bluuebunny/crossref_metadata_2025 huggingface dataset:
Satellite observations of sea surface cooling by hurricanes
Authors: Stramma Lothar , Cornillon Peter , Price James F.
Published: February 2008

Sea surface cooling associated with 13 hurricanes in the western North Atlantic between September 1981 and December 1984 is examined using satellite‐derived sea surface temperature fields. Some surface cooling is observed in all cases; however, because of cloud cover and the fairly weak signal in some cases, we see pronounced cooling along an extensive and continuous portion of the storm path for only three strong hurricanes. The persistence of cooling following the passage of a hurricane varies from a few days to at least 16 days. The amplitude of cooling is moderately well correlated with hurricane strength and is as large as 3.5°C. When the hurricanes move rapidly, the maximum cooling occurs well to the right of the track (approximately 70 km), whereas for slowly moving hurricanes the maximum cooling occurs near or on the track. Because western North Atlantic hurricanes are often found in close proximity to high pressure systems, daytime satellite images must be made with some care because of diurnal warming.
A simple, objective analysis scheme for scatterometer data
Authors: Levy Gad , Brown Robert A.
Published: February 2008

A simple economical objective analysis scheme is devised and tested on real scatterometer data. It is designed to treat dense data such as those of the Seasat A satellite scatterometer (SASS) for individual or multiple passes and preserves subsynoptic scale features. Errors are evaluated with the aid of sampling (“bootstrap”) statistical methods. In addition, sensitivity tests have been performed which establish qualitative confidence in calculated fields of divergence and vorticity. The SASS wind algorithm could be improved; however, the data at this point are limited by instrument errors rather than analysis errors. The analysis error is typically negligible in comparison with the instrument error but amounts to 30% of the instrument error in areas of strong wind shear. The scheme is very economical and thus suitable for large volumes of dense data such as SASS data.
On the baroclinic response of the zonal pressure gradient in the equatorial Atlantic Ocean
Authors: Weisberg R. H. , Weingartner T. J.
Published: February 2008

Temperature time series obtained from surface moorings deployed along the equator in the Atlantic Ocean during the Seasonal Response of the Equatorial Atlantic Experiment and the Programme Français Océan et Climat dans l'Atlantique Equatorial were used to investigate the baroclinic response of the zonal pressure gradient due to the sloping isopycnals. The zonal pressure gradient evolved as a complicated function of time, depth, and zonal position. The most rapid and spatially inhomogeneous variations corresponded to periods of rapidly changing easterly wind stress. Following these periods the baroclinic response due to the sloping isopycnals was observed to overshoot its intended equilibrium before relaxing to it. In so doing, it tended to buffer pressure gradient variations at the depth of the Equatorial Undercurrent (EUC). Over much of the year the isopycnal slopes opposed the surface slope. After the winds relaxed in winter, however, the isopycnal slopes reversed and acted in concert with the surface slope, thereby enhancing the pressure gradient at the depth of the EUC relative to that at the surface. This reversal might be important in maintaining the EUC during times of weak easterly wind stress. The vertical structure of the zonal pressure gradient varied with the depth of the thermocline. When the winds were weak and the thermocline was shallow, the baroclinic response of the zonal pressure gradient due to the sloping isopycnals was primarily effected in the upper 50 m. After the winds intensified and the thermocline deepened the baroclinic response extended down to at least 150 m.
Accurate measurement of mean sea level changes by altimetric satellites
Authors: Born G. H. , Tapley B. D. , Ries J. C. , Stewart R. H.
Published: February 2008

We examine here a novel yet simple technique for monitoring changes in global mean sea level over periods of weeks to years with an accuracy of a few centimeters using altimeter data from a well‐tracked satellite. The technique is based on the following argument. A satellite's orbit period and, hence, the mean semimajor axis of the orbit, are accurately determined by tracking systems located on the earth's surface. With laser or radiometric tracking systems, the mean semimajor axis can be determined with an accuracy of better than a centimeter. If the satellite carries an accurate altimeter, the difference between the mean semimajor axis and the global mean height measured by the altimeter is mean sea level. Any temporal change in the measurement of sea level must be due to drift in the altimeter or to change in the volume of the sea. To demonstrate the application of this technique, the fully corrected altimeter measurements of sea level obtained by Seasat during a 24‐day period when the satellite was in an exactly repeating orbit were separated into eight 3‐day segments and averaged over each of these periods. The calculated mean sea level relative to the Goddard Earth Model‐10B geoid varied over a range of ±7 cm during these eight periods. The variation is due primarily to errors in the vertical component of the satellite's ephemeris, which had a standard deviation of approximately 1.3 m. The results have important consequences. The proposed Topex/Poseidon altimetric satellite mission should have an ephemeris error of around 10 cm, and the satellite's ground track will repeat every 10 days. Thus, we expect that data from this satellite could be used to monitor variations in mean sea level with an accuracy of 1 or 2 cm during the 3‐ to 5‐year duration of the mission. Errors in the observations will be due primarily to either drift in the altimeter or orbit error. If an alternate technique is available to monitor the altimeter drift, the measurements can be used to monitor mean sea level with an accuracy which may be sufficient to detect global climate change.
Atmospheric boundary layer modification in the marginal ice zone
Authors: Bennett Theodore J. , Hunkins Kenneth
Published: February 2008

A case study of the Andreas et al. (1984) data on atmospheric boundary layer modification in the marginal ice zone is made. Our model is a two‐dimensional, multilevel, linear model with turbulence, lateral and vertical advection, and radiation. Good agreement between observed and modeled temperature cross sections is obtained. In contrast to the hypothesis of Andreas et al., we find the air flow is stable to secondary circulations. Adiabatic lifting and, at long fetches, cloud top longwave cooling, not an air‐to‐surface heat flux, dominate the cooling of the boundary layer. The accumulation with fetch over the ice of changes in the surface wind field is shown to have a large effect on estimates of the surface wind stress. We speculate that the Andreas et al. estimates of the drag coefficient over the compact sea ice are too high.
Structure and dielectric properties at 4.8 and 9.5 GHz of saline ice
Authors: Arcone Steven A. , Gow Anthony J. , McGrew Seth
Published: February 2008

The structure and salinity characteristics of saline ice slabs removed from ice sheets grown in an outdoor pool have been studied and related to the complex relative dielectric permittivity measured, utilizing free space transmission techniques, at 4.8 and 9.5 GHz. The saline ice closely simulated Arctic sea ice in its structural and salinity characteristics which were regularly monitored in a number of ice sheets grown during the winters of 1983–1984 and 1984–1985. In‐situ transmission measurements at similar frequencies were also made on the ice sheet itself using antennas located above and beneath the ice. The slab measurements were made during warming from −28°C to −2°C on slabs grown during the winter of 1983–1984 (4.75 GHz) and during a warming and cooling cycle over a slightly larger temperature range on slabs grown during the winter, 1984–1985 (4.80 and 9.50 GHz). The 1983–1984 results show both the real εr′ and imaginary εr″ parts to vary almost in direct proportion to the brine volume νB at values less than about 50‰. The 1984–1985 slabs showed only εr′ to depend strongly on νB while values of εr″ were considerably less than in the previous year. This difference may have been due to greater electrical conductivity in the 1983–1984 slabs, which could be related to distinct differences seen in brine pocket structure between the two winters. Values of εr′ as a function of νB were slightly lower on the average at 9.50 GHz than at 4.80, and most values of εr′ agreed with the results of others when their temperature and salinity values were converted to values of νB. Changes in εr′ due to thermal modification (laboratory warming) seem more strongly related to a gain in air volume due to brine drainage than to the redistribution of brine inclusions. The in‐situ measurements showed extremely high attenuation for the young (<12 cm) brine‐rich ice. Good agreement was found between data for the more desalinated samples and theoretical values predicted by a previously proposed dielectric mixing model that was modified to account for the brine pocket geometry observed in thin sections, and also by including a bulk conductivity term to account for the observed loss.
The marine atmospheric boundary layer jet in the Coastal Ocean Dynamics Experiment
Authors: Zemba Jan , Friehe Carl A.
Published: February 2008

The vertical and horizontal structure of the atmospheric boundary layer near the northern California coast was investigated during spring upwelling conditions as part of the 1981 Coastal Ocean Dynamics Experiment. Two daytime aircraft flights were devised to measure mean and turbulent quantities for 25‐km tracks along and across the continental shelf from 30‐ to 1200‐m altitude. The Pacific high offshore and an inland thermal low characterized the synoptic situations, and equatorward winds resulted, which produced intense ocean upwelling. The wind profile was found to be jet shaped: maximum wind speeds were 25 m s−1 and 16 m s−1 at 400 and 100 m, respectively, in the two flights. Above and below the heights of the jet speed maxima, the wind speed decreased rapidly. Sharp density inversions existed at the levels of the peak wind speeds; in one flight the inversion also sloped down toward the coast. Turbulence was effectively confined below the inversions. Strong, zonal temperature gradients above the inversion between the hot land and cool marine air caused a thermal wind for which the wind speed decreased with height. Below the inversion, turbulent stress divergence was large and effective in transferring the horizontal momentum of the wind to the sea, slowing the wind. There was also a small thermal wind below the inversion but opposite to the one above owing to the well‐mixed air temperature following the sea surface temperature, which was cold at the coast and relatively warmer offshore owing to the upwelling. These effects explain the jet‐shaped wind profile. The mean momentum equations show that an acceleration toward the coast can balance the pressure gradient, Coriolis, and turbulent stress divergence forces, and there were some observations to support this. Complete balance was not obtained for the turbulent kinetic energy budget; inferred dissipation rates were too large.
A random discontinuous model of sea ice motion
Authors: Thorndike A. S.
Published: February 2008

The rate at which the sea ice pack spreads apart, exposing the warm ocean to the cold atmosphere, controls the air‐sea heat exchange in the Arctic and the production of ice mass. The rate of spreading, or opening, can be estimated from observations of ice motion, using a model of the ice pack which accounts for the random manner in which the ice is broken into rigid pieces. In a region intersected by many cracks, some cracks will typically be opening while others are closing. In this case the total of the openings will exceed the average divergence of the region. A few measurements of the ice motion cannot resolve the openings at each crack, so that any estimate of opening will be accompanied by estimation errors. The random model adopted here imagines the leads to be distributed according to the Poisson distribution and the relative displacements at any crack to be Gaussian. Under these assumptions it is determined how the total opening is related to the average deformation, and how this relationship depends on the size of the region and on the number of points used to determine the average deformation.
Marine condensation nucleus generation inferred from whitecap simulation tank results
Authors: Cipriano Ramon J. , Monahan Edward C. , Bowyer Peter A. , Woolf David K.
Published: February 2008

The condensation nuclei (CN) produced during a set of experiments in the Whitecap Simultation Tank at University College, Galway, were measured with a TSI 3020 nucleus counter. The total number of CN produced per breaking wave event was 3.5 ± 0.5 × 107 for a seawater temperature near 15°C. The CN production per unit area of whitecap (108 m−2) and the previously observed whitecap time decay constant of ∼3.5 s implies a whitecap CN flux Fw of ∼2.8 + 0.9 × 107 m−2 s−1. This can be combined with the whitecap coverage W versus 10 m wind speed U relation of E. C. Monahan and I. O'Muircheartaigh (1980), W(U) = 3.84 × 10−6 U3.41, to estimate the general oceanic CN flux F0 = WFW. For U = 10 m s−1, this relation gives W = 1%, and thus F0 is ∼2.8 × 105 m−2 s−1. Using the same Whitecap Simulation Tank and a PMS classical aerosol spectrometer, E. C. Monahan et al. (1982) determined that the whitecap flux Fw of giant particles (radii > 1 μm at relative humidity = 80%) was ∼2 × 106 m−2S−1. Clearly, most of the CN produced by this whitecap simulation are of submicron size, and this was also the case in the model breaking wave experiments of R. J. Cipriano et al. (1983). Both laboratory whitecap simulations suggest that the ocean contributes significantly to the CN and cloud condensation nuclei populations of the marine atmospheric boundary layer far from land.
Wind stress measurements over rough ice during the 1984 Marginal Ice Zone Experiment
Authors: Anderson R. J.
Published: February 2008

The indirect dissipation method has been used to estimate momentum fluxes from a ship working in the outer marginal ice zone of the East Greenland Sea during the 1984 Marginal Ice Zone Experiment. These indirect measurements have been compared with direct eddy correlation measurements whenever the ship was moored to an ice floe and a sonic anemometer could be deployed. Neutral drag coefficients referenced to 10 m have been grouped in categories for various ice types and concentrations during 4‐ to 11‐m/s winds. There is a gradual increase in the neutral drag coefficient with ice concentration and a doubling of the value in 70–90% concentration from 2.7 ± 0.3 × 10−3 (mean plus or minus standard deviation) for a mixture of brash, small, and medium floes with rafted edges to 5.3 ± 0.5 × 10−3 over very rough cakes and brash with many sharp vertical edges. Drag coefficients in this region of multiyear floes with larger roughness features are typically higher than most values obtained over ice and reported in the literature and up to 5 times larger than open ocean values for similar wind speeds. The drag coefficient is determined primarily by floe size, roughness, and concentration.
On the relationship between atmospheric circulation and the fluctuations in the sea ice extents of the Bering and Okhotsk Seas
Authors: Cavalieri D. J. , Parkinson C. L.
Published: February 2008

Monthly and 3‐day averaged NIMBUS 5 electrically scanning microwave radiometer sea ice data have been analyzed to document the fluctuations of the Bering Sea and Sea of Okhotsk ice covers for the four winters 1972–1973 through 1975–1976 on the short‐term, seasonal, and interannual time scales and to define those periods for which there is an out‐of‐phase relationship between the fluctuations of the two sea ice covers. The sea ice fluctuations are shown to be related to changes in the position and intensity of quasi‐stationary high‐ and low‐pressure systems associated with large‐scale standing wave patterns in the atmosphere through a comparison of the areal changes in ice cover with changes in the amplitude and phase of zonal harmonics 1, 2, and 3 of the sea level pressure field. On the seasonal time scale, the sea level pressure for December, the month of most rapid seasonal sea ice growth for both the Bering and Okhotsk seas, is dominated by harmonic 2, which explains almost 60% of the total sea level pressure variance on average over the four winters. The phase of harmonic 2, which is associated with the position of the Aleutian Low, shifts from 156°E in 1972–1973 to 190°E in 1975–1976, thus providing a connection between the increasingly heavy Bering Sea ice cover over these four winters and the general circulation of the atmosphere. On the short‐term, episodes of midwinter Bering Sea ice retreat are generally preceded by or coincident with the breakdown of harmonic 1 and the intensification of harmonics 2 and 3. These episodes are also related to the coincidence of the phases of harmonics 2 and 3 with a mean position of 165°E. This result is in excellent agreement with a study of the North Pacific Oscillation showing that the two modes of the oscillation are associated with the longitudinal position of the Aleutian Low. It is suggested here that these two modes result from changes in the amplitudes and phases of atmospheric long waves 1, 2, and 3. Evidence is also presented indicating that the interaction of standing and transient components of wave 1 may play an important role in these fluctuations. Finally, these results establish an observational connection relating climate dynamics to changes in ice covers in seasonal sea ice zones.
On the interaction of a vortex with a shear flow
Authors: Stern Melvin E. , Flierl Glenn R.
Published: February 2008

The interactions between a point vortex and various kinds of shear flows on the ƒ plane are studied using barotropic and equivalent barotropic contour dynamics models. The shear flows are represented by a single interface separating two regions of constant, but different, potential vorticities. Linearized calculations, applicable when the vortex is far from the interface, show that an anticyclonic vortex to the “north” of a region of cyclonic shear will generate a localized northward perturbation on the interface. The interaction between the vorticity anomaly created by this displacement and the vortex result in “westward” propagation. Numerical calculations confirm this propagation tendency but also show that when the separation is small enough, the vortex will capture a segment of the interface by winding it up and around the vortex. When an anticyclone is embedded in the cyclonic half of a jet (with anticyclonic shear to the south of the interface), a second phenomenon is noticed; the vortex is drawn in toward the jet axis. The reason for this is discussed using first a simple linear theory and then a strongly nonlinear case. The dynamic processes described here should play a significant role in many oceanic situations such as the interaction between Gulf Stream rings and the stream.
Satellite observations of a western boundary current in the Bay of Bengal
Authors: Legeckis Richard
Published: February 2008

Satellite infrared observations of the Bay of Bengal during the latter part of February 1985 reveal the existence of two bands of warm water that resemble western boundary currents along the east coasts of India and Sri Lanka. A recently formed elliptical warm core eddy, with a major axis of nearly 150 km, appears at longitude 90°E and latitude 19°N at the end of the axis of the current. Color infrared images of sea surface temperature are used to illustrate the sea surface temperature patterns and to estimate their displacements with time.
Shelf water entrainment by Gulf Stream warm‐core rings
Authors: Garfield Newell , Evans David L.
Published: February 2008

Examination of 7 years of satellite advanced very high resolution radiometer imagery demonstrates that shelf water removal by entrainment adjacent to warm‐core rings is a common phenomenon, representing an important process for shelf water budgets. South of Georges Bank, streamer entrainment occurred 69 ± 20% of the time. In addition, 9 ± 6% of the time more than one streamer was active. The data show little mean seasonal variability but large interannual variability in streamer occurrence. Most of the variability is related to the passage of warm‐core rings south of Georges Bank. An instantaneous streamer transport value of 2.5 × 105 m3 s−1 was determined from ship‐tracked drogues and hydrographic data. Reducing this value to 70% gives an estimated mean annual shelf water removal by streamer entrainment of 1.8 × 105 m3 s−1 (5700 km3 yr−1) for this segment of the shelf. A balanced Gulf of Main transport budget can not be obtained when this value is compiled with transports across the other boundaries of the gulf; instead a net export of 16 × 104 m3 s−1 of water results. This lack of a balance emphasizes the uncertainty of the existing transport measurements. The fate of streamers includes incorporation into the warm‐core ring and detrainment from the ring with either the formation of cold cyclonic rings in the slope water or entrainment into the northern edge of the Gulf Stream. In addition to streamer entrainment, the satellite imagery reveals that a number of different phenomena are occurring which move shelf water across the shelf‐slope front. In 86 ± 13% of the images, some type of offshore transport is observed.
Changes in the marine biota coincident with the 1982–1983 El Niño in the northeastern Subarctic Pacific Ocean
Authors: Pearcy W. G. , Schoener A.
Published: February 2008

The very strong 1982–1983 El Niño is implicated in extraordinary northern range extensions and shifts in population distributions of many species of marine organisms from Oregon to Alaska during 1983. Some species such as Pacific and jack mackerel maintained large populations in the Pacific Northwest during the summer of 1983, as well as the summer of 1984, a year after physical subsidence of the event. Although salmon catches were large in Alaskan waters, populations off Oregon were severely reduced during this El Niño period. Mortality of maturing coho was unprecedented; the sizes of both coho and Chinook salmon in fisheries were at record lows, and survival of juvenile coho that entered the ocean in 1983 and 1984 was low. Decreased reproductive success and increased mortality of seabirds were observed during 1983 from Oregon, Washington, and Alaska and were probably related to decreased availability and productivity of usual prey in the abnormally warm surface waters. The large numbers of independent observations on unusual biological events during 1983 and the coincidence of occurrences of some species with previous strong El Niños infer that some changes observed in 1983 were a consequence of the strong 1982–1983 El Niño.
A heat budget for the Northern California Shelf during CODE 2
Authors: Lentz Steven J.
Published: February 2008

Moored current, water temperature, and meteorological observations made during the summer of 1982 as part of the Coastal Ocean Dynamics Experiment (CODE 2) are used to study both the mean and fluctuating heat budget for the northern California shelf. The volume considered extends from the sea surface to the bottom, from the coast to near the shelf break (13 to 23 km offshore), and 56 km alongshore. The largest terms in the mean heat budget over a 105‐day period spanning the summer season are a surface heat flux of 1.6 × 1011 W into the ocean and an offshore heat flux of 2.4 × 1011 W due primarily to an offshore flow of relatively warm water in the upper 30 m. Cooling due to an alongshore heat flux divergence is 0.6 × 1011 W. Fluctuations with time scales from days to weeks are large relative to the means. The correlation between observed changes in the heat content of the volume and the changes predicted by estimating the heat fluxes into and out of the volume is 0.82. The primary balance in the fluctuating heat budget is heating and cooling of the volume in response to on/offshore fluxes of heat in the upper 30 m. A simple two‐dimensional Ekman model reproduces the major features of the observed offshore heat flux fluctuations, correlation 0.82, indicating that this offshore heat flux is consistent with wind‐driven upwelling. However, at alongshore scales less than 56 km there is considerable alongshore variability in the cross‐shelf heat flux, particularly over the outer shelf. This spatial variability is presumably due to eddy motions. Standard deviations of the alongshore heat flux are about 50% of the cross‐shelf heat flux. Two modes of alongshore heat flux variability are observed. The dominant mode is characterized by large equatorward heat fluxes over the outer shelf during the early part of the upwelling season. This mode is associated with strong vertical shears in alongshore velocity in the vicinity of the upwelling front which results in equatorward flow of the warm surface water relative to the colder deep water. The second mode of alongshore heat flux variability is concentrated over the inner half of the shelf and is related to the wind such that poleward heat fluxes occur in the northern portion of the volume during wind relaxations (periods of weak winds). The presence of an anomalous lens of warm water over the shelf during CODE 2 is also examined.
The Natal pulse: An extreme transient on the Agulhas Current
Authors: Lutjeharms J. R. E. , Roberts H. R.
Published: February 2008

An analysis of satellite data collected over a period of 9 years as well as historic hydrographic data show that the northern Agulhas Current is subject to large, intermittent, and solitary meanders. These transient events, collectively named the Natal pulse, progress downstream at consistent rates of 21 cm/s. Upon reaching the area where the shelf broadens, their rate of progression slackens to 5 cm/s. They are present in some stages of development at least 17% of the time, extend offshore by about 170 km on average, and show a continuous lateral growth on moving downstream. With few exceptions the pulses are spawned as cold core, cyclonic, trapped lee eddies in the Natal Bight. They are held responsible for the intermittent coastal counter currents observed inshore of the Agulhas Current along the southern African coast and may play a crucial role in sediment distribution on the shelf.
Radar signatures of oil films floating on the sea surface and the Marangoni effect
Authors: Alpers Werner , Hühnerfuss Heinrich
Published: February 2008

Airborne radar backscattering experiments carried out recently by Singh et al. (1986) over sea surfaces covered with mineral oil films show that the radar cross section depression has a maximum as a function of incidence angle. In this paper we show that Singh et al.'s measurements can be explained by the Marangoni effect if the assumption is made that the mineral oil spill contained surface active material as “impurities.” The Marangoni effect causes a resonance‐type wave damping in the short gravity wave region when the sea surface is covered with a viscoelastic film. Maximum wave damping was observed by Singh et al. (1986) at frequencies around 8 Hz. Marangoni theory predicts such a maximum for surface active compounds of medium to low wave damping ability with a dilational modulus of the order of 0.01 Nm−1 Furthermore, it is demonstrated that the Ku band and C band radar backscattering depression curves do not contradict each other. It is pointed out that when converting the radar data into information on depression of spectral energy density of short surface waves, one has to take into account that the radar backscattering at low incidence angles is dominated by specular reflection, while at intermediate incidence angles it is dominated by Bragg scattering.
Effect of small‐wavelength waves on gas transfer across the ocean surface
Authors: Back D. D. , McCready M. J.
Published: February 2008

Transfer of slightly soluble gases across the air‐sea interface under conditions where no significant wave breaking is occurring is considered. The flow field near the interface is described by an Orr‐Sommerfeld equation with the key boundary condition being the variation in interfacial stress caused by a turbulent wind flow over small‐wavelength waves. Spectra for normal velocity fluctuations are calculated from measured wave amplitude spectra, and it is shown that very strong flows, which are in the close proximity of the interface and should be effective at enhancing mass transfer, occur and that only small‐wavelength waves (less than about 4 cm) contribute. Mass transfer coefficients, determined by solution to the advection‐diffusion equation with the reconstructed velocity field, agree well with available measurements. When the wave‐induced shear variation boundary condition is omitted, much smaller fluctuations and correspondingly lower mass transfer rates ensue; this second solution seems to be similar to the mechanism proposed by Coantic [1986].
Sea surface flow estimation from advanced very high resolution radiometer and coastal zone color scanner satellite imagery: A verification study
Authors: Svejkovsky Jan
Published: February 2008

A refined technique for estimating surface currents from the displacement of features in sequential advanced very high resolution radiometer (AVHRR) and coastal zone color scanner (CZCS) images is presented. It is used to calculate flow fields in two regions along the California coast, and the results are compared to concurrent drifter drogue observations. There is overall agreement to within approximately 6 cm/s, with somewhat better agreement at velocities less than 40 cm/s. The poorer performance of the technique at high velocities was due to difficulties in identifying and tracking features in areas of rapid flow. The accuracy of the measurements is primarily affected by the analyst's precision in tracking each feature which, in turn, depends on how well the 2‐ to 6‐km features preserve their identity from one image to the next. A 12‐ to 24‐hour interval yielded the best results in this study. The directional component of the satellite‐derived flow field was representative of subsurface flow patterns down to at least 100 m. Although velocities obtained from AVHRR infrared and CZCS visible images may not always represent flow at the same depth, the measurements were practically identical with the data used.
Interannual fluctuations of the Mindanao Current inferred from sea level
Authors: Lukas Roger
Published: February 2008

Some recent hypotheses for the El Niño‐Southern Oscillation (ENSO) imply that fluctuations of the Mindanao Current may be involved in the early stages of the phenomenon. In this paper, first the relatively sparse knowledge of this southward flowing western boundary current is reviewed, and then the difference in sea level between the islands of Mindanao in the Philippines and Malakal in Palau is used as an index of Mindanao Current fluctuations. The difference series spans the period 1974 through 1985, encompassing the 1976 and 1982–1983 ENSO events. In addition, the somewhat anomalous (but non‐ENSO) 1980 year is included in the record. The dominant signal in the sea level difference is a biannual oscillation. Estimated transport changes are at least 16 Sv, or about 50% of the mean transport. In the year prior to the two ENSO events, the Mindanao Current is relatively weak, while during the ENSO year the current is stronger than average. However, the strongest fluctuations occur in the non‐ENSO period 1979–1980, and there is no apparent relationship between the fluctuations of the Mindanao Current and the strength of the ENSO signal.
Moisture and latent heat flux variabilities in the tropical Pacific derived from satellite data
Authors: Liu W. Timothy
Published: February 2008

A method of determining ocean‐atmosphere moisture and latent heat fluxes using spaceborne sensors is presented and evaluated. The satellite data used are the geophysical parameters: sea surface temperature, precipitable water, and surface wind speed, derived from observations of the microwave radiometer on the Nimbus 7 spacecraft from 1980 to 1983 in the tropical Pacific. The period included one of the most intense El Niño‐Southern Oscillation (ENSO) episodes of this century. The surface humidity is first derived from the precipitable water using a global empirical relation and is found to be in close agreement with in situ measurements in the ascending and the descending branches of the Hadley and Walker circulations during both ENSO and non‐ENSO periods. The latent heat flux is then computed with a bulk parameterization model. At monthly and 2° latitude by 2° longitude resolution, the random error of the computed latent heat flux is estimated to approximately 26 W/m2 with the flux variability in the order of 100 W/m2. In areas covered by surface convergence, the moisture flux is found to be low, with the temporal variability due mostly to the variability of wind speed. Elsewhere, the variability of sea‐air humidity difference plays a more important role. During the early phase of the 1982–1983 ENSO, a surface convergence center moves east leading the anomalous equatorial westerlies. At this center, the low wind and high humidity caused negative (low) latent heat flux anomalies despite anomalously high sea surface temperatures. Latent heat flux is found to play an important role in the seasonal cooling of the upper ocean except in areas covered by major surface convergence zones where the variability of insolation is expected to be large and in areas of ocean upwelling where ocean dynamics perturb the upper ocean heat balance. The latent heat flux from the general circulation model of the European Center of Medium Range Weather Forecast is found to be inadequate in capturing the temporal and spatial variations computed from the satellite data.
Temporal variations of particle fluxes in the deep subtropical and tropical North Atlantic: Eulerian versus Lagrangian effects
Authors: Deuser W. G. , Muller‐Karger F. E. , Hemleben C.
Published: February 2008

The flux of particles measured by sediment traps in the deep water of the Sargasso Sea and western tropical North Atlantic undergoes pronounced temporal variation. In the Sargasso Sea the variability is largely due to seasonal changes in mixed‐layer depth and attendant changes in primary productivity affecting a wide region. By contrast, the variability in the western tropical Atlantic appears to be caused by patches of elevated nutrient and pigment concentrations which have their origin in the plumes of the Amazon and Orinoco rivers. Coastal zone color scanner scenes demonstrate the great seasonal and interannual differences in the direction and dispersal patterns of the plumes. The river plumes break up into irregular patches which may pass through the catchment area of a sediment trap at varying rates, thereby creating the impression of almost random temporal flux variability at a fixed trap site.
Basin sedimentation and the growth of prograding deltas
Authors: Syvitski James P. M. , Smith John N. , Calabrese E. A. , Boudreau B. P.
Published: February 2008

A theoretical model is developed for the infilling of a basin by the progradation of a delta. The model simulates four mechanisms for the transfer of sediment from the land to the sea: (1) bed load dumping along the delta front, (2) hemipelagic sedimentation under the seaward flowing river plume, (3) proximal slope bypassing by turbidity currents, and (4) the combined effects of both short‐term (wave and tidal action) and long‐term (creep and small slides) downslope diffusion of the accreting sediment mass. The general model is of relatively low precision, useful for predicting basin infilling on time scales greater than a few hundred years. The river plume portion of the model can predict sedimentation on time scales of less than a year and is designed to reflect the dynamics of a free, two‐dimensional, buoyant jet that transports a composite size population of suspended particles. The general model allows the prediction of lithologies changing with time and space. The model has been used to simulate infilling processes for Knight and Bute inlets, two grabenlike (fjord) basins along the coast of British Columbia. Model simulations of delta progradation over the last 10,000 years favorably predicted the modern seafloor bathymetry and sediment accumulation rates to within a factor of 2 of measured (210Pb, 137Cs, and sediment trap) rates.
Dynamics of saltwater intrusion in coastal channels
Authors: Wang Flora Chu
Published: February 2008

The dynamic behavior of saltwater intrusion in coastal channels with small tidal range is often dependent upon motions induced by freshwater inflow from the upstream drainage basin. In coastal Louisiana the salinity distribution in channels encompasses well‐mixed, partially stratified, and highly stratified phenomena. A two‐dimensional, laterally averaged, and semi‐implicit hydrodynamic model coupled with a salt flux transport model is developed to quantify the saltwater intrusion due to interactions of freshwater discharge, tidal activity, prevailing wind, and the density gradient caused by variations in salinity. In the model, the coefficients of eddy and salt diffusivity are varied as functions of space and time. The values of coefficients fitted from the field data are comparable to those reported by others. The numerical model, calibrated with independent field data sets, is then applied to predict the changes in the patterns of salinity distribution in channels resulting from changes in channel dimensions. Both computed and field results reveal that the salinity intrusion in coastal channels is highly dependent on the freshwater inflow and the channel dimensions.
Seasonal changes in the North Atlantic subtropical gyre
Authors: Stramma Lothar , Siedler Gerold
Published: February 2008

The eastern part of the North Atlantic subtropical gyre is found in the region between the Azores and the Cape Verde Islands. A study of the gyre structure in the area east of 35°W between 8°N and 41°N is presented. The geostrophic flow field determined from historical temperature‐salinity data sets by objective analysis indicates seasonal variations in shape but no significant changes in the magnitude of volume transports. The eastern part of the gyre has a larger east‐west and smaller north‐south extension in summer compared with the winter season. The center shifts by about 2° latitude to the south from winter to summer. Long‐term temperature time series (6.5 years) from a mooring near the Azores are consistent with these results, showing always a consistent temperature increase at the beginning of the year which is apparently due to the displacement of the northeastern part of the gyre. A comparison between the mean flow fields and fields obtained from individual zonal sections indicates large deviations north and south of the gyre but small deviations within the gyre.
Measurements of the angle between the wind vector and wind stress vector in the surface layer over the North Sea
Authors: Geernaert G. L.
Published: February 2008

Measurements of surface layer turbulence, in addition to full meteorological and oceanography quantities, over the North Sea indicated that the stress vector on long time scales is often aligned with a direction slightly different from the mean wind flow. When stratifications were near neutral, the angle difference between the stress and wind exhibited a dependence on the heat and momentum fluxes. In general, the stress vector was observed to be to the left of the flow during stable stratifications, while for unstable stratifications, it was to the right. This finding was consistent using two independent sets of wind stress data, i.e., from MARSEN (1979) and the North Sea Platform Winter Exercise (1985).
Modulation of radar backscatter from the ocean by a variable surface current
Authors: Caponi E. A. , Crawford D. R. , Yuen H. C. , Saffman P. G.
Published: February 2008

Calculations of surface wave and radar cross section modulation induced by a spatially varying surface current have been compared with field measurements made with synthetic aperture radar (X and L bands), real aperture radar ( X band), laser slope gauge, and charge‐coupled device video camera during the Joint Canada‐U.S. Ocean Wave Investigation Project (JOWIP), which took place in August 1983. The comparison reveals that (1) many existing wind relaxation models underpredict the hydrodynamic effect of the current, (2) the simple Bragg scattering model underpredicts radar backscatter modulation for higher‐frequency radars (e.g., X band) but appears acceptable at lower radar frequencies (e.g., L band), and (3) the discrepancy between measurements and calculations at high radar frequency is reduced, but not eliminated, when the effects of long surface waves have been accounted for.
Analysis of nonlinear internal waves in the New York Bight
Authors: Liu Antony K.
Published: February 2008

This paper presents the results on internal wave analysis of the current meter mooring data in the New York Bight from the SAR Internal Wave Signature Experiment (SARSEX). Selective sets of current and temperature measurements are analyzed for a parametric study of internal wave characteristics and shear effects on wave parameters are studied based on the limited data from moorings. The solitary wave theory has been extended for the wave evolution on a continental shelf by including dissipation and shoaling effects; a series of numerical simulations are performed to demonstrate the relative importance of dissipation and shoaling effects. From an observed initial wave packet at the upstream mooring, the numerical evolution simulation compares reasonably well with the measurements at the distant mooring for the leading two large solitons.
Comparisons of sea level and bottom pressure measurements at Drake Passage
Authors: Peterson Ray G.
Published: February 2008

Tide gauge and atmospheric sea level pressure measurements from each side of Drake Passage are compared with multiyear time series of bottom pressure at 500 m depth. Synthetic subsurface pressure (SSP), smoothed with a 40‐hour low‐pass filter, derived from tidal and sea level pressure records from the British Antarctic Survey base Faraday is coherent with bottom pressure from southern Drake Passage for periods of 6 to 600 days, but it is about 60° out‐of‐phase at the annual period. The difference between the two series for periods longer than 60 days is mainly annual and is as large as, or larger than, the seasonal variability of bottom pressure itself. Annual variations in open ocean mixed‐layer density near Antarctica are too small to account for the difference. The Faraday SSP series spans 21 years, slightly longer than the 18.6‐year lunar nodal tide, which appears to exist in the record. At the northern side of Drake Passage, SSP from Puerto Williams, Chile, does not compare well with nearby bottom pressure for any band of periods, apparently due to local winds for periods under 100 days and to annual cycles in upper layer density. Barotropic changes in transport of the Antarctic Circumpolar Current cannot be directly estimated using these surface observations, even though over seasonal periods they are an order of magnitude larger than the baroclinic changes due to variations in upper layer density.
Numerical simulations of the profile properties of undeformed first‐year sea ice during the growth season
Authors: Cox G. F. N. , Weeks W. F.
Published: February 2008

A simulation scheme is developed that estimates salinity profiles for first‐year sea ice during the growth season as a function of the growth history of the ice. The model considers the dependence of the initial ice salinity on ice growth velocity and sea water salinity and also the subsequent drainage of brine from the ice. The equation for ice growth assumes a linear temperature profile within the ice and is driven by surface heat balance equations that are based on smoothed climatic data for the central Arctic Basin. The estimated salinity profiles are in good agreement with natural profiles. Although temperature and salinity profiles depend upon the time of the year when ice growth is initiated, the brine volume profiles which they specify are essentially a unique function of ice thickness; a conclusion that holds even when the insulative effects of snow are considered. The temperature and brine volume profiles are then utilized to calculate the ice strength and elastic modulus profiles, which in turn specify the composite mechanical properties of the ice sheets through the application of a theory developed by Assur (1967). Significant differences, which are largest for thin ice sheets, are observed between ice sheet properties as calculated using composite plate theory and properties calculated from uniform plate theory and average ice properties. These results provide a justification for the practice, common within the ice modeling community, of parameterizing the mechanical behavior of pack ice on the basis of the ice thickness distribution.
Flume evaluation of the relationship between suspended sediment concentration and excess boundary shear stress
Authors: Hill Paul S. , Nowell Arthur R. M. , Jumars Peter A.
Published: February 2008

A flume study was undertaken to determine the source of the large variability in field estimates of γ, the coefficient of proportionality between excess shear stress and concentration of suspended sediment at a reference height above the bed. Accuracy in predicting suspended sediment concentration and particle flux demands accurate knowledge of this coefficient. To avoid error due to incorrect assumptions concerning the eddy diffusion coefficient for mass, reference concentration was estimated from concentration profiles. A linear relationship was found adequate to describe the dependence of reference concentration on excess boundary shear stress. The value of γ was determined to be 1.3×10−4. Values for the coefficient range between only 0.8×10−4 and 4.9×10−4 at the 95% confidence level. We show that the variability in previous field‐derived estimates of γ over 4 orders of magnitude is not attributable to unsound theory relating reference concentration to excess shear stress, but is most likely due to improper treatment of the eddy diffusion coefficient for mass and to measurement error.