bluuebunny/crossref_metadata_2025 huggingface dataset:
The thermal structure of the atmospheric surface boundary layer on Mars as modified by the radiative effect of aeolian dust
Authors: Pallmann Albert J.
Published: February 2008

A 52‐level time‐dependent radiative‐convective‐conductive heat transfer model, paired with a 30‐level ground conduction subroutine and a detailed soil‐atmosphere heat balance equation, is applied to heavy and slight dust‐laden atmospheric conditions on Mars. High spectroscopic, spatial, and temporal resolution is necessary to approximate the thermal structure of the atmospheric surface boundary layer under both conditions. The results show that heat is effectively exchanged across the surface layer, even in the absence of turbulent convection, by means of weak‐line and strong‐line transmission of radiant energy in both the solar (short‐wavelength) and planetary (long‐wavelength) domains. The diurnal temperature variation at the top of the boundary layer (∼2O m) covers about 75% of that of the surface in opaque dust‐laden and about 60% under thin dust conditions. The dust phase diminishes the spectral gappiness inherent in the CO2 absorption bands within the solar and planetary infrared.
A two‐dimensional photochemical model of the atmosphere: 2. The tropospheric budgets of the anthropogenic chlorocarbons CO, CH4, CH3Cl and the effect of various NOx sources on tropospheric ozone
Authors: Crutzen Paul J. , Gidel Louis T.
Published: February 2008

This paper presents two‐dimensional photochemical model simulations that show the influence of the various NOx sources from industry, lightning, the stratosphere, and aircraft on the tropospheric distributions of NOx, HNO3, and O3. We found that, by far, the best agreement with the global observations is obtained if the industrial sources are included in the calculations. Industrial activities have led to substantial increases of ozone concentrations in the lower troposphere of the northern hemisphere. Emissions of NOx by high‐flying aircraft have only a small effect on ozone concentrations in the troposphere. The ability of the model to simulate the global distributions of the long‐lived chlorocarbons CFCl3 and CF2Cl2 indicates that the interhemispheric exchange is rather well described. The model confirms an earlier finding by Rowland et al. (1982) that the CF2Cl2 emission rates estimated by the Chemical Manufacturers Association (CMA) may be 35–40% lower for the period 1976 through 1980. The model also supports the earlier finding of Hyson et al. (1980) that CFCl3 is apparently increasing roughly 10% faster than the CMA emission rates can account for during the period 1976 through 1980. Although this disparity could be explained by assuming 10% higher emission rates for CFCl3 during the period, the behavior of the interhemispheric gradient indicates that errors in the determination of the absolute concentrations could also be an explanation. The ability of the model to simultaneously simulate measured distributions of the shorter‐lived chlorocarbons CH3CCl3, CH2Cl2, C2HCl3, and C2Cl4 indicates that its average OH concentrations are also about correct. Based on these OH concentrations, the model tropospheric budgets of CO, CH4, and CH3Cl are calculated. The computed losses of CO, CH4, and CH3Cl by reaction with OH are 2.1×1015 g CO yr−1, 3.2×1014 g CH4 yr−1, and 1.9× 012 g CH3Cl yr−1, respectively.
Relationships between Pb and 210Pb in aerosol and precipitation at a Semiremote Site in northern Wisconsin
Authors: Talbot R. W. , Andren A. W.
Published: February 2008

Measurements of Al, Pb, 210Pb, and 210Po in precipitation and aerosol were used to estimate wet and dry components of the atmospheric flux at a semiremote site in northern Wisconsin. Wet deposition was primarily responsible for removing airborne Pb, 210Pb, and 210Po, while dry deposition was also important for Al. Although Pb and 210Pb both exhibited a wet/total ratio of about 0.8, precipitation washout ratios for Pb and 210Pb suggested that 210Pb was washed from the atmosphere with greater efficiency than was Pb. This phenomenon was also illustrated by comparing the weighted mean annual specific activity in precipitation (976 pCi 210Pb mg−1 Pb) and in aerosol (476 pCi 210Pb mg−1 Pb) at this site between June 1979 and June 1980. By consideration of the apparent differential precipitation washout of Pb and 210Pb, a reasonable estimate of the atmospheric flux of Pb was obtained by using the mean Pb/210Pb ratio in aerosol and the 210Pb flux. The atmospheric flux to northern Wisconsin was estimated to be 0.8 μg cm−2 yr−1 for Pb and 0.70 pCi cm−2 yr−1 for 210Pb.
On the remote acoustic detection of suspended sediment at long wavelengths
Authors: Hay Alex E.
Published: February 2008

Experimental results are presented which indicate a linear relation between the time‐averaged amplitude of the envelope of the backscattered acoustic pulse at 192 kHz and the square root of suspended sediment concentration in the 10 to 103 mg 1−1 range. Particle sizes ranged from 2 to 140 μm. The measurements were made in a negatively buoyant, mine‐tailing discharge plume in a submarine channel at depths of 60 to 90 m in Rupert Inlet, British Columbia. From the theory of acoustic backscatter from a solid elastic sphere in the Rayleigh region it is shown that if the pressure amplitude of the backscattered wave is Rayleigh distributed, then such a linear relation is to be expected. Expressions for the optimum acoustic frequency for the detection of dilute suspensions at a given range and for the minimum detectable concentration are obtained assuming a thermal noise background. The possibility that bubbles contribute to the backscatter is considered and found to be unlikely on the basis of probable bubble lifetimes.
Particulate size spectra, behavior, and origin of nepheloid layers over the Nova Scotian Continental Rise
Authors: McCave I. N.
Published: February 2008

Samples of suspended sediment and light transmissometer observations were taken on two occupations of a transect of the Nova Scotian continental rise in 1980. Initial low suspended sediment concentrations were followed by high values 10 days later. Patches of high concentration were found on the edges of zones of cold (θ<1.78°C) water. Particle volume concentrations in the diameter range 1.26–32 μm measured by Coulter Counter on 10 cm3 samples correlate linearly with light beam attenuation coefficient. Correlation between particle volume and weight concentration indicates lower apparent particle density for low‐concentration suspensions, a feature that is attributed to aggregation during aging of the suspension. Particle size distributions show unimodal form with a peak at ∼4 μm in high concentrations near the bed changing to a bimodal form with an additional mode at ∼16 μm in low concentrations high above the bed (500 and 1000 m.a.b. (meters above bottom)). The presence of the coarse mode at 1000 m.a.b. coupled with its increase in the lower 250 m of the water column suggests that it both settles from the surface and is resuspended from the bed. Ultrasonic disaggregation experiments show that much of the fine mode is of aggregates, but the coarse mode is single solid particles. Distributions with a low volume‐concentration increase in volume when disaggregated and are interpreted as having a relatively large part of their total distribution in unmeasured sizes >32 μm. Distributions with a high concentration decrease in counted volume on disaggregation. Inversions in the light attenuation profiles are taken to indicate the presence of former bottom mixed layers, and their occurrence suggests thickening of the nepheloid layer by detachment and lateral injection of these turbid mixed layers. They occur at levels sufficiently high as to provide a nepheloid layer over 1500 m thick over the adjacent Sohm Abyssal Plain. The coarse mode probably comprises solid particles with a calculated settling velocity of ∼12 m day−1. Its absolute concentration increases toward the bed, but as a proportion of the distribution it increases upward. It is thus thought to be particles of surface origin both settling to the bottom and, in the lower 250 m of the water column, resuspended from the bed. The fine mode at 4 μm has a spatially constant form thought to be controlled by physical coagulation mechanisms. Rates of coagulation estimated from shear mechanisms suggest that the postulated change of peaked into flat size distribution by particle aggregation and settling has a time scale of a few years rather than months, which is probably long when compared with the lateral injection process lower in the nepheloid layer. For that reason, distribution with a fine mode peak are found well above the bottom mixed layer.
Observations of changing mesoscale circulation patterns in the western Gulf of Mexico
Authors: Merrell William J. , Vázquez Alberto M.
Published: February 2008

In the western Gulf of Mexico, depth contours of the 15°C isotherm are compared during two observation periods: April 1–12 and April 12–26, 1978. Comparison of the two isothermal maps allows one to estimate changes in the mesoscale current patterns. A cyclonic circulation feature and an anticyclonic feature are found in both data sets and seem to have intensified and weakened respectively. Two possible causal mechanisms are discussed. The observed changes may be due to the effects of a severe norther (cold air outbreak) that occurred between the observation periods. An alternate mechanism is the dissipation of energy associated with the spindown of a westward moving anticyclone as it reaches the western boundary of the Gulf of Mexico.
The Atmospheric Lifetime Experiment: 5. Results for CH3CCl3 based on three years of data
Authors: Prinn R. G. , Rasmussen R. A. , Simmonds P. G. , Alyea F. N. , Cunnold D. M. , Lane B. C. , Cardelino C. A. , Crawford A. J.
Published: February 2008

We present gas chromatographic determinations of the concentrations of CH3CCl3 at Adrigole (Ireland), Cape Meares (Oregon), Ragged Point (Barbados), Point Matatula (American Samoa), and Cape Grim (Tasmania) for the 3‐year period July 1978 through June 1981. The determinations involve approximately four measurements each day with on‐site calibration. The absolute values and trends for these observed concentrations are interpreted in terms of the industrial production, global circulation rate, and atmospheric lifetime of CH3CCl3 by using an optimal estimation technique that incorporates a nine‐box model of the atmosphere. The globally and annually averaged trend in the lower troposphere at the midpoint of the second year of the experiment is 8.7% per year, and the inferred global atmospheric content of CH3CCl3 at this midpoint is 2.58×109kg. The global atmospheric lifetime deduced by using the observed trends and global content together with current estimates of industrial CH3CCl3 emissions is
years. This deduced lifetime is sufficiently long to imply that the observed variability in the data on seasonal and shorter time scales must be dominated by meteorological (and perhaps industrial emission) variabilities rather than by spatial and temporal variations in the rate of chemical destruction of CH3CCl3 by OH. However, the observed variations on annual and longer time scales are sensitive to the spatially and temporally averaged OH concentrations. In particular, the globally averaged tropospheric OH concentration compatible with the above‐deduced CH3CCl3 lifetime is (5 ± 2) × 105 molecule cm−3; in reasonable agreement, for example, with the value of (
) × 105 molecule cm−3 deduced by Volz et al. (1981) from measurements of CO. Our results are sensitive to constraints imposed on uncertainties in the CH3CCl3 emissions and absolute mixing ratios. If we decrease emissions by ≲8% in the years 1976–1978 and increase emissions in 1979–1981 to compensate, and if absolute mixing ratios are decreased by about 18%, then the best estimate of the lifetime from our data decreases to 6.5 years.
A study on the spectral models for waves in finite water depth
Authors: Huang Norden E. , Hwang Paul A. , Wang Hsiang , Long Steven R. , Bliven Larry F.
Published: February 2008

Spectral models for waves in finite water depths are developed based on an extension of the Wallops Spectrum (Huang et al., 1981a) for the deep water waves. It is found that for intermediate water depth, Stokes wave expansions offer a good approximation. In this case, the spectral function is controlled by three parameters: the significant slope, §; the nondimensional depth, kh; and the peak frequency, n0. For the shallow water waves, solitary and cnoidal wave models have to be used. The controlling parameters now reduce to two again, that is, the Ursell number, ur = [2π§/(kh)3], and the peak frequency. The resulting spectral models are designed with a specific emphasis on but not limited to the energy containing range of the spectrum; they are also not limited to any particular sea state. They offer a possible explanation of the variations in the spectral slope observed by previous investigators. Comparisons with observational results from both laboratory and field show good agreements.
A comparison of observed and geostrophically calculated wintertime surface winds over the East China Sea
Authors: Hsueh Y. , Romea Richard D.
Published: February 2008

Wintertime geostrophic winds (
), calculated over the East China Sea from surface pressure maps, are compared to observed winds (
) from the region. For mean winds, the average counterclockwise veering angle from
to
is 37°, and the average reduction in amplitude is 39%. For fluctuating winds the average veering and attenuation are 25° and 55% The greatest reduction occurs for land stations, while the lowest (33%) occurs at an offshore buoy station. Evidence from power spectral computations suggests that the spectral contents of
and
are very similar, even for cases where observed winds are of much lower amplitude and do not appear to be reliable.
Observations of a loop current frontal eddy intrusion onto the West Florida Shelf
Authors: Paluszkiewicz Theresa , Atkinson Larry P. , Posmentier Eric S. , McClain Charles R.
Published: February 2008

Hydrographic and satellite data from the west Florida shelf between April 1–7, 1982 showed the intrusion of a Loop Current frontal eddy onto the shelf. Data were examined to describe the structure of this feature and study effects of its intrusion on water masses in the outer shelf region. A frontal eddy, consisting of a warm filament separated from the main current by a region of cooler water, propagated southeastward at 30 cm/s intruding onto the shelf near 26°N between April 4 and 6. Temperature‐salinity (T‐S) properties revealed that water in the filament was Loop Current water that had been contiguous with 80 m deeper Loop Current water in the main body of the current; water in the cold region was Continental Edge water, a transitional water mass with cooler, fresher T‐S characteristics. Upwelling of deeper Loop Current water occurred under this region, and elevated nutrient concentrations were found in the upwelled dome under the cold region. Interleaving occurred along water mass boundaries enabling the exchange of heat and salt. This mixing and the supply of cool, nutrient‐rich water to the outer shelf was the major consequence of the intrusion. The length scale and speed of this Loop Current frontal eddy was similar to Gulf Stream frontal eddies through the upwelling was not as intense as in intrusions of Gulf Stream frontal eddies.
Geochemistry of the Amazon: 2. The influence of geology and weathering environment on the dissolved load
Authors: Stallard R. F. , Edmond J. M.
Published: February 2008

In the Amazon Basin, substrate lithology and erosional regime (seen in terms of transport‐limited and weathering‐limited denudation) exert the most fundamental control on the chemistry of surface waters within a catchment. Secondary effects, such as the precipitation of salts within soils and in stream beds, biological uptake and release, and cyclic salt inputs, are more difficult to discern. Samples can be separated into four principal groupings based on relationships between total cation charge (TZ+) and geology. (1) Rivers with 0<TZ+<200 μeq/l drain the most intensely weathered materials (Upper Tertiary sediments, soils of the Negro Basin, and similarly weathered regions). These rivers show high levels of Fe, Al, H+, and coloration and are enriched in Si relative to other major species; they exhibit cation ratios similar to those of substrate rocks. (2) Rivers with 200<TZ+<450;μeq/l drain siliceous terrains. These rivers are also rich in silica relative to other species. Rivers draining weathering‐limited siliceous terrains exhibit the highest TZ+ and their cation load is typically preferentially enriched in Na over K and Ca over Mg when compared to the rocks in their catchments. (3) Rivers with 450<TZ+<3000 μeq/l drain marine sediments or red beds with high cation concentrations (resulting from the presence of carbonates and minor evaporites in the Peruvian Andes and reduced shales and minor carbonates in the Bolivian Andes). These rivers exhibit relatively high levels of Ca, Mg, alkalinity, and SO4(in rivers draining reduced shales and minor evaporites). (4) Rivers with TZ+>3000 μeq/l drain massive evaporites. These rivers are rich in Na and Cl. In the third and fourth categories, rivers tend to have 1:1 (equivalent) ratios of Na:Cl and (Ca+Mg):(alkalinity+SO4), caused primarily by the weathering of carbonates and evaporites. Supplement available with entire article on microfiche. Order from the American Geophysical Union, 2000 Florida Avenue, N.W., Washington, DC 20009. Document C83‐002; $2.50. Payment must accompany order.
Analysis of scatterer motion effects in Marsen X band SAR imagery
Authors: Lyzenga D. R. , Shuchman R. A.
Published: February 2008

Synthetic aperture radar X band images collected over the North Sea during the 1979 MARSEN experiment show numerous apparent point scatterers imaged with a degraded resolution in the along‐track direction. The observed resolution of these features is consistent with a scatterer coherence time of the order of 10−2 s or a vertical acceleration of the order of 5 m/s2. Observations of the resolution as a function of the processor integration time tend to support the coherence time explanation. Similar coherence times have been measured for breaking waves by conventional high‐resolution radars, suggesting that the same phenomena may be responsible for the features observed on the synthetic aperture radar imagery.
Numerical model for nonstationary shallow water wave spectral transformations
Authors: Chen Yun‐Hai , Wang Hsiang
Published: February 2008

A nonstationary wave transformation model is developed, based upon a finite difference scheme. This model computes spatial and temporal distributions of wave spectral density in shallow water areas with irregular bottom topography. Current knowledge of the dynamic and kinematic processes is incorporated into the model, which include the usual wave refraction and shoaling effects as well as nonlinear dissipative processes (breaking, bottom friction, and a constraint on total energy growth in a depth‐limited situation), and local wind wave generation processes (a combined Phillips‐Miles model). Another important feature of the model is the inclusion of current effects; spatial and temporal current distributions can be introduced as input conditions. Based upon this model, a number of sample computations are given to examine the characteristics of nonstationary wave transformation processes. Finally, one set of wave data collected in the North Sea during the MARSEN Project is used to compare with numerical model computations.
Water mass analysis in the German Bight during Marsen, Phase I
Authors: Becker Gerd A. , Fiúza Armando F. G. , James Ian D.
Published: February 2008

In the initial phase of MARSEN (marine remote sensing experiment), three main water masses and North Frisian Wadden Sea Water were found in the German Bight in the late summer of 1979. This is shown by t/S diagrams of the CTD data obtained with the RV Friedrich Heincke and the RRS John Murray. For each t/S pair the percentage composition of the three main water masses is estimated by applying the linear mixing theory. The distribution of the main water masses indicates a frontal structure in the German Bight, A clearly separated water mass, which originates from the mixing of North Sea bottom water and Elbe estuary water, is found in the frontal area. This frontal water is apparently trapped by the vertical current shear and the topography of the post‐glacial valley of the Elbe.
Estimating particle sizes, concentrations, and total mass of ash in volcanic clouds using weather radar
Authors: Harris David M. , Rose William I.
Published: February 2008

Observations of the March 19, 1982 ash eruption of Mount St. Helens, made by the National Weather Service (NWS, Portland, Oregon) on 5‐cm radar, were used to estimate the volume of the ash cloud (2000 ±500 km3), the concentration of ash (0.2–0.6 g m−3). and the total mass of ash erupted (3–10×1011 g). The position of the cloud was also tracked by radar. Particle sizes in the ash cloud were estimated from settling velocities suggested by decreases in maximum ash cloud height with time as it moved away from the volcano. The March 19, 1982 ash blanket was sampled and mapped. Ash fallout times and accumulation rates were reconstructed from ground observations. Grain size distributions for various samples were used to obtain particle concentration (0.2 g m−3), total ashfall mass (1–3×1011 g), and radar reflectivity factor (4–5 mm6 m−3) for the ash cloud. Our preferred estimate for total ashfall mass (4×1011 g) is that obtained from the product of the ash cloud volume determined by radar (2000±500 km3) and the particle concentration inferred from ashfall data (0.2 g m−3). Previously published ashfall data for the May 18, 1980 Mount St. Helens eruption has been studied using our ashfall inversion technique to estimate 6‐hour mean particle concentration (3 g m−3), the size distribution, total ashfall mass (5×1014 g), and radar reflectivity factors (7–60 mm6 m−3) for the ash cloud. A somewhat higher value (9 g m−3) for particle concentration was estimated from radar observations [Harris et al., 1981] for an ash cloud formed during the peak eruption rate at Mount St. Helens. The two independent estimates are consistent, given the many uncertainties of the problem. The reflectivity factors for very dense ash clouds (3–9 g m−3) are several orders of magnitude smaller than for severe weather considered routinely detectable by airborne weather radar and dangerous for aviation. Because volcanic ash clouds with particle concentrations of at least 0.2 g m−3 are produced in extremely small eruptions (in terms of total ashfall mass) of duration less than 1 minute, volcanic ash clouds must be considered an extremely serious hazard to in‐flight aircraft, regardless of eruption magnitude. These factors should be considered in hazard evaluations for known volcanoes located near air routes. Radar observations and calculations can provide scientists monitoring eruptive activity with significant information for estimating duration of eruption, particle concentrations in ash clouds, total mass of solid material erupted, magma eruption rate, potential ashfall mass, ashfall locations and accumulation rates, and duration and amounts of ashfall. Detailed analysis of ashfall data and NWS radar observations of ash clouds from Mount St. Helens demonstrate that weather radar can yield such timely information during and following volcanic eruptions.
Numerical simulations of the Ross Sea tides
Authors: MacAyeal Douglas Reed
Published: February 2008

Tidal currents below the floating Ross Ice shelf are reconstructed by using a numerical tidal model. They are predominantly diurnal, achieve maximum strength in regions near where the ice shelf runs aground, and are significantly enhanced by topographic Rossby wave propagation along the ice front. A comparison with observations of the vertical motion of the ice shelf surface indicates that the model reproduces the diurnal tidal characteristics within 20%. Similar agreement for the relatively weak semi‐diurnal tides was not obtained, and this calls attention to possible errors of the open boundary forcing obtained from global‐ocean tidal simulations and to possible errors in mapping zones of ice shelf grounding. Air‐sea contact below the ice shelf is eliminated by the thick ice cover. The dominant sub‐ice‐shelf circulation may thus be tidally induced. A preliminary assessment of sub‐ice‐shelf conditions based on the numerical tidal simulations suggests that (1) strong barotropic circulation is driven along the ice front and (2) tidal fronts may form in the sub‐ice‐shelf cavity where the water column is thin and where the buoyancy input is weak.
Antarctic sea ice microwave signatures and their correlation with in situ ice observations
Authors: Comiso J. C. , Ackley S. F. , Gordon A. L.
Published: February 2008

The general characteristics and microwave radiative properties of sea ice in the Weddell Sea region during the onset of spring are studied by using the NIMBUS 7 Scanning Multichannel Microwave Radiometer (SMMR) and other satellite sensors in conjunction with in situ observations from the Mikhail Somov. The position of the ice edge, the gradient of ice concentration, and the width of the Marginal Ice Zone are inferred from the microwave data and are found to be consistent with ship observations especially at 18 GHz. The sensitivities of the various SMMR frequencies to surface and other effects are investigated by using multi‐spectral cluster analysis. The results show considerable variability in emissivity, especially at 37 GHz, likely associated with varying degrees of surface wetness. Ice concentrations are derived by using two methods: one that assumes fixed emissivities for consolidated ice and an iterative procedure that accounts for the variable emissivities observed. By using the procedure that allows the emissivities to be variable gives ice concentrations that are more consistent with qualitative field observations.
Cold air outbreaks over the northwest Florida continental shelf: Heat flux processes and hydrographic changes
Authors: Huh Oscar Karl , Rouse Lawrence J. , Walker Nan Delene
Published: February 2008

An experimental study of the meteorology and oceanography of the cold air outbreak cycle was conducted during the fall of 1978 off Panama City, Florida. Details of the air‐sea interaction processes they induce on such upwind continental shelves are poorly known because of lack of appropriate measurements. Shallow depths and proximity to land make the processes significantly different from their deepwater counterparts. The cycle has three phases recognizable in the measurements: the prefrontal, frontal passage, and cold air outbreak/high‐pressure phases. The time variability of oceanic heat fluxes was monitored through the cycle in two ways: by measuring heat content changes and by measuring turbulent and radiative heat fluxes. Advective effects on the heat budget were minimized by the site selection. A mild cold air outbreak stripped 26.8×106 J m−2 (640 cal cm−2) of heat and 1.1 cm of liquid water from the shelf in 63 hours, and a severe cold air outbreak removed 147.6×106 J m−2 (3528 cal cm−2) and 4.4 cm of liquid water in 87 hours. For these events, evaporation, sensible heat loss, and radiative heat loss were 51, 16, and 33, and 58, 25 and 17% of the totals, respectively. A simple one‐dimensional shallow water heat flux model predicted temperature and heat content changes during severe cold air outbreaks to within 8%. Observations indicate the extreme time variability of heat flux processes and the hazards of extrapolating to daily rates from spot measurements or very short time series.
A theoretical response of a wind‐driven oceanic surface layer and its application to the analysis of Lagrangian measurements
Authors: Lewis James K. , Denner Warren W.
Published: February 2008

An analytical response of an oceanic surface layer to wind stress is given for those situations in which horizontal pressure and stress gradients are neglected. The vertically averaged velocity U of the surface layer is seen to be the sum of time‐damped inertial oscillations. For the wind stress τs that is relatively constant, the analytical solution reduces to U = Aτs, with both the Coriolis and bottom friction effects included in the matrix A. An empirical analysis method is presented which compares the theoretical transports based on wind data with actual velocities as determined by Lagrangian observations. This method can be used to determine the effect of bottom friction, the depth of the wind‐driven surface layer, and the time‐integrated effect of horizontal pressure and stress gradients. An example is presented using wind and position data collected on the Arctic ice pack during the summer of 1975.
Oceanic winds measured from the seafloor
Authors: Evans David L. , Watts D. Randolph , Halpern David , Bourassa Susan
Published: February 2008

Acoustic ambient noise in the ocean at frequencies of 4.3, 8.0, and 14.5 kHz has been shown to be highly correlated with surface wind speed. Measurement of noise at the sea floor yields estimates of wind speed to within ±1 m/s (r2≥0.845) when compared with coincident surface observations. The frequency dependence of the wind speed‐noise relation reported by others (17 dB/decade) has been confirmed, except that separate calibrations are required above and below the speed characterizing whitecap formation. There is also some evidence of local hydrography influencing the absolute calibration.
An in situ erosion rate for a fine‐grained marine sediment
Authors: Lavelle J. W. , Mofjeld H. O. , Baker E. T.
Published: February 2008

Near‐bottom current and particulate concentration data and a theoretical model of sediment resuspension together have led to inferences about the erosional response of a fine‐grained sediment to bottom stress. Tidal boundary layer observations, made 5 m from the bottom in the main basin of Puget Sound, Washington, show that currents with speeds exceeding 40 cm/s cause an increase in concentration as much as sixfold from a background level of 1 mg/1. When the erosion rate, E = α|τ|η, is given a power law dependence on bottom stress τ, in accord with laboratory fine‐sediment entrainment measurements, the field data and theoretical model together suggest that η = 4.0 and α = 1.7 × 10−6 g/cm2/s. Uncertainty in these values stemming from a variety of factors is discussed. The analysis also points to sediment resuspension of material with relatively large settling velocity (ws = 0.1 cm/s) taking place against a background of much finer particles and a depth of sediment reworking of approximately 0.3 mm under typical strong flow conditions. Comparison of this in situ erosion rate with previous laboratory rate estimates shows it to be comparable to rates measured for some freshwater sediments.
The estimation of “global” sea level change: A problem of uniqueness
Authors: Barnett T. P.
Published: February 2008

An objective method of estimating regional averages of coherent sea level (SL) change is developed. The technique is applied to a large set of SL data representative of most of the world's continental margins. The results show highly coherent SL changes over many of the regions studied. The method is then applied to the regional averages themselves to develop an overall estimate of the coherent pattern of SL variations existing in the historical SL data set. The pattern is characterized by a coherent rise of SL in all regions except Alaska, Scandinavia (both areas of notorious crustal uplift), and Southeast Asia, where SL appears to be falling. The analysis suggests little or no change in SL prior to the early 1900's. The period since that time has seen an increase in SL that is optimally fit by a linear trend of 23 cm/century. The study results suggest that it is not possible to uniquely determine either a global rate of change of SL or even the average rate of change associated with the existing (inadequate) data set. Indeed, different analysis methods, by themselves, can cause 50% variations in the estimates of SL trend in the existing data set. A signal/noise analysis suggests it should be easy to detect small, future changes in the SL trends estimated for the period 1930–1980. However, detection of theoretically predicted low‐frequency signals (e.g., caused by CO2 warming) will be difficult in view of the huge, low‐frequency, natural variability associated with glacial/tectonic processes.
Turbulent wave boundary layers: 2. Second‐order theory and mass transport
Authors: Trowbridge John , Madsen Ole Secher
Published: February 2008

The solution for the turbulent near‐bottom boundary layer produced by a progressive wave train is advanced to second order in wave steepness. As in the first‐order analysis (part 1) the effective viscosity is assumed to be the product of a vertical length scale and the first few Fourier components of a shear velocity based on the instantaneous, local bed shear stress. An analytical solution for the second‐order flow field is obtained, with attention directed primarily toward the second‐order, wave‐induced steady current or mass transport. The mass transport is found to depend critically on temporal variation of the effective viscosity. The most dramatic result of the analysis is a predicted reversal of the mass transport produced by relatively long waves. This result, for which supporting experimental evidence is presented, has not been predicted previously and cannot be obtained by a time‐invariant eddy viscosity model. Implications of the present results for related problems are discussed.
A theoretical, laboratory, and field study of ice‐coupled waves
Authors: Squire Vernon A.
Published: February 2008

Field and laboratory data of ice‐coupled waves propagating beneath shore fast ice are presented and compared with a theoretical model for sea ice which allows temperature variation. Although the laboratory data set is essentially qualitative because of scaling problems, the measured wave characteristics compare favorably with those seen in the field. The theory fits the field data set well, both for the dispersive behavior and for the energy decay as the ice‐coupled waves penetrate the ice sheet. Moreover, a maximum displacement suggested by theory is seen in field data for the first time. It is proposed that this peak may be associated with the breakup of shore fast ice in exposed regions. The theoretical treatment presented assumes sea ice to be thermorheologically simple, an untested hypothesis which will require later experimental verification. However, the theory is quite general and can be used to solve a variety of sea ice mechanical problems where creep is considered important, but where the loads and displacements are small enough that linearity prevails.
A simple model of the relation between tidal quality and dissipation
Authors: Platzman George W.
Published: February 2008

The parametric relation between output quality and dissipation in a one‐dimensional ocean with radiative dissipation is shown to be qualitatively and quantitatively similar to the relation derived numerically by synthesis of the world ocean tide from normal modes. The relation indicates that the equivalent oscillator is near resonance at its fundamental frequency.
Measurements of bubbles in a stationary field of breaking waves by a laser‐based single‐particle scattering technique
Authors: Baldy Serge , Bourguel Maurice
Published: February 2008

Bubble measurements were performed in a wind‐water simulating facility with a laser‐based single‐particle scattering technique. To avoid the usual ambiguity in this technique about the cross section, an original numerical processing of the scattered intensities, taking advantage of the low particle (bubble) velocities, was used. This treatment allowed one to directly obtain concentration probability densities. Moreover, other information, such as the crossing frequency, arrival time interval, or estimated speed distributions, that provides additional insight into the bubble distribution processes is available. The investigations were carried out in the immediate vicinity of breaking waves generated either by the wind flow or by the cumulative effects of the wind and a wavemaker. High bubble concentrations, no peaked distributions, and important modifications of these distributions with wave age were observed. The bubble speed and additional arrival time information allowed further notice of high fluid‐estimated velocities and characterization of bubble clusters in the vicinity of breaking waves. Distinctive features of previous approaches, or models about wave‐breaking bubbles, may be found in this investigation.
Regional river sulfur runoff
Authors: Husar Rudolf B. , Husar Janja Djukic
Published: February 2008

The water and sulfur runoff data for 54 large river basins were assembled, covering 65% of the nondesert land area of the world. The sulfur concentration ranges from 0.5 mg S/L for the West African rivers Niger and Volta to 100 mg S/L in the Colorado River; the world average is 3.2 mg S/L. The concentrations in central and eastern Europe as well as central and eastern North America exceed 8 mg S/L. The sulfur runoff density is also highest in the river basins over these industrialized regions, exceeding 2 g S/m2/yr. However, high sulfur runoff density in excess of 3 g S/m2/yr is also measured over the Pacific islands New Zealand and New Guinea and the archipelagos of Indonesia and the Philippines. The natural background sulfur runoff was estimated by assuming that South America, Africa, Australia, and the Pacific Islands are unperturbed by man and that the average river sulfur concentration is in the range 1–3 mg S/L. Taking these background concentration values, the man‐induced sulfur runoff for Europe ranges between 2 and 8 times the natural flow, and over North America, man's contribution ranges between 1 and 5 times the natural runoff. The global sulfur flow from nondesert land to the oceans and the Caspian Sea is estimated as 131 Tg S/yr, of which 46–85 Tg S/yr is attributed to natural causes. The regional river sulfur runoff pattern discussed in this paper does not have enough spatial resolution to be directly applicable to studies of the environmental effects of man‐induced sulfur flows. However, it points to the continental‐size regions where those perturbations are most evident and to the magnitude of the perturbations as expressed in units of the natural flows.
Rotary motions and convection as a means of regulating primary production in warm core rings
Authors: Yentsch Charles S. , Phinney David A.
Published: February 2008

We believe that two mechanisms are important in regulating primary production and hence the abundance of phytoplankton in warm core rings. The first mechanism, anticyclogenesis, is associated with the rotary motion of rings since the resultant geostrophic forces are believed to be the basis for nutrient enrichment in the high velocity region. Phytoplankton populations in this peripheral region experience a near steady state growth closely coupled with the rotational velocity of the ring. The second mechanism is that phytoplankton populations in the ring center rely on seasonal changes in the depth of the mixed layer due to convection and stabilization. This process regulates both the mean light energy reaching phytoplankton and equalizes the nutrient distribution over the water column. Growth in populations at ring center occurs as pulses, responding to changes in the depth of the mixed layer.
Oceanic gyres forced by the wind and surface density fluxes
Authors: Olson Donald B.
Published: February 2008

The influence of diabatic modifications of density at the sea surface on the steady state circulation in ocean gyres is explored. A potential vorticity equation for gyre‐scale, forced circulations in the presence of a density source is derived. A scaling of the problem implies that the diabatic changes in density produce a forced circulation of the same order of magnitude as those induced by the wind. This conclusion depends to some extent upon the relative depth of penetration for the two forcing terms. Since the model itself cannot predict these penetration depths, the depth of the observed thermoclines in the oceans is chosen for both. The importance of this assumption is discussed. Although the equations for the continuously stratified case are derived the actual problem solved is a layered equivalent to the more general case. Three patterns of forcing are considered, based on an investigation of the observed distribution of density flux as a function of latitude in the ocean. The typical distribution of the density flux divergence opposes the Sverdrup response to the wind in the southern portions of subtropical gyres. In the regions in which the density flux divergence is positive the forced response is anticyclonic. Therefore in the subtropical gyres the northern portions have stronger circulation in the situation in which there is both wind and density flux. A pair of two gyre models suggest that the diabatic forcing will cause an expansion of the subtropical gyre across the wind stress maximum. The northern gyre is strengthened (weakened) in the case where the surface fluid is lightened (made more dense). This would suggest that there may be a difference between the subpolar gyres in the Atlantic and Pacific caused by the different E ‐ P and heat budgets over the two basins. The models suggest that subtropical fronts may arise in part because of the change of sign in the density forcing at mid‐latitudes. Finally, the gyres computed from the model are shown to be unstable to a long‐term thermohaline mode whose structure may in part be determined by the potential vorticity field predicted in the present calculations.
Azimuthal variations in tsunami interactions with multiple‐island systems
Authors: Hebenstreit Gerald T. , Bernard Eddie N.
Published: February 2008

The purpose of this study is to examine variations in the response of an island system (the Hawaiian Islands, in this case) to an incoming tsunamilike wave pulse approaching the system along various azimuths. Simulations were carried out numerically by using an explicit finite‐difference analog for the linearized equations of motion and continuity for long waves in a variable depth ocean. The model topography is based on the submarine topography of the Hawaiian Island region. Island coastlines are fully reflecting, so no attempt to simulate runup was made. Qualitative comparisons between model results and historical data from tsunamis approaching along similar azimuths show that the model produces realistic simulations. Azimuths were chosen for waves approaching from four general geographic areas: South America, Alaska, Aleutians‐Kuriles‐Japan‐Philippines, and Southwest Pacific. Nearly all distant tsunamis striking Hawaii have come from one of these areas. Our conclusions are: (1) Tsunami response in the overall system does not vary greatly over small (10°–15°) changes in azimuth but does vary significantly over large changes (>60°). (2) Local response may vary greatly with azimuth, but certain areas seem to respond strongly to tsunamis approaching from almost any direction. (3) Topographic focusing seems to play the dominant role in determining localized response.
Observing large‐scale temporal variability of ocean currents by satellite altimetry: With application to the Antarctic Circumpolar Current
Authors: Fu Lee‐Lueng , Chelton Dudley B.
Published: February 2008

A new method is developed for studying large‐scale temporal variability of ocean currents from satellite altimetric sea level measurements at intersections (crossovers) of ascending and descending orbit ground tracks. Using this method, sea level time series can be constructed from crossover sea level differences in small sample areas where altimetric crossovers are clustered. The method is applied to Seasat altimeter data to study the temporal evolution of the Antarctic Circumpolar Current (ACC) over the 3‐month Seasat mission (July–October 1978). The results reveal a generally eastward acceleration of the ACC around the Southern Ocean with meridional disturbances which appear to be associated with bottom topographic features. This is the first direct observational evidence for large‐scale coherence in the temporal variability of the ACC. It demonstrates the great potential of satellite altimetry for synoptic observation of temporal variability of the world ocean circulation.
Processes and imagery of first‐year fast sea ice during the melt season
Authors: Holt Benjamin , Digby Susan A.
Published: February 2008

An analysis of first‐year fast sea ice during the melt season has been made by using surface measurements and aircraft radar and photographic imagery obtained during a field study near Prince Patrick Island in the Canadian Archipelago from June 13 to July 13, 1982, and satellite imagery from Landsat and Seasat. Distinct changes observed in the properties of the snow layer and the sea ice were a temporary increase in small‐scale surface roughness caused by formation of nodules of ice at the snow/ice interface; extensive snow melt and surface flooding; development of surface water drainage networks and low topography around fractures and seal breathing holes; and a rapid draining of much of the surface water. From the extensive salinity profiles obtained, two zones of rapid desalination in the first‐year ice were observed: one zone extending from the air/ice interface downward toward the center of the ice sheet that resulted from surface warming and drainage of the surface melt water through the ice and the other zone extending from the sea/ice interface upward toward the center of the ice sheet that resulted from heating and separation of seawater and ice caused by a layer of low‐salinity meltwater beneath the ice formed from surface meltwater runoff. Aircraft radar imagery detected changes in the amount of surface water and in the development of topography surrounding drainage features. Similar changes were detected in coincident Landsat multispectral scanner (MSS) imagery of the study area and in SEASAT radar imagery and Landsat MSS imagery of the Prince of Wales Strait from July 1978.
The influence of the Hawaiian Archipelago upon the wind‐driven subtropical gyre in the western North Pacific
Authors: White Warren B. , Walker Arthur E.
Published: February 2008

In the middle of the Subtropical Gyre in the western North Pacific is the Subtropical Counter‐current, comprised of at least three narrow bands of eastward geostrophic mean flow near 20°N, 24°N, and 26°N, each extending from the sea surface through the main pycrocline. The origin of these narrow bands of eastward mean flow has not previously been explained. In this study, these bands are shown in the mean to extend zonally from the Philippine Sea (i.e., 140°E) to the vicinity of the Hawaiian Archipelago (i.e., 160°W). East of there, they cannot be found. Therefore a hypothesis is presented wherein the Hawaiian Archipelago (extending from 19°N to 26°N near 165°W) is seen to act as an effective barrier, modifying the response of the western subtropical North Pacific to wind‐driven effects in the eastern subtropical North Pacific and, in so doing, giving rise to these bands of eastward mean flow in the middle of the western Subtropical Gyre. A test of this hypothesis utilizes a Sverdrup [1947] model, driven by the annual, long‐term, mean wind stress curl, constructed on a 2° latitude/longitude grid from synoptic (6 hourly) surface wind observations for the 13‐year period 1968–1980. Two model simulations are conducted, one in the absence of the Hawaiian Archipelago and one in the presence of it. In the absence of the archipelago, none of the bands of eastward mean flow are simulated. In the presence of the archipelago, the narrow bands of eastward mean flow at 20°N, 26°N, and 24°N are simulated, although the latter band is very weak. These narrow bands of eastward flow are shown to occur in response to the deflection northward of the wind‐driven geostrophic streamlines in the central subtropical North Pacific by the Hawaiian Archipelago.