bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical simulation of two‐dimensional salt fingers
Authors: Shen Colin Y. , Veronis George
Published: February 2004

Numerical calculations of unperturbed, regularly spaced fingers in the heat‐salt system (with a ratio of salt to heat diffusivities of 1/80) were carried out for a configuration in which a reservoir of uniformly salty, warm fluid lies initially above a reservoir of fresh, cold fluid. Cases were calculated in which the stability ratio, Rρ, was 1.5 and 3.0, and they were calculated for different magnitudes of the destabilizing salt increment, ΔS, expressed in terms of a salt Rayleigh number, Rs. Blobs of fluid with a salt anomaly accumulate at the ends of the evolving fingers. The magnitude and size of the anomaly increase with decreasing Rρ and increasing Rs. The density of those blobs is gravitationally unstable to perturbations. In the range of parameters used in these calculations the ratio of the flux of density due to heat to that due to salt varies from 0.17 to 0.74 for the unperturbed fingers. Essentially, the flux ratio decreases when the vertical velocity in the fingers is small, so that a relatively large amount of heat is diffused laterally from warm, salty descending fingers to cool, fresh ascending ones. A detailed account of the evolution of the perturbed system describes the various stages of the instability, concluding with the formation of larger structures in the reservoirs, which squash the fingers near the interface, so that isotherms and isohaline contours at midlevel are more or less horizontal. There is an indication of three period doublings in the spacing of the unstable blobs as they penetrate into the lower reservoir. The destruction of the regular array of upright, uniformly spaced fingers appears to be the natural evolution of perturbed systems in which Rρ is near unity and Rs is large.
How does the El Niño‐generated coastal current propagate past the Mendocino escarpment?
Authors: Allen Susan E. , Hsieh William W.
Published: February 2004

During an El Niño, an internal coastal Kelvin wave bore propagates poleward along the west coast of North America, leaving behind a steady anomalous coastal jet. A nonlinear, two‐layer, ƒ plane, shallow‐water model is used to determine the amplitude change of the steady coastal current over an escarpment. As the El Niño‐generated warm coastal current passes the Mendocino escarpment off northern California, its amplitude is marginally enhanced. In contrast, for a cold coastal current, the amplitude will be reduced north of the Mendocino escarpment. When the Kelvin wave bore travels over a depth increase, the amplitude change is predicted to be much larger than over a depth decrease (as in the case of the Mendocino escarpment). This model is also applicable to bottom water flowing equatorward along a western boundary. In this case, much larger amplitude changes are found.
Variability in the location of the Antarctic Polar Front (90°–20°W) from satellite sea surface temperature data
Authors: Moore J. Keith , Abbott Mark R. , Richman James G.
Published: February 2004

The path of the Antarctic Polar Front (PF) is mapped using satellite sea surface temperature data from the NOAA/NASA Pathfinder program. The mean path and variability of the PF are strongly influenced by bathymetry. Meandering intensity is weaker where the bathymetry is steeply sloped and increases in areas where the bottom is relatively flat. There is an inverse relationship between meandering intensity and both the width of the front and the change in temperature across it There is a persistent, large separation between the surface and subsurface expressions of the PF at Ewing Bank on the Falkland Plateau.
Katabatic wind fields in coastal areas studied by ERS‐1 synthetic aperture radar imagery and numerical modeling
Authors: Alpers Werner , Pahl Ulrike , Gross Günther
Published: February 2004

Synthetic aperture radar (SAR) images acquired over Mediterranean coastal waters from the first European Remote Sensing Satellite (ERS‐1) showing sea surface manifestations of katabatic wind fields are presented. In particular, sea surface roughness patterns generated by katabatic winds blowing from 1800 in high mountains through a broad valley at the western coast of Calabria (southern Italy) into the Gulf of Gioia is investigated. The ERS‐1 SAR images show that their areal extent and shape vary strongly, depending on the meteorological conditions. The roughness pattern sometimes has the form of a mushroom, an elongated tongue, a broad blob, or a narrow truncated band. For one event (September 8, 1992) we have simulated the wind field at the sea surface by using a nonhydrostatic mesoscale atmospheric model and then compared it with the wind field derived from the ERS‐1 SAR image by using the C band wind scatterometer model CMOD4. The comparison shows that the atmospheric model reproduces quite well the mushroom‐like form of the wind field pattern, while the wind speed is obtained somewhat lower than the one inferred from the SAR image. This study demonstrates that SAR images acquired over coastal waters are well suited to study local wind fields in coastal areas and to test numerical models that describe local wind fields which extend from the coast onto the sea.
Imaging of biogenic and anthropogenic ocean surface films by the multifrequency/multipolarization SIR‐C/X‐SAR
Authors: Gade Martin , Alpers Werner , Hühnerfuss Heinrich , Masuko Harunobu , Kobayashi Tatsuharu
Published: February 2004

Results from the analyses of several spaceborne imaging radar‐C/X‐band synthetic aperture radar (SIR‐C/X‐SAR) images are presented, which were acquired during the two SIR‐C/X‐SAR missions in April and October 1994 by the L‐, C‐, and X‐band multipolarization SAR aboard the space shuttle Endeavour. The images showing natural (biogenic) surface slicks as well as man‐made (anthropogenic) mineral oil spills were analyzed with the aim to study whether or not active radar techniques can be applied to discriminating between these two kinds of surface films. Controlled slick experiments were carried out during both shuttle missions in the German Bight of the North Sea as well as in the northern part of the Sea of Japan and the Kuroshio Stream region, where surface films of different viscoelastic properties were deployed within the swath of the shuttle radars. The results show that the damping behavior of the same substance is strongly dependent on wind speed. At high wind speed (8–12 m/s) the ratio of the radar backscatter from a slick‐free and a slick‐covered water surface (damping ratio) is smaller than at low to moderate wind speeds (4–7 m/s). At 12 m/s, only slight differences in the damping behavior of different substances were measured by SIR‐C/X‐SAR. Furthermore, several SAR scenes from various parts of the world's oceans showing radar signatures of biogenic as well as anthropogenic surface films at low to moderate wind speeds are analyzed. The damping behavior of these different kinds of oceanic surface films varies particularly at Lband where the biogenic surface films exhibit larger damping characteristics. Results of polarimetric studies from multipolarization SAR images showing various surface films are presented. It can be delineated from these results that Bragg scattering as well as specular reflection contribute to the backscattered radar signal at low incidence angles (up to 30°). It is concluded that at low to moderate wind speeds, multifrequency radar techniques seem to be capable of discriminating between the different surface films, whereas at high wind conditions a discrimination seems to be difficult.
An oceanographic nowcast/forecast system for the Red Sea
Authors: Clifford Melody , Horton Charles , Schmitz Joyce , Kantha Lakshmi H.
Published: February 2004

We describe the application of a nowcast/forecast system for three‐dimensional currents, temperature, and salinity to the Red Sea. The modeling system is constructed around a high‐resolution (6×7 km) primitive‐equation numerical circulation model with complete thermodynamics and an imbedded turbulence closure submodel. It is coupled to near‐real‐time databases containing meteorological forecasts and remotely sensed and in situ temperature and salinity data. The temperature and salinity data are ingested into the model daily using a nudged objective analysis technique. Because the Red Sea is a relatively narrow basin bounded by typically high and complex orography, a single‐layer atmospheric boundary layer submodel has been used to increase the effective resolution of the original 40‐km resolution meteorological fields by taking into account orographic steering of the low‐level winds. In order to validate the modeling system, two very complete hydrographic surveys of the Red Sea were undertaken, and their results are described. Both the surveys and the modeling system nowcasts demonstrate that the circulation pattern of the Red Sea is variable and often composed of a series of eddies or subgyres, mainly anticyclones. Immediately before one survey, the winds tended to be along axis, while just before the second, they tended to be cross axis. The Red Sea circulation was much more eddy‐like when the winds were cross‐axis. By forcing the modeling system with and without orographically steered winds we were able to establish that the complex eddy structure is a response to a wind field which can be highly structured and vorticity rich because of interaction with the high and variable adjacent orography. When the winds are more along axis, there is less interaction with the adjacent orography, and consequently, there are fewer eddies in the Red Sea.
Determination of the geophysical model function of the ERS‐1 scatterometer by the use of neural networks
Authors: Mejia Carlos , Thiria Sylvie , Tran Ngan , Crépon Michel , Badran Fouad
Published: February 2004

We present a geophysical model function (GMF) for the ERS‐1 scatterometer computed by the use of neural networks. The neural networks GMF (NN GMF) is calibrated with ERS‐1 scatterometer sigma 0 collocated with European Center for Medium‐Range Weather Forecasts (ECMWF) analyzed wind vectors. Four different NN GMFs have been computed: one for each antenna and an average NN GMF. These NN GMFs do not present any significant differences which means that the three antenna are quasi‐identical. The NN GMFs exhibit a biharmonic dependence on the wind azimuth with a small upwind‐downwind modulation as found on previous GMFs. In order to check the validity of the NN GMF systematic comparisons with the European Space Agency (ESA) C band model (CMOD4) GMF (version 2 of March 25, 1993) and the Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER) CMOD213 GMF are done. It is found that the NN GMFs are highly accurate and relevant functions to model the ERS‐1 scatterometer sigma 0.
Intermittent stability and frontogenesis in an area influenced by land runoff
Authors: Czitrom S. P. R. , Simpson J. H.
Published: February 2004

A frontal structure in Liverpool Bay was studied using conductivity‐temperature‐depth (CTD) and current meter data. At times of weak vertical mixing by wind and tides, a density‐driven gravity flow, induced by river discharge, distorts the thermohaline field, so that an expanding stratified region develops, bounded offshore by a surface front. Expansion of this frontal structure is increasingly curbed by rotation as a near‐geostrophic balance is attained. Owing to friction, the space scale and time scale of frontogenesis are somewhat greater than two internal Rossby radii and an inertial period, respectively. At times of increased mixing, the frontal structure is destroyed and the enhanced friction between layers inhibits gravity flow, hampering the frontogenesis mechanism. Large variability in mixing conditions results in an intermittent frontal structure.
An inertial‐dissipation method for estimating turbulent flux in buoyancy‐driven, convective boundary layers
Authors: McPhee Miles G.
Published: February 2004

A method is developed for using wavenumber spectra of scalar contaminants in a boundary layer dominated by buoyancy‐driven convection to estimate the magnitude of vertical turbulent fluxes. The technique is analogous to the conventional inertial‐dissipation method (IDM) for obtaining fluxes from variance spectral density levels in the inertial subrange but differs in the way that turbulence scales are combined to provide an “eddy density diffusivity” for relating flux magnitude to variance dissipation rate. The method is illustrated using spectra and direct flux covariance data from the oceanic boundary layer at the edge of a freezing lead during the 1992 Lead Experiment in the Arctic Ocean. There, density was controlled almost exclusively by salinity, and it is argued that the turbulent length and velocity scales governing vertical exchange were the inverse of the wavenumber at the peak in the weighted salinity spectrum (considerably less than the mixed layer depth) and the cube root of the product of turbulent length scale and the buoyancy flux magnitude, respectively. The sign of the skewness of temperature or salinity time series is shown to be a robust indicator of the (negative) direction of vertical flux. The “free convection” approach is valid (i.e., should be used instead of the conventional IDM) only if the convective turbulent scale velocity is appreciably larger than friction velocity (square root of the Reynolds stress), so that turbulent kinetic energy dissipation is approximately equal to buoyancy production.
Vertical profiles of longshore currents and related bed shear stress and bottom roughness
Authors: Faria A. F. Garcez , Thornton E. B. , Stanton T. P. , Soares C. V. , Lippmann T. C.
Published: February 2004

The vertical structure of the mean wave‐driven longshore current over a barred beach is examined on three strong current days during the DUCK94 experiment, and it is found that the bottom boundary layer is well described by a logarithmic profile (mean correlation coefficient for all 22 profiles, 0.98). The logarithmic profile fits better in the trough, where turbulent bottom boundary layer processes predominate, than over the bar, where breaking‐wave‐induced turbulence generated at the surface modifies the profile. The surface layer in the presence of waves is well described by adjusting the logarithmic profile for the intermittent presence of water and adding the alongshore component of the mass transport velocity (slope of the least squares linear regression between model predictions and observations, 1.005 and root‐mean‐square (rms) error of 7%). Bed shear stresses calculated from logarithmic velocity profiles are equated to a quadratic bottom shear stress formulation. The associated bed shear stress coefficients vary by more than an order of magnitude across the surf zone (0.0006–0.012). Bottom roughness was measured throughout the nearshore using a sonic altimeter mounted on a moving platform. The bed shear stress coefficients are positively correlated with bottom roughness (linear correlation coefficient, 0.6). A higher linear correlation coefficient (0.8) is obtained by subtracting skin friction from the total bed shear stress.
Variability of pCO2 in the tropical Atlantic in 1995
Authors: Lefèvre Nathalie , Moore Gerald , Aiken Jim , Watson Andrew , Cooper David , Ling Roger
Published: February 2004

Atmospheric and oceanic partial pressures of CO2 (pCO2) have been recorded automatically along two Atlantic meridional transects in 1995. The tropical Atlantic ocean (20°S–20°N) is generally a source of CO2 for the atmosphere, but in the region of the North Equatorial Countercurrent an undersaturation of CO2 has been observed. Undersaturations previously reported in the literature are explained by the decrease of salinity due to the high precipitations associated with the Intertropical Convergence Zone. In June 1995, strong CO2 undersaturations (ΔpCO2 = −70μatm) were observed near 8°N, which suggests, in addition of the salinity effect, an uptake of CO2 due to biological activity. This undersaturation, although weaker than in spring, also appeared at other periods of the year 1995.
Spatial and temporal evolution of a Gulf Stream crest‐warm core ring interaction
Authors: Hummon Julia M. , Rossby Thomas
Published: February 2004

An intensive, near‐synoptic hydrographic study of the reabsorption of a warm core ring into the Gulf Stream at a meander crest was conducted near 70°W in fall 1988. Using a mixture of measurement techniques and statistical optimal interpolation to map the velocity and density fields, the study documents how the normally robust cross‐stream structure of the Gulf Stream breaks down and the process by which a high pressure ridge between the stream and the ring develops. Examination of the layer potential vorticity (LPV) structure on two specific volume anomaly (δ) surfaces (approximately 18°C and 10°C) showed different characteristics of cross‐stream LPV structure. On the shallower surface the cross‐stream LPV structure was dominated by the cross‐stream gradient of layer thickness; on the deeper surface the much weaker cross‐stream LPV structure reflected the structure of the relative vorticity field. During the 10‐day period of ringstream contact, considerable water was exchanged, rupturing the ring and eventually resulting in the ring's reentrainment by the Gulf Stream. Time‐varying transports as large as 30 Sv were exchanged to the north and south between the surface and 5°C. The Gulf Stream bifurcates in such a way that the anticyclonic (southern) side continues through the meander crest uninterrupted, while the cyclonic side is diverted to the north to replace the low potential vorticity waters of the ring with waters of high potential vorticity. Contact between the ring and the stream is established first at the surface and progresses downward with increasing time. The decreased time needed to remove the ring's vorticity in the lower layers is consistent with the geometrical picture of the Gulf Stream colliding with a bowl‐shaped ring. The flushing time for the lens of δ(18°C) water in the ring is on the order of 5 days, slightly longer than the 2–3 days for the relative vorticity of the δ(10°C) surface.
A comparison of temperature, salinity, and chlorofluorocarbon observations with results from a 1° resolution three‐dimensional global ocean model
Authors: Craig A. P. , Bullister J. L. , Harrison D. E. , Chervin R. M. , Semtner A. J.
Published: February 2004

We describe the ability of a moderate‐resolution global ocean model to simulate the general circulation and the ocean‐atmosphere exchange and redistribution of chlorofluorocarbons (CFCs). The model was spun up from climatological initial conditions and has been integrated for decades representing 1930 to the present. Climatological monthly mean winds were imposed during the spin‐up and first 50 years of the integration. From 1980, monthly mean European Centre for Medium‐Range Weather Forecasts (ECMWF) wind stress fields were used. We compare model results to cruise data and to long‐term mean observations and find good qualitative agreement in most areas. Overall, the model agrees reasonably well in regions where measurable CFCs have been observed, and the large‐scale model ventilation pathways appear realistic. One of the most conspicuous shortcomings is the small volume of Antarctic Intermediate Water in the model results. This leads to errors in the general water mass structure and in CFC concentrations in the model in other regions. Notable CFC differences are found in regions where deep water masses are formed and in the upper subtropical gyre regions in which the Kuroshio extension exists. The model oceanic CFC sink represents <1% of all CFCs produced since 1930 and is small relative to the stratospheric sink for these compounds.
Temporal variability in dissolved organic carbon and radiocarbon in the eastern North Pacific Ocean
Authors: Bauer James E. , Druffel Ellen R. M. , Williams Peter M. , Wolgast David M. , Griffin Sheila
Published: February 2004

The factors regulating the steady state inventories and residence times of dissolved organic carbon (DOC) in the deep ocean are not well established. Previous studies of DOC have been limited to single time‐point profiles that provide general information on the potential role of vertical advective‐diffusive processes in controlling DOC distributions and mean apparent ages. We present results from a 2‐year time series station in the eastern North Pacific (station M) where short‐term (months) changes in inventories and Δ14C signatures of DOC as measured in deep profiles were examined in conjunction with changes in particulate organic carbon (POC) pools. Significant long‐term (i.e., months to years) changes in both DOC concentrations and Δ14C values were observed. These changes were especially evident at mesopelagic (∼450 and 700 m) depths, close to the oxygen minimum. Both within the mixed layer and at mesopelagic depths, positive relationships were found between DOC Δ14C values and concentrations of station M, primarily reflecting diminishing vertical inputs of “recent” DOC throughout the main thermocline. At abyssal depths (≥1600 m), however, Δ14C was inversely correlated with DOC concentration. The Δ14C signature of the less abundant suspended and sinking POC pools has been observed to fluctuate over seasonal timescales at station M, presumably due in part to sorption of DOC to POC [Druffel et al., 1996]. However, the Δ14C values and concentrations of the correspondingly much larger DOC pool do not appear to be related to seasonal changes in either sinking POC fluxes or suspended POC abundances. Significantly elevated concentrations of DOC were observed at station M when compared with a previously occupied site in the north central Pacific (NCP) in all regions of the water column except mesopelagic depths, where concentrations were lower. The corresponding Δ14C values of DOC at all depths at station M were lower than in the NCP. We speculate that dissimilarities in the size and Δ14C signature of the DOC pools at seasonally productive station M and the oligotrophic NCP result from differences in DOC sources and sinks between the two regions, as well as from the magnitude of interaction between DOC and POC at these sites.
Role of deep stratification in transporting deep water from the Atlantic to the Pacific
Authors: Nakata Minoru , Suginohara Nobuo
Published: February 2004

We investigate the mechanism of the connection between the Atlantic and the Pacific deep water through the Antarctic Circumpolar Current by using an idealized two‐basin model. It is found that the presence of the marked density stratification in the circumpolar region well below the Drake Passage sill is essential for reproducing the realistic connection. The deep stratification forms when a body forcing is imposed at the bottom level in the bottom water formation region. The body forcing is to mimic the formation process of the Antarctic Bottom Water, in which its characteristics are obtained through entrainment during downwelling. Then the bottom water is confined to the depths well below the Drake Passage sill and the deep water from the north tends to occupy the depths even below the Drake Passage sill. Flowing around Antarctica the water from the north upwells owing to the Ekman suction. Consequently, realistic water property distributions in the deep Pacific are well reproduced. It is demonstrated that this mechanism works in the world ocean model.
Tracking storm‐generated waves in the northeast Pacific Ocean with ERS‐1 synthetic aperture radar imagery and buoys
Authors: Holt Benjamin , Liu Antony K. , Wang David W. , Gnanadesikan Anand , Chen H. S.
Published: February 2004

This paper examines the capability of synthetic aperture radar imagery from ERS‐1 and buoys to track the wave field emanating from an intense storm over a several‐day period. The first part of the study is a validation component that compares SAR‐derived wave length and direction with buoy data from two locations over 10 different dates in late 1991 and National Oceanic and Atmospheric Administration (NOAA) wave model (WAM) wave direction results. When the SAR is linear (8 out of 10 cases), mean wavelength is within 5% of the buoy measurements and mean wave direction is within 1° of direction derived from the wave model (albeit with a large standard deviation of 27°), indicating close agreement. The wave field generated from the intense storm in late December 1991 was measured by three separate ERS‐1 SAR passes over a 3‐day period. A simple kinematic model was used for waves propagating from a storm. Comparing the model results with both SAR and buoy data indicates that SAR‐derived peak wavelength and direction measurements can be reliably used to predict arrival times and propagation direction over a several‐day period and considerable distances. The measurements can also be used to derive estimated wave generation source regions about the storm as well. Such measurements are useful for comparing with wave model results, which perform less accurately for direction than wave height for example, and for predicting hazardous conditions for ship navigation and coastal regions.
Shallow, brine‐driven free convection in polar oceans: Nonhydrostatic numerical process studies
Authors: Kämpf Jochen , Backhaus Jan O.
Published: February 2004

A three‐dimensional nonhydrostatic convection model, which accounts for small‐scale ice‐ocean interactions, is used to study convection in shallow sea (coastal) ice formation regions which contribute significantly to water mass formation in both the Arctic and Antarctic Ocean. For certain conditions the results presented in this paper are also transferable to shallow open ocean convection. The model is applied to an initial well‐mixed ocean at rest with a temperature close to the freezing point. The ocean, initially free of ice, is exposed to cold and dry polar air. We consider situations in which the mean wind stress is negligible but wind fluctuations result in (small) sensible and latent heat fluxes corresponding to a wind speed of 2 m s−1. Cellular convection patterns develop in the ocean, finally occupying a mean aspect ratio of 2. Convection is driven by salt release during frazil ice formation due to supercooling. Newly forming sea ice is collected along convergent (downwelling) regions at the surface, thus showing also cellular structures. Because the area of insulating sea ice remains small, new ice can be formed continuously, and the surface buoyancy forcing remains large. This collection of ice in small fractions of the sea surface results in a latent heat polynya type, which is very effective in terms of dense water mass formation. A comparison of the three‐dimensional model and a two‐dimensional (slice) model shows that key results can be reproduced with the slice model. In summary, the results of the process studies indicate that cellular features in the sea ice cover, which may be detectable by remote sensing techniques, are closely related to active brine‐driven convection.
Mesoscale wind measurements using recalibrated ERS SAR images
Authors: Lehner S. , Horstmann J. , Koch W. , Rosenthal W.
Published: February 2004

The precision images (PRI) of the synthetic aperture radars (SAR) on board the European Remote Sensing Satellites ERS‐1 and ERS‐2 are used to derive mesoscale wind fields over the ocean. For calculation of the wind speed the C‐band model (CMOD4) is used, which was originally developed by Stoffelen and Anderson [1993] for the European Space Agency (ESA) to derive wind fields from measurements of the wind scatterometer (SCAT). In the case of the ERS‐1/2 SAR the CMOD4 is used to compute the wind speed from the normalized radar backscatter cross section (NRCS) and the incidence angle of the radar beam, both computed from the SAR.PRI data. The third input variable is the wind direction, which is estimated from the wind streaks in the images or from ground truth measurements. The SAR data are affected by a power loss, caused by saturation of the analog to digital converter (ADC) of the SAR. Therefore the images have to be recalibrated. Errors in the derived wind speed are mainly due to ADC saturation and uncertainties of the input wind direction. These errors are estimated for various wind conditions. Mesoscale wind fields computed from ERS‐1/2 SAR.PRI images taken between the Shetland Islands and the west coast of Norway are compared to ground truth measurements and modeled wind fields from the German weather service (DWD). Wind fields of the nonhydrostatic mesoscale model Geesthacht simulation model of the atmosphere (GESIMA) are compared to the derived wind field of the ERS‐1 SAR.PRI image at the island Rügen in the Baltic Sea.
Directivity of wind vectors derived from the ERS‐1/AMI scatterometer
Authors: Ebuchi Naoto , Graber Hans C.
Published: February 2004

Directional distribution of the wind vectors observed by the ERS‐I active microwave instrument (AMI) scatterometer over the global oceans is investigated to examine effects of errors in the geophysical model function used to retrieve the wind vectors from backscattering measurements. Three scatterometer data products, together with wind data derived from two operational meteorological analysis models, are analyzed and compared with each other for a period of 2 months. Frequency distributions of the wind directions relative to the midbeam looking direction are calculated in bins of 10°. It is found that scatterometer‐derived wind vectors may exhibit systematic directional preference relative to the antenna beams in comparison with those of the model winds. This artificial directivity is considered to be caused by imperfections in the model function used to retrieve the wind vectors. Dependencies of the directional distributions on incidence angle and wind speed are also discussed for each data products. The distribution, of wind directions is very sensitive to the errors in the model function and can be used as an effective measure of self‐consistency to validate the model function and retrieved wind vectors.
Measurements of the diffusion coefficients of CFC‐11 and CFC‐12 in pure water and seawater
Authors: Zheng Min , De Bruyn Warren J. , Saltzman Eric S.
Published: February 2004

Trichlorofluoromethane (CCl3F; CFC‐11) and dichlorodifluoromethane (CCl2F2; CFC‐12) have been widely used as tracers of oceanic circulation and mixing on decadal timescales. In order to estimate their transfer rate across the air‐sea interface, liquid‐phase diffusion coefficients are needed In this study the diffusivities of CFC‐11 and CFC‐12 in pure water were measured over the temperature range 0.6–30°C. Diffusivities of CFC‐11 in pure water ranged from (5.24±0.25)×10−6 cm2S−1 at 0.6°C to (1.13±0.05)×10−5 cm2S−1 at 30.3°C and a fit to the data yielded the equation DCFC‐11 = 0.015 exp (−18.1/RT), where R is the universal gas constant in kJ mol−1 K−1 and T is the temperature in Kelvin. Diffusivities of CFC‐12 in pure water ranged from (5.38±0.22)×10−6 cm2 s−1 at 0.6°C to (1.26±0.05)×10−5 cm2 s−1 at 30.3°C and the temperature dependence can be expressed as DCFC‐12= 0.036 exp (−20.1/RT). The estimated uncertainty in both equations is <3%. Experiments were also carried out in seawater for each compound. For CFC‐11 the diffusivity in seawater was not significantly different from that in pure water. However, the diffusivity of CFC‐12 in seawater was found to be 7.2±3.0% lower than that in pure water. Schmidt numbers for both CFC‐11 and CFC‐12 in pure water and seawater were estimated from the data.
Fluid and sediment dynamics of upper stage plane beds
Authors: Bennett Sean J. , Bridge John S. , Best James L.
Published: February 2004

To understand more fully the fluid and sediment dynamics of upper stage plane beds, laboratory experiments were conducted using mobile and fixed beds where turbulent motions of fluid and sediment were measured using laser anemometry. Bed‐elevation fluctuations on mobile upper stage plane beds reveal millimeter‐high bed waves. Vertical profiles of flow velocity, mixing length, and eddy viscosity (diffusivity) are represented well by the law of the wall. For the mobile bed, von Kármán/s κ ≈ 0.33 and equivalent sand roughness to mean bed‐grain size varies from 9 to 17 because of the presence of bed load and low‐relief bed waves. For fixed beds with no sediment transport, κ ≈ 0.41 and equivalent sand roughness is equal to the mean bedgrain size. The decrease in κ for mobile beds is related to the relative motion of grains and fluid. Mobile‐bed turbulence intensities are greater than those for sediment‐free fixed beds because of enhanced wake formation from the lee side of near‐bed grains and low‐relief bed waves. Sediment diffusivities εs calculated in a similar way to fluid diffusivities ε indicate that εs≈ε. Sediment diffusivities calculated using the equilibrium balance between upward diffusion and downward settling of sediment are similar to ε in near‐bed regions (y/d < 0.3) but are larger than ε higher in the flow, suggesting that suspended‐sediment concentration higher in the flow is not closely related to mean fluid turbulence. Sediment diffusivities calculated for high‐magnitude ejection events are comparable to those calculated using the diffusion‐settling balance for y/d > 0.3, suggesting that larger, more energetic turbulent eddies are responsible for sediment suspension higher in the flow.
Effects of topographic steering and ambient stratification on overflows on continental slopes: A model study
Authors: Jiang Lin , Garwood Roland W.
Published: February 2004

The three‐dimensional flow structures of cold dense overflow water on continental slopes with and without along‐slope topographic variations and ambient slope water stratification are investigated, using a three‐dimensional numerical ocean model. We discuss the effects of topographic steering and ambient stratification on the downslope transport of dense overflow on continental slopes. A constant upstream inflow of dense water is specified at the upper edge of the slope that represents an overflow from a marginal sea. We present the numerical simulations for overflow plumes in the presence of three topographic features: a cross‐slope canyon that leads from the coast to the deep ocean, a cross‐slope ridge, and a seamount. We compared the numerical results with the previously published results of overflow plumes on a uniform slope without ambient water stratification. In the presence of a canyon, a portion of the dense water descends into the canyon, forming a bottom‐trapped plume that flows offshore along the right side (facing the ocean) of the canyon. The numerical result indicates that intensive mixing and entrainment occur in the canyon plume. The remainder of the overflow flows across the canyon and keeps descending on the slope while being deflected to the right‐hand side of the inflow. In the presence of a cross‐slope ridge, part of the water is blocked by the ridge and the flow is confined along the left side of the ridge. The remaining portion of the plume water flows over the ridge toward the right‐hand side of the inflow. The presence of a canyon or a ridge significantly enhances the downslope transport of dense water compared with the uniformly sloping bottom case. A seamount does not affect the cross‐isobath transport of dense water as much as does a canyon or a ridge. A seamount does influence the mixing, entrainment, and the plume trajectories. Ambient slope water stratification has significant influence on the mixing and cross‐slope penetration of the overflow plumes. It has hindered the downslope penetration of the plumes as a result of enhanced mixing and entrainment when the plumes encounter deep denser water.
Regime shifts in mesoscale deformations of sea ice during the winter
Authors: Korsnes Reinert
Published: February 2004

Large temporary rigid areas in the Arctic sea ice cover form and disintegrate in a few days during winter. When these rigid areas are shore‐fast, they eliminate moment flux from air to water via wind forcing on the ice. Temporary shore‐fast ice causes mixing of upper stratified waters below the ice in areas of strong tidal currents. Satellite data and observations by explorers in the Arctic show that large rigid areas tend to break up during the summer. We can conclude that formation and breakup of rigid areas are sensitive to temperature. The present study illustrates techniques for satellite observation of the dynamics of the Arctic sea ice cover during winter. Better understanding of the physical mechanisms involved will enhance codes for such satellite observations. The study indicates anomalous/“critical” dynamics and scale invariance in the formation and breakup of rigid areas. These indications come from direct satellite observations and are supported by generic conceptual models for ice dynamics during winter. Critical phenomena often form fractal structures with no natural lengths.
Determining geostrophic velocity shear profiles with inverted echo sounders
Authors: He Yuguang , Watts D. Randolph , Tracey Karen L.
Published: February 2004

It is known that vertical acoustic travel time (τ), round‐trip from the seafloor to the sea surface as measured by inverted echo sounders (IESs), can be interpreted in terms of dynamic height. This relationship is generalized and quantified in this paper for dynamic height (ΔDi, j) integrated between a variety of pressure limits (pi, pj) which span different portions of the main thermocline. The generalized form of the ΔDi,j(τ) relationships is nonlinear; the conventional linear relationship is valid when the limits of integration span the entire main thermocline. Velocity and temperature records are shown to be highly correlated vertically, indicating that the variability of the Gulf Stream and adjacent eddy field is dominated by the lowest baroclinic mode, which is called a gravest empirical mode (GEM). A “parallel isotherms model” is used to approximate the GEM and to develop analytic expressions for the observed ΔDi,j(τ) relationships in the Gulf Stream. The analytic expressions represent the observations well, with noise‐to‐signal variance ratios that are typically 1%. Using these new ΔDi,j(τ) relationships, the baroclinic velocity structure can be determined geostrophically by measuring the horizontal gradients with laterally separated τ measurements from IESs. Baroclinic velocities determined from a two‐dimensional array of IESs in the Gulf Stream during 1988–1990 agree with velocity shears directly measured by current meters. The rms velocity difference between these two measurements of velocity shear at 400 dbar relative to 1000 dbar was 12 cm s−1 in the presence of typical currents of 50 cm s−1. Ageostrophic motions (at both mesoscale and submesoscale), measured by the current meters but not by the IESs, contribute most of the velocity differences.
Hydrographic changes in the Canada Basin of the Arctic Ocean, 1979–1996
Authors: Melling Humfrey
Published: February 2004

Hydrographic surveys of the southern Canada Basin have been conducted in winter almost annually since 1979. Coverage has extended 100–200 km beyond the shelf to water depths of 2000–3000 m. Water properties in the upper 1500 m have fluctuated over intervals of a few years, and progressive changes have taken place during the 17 years of this study. At depths below the warm core of the Atlantic layer, water is warmer and fresher now than in the early 1980s. These changes reflect a thickening of the warm core at its lower boundary by more than 100 m. The maximum temperature of the Atlantic water has decreased by 0.06°C, and the salinity at the maximum has decreased by 0.027. Above the Atlantic layer the lower halocline (34.5 isohaline) has cooled by 0.12°C, a change which may indicate that ventilation of this level on the European side of the Arctic has been more effective in recent years. A good correlation between temperature fluctuations on the 34.5 isohaline and depth fluctuations of the lower 0°C isotherm suggests common forcing of both parameters. Variation in the flow through the Barents Sea into the Arctic is proposed as that common influence. The upper halocine has warmed by 0.15°C on the 33.5 isohaline. This trend could be a consequence of decreasing ventilation of the upper halocline over the broad shallow shelves on the Pacific side of the Arctic Ocean and may be related to the decrease in the strength of the Siberian High during the same time. The net result of changes in the hydrography of the Canada Basin has been an increase of 0.2 GJ m−2 in stored sensible heat, an amount sufficient to melt about 0.7 m of sea ice. The bulk of the increase results from the thickening of the Atlantic layer below 500 m.
Water property and current distributions along the WHP‐P9 section (137°–142°) in the western North Pacific
Authors: Kaneko Ikuo , Takatsuki Yasushi , Kamiya Hitomi , Kawae Satoshi
Published: February 2004

The Japan Meteorological Agency carried out full‐depth, high‐resolution hydrographic measurements in July‐August 1994 along the 137°–142°E line as a contribution to the World Ocean Circulation Experiment. The line spans the subtropical and tropical regions of the western North Pacific with a full set of water mass and current distributions. At 28°N to the south of the Kuroshio recirculation, there exists an eastward current distinct from the currents associated with the subtropical fronts. The eastward current is characterized by the meridional thermal gradient extending down to 1500‐m depth. Deep silicate has a meridional boundary at 25°N, forming two cores of the maximum to the north and south of the boundary. The northern core centered at 28°N is meridionally coincident with other property extrema, indicating an inflow from the Northwest Pacific Basin down to 2000‐m depth. The southern core centered at 16°N suggests another westward inflow from the East Mariana Basin to the West Mariana Basin. A broad isopycnal depression at middepths and bottom water properties over the Shikoku and West Mariana Basins indicate a near‐bottom circulation along which the inflow water through the Yap‐Mariana Junction at 12°N fills the West Mariana Basin and then spreads to the Shikoku Basin and Philippine Basin successively. A part of the bottom water from the South Pacific bifurcates around the Yap‐Mariana Junction and enters the West Caroline Basin via the Yap Trench. This supports another path of deep water inflow to the Philippine Basin from the southernmost channel at 4000‐m depth.
Measurement of extinction‐to‐backscatter ratio for near‐surface aerosols
Authors: Rosen James M. , Pinnick Ronald G. , Garvey Dennis M.
Published: February 2004

A method for measuring the local extinction‐to‐backscatter ratio of atmospheric aerosols is described and demonstrated using aerosols indigenous to the arid southwestern United States. The approach employs simultaneous observations from two separate devices: one a nephelometer (for the extinction measurement) and the other a backscattersonde operated at ground level (for the backscatter measurement). Since the instruments may be deficient in measuring the true scattering coefficients for some aerosols, optical response models are employed to estimate the magnitude of possible errors and make modest corrections to improve the accuracy of the final values. It is found that the measured extinction‐to‐backscatter ratio is similar to the values calculated from a simple optical model employing homogeneous spherical aerosols with sizes and bulk composition comparable to the aerosol associated with the measurements. Thus possible nonspherical particle scattering effects were not distinctly observed for the aerosols sampled.
An internally consistent set of globally distributed atmospheric carbon monoxide mixing ratios developed using results from an intercomparison of measurements
Authors: Novelli P. C. , Connors V. S. , Reichle H. G. , Anderson B. E. , Brenninkmeijer C. A. M. , Brunke E. G. , Doddridge E. G. , Kirchhoff V. W. J. H. , Lam K. S. , Masarie K. A. , Matsuo T. , Parrish D. D. , Scheel H. E. , Steele L. P.
Published: February 2004

The Measurement of Air Pollution from Satellite (MAPS) instrument measures carbon monoxide (CO) in the middle troposphere from a space platform. In anticipation of the deployment of MAPS aboard the space shuttle Endeavor for two 10‐day missions in 1994, plans were made to prepare a set of correlative measurements which would be used as part of the mission validation program. Eleven laboratories participated in the correlative measurement program by providing NASA with the results of their CO field programs during April and October 1994. Measurements of CO in the boundary layer, while not used in the MAPS validation, provide a picture of CO in the lower troposphere. Because measurements of CO made by different laboratories have been known to differ significantly, all correlative team members participated in an intercomparison of their measurements to define potential differences in techniques and calibration scales. While good agreement was found between some laboratories, there were differences between others. The use of similar analytical techniques and calibration scales did not always provide similar results. The results of the intercomparisons were used to normalize all ground‐based measurements to the National Oceanic and Atmospheric Administration/Climate Monitoring and Diagnostics Laboratory CO reference scale. These data provide an internally consistent picture of CO in the lower atmosphere during spring and fall 1994.
Remote sensing of carbon monoxide over the continental United States on September 12–13, 1993
Authors: McMillan W. W. , Strow L. L. , Smith W. L. , Revercomb H. E. , Huang H. L. , Thompson A. M. , McNamara D. P. , Ryan W. F.
Published: February 2004

Tropospheric carbon monoxide (CO) column densities were retrieved from 491 nadir infrared spectra obtained by the University of Wisconsin's High‐Resolution Interferometer Sounder (HIS) during a cross‐country flight of a NASA ER‐2 on September 12–13, 1993 (UT). A classical, Fourier‐based signal‐processing technique was utilized to retrieve the CO column density from the 2135–2200 cm−1 portion of the CO 1–0 vibration‐rotation band. Error analysis indicates column CO retrieval uncertainties of approximately ±10%. Retrieved CO column densities over the western United States from this flight, ∼1.2×1018 cm−2, agree well with previous ground‐based CO column measurements over the western United States at the same season. Derived CO sensitivity functions for these measurements possess a broad peak centered in the 500–600 mbar region, thus implying the retrieved tropospheric CO mixing ratios are indicative of the mean free troposphere (mft). Across the United States, three spatial groupings of CO were observed: west, mft CO ∼76 parts per billion by volume (ppbv); midwest, mft CO ∼56 ppbv; and east, mft CO ∼71 ppbv. Weather map and back trajectory analyses indicate different source regions for the air parcels in each of these regions. The low CO amounts over the midwest most likely result from the mixing of rapidly subsiding air naturally low in CO with a low‐altitude inflow of similarly clean subtropical air off the Gulf of Mexico. These results demonstrate the utility of satellite infrared spectrometer observations to globally map tropospheric CO abundances and further reveal the impact of synoptic scale atmospheric circulations on CO abundances.