bluuebunny/crossref_metadata_2025 huggingface dataset:
Cesium 137 transport into the Arctic Ocean through Fram Strait
Authors: Smith J. N. , Ellis K. M. , Jones E. P.
Published: February 2008

Cesium 134 and 137Cs activities were measured in water samples collected in March–April 1981 at the Fram 3 ice station located 200 km north of Fram Strait. The water depth profiles of these isotopes reveal the presence of two pathways for the entry of anthropogenic tracers into the Arctic Ocean through Fram Strait. Atlantic water passing across the Yermak Plateau at the 100–200 m level is labeled by elevated concentrations of 134Cs and 137Cs associated with inputs from the Sellafield reprocessing plant in the United Kingdom. The 134Cs/137Cs ratio is consistent with a transit time into the Nansen Basin from the Sellafield, United Kingdom, vicinity of 5–6 years. An elevated concentration of 137Cs at the 1500‐m level is associated with inputs of recently ventilated water from the Greenland‐Norwegian seas or as a consequence of brine formation and off‐shelf transport from the Barents Sea.
Verification of Geosat altimetry for operational use in the Gulf of Mexico
Authors: Forristall George Z. , Schaudt Kenneth J. , Calman Jack
Published: February 2008

Geosat altimetry is well suited for locating large eddies shed by the Loop Current in the Gulf of Mexico. We have compared the altimeter data with in situ data obtained during a survey of Eddy Murphy in June 1988. Since there is no significant mean circulation in the central gulf, we used the mean sea surface from the first year of altimeter data as a geoid estimate. The dynamic height change due to the eddy closely matched the altimeter data, although the eddy moved about one third of a degree between the survey and the satellite pass. The motion of the eddy was confirmed by the track of an Argos buoy.
Instabilities of fronts over a continental margin
Authors: Chao Shenn‐Yu
Published: February 2008

Over a continental slope, a negatively buoyant density forcing from the coastline generates a “GuIf Stream front” if the receiving water is initially homogeneous and a coastal upwelling front if the receiving water is stratified. A positive buoyancy forcing produces density‐driven coastal currents whether the ambient water is stratified or not. The four types of fronts are analyzed and compared to lowest order. If instability is measured in terms of the cross‐shelf excursion and the alongfront asymmetry of unstable waves, our impression is that a coastal upwelling front is the most unstable and a Gulf Stream front along the south Atlantic Bight is the second. Fronts associated with density‐driven coastal currents are only marginally unstable. Ambient stratification destabilizes the coastal current. More quantitatively, there are more cyclonic vorticities near prograde (or seaward deepening) fronts such as the Gulf Stream front and coastal upwelling front than near retrograde (or landward deepening) fronts associated with coastal currents. Reasons are discussed in the text. The relaxation of fronts consistently enhances meander growth and eddy genesis. The resultant eddies are mostly cyclonic near prograde fronts and anticyclonic near retrograde fronts.
Dependence of the microwave radar cross section on ocean surface variables: Comparison of measurements and theory using data from the Frontal Air‐Sea Interaction Experiment
Authors: Weissman David E.
Published: February 2008

The purpose of this investigation was to study the ability of theoretical radar cross section (RCS) models to predict the absolute magnitude of the ocean radar cross section under a wide variety of sea and atmospheric conditions. The dependence of the RCS on wind stress (as opposed to wind speed) was also studied. An extensive amount of experimental data was acquired during the Frontal Air‐Sea Interaction Experiment (FASINEX). This consisted of RCS data from the NASA‐Jet Propulsion Laboratory Ku band scatterometer mounted on a C130 aircraft (10 separate flights), as well as a wide variety of atmospheric measurements (including stress) and sea conditions. Measurements across an ocean front demonstrated that the vertical polarization (V‐pol) and horizontal polarization (H‐pol) radar cross section were more strongly dependent on wind stress than on wind magnitude. Current theoretical models for the RCS, based on stress, were tested with this data. In situations where the Bragg scattering theory does not agree with the measured radar cross section (magnitude and angle dependence), revisions are hypothesized and evaluated. For example, the V‐pol theory worked well in most cases studied, while the H‐pol theory was usually too low by about a factor of 2 at incidence angles of 50° and 60°.
Comparison of Seasat scatterometer winds with tropical Pacific observations
Authors: Davison Jerry , Harrison D. E.
Published: February 2008

The Seasat‐A satellite scatterometer (SASS) observed near‐surface vector winds over the world ocean from an 800‐km orbit by measuring radar backscatter from the wind‐roughened surface. The early end of the mission in 1978 forestalled some of the planned ground‐truth validation experiments; questions remain about the instrument's performance, in particular away from mid‐latitudes. To increase the geographical range of SASS and in situ comparison experiments, we have compared data from nine islands in the tropical Pacific and contemporaneous scatterometer winds. We used satellite winds derived from two different wind vector algorithms (the signal processing that reduces the radar backscatter to wind speed and direction). The SASS‐2 algorithm due to Wentz provides clearly better agreement in wind speed than the earlier SASS‐1 algorithm. SASS‐1 speeds tend to be higher than the island measurements by about 1 m s−1, while daily mean SASS‐2 minus island wind speed differences average −0.07 m s−1. The rms differences between SASS‐2 and the daily mean island data average 1.7 m s; the SASS‐1 rms differences average 2.2 m s−1. Because the Seasat wind algorithms yield solutions with more than one possible direction, a single direction can only be selected from the others using ancillary information. We compared direction results from the objective selection method developed at the Goddard Laboratory for Atmospheres, as well as results from the somewhat artificial method of selecting the SASS direction closest in agreement with the comparison island direction. When averaged over tens of days the Goddard directions agree closely with the island observations. However, Goddard daily mean directions exhibit considerably higher variance than those measured at the islands. The closest direction technique gives daily mean SASS minus island rms direction differences averaging 20°; the Goddard rms differences average 52°.
Effect of orbit error on determining sea surface variability using satellite altimetry
Authors: Rosborough George W. , Marshall J. Andrew
Published: February 2008

Satellite altimetry data provided by GEOS 3, Seasat and currently Geosat have been successfully used to measure sea surface variability. The determination of the ocean variability has been accomplished through either examination of differences along collinear tracks or differences at points where tracks cross. In either case it is first necessary to remove the relatively large long‐wavelength error that exists in the sea surface heights due to inaccuracies in the estimation of the satellite altitude from ground based tracking data. This long‐wavelength altitude error has generally been an order of magnitude larger than the short‐wavelength variability that is being sought. A number of techniques have been applied to eliminate the altitude error with the most common being a simple modeling of the orbit error as a linear trend over the region of interest. The intent of this study is to quantify the effectiveness of using a linear model of altitude error when attempting to estimate sea surface variability. Although there are many sources of altitude error, only the influence of gravity modeling errors will be considered here. This is justified since this is the dominant error source in the estimation of the satellite altitude from ground based data. Additionally, gravity model errors are the primary source of altitude errors with wavelengths shorter than once per revolution. Analyses are presented for the case of Geosat and TOPEX altitude errors due to the expected modeling uncertainties of the GEM‐L2 and GEM‐T1 gravity fields. Results are given in terms of the rms of the crossovers after removing linear trends along track and minimizing the crossovers. It is found that for scales below 10,000 km, both gravity models are equally effective. Also, the higher altitude of TOPEX provides for significantly better performance of the linear orbit error correction model. The results indicate that the current GEM‐T1 model induces crossover discrepancies of less than 5 cm rms at scales up to 10,000 km.
A Comparison Between the Generalized Digital Environmental Model and Levitus climatologies
Authors: Teague William J. , Carron Michael J. , Hogan Patrick J.
Published: February 2008

Two ocean climatologies of temperature and salinity, the Generalized Digital Environmental Model (GDEM) and the Climatological Atlas of the World Ocean, are compared. Dynamic height fields are computed by season from each climatology for the North Atlantic, North Pacific, and Indian oceans and are compared on a 1° latitude‐longitude grid. Large‐scale oceanographic features are generally found to be similarly represented in both climatologies. GDEM appears to render better representations of seasonal variability and regions of high current shear, such as the Gulf Stream, because of a different smoothing method and a finer grid spacing. Maps of dynamic heights from both climatologies are presented, and their similarities and differences are discussed. The methodology for the construction of GDEM is also described in detail.
Testing alternative parameterizations of lateral melting and upward basal heat flux in a thermodynamic sea ice model
Authors: Harvey L. D. Danny
Published: February 2008

A zonally averaged, physically based sea ice model is coupled to an energy balance climate model with prescribed observed atmospheric temperatures and used to investigate the sea ice model sensitivity to alternative parameterizations of (1) the upward heat flux Fb to the ice base, and (2) lateral melting of ice from open water. The parameterizations tested here are taken from the climate and sea ice modeling literature. The different parameterizations for each of these processes can lead to dramatically different results in simulated sea ice area, sea ice thickness, or both. Parameterizing Fb by prescribing (or computing) an upward heat flux at the mixed layer base and either constraining the subice mixed layer temperature to equal the freezing point of seawater or parameterizing Fb as a function of subice mixed layer temperature has the advantage of incorporating the effects on heat fluxes to the ice base of both convective overturning and meridional oceanic heat flux convergence. Parameterizing lateral melting as a function of lead temperature Tlead, rather than making it depend on ∂Tlead/∂t, has relatively little impact on simulated winter ice extent, and no impact on summer ice extent.
Enhancement of fronts by vertical mixing
Authors: Dewey Richard K. , Moum James N.
Published: February 2008

Microstructure observations near upwelled fronts indicate considerable variation in the structure of vertical mixing across the frontal region. Observations of cool filaments off northern California indicate that within the cool (dense) core of filaments the raised pycnocline inhibits the penetration to middepths of surface‐generated mixing. The microstructure profiles are used to estimate the available wind energy for mixing as a function of pycnocline, or mixed layer depth. A greater portion of energy input at the surface is available for entrainment of dense fluid through the pycnocline and into the surface mixed layer where the pycnocline is shallow. Hence surface‐forced mixing may cause a more rapid increase in mixed layer density within the cool filament than outside the filament, resulting in an enhanced horizontal density gradient in the mixed layer. Assuming the flow adjusts towards geostrophy, the enhanced horizontal density gradient at the front could result in an accelerated mixed layer in the direction of the preexisting geostrophic flow. Proportions relating the gain in potential energy to the wind energy vary with pycnocline depth and differ by as much as an order of magnitude from the findings of Denman and Miyake (1973) and Davis et al. (1981). Horizontal variability of pycnocline erosion may not be properly taken into account in some models and should more realistically be parameterized by including dependence on pycnocline depth.
The sensitivity of latent heat flux to the air humidity approximations used in ocean circulation models
Authors: Liu W. Timothy , Niiler Pearn P.
Published: February 2008

In deriving the surface latent heat flux with the bulk formula for the thermal forcing of some ocean circulation models, two approximations are commonly made to bypass the use of atmospheric humidity in the formula. The first assumes a constant relative humidity, and the second supposes that the sea‐air humidity difference varies linearly with the saturation humidity at sea surface temperature. Using climatological fields derived from the Marine Deck and long time series from ocean weather stations, the errors introduced by these two assumptions are examined. In the extratropical oceans, large meridional and seasonal variations of relative humidity are found, and the seasonal cycle of sea‐air humidity difference is out of phase with that of sea surface temperature. The air humidity reaches the minimum earlier than the sea surface temperature during winter cooling. The errors reach above 100 W/m2 over western boundary currents and 50 W/m2 over the tropical ocean. The two approximations also introduce erroneous seasonal and spatial variabilities with magnitudes over 50% of the observed variabilities. Meteorological reports from atolls in the tropical Pacific indicated that in the atmosphere the humidity anomalies were much more pronounced than the temperature anomalies as the center of deep convection was dislocated during the 1982–1983 El Niño‐Southern Oscillation episode.
Evidence for wind‐driven current fluctuations in the eastern North Atlantic
Authors: Samelson R. M.
Published: February 2008

Evidence is presented for local and remote wind‐forcing of deep ocean currents in three frequency bands (corresponding to 3.7–8 day, 8–22 day, and 23–82 day periods) at a two‐year mooring in the eastern North Atlantic. Coherence between current meter velocities and estimated wind stress curl is largest for the deepest instrument (3000 m) and decreases toward the surface. The strongest evidence is found at 3000 m depth in the high frequency (3.7–8 day) band, where both components of velocity are significantly coherent with wind stress curl. Meridional velocity at 3000 m is also significantly coherent with wind stress curl in the low frequency (23–82 day) band, while zonal velocity in the low frequency band and both velocity components in the intermediate frequency (8–22 day) band are only marginally coherent. The results are compared with a stochastically‐forced linear quasi‐geostrophic model that includes a simple representation of the mid‐Atlantic Ridge. Good agreement between predicted and observed coherences is found for the 3000 m currents in the high frequency band, but only partial agreement is found between predicted and observed coherences in the low frequency band, and little agreement in the intermediate band. Kinetic energy levels at 3000 m are well predicted in all three bands. For the shallower instruments (1100 m and 500 m), observed coherences are at most marginally significant and energy levels are considerably higher than the theory predicts. Including an upper‐layer mean flow in the model improves the prediction of energy levels at the shallower instruments.
“Turbulent mixing” in a salt finger staircase
Authors: Marmorino G. O.
Published: February 2008

Towed thermistor chain measurements are examined for patches of “turbulent mixing” occurring within salt finger interfaces in the Caribbean staircase (the Caribbean Sheets and Layers Transects (C‐SALT) experimental area). Patches are identified as regions having short overturning internal waves, resembling Kelvin‐Helmholtz billows, and higher‐wave number, more random fluctuations. For a patch turbulent dissipation rate of ≈ 2×10−8 W kg−1 (based on other C‐SALT measurements and consistent with the observed billow heights of 2–5 m) and an observed patch occurrence of ≈1%, the mean dissipation rate is ≈ 2×10−10 W kg−1. This amount of turbulence would increase the buoyancy flux of heat and salt by 10–20% over fluxes from fingers acting alone and would increase the flux ratio by about 10% to 0.83, close to the value inferred from conductivity‐temperature‐depth data by Schmitt et al. (1987).
A mesoscale eddy dipole in the offshore California Current
Authors: Simpson James J. , Lynn Ronald J.
Published: February 2008

There is a transition zone in the California Current system between inshore coastal and offshore oceanic flow. This transition zone is associated with the main core of the California Current and is populated with offshore mesoscale eddies. The structure of isolated eddies and dipole eddy pairs found within the transition zone is examined using water mass analysis (spiciness and dissolved oxygen). The analyses show that these offshore mesoscale eddies have cores which contain California Undercurrent water. These observations and independent observations of the Sitka eddy near Sitka, Alaska, support the conclusion that a bathymetrically induced instability of the California Undercurrent is a likely generation mechanism for the offshore eddies. This conclusion also is consistent with mathematical models of eddy generation in a subsurface, poleward baroclinic current. The similarity between long‐term mean conditions (CaICOFI), conditions observed during January 1981 and July 1985, and those of the Sitka eddy, coupled with the bathymetric effects, provides a plausible explanation for the recurrence of offshore mesoscale eddies at preferred locations within the transition zone.
An acoustic remote sensing and submersible study of an Arctic submarine spring plume
Authors: Colbourne Eugene B. , Hay Alex E.
Published: February 2008

Results from a field study of a submarine spring and its associated brackish water plume at the head of Cambridge Fiord, Baffin Island, are presented. Computer‐enhanced 1920‐kHz acoustic backscatter images yield measures of maximum height of rise, plume geometry, and vertical velocities in the rising plume. Submersible observations indicate that the freshwater discharge is localized, being about 5 m in horizontal extent. A thriving benthic community was found within this area. The initial geometry and water properties of the flow at the vent, together with the ambient stratification and a numerical buoyant plume model, are used to show that the probable freshwater discharge rate lies in the range 0.10 to 0.20 m3/s. Computed vertical velocities on the plume axis are significantly greater than the vertical velocities inferred from scattering structure trajectories in the acoustic images. The decay of acoustic backscatter amplitude as a function of radial distance in the neutrally buoyant spreading plume is comparable to the radial decay of temperature fine structure, and the radial decay scales are consistent with those expected from molecular dissipation of turbulent microstructure.
Momentum flux in breaking wavelets
Authors: Csanady G. T.
Published: February 2008

A breaking wavelet is taken to consist of a roller and a trailing turbulent wake, both riding on an irrotational wave. The shear stress force on the separation streamline between the roller and the underlying flow is balanced mainly by the horizontal pressure force on the same streamline. The pressure force acts on the underlying flow and reduces wavelet momentum; the shear force generates the momentum deficit of the wake. In this manner, wavelet momentum is turned into shear flow momentum. In wind‐driven wavelets the shear force of the wind aids roller formation: rollers form at a relatively low approach momentum from boundary layer fluid generated by surface shear. Breaking wavelets have been modeled by superimposing the surface disturbance generated by a roller on a sinusoidal wave. The phase relationship of the two components determines how much momentum is extracted from the wave. The models show the characteristic asymmetric, forward leaning shape of breakers. The wave under the roller is shortened, so that the steepness of the breaker is even greater than it would be on account of the roller's presence alone. Ahead of the roller's toe, capillary waves are generated. On short waves these are of easily visible amplitude and serve to identify the presence of a roller.
A simple eddy kinetic energy model for simulations of the oceanic vertical mixing: Tests at station Papa and long‐term upper ocean study site
Authors: Gaspar Philippe , Grégoris Yves , Lefevre Jean‐Michel
Published: February 2008

A simple eddy kinetic energy parameterization of the oceanic vertical mixing is presented. The parameterization scheme is based on recent works on atmospheric turbulence modeling. It is designed to simulate vertical mixing at all depths, from the upper boundary layer down to the abyss. This scheme includes a single prognostic equation for the turbulent kinetic energy. The computation of the turbulent length scales is diagnostic, rather than prognostic. In weakly turbulent regions the simulated vertical diffusivity is inversely proportional to the Brunt‐Vaïsala frequency. In the first validation experiments presented here, the vertical mixing scheme is embedded into a simple one‐dimensional model and used for upper ocean simulations at two very different test sites: the station Papa in the Gulf of Alaska and the Long‐Term Upper Ocean Study (LOTUS) mooring in the Sargasso Sea. At station Papa the model successfully simulates the seasonal evolution of the upper ocean temperature field. At LOTUS the focus is on a short 2‐week period. A detailed analysis of the oceanic heat budget during that period reveals a large bias in the bulk‐derived surface heat fluxes. After correction of the fluxes the model does well in simulating the evolution of the temperature and wind‐driven current. In particular, the large observed diurnal cycles of the sea surface temperature are well reproduced. During the second (windy) week of the selected period the model accounts for about two thirds of the kinetic energy of the observed upper ocean currents at periods larger than 6 hours. The local wind forcing thus appears to be the dominant generation mechanism for the near‐inertial motions, which are the most energetic. The velocity simulation is especially good at the low frequencies. During the second simulated week the model accounts for as much as 78% of the kinetic energy at subinertial frequencies. The simulated mean velocity profile is reminiscent of an Ekman spiral, in agreement with the observations.
Similarity analysis of the temporal variation of suspended sediment profiles
Authors: Abdelrhman Mohamed A. , Bedford Keith W.
Published: February 2008

Storm‐induced flow fields produced temporal variations in the shapes of 72 consecutive time‐averaged suspended sediment concentration profiles, in the lowest l m of a bottom boundary layer on the inner continental shelf off the south shore of Long Island. Different combinations of wave and current flows existed with variations in the magnitude of the horizontal currents up to 30 cm/s and between 5 and 80 cm/s in the rms horizontal wave velocities. Pattern recognition methods are implemented in order to identify the nonperiodic changes in the profile shape. A similarity analysis of these concentration profiles indicates that almost all the profiles in the data have the same shape which varies during storm periods within an amplification and/or translation factor. These two factors reflect the different storm‐generated flows and define periods as well as rates of resuspension and deposition during such events. The concentration versus depth relationship for the fundamental profile shape is semilogarithmic. A summary analysis of this profile shape as well as its temporal variation is also presented, especially as regards how changes of the amplification and translation factors relate to the physics.
Some observational evidence on the effect of atmospheric forcing on tidal variability in the upper Delaware Bay
Authors: Wong Kuo‐Chuin , Trowbridge John H.
Published: February 2008

Until quite recently, most oceanographic research relating to the tidal variability in an estuary has ignored the effect of atmospherically forced motions on the tidal motions. Mechanisms exist, however, through which high frequency wind waves and low frequency subtidal variability can interact nonlinearly with the tide and modify the tidal response of an estuary significantly. A set of current and sea level observations in the upper Delaware Bay provides observational evidence which suggests that tidal variability in the interior of the bay was appreciably modified during two moderately strong atmospheric events.
Tower Ocean Wave and Radar Dependence Experiment: A synthesis
Authors: Shemdin O. H.
Published: February 2008

The Tower Ocean Wave and Radar Dependence Experiment (TOWARD) was conceived to provide an experimental data base to resolve the disparity among the different synthetic aperture radar (SAR) imaging theories of the ocean surface. This goal has been achieved through publication of two collections of scientific papers of which the second is part of this issue. There is now a framework and consensus on how SAR images the ocean surface.
Coupling of coastal zone color scanner data to a physical‐biological model of the southeastern U.S. continental shelf ecosystem: 2. An Eulerian model
Authors: Ishizaka Joji
Published: February 2008

A four‐component (nutrient, phytoplankton, zooplankton, and detritus) physical‐biological model was constructed for the southeastern U.S. continental shelf ecosystem for a horizontal plane at a nominal depth of 17 m. An optimal interpolation procedure was applied to current meter measurements made in this region to obtain the flow and temperature fields that were used for the model. The physical‐biological model was used to simulate the horizontal chlorophyll distributions at 17 m on the southeastern U.S. continental shelf for several days in April 1980. These simulated phytoplankton fields were compared statistically with the chlorophyll distributions obtained from Coastal Zone Color Scanner (CZCS) measurements for this region in April 1980. Model simulations using various physical‐biological dynamics and various boundary conditions show that the variability of chlorophyll distributions on the outer southeastern U.S. continental shelf is controlled primarily by horizontal advection. The biological processes associated with nutrient input by upwelling create the across‐shelf gradient of chlorophyll concentration observed on the midshelf to outer shelf and also maintain the chlorophyll concentration in this region. The simple biological model that included horizontal advection and upwelling processes contained all the conditions necessary to reproduce the chlorophyll patterns on the outer southeastern U.S. continental shelf. However, the technique used to estimate upwelling processes may be a source of error for the simulated distributions. Statistical comparisons between the simulated and CZCS‐derived chlorophyll fields are useful for evaluating a large number of model simulations and for determining the pattern of the error associated with the simulated distributions. Also, statistical comparisons allow determination of values for an optimal parameter set for the biological model. However, implementation of the optimal parameter set should be done carefully. The best approach is to optimize the physical model with some other constraints and then use the CZCS chlorophyll distributions to improve the choice of values for the biological parameters.
Observational and model studies of physical processes affecting benthic larval recruitment in Delaware Bay
Authors: Jacobsen Timothy R. , Milutinovic James D. , Miller James R.
Published: February 2008

Physical processes are important in determining benthic recruitment success in estuarine ecosystems. We have conducted two field studies with passive surface drifters to examine the large‐scale advection and local dispersion in the region of the oyster seed beds in Delaware Bay. The two studies show that the wind is critical in determining the final location of the drifters and that axial fronts in the bay may play an important role in reducing cross‐bay particle dispersion and may keep particles in the nearshore oyster beds. Simulations of particle trajectories from a three‐dimensional numerical model of Delaware Bay were also analyzed to determine the sensitivity of particle trajectories to varying wind conditions and different assumptions about larval vertical migration.
Characteristics of lightning vhf radiation near the time of return strokes
Authors: Hayenga Craig O.
Published: February 2008

By using a crossed base line interferometer, lightning VHF source positions correlated in time with electric field change measurements have been obtained. We present data in this paper showing azimuth and elevation pictures with high time resolution of the VHF (34.3 MHz) radiation for events near the time of return strokes. From their common characteristics we infer spatial and temporal features of these processes. No radiation was seen that could be attributed to the return stroke wave front itself. Radiation from stepped leaders continued up to and, in some cases, after initiation of the first return stroke. A strong burst of radiation often followed the first return stroke. Strong radiation began before subsequent return strokes, coinciding with the electric field change usually associated with the dart leader. The end of the radiation was independent of the return stroke. The source of this radiation was a well‐defined region within the cloud. A second burst often followed the return stroke located in the same region as that prior to the stroke. Sources from stroke to stroke showed horizontal displacement with little apparent change in elevation.
A model of interfacial gas transfer for a well‐roughened sea
Authors: Kerman Bryan R.
Published: February 2008

A model is presented for the flux of a nonreactive gas through the air‐sea interface characterized by patches of breaking waves. A jet of entrained air bubbles resulting from sufficiently large convergence of the surface drift current is visualized as the physical mechanism associated with the gas transfer. The development is based on the work of Yaglom and Kader for rough wall transfer of heat and momentum and is applied here to a compliant rather than a solid surface. An extension of the Charnock relationship for surface roughness is provided to account for contributions to surface root mean square elevation from a band of wave numbers, centered about the minimum phase velocity of short gravity‐capillary waves, which are hypothesized to support most of the wind stress. The transfer is considered to occur only in regions of active breaking, not necessarily visible, which, although occupying a small percentage of the total surface area, are quite sensitive to wind effects. Comparison with data confirms the general validity of the model, but the scatter and limited representativeness of various data sets precludes a more definitive testing of the model.
Stratospheric NO2 at night from balloons
Authors: Naudet J. P. , Rigaud P. , Huguenin D.
Published: February 2008

Stratospheric NO2 was measured at night by means of a balloon‐borne spectrometer pointing at a bright rising or setting star in the 440‐nm region. Four flights were made from May 1976 to September 1981. For the last flight, two vertical profiles of the NO2 mixing ratio were recorded within a time span of 2 hours. The two profiles were identical within the error range and the average profile is in good agreement with the results of previous flights. The NO2 mixing ratio increased from about 6.1 ppb at 26 km to about 13.2 ppb at 35 km. It favorably compares with theoretical predictions above 30 km and with observations of NOx = NO + NO2 by solar occultation.
Sample size and scene identification (Cloud): Effect on albedo
Authors: Vemury Sastri K. , Stowe Larry , Jacobowitz Herbert
Published: February 2008

Scan channels on the NIMBUS 7 Earth Radiation Budget (ERB) instrument sample radiances from underlying earth scenes at a number of incident and scattering angles. A sampling excess toward measurements at large satellite zenith angles is noted. Also, at large satellite zenith angles, the present scheme for scene selection is causing many observations to be classified as cloud, resulting in higher flux averages. Thus, the combined effect of sampling bias and scene identification errors is to overestimate the computed albedo. It is shown, using a process of successive thresholding, that observations with satellite zenith angles greater than 50°–60° lead to incorrect cloud identification. Elimination of these observations has reduced the albedo from 32.2 to 28.8%. This reduction is very nearly the same and in the right direction as the discrepancy between the albedoes derived from the scanner and the wide field‐of‐view (WFOV) channels.
Solar irradiance variation near 2075 Å
Authors: Hall L. A. , Anderson G. P.
Published: February 2008

Measurements of solar radiation in the vicinity of the Al I absorption edge at 2075 Å provide a means of comparing the magnitude of the 11‐year variation in solar activity with that of the 27‐day variation. The ratio of the solar irradiance in the band 2030–2070 Å to that in the band 2100–2140 Å has been determined from five measurements made in the period 1977–1983. This ratio, is an almost purely relative measurement, avoids the problem of absolute irradiance comparisons over long periods of time. The magnitude of the 11‐year effect in this ratio is about ±1%, which is comparable to that in the 27‐day effect measured at solar maximum.
Gas‐ and aqueous‐phase chemistry of HO2 in liquid water clouds
Authors: Schwartz Stephen E.
Published: February 2008

A model for reversible mass transport of HO2 between the gas and aqueous phases of liquid water clouds is used to examine the coupling of reaction kinetics of this species in the two phases. The Henry's law coefficient of HO2 necessary for this analysis is evaluated by means of a thermochemical cycle involving O2 −(aq) to be (1–3) × 103 M atm−1. The mass accommodation coefficient α for uptake of HO2 by liquid water is not known and is treated as an adjustable parameter. Results are expressed in terms of yields of HNO3(g), H2O2(g) and H2O2(aq) relative to the initial photochemical generation rate of OH(g). For large values of α (≳10−3) aqueous‐phase H2O2 formation may be a major radical sink process, but the rate of aqueous‐phase H2O2 production decreases strongly with α ≲10−3. Substantial difference, e.g., a factor of as much as 50 in gas‐phase HO2 concentration, is found between kinetic calculations where uptake of HO2 by cloud droplets is treated reversibly versus irreversibly. Such differences demonstrate the need to treat the dissolution process as reversible, even for reactive free‐radical species.
A field intercomparison of methods for the measurement of particle and gas dry deposition
Authors: Dolske Donald A. , Gatz Donald F.
Published: February 2008

Concurrent measurements of the dry deposition of sulfate, particulate sulfur, nitrate, sulfur dioxide, ozone, and nitric acid were made during September 1981 and June 1982, using several independent methods. The measurements were conducted at a common site, which was a grasscovered 32‐ha field in a topographically flat, rural area 14 km southwest of Champaign, Illinois. Research groups from 14 U.S. and Canadian institutions participated in the study, which was coordinated by the Illinois State Water Survey. Micrometeorological methods such as eddy correlation, variance, concentration gradient/modified Bowen ratio calculation, and eddy accumulation were used. Deposition collection methods such as surrogate surface sampling and vegetation washing were also employed. Sampling schedules and heights of measurements were arranged to maximize the comparability of results from the various flux determination techniques. Sulfate and particulate sulfur mean deposition velocities, vd, on the order of 0.3 cm/s were found by several methods. Nighttime values were small, generally near zero, while daytime vd of up to 1.0 cm/s were observed. A possibly significant contribution to the total sulfur flux by large (diameter >2.0 μm) particle associated sulfate was noted in some periods. Daytime sulfur dioxide and nitric acid vd of greater than 3.0 cm/s were measured, suggesting near‐zero vegetation canopy resistance to mass transfer for these gases.
Sulfur dioxide deposition velocity by a concentration gradient measurement system
Authors: Davis C. S. , Wright R. G.
Published: February 2008

Instrumentation for the measurement of the dry deposition velocity of SO2 by the concentration gradient method has been developed. The instrumentation consists of a sensitivity enhanced Meloy SA260 sulfur analyzer together with appropriate sampling hardware. The system was field tested at the U.S. EPA sponsored dry deposition intercomparison study held in June 1982 at Champaign, Illinois.
Dry deposition of sulfate onto surrogate surfaces
Authors: Davidson Cliff I. , Lindberg Steven E. , Schmidt Jill A. , Cartwright Lawrence G. , Landis Laurence R.
Published: February 2008

Measurements of SO42− fluxes to surrogate surfaces have been conducted as part of the Dry Deposition Intercomparison Study in Champaign, Illinois. Data for Teflon plates without rims and for polycarbonate petri dishes with 1‐cm rims have been obtained and compared with data for Teflon sheets and polyethylene dustfall buckets used by other investigators. Results show that deposition velocities for the Teflon plates are in the range of 0.17–0.42 cm/s, while corresponding values for the petri dishes are in the range of 0.18–0.61 cm/s. Comparisons among the four types of surrogate surfaces show deposition velocities which increase in the order Teflon sheets ∼ Teflon plates < petri dishes < dustfall buckets. Differences in collector geometry as well as composition are responsible for these trends. Airborne size distribution data obtained during the study show that much of the SO42− mass is associated with particles of 0.5–1‐μm aerodynamic diameter. However, using the size distributions as inputs to dry deposition models in the literature suggests that larger particles are responsible for most of the SO42− mass deposition onto the surrogate surfaces. The calculated values for natural grass surfaces are in reasonable agreement with measured deposition velocities onto the petri dishes. Overall, the results of this study suggest that inertial impaction and sedimentation of supermicron airborne particles are more important than deposition of submicron material in influencing total SO42− mass deposition onto surrogate surfaces and onto natural vegetation at this site.
Behavior of zonal mean aerosol extinction ratio and its relationship with zonal mean temperature during the winter 1978–1979 stratospheric warming
Authors: Wang Pi‐Huan , McCormick M. P.
Published: February 2008

The behavior of the zonal mean aerosol extinction ratio in the lower stratosphere near 75°N and its relationship with the zonal mean temperature during the January–February 1979 stratospheric sudden warming have been investigated based on the satellite sensor SAM II (Stratospheric Aerosol Measurement) and auxiliary meteorological measurements. The results indicate that distinct changes in the zonal mean aerosol extinction ratio occurred during this stratospheric sudden warming. It is also found that horizontal eddy transport due to planetary waves may have played a significant role in determining the distribution of the zonal mean aerosol extinction ratio.
An estimate of the biotic contribution to the atmospheric CO2 increase based on direct measurements at Mauna Loa Observatory
Authors: Elliott William P. , Machta Lester , Keeling C. D.
Published: February 2008

The CO2 concentrations recorded at Mauna Loa Observatory from 1958–1983 were examined to detect the existence of any significant sources of CO2 other than fossil fuel combustion. The observed annual CO2 concentrations were compared with concentrations calculated assuming a number of hypothetical constant, nonfossil fuel emission scenarios added to the fossil fuel emissions. It was found that constant nonfossil fuel sources must have been 10% or less of the fossil fuel sources. This conclusion assumes that a constant fraction of the total emissions went into the oceans and that the nonfossil fuel emissions were invariant from year to year. When this latter restriction was relaxed, almost any nonfossil fuel source was possible if its history closely matched that of the fossil fuel emissions. We conclude that it is unlikely that biotic or other nonfossil fuel sources could have exceeded about 0.5 GT of carbon per year except in the unlikely event that they grew at a rate close to that of the fossil fuel emissions.
Tropospheric light alcohols, carbonyls, and acetonitrile: Concentrations in the southwestern United States and Henry's Law data
Authors: Snider Jefferson R. , Dawson G. A.
Published: February 2008

Aliphatic alcohols (C1 ‐ C4), aldehydes (C1 ‐ C2) and ketones (C3 ‐ C4) have been determined at Tucson, Arizona, and at two rural sites about 40 km distant. Acetonitrile was also measured at the rural sites. The method involved condensation sampling, condensate preconcentration, and gas chromatography. Henry's law coefficients were required for all components and were determined. Mean concentrations in Tucson were higher than those in the rural areas by factors typically between 2 and 8; urban formaldehyde was only slightly elevated. Mean alcohol concentrations ranged from 7.9 ppb (C1) to 0.12 ppb (C4) within the city and from 2.6 ppb (C1) to 0.06 ppb (C4) at the rural sites. Acetone was found at 12 ppb in the city and 2.8 ppb at the rural sites. Concentrations of butanone were a factor of 5 lower. Acetaldehyde, at 23 ppb (city) and 6.9 ppb (rural), far exceeded formaldehyde concentrations (1.8 ppb in the city, and 1.5 ppb at the rural sites). Acetonitrile was found at the rural sites at a mean concentration of 60 ppt. A dimensionless Henry's law coefficient (mol L−1 of liquid/mol L−1 of vapor) was suprisingly similar for the alcohols at 0°C, ranging between 2×104 and 3.4×104 (900–1500 mol L−1 atm−1) the ketones were a factor of 10 lower. For acetaldehyde the coefficient was 1.7×103 (76 mol L−1 atm−1) and for acetonitrile 3.7×103 (165 mol L−1 atm−1). Concentrations of oxygenated organics in the condensates and in precipitation were compared; it was tentatively concluded that concentration differences of the carbonyls were consistent with these species being produced within the cloud, for example, by aqueous photochemistry.
Satellite observations of the nitric oxide dayglow: Implications for the behavior of mesospheric and lower‐thermospheric odd nitrogen
Authors: Frederick J. E. , Serafino G. N.
Published: February 2008

The solar backscattered ultraviolet spectral radiometer on the Nimbus 7 satellite routinely measures fluorescence emissions from the nitric oxide (1, 4) gamma band that are imposed on the large Rayleigh‐scattered signal in the wavelength range 255–256 nm. The gamma band feature, when isolated from the background radiance, provides information on the seasonal and latitudinal variations in the nitric oxide column abundance over the altitude region from 40 to 45 km upward through the thermosphere. At latitudes from 30° to 45° in the northern hemisphere the measurements show an annual cycle with maximum nitric oxide abundance in summer. The southern hemisphere pattern is qualitatively similar to this, although the amplitude of the seasonal variation is substantially smaller. The most prominent feature of the data base is a large maximum in nitric oxide emission that develops poleward of 45° latitude in both hemispheres during late autumn and early winter. These maxima dissipate rapidly as spring approaches and are no longer evident in the data for northern hemisphere March and southern hemisphere September.
Contributions of high‐altitude winds and atmospheric moment of inertia to the atmospheric angular momentum‐Earth rotation relationship
Authors: Taylor H. A. , Mayr H. G. , Kramer L.
Published: February 2008

Correlations of atmospheric angular momentum (M) and change in length of day (ΔLOD) generally indicate conservation of momentum between the atmosphere and the crust, yet short‐term, weekly to monthly discrepancies of as much as 30% of the annual variation in either parameter are unexplained. Given the uncertainties present in each data set, it is possible that significant parts of these discrepancies may arise either from undetermined contributions or from incompleteness in the sampling of the atmospheric data. We examine the contributions of upper stratosphere winds (100–0.4 mbar) and of atmospheric moment of inertia terms (MI) for possible evidence of the discrepancies apparent between M and ΔLOD. For the period December 1978 to December 1979, time series of these parameters are calculated from the U.S. National Meteorological Center meteorological data set. Contributions of MI to M are not negligible. This parameter exhibits monthly scale variations of as much as 1.2×1025 kg m2 s−1. Assuming that momentum is conserved between the atmosphere and the earth's crust and that the ΔMI, variations are fully effective in exciting changes in the earth rotation, these monthly variations in MI would be equivalent to variations of as much as 0.2 ms in the change in the length of day (ΔLOD). This would be an upper limit for the MI contribution, however, since not all of the variation in MI may equate to variation in ΔLOD. The momentum contribution from upper stratospheric winds to M and ΔLOD is also nontrival, exhibiting variations which would stimulate ΔLOD changes of the order of 0.2–0.3 ms. The time series of the high‐altitude momentum component is seasonally shifted with respect to that of MI. Combining both terms with earlier values for M, we find that the main discrepancies between ΔLOD and M remain. Since the upper winds and atmospheric moment of inertia cannot explain the discrepancies, we comment on some other uncertainties which must be clarified to understand the global ΔLOD‐M relationship. We conclude that other unknowns, among the components of atmospheric and crustal angular momentum or within the measurement of ΔLOD, are probably responsible for the apparent discrepancies.