is also examined. The main deficiencies in the simulation are related to the influence of advective events in the BATS record and to possible shifts in the ECMWF model, and preliminary techniques for addressing these problems by incorporating the horizontal advective effects are presented. The difficulties associated with directly verifying local one‐dimensional models using coarsely sampled time‐series data is also discussed.
Deep water properties near 35°N, 143°E, observed during the Kuroshio Extension Regional Experiment
Authors: Shiller A. M. , Teague W. J. , Hallock Z. R.
Published: February 2004

Deep water measurements were obtained from a closely spaced conductivity‐temperature‐depth hydrographic section that crossed the Japan Trench and the Kuroshio in the vicinity of the Kashima 1 Seamount near 35°N, 143°E. Vertical sections of temperature, salinity, density, oxygen, and nutrients are discussed for water below 1000 m. At the northwestern extreme of the section, the existence of a southward‐flowing deep western boundary current is suggested by the silica distribution as well as by geostrophic calculations. In the vicinity of the seamount, hydrographic properties are perturbed and contrasting variabilities are found in the deep water characteristics along the section. The measurements also suggest a deep northward flow associated with the trench. Current meter observations [Hallock and Teague, 1996] along the section lend credence to these interpretations. These observations help piece together an overall picture of the deep and abyssal circulation of the northwest Pacific.
Seasonal seawater optical properties of the U.S. Middle Atlantic Bight
Authors: DeGrandpre M. D. , Vodacek A. , Nelson R. K. , Bruce E. J. , Blough N. V.
Published: February 2004

Optical properties of seawater in the U.S. Middle Atlantic Bight (MAB) were measured during four cruises spanning 1993–1994. Samples were collected in August and November 1993 and March and April 1994 along a cruise track extending from Delaware Bay to the Sargasso Sea. Each sample was analyzed for colored dissolved organic matter (CDOM) and particulate absorption and chlorophyll a (chl a). In situ attenuation and reflectance were also measured at selected stations using underwater spectroradiometers. The overall seasonal and spatial ranges for CDOM and particulate absorption (442 nm) and chl a concentration were 0.02–0.41 m−1, 0.01–0.49 m−1, and 0.07–9.4 mg m−3, respectively. CDOM absorption ranged from twofold to threefold between seasons on the MAB shelf, whereas particulate absorption ranged from threefold to sevenfold at the same locations. The results indicate that although CDOM absorption often dominated water column light attenuation at chl a absorbing wavelengths (e.g., 442 nm), chl a could be estimated from in situ reflectance spectra with an average error of ±20% using a relationship previously determined for coastal and open ocean waters. It appears that reflectances at 442 nm (R442) within the MAB shelf are typically low and invariable and most of the chl a sensitivity is contained in the ratio denominator (R554), resulting in relative insensitivity to CDOM absorption. Furthermore, CDOM absorption could not be explicitly determined using reflectance ratios (R412/R490); rather, the reflectance ratios correlated more closely with total (CDOM plus particulate) absorption.
Preservation efficiencies and accumulation rates for biogenic silica and organic C, N, and P in high‐latitude sediments: The Ross Sea
Authors: DeMaster David J. , Ragueneau Olivier , Nittrouer Charles A.
Published: February 2004

Rates of biogenic sediment accumulation (biogenic silica and organic C, N, and P) and pore water flux have been established for a variety of depositional environments in the Ross Sea. On the basis of 14C measurements in kasten cores, sediment accumulation rates ranged from 250 cm kyr−1 in the coastal basin of Granite Harbor to 1–2 cm kyr−1 in the shelf and slope environments of the northern and eastern Ross Sea. Burial of biogenic material was most rapid in the southwestern Ross Sea, where biogenic silica accumulation rates ranged from 2 to 31 g cm−2 kyr−1 and organic carbon accumulation rates ranged from 0.05 to 1.4 g cm−2 kyr−1. In the northern and eastern Ross Sea, biogenic silica and organic carbon accumulation rates typically equaled 0.02–0.03 g SiO2 cm−2 kyr−1 and 0.002–0.004 g C cm−2 kyr−1. Flux core measurements were used to estimate seabed regeneration rates for biogenic silica, organic carbon, and phosphorus. Pore water fluxes, in general, showed much less variability across the Ross Sea than did the biogenic accumulation rates. Pore water silicate fluxes in the study area ranged from 0.6 to 5.3 g SiO2 cm−2 kyr−1, whereas carbon fluxes ranged from 0.1 to 1.2 g C cm−2 kyr−1 and phosphate fluxes varied from −0.006 to 0.012 g P cm−2 kyr−1. Seabed preservation efficiencies were calculated for biogenic silica, organic carbon, and phosphorus by combining the solid‐phase and pore water data. The seabed preservation efficiencies for biogenic silica (1–86%) were greater than for organic carbon (1–71%) at all nine stations examined. The preferential preservation of biogenic silica relative to organic carbon also was apparent in Ross Sea sediments because the biogenic silica/organic carbon ratio in the material buried in the seabed generally was 2 times greater than the ratio in sediment particles arriving at the sediment‐water interface. Sediment accumulation rate correlated strongly with both the biogenic silica and the organic carbon preservation efficiency data. P preservation efficiencies remained relatively high (24–65%) even when the accumulation rates were low (1–2 cm kyr−1) because of the near‐zero phosphate fluxes out of the seabed. Of the total P in the seabed (0.04–0.09 wt. %), approximately 25% existed in the form of organic P. The total amount of biogenic silica accumulating on the Ross Sea shelf is ∼2.3 × 1012 g SiO2 yr−1, which is approximately an order of magnitude less than the Ledford‐Hoffman et al. [1986] estimate that was based on 210Pb chronologies. Biogenic silica accumulation rates in the southern, central, and western Ross Sea increased during the mid and late Holocene, reaching their maximum values during the past 500 to 1000 years.
Remotely sensed surface currents in Monterey Bay from shore‐based HF radar (Coastal Ocean Dynamics Application Radar)
Authors: Paduan Jeffrey D. , Rosenfeld Leslie K.
Published: February 2004

Near‐surface currents in Monterey Bay derived from a network of shore‐based HF radars are presented for August–December 1994 and compared with those from April to September 1992. Focus is placed on the low‐frequency (2‐ to 30‐day period) motions in the remotely sensed data and on comparison of radar‐derived currents with moored current and wind observations, ship‐based acoustic Doppler current profiler observations, satellite‐based surface temperature imagery, and surface drifter velocities. The radar‐derived picture of the late summer mean flow is very similar in the two realizations and is consistent with historical data. Flow is equatorward in the outer part of the bay, poleward in a narrow band nearshore, and very sluggish in the middle of the bay. Low‐pass‐filtered time series of radar‐derived currents are highly correlated with moored current observations and with winds in the outer part of the bay. The vector time series are also coherent across a broad frequency band with currents typically in phase between 1‐ and 9‐m depths and with 1‐m currents typically 40°–60° to the right of the wind. Overall, these results confirm the utility of Coastal Ocean Dynamics Applications Radar (CODAR)‐type HF radars for the study of coastal surface currents out to ranges ∼50 km from shore, particularly for highly averaged fields. Data variability and comparison with in situ observations for high‐frequency (1‐ to 48‐hour period) motions point to the need to better characterize and minimize sources of error in the radar observations.
Observed wavenumber‐frequency properties of microwave backscatter from the ocean surface at near‐grazing angles
Authors: Frasier Stephen J. , McIntosh Robert E.
Published: February 2004

This paper presents microwave observations of the ocean surface obtained with a high‐resolution X band imaging Doppler radar during March 1994. Besides providing time‐series imagery of the ocean surface, the radar has sufficient spatial resolution to produce wave vector‐frequency (three‐dimensional) spectra of observed power and Doppler frequency modulations due to the wind waves. The wave vector‐frequency spectra provide a complete representation of the mean spatio‐temporal properties of vertically polarized X band ocean backscatter at near‐grazing incidence. Evident in the spectra are the expected contributions from linear gravity waves exhibiting high coherences between power and Doppler (orbital) velocity and consistent with the composite‐surface‐model view of sea surface microwave backscatter. Occasionally, gravity wave harmonics possibly indicative of wave nonlinearities are observed. Also readily identified in the spectra are spatially broadband modulations due to localized scattering sources which are influenced by young gravity waves and the wind. Contributions from these apparently “non‐Bragg” scattering sources account for a significant part of the observed coherent modulations. The propagation velocity of this modulation is consistent with scattering from short gravity waves well beyond the spectral peak.
Comparison between weather buoy and Comprehensive Ocean‐Atmosphere Data Set wind data for the west coast of Canada
Authors: Cherniawsky Josef Y. , Crawford William R.
Published: February 2004

We describe surface wind data from Canadian weather buoys in the northeast Pacific and compare monthly mean wind speed and direction during 1987 to 1992 from these buoys with monthly mean values in the Comprehensive Ocean‐Atmosphere Data Set (COADS). The latter is based mainly on data from volunteer observing ships (VOS), binned in 2° × 2° squares. The number of VOS observations in each square in Hecate Strait, Dixon Entrance, and Queen Charlotte Sound is too low to produce reliable averages. Near other buoys we find COADS wind speeds to be higher than buoy wind speeds by about 1 to 2 m s−1. This difference shows some dependence on wind speed and is in qualitative agreement with previous comparisons between VOS and weather buoy winds. In addition, we find direction‐dependent differences in wind direction, with COADS wind vectors to the right of buoy wind vectors for alongshore winds from the northwest near the Vancouver Island coast. These results suggest that high placement of anemometers (above 25–30 m) on large modern vessels is partly responsible for higher COADS wind speeds, while rotation of wind vectors along mountain ranges and inadequate VOS coverage in coastal waters is biasing wind direction in COADS data toward the open ocean winds.
How well does a 1/4° global circulation model simulate large‐scale oceanic observations?
Authors: Stammer Detlef , Tokmakian Robin , Semtner Albert , Wunsch Carl
Published: February 2004

Numerical high‐resolution ocean general circulation models have experienced a revolutionary development during the last decade. Today they are run globally in realistic configuration with realistic surface boundary forcing. To fully use the results of those models in understanding various aspects of the ocean general circulation and to combine ocean observations with models (state estimation) in a manner consistent with the data and model dynamics, stringent model‐data comparisons are a necessary first step. In this paper a quantitative model‐data comparison is carried out for the global Parallel Ocean Climate Model (POCM), known also as the Semtner and Chervin model, with nominal lateral resolution of 1/4°. The focus is on various aspects of the simulated large‐scale circulation and their relation to the TOPEX/POSEIDON sea surface height (SSH) observations and World Ocean Circulation Experiment (WOCE) hydrography. Comparisons are made for (1) the global mean sea surface circulation and absolute slopes, (2) rms SSH variability and eddy kinetic energy, (3) the simulation of the observed seasonal cycle in SSH, (4) two‐dimensional frequency‐wavenumber spectra of the large‐scale fluctuations, as well as (5) the hydrography for WOCE sections. Recent improvements in external surface forcing fields including daily wind‐stress fields and sea surface heat fluxes lead to a significant improvement in the overall agreement of the simulated and observed large‐scale mean circulation and its variability. However, simulated amplitudes of variability remain low by about a factor of 2 to 4 over a broad spectral range, including the long wavelengths and periods. Both the causes and consequences of this low variability remain obscure.
Evaluation of turbulent fluxes at the ocean surface using surface renewal theory
Authors: Clayson C. A. , Fairall C. W. , Curry J. A.
Published: February 2004

An internally consistent model is presented that can be used to determine the ocean surface fluxes of heat, moisture, and momentum, given bulk sea surface temperature and atmospheric temperature, humidity, and winds measured at a single level within the atmospheric surface layer. This model is based upon surface renewal theory as described by Brutsaert [1975a]. Liu et al. [1979] (hereinafter referred to as LKB) made partial use of this theory, and further improvements to the LKB parameterization have been made by Fairall et al. [1996a]. The present model includes the following improvements relative to the LKB and Fairall et al. bulk flux models: incorporation of a new time‐scale parameterization for surface renewal, inclusion of capillary waves in the surface roughness model, derivation of the surface roughness scales of water vapor and heat based solely upon surface renewal theory; and incorporation of a new surface skin temperature model. The model is validated using shipborne observations of surface fluxes and surface meteorology that were obtained in the central Pacific Ocean, the western tropical Pacific, the subtropical Pacific, and the midlatitude North Atlantic. Comparisons of model results with covariance fluxes of latent heat show biases of less than 3% for all locations, with little dependence of error on wind speed; similar results are obtained for sensible heat and momentum flux. An assessment is given of the advantages of the present scheme over the LKB and Fairall et al. schemes. The model results are interpreted in the context of the physical processes involved in determining the surface roughness length and the surface renewal timescale.
Climatic implications of background acidity and other chemistry derived from electrical studies of the Greenland Ice Core Project ice core
Authors: Wolff Eric W. , Moore John C. , Clausen Henrik B. , Hammer Claus U.
Published: February 2004

High‐resolution continuous profiles were obtained on the Greenland Ice Core Project (GRIP) ice core using two different electrical methods. After correction for temperature and density, the electrical conductivity method (ECM) technique responds only to acidity, while dielectric profiling (DEP) responds to acid, ammonium, and chloride. Detailed chemistry on a section of glacial‐age ice allows us to confirm the calibration factor for chloride in DEP. Acidity dominates the DEP variability in the Holocene, Allerod/Bolling, and larger interstadials; ammonium dominates in the Younger Dry as, while chloride is the major contributor in cold periods including smaller interstadials. From the electrical signals plotted on a linear timescale we can deduce the background (nonvolcanic) acidity of the ice, varying from always acidic in the Holocene to always alkaline in the cold periods. In the interstadials, the ice is close to neutral, with most of it acidic in larger interstadials, most of it alkaline in smaller ones, and rapid alternations within interstadials. It is not clear whether neutralization of individual acidic particles occurred in the atmosphere or whether acid and alkaline particles coexisted until deposition in the snowpack. The changes in acidity observed at GRIP apply at least to all of Greenland and probably to much of North America. There would have been ecological effects and important changes in the uptake of some chemicals onto ice. If acidic sulfate particles were neutralized and removed from the atmosphere, which remains uncertain, then there are atmospheric chemistry and radiative effects that require further investigation.
High‐resolution measurements made across a tidal intrusion front
Authors: Marmorino G. O. , Trump C. L.
Published: February 2004

High spatial resolution current and hydrographic measurements have been made across a tidal intrusion front in the James River estuary, Virginia, during the first few hours of flood. The current measurements were made with a surface‐towed acoustic Doppler current profiler which was used in both profile and side‐scan configurations. The profile data show a 30–50 cm s−1inflow of water from the Chesapeake Bay, a time‐evolving across‐front density gradient, and downward velocity beneath the front of about 15 cm s−1. The side‐scan observations directly measure the across‐front change in current and provide a view of the three‐dimensional character of the frontal interface. The near‐surface horizontal strain rate, a critical parameter for understanding the modulation of surface waves across the front, is estimated to be about 0.04 s−1. UsingPhillips' [1984] theory as a guide, fronts with such large strain rates as these should be discernible in imagery from the ERS 1 C band synthetic aperture radar for wind speeds of ≤4 m s−1.
Winter transport and sea level fluctuations in Hecate Strait, British Columbia
Authors: Hannah Charles G. , Crawford William R.
Published: February 2004

Observed winter transport and adjusted sea level fluctuations in Hecate Strait were investigated using empirical orthogonal function and coherence analyses. The responses to large‐scale and local wind forcings were identified by the distinctive spatial patterns of their adjusted sea level responses. At the resolved periods of 2 to 48 days, the large‐scale and the local wind forcings were of roughly equal importance in driving transport fluctuations. Comparison of observations with a conceptual model indicates that the adjusted sea level in the northeast corner of the strait gives a good measure of response to both the local and large‐scale wind forcings. This provides a physical explanation for the observed high correlation between the adjusted sea level at Prince Rupert and the winter transport fluctuations in Hecate Strait. We also show that the transport fluctuations are associated with a particular spatial pattern of the velocity field, which represents roughly 1/4 of the energy in the observed winter velocity fluctuations measured at an array of current meters. This has implications for the use of surrogate transport series to hindcast oceanographic conditions in Hecate Strait.
Variability and climate sensitivity of landfast Arctic sea ice
Authors: Flato Gregory M. , Brown Ross D.
Published: February 2004

A one‐dimensional thermodynamic sea ice model is used to perform multiyear simulations of land‐fast sea ice and its snow cover. The model is applied to two locations in the Canadian high Arctic: Resolute and Alert, Northwest Territories. The sites are chosen because meteorological observations and ice and snow depth measurements spanning the period 1955–1990 are available. Bulk formulae are used to convert standard meteorological observations into surface fluxes, snowfall is specified from observed annual accumulation, and a crude oceanic mixed layer is included to allow heat storage during ice‐free summer months. The model is successful at reproducing seasonal and interannual variability in maximum ice thickness, snow depth, freeze‐up, and breakup dates. Sensitivity studies demonstrate the relative importance of variables such as air temperature and snowfall rate on interannual variability of maximum ice thickness and the duration of the ice‐free season. Multiple equilibria, corresponding to thin, seasonal ice and thick, perennial ice, are shown to exist in the model. Climate sensitivity experiments illustrate the potential effects of changes in air temperature and snowfall on ice thickness and open water duration in the Canadian Archipelago.
Subtidal circulation patterns in a shallow, highly stratified estuary: Mobile Bay, Alabama
Authors: Noble Marlene A. , Schroeder William W. , Wiseman William J. , Ryan Holly F. , Gelfenbaum Guy
Published: February 2004

Mobile Bay is a wide (25–50 km), shallow (3 m), highly stratified estuary on the Gulf coast of the United States. In May 1991 a series of instruments that measure near‐surface and near‐bed current, temperature, salinity, and middepth pressure were deployed for a year‐long study of the bay. A full set of measurements were obtained at one site in the lower bay; all but current measurements were obtained at a midbay site. These observations show that the subtidal currents in the lower bay are highly sheared, despite the shallow depth of the estuary. The sheared flow patterns are partly caused by differential forcing from wind stress and river discharge. Two wind‐driven flow patterns actually exist in lower Mobile Bay. A barotropic response develops when the difference between near‐surface and near‐bottom salinity is less than 5 parts per thousand. For stronger salinity gradients the wind‐driven currents are larger and the response resembles a baroclinic flow pattern. Currents driven by river flows are sheared and also have a nonlinear response pattern. Only near‐surface currents are driven seaward by discharges below 3000 m3/s. At higher discharge rates, surface current variability uncouples from the river flow and the increased discharge rates drive near‐bed current seaward. This change in the river‐forced flow pattern may be associated with a hydraulic jump in the mouth of the estuary.
Evolution of stable internal boundary layers over a cold sea
Authors: Smedman Ann‐Sofi , Bergström Hans , Grisogono Branko
Published: February 2004

The situation studied in this paper relates to air flow from a heated land surface out over a water surface with much lower temperature. Observations from the Baltic Sea, where this kind of situation prevails for two thirds of the time, indicate that several distinct flow regimes occur. Simulations with a numerical boundary layer model for various combinations of geostrophic wind speed, Vg, and bulk temperature difference between land and sea, ΔΘ, have been performed. They show that, initially, stratification is always stable in the air layers near the sea surface but after some time transition to a near‐neutral layer capped by an inversion takes place. The simulations, as well as the results of a simple analytical study, indicate that the transition takes place at a certain time of over water transport, te, which can be calculated when the bulk parameter ΔΘ is known. Measurements of boundary layer temperature and wind profiles at three sites in the Baltic Sea area strongly support this result. Thus, for measurements representing traveling times less than te, derived with the above mentioned expression, a stable boundary layer is always found. For traveling times larger than te, a mixed layer is found (provided ΔΘ is not large enough to cause quasi‐frictional decoupling). Turbulence measurements made at the three sites simultaneously with the profiles show that (u*/Vg)103 is between almost zero and 25 for the stable cases and between 25 and 46 for the mixed layer cases.
Mapping submarine sand waves with multiband imaging radar: 2. Experimental results and model comparison
Authors: Vogelzang J. , Wensink G. J. , Calkoen C. J. , Van der Kooij M. W. A.
Published: February 2004

On August 16, 1989, and on July 12, 1991, experiments were performed to study the mapping of submarine sand waves with the airborne imaging radar, a polarimetric (and, in 1991, interferometric) airborne P, L, and C band synthetic aperture radar system. The experiments took place in an area 30 km off the coast of the Netherlands, where the bottom topography is dominated by sand waves with a height between 2 and 6 m and a crest‐to‐crest distance of about 400 m at an average depth of 22 m. Ground measurements were recorded on a nearby platform and on a ship in the test area, which also acted as a position fix. On August 16, 1989, the wind was 5 m/s directed toward the northeast, while the surface current velocity was around 0.5 m/s directed toward the southwest. One overflight was made, with the flight direction parallel to the sand wave crests and the radar looking upwind. At P band, the sand waves are clearly visible as dark bands, as predicted by theory, while at L band the sand waves show up as sawtooth‐shaped modulations. On July 12, 1991, wind and surface current had the same (opposite)‐directions as in 1989, though the wind was much higher (10 m/s). Three flights were made, with the radar pointing upwind, cross wind, and downwind. The upwind and downwind images are very similar. Despite the high wind speed, the sand waves are clearly visible as sawtooth‐shaped modulations at P band and vaguely visible at L band. At C band, only wind streaks can be seen. All cross wind images show the sand waves as dark bands, now with the highest modulations at C band. The wind streaks that dominated the upwind and downwind images at C band are much less pronounced in the cross wind images. The images are compared with predictions from a new model of the imaging mechanism which includes contribution to the radar cross section of waves moving both from and to the radar. Wave blocking or wave reflection is treated in an approximate manner. For the radar looking upwind or downwind, the predicted modulations at P and L band agree well with the observations, while those at C band are too high. For the radar looking cross wind, the model severely underestimates the modulations. It is questioned whether a local relaxation source term can describe such a situation. The interferogram shows some structure caused by bottom‐induced surface current variations.
The influence of the marine atmospheric boundary layer on ERS 1 synthetic aperture radar imagery of the Gulf Stream
Authors: Beal R. C. , Kudryavtsev V. N. , Thompson D. R. , Grodsky S. A. , Tilley D. G. , Dulov V. A. , Graber H. C.
Published: February 2004

In September 1991, the ERS 1 synthetic aperture radar (SAR) collected a set of four colocated images over the western Gulf Stream (GS). The SAR images were supplemented by satellite infrared imagery and measurements of the marine atmospheric boundary layer (MABL) from both a pair of surface buoys and a suite of instrument on the Ukrainian research vessel R/V Vernadsky, which between September 15 and 19 made six transects across the GS northern boundary within the SAR swaths. The influence of wind variations within the MABL was evident in each of the four SAR images. Evidence for thermal wind effects is seen in the changing character of the imagery as the mean wind across the sea surface temperature boundary changed direction from pass to pass. Both in situ data and analytical models suggest that much of the day‐to‐day SAR image variability was the result of changes in the character of the MABL, especially evident near the northern GS boundary where the sign of the atmospheric stability fluctuated over short spatial scales. Because many of the governing parameters of the MABL rapidly decorrelate, significant changes in the SAR imagery occurred during the 3 days between passes. Nevertheless, at least some manifestation of the GS was evident in the SAR imagery on each of the four passes.
Volcanic aerosol records and tephrochronology of the Summit, Greenland, ice cores
Authors: Zielinski Gregory A. , Mayewski Paul A. , Meeker L. David , Grönvold Karl , Germani Mark S. , Whitlow Sallie , Twickler Mark S. , Taylor Kendrick
Published: February 2004

The recently collected Greenland Ice Sheet Project 2 (GISP2) and Greenland Ice Core Project ice cores from Summit, Greenland, provide lengthy and highly resolved records of the deposition of both the aerosol (H2SO4) and silicate (tephra) components of past volcanism. Both types of data are very beneficial in developing the hemispheric to global chronology of explosive volcanism and evaluating the entire volcanism‐climate system. The continuous time series of volcanic SO42− for the last 110,000 years show a strong relationship between periods of increased volcanism and periods of climatic change. The greatest number of volcanic SO42− signals, many of very high magnitude, occur during and after the final stages of deglaciation (6000–17,000 years ago), possibly reflecting the increased crustal stresses that occur with changing volumes of continental ice sheets and with the subsequent changes in the volume of water in ocean basins (sea level change). The increase in the number of volcanic SO42− signals at 27,000–36,000 and 79,000–85,000 years ago may be related to initial ice sheet growth prior to the glacial maximum and prior to the beginning of the last period of glaciation, respectively. A comparison of the electrical conductivity of the GISP2 core with that of the volcanic SO42− record for the Holocene indicates that only about half of the larger volcanic signals are coincident in the two records. Other volcanic acids besides H2SO4 and other SO42− sources can complicate the comparisons, although the threshold level picked to make such comparisons is especially critical. Tephra has been found in both cores with a composition similar to that originating from the Vatnaöldur eruption that produced the Settlement Layer in Iceland (mid‐A.D. 870s), from the Icelandic eruption that produced the Saksunarvatn ash (∼10,300 years ago), and from the Icelandic eruption(s) that produced the Z2 ash zone in North Atlantic marine cores (∼52,700 years ago). The presence of these layers provides absolute time lines for correlation between the two cores and for correlation with proxy records from marine sediment cores and terrestrial deposits containing these same tephras. The presence of both rhyolitic and basaltic shards in the Z2 ash in theGISP2 core and the composition of the basaltic grains lend support to multiple Icelandic sources (Torfajökull area and Katla) for the Z2 layer. Deposition of the Z2 layer occurs at the beginning of a stadial event, further reflecting the possibility of a volcanic triggering by the effects of changing climatic conditions.
More on the births of jet drops from bubbles bursting on seawater surfaces
Authors: Spiel Donald E.
Published: February 2004

The parameters of the births of jet drops originating from bubbles bursting on seawater surfaces are presented. This report supplements an earlier one by providing the birth times and heights of all the jet drops, not just the top. Results are given for bubble sizes from 350‐ to 1500‐μm equivalent volume radius. The ejection speeds of the jet droplets generated by a collapsing bubble and the height above the surface, as well as the time, at which all the drops break off the ascending jet have been measured. For the bubble sizes used in this study, the first drop emitted, the top drop, is closest to the surface at birth, the second is the highest, and all subsequent drops are at intermediate heights. Furthermore, each drop after the second is born at a height that is lower than the drop that preceded it. Size distributions of the jet drops from each of 10 bubble sizes are reported. They differ from size distributions published earlier in that the sizes of the lower drops are not bimodally distributed. This difference is attributed to a difference in water temperature.
Tidal residual currents in the Gulf of California: Is the M2tidal constituent sufficient to induce them?
Authors: Marinone S. G.
Published: February 2004

A two‐dimensional vertically integrated numerical model has been used to study residual, that is, mean and low‐frequency (<0.5 cycles per day) currents, in the Gulf of California. The model is forced at the mouth with the most important tidal constituents, allowing them to interact through the nonlinear terms. Previous nonlinear models of the gulf were forced only with the most energetic M2constituent. The mean residual currents obtained with the semidiurnal constituents are all of the same order (1–2 cm s−1) as those obtained with the M2alone and are larger by an order of magnitude than those produced by the diurnal components. The time‐mean residual obtained with all seven constituents is very close to that obtained with only the M2. When several constituents are included simultaneously, fluctuating residuals arise in the model through nonlinear interactions. The fortnightly variation produced by the interaction of M2and S2constituents is the most important, and it is of the same order of magnitude as the time‐mean residual. The model shows that time‐averaged residuals can effectively be computed from the M2component alone, whereas the fluctuating residual, which is equally important, requires the inclusion of the S2constituent as well. Thus computations with only the M2and S2constituents yield a very good approximation for computing tidally induced residual currents in the Gulf of California.
Turbulence and stratification on the Tropical Ocean‐Global Atmosphere‐Coupled Ocean‐Atmosphere Response Experiment microstructure pilot cruise
Authors: Brainerd K. E. , Gregg M. C.
Published: February 2004

On the Tropical Ocean‐Global Atmosphere‐Coupled Ocean‐Atmosphere Response Experiment pilot cruise, at 147°E, in the western Pacific Warm Pool, we profiled for 17 days at 0°N and for 5 days at 2°N. Winds were generally light and variable in direction, but rainfall was often quite intense. Contrary to what is seen in the central equatorial Pacific, we did not observe a deep diurnal cycle in dissipation extending below the mixed layer. Strong daytime restratification often prevented nightly convective deepening down to the seasonal thermocline, resulting in surface forcing remaining trapped in a shallow layer. The relaxation of horizontal density gradients into vertical appears to be an important process driving restratification. Turbulent fluxes in the bottom of the mixed layer were generally small. Following rainfall, we observed pools of fresh water that typically disappeared within a few hours, leaving the mixed layer nearly homogeneous in salinity; thus we did not observe a permanent barrier layer. Modeling such events using the Price‐Weller‐Pinkel model suggests a fresh pool will be mixed away on timescales of a few days, primarily by nighttime convection. The observed vertical structure can be accounted for by local vertical mixing processes.
Decadal variability of hydrography in the upper northern North Atlantic in 1948–1990
Authors: Reverdin G. , Cayan D. , Kushnir Y.
Published: February 2004

We investigate the variability of the North Atlantic subarctic gyre in recent decades from time series of station temperature and salinity. Decadal variability stronger at the surface is identified, which exhibits vertical coherence over a layer deeper than the late winter mixed layer. In the northwestern Atlantic, it corresponds to the layer with a component of water from the Arctic Ocean or from the Canadian Arctic. The spatial coherence of the signal is investigated. An empirical orthogonal function decomposition of lagged time series indicates that a single pattern explains 70% of the variance in upper ocean salt content, corresponding to a propagating signal from the west to the northeast in the subarctic gyre. The most likely interpretation is that the salinity signal originates in the slope currents of the Labrador Sea and is diffused/advected eastward of the Grand Banks over the near western Atlantic. In the northwestern Atlantic, temperature fluctuations are strongly correlated to salinity fluctuations and are aligned along the average T‐S characteristics. This signal suggests large variations in the outflow of fresh, cold water in the slope current, and is strongly correlated with ice cover. A basin scale atmospheric circulation of weakened westerlies at 55°N, weaker northwesterlies west of Greenland and weaker southerlies over the central and eastern North Atlantic is associated with the high salinity and warm water phase of the first principal component. This circulation pattern leads fluctuations in the northeast Atlantic and lags those in the northwestern part of the basin. The wind indices also suggest that the fluctuations of the fresh water outflow occur during intervals of anomalously northerly winds, either east of Greenland (1965, 1968–1969) or off the Canadian Archipelago (1983–1984).
Oxygen isotope exchange between carbon dioxide and water following atmospheric sampling using glass flasks
Authors: Gemery Pamela A. , Trolier Michael , White James W. C.
Published: February 2004

Measurements of the 18O/16O isotopic ratio of atmospheric carbon dioxide made by the University of Colorado, Boulder on flask samples provided by the Climate Monitoring and Diagnostics Laboratory of the National Oceanic and Atmospheric Administration appear to have been contaminated by oxygen isotope exchange between CO2 and water inside the glass flasks. The 18O/16O ratios measured for samples from high‐humidity sites collected during 1990–1993 show considerable scatter and are believed not to represent the true oxygen isotopic composition of atmospheric CO2. Laboratory experiments have demonstrated that oxygen isotope exchange occurs between CO2 and water condensed on the flask walls. Complete isotopic equilibrium is not observed, even for storage times greater than 1 month; the extent of exchange differs for individual flasks. The experiments show that air samples to be stored in glass flasks must be dried to a dew point of 2°C or lower before storage to eliminate artifacts associated with oxygen exchange.
Comparison of air mass computations
Authors: Slusser James , Hammond Kyle , Kylling Arve , Stamnes Knut , Perliski Lori , Dahlback Arne , Anderson Donald , DeMajistre Robert
Published: February 2004

Knowledge of air mass is vital for the interpretation of twilight measurements of trace gases, as well as the conversion of measured slant column amounts to vertical abundances for comparison with model predictions. Radiative transfer computations were used to determine NO2 air mass values for clear skies at 450 and 650 nm using a discrete ordinate (two different formulations), Monte Carlo, and an integral equation method. All four methods yielded agreement to within 6% at a solar zenith angle of 90° when the absorber was located in the stratosphere. For a tropospheric absorber, differences as large as 21% occurred at 90°. Since only the Monte Carlo method treats the scattered radiation in spherical geometry, it is more accurate for computing tropospheric air masses where multiple scattering is significant. The other three models use a conceptual approximation by treating the scattered radiation in plane parallel geometry. However, for absorbers in the stratosphere, major saving of computing time without any loss of accuracy is obtained using the discrete ordinate or integral equation method as compared to the Monte Carlo method.
Photooxidants in the marine Arctic troposphere in summer
Authors: Weller R. , Schrems O.
Published: February 2004

The air chemistry investigations, performed on R/V Polarstern during the expedition ARK X/1 in July/August 1994, comprised a mapping of the vertical ozone distribution by ozone soundings and the surface mixing ratios of H2O2 and NO above the East Greenland Sea between 70°N and 80°N. The observed H2O2 mixing ratios varied from about 100 parts per trillion by volume (pptv) up to around 1000 pptv. Surface ozone concentrations can be correlated with the source region of the advected air masses. Ozone mixing ratios from around 33 parts per billion by volume (ppbv) up to 60 ppbv have been observed in air parcels emanating from industrialized regions. In contrast, pristine Arctic air masses showed low ozone mixing ratios of about 23 ppbv. The tropospheric part of the vertical ozone profiles occasionally exhibited significant maxima above the planetary boundary layer. Apart from cases where intrusions of stratospheric ozone were obvious, photochemical ozone formation along trajectories originating from polluted regions was most probably the reason for layers with enhanced ozone concentrations. The measured surface NO mixing ratios were extremely low, typically between 3 and 8 pptv. Thus local photochemical surface ozone production could be largely ruled out. In conclusion it can be stated that in summer, intrusion of ozone rich stratospheric air and advection of polluted air masses from lower latitudes appeared to be the dominant ozone sources of the marine Arctic troposphere.