bluuebunny/crossref_metadata_2025 huggingface dataset:
Partial melting of mantle wedge and evolution of island arc crust
Authors: Kushiro Ikuo
Published: February 2008

Evolution of the crust in the northeast Honshu arc is discussed on the basis of the melting experiments of a peridotite under hydrous conditions and the crustal compositions estimated from deep crustal xenoliths and seismic velocity data. The chemical compositions of melts formed by partial melting of a hydrous peridotite within the pressure‐temperature conditions for shallow parts of the mantle wedge (1.2–2.0 GPa) have been experimentally determined with the “sandwich experiment” technique. The melts range from olivine tholeiitic to magnesian andesitic compositions (SiO2 48–56 wt %; MgO 9–14 wt %) beneath the volcanic front in the northeast Honshu arc and are slightly less silicic beneath the coast of the Sea of Japan. The crustal compositions of the volcanic zone in the northeast Honshu arc estimated from deep‐seated crustal inclusions in volcanic rocks and the velocity structures of the crust are andesitic in the central zone and high‐alumina basaltic near the coast of the Sea of Japan. The compositions of possible primary melts formed in the mantle wedge are significantly more mafic than these crustal compositions. Consequently, if the major part of the crustal materials in the volcanic zone was formed by magmas generated in the mantle wedge, thick (up to 30 km) ultramafic cumulates including olivine pyroxenite must have been formed beneath Moho during fractional crystallization and would constitute the upper part of the mantle wedge. The volume of the mantle wedge consisting entirely of even fertile peridotite was not sufficient to produce crustal materials and cumulates in the volcanic zone by such processes in the northeast Honshu arc. A static mantle wedge model is, therefore, not satisfactory for the growth of the crust in northeast Honshu arc. A dynamic model is suggested in which the mantle materials have been supplied into the mantle wedge from the back arc side by a convective flow.
Multiple phase analysis of the shear velocity structure in the D″ region beneath Alaska
Authors: Young Christopher J. , Lay Thorne
Published: February 2008

A large data set (more than 990 total waveforms) comprised of North American station recordings of a variety of long‐period S phases (S, ScS, Sdiff, sS, sScS, SKS, SKKS) from 36 earthquakes in western Pacific subduction zones is analyzed to determine characteristics of the shear velocity structure in the D″ region beneath Alaska. Three hypotheses that have been proposed to explain observed ScS precursors and S waveform distortions for this region are appraised with the multiple phase data set, and the radial and lateral variations of the shear velocity structure in the 1500‐km broad portion of D″ sampled are also assessed. The observed travel time and waveform variations may result from diffraction by near‐source slab structure, scattering by low‐velocity heterogeneity in the lower mantle, or interaction with complex velocity gradients in D″ associated with a deep mantle velocity discontinuity. We utilize waveform modeling and differential time analysis to resolve greater detail of the structure than can presently be obtained by standard travel time tomography techniques, and find that the discontinuity model is most consistent with the data. Subdivision of the data by source region and source to receiver azimuth establishes that the observations exhibit fairly stable behavior, which is consistent with extensive local stratification of D″. The data show sufficient coherence over the 1500‐km broad region that we find it useful to present a local average radial model. The preferred model, SYLO, has a 2.75% velocity increase 243 km above the core mantle boundary and a negative velocity gradient within the D″ layer. Analysis of SKS‐S, SKS‐ScS, and SKS‐SKKS differential times also indicates that the outermost 100 km of the core below the fast D″ region underlying Alaska must be slower than the PREM structure. The observations exhibit significant scatter, most of which can be attributed to unmodeled heterogeneity in the midmantle and near‐source regions, as well as lateral variations in the D″ region. The complex structure of D″ that we prefer may be associated with large‐scale downwelling in the lower mantle, but it is not certain whether it is a purely thermal or a combined chemical and thermal effect.
Factors controlling the location of compressional deformation of oceanic lithosphere in the central Indian Ocean
Authors: Karner Garry D. , Weissel Jeffrey K.
Published: February 2008

The prominent example of compression of oceanic lithosphere in the Central Indian Ocean south of the Indian peninsula does not occur where recent models for the state of stress in the Indo‐Australian plate predict maximum horizontal compressive stress. The Afanazy‐Nikitin seamount group, which was erupted in Late Cretaceous or Early Tertiary time, is centrally located in the region where deformation is best developed. We suggest that critical wavelength components in the deflection caused by the emplacement of these seamounts were preferentially amplified when north‐south directed compression was applied to the northern part of the Indo‐Australian plate in the late Miocene. To test this hypothesis, we develop simple one‐ and two‐dimensional models for compression of a thin elastic plate overlying an inviscid fluid, where the plate contains a preexisting deflection. The ≤ 2 km peak‐to‐trough amplitude and 200 km average wavelength characteristics of the broad‐scale crustal deformation and the observed east‐west trending pattern of free‐air gravity anomalies are best matched in the modeling with an applied horizontal compression of 1.5–2.0×1013 N m−1, and a plate with an effective elastic thickness of 10–15 km at the time of compression. In addition, the lithosphere is particularly susceptible to deformation by horizontal compression if seawater initially filled the deflection due to seamount emplacement, but Bengal Fan sediment fills the additional deflection caused by compression. The value of effective elastic thickness determined for the deformed lithosphere is about a factor of 2 less than values obtained from flexure of comparably aged lithosphere beneath seamounts and at trenches (≈ 20–30 km). We attribute this to plastic yielding at the top and bottom of the lithosphere in response to horizontal loading. We determine a north‐south shortening rate of ≈ 1 mm yr−1 from the amplitude of horizontal compression, the width of the deformed region, and the time interval over which the deformation has occurred. This shortening rate is similar to estimates determined from present‐day plate motion studies.
Rift and grain in two granites of the White Mountain magma series
Authors: Fleischmann Karl H.
Published: February 2008

New England granites commonly have two subperpendicular weakness directions, called rift and grain, which are exploited during quarrying. Field and thin section study of granites from the White Mountain Batholith (Jurassic) and the Mount Ascutney Intrusive (Cretaceous) show that the rift and grain directions are consistently developed parallel to Mesozoic joints and suggests that the rift is the result of a preferentially oriented microcrack fabric and topographically controlled near‐surface in situ stresses. The microcrack fabric is made up of fluid inclusion planes and open microfractures. Fluid inclusions developed during postemplacement cooling and represent healed microfractures. Open microcracks developed during uplift by recracking fluid inclusion planes, so there is a strong similarity of orientation between elements in the microfracture fabric. The influence of gravity sets up downslope acting near‐surface stresses which favor the development of open microfractures striking perpendicular to the downslope stresses. Joints and microfractures are best developed perpendicular to the local slope directions. Replotted and field checked data from Dale (1923) demonstrate that in 53 turn‐of‐the‐century New England quarries, rift and grain are parallel and perpendicular, respectively, to the direction of topographic slope. Thus rift and grain in granites of the White Mountain Batholith (Jurassic) and the Mount Ascutney Intrusive (Cretaceous) result from a combination of a properly oriented microcrack fabric and topographically controlled near‐surface in situ stresses.
Shock temperature measurements in metals: New results for an Fe alloy
Authors: Bass Jay D. , Ahrens Thomas J. , Abelson John R. , Hua Tan
Published: February 2008

The temperature of a Fe‐Cr‐Ni alloy (304 stainless steel) has been measured during shock compression using a high‐speed radiometric technique. Experiments were performed on high‐quality thick films deposited on sapphire and LiF windows. The samples had no observable porosity or defects and closely meet the ideal criteria for shock temperature measurements. Data obtained with both Al2O3 and LiF windows are internally consistent, indicating that they remain transparent to high pressures and are thus suitable windows for shock temperature measurements. Our data yield stainless steel melting temperatures ranging from 4570±310K at 138 GPa to 5710±340 K at 215 GPa, and additionally provide bounds on the initial Hugoniot temperatures of the sample between 5600±340 K at 234 GPa (near the solidus) and 6580±440 K at 283 (in the liquid field). Taken together, these data define a smooth curve for melting of the alloy up to 271 GPa and 5860 K, which should represent a point on the Ii qui dus. Melting along the Hugoniot begins at approximately 234 GPa and 5600 K, as compared with 242 GPa and 6400 K for pure Fe. At the pressure of the inner core‐outer core boundary, the melting point of 304 stainless steel is lower than that of pure Fe by ≈ 1450 K, as compared with only 110 K at 1 atm. These results demonstrate that upon alloying with Ni and Cr the melting point depression of Fe and thus material likely to comprise the inner core increases with increasing pressure.
The crustal structure of the Northwestern Basin and Range Province, Nevada, from wide‐angle seismic data
Authors: Holbrook W. Steven
Published: February 2008

I present a model of lithospheric P‐wave velocity structure in the northwestern Basin and Range province, Nevada, based on wide‐angle seismic data collected in 1986 under the auspices of the Program for Array Seismic Studies of the Continental Lithosphere (PASSCAL). The lithosphere in the Basin and Range consists of (1) 2‐ to 3‐km‐thick low‐velocity (2.5–4.0 km/s) sedimentary basins and high‐velocity (>4.5 km/s) ranges overlying a basement of velocity 5.5–6.1 km/s, (2) a mid‐crust (6.1–6.2 km/s) which consists of rocks of probable granitic to granodioritic composition in greenschist to amphibolite facies and which includes two local low‐velocity zones (5.5–5.7 km/s), (3) a laterally varying lower crust which consists of rocks of probable gabbroic composition in upper amphibolite to granulite fades and which comprises layers of 6.6 and 7.0–7.2 km/s average velocity, (4) a complex crust‐mantle transition best modeled as a velocity gradient zone 1–2 km thick, and (5) an upper mantle with velocities of 7.7–7.9 km/s which includes a local low‐velocity zone (7.5 km/s). Crustal thickness in the region varies laterally from 28 to 37 km, significantly thicker than several previous estimates. The upper mantle velocities and velocity gradients differ slightly on the two perpendicular profiles, suggesting possible azimuthal anisotropy. A wedge‐shaped, eastward‐thickening lower crust of high seismic velocity (7.0–7.2 km/s) on the eastern pan of the survey may represent the westward edge of “rift‐stage” Précambrien continental crust or, alternatively, mafic material underplated and intruded into the crust during Cenozoic extension. Comparison of the velocity model with coincident seismic reflection data shows that the reflection and refraction Mohos are coincident across the entire profile, thus indicating that deep reflections (4–10 sec two‐way travel time) seen on COCORP and PASSCAL‐piggyback reflection profiles originate entirely within the crust. The top of the reflective zone, however, lies consistently above the mid‐crustal increase in average velocity, indicating that the reflectivity is not restricted to the mafic part of the crust; on PASSCAL piggyback profiles, in fact, the middle (silicic) crust appears more reflective than the lower (mafic) crust This can be explained as the result of either mafic, sill‐like intrusions or ductile strain fabrics. Both of these processes are likely to have accompanied Cenozoic extension in the region.
The occurrence of ground level gravity waves in Southeastern Australia as detected by microbarographs
Authors: Essex E. A. , Love G. B.
Published: February 2008

Ground level gravity waves have been detected on an array of three microbarographs operated in the Ballarat region of Victoria during the period October–December 1974. A number of occasions of enhanced microbarograph activity were observed. The period of these waves had a sharp cutoff for frequencies greater than about 2.5 × 10−3 Hz with propagation velocities of from 5 to 35 m s−1. The duration of enhanced activity was from 3 to 50 hours. Comparison with meteorological data obtained during enhanced microbarograph activity indicated that the southern hemisphere polar front jet at the 300‐mbar level was the probable source of the gravity waves. Comparison of theoretically calculated characteristics of the wind shear‐generated gravity waves and the experimentally observed ones shows reasonable agreement.
Observations of coastal water surface currents using an airborne inertial sighting system
Authors: Gower J. F. R. , Oliver B. M.
Published: February 2008

This paper describes the use of an inertial sighting system for measuring the positions of surface water features from an aircraft. Sight angle and navigation data for any target sighted by the system operator during flight are recorded and can later be used to compute the target's position to an accuracy of about 10 m. The system makes use of a standard inertial navigation unit. The drift errors inherent in these units are corrected by making periodic sightings of reference targets. The system also has the capability of recording data from a variety of other airborne sensors. This paper describes the accuracy and limitations of the system and discusses examples of measurements of position and movement of surface water features and drogues.
Normal rossby modes of a closed basin with topography
Authors: Ripa P.
Published: February 2008

A variational principle is used to develop an approximate analytical method for the evaluation of the nondivergent normal modes of a rotating closed basin with topography. As an example, the effects of a continental shelf, a mid‐ocean ridge, and a seamount on the modes of an otherwise flat basin are studied. The dependence of the frequency of the higher modes on the parameters of the problem is shown; in particular, emphasis is given to the relative importance of the width and height of the topography and the gradient of planetary vorticity β. A suitable parameter to measure the relative weight of both effects is τ = ∫∫ƒ2(∇ ln h)2 dΛ/∫∫β2, dA where h is the depth, ƒ is the Coriolis parameter, and the integration is carried over the whole basin. In the three cases studied, topographic effects are important for the fundamental mode for values of τ larger than 0.25/δ, for a square basin with a shelf or a ridge of relative width δ, and τ ∼0.5 for a circular basin with a seamount. When the topography is important, large departures from the flat bottom case are found for both the structure and the frequency of the modes. Longuet‐Higgins showed that for a constant depth the modes extended over the whole basin. The frequency of the gravest mode is approximately ω = βL/2π, where the length scale L is of the order of the dimensions of the basin; higher modes have larger periods with an accumulation point at zero frequency. In the cases studied above the modes tend to be trapped over the topographic features as τ increases, and thus the length scale is reduced to something of the order of the width of the topography. But on the other hand, the effective value of β is considerably increased to the magnitude of h∇(ƒ/h) in the trapping region. The net result is an increase of the eigenfrequencies. The results are compared with those of numerical models, and approximate formulae, valid for strong topography, are developed for the shelf and ridge cases.
Effect of changes in stratospheric water vapor on ozone reduction estimates
Authors: Luther Frederick M. , Duewer William H.
Published: February 2008

Previous studies of the effect of water vapor on the destruction of ozone in the stratosphere perturbed by NOx or ClX pollutants did not include temperature feedback effects (i.e., they assumed a fixed temperature profile). These studies indicated that if an increase in stratospheric water vapor concentration were induced (perhaps as a result of an increase in the temperature of the tropical tropopause caused by a change in stratospheric ozone), there would be a significant further reduction in total ozone. Our results from using a one‐dimensional transport kinetics model with a fixed temperature profile confirm these earlier findings. However, when the temperature profile is allowed to change as the species concentrations change, the sensitivity of total ozone to changes in water vapor abundance is greatly reduced. In the case of an NOx injection at 20 km there is even a reversal of sign such that an increase in stratospheric water vapor leads to an ozone increase relative to the case with no change in water vapor.
Observations of the relationship between dew and radiation fog
Authors: Pickering K. E. , Jiusto J. E.
Published: February 2008

A preliminary micrometeorological field study conducted on the campus of the State University of New York at Albany indicated that dew formation strongly influences the formation of fall radiation fog. The initiation of dewfall (moisture from the air transported downward) corresponded to the beginning of a dew‐point decrease at 2 m. Two methods of differentiating dewfall from distillation (soil moisture), both comprising the total dew, were attempted. During the 1974 autumn season in Albany, indications were that a slightly larger portion of the total dew was derived from the soil. In several case studies, radiation fog was either delayed or prevented by the removal of water vapor from the low levels through the mechanism of dewfall. From the observed low‐level vapor gradients and the measured dewfall, values of the eddy exchange coefficient K for water vapor were calculated. Small values of K, of the order of 100 cm2 s−1, were indicated.
Atmospheric N2O: Measurements to determine its sources, sinks, and variations
Authors: Cicerone R. J. , Shetter J. D. , Stedman D. H. , Kelly T. J. , Liu S. C.
Published: February 2008

Measurements of atmospheric N2O concentrations in and around Ann Arbor, Michigan, between August 1976 and September 1977 yielded 329.5 ppb (parts per billion) (mole fraction in whole air samples) as the average with a standard deviation of 3.3 ppb. No seasonal or overall trend is discernible. Small, marginally significant diurnal variations of N2O concentrations in the lowest 0.5 m of atmosphere can be seen in our data. Gas collectors applied to soils near our laboratory provided evidence that soils can consume atmospheric N2O under some conditions. Soils were seen to be N2O sources more often than sinks. Stronger source activity was evident in compost piles. Exhaust samples taken from several conventional vehicles showed less than ambient N2O concentrations, while catalytic converter equipped autos produce N2O. Samples of steaming volcanic vent air from Hawaii indicate that volcanoes are probably a source of atmospheric N2O, although emissions at the Sulphur Bank contain much less than ambient values of N2O. All measurements were made by electron capture‐gas chromatography; techniques and equipment are described.
Interleaving at the subsurface front in the slope water off Nova Scotia
Authors: Horne Edward P. W.
Published: February 2008

It has been known for some time that a frontal zone exists in the slope water, which lies between the Gulf Stream and the shelf break off Nova Scotia, where the temperature jumps from 7°C to 11°C and the salinity from 34.8‰ to 35.2‰ in a horizontal distance of a few kilometers. Data taken from this area with a yo‐yoing CTD (conductivity‐temperature‐depth probe) have been analyzed and show that at the front the two water masses interleave with a vertical scale of the order of 10 m. The interleaving layers are coherent for several kilometers in the cross‐frontal direction and for at least 17 km in the long‐frontal direction. The data suggest that considerable vertical mixing, through double diffusive processes, and horizontal mixing, through interleaving processes, occur in the frontal zone. Vertical eddy coefficients of 8 × 10−4 m2/s for heat and 3 × 10−4 m2/s for salt are calculated for the water column between 40 and 160 m at the front by using Turner's (1965, 1967) formulae to calculate the double diffusive fluxes across the interfaces of the layers. The horizontal eddy diffusion coefficients at the front are calculated to be 10 m2/s for heat and 9 m2/s for salt. The estimated annual vertical heat flux at the front into the coastal water is 15% of the solar input to the shelf water, and the salt flux is 10% of that needed to produce shelf water from the freshwater runoff. Horizontal mixing across the front is shown to be large enough to explain the observed annihilation of the Labrador Slope Water during the time that it takes to travel along the Scotian Shelf. The high vertical mixing at the front may provide a significant vertical nutrient flux.
Tropospheric ozone distributions measured with an airborne laser absorption spectrometer
Authors: Menzies R. T. , Shumate M. S.
Published: February 2008

Measurements of tropospheric ozone have been made in the southern and middle California regions and over the Pacific Ocean during two series of flights in February and May 1977. The data were obtained by using a laser absorption spectrometer, a nadir‐viewing instrument which remotely measures the ozone column abundance between ground level and aircraft altitude by interacting with ozone at specific wavelengths near 9.5 μm. The measurements indicate significantly lower ozone abundances above the Mojave Desert region as compared with farm, forest, and urban areas. The average tropospheric column density was found to be 2.7 × 10−3 atm cm/km over the California region and 3.5 × 10−3 atm cm/km over the Pacific Ocean region 1000–2000 km west of the coast of Mexico.
A survey of worldwide sea surface temperature fronts detected by environmental satellites
Authors: Legeckis Richard
Published: February 2008

The recent improvement of infrared scanners on the polar and geostationary environmental satellites operated by the National Oceanic and Atmospheric Administration has enabled the detection of many sea surface temperature fronts associated with ocean currents and upwelling. The present capabilities and limitations of these satellites in ocean applications are summarized. Examples of infrared imagery are used to illustrate the horizontal temperature distribution at the ocean thermal fronts. It is postulated that future improvements in satellite systems will increase further our capability to detect ocean fronts.
Scales of motion in the subtropical convergence zone
Authors: Leetmaa A. , Voorhis Arthur D.
Published: February 2008

Satellite infrared data show that the sea surface temperature pattern in the subtropical convergence consists of meridionally oriented alternating warm and cold plumes with a wavelength of about 200 km. In 1973, shipboard measurements during the Mid‐Ocean Dynamics Experiment (Mode) revealed that the cold plumes resulted from southward advection of the surface water on the eastern flank of the Mode eddy and that the warm plumes were a result of northward advection on the western side. Along the edges of the plumes, small‐scale frontogenesis was observed but was not resolved by the sampling scheme. Detailed measurements were made in March 1977 of the frontal structure at the southern end of a cold plume. These revealed the presence of smaller‐scale motions with wavelengths of the order of 50 km. Temporal evolution of surface features in the vicinity and along the front occurred extremely rapidly and was barely resolved by surveys spaced 3–5 days apart.
Recent observations of the Alboran Sea frontal system
Authors: Cheney Robert E.
Published: February 2008

Past studies in the Alboran Sea have shown the existence of a strong oceanic front during summer, yet few observations have been made in other seasons. This note presents two sets of XBT data obtained in the Alboran Sea in fall and winter, 1976–1977. These data indicate that the Alboran Sea Front persists throughout the year. It meanders from Gibraltar eastward through the basin, sometimes establishing a series of alternating anticyclonic and cyclonic gyres. The front is confined to the upper 200 m and has a typical width of 35 km. A horizontal temperature difference of 2–4°C is maintained across the front at a depth of 100 m. The Alboran Sea Front forms the northern half of an anticyclonic gyre in the western basin. This gyre has a diameter of 75–100 km and appears to be a normal feature of the circulation pattern. When cold surface water along the southern coast of Spain is entrained into the gyre, the main features of the Alboran Sea circulation are enhanced and can be seen clearly on satellite infrared imagery.
A model of narrow jets in a zonal Ocean
Authors: Johnson John A.
Published: February 2008

The model illustrates the interaction between zonal jets associated with topography and with temperature fronts. In general, the effect of stratification is to enhance the eastward flow on the equatorward side of a zonal ridge.
Measurement of ocean wave heights using the Geos 3 altimeter
Authors: Rufenach Clifford L. , Alpers Werner R.
Published: February 2008

Radar altimeter signals transmitted from the low‐orbiting satellite Geos 3 were analyzed for two selected orbits over high seas associated with hurricane ‘Caroline’ in the Gulf of Mexico and a North Atlantic storm. The measured values of significant wave height are in reasonable agreement with surface measurements, provided that the altimeter data are properly edited. The internal consistency of estimated wave heights for the North Atlantic storm, a standard deviation of 0.6 m or less, and the good agreement with surface truth lend credence to the method. A statistical analysis of the pulse slope variation gives estimated values of significant wave height within ±1 m of the true values 75% of the time for spatial averaging over 70 km.
Oceanographic conditions in lower cook inlet: spring and summer 1973
Authors: Muench R. D. , Mofjeld H. O. , Charnell R. L.
Published: February 2008

Current, salinity, and temperature data obtained from lower Cook Inlet during May‐September 1973 have been analyzed. These data define a regional mean circulation whose main features are (1) a concentrated southward flow along the western shore of lower Cook Inlet of water from upper Cook Inlet which has been diluted by river input, (2) an intense westerly flow across the lower inlet which originates from Kennedy Entrance, exits via Shelikof Strait, and is bathymetrically steered in a cyclonic sense during its transit across the inlet, and (3) a slow northward drift in eastern lower Cook Inlet. The southward flow is an estuarine mode due to freshwater input to upper Cook Inlet. The westerly flow is driven by the westward flowing Alaska Current. The weak northward drift replaces water which has been entrained into the south flowing current. Large tidal and wind‐induced currents are superposed on this mean flow and contribute to complex temperature and salinity distributions. The circulation scheme as redefined here allows for vertical motions and has important consequences in relation to high regional biological productivity and fates of contaminants.
Tritium distributions in Weddell Sea water masses
Authors: Michel Robert L.
Published: February 2008

During the 1975 and 1976 International Weddell Sea Oceanographic Expeditions, samples were collected for analysis by the Mount Soledad Tritium Laboratory. Most samples were of near‐bottom water in the western and northern Weddell Sea. Some samples were also collected of Warm Deep Water, Winter Water, and surface water. Highest tritium concentrations in bottom water were found in the northern Weddell Sea and along the western continental shelf. This indicates that the most recently formed bottom water is in these areas. In the central Weddell Sea, concentrations were lower, indicating slower renewal of bottom water. An upper limit of 3.5 × 106 m3/s is obtained for the formation rate of Weddell Sea Bottom Water. This yields a production rate of about 7×106 m3/s for classical Antarctic Bottom Water. Surface water and Winter Water also showed a strong gradient in tritium concentrations between the central Weddell Sea and the continental shelf.
Stratospheric source for unexpectedly large values of ozone measured over the Pacific Ocean during Gametag, August 1977
Authors: Danielsen E. F.
Published: February 2008

Unexpectedly large ozone mixing ratios measured on the August 1977 Global Atmospheric Measurements Experiment of Tropospheric Aerosols and Gases (Gametag) flight from San Francisco, Calif., to Hilo, Hawaii, are first shown to be of stratospheric origin, then the most probable mode of transport is determined. Isentropic trajectories are traced backward in time from the observations to the boundaries of the stratosphere, close to the northern section of the Asiatic continent. A travel time of only 3 days via the large‐scale waves is almost 100 times faster than that computed from the zonal‐seasonal mean circulations. Also, the laminar structure of the ozone distribution is consistent with a folded tropopause.
Features of the organized motion in the atmospheric surface layer
Authors: Phong‐anant D. , Antonia R. A. , Chambers A. J. , Rajagopalan S.
Published: February 2008

Simultaneous temperature traces at several heights in the first 8 m of the atmospheric surface layer indicate the presence of an organized structure with a spatially coherent upwind interface characterized by a sharp decrease in temperature. The convection speed of this interface, obtained by different methods, increases with height and is approximately equal to the local mean wind velocity. The inclination of this interface to the horizontal also increases with height. Associated with the sharp decrease in temperature θ at the interface is a relatively less sharp jump in streamwise u and a decrease in vertical w velocity fluctuations. Ensemble‐averaged distributions of u, w, θ, uw, and wθ, relative to the location of the interface, have been obtained for several occurrences of the interface for different stability conditions. These distributions effectively represent signatures of the organized motion and are qualitatively similar to those obtained in the laboratory boundary layer. Signatures of velocity and temperature, normalized by the friction velocity and temperature, respectively, exhibit a fair degree of similarity over different stability conditions when the time measured from the interface is normalized by the average period between signatures. For unstable conditions these signatures contribute over 40% to the average local heat flux
and about 20% to the average Reynolds shear stress
. This contribution to
and is less than 10% for nearly neutral or moderately stable conditions.
Ocean transients as observed by Geos 3 coincident orbits
Authors: Gordon A. L. , Baker T. N.
Published: February 2008

Ocean mesoscale transients are revealed in Geos 3 altimeter data. The transients are brought out by inspection of the differences within groups of coincident orbits in the western subtropical North Atlantic Ocean. Each of the five groups, used in the study, is composed of three individual Geos 3 orbits, lying within 2 km of the mean orbit of the group. The difference of each orbit from the group mean contains sea level transients and instrumental noise; the steady state geoid is removed. The noise dominates the spectrum below 200 km wavelength, whereas ocean mesoscale transient features dominate above 200 km. At the low frequency end of the spectra the time separation of the individual orbits may attenuate the signal of the long wavelength transients.
Fine structure measurements in a temperature‐compensated halocline
Authors: Middleton Jason H. , Foster Theodore D.
Published: February 2008

A study was made of the upper ocean region separating the winter water from the warm deep water of the northwestern Weddell Sea, using a series of 25 conductivity‐temperature‐depth casts. From 90 to 600 m the temperature and salinity increase by about 2°C and 0.2‰, respectively, while fine structure variations on both large and small scales are evident. The large‐scale variations appear to be primarily due to isopycnal mixing (horizontal interleaving) below about 450 m and primarily due to internal waves of 8‐to 10‐hour period above 300 m. There is also evidence of isopycnal mixing in the upper region, especially in the latter casts where inversions appear, and some evidence of internal waves in the lower region. The small‐scale structure, which shows steps in temperature, salinity, and density, is shown not to be wave induced. The steplike structures are most evident in the region of strongest vertical temperature and salinity gradients, and double‐diffusive effects appear to be important. Estimates of the upward heat and salt fluxes, obtained by comparison of the present data with previous laboratory experiments, are 7.65×10−5 cal cm−2 s−1 and 3.78×10−9 g cm−2 s−1, respectively. Additional measurements taken in the central Weddell Sea show larger step structures and an upward displacement of isotherms relative to the present data, supporting earlier conclusions of upwelling toward the gyre center.
The distribution of sea ice meltwater in the eastern Canadian Arctic
Authors: Tan F. C. , Strain P. M.
Published: February 2008

The distribution of sea ice meltwater and meteoric water in the eastern Canadian Arctic has been studied by oxygen isotope techniques. The distribution pattern of sea ice meltwater is presented. A comparison of the relative amounts of sea ice meltwater and meteoric water in the surface layer shows that more than 25% of all the samples with sea ice input contained more sea ice input than meteoric input. Sea ice meltwater/meteoric water ratios as high as 4.7 have been observed. The depth of sea ice meltwater penetration varies from 50 m in Baffin Bay to 140 m in Lancaster Sound. Calculated sea ice thicknesses range from 0.5 to 4.5 m with a mean of 1.5 m, in good agreement with ice core data. The significance of sea ice meltwater for chemical, physical, and biological oceanography is briefly discussed. The principles and limitations of using oxygen isotopes to detect brines are discussed in the Baffin Bay setting. The isotopic compositions of possible source waters for Baffin Bay bottom water are examined.
General circulation model estimates of the net vertical flux of ozone in the lower stratosphere and the implications for the tropospheric ozone budget
Authors: Gidel Louis T. , Shapiro M. A.
Published: February 2008

Estimates of the net vertical flux of ozone in the lower stratosphere were made on the basis of the net vertical flux of potential vorticity in the lower stratosphere in two general circulation model runs. Potential vorticity fluxes, calculated from the January and the July simulations, were combined with observed ozone distributions to estimate average net vertical fluxes of ozone of 0.49 and 0.25×1011 molecule cm−2 s−1 for the northern and the southern hemispheres, respectively. This suggests a hemispheric asymmetry in the vertical transports, although it is insufficient to account for all the asymmetry in the tropospheric ozone distribution. Combined with surface deposition fluxes for ozone of 0.82 and 0.48×1011 molecule cm−2 s−1 for the northern and the southern hemispheres, respectively, these net vertical fluxes of ozone in the lower stratosphere support the hypothesis of a hemispherically asymmetric photochemical source of ozone in the troposphere.
The effect of Earth's atmosphere on contrast reduction·for a nonuniform surface albedo and ‘two‐halves’ field
Authors: Mekler Yuri , Kaufman Yoram J.
Published: February 2008

A model for contrast reduction by atmospheric haze is developed for the ‘two‐halves’ field of the earth's surface (two halves of field of a different surface albedo such as in the case of a seashore) and other geometries of the earth's surface albedo. The model is based on a simplified solution of the equation of radiative transfer in two dimensions, resulting in a method for calculation of the upward zenith intensity in the atmosphere, as a function of the distance from the border between the two half planes, for an unabsorbing atmosphere. The adjacency effect between two infinitesimal areas of different albedos is calculated. The resultant simplified solution is used to develop expressions for the line‐spread function of the atmosphere and the modulation transfer function. This modulation transfer function is a general form to express the atmospheric effect on the transmission of radiation from the earth's surface to the detection instrument looking downward at zenith. It contains the effect of atmospheric scattering by attenuation of the signal from earth's surface and by an effective transfer of radiation from bright surfaces to adjacent dark surfaces. The line‐spread function is used to calculate the point‐spread function, which can be used to calculate the intensity above any surface with given spatial dependence of the reflectivity. In the present paper an example is given in applying this point‐spread function for the calculation of intensity above the center of a square of different reflectivity than its surrounding. The results of the intensity above the two‐halves field and above the center of the square, as was detected by a satellite of a 30‐m square pixel, are compared with numerical results calculated by the Monte Carlo method. The modulation transfer function is also compared with Monte Carlo results. A good agreement is shown, This model is applicable for remote sensing of the earth's surface albedo, in the presence of seashores or other borders between areas of different albedos. A correlation between the vertical aerosol distribution and the range of the adjacency effects is shown. This correlation can be used to estimate the vertical scale height of the aerosol layer from satellite images.
Diurnal variations of radon and mixing heights along a coast: A case study
Authors: Hsu S. A. , Larson R. E. , Bressan D. J.
Published: February 2008

Simultaneous measurements of radon concentration, wind speed and direction near the surface, and atmospheric mixing height within the first kilometer of the planetary boundary layer were made at a beach site on the U.S. Gulf Coast during November–December 1978. Vertical distribution of temperature, humidity, and wind also were available four times daily at approximately 6‐hour intervals from two standard rawinsonde stations about 80 km on either side of a beach station along the coast. The mixing height was determined mainly from an acoustic radar (sounder) recorder, but these measurements were supplemented by rawinsonde data. The mixing height as determined by the sounder was verified at least once a day by the rawinsondes before it was correlated with the radon concentration. It was found that after the passage of cold fronts, the meteorology was dominated not only by cold, dry, offshore wind conditions but also by a well‐behaved diurnal cyclic variation of both radon concentration and the mixing height. The radon concentration was found to have an inverse linear dependence on the mixing height, with an unexpectedly high linear correlation coefficient of about −0.96 and conversely to be much less dependent on wind speed than was expected.
Monitoring of sulfuric acid episodes in St. Louis, Missouri
Authors: Cobourn W. G. , Djukic‐Husar J. , Husar R. B.
Published: February 2008

During July 1977 and again in February 1978 in St. Louis, Missouri, episodes of about 3‐day duration occurred in which sulfuric acid persisted as part of the regional haze aerosol. These sulfuric acid episodes were monitored with 15‐min time resolution by a thermal analysis‐flame photometric detection particulate sulfur monitor. The measurement technique detects the concentration of total particulate sulfur as well as the fraction as H2SO4. However, it cannot distinguish between (NH4)2SO4and NH4HSO4; thus it is not specific for the detection of total hydrogen ion concentration associated with particulate sulfur. In the summer, July–August 1977, total particulate sulfur average was 3.8 μgS/m3, and the H2SO4(measured as sulfur) average was below 0.5 μgS/m3, while in the winter, February–March 1978, it was 3.2 and 0.8 μgS/m3, respectively. During the summer episode the H2SO4(as sulfur) peaked at about 10 μgS/m3, compared to a total particulate sulfur peak concentration of 20 μgS/m3. During the winter episode the H2SO4concentration peaked at about 4 μgS/m3, compared to a particulate sulfur peak concentration of 6 μgS/m3. Daily average particulate sulfur and light scattering from July–August 1977 and February–March 1978 show a strong correlation (r> 0.8). There were several general differences between the summer and winter data which suggest chemical and physical changes in the atmospheric aerosol. Analysis of the summer data revealed overall diurnal patterns in particulate sulfur and acidity, but these patterns did not show up with the winter data. The strong correlation between light scattering and particulate sulfur indicates that sulfur compounds play a prominent role in visibility degradation by fine particles.
Conversion of nitrogen oxide gases to nitrate particles in oil refinery plumes
Authors: Parungo F. P. , Pueschel R. F.
Published: February 2008

An instrumented aircraft was used to survey the plume constituents of oil refineries in southern Los Angeles. Concentrations of NO, NO2, O3, Aitken nuclei, and aerosol size distribution were measured continuously in situ. Aerosols were collected with an impactor and were later analyzed with an electron microscope for particle morphology and chemical composition. The results led to the following conclusions: (1) The refineries are a strong source of NO; as the plume travels, NO reacts with entrained O3 to form NO2 and subsequently converts to nitrate particles. (2) Diurnal variations in NO, NO2, and O3 concentrations are directly correlated with solar radiation. In nocturnal stable conditions, NO concentration is as high as 0.7 ppm in the plume. NO2 is low, and O3 approaches nil. After sunrise, NO decreases, and NO2 and O3 increases. (3) Inorganic nitrate particles, which can be identified with an electron microscopic spot test, are found farther downwind of the refineries. They are observed as particles imbedded in droplets with diameters between 1 and 10 μm. (4) Because these large nitrate particles are hygroscopic, they can serve as cloud condensation nuclei to form large cloud droplets and enhance droplet coalescence. Thus they play very important roles in the processes of cloud formation and precipitation.
Arsenic in rain and the atmospheric mass balance of arsenic
Authors: Andreae Meinrat O.
Published: February 2008

An attempt to construct a mass balance of arsenic in the world atmosphere showed that the published data on arsenic concentrations in rain were not compatible with measured values of atmospheric concentrations at remote sites and with estimates of arsenic fluxes into the atmosphere. To resolve this problem, samples of rainwater and snow from eight sites in California, Washington, and Hawaii were analyzed for arsenite, arsenate, and methylated forms of arsenic. The inorganic species were detectable in most samples, but no methylated forms were present above the detection limit of 0.2 ppt. Between October 1976 and March 1978, 43 samples of rain were collected at three locations near the coast in La Jolla. No significant differences between these sites were evident. The average concentration, weighted for rainfall amounts, was 0.007 ppb arsenite and 0.012 ppb arsenate, giving a total concentration of 0.019 ppb As. The samples from Kauai gave an average total arsenic identical to that from La Jolla. This suggests that the La Jolla samples, most of which were collected during strong onshore flow of air from the Pacific, represent very clean air. During some periods of pollutant buildup, values up to 0.59 ppb were found in La Jolla. In a few samples, on the other hand, the arsenic concentrations were below the detection limit of 0.004 ppb. Comparable values were also found in samples of snow from Norden, California, a site at 2225 m elevation in the Sierra Nevada. These values fit well with concentrations modeled on the basis of aerosol analyses from remote sites. The average arsenic concentration at Anacortes Island, Washington, was significantly higher: 1.06 ppb with 88% of the arsenic in the form of arsenite. This value can be explained by a Gaussian plume model with the Tacoma smelter at its origin. This plant, which is 154 krn from the sampling site, emits ∼180 kg of arsenic per day in the form of arsenic trioxide, which is transported northward by the prevailing winds. The ratio of arsenite to arsenate in rain varies over a wide range. This is interpreted as a result of different oxidation states of arsenic in the source emissions and to redox reactions within atmospheric particulates and hydrometeors. By using the data from this study, a mass balance can be constructed for arsenic in the atmosphere which does not require biogenic methylation or hitherto unknown processes as a source for atmospheric arsenic.
An investigation of the modulation of capillary and short gravity waves in the open ocean
Authors: Evans Daniel D. , Shemdin Omar H.
Published: February 2008

A preliminary investigation of the modulation of capillary and gravity waves by long ocean waves is described. A pressure transducer is used to obtain water surface displacements, and a high‐response laser‐optical system is used to detect short‐wave slopes. Analytical techniques are developed to account for the orbital motion of long waves. The local mean squared wave slope is found to be maximum leeward of the long‐wave crests. For the long waves studied here and for short waves from 1 cm to 1 m, the longer a short‐wave component is, the more leeward its maximum tends to occur. Also, the shortest waves tend to modulate least. The modulation of short waves is found to be strong enough to be an important component of the synthetic aperture radar image formation mechanism for long ocean waves.
Direct measurements of atmospheric CH2O, HNO2, O3, NO2, and SO2 by differential optical absorption in the near UV
Authors: Platt U. , Perner D.
Published: February 2008

Measurements of CH2O, HNO2, O3, NO2, and SO2 at four different sites in western Europe are reported. At the maritime sites (Loophead, Ireland, and Dagebüll, Germany) the mixing ratios of the pollution indicators SO2 and NO2 are <0.5–2 ppb, while concentrations of several tenths of a part per billion of CH2O are consistent with photochemical equilibrium. HNO2 was only found at continental sites (Jülich and Deuselbach) with SO2 and NO2 mixing ratios up to 100 ppb. Surprisingly, NO3 was found to be at least 10 times lower than expected in most cases.