bluuebunny/crossref_metadata_2025 huggingface dataset:
Paleointensity of the geomagnetic field from dated lavas of the Chaîne des Puys, France: 1. 7–12 Thousand years before present
Authors: Salis Jean‐Sébastien , Bonhommet Norbert , Levi Shaul
Published: February 2008

Paleointensities were determined by the Thellier method for six dated lava flows from the Chaîne des Puys (France), with ages from 7 to 12 ka (ka = kiloannum before present). The three younger flows overlap the archaeomagnetic period for Europe, and the older flows extend the record to more ancient times. Our results support the quasi‐sinusoidal variation of the geomagnetic field intensity since 10 ka for Europe, punctuated by a peak virtual dipole moment of about 11×1022 A m2 between 8 and 10 ka; the data from 10 to 12 ka show considerably lower virtual dipole moments between 4 and 5 × 1022 A m2, about 60% of the global average since 10 ka. When compared with available worldwide data, the maximum in the virtual dipole moment between 8 and 10 ka is supported by measurements from Japan and possibly Hawaii. Lower than average virtual dipole moments between 10 and 12 ka have also been observed in North America and Hawaii. The existing data suggest that from 8 to 10 ka the geomagnetic field supported a dipole moment up to 30% above and from 10 to 12 ka about 30% below the average value since 10 ka.
Mid‐Tertiary structural evolution of the Old Woman Mountains Area: Implications for crustal extension across southeastern California
Authors: Hileman Gregg E. , Miller Calvin F. , Knoll Martin A.
Published: February 2008

Investigations in the Old Woman Mountains area provide insights into mid‐Tertiary extensional tectonism in southeastern California. The Old Woman Mountains area is a moderately extended region that lies between two highly extended terranes, the Central Mojave Extensional Complex and the Colorado River Extensional Corridor. Two normal faults and a high‐angle fault that we interpret to be a transfer structure divide the area into four distinct structural blocks. These blocks correspond to the four mountain ranges of the area: the Old Woman, Piute, Little Piute, and Ship mountains. Other major faults involved in tilting are inferred to be buried beneath alluvium in surrounding valleys. Deformation occurred in part before, but primarily after, deposition of the Peach Springs Tuff, an 18.5 Ma regional stratigraphic marker. Transport directions of hanging walls are westward on the west side of the Old Woman Mountains area and east‐southeastward on the east side. We suggest that the Old Woman Mountains area is a less extended portion of a continuous extensional terrane that stretches from the central Mojave Desert across the Colorado River to the transition zone of the Colorado Plateau. Lower strain in the Old Woman Mountains area than in most of the Colorado River Extensional Corridor and Central Mojave Extensional Complex and age relations across the terrane can be explained by a model in which the principal locus of upper crustal breakaway to an east dipping low‐angle simple shear zone shifted at about 18–20 Ma from a position far to the west to just east of the Old Woman Mountains area.
Interpretation of reconnaissance gravity and aeromagnetic surveys of the Antarctic Peninsula
Authors: Garrett S. W.
Published: February 2008

Two‐dimensional models are presented for the crustal structure of the Antarctic Peninsula, a Mesozoic‐Cenozoic magmatic arc on the southeast Pacific margin. The models are constrained by measured rock properties. The West Coast Magnetic Anomaly (WCMA) is caused by a zone of mafic plutons which is 70–150 km wide and over 1500 km long. In modelling of Bouguer anomalies, isostatic compensation is maintained by crustal thickness variations. The model Moho is deepest (35 km) beneath the mid‐Cretaceous axis of the arc and shallowest (<20 km) beneath a Late Cenozoic marginal basin. Positive isostatic residual gravity anomalies are associated with the WCMA and a mafic terrane in the Mesozoic accretionary complex. Three broad areas of consistent crustal structure are identified. The junctions of these areas are sinistral fault zones which displace the curvilinear magnetic, physiographic, and gravity patterns by several tens of kilometers.
Elastic wave velocities within oceanic layer 2 from sonic full waveform logs in Deep Sea Drilling Project Holes 395A, 418A, and 504B
Authors: Moos Daniel , Pezard Philippe , Lovell Michael
Published: February 2008

Multichannel full waveform acoustic logs were recorded in Deep Sea Drilling Project (DSDP) hole 418A during Ocean Drilling Program (ODP) leg 102, DSDP hole 395A during ODP leg 109, and DSDP hole 504B during ODP leg 111, to provide nearly continuous measurements of elastic wave velocities as a function of depth within oceanic layer 2 for different spreading rates and crustal ages. The velocities depend primarily on the morphology of the basalt. Massive units have Vp above 5 km/s, Vs above 2.8 km/s, and Vp/Vs below 1.9. Their velocities increase with depth as expected from crack closure due to confining stress and are lower where fractures are present. Vp and Vs within pillows are quite variable but in general are lower than in massive units, and Vp/Vs is higher. Velocities within breccias are similar to or lower than those of pillows. Within a given morphology the elastic properties do not depend on spreading rate. Within pillows, velocity variations depend primarily on the degree of alteration infilling and the mineralogy of the infilling material, and secondarily on conditions at emplacement. Coherent shear arrivals are sometimes not found within shallow pillows, and in extreme cases the compressional arrival is also incoherent, because of scattering resulting from the similarity between the sonic wavelength and the pillow size. This “sampling bias” in the sonic log is the most likely cause of somewhat higher average sonic than seismic velocities measured within extrusive basalts at shallow depths. Other causes include the fact that laterally finite massive units may be oversampled by borehole measurements and that voids between pillows and fractures, whose size is within an order of magnitude of the sonic wavelength, have less effect on sonic than on seismic velocities. The crustal section can be separated only roughly into seismic layers on the basis of the sonic velocities. Changes in velocity with depth within the extrusive section at a single site giving rise to previously defined seismic layers 2A and 2B are due to a change with depth in the properties of the pillows, associated with differences in the amount and type of infilling materials, rather than to a change with depth in the relative proportion of pillows and massive units. Because alteration occurs early and its history is different at different depths, depth‐dependent variations in pillow properties are (1) established at young age and (2) persist even in old crust. Within the intrusive section of DSDP hole 504B, velocities are similar to or higher than those measured in saturated minicores at atmospheric pressure, and seismic and sonic velocities are approximately equal, suggesting that little large‐scale porosity is present.
Electrical properties of mid‐ocean ridge basalt and implications for the structure of the upper oceanic crust in Hole 504B
Authors: Pezard Philippe A.
Published: February 2008

The electrical resistivity, porosity, and cation exchange capacity (CEC) of mid‐ocean ridge basalt (MORB) samples from Deep Sea Drilling Project hole 504B have been measured in the laboratory. The presence of chlorites, zeolites and particularly smectites as alteration products of MORB is reflected by high values of CEC, with high and uniform CEC values in the massive units of layers 2A and 2B, and even higher values in the pillows. The porosity and the “intrinsic” formation factor are related, in the massive units, by an inverse power law similar to Archie's formula, with m = 1.0 and a = 10.0. Such a low m value equates to current conduction in cracks and microcracks present at mineral scale throughout the rock. During leg 111 of the Ocean Drilling Program, the Joides Resolution D.V. returned in the equatorial Pacific to deepen hole 504B and to perform a series of downhole experiments. A continuous electrical resistivity profile permitted to discriminate the large‐scale seismic layers of the upper oceanic crust and to isolate individual lithologic units. In the extrusive part of the crust, the massive flows (10‐m‐thick or more) are found to constitute permeability barriers and, subsequently, to constrain fluid circulation. Within layer 2A, the massive flows of unit 2D are associated with the underpressured aquifer located underneath, within Unit 3. In layer 2B, unit 27 is the boundary between low‐temperature, seawater alteration facies of basalt, and higher‐temperature alteration phases. This relationship between morphology, hydrological regime, and therefore alteration of the basaltic basement is proposed to be related to the accretion process of the upper oceanic crust. The porosity estimate derived from in situ measurements of electrical resistivity is reduced when accounting for surface conduction, with high values computed in layer 2A only. A permeability profile computed on the basis of in situ resistivity measurements reproduces those obtained in situ from packer experiments, and therefore provides a key to the low‐permeability high‐“apparent”‐porosity paradox obtained in the past.
Migration of wide‐angle seismic reflection data from the Grenville Front in Lake Huron
Authors: Milkereit B. , Epili D. , Green A. G. , Mereu R. F. , Morel‐à‐l'Huissier P.
Published: February 2008

Under the auspices of the Great Lakes International Multidisciplinary Program on Crustal Evolution (GLIMPCE), coincident steep‐ and wide‐angle seismic reflection data sets were acquired in Lake Huron. The wide‐angle data were recorded at stationary onshore receivers during the shooting and recording of the conventional marine steep‐angle survey. To extract information from the wide‐angle data, a variety of processing techniques including automatic trace editing, amplitude balancing, F‐K filtering, static corrections, and predictive deconvolution were applied to the wide‐aperture common‐receiver gather before migration. The application of a slowness‐weighted depth migration algorithm, which was first tested on synthetic data and which included a slowness filter, resulted in an image of the Grenville Front tectonic zone (GFTZ) remarkably similar to that observed in the multichannel steep‐angle section. The migrated wide‐angle data suggest that prominent bands of east dipping seismic reflections observed across the GFTZ extend unattenuated to depths of at least 45 km.
Crustal structure of the Celtic Sea and western approaches from gravity data and deep seismic profiles: Constraints on the formation of continental basins
Authors: Sibuet Jean‐Claude , Dyment Jerome , Bois Christian , Pinet Bertrand , Ondreas Helene
Published: February 2008

A free‐air anomaly map of the Celtic Sea and the Western Approaches is presented including all available marine gravimetric data and Bouguer anomalies on land. N60° features are predominant in the area. They correspond to the N60° so‐called Caledonian grain which played a major role in the Variscan orogeny and in the formation of the Permo‐Triassic sedimentary basins. The fundamental new point which comes out from this gravimetric map is the existence of a closely spaced pattern of N105° features which we regard as late Carboniferous transpressional structures. In the eastern pan of the Celtic Sea, thrusts are in the same N105° direction. West of 6°W longitude, however, folds and thrusts trend preferentially in a N60° direction, following the older grain. There, the N105° lineaments may be regarded as dextral shear structures with a possible compressive component. The Hercynian shortening of the Celtic Sea domain, located between the Variscan Front and the Lizard suture, resulted from the displacement, along the N160° direction of the two adjacent rigid domains. North of the Variscan Front, the N105° and N135° features were possibly active in more recent times. Then, both the N60° and N105° trends controlled the formation of Permo‐Triassic basins, the N105° directions being transfer faults. Two‐dimensional gravity modelling of the SWAT profiles in the Celtic Sea shows that the base of the reflective lower crust may be associated with the Moho discontinuity everywhere in the Celtic Sea except below the Saint George's Channel basin. The lower crust does not change significantly in depth and thickness beneath the Permo‐Triassic basins. None of the available models simply satisfies such conditions. They all require at least a modification of the geometry of the lower crust after the formation of the Celtic Sea basins. Nevertheless, if the simple shear model can be ruled out mainly from structural arguments, the uniform stretching and to a lesser degree the thermomechanical models seem to be more relevant models. However, two additional conditions are necessary: (1) the preservation of crustal seismic features formed before the creation of basins must be explained and (2) a significant portion of the volume of the stretched lower crust (about 40% of this volume for the North Celtic Sea basin) must be added below or perhaps partly above the lower crust by lateral flow of the crust or at the expense of the upper mantle.
Changes in shear wave splitting at Anza near the time of the North Palm Springs Earthquake
Authors: Crampin Stuart , Booth David C. , Evans Russ , Peacock Sheila , Fletcher Jon B.
Published: February 2008

Changes in shear wave splitting are observed at KNW before and after the M = 6 North Palm Springs earthquake of July 8, 1986. KNW is a station of the Anza seismic network monitoring the Anza seismic gap on the San Jacinto fault, southern California. The gradual increase in the delays between the split shear waves over 3 years at KNW, reported by Peacock et al. (1988), ended in June 1986. The further 2 years of observations analyzed here show that the behavior of the delays changed abruptly near the time of the North Palm Springs earthquake, 33 km north of KNW. Peacock et al. demonstrated that the increase in delays could be simulated by increasing the aspect ratio of stress‐aligned fluid‐filled inclusions, and speculated that this increase might be the result of a build up of stress before an impending earthquake. The new data appear to confirm this speculation, but the temporal variations require a more complex interpretation, although they still suggest that the changes in shear wave splitting are caused by earthquake‐induced stress changes to the fluid‐filled inclusions throughout the rockmass. Central to our interpretation of temporal changes in shear wave splitting is the well established existence, throughout at least the uppermost 10 to 20 km of the crust, of small fluid‐filled cracks, microcracks, and pores. The existence of such inclusions introduces a compliant quality to otherwise stiff crustal rock. We term these distributions of inclusions extensive dilatancy anisotropy or EDA, and the individual inclusions EDA cracks because, although they may include a wide range of shapes, many of the seismic properties can be simulated by distributions of thin parallel cracks.
On the atmospheric origin of weak absorption features in the infrared spectrum of Mars
Authors: Encrenaz Thérèse , Lellouch Emmanuel
Published: February 2008

Two weak absorption features identified in the near‐infrared of Mars, at 2.35 μm and 3.8 μm, have been tentatively identified as mineralogic signatures. We suggest that these features are mostly due to the Martian atmosphere. The 3.8‐μm feature, as well as other weaker features around 3.6 and 4 μm, is probably due to weak isotopic bands of carbon dioxide and is well fitted with a nominal atmospheric model assuming a CO2 pressure of 7 mbar at the zero‐altitude level. The 2.35‐μm feature observed in the region of Arabia is primarily due to the 2–0 band of CO in the Martian atmosphere and, at first order, is well fitted with the same nominal atmospheric model, assuming the canonical value CO/CO2 = 0.0007. There might be a weak remaining absorption of mineralogic origin, especially at 2.285 μm and 2.41 μm.
Chemical diffusion of ferrous iron in a peraluminous sodium aluminosilicate melt: 0.1 MPa to 2.0 GPa
Authors: Dunn Todd , Ratliffe William A.
Published: February 2008

The chemical diffusion of ferrous iron has been measured in a peraluminous sodium aluminosilicate melt using a diffusion couple technique. Polythermal measurements (1250°–1450°C) were made at 0.1 MPa and at 1.0 GPa and polybaric measurements (0.1 MPa to 2.0 GPa) were made at 1400°C in order to determine the temperature and pressure dependencies of ferrous iron diffusion. The 0.1 MPa polythermal results show that the diffusivity of ferrous iron is non‐Arrhenian at temperatures below 1300°C, but is Arrhenian at higher temperatures. The non‐Arrhenian behavior is interpreted either as indicating temperature dependent anionic disproportion in the melt or as being due to a change in the diffusive jump frequency from similar to that of Si‐O bond exchange to faster than Si‐O bond exchange with increasing temperature. The 0.1 MPa data are adequately described by a Fulcher equation: log10D = −7.16±0.79 ‐ 280±43/(T−1366), where the diffusion coefficient is in units of cm2/s and T is the absolute temperature. The 1.0 GPa polythemial results are adequately described by an Arrhenius equation: log10D = 1.87±0.07 ‐ 297,400±39,000/2.303RT, where the diffusive activation energy is 297±39 kJ/mol. The polybaric results show that there is a significant increase in ferrous iron diffusivity from 0.1 MPa to 0.6 GPa, but that the diffusivity is independent of pressure at higher pressures. The sharp change in the diffusivity is interpreted as indicating changes in the melt structure via anionic disproportionation reactions (e.g., 2Q3 ↔ Q2 + Q4) with large (greater than −34 cm3/mol) negative volume changes that occur somewhere in the 0.1 MPa to 0.6 GPa pressure range.
Rift valley/no rift valley transition at mid‐ocean ridges
Authors: Chen Yongshun , Morgan W. Jason
Published: February 2008

A simple mechanical model for the axial topographic and gravity variations with spreading rate is developed. The model emphasizes the rapid transition from one mechanism to another with changing spreading rate. Our model has a brittle layer over a ductile layer which are being pulled by forces away from the ridge axis. There exists a potential failure zone of width Lf where the stresses within the brittle plate exceeds its yield strength. If the yield strength of the brittle plate is nearly constant, this width is largely determined by the strain rate and the viscosity of the “strong” mantle. The high ductility of oceanic crust at high temperatures relative to that of mantle at the same temperatures leads to the concept of a decoupling region, a critical feature in this model. The size of the decoupling region Ld is determined by the thickness of the oceanic crust and temperatures within the crust. If the decoupling region is small (Ld < Lf), as shown by numerical results to be the case for slow spreading ridges, strong coupling of the brittle plate to the ductile flow of the mantle would cause the brittle layer to deform plastically and a rift valley to be produced as a result of a steady state necking process. However, if the decoupling region is large (Ld > Lf), as shown to be the case for fast spreading ridges, then each of the two layers responds separately to the horizontal stretching. The brittle plate will be broken only at the axis, and any buoyant force of the region would lift it up to form the rise crest high as a result of local isostasy. The changing size of the decoupling region gives rise to the transition from Atlantic type axial topography to Pacific type, as well as the transition from a high amplitude, highly variable gravity signature to a low amplitude, very uniform gravity signature. Parameters can be chosen so that such a transition occurs at a half‐rate of 35 mm/yr, which is the critical half‐rate suggested by both topographic and gravity data.
The structure and subsidence of Rockall Trough from two‐ship seismic experiments
Authors: Joppen Mathias , White Robert S.
Published: February 2008

Coincident multichannel seismic reflection and refraction profiles acquired northwest of Britain during a two‐ship seismic experiment in the southern Rockall Trough provide evidence for a thin (6 km) syn‐rift crust below Rockall Trough. The variation of seismic velocity with depth is consistent with either oceanic crust similar to that found in other parts of the North Atlantic or with thinned continental crust heavily intruded by syn‐rift igneous rocks. The syn‐rift crust beneath Rockall Trough is now buried by nearly 5 km of sediments that are intruded by Tertiary volcanics varying in extent from isolated sills to a large sill complex extending 100 km laterally. The basement imaged on seismic profiles exhibits a band of subhorizontal reflectors that extend laterally over distances of up to 40 km which we interpret as sediments intercalated with submarine lava flows generated during the opening of the Trough. Estimates of stretching from crustal thinning and from subsidence indicate that Rockall Trough has undergone extensive rifting (β > 6). Upwelling asthenosphere beneath the thinned lithosphere generated at least 1–3 km thickness of melt as it decompressed. The molten rock rose upward from the mantle until it was in part extruded as lava flows and in part intruded into the crust.
Fluctuating winds: An energy source for mesoscale motions
Authors: Leetmaa A.
Published: February 2008

Phillips (1966) considered a linear, barotropic, nondivergent model driven by time‐dependent winds in an attempt to explain the Aries observations. He found that the model greatly underestimated the response as compared to the observations. The model is reexamined by using newer estimates of the wind stress (Bunker, 1975) and of the eddy kinetic energies (Freeland et al., 1975). With these the model predicts reasonably well the time and space scales and the amplitude of the barotropic mesoscale variability south of Bermuda. It is suggested that the low‐frequency temperature fluctuations observed in the Panulirus data near Bermuda result from the advection of the mean baroclinic field past Bermuda by the barotropic fluctuations.
A 10‐year study of thunderstorm electric fields
Authors: Freier George D.
Published: February 2008

The paper summarizes a 10‐year study of thunderstorms at Minneapolis by means of electric field signatures at the ground. The analysis considers the frequency of storms, the number of storm hours, and the number of storm days as functions of time of day, day of week, and year. The thunderstorm activity is compared with sunspot activity, and I conclude that there is little evidence for direct coupling between electrical activity in solar events and thunderstorm events. The analysis includes the drought year of 1976 in this area so that comparisons can be made between this year and other more normal years.
Monitoring the strength of equatorial currents from XBT sections and sea level
Authors: Wyrtki Klaus
Published: February 2008

Transequatorial expendable bathythermograph (XBT) sections in the central Pacific are used to compute dynamic height profiles by means of temperature‐sigma t relations. Dynamic height differences and geostrophic transport indices are derived, and it is demonstrated that they correlate extremely well for each of the four equatorial currents, making surface slope an excellent indicator of the geostrophic transport. This is due to the strong baroclinity of the equatorial current system. Indices of the strength of equatorial currents derived from computations of dynamic height, from sea level observations, and from a two‐layer approximation agree very well, which allows the use of each method for monitoring. It is concluded that low‐frequency variations of the equatorial current system may be suitably monitored by such simple methods as repeated XBT sections or sea level observations.
A filtration model for aerosol dry deposition: Application to trace metal deposition from the atmosphere
Authors: Davidson C. I. , Friedlander S. K.
Published: February 2008

The dry deposition of Pb, Zn, and Cd containing particles from the atmosphere was studied by comparing theory with experiment for two types of surfaces: first, smooth flat teflon plates mounted on a smooth building roof and, second, fields of Avena fatua, wild oat grass, about 50 cm tall. Gravitational sedimentation controlled the dry deposition of these trace metals on flat surfaces, while inertial impaction was the controlling mechanism for the vegetated surfaces. Convective diffusion to the grassy surfaces controlled the deposition of particles smaller than 0.1 μ (condensation nuclei) over the grassy fields; this mechanism contributed little to total trace metal deposition. Theories for these three mechanisms were then used to construct a plot of deposition velocity versus particle diameter for Avena, The model incorporates a novel two‐step deposition process: eddy diffusion and sedimentation from the atmosphere to the grassy field followed by filtration by the grass elements. The results of the calculations compared well with literature data for the total lead deposition on fields of Avena. Brownian diffusion was negligible, while impaction on the plant elements was responsible for nearly all of the deposition. Of these particles, about one‐fourth were brought from the atmosphere into the canopy by sedimentation; wind eddy transport was responsible for the remaining fraction.
The density of North Pacific Ocean waters
Authors: Millero Frank J. , Forsht Donald , Means Dana , Gieskes Joris , Kenyon Kern E.
Published: February 2008

The densities of 124 samples of seawater from stations at 35°N in the Pacific Ocean have been measured with a vibrating flow densimeter at 25°C. The measured densities were compared with those calculated from the equation of state of Millero et al. (1976b), derived for seawaters of constant relative composition. Values for the excess density Δd(excess) = d(meas) ‐ d(calc) were found to be ±3.8 ± 3.0 × 10−6 g cm−3 from 0 to 490m, 12.5 ±4.2 × 10−6g cm−3 from 490 to 1000 m,; and 17.6 ± 2.6 × 10−6g cm−3 from 1000 to 5834 m. The excess densities for the deep waters are in good agreement with our earlier measurements: 16.1 ± 3.6 × 10−6g cm−3 (Millero et al., 1976c). The values of Δd(excess) predicted by correcting for the increase of alkalinity (ΔAT), total carbon dioxide (ΣCO2), and dissolved silica (ΔSiO2) and nitrate (ΔNO3) in the deep waters (Brewer and Bradshaw, 1975; Millero et al., 1976c) agree with the measured values on the average to ±5.2 × 10−6 g cm−3. In the deep waters the measured values of Δd(excess) are ∼6 × 10−6 g cm−3 higher than the predicted values. The values of Δd(excess) were also calculated by assuming that the changes in salinity due to the added solids affect the density by the same amount as changes in weight‐diluted standard seawater: 106Δd = 757ΔS(‰). The values of Δd(excess) calculated from 106Δd(excess) = 37.9ΔAT + 72.8ΔSiO2 + 47.7ΔNO3 agree with the measured values on the average to ±4.3 × 10−6 g cm−3, independent of the depth. These results indicate that the density changes due to small changes in the composition of deep ocean waters can be accounted for by changes in the salinity due to the mass of added dissolved solids (ΔS(‰) = ΣMi Δni, where Mi is the equivalent or molecular weight and Δni is the change in the equivalents or moles of solute i in 1 kg of seawater).
Uncertainty propagation in a stratospheric model 2. Monte Carlo analysis of imprecisions due to reaction rates
Authors: Stolarski R. S. , Butler D. M. , Rundel R. D.
Published: February 2008

A concise stratospheric model has been used in a Monte Carlo analysis of the propagation of reaction rate imprecisions through the calculation of an ozone perturbation due to the addition of chlorine. Two thousand Monte Carlo cases were run in which all 55 reaction rates were varied simultaneously and individually. Excellent convergence was obtained in the output distributions because the model is sensitive to the imprecisions in only about 10 reactions. For a 5.7 ppbv (parts per billion by volume) chlorine perturbation added to a 1.5 ppbv chlorine background the resultant 1σ imprecision in the ozone perturbation is a factor of 1.35 on the high side and 1.69 on the low side. The corresponding 2σ factors are 1.81 and 2.86. Results are also given for the imprecisions, due to reaction rates, in the ambient concentrations of stratospheric species.
Comprehensive study of physical and chemical properties of the surface aerosols in the Cape Verde Islands region
Authors: Jaenicke Ruprecht , Schütz Lothar
Published: February 2008

The surface aerosol in the NE trade wind region at the island of Sal, Cape Verde Islands, was studied in a comprehensive research program. The knowledge of this aerosol is important in view of the large source represented by the Sahara for mineral particles and the worldwide transport over the Atlantic Ocean and further. Aerosol properties such as total size distribution, mass, sea salt, mineral, organic compound content, water adsorption, optical properties, and soil material were studied in a 3‐week field campaign in summer 1973. The aerosol observed has a particle concentration comparable to that of ‘clean air’ and a total mass like that of ‘polluted air’ (see the definition by Study of Man's Impact on Climate (1971)). Its sea salt content is comparatively small, and its water uptake is somewhat similar to that of pure ammonium sulfate. The content of organic material is similar to that of background aerosols, but the turbidity resembles that of polluted city air. The source strength of the Sahara desert for aerosol particles was estimated from 2 years of optical measurements and found to be greater than was previously estimated.
Estimation of rates of frontogenesis and frontolysis in the North Pacific Ocean using satellite and surface meteorological data from January 1977
Authors: Roden Gunnar I. , Paskausky David F.
Published: February 2008

A simple prognostic model based on Ekman dynamics and available satellite sea surface temperature and wind data is used to estimate rates of frontogenesis and frontolysis in the central North Pacific in the winter of 1977. The computed patterns and rates are compared to those sensed by satellite, and reasonable agreement is found. In the subtropical region, frontogenetic and frontolytic bands tend to occur in pairs, an occurrence which is attributed to a wind stress maximum over the area. Typical observed frontogenetic rates are 0.5–1°C/100 km per week. The computed rates underestimate the observed ones.
Evidence of subarctic water mass intrusions at ocean weather station November
Authors: Bourke R. H. , Pfeiffer J. F.
Published: February 2008

The monthly horizontal thermal advection in the upper 250 m of the water column at ocean weather station (OWS) November was calculated by means of a divergent heat budget equation. This station is located on the southern boundary of the transition zone separating the subarctic and subtropic water masses. Bathythermograph data from 1962 to 1970 indicate that thermal advection occurs as surges of cold water across this front at intervals of 7–8 months with a duration of 3–4.5 months. Salinity data from 1968 to 1970 show a significant decrease (approximately 0.12‰ at 200 m) and a subsequent increase concurrent with each cooling and heating trend, respectively. Evidently, cool, low‐salinity subarctic water replaces the normally warm, salty subtropic water of OWS November in periodic but nonseasonal surges.
Surface intrusions, fronts, and internal waves: A numerical study
Authors: Kao Timothy W. , Pao Hsien‐Ping , Park Cheol
Published: February 2008

Buoyant surface discharge into an ambient body of water is studied two‐dimensionally by using the full Navier‐Stokes and diffusion equations. The study extends an earlier paper by the authors to include the effects of the earth's rotation and ambient stratification. It is found that for low Rossby numbers, quasigeostrophic balance is achieved in time ≈10/ƒ. The deflection, due to the Coriolis effect, of the forward motion of the buoyancy‐driven current to the along‐front direction decreases the forward speed of the front during the passage toward steady state. When the steady state is achieved, the front becomes stationary in relation to the ambient fluid ahead of it, The structure of the front in the steady state now includes a strong baroclinic along‐front jet and surface convergence and downwelling at the front. The vorticity in the frontal region is shown to be in thermal wind balance except near the free surface where the diffusional effect becomes dominant. A comparison with field data is given. It is also found that front progression, when it occurs, is an efficient mechanism for the generation of internal waves at the thermocline. The effect of wind is also briefly explored.
Light‐scattering observations in frontal zones
Authors: Kullenberg Gunnar
Published: February 2008

Light‐scattering measurements in three different frontal zones are presented, namely, in the coastal upwelling areas outside northwest Africa and central Peru and in the open ocean Antarctic Polar Front in Drake Passage. The observations were made with in situ instrumentation, reaching depths of 1000 m, in conjunction with CTD profiles, in repeated sections across the frontal zone. The scattering distributions, giving the distribution of suspended matter, are compared with the temperature distributions. In the African upwelling region there was good correspondence between these two distributions. Frontal zones were present over the shelf break and slope. The Peru upwelling area was quite different with only very limited correspondence between the temperature and scattering distributions and weak indications of frontal zones over the slope. Across the polar front a markedly layered structure was observed with a clear correspondence between temperature and scattering. The cold water south of the front contained more scattering material than the warm water north of the front. The layers could be traced across the front. In addition, several distinct patches of high and low scattering were observed in the vicinity of the front, indicating mixing across the front. The results show that scattering observations can reflect processes occurring in frontal zones and that it is useful to include such observations in programs aimed at elucidating various physical, chemical, and biological processes in frontal zones.
A census of Gulf Stream rings, spring 1975
Authors: Richardson P. L. , Cheney R. E. , Worthington L. V.
Published: February 2008

During 1975 several shipboard expendable bathythermograph surveys plus satellite infrared imagery provided a nearly synoptic view of the distribution and number of Gulf Stream rings in the western North Atlantic. Twelve rings were identified; nine were cyclonic (cold core) rings and three were anticyclonic (warm core) rings. This is the largest number of rings ever observed during a short period of time (4months). Evidence suggests that the mean movement of these rings was southwestward.
Thermal response to ozone fluctuations of the stratosphere
Authors: Stanulonis Stanley F. , Chamberlain Joseph W.
Published: February 2008

Although the stratospheric temperature inversion is clearly due to absorption of sunlight (and terrestrial emission in the infrared), it is not established that fluctuations in ozone are responsible for fluctuations in stratospheric temperatures. A large data base of radiosonde temperatures is available, but the only comparable data for ozone are the total column densities. We find that fluctuations in total ozone and radiosonde temperatures in the lower stratosphere (50–100 mbar) show correlations of the magnitude expected for ozone control of the heating. At the higher altitudes examined in this study (10–30 mbar) the relationship between ozone and temperature is diminished, possibly because of (1) overhead changes in opacity with a change in the local ozone concentration (negative feedback), (2) dependence of the local ozone concentration on temperature (which offsets the dependence of T on [O3]), and (3) adiabatic dependences of T on density arising from the vertical components of ozone transport (which are not necessarily dependent on ozone absorption). At low altitudes, just above the tropopause in the subtropical summer, the heating of the stratosphere is due mainly to absorption of ground radiation in the 9.6‐μm O3 band and direct solar radiation in the near ultraviolet, and the confusing factors that occur at higher levels and high latitudes are diminished.
The active and passive microwave response to snow parameters: 2. Water equivalent of dry snow
Authors: Ulaby Fawwaz T. , Stiles William H.
Published: February 2008

Experimental measurements of the variation of the radar backscattering coefficient σ° and microwave emissivity ∈ with water equivalent W of dry snow are presented and compared to predictions of simple semiempirical scattering and emission models. The results show that σ° and ∈ are generally dependent on the snowpack water equivalent as well as contributions by the underlying soil, and that the variation with W is a function of frequency and angle of incidence.
Trace gas concentrations in the stratosphere of the northern hemisphere during 1976
Authors: Leifer R. , Toonkel L. , Larsen R. , Lagomarsino R.
Published: February 2008

Stratospheric inventories and distributions for CCl3F, CCl2F2, CCl4, and N2O in the northern hemisphere for May, August, and November 1976 are presented. The November inventories for CCl3F, CCl2F2, CCl4, and N2O were 186 Gg, 279 Gg, 163 Gg, and 169 Tg, respectively. From 1974 to 1976 the concentration of CCl3F in the stratosphere of the northern hemisphere increased at an average rate of 21%±7% per year. This may be compared with an estimated CCl3F emission rate, prior to 1976, of 15% per year.
Permittivity of ice and water at millimeter wavelengths
Authors: Blue M. D.
Published: February 2008

Measurements of reflectivity of water and ice at 100 GHz, 140 GHz, and 180 GHz are reported. Measurements on water covered the temperature range 0°C to 50°C. No anomalies in the dielectric properties of water due to the presence of either salts or organic matter were found. The reflectivity of water and its temperature dependence are consistent with recent dielectric property models derived from data at other wavelengths. The index of refraction of fresh ice is constant at 1.78 throughout this region.
Temporal and spatial variability in longshore motion along the Texas Gulf coast
Authors: Smith Ned P.
Published: February 2008

Recording current meter data from a 43‐day period in the summer of 1977 are used to investigate longshore coherence at three study sites along the central and lower Texas coast in the northwestern Gulf of Mexico. Mid‐depth current data from inner shelf waters reveal an alternating longshore motion that is coherent with the longshore component of the wind stress. Current reversals occur over time scales of the order of 1–2 weeks, but there is a net displacement into the north‐northeasterly quadrant at all three locations. Transient periods of convergence and divergence are suggested between adjacent study sites as a result of not quite simultaneous reversals in longshore motion, or gradients in longshore motion in the same sense. Spectral analysis of the longshore current components indicates that motion is very nearly in phase along this part of the coast and that the flow is highly coherent over time scales in excess of about 3 days.
On the variability of surface temperature fronts in the western Pacific, as detected by satellite
Authors: Roden Gunnar I.
Published: February 2008

The variability of sea surface temperature fronts in the western North Pacific is investigated by using satellite and shipboard data. On a 100 km by 100 km grid and on a time step of 1 week the satellite recognizes the subarctic front, the subtropical fronts, and one to two fronts associated with the Kuroshio intrusion. The subarctic front is centered near 42°N and can be seen throughout the year. Frontal gradients vary from 5°C/100 km in winter to 2°C/100 km in summer, and deviations from the mean latitude are small. The subtropical front is seen only from late fall to early summer in the latitude range between 28°N and 33°N. Maximum frontal gradients are of the order of 3°C/100 km and occur in late spring. Kuroshio fronts occur sporadically in the latitude range between 35°N and 37°N. Because of the mean dering nature of this current and of the rather coarse resolution used, these fronts are not consistently seen. The findings by satellite are in broad agreement with those derived from shipboard observations employing a similar sampling scheme. To study the relationship between satellite‐derived temperature fronts and atmospheric flow patterns, the subtropical front was related to the configuration of the wind stress field. It was found that the oceanic front occurred near a persistent atmospheric front in a region where the vorticity and deformation of the wind stress change sign.
Processes affecting the oceanic distributions of dissolved calcium and alkalinity
Authors: Shiller Alan M. , Gieskes Joris M.
Published: February 2008

Recent studies of the CO2 system have suggested that chemical processes in addition to the dissolution and precipitation of calcium carbonate affect the oceanic calcium and alkalinity distributions. Calcium and alkalinity data from the North Pacific have been examined both by using the simple physical‐chemical model of previous workers and by a study involving the broader oceanographic context of these data. The simple model is shown to be an inadequate basis for these studies. Although a proton flux associated with organic decomposition may affect the alkalinity, previously reported deviations of calcium‐alkalinity correlations from expected trends appear to be related to boundary processes that have been neglected rather than to this proton flux. The distribution of calcium in the surface waters of the Pacific Ocean is examined.
Mean summer circulation in Lake Ontario within the coastal zone
Authors: Csanady G. T. , Scott J. T.
Published: February 2008

Arithmetic averages of daily temperature and current surveys during July‐August 1972 are used to define a mean summer coastal circulation pattern in Lake Ontario. Some of the important features of this mean flow pattern may be explained by simple equilibrium models of wind‐driven flow. Discrepancies between these models and coastal zone observations appear to be due mainly to advection of momentum during transient flow episodes, especially those involving the intermittent appearance of full upwelling along the north shore. The south shore flow pattern consists of divergent coastal jets, much as the theoretical steady response of a frictionless two‐layer basin to an eastward wind. At the eastern end of the lake a deep current is generated by interface friction below the strong coastal jets. Along the north shore there is no mean coastal jet pattern, and the return flow of warm water must be supposed to be accomplished some distance offshore.
Geostrophic vorticity balance in midocean
Authors: Bryden Harry L.
Published: February 2008

Advection of planetary vorticity and vortex stretching estimated from moored current meter measurements of 8 month duration in the western North Atlantic balance within small errors. This result is the first confirmation with direct current measurements of the geostrophic vorticity balance which is widely used in models of large‐scale circulation in the midocean.
Optical determination of the phase velocity of short gravity waves
Authors: Gotwols B. L. , Irani G. B.
Published: February 2008

Images of short wind‐driven gravity waves were taken from an offshore platform, using a charge coupled device television camera recording diffuse sky radiance reflected from the ocean surface. A two‐dimensional power spectrum was calculated from nine statistically independent images. The resultant ensemble‐averaged spectrum exhibited good statistical stability and provided information on the angular spread and direction of the wave components present. One‐dimensional sampling of each image in a sequence allowed a space‐time image to be constructed which clearly shows the effects of wave dispersion as well as the modulation of the phase velocities of the short wavelength waves by the long wavelength components. An ensemble‐averaged space‐time spectrum, when combined with the directional parameters, is compared with the predictions of linear gravity wave dispersion theory. Two distinct wave systems were present: the local wind driven system showed a space‐time spectrum in agreement with linear theory out to ∼1 cyc/m, but with excess phase velocity at higher spatial frequencies. The second wave system, which was presumably generated by a distant wind field, showed a deficiency in phase velocity when compared to linear theory.
Long‐range transport model of SO2 and sulfate and its application to the eastern United States
Authors: Henmi Teizi
Published: February 2008

A long‐range transport model of SO2 and sulfate has been developed. The model consists of two major programs: (1) A program that calculates the trajectories of plumes leaving from any chosen source area (s), dispersion parameters, and the parameters necessary for concentration calculations along trajectory segments using observed wind data. (2) A program that calculates the concentrations of SO2 and sulfate along trajectory segments and interpolates the plume concentrations to grid intersections. In the model the effect of the diurnal change of mixing layer height is taken into consideration. Trajectories of mean winds of the nighttime and daytime mixing layer, and trajectories of the mean wind of the layer between daytime mixing height and nighttime mixing height, are included. Removals, owing to dry deposition and precipitation, are also included. The model is applied to calculate the distributions of 24‐hour average concentrations of SO2 and sulfate over the eastern United States. The distribution patterns of calculated concentrations of SO2 and sulfate were statistically related to those of observed concentrations.