bluuebunny/crossref_metadata_2025 huggingface dataset:
Heat and mass transport processes in subsea permafrost 1. An analysis of molecular diffusion and its consequences
Authors: Harrison W. D. , Osterkamp T. E.
Published: February 2008

Some heat and mass transport processes in subsea permafrost are discussed. An exact solution is given for a coupled model in which both heat and salt are transported solely by diffusion. The model describes the development of a thawed layer beneath the seabed after an ocean transgression over deeply frozen ground and is a generalization of the well‐known Stefan problem. A stability calculation indicates that such a diffusive regime should be unstable to convection of the interstitial water in the thawed layer after a critical thickness has been reached. The theory is compared with observations from two sites in the Beaufort Sea, Alaska. In western Elson Lagoon, near Barrow, the diffusive regime may be stable, but at Prudhoe Bay it is not, and interstitial water motion is important. At Prudhoe Bay the salt and heat transport regimes are convective and diffusive, respectively.
Numerical study of cloud electrification in an axisymmetric, time‐dependent cloud model
Authors: Chiu Chin‐Shan
Published: February 2008

An axisymmetric, time‐dependent, numerical cloud model has been applied to study how an isolated convective cloud can be electrified when rain and cloud particles are allowed to be charged by two particle charging mechanisms: ion attachment and polarization. Charge transports by electrical conduction, air convection, turbulent mixing, and the particle terminal velocities are all simulated. The close tie‐in of the electrical development with the evolutions of the cloud growth is one of the distinctive features of the study. The full dynamical‐microphysical‐electrical interactions are allowed in the simulation. The results of numerical experiments make it appear likely that the polarization charging mechanism is an important one for the electrification of warm clouds. The results also show that with the inclusion of the polarization charging mechanism and depending on the growth stage of the cloud the cloud can be electrified into various charge center structures, which have been observed and reported in the literature for many years. The numerical results show that the cloud cannot be rapidly electrified until rainwater forms and the polarization charging mechanism operates. Initially, the cloud is charged into a ‘positive dipole’ structure with a positive charge center in the upper part of the cloud and a negative one below. As the cloud grows further, another positive charge center forms below the main negative one. This weaker positive center is closely associated with the positively charged rain formed in that region. As the rain falls out of the cloud, this positive center extends below the cloud base. When the cloud top reaches its maximum level, the cloud base starts to rise and the cloud grows weaker thereafter. In the later stage of the development the charge distribution patterns of the rain field dominate the whole electrical structure of the model. The electrical pattern thereafter is greatly affected by the downward movement of the rain. With the fallout of the rain the cloud charge centers exhibit successfully a positive dipole structure and then a ‘negative dipole’ structure consisting of a negative charge center in the upper part of the cloud and a positive one below. The electrical force effects on the terminal velocities of the rain and cloud particles are also included in the study. The results show that the rain particle terminal velocities start to decrease by a few meters per second in a region where the electric field strength grows beyond 2 × 105 or 3 × 105 V/m. The cloud particle terminal velocities reach only several centimeters per second, even in the thunderstorm electrical state. As a result of the levitation effect on rain, the simulated cloud in the present study develops double maxima in the cloud water content, giving it a more irregular appearance than the weakly electrified or nonelectrified cloud.
A methodology for determining the atmospheric lifetime of fluorocarbons
Authors: Cunnold D. , Alyea F. , Prinn R.
Published: February 2008

We discuss the atmospheric variability and instrumental uncertainties which limit the determination of the atmospheric lifetime of fluorocarbons. These factors produce substantial uncertainties in the current estimates of fluorocarbon lifetimes. However, because fluorocarbon production has remained relatively constant over the past few years, the atmospheric lifetime may now be determined with considerably improved accuracy. Analysis of the data by trend and total overburden techniques are compared; the trend method is to be preferred after the first year or two because it allows systematic errors to be reduced. The detectability of a sink is illustrated for a network of four stations spaced around the globe at which measurements are made at least daily. We conclude that 5 years of operation of such a network should enable us to establish whether atmospheric lifetimes of 20 years or less exist.
The enrichment of volatile elements in the atmosphere by volcanic activity: Augustine volcano 1976
Authors: Lepel E. A. , Stefansson K. M. , Zoller W. H.
Published: February 2008

Samples of atmospheric particulate material were collected in the plume of Augustine volcano in February 1976 by using the high‐volume filtration system aboard the National Center for Atmospheric Research Lockheed Electra. The samples were analyzed for 38 elements by a combination of instrumental neutron activation analysis and atomic absorption spectrometry. The results indicate that the volatile elements Zn, Cu, Au, Pb, As, Cd, Cl, Br, Se, Sb, Hg, and S are enriched in the atmospheric samples in relation to bulk ash by factors ranging from 10 to several thousand. The enrichments compare closely with those observed for other volcanic emanations and for background aerosols in remote areas of the earth. Samples collected early in the eruption cycle had a much higher quantity of volatile elements in relation to ash than the later samples, indicating a substantial change in the emission of volatiles with time and eruptive cycle.
Parameterization of the atmospheric heating rate from 15 to 120 km due to O2 and O3 absorption of solar radiation
Authors: Strobel Darrell F.
Published: February 2008

The atmospheric heating rate due to O2 and O3 absorption of solar radiation is parameterized with an accuracy of ±5% in the altitude region 15–120 km. For relevant wavelengths the effects of multiple scattering and ground reflection are also included. These parameterizations are computationally fast, efficient, and suitable for use in numerical models of atmospheric circulation.
Water‐soluble potassium, calcium, and magnesium in the aerosols over the tropical North Atlantic
Authors: Savoie D. L. , Prospero J. M.
Published: February 2008

During July, August, and September of 1974, daily aerosol measurements were made at three station in the tropical North Atlantic: Sal Island, Cape Verde Islands; Barbados, West Indies; Miami, Florida. The two major components of the aerosols at each station were mineral aerosol, comprising Saharan dust, and sea salt. Fifty‐eight samples were analyzed to determine the atmospheric concentrations of water‐soluble sodium, potassium, magnesium, and calcium and of the mineral aerosol. By using a multiple variable regression technique, the dominant source of water‐soluble potassium was found to be sea salt; the Saharan dust did, however, contribute a significant and sometimes quite substantial fraction (up to 38%). The soluble magnesium was almost exclusively a consequence of the presence of sea salt aerosols. In contrast, the soluble calcium at Sal Island and Barbados was derived predominantly (∼80%) from the Saharan dust; at Miami the contribution from Saharan aerosols (∼50%) and locally generated soil aerosols (∼40%) dominated the sea salt aerosol with respect to the amount of soluble calcium contributed. In comparison to the global continent‐to‐ocean flux via streams, the flux of soluble potassium via the atmosphere is probably negligible; the flux of soluble calcium via the atmosphere, however, may be of the order of 10% of that via streams.
Description of nonlinear internal wave interactions using Langevin methods
Authors: Pomphrey Neil , Meiss James D. , Watson Kenneth M.
Published: February 2008

A comparison is made between several methods for calculating energy transport among the linear normal modes of the internal wave field. Two Langevin techniques are presented. The first is based on the fluctuation‐dissipation theorem and provides a relaxation rate νF and a transport equation. The second method is an application of the Krylov‐Bogoliubov‐Mitropolsky perturbation theory and provides a Langevin rate constant νp calculated here only to lowest order. The two formulations are closely related to the radiative transfer (Boltzmann) equation, whose rate is the difference between νF and νp. Computations confirm the conclusion of McComas and Bretherton that the GM‐76 spectrum is approximately a steady state spectrum for three‐wave interactions except for frequencies near the inertial frequency and at the lowest vertical modenumbers. The sensitivity of νF and νp to spectral form is also discussed. Simple analytic expressions for the rates are derived for the induced diffusion, elastic scattering, and parametric subharmonic instability mechanisms. The first of these expressions provides a useful fit to the full computation over much of the spectrum. Finally, net energy flow in the nonequilibrium portion of the GM‐76 spectrum is discussed.
Scattering of continental shelf waves by longshore variations in bottom topography
Authors: Hsueh Y.
Published: February 2008

Forward scattering of continental shelf waves due to the presence of longshore topographic variations on scales comparable to those of the shelf waves is investigated. It is established that for variations for which distances from isobaths to the shore remain a fixed fraction of the local shelf width, no scattering could occur,even though the amplitude of such variation may be finite. Only deviations from shelf‐similar depth profiles cause scattering which, for an exponentially deepening shelf, is likely to be limited to the lowest couple of shelf wave modes. The scattering gives rise to cross‐shelf differences in the arrival time of flow events at points ‘forward’ from a topographic irregularity. The rate of this phase change (∼1.5° km−1) for a topographic feature of moderate amplitude appears to be comparable to that observed.
The scaling of vertical temperature gradient spectra
Authors: Caldwell D. R. , Dillon T. M. , Brubaker J. M. , Newberger P. A. , Paulson C. A.
Published: February 2008

Tests of a formula derived for the cutoff wave number of vertical temperature gradient spectra, using data taken in the upper layers of the North Pacific, show encouraging results. To derive this formula, the cutoff wave number is assumed to be the Batchelor wave number, with kinetic energy dissipation calculated by combining a form used in the atmosphere for calculating the vertical eddy diffusivity in terms of the dissipation with the Osborn‐Cox formula for calculating eddy diffusivity from the variance of the temperature gradient spectrum. Kinetic energy dissipation in the water column can be determined in this way; a vertical profile of dissipation shows values of the order of 10−3 cm2 s−3 at the base of a stormtossed mixing layer. In the thermocline below, dissipation occurs in patches.
The dynamic response of glass rod thermistors
Authors: Gregg M. C. , Meagher T. B.
Published: February 2008

The dynamic response characteristics of 0.4‐mm‐diameter glass rod thermistors, which are used frequently in fast‐response CTD and microstructure instruments, have been determined over the speed range of 0.08–3.8 m/s. The spectral transfer function was obtained by firing the probes through a thin plume and then comparing the power spectrum of the shot data with that of a slow‐speed map of the plume. The spectral transfer functions are described accurately by a two‐pole filter for frequencies less than 25 Hz, although a single‐pole form is an equally good representation for less than 10 Hz, The frequency of the ½‐power (3‐dB) attenuation point scales as U⅓. Although the spectral forms and velocity scaling of the responses of the different probes tested are the same, the levels show significant differences due to irregularities in the glass coatings around the thermistor material.
The entrainment of cohesive sediments in freshwater
Authors: Fukuda Michael K. , Lick Wilbert
Published: February 2008

Presented in this study are experimentally measured characteristics of the entrainment rate and settling speeds of fine‐grained, cohesive sediments in freshwater. The investigation focused on three different sediments of varying mineral composition which are representative of the sediments of Lake Erie. The influences of the bulk sediment water content and of the mineral and size composition on the entrainment rate and equilibrium concentration of these suspended sediments were determined. Linear increases in the bulk sediment water content resulted in logarithmic increases in the entrainment rate and equilibrium concentration. For a limited range of shear stresses near that needed to initiate noticeable entrainment the entrainment rate and equilibrium concentration increased logarithmically as the applied shear stress was increased linearly. For larger stresses, linear increases in the applied shear stress caused approximately linear increases in the entrainment rate and equilibrium concentration. At fixed values of water content and shear stress the entrainment rate and equilibrium concentration increased as the clay mineral content of the sediment increased and as the median particle size decreased. Settling speed experiments demonstrated that the median settling speed of the suspended sediment particles in a quiescent fluid increased as the ionic strength of the solution increased. At a fixed ionic strength the settling speed decreased with increased clay mineral content.
Triggered lightning strokes originating in clear air
Authors: Waldteuffl P. , Metzger P. , Boulay J.‐L. , Laroche P. , Hubert P.
Published: February 2008

During the 1978 campaign of the triggered lightning program at Saint‐Priyat d'Allier (France), simultaneous data from a movie camera, a coaxial shunt amperometer, a network of electric field mills, and a weather radar, were collected during the initial phase of a particular triggered event. These data are shown to exhibit a high degree of consistency, leading to the conclusion that charges totaling several coulombs were present in cloudfree air in the vicinity of a stormy area.
Determination of energy interaction terms and horizontal wavelengths for low‐frequency fluctuations in the Norwegian Current
Authors: Schott Friedrich , Bock Matthias
Published: February 2008

Current and temperature measurements with moored instruments in the Norwegian Current showed considerable fluctuations with periods of 2–3 days. An analytical model calculation (Mysak and Schott, 1977) suggested that these current fluctuations are most likely due to baroclinic instability of the mean flow. For current and temperature measurements from a cross of moorings, and from ship section data, vertical profiles of the barotropic and baroclinic instability terms are calculated. It is found that at the position of the mooring cross, energy is transferred into the perturbations by baroclinic instability, but that the barotropic terms transfer energy from the perturbations into the mean flow at a larger rate. The wavelengths of the fluctuations, calculated by high‐resolution directional spectra, are in the range of 30–40 km, in agreement with the analytical model results.
Evaluation of various total ozone sampling networks using the GFDL 3‐D tracer model
Authors: Moxim W. J. , Mahlman J. D.
Published: February 2008

Data sets generated by the Geophysical Fluid Dynamics Laboratory (GFDL) 3‐D general circulation/tracer model for an ozone experiment are used to compare the accuracy of various total ozone networks in calculating global and hemispheric means of total ozone and annual trends of monthly mean total ozone. The advantage of such an approach is that model integrals and trends are known exactly, thus providing an ability to examine the errors expected in present and hypothesized sampling networks. The effects of both spatial and temporal sampling errors are presented. Because the 3‐D tracer model uses the same time‐dependent wind fields from year to year, the influence of interannual meteorological variability and the sampling error resulting from long‐term ozone trends cannot be evaluated. Utilizing varying numbers of observations per month, total ozone networks of 9, 53, and 181 stations are compared. In addition, a case of 53 H‐15 new, judiciously placed stations is examined. Model network evaluations, of global mean ozone show underestimates of 1–3% occurring because of a compensation of northern and southern hemispheric errors up to −6% and +3%, respectively. An examination of the error of global mean ozone from random sampling networks for various months is made, showing rapid improvement from 9 to 1% for addition of random stations from 5 to 100. Markedly slower improvement is seen with further increases in the number of stations. One‐year trend analyses of total ozone are compared for various networks and individual stations. Sampling errors of nearly 1% per year are seen for the 53 station case, using four perfect, equally spaced observations per month. The errors grow substantially larger with fewer observations. The effect on global and hemispheric means of stations not taking measurements during cloudy periods also is investigated. Results indicate that the weak annual mean cloud bias error (0.285%) is overwhelmed by the larger error produced by the decrease in effective network density.
Refraction of microwave signals by water vapor
Authors: Goldfinger Andrew D.
Published: February 2008

Tropospheric water vapor causes a refractive path length effect which is typically 5–10% of the ‘dry’ tropospheric effect and as large as several meters at elevation angles below 5°. The vertical water vapor profile is quite variable, and measurements of intensive atmospheric parameters such as temperature and humidity limited to the surface do not adequately predict the refractive effect. With the advent of multifrequency microwave radiometry, it has become possible to measure extensive parameters such as total amount of precipitable water, W. Our analysis shows that the refractive effect at the zenith can be written as a series of integrals representing moments of the water vapor density, the zeroth moment being identical to the above‐defined quantity W. We proceed to the hypothesis that a water vapor refraction model that is a function of W alone can be successful at low elevation angles. From an extensive study of numerical ray tracings through radiosonde balloon data, we have constructed such a model in the form Δlw = ƒ(W, E, L, T0) where Δlw is the ‘wet’ refractive effect, E is the elevation angle, L is the latitude, and T0 is the surface temperature. The model predicts the effect at all latitudes and elevation angles between 2° and 10° to an accuracy of better than 4% (11 cm at 3° elevation angle).
Contribution of hydrogen production by biological nitrogen fixation to the global hydrogen budget
Authors: Conrad Ralf , Seiler Wolfgang
Published: February 2008

Measurements taken at two field stations in Germany have shown that H2 is evolved from the soil into the atmosphere in the presence of leguminous plants. H2 evolution rates were found to be dependent on N2 fixation rates and decreased rapidly when the plants (Trifolium hybridum) were topped, kept in darkness, or fertilized with NH4Cl. Maximum H2 evolution rates were observed during the main vegetation period, from April to June, with average rates of 5–7×10−8 cm3 cm−2 s−1. During this period, soil covered with legumes represented a net source of atmospheric H2 with an estimated global source strength of 0.9–1.2 Tg yr−1. Assuming that other biological N2 fixation processes contribute similarly to the global H2 budget, the total H2 source due to biological N2 fixation is estimated to be 2.4–4.9 Tg yr−1. The average H2 deposition velocity was found to be 7×10−2 cm s−1, resulting in a global H2 sink strength of soil of 70–110 Tg yr−1. The global H2 budget is discussed with respect to its various sources and sinks.
Threshold velocities for input of soil particles into the air by desert soils
Authors: Gillette Dale A. , Adams John , Endo Albert , Smith Dudley , Kihl Rolf
Published: February 2008

Desert soils mostly from the Mojave Desert were tested for threshold friction velocity (the friction velocity above which soil erosion takes place) with an open‐bottomed portable wind tunnel. Several geomorphological settings were chosen to be representative of much of the surface of the Mojave Desert, for example, playas, alluvial fans, and aeolian features. Variables which increase threshold velocity are decreasing proportion of sand, increasing size of dry aggregates of the soil, and increasing fraction of the soil mass larger than 1 mm. Threshold velocity increases with different types of soil surfaces in the following order: distrubed soils (except disturbed heavy clay soils), sand dunes, alluvial and aeolian sand deposits, disturbed playa soils, skirts of playas, playa centers, and desert pavements (alluvial deposits).
Latitudinal distributions of CO and CH4 over the Pacific
Authors: Heidt L. E. , Krasnec J. P. , Lueb R. A. , Pollock W. H. , Henry B. E. , Crutzen P. J.
Published: February 2008

Measurements on Gametag (Global Atmospheric Measurements Experiment of Tropospheric Aerosols and Gases) in April and May 1978 indicate volume mixing ratios of CH4 of 1.62 ppmv south of the intertropical convergence zone and 1.72 ppmv north of 20°N. For CO south of 10°S, the CO volume mixing ratios were rather constant and equal to 57 ppbv. Poleward of 30°N in the northern hemisphere we measured average mixing ratios of 175 ppbv. Both for CO and for CH4 a gradual transition from lower southern hemispheric to higher northern hemispheric values were observed between 10°S and 20°N. The uncertainties in our measurements are 15% for CO and 3% for CH4. By comparing our observations with earlier ones (Seiler, 1974; Ehhalt, 1978), we can not detect any changes in the atmospheric abundances of CO and CH4 from 1972 to 1978 outside the uncertainty limits of the measurements.
Sea ice and temperature variability in the eastern Bering Sea and the relation to atmospheric fluctuations
Authors: Niebauer H. J.
Published: February 2008

An analysis of fluctuations in weekly mean percent ice cover, degree‐days, and surface winds and monthly mean sea surface temperatures from the eastern Bering Sea shelf region is presented for the period 1973–1979. The seasonal advance of the ice begins at the Bering Strait in November, reaches its southern maximum extent in March–April, and has completely disappeared by early July. Large year‐to‐year deviations from the seasonal means are observed in the data. These time series are divided into two sections with the first (∼1973–1976) characterized by lower (and slightly falling) temperatures and greater than normal (and slightly increasing) northerly surface winds and ice cover. The following period (∼1976–1979) is characterized by strong rises in air and sea temperatures, a precipitous fall in ice cover, and a fall in the northerly component of the surface wind with more southerly flow. These observations lead to a conceptual model in which the mean winter atmospheric circulation is the driving force behind the large year‐to‐year fluctuations in the various data sets. On shorter time scales, two relatively minor but persistent ice retreats are shown to occur each year generally around the end of December and the end of February. These retreats last 2–3 weeks, range between 5 and 20% reduction in ice cover and appear to be caused by south winds causing compaction of the ice edge. South winds associated with east sides of low‐pressure systems, either progressing or retrograding over the Bering Sea, appear to be the driving force for this phenomenon.
Latitudinal distribution of Mercury over the Atlantic Ocean
Authors: Slemr F. , Seiler W. , Schuster G.
Published: February 2008

Mercury in air and in surface water has been measured during a ship expedition across the Atlantic Ocean between Hamburg (50°N) and Buenos Aires (35°S). The data show an interhemispherical difference of total gaseous mercury, with average concentrations of 1.56 ± 0.32 ng/m3 in the northern hemisphere and 1.05 ± 0.22 ng/m3 in the southern hemisphere. Dimethyl mercury concentrations in clean marine air are ≤0.1 ng Hg/m3 or ≤10% of the total gaseous mercury. The interhemispheric concentration difference and the variability of gaseous mercury of ±16% imply a mean tropospheric residence time of atmospheric mercury of approximately 0.9 years. With a total tropospheric burden of 5.0 × 109 g, source and sink strengths are estimated to be 6 × 109 g mercury per year. Most of the mercury produced must originate from continental sources, by both anthropogenic and natural processes. The oceans seem to be only of minor importance in the global atmospheric mercury budget. The mercury content in water was 2–8 ng/1. The mercury concentrations in air and in water did not correlate.
Small‐scale shear measurements during the fine and microstructure experiment (Fame)
Authors: Gargett A. E. , Osborn T. R.
Published: February 2008

The turbulent kinetic energy dissipation rate ε is estimated from measurements of small‐scale shear taken with a vertical profiler during the Fine and Microstructure Experiment (Fame). Typical profiles of ε are presented for the different oceanographic regions sampled, the Gulf Stream, a mid‐Sargasso site, and locations within and without the 1000 fathom (∼2000 m) contour about the island of Bermuda. Heavily averaged values of ε are presented as a function of mean Väisälä frequency
, a fundamental scaling parameter for the oceanic internal wave field. A dependence of
is found for an ensemble of stations near Bermuda; functional dependence for an ensemble of stations at the mid‐Sargasso site is less clear, with results exhibiting an undesirable sensitivity to infrequent large events. Dissipation is found to increase as the island of Bermuda is approached from any direction: the density of measurements is insufficient to determine any azimuthal variation resulting from the anisotropic mean flow field about the island at the time. A set of three profiles across the Gulf Stream suggests that this is not a region of abnormally high dissipation, a conclusion supported by previous and concurrent measurements of temperature finestructure and microstructure.
Optical properties of the crustal aerosol: Relation to chemical and physical characteristics
Authors: Patterson E. M.
Published: February 2008

We have measured crustal aerosol absorption, expressed as a wavelength dependent imaginary index of refraction (nIM) at both visible and infrared wavelengths. Measurements at visible wavelengths show values of nIM that range from ∼0.02 at 300 nm to ∼0.004 to 700 nm. Infrared measurements show an absorption that is dominated by a silicate absorption with a maximum value of nIM ∼ 1 near 10 μm. Comparisons of our measurements with other reported measurements of well‐documented crustal aerosols show a great deal of similarity among the measured values. We have shown that these measured optical properties, and the similarities and differences in the measured values, can be understood in terms of mineralogical characteristics of the aerosol and fractionation processes that occur in the generation and transport of these aerosols.
Hydrographic observations off Northern California during May 1977
Authors: Freitag H. Paul , Halpern David
Published: February 2008

A hydrographic survey of 286 CTD stations was made in May 1977 in the region between 37°N (i.e., near San Francisco) and 43°N (i.e., Cape Blanco in southern Oregon). Coastal upwelling was most intense south of Cape Mendocino. At 300 m an intense temperature and salinity frontal zone occurred between 38°N and 39°N. The dynamic height topographies 0/900 dbar and 300/900 dbar contained regions of highs and lows with length scales of 100–150 km. North of Cape Mendocino the warm saline water identified as the poleward California Undercurrent was not observed, and the transport integrated above 900 dbar was southward.
Long wavelength carbonyl sulfide photodissociation
Authors: Turco R. P. , Cicerone R. J. , Inn E. C. Y. , Capone L. A.
Published: February 2008

The aeronomic implications of a preliminary observation of weak OCS photoabsorption above 270 nm are investigated. It is argued that the measured cross section is consistent with a forbidden transition in this wavelength region. Model calculations are made for the OCS photodissociation rates in daylight, the OCS and SO2 distributions in the upper atmosphere, and the budgets of sulfur in the stratosphere and OCS in the troposphere, assuming various extrapolations of the measured OCS absorption cross sections and quantum yields to longer wavelengths. It is shown that weak OCS absorption above 300 nm can have important consequences for all of these quantities. Laboratory and field experiments are identified which might lead to a better understanding of the atmospheric OCS cycle.
Thermohaline steps induced by melting of the Erebus Glacier Tongue
Authors: Jacobs S. S. , Huppert H. E. , Holdsworth G. , Drewry D. J.
Published: February 2008

A vertically stable, step‐like thermohaline structure is observed throughout a continuous, 400 m conductivity‐temperature‐depth (CTD) profile taken near the Erebus Glacier Tongue, McMurdo Sound, Antarctica. The pattern is best developed between the sea surface and 250 m depth, the interval corresponding to that of the irregular underwater profile of the Glacier Tongue. The steps average 17 m in thickness and typically display discontinuities of 0.1°C in temperature, 0.04‰ in salinity and 3.5 × 10−4 g cm−3 in density. The observations are compared with theory and laboratory experiments of cell development and lateral flow near ice melting into vertically stratified salt water. At this location, subsurface seawater is inferred to remain above the in situ freezing point year‐round, and contains sufficient heat to account for much of the Glacier Tongue thinning by basal melting. An adequate volume of meltwater would result to produce the measured salinity steps. We discuss related observations and some implications of this process for ocean circulation and biological productivity in the Antarctic.
Wind‐water tunnel simulation of small‐scale ocean‐atmosphere interactions
Authors: Coantic Michel , Ramamonjiarisoa Alfred , Mestayer Patrice , Resch François , Favre Alexandre
Published: February 2008

Various results obtained at the Institut de Mecanique Statistique de la Turbulence wind‐water facility, where small‐scale dynamic and thermodynamic air‐sea exchange processes can be partially simulated, during the past 10 years are reviewed in the light of present ideas on ocean‐atmosphere interactions. The object here is to draw conclusions on both the validity and the usefulness of such laboratory studies. Large‐ and small‐scale turbulent velocity and temperature fields exhibit good similarity and general agreement with surface layer observations but also exhibit interesting departures from local isotropy. The spectral characteristics of waves in the laboratory are quite similar to short‐fetch field data. An inherently nonlinear ‘dominant wave’ is found to have a major influence upon properties and upon the dispersion relation of wind waves in the laboratory and in the field. Wind‐wave coupling is observed and investigated through linear and nonlinear methods. Turbulent heat and mass transfer processes, studied through different techniques, show that evaporation rates and diffusive sublayer thicknesses compare well with other estimates. Observed density stratification effects can be interpreted in terms of the accepted description for atmospheric surface layer. These data as a whole demonstrate that laboratory studies on small‐scales air‐sea interaction mechanisms can provide an insight into the naturally occurring physical processes.
Vertical profiles of ethane and propane in the stratosphere
Authors: Rudolph J. , Ehhalt D. H. , Tönnissen A.
Published: February 2008

Stratospheric measurements of the C2H6 mixing ratio up to 30 km and of the C3H8 mixing ratio up to 18 km altitude are reported. The observed vertical gradient of C2H6 is much weaker than that calculated from a one‐dimensional steady state model, indicating lower concentrations of atomic chlorine in the lower stratosphere than those predicted by models. From the measured C2H6 profile a tentative estimate for the Cl concentration is derived.
Simultaneous spectroscopic determination of the latitudinal, seasonal, and diurnal variability of stratospheric N2O, NO, NO2, and HNO3
Authors: Coffey M. T. , Mankin W. G. , Goldman A.
Published: February 2008

The importance Of NOx compounds to stratospheric chemistry has been clearly established. We report below on a program to measure latitudinal, seasonal, and diurnal variations in stratospheric N2O, NO, NO2, and HNO3 amounts. Through the use of airborne Fourier transform absorption spectroscopy, we determine simultaneously column amounts above 12 km of the four molecules listed above. Nitrous oxide (N2O) is found to have a fairly uniform distribution with latitude and season, with a stratospheric column abundance of 8.1 × 1017 molecules cm−2. Nitric oxide (NO) amounts are shown to decrease with increasing latitude in winter. A 50% decrease in high latitude winter amounts is observed as compared with low latitude values near 3.0 × 1015 molecules cm−2. Nitrogen dioxide (NO2) stratospheric amounts increase in summer with increasing latitude. Equatorial values are near 3.0 × 1015 molecules cm−2 above 12 km. A factor of 3–4 increase in higher latitude summertime NO2, as compared to winter NO2, is observed. Nitric acid (HNO3) amounts show a general increase toward higher latitudes and a marked increase in mid‐latitude winter as compared to summer. Winter amounts may be highly variable with a value near 1.0 × 1016 molecules cm−2.
Measurement of atomic oxygen and related airglows in the lower thermosphere
Authors: Thomas R. J. , Young R. A.
Published: February 2008

Instruments on‐board a sounding rocket were used to make simultaneous observations of atomic oxygen density and airglow emissions between 80 and 120 km. Atomic oxygen was measured with a resonance lamp and was found to have a peak density of 6 × 1011 at 94 km. Similar structure is seen in the oxygen‐density profile on both uplegs and downlegs. The following airglow emissions were measured by using vertical‐viewing photometers: Herzberg I bands near 300 nm; O(1S) green line at 557.7 nm; background at 566 nm; O2(1Δg) bands at 1.27 μm; and OH (X2π) Meinel bands near 1.7 μm.
Application of GOES visible‐infrared data to quantifying mesoscale ocean surface temperatures
Authors: Maul George A.
Published: February 2008

Application of GOES archived data to determining sea surface temperature in the Gulf of Mexico is investigated for October 1977, a period when two research ships and three environmental buoys were available to provide surface calibration data. A theoretical error analysis is first used to explain the persistent differences between ship and operationally derived satellite temperatures and then is used to dictate a technique for applying full resolution archived GOES visible and infrared data to the problem. The technique developed first remaps the satellite scanline data into a rectangular matrix that covers the region of interest. Second, radiative transfer calculations are performed at each ‘cloud‐free’ station around the Gulf's periphery using LOWTRAN‐4. Third, least squares polynomial surfaces of atmospheric corrections are fitted to the perimetric radiative transfer results. Fourth, a bivariate Bayesian discriminant function, which uses cloud‐free areas as training sets, is used to classify objectively clear ocean radiance measurements. Fifth, the GOES is calibrated by comparing in situ measurements with calculated theoretical satellite temperatures. Sixth, maps of sea surface temperature are produced and compared with ship reports and a marine atlas. Root‐mean‐square calibration errors of GOES surface temperature determined by the above outlined approach was ±1.2 K when using all available surface reports and ±0.5 K when using only research ship, XBT, and environmental buoy reports. Evaluation of the infrared multispectral approach planned for NOAA‐C shows that for a mesoscale area the two techniques result in similar errors, and that ±1.0 K or slightly less is probably the geophysical limit of accuracy.
Sediment mixing and accumulation rate effects on radionuclide depth profiles in Hudson estuary sediments
Authors: Olsen C. R. , Simpson H. J. , Peng T.‐H. , Bopp R. F. , Trier R. M.
Published: February 2008

Measured anthropogenic radionuclide profiles in sediment cores from the Hudson River estuary were compared with profiles computed by using known input histories of radionuclides to the estuary and mixing coefficients which decreased exponentially with depth in the sediment. Observed 134Cs sediment depth profiles were used in the mixing rate computation because reactor releases were the only significant source for this nuclide, whereas the inputs of 137Cs and 239,240Pu to the estuary were complicated by runoff or erosion in upstream areas, in addition to direct fallout from precipitation. Our estimates for the rates of surface sediment mixing in the low salinity reach of the estuary range from 0.25 to 1 cm2/yr, or less. In some areas of the harbor adjacent to New York City, where fine‐particle accumulation rates are generally >3 cm/yr, and often as high as 10 to 20 cm/yr, sediment mixing rates as high as 10 cm2/yr would have little effect on radionuclide peak distributions. Consequently, anthropogenic radionuclide maximum activities in subsurface sediments of the Hudson appear to be useful as time‐stratigraphic reference levels, which can be correlated with periods of maximum radionuclide inputs for estimating rates and patterns of sediment accumulation.
The diurnal variation of NO3
Authors: Platt U. , Perner D. , Schröder J. , Kessler C. , Toennissen A.
Published: February 2008

Nighttime concentration profiles of the nitrate radical (NO3) together with NO2 and O3 were observed spectroscopically. Kinetic analysis of the NO3 formation, the early morning photolysis of NO3, and stoichiometric considerations allowed three independent estimates of the equilibrium constant Keq = [NO3] · [NO2]/[N2O5]. From those observations an average Keq of (2.0±l) × 1010 cm−3 (at 10°C) is derived. Maximum concentrations of NO3 were found to be highly variable. Lifetimes for NO3 shorter than l min in the presence of fog indicate a fast reaction of N2O5 with liquid water droplets. At relative humidities below 50% the maximum NO3 concentrations were still lower than expected from the NOx–O3 reaction sequences which must be due to unknown sinks for NO3 and/or N2O5 or to an inadequacy in the presently accepted reaction scheme.
Total ozone seasonal and interannual variations derived from the 7 year Nimbus‐4 BUV data set
Authors: Hilsenrath Ernest , Schlesinger Barry M.
Published: February 2008

Backscattered ultraviolet (BUV) data from the Nimbus‐4 spacecraft for the period 1970–1977 have been recently processed to final form. This paper is based upon an analysis of all the total ozone data available in the 7‐year data set. The seasonal and interannual variations of total ozone over the globe are examined, using daily zonal means of 10° latitude bands and a time latitude cross section. A harmonic analysis was performed on the daily zonal means, and the amplitude, phase, and percentage of variance were computed for the annual, semiannual, and higher harmonics for several years and for individual years. Many of the features observed earlier for the period 1970–1972, such as the asymmetry of the annual wave in the two hemispheres, persist over the longer data period. Variations with regular periods shorter than a few months were sought, but none were evident systematically throughout the latitude zones. Examination of the zonal mean data with the mean annual wave removed revealed a clear quasibiennial oscillation (QBO) strongest in the tropics, where it is comparable to the annual wave, persisting to mid‐latitudes in both hemispheres with some evidence of its existence at high latitudes. An estimation of the QBO period, using a superposition analysis (for no more than three cycles) for each latitude zone, revealed a decreasing period with latitude in both hemispheres. The maximum period of 27 months occurs in the tropics while the minimum in the northern hemisphere is about 20 months. This result suggests that the observed QBO in total ozone at high and low latitudes may not be directly related. This is of particular significance to studies of ozone trends since the result indicates interannual variations are latitude dependent.
A numerical model of the wind‐driven transient motion in Bass Strait
Authors: Fandry C. B.
Published: February 2008

The dynamical equations governing the wind‐induced barotropic motion of the shallow water in the Bass Strait basin with variable bathymetry are discussed qualitatively and solved numerically with a view of explaining and describing the circulation and sea‐surface elevation fields. Immediately after the onset of a steady uniform wind, fluid is accelerated in the direction of the wind, and the sea‐surface elevation gradient builds up at coastal boundaries to satisfy the condition of zero normal flow. During the intermediate stages toward steady state the effects of topography, the earth's rotation, and bottom friction come into play, and simple arguments based on the momentum and vorticity balances are used to describe their relative importance. A numerical model of the hydrodynamics of the Bass Strait waters is presented and the results interpreted in terms of the above theoretical ideas. Of special significance is the dominance of the topographic effect which acts to produce barotropic currents, which are much larger than those in a flat bottom basin and which flow in a direction along the depth contours. It is shown that these currents are controlled by the component of wind stress acting along the isobaths, which is balanced by the bottom friction. The energy balance within the strait is discussed and shown to be highly dependent on the wind stress distribution. The degree of mixing by the wind as estimated by the stratification index H/u3, is shown to be small. A comparison with the very limited number of observations validates some of the more prominent features of the model results.
Dissolved hydrogen, carbon monoxide, and methane at the CEPEX site
Authors: Bullister John L. , Guinasso Norman L. , Schink David R.
Published: February 2008

Concentrations of three trace gases—H2, CO, and CH4—were measured in the upper waters and in the near‐surface atmosphere at the Controlled Ecosystem Population Experiment (CEPEX) site in Saanich Inlet, B.C., Canada. The upper 20 m of water contained these reduced gases at concentrations significantly higher than atmospheric equilibrium values in the presence of high levels of dissolved oxygen. Because vertical mixing was quite weak within the CEPEX container, distributions of CO, CH4, and H2 were most strongly influenced by in situ production and consumption. Concentrations of hydrogen and carbon monoxide were generally highest at or near the surface in all containers. Daily cycles of CO concentrations in the CEPEX enclosures and in the water outside the enclosures were observed. A similar, but less pronounced, H2 cycle was seen only inside the enclosure. In the CEPEX container that received no nutrient additions, a methane maximum was commonly found at depths between 8 and 12m. Methane concentrations and distributions in this container showed little change over a period of several weeks. Methane distribution did undergo significant change in the nutrient enriched containers. In Saanich Inlet, the CH4 maxima occurred deeper in the water column. No excess of H2 or CO was found in this methane‐rich deeper water. Within the containers, changing hydrogen concentrations seem related to phytoplankton abundance, but the hydrogen distribution suggests zooplankton play a role. Carbon monoxide abundance varies with the amount of illumination received by the waters. Probably a variety of factors influence the distribution of each of the gases. Seawater samples collected at the site and incubated in dark containers, at in situ temperature, showed rapid decreases of CO and H2 levels to below air equilibrium. Carbon monoxide in these incubated samples reached subequilibrium levels within 12 hours. Shallow and deep water samples that had been briefly exposed to sunlight during sample handling subsequently showed higher levels of dissolved CO than did samples that were carefully shielded from outside light. Care is needed to avoid such artifacts when studying diurnal variations in dissolved CO.
The SEASAT‐A satellite scatterometer: The geophysical evaluation of remotely sensed wind vectors over the ocean
Authors: Jones W. Linwood , Schroeder Lyle C. , Boggs Dale H. , Bracalente Emedio M. , Brown Robert A. , Dome George J. , Pierson Willard J. , Wentz Frank J.
Published: February 2008

On the SEASAT‐A satellite, a microwave scatterometer was used to determine the vector wind over the world's oceans. The technique is based on the sensitivity of microwave radar backscatter to the centimeter length ocean waves created by the action of the surface wind. This paper describes the algorithm used to convert the scatterometer's measurements of ocean normalized radar cross section, σ°, to the neutral stability vector wind at 19.5 m height and the comparison of these winds with high quality surface observations. The wind vector algorithm used an empirical σ° model function to describe the dependence of the ocean σ0 on the 19.5‐m neutral stability wind vector. Two model functions, developed from a limited base of aircraft and satellite σ° measurements, were evaluated by using an independent set of in situ surface wind observations from the Joint Air Sea Interaction Experiment (JASIN). Although these model functions were found to have some weaknesses, the results of these comparisons produced better results than the SEASAT specifications of wind speed accuracy of ±2 m/s and wind direction accuracy of ±20° over the 0–16 m/s range of winds observed during JASIN. An improved model function was later developed by ’tuning‘ to these JASIN data so that the remaining biases between the observed surface winds and the scatterometer‐derived winds were minimized. Results are presented for this model function compared against other surface wind observations from the Gulf of Alaska SEASAT Experiment and the SEASAT Storms (Hurricane) Experiment.
Mean sea level variations and their practical applications
Authors: Palumbo A. , Mazzarella A.
Published: February 2008

Daily mean sea level time series recorded in Naples (1959–1976) and the joint variation of sea level, atmospheric pressure, and wind together with the values of water density and marine currents are analyzed. The daily mean sea level series adjusted according to the hydrostatic hypothesis shows a pronounced seasonal cycle, principally explained by the seasonal cycle of water density. The cross‐spectral analysis shows surprisingly small barometric factor values for periods shorter than a week, explained mostly by the influence of local wind. An autoregressive model for mean sea level forecasting has been set up and satisfactorily applied to practical problems such as the discharge of rivers and the continuous surveying of movement of the ground from a tide gage alone.