bluuebunny/crossref_metadata_2025 huggingface dataset:
Cinder cone clustering in the TransMexican Volcanic Belt: Implications for structural and petrologic models
Authors: Connor Charles B.
Published: February 2008

Cinder cone distributions have most often been characterized using univariate statistics. Here a new technique to volcano distribution studies, cluster analysis, is applied to cinder cone distribution in the central TransMexican Volcanic Belt (TMVB). A total of 1016 cinder cones are identified over an area of approximately 60,000 km2. Application of cluster analysis reveals structure in cinder cone distribution. Using a search radius parameter of 16 km, 75% of the cinder cones within the central TMVB are found within eight clusters of 45–159 cones each. These clusters are each 2000 to 5000 km2in area. Only 22 cones are found within clusters of three or fewer cinder cones, indicating that clustering is a pervasive phenomenon. Some petrologic variation is evident among clusters; low‐Mg alkaline cinder cones are found within a single cluster, 360–400 km from the trench. Application of alignment analysis techniques, including the two‐point azimuth method, the Hough transform, and two‐dimensional Fourier analysis demonstrates that cinder cone alignments have common orientations on a regional scale within three clusters, all located in the southernmost part of the Michoacán‐Guanajuato volcanic field in the western portion of the study area. These alignments consist of tens of cinder cones, are 20–50 km long, and are all oriented with azimuths of 020°–040°, parallel to the direction of plate convergence. High‐Mg lavas, which last fractionated at pressures in excess of 8 kbar, are only found associated with these alignments, indicating that magma transport is significantly enhanced in these areas. Although local alignments of three to six cinder cones occur within mapped fault zones that transect the area, regional cinder cone alignment patterns, and the distribution of clusters themselves, do not appear to be affected by the presence of these fault zones. The cluster analysis, the alignment analysis, and some petrologic data support the hypothesis that the TMVB is segmented near 101°W.
Paleomagnetic rotations and the cenozoic tectonics of the Cascade Arc, Washington, Oregon, and California
Authors: Wells Ray E.
Published: February 2008

Paleomagnetic results from Cenozoic (62–12 Ma) volcanic rocks of the Cascade arc and adjacent areas indicate that moderate to large clockwise rotations are an important component of the tectonic history of the arc. Two mechanisms of rotation are suggested by the regional pattern of paleomagnetic rotations. The progressive increase in rotation toward the coast in arc and forearc rocks results from distributed dextral shear, which is likely driven by oblique subduction of oceanic plates to the west. Simple shear rotation is accommodated in the upper crust by strike‐slip faulting. The right‐lateral Mount St. Helens seismic zone may be an active manifestation of this process. Dextral shear probably obscures a subequal contribution to arc and forearc rotation that is driven by intraarc or backarc extension. This rotation is suggested by the average southward increase in continental margin rotations into the region outboard of the Basin and Range. The southward increase in rotation parallels a change in the arc tectonic regime from largely compressional in northern Washington to extensional in Oregon. Concomitant with this change is a southward increase in the volume of eruptive rocks and the number of basaltic vents in the arc. A progressive eastward shift of the arc volcanic front with time in the rotated arc terrane is the result of the westward pivoting of the arc block in front of a zone of extension since Eocene time. Westward migration of bimodal Basin and Range volcanism since at least 16 Ma is tracking westward rotation of the frontal arc block and growth of the Basin and Range in its wake.
Heat flow in the state of washington and thermal conditions in the Cascade Range
Authors: Blackwell David D. , Steele John L. , Kelley Shari , Korosec Michael A.
Published: February 2008

Heat flow data for the state of Washington are presented and discussed. The heat flow in the Okanogan Highland averages 75 mW m−2, and the gradient averages 25°C km−1. The heat flow in the Columbia Basin averages 62 mW m−2, and the mean gradient is 41°C km−1. Both of these provinces are interpreted to have a mantle heat flow of about 55–60 mW m−2, the same value as in the Basin and Range province to the south and the intermountain region of Canada to the north. These areas comprise the high heat flow, back arc region of the Cordillera. In the coastal provinces and the western part of the southern Washington Cascade Range the heat flow is below normal and averages 40 mW m−2 with an average gradient of 26°C km−1. This low heat flow is related to the absorption of heat by the subducting slab, part of the Juan de Fuca plate, that is beneath the Pacific Northwest. Thus the low heat flow area represents the outer arc part of the subduction zone. Within the volcanic arc, the Cascade Range, the heat flow pattern is complicated. The heat flow is best characterized in the southern Washington Cascade Range. The heat flow there averages 75 mW m−2 and the gradient averages 45°C km−1. The heat flow peaks at over 80 mW m−2 along the axial region that coincides with the Indian Heaven, Mount Adams, and Goat Rocks centers of Quaternary volcanism. As is the case in northern Oregon and southern British Columbia, the western edge of the region of high heat flow has a half width of 10 km, implying a heat source no deeper than about 10 km. In the northern Washington Cascade Range the data are too sparse to determine the average heat flow. There are two saddles in the heat flow pattern in Washington, along the Columbia River and in central Washington. The origin for the contrasting heat flow may be segmentation of the heat source or some more local effect. The heat flow of the Cascade Range is well characterized in several locations, and the pattern is similar at all localities. The most striking feature is the 10 km half width of the western side of the high heat flow region where it abuts the low heat flow outer arc region. The axial heat flow ranges from about 80 to greater than 100 mW m−2. The midcrustal temperatures are interpreted to range from about 400°C to 800°C. The source of these high temperatures is interpreted to be a long‐lived midcrustal zone of magma residence that is characteristic of the Cascade Range regardless of erustal type, rate of volcanism, or composition of volcanism. For example, in southern Washington the region of high heat flow spans the width of the Quaternary zone of volcanism with Mount St. Helens and Mount Adams at the west and east edges, respectively. On the other hand, most of the Oregon stratovolcanoes are near the center of anomalous region.
Post‐11,000‐year volcanism at Medicine Lake Volcano, Cascade Range, northern California
Authors: Donnelly‐Nolan Julie M. , Champion Duane E. , Miller C. Dan , Grove Timothy L. , Trimble Deborah A.
Published: February 2008

Eruptive activity during the past 11,000 years at Medicine Lake volcano has been episodic. Eight eruptions produced about 5.3 km3 of basaltic lava during an interval of a few hundred years about 10,500 years B.P. After a hiatus of about 6000 years, eruptive activity resumed with a small andesite eruption at about 4300 years B.P. Approximately 2.5 km3 of lava with compositions ranging from basalt to rhyolite vented in nine eruptions during an interval of about 3400 years in late Holocene time. The most recent eruption occurred about 900 years B.P. A compositional gap in SiO2 values of erupted lavas occurs between 58 and 63%. The gap is spanned by chilled magmatic inclusions in late Holocene silicic lavas. Late Holocene andesitic to rhyolitic lavas were probably derived by fractionation, assimilation, and mixing from high‐alumina basalt parental magma, possibly from basalt intruded into the volcano during the early mafic episode. Many basaltic to andesitic lavas contain iron‐rich crystals and have high FeO*/MgO (characteristics caused by mixing of high‐alumina basalt with ferrobasalt liquid produced by fractionation of parental high‐alumina basalt). When ferrobasalt and high‐alumina basalt are contaminated with a granitic crustal component, a calc‐alkaline trend is produced. Some eruptions have produced both tholeiitic and calc‐alkaline compositions. The eruptive activity is probably driven by intrusions of basalt that occur during east‐west stretching of the crust in an extensional tectonic environment. Vents are typically aligned parallel or subparallel to major structural features, most commonly within 30° of north. Intruded magma should provide adequate heat for commercial geothermal development if sufficient fluids can be found. The nature and timing of future volcanic activity cannot be predicted from the observed pattern, but eruptions high on the edifice could produce high‐silica products that might be accompanied by explosive activity, whereas eruptions lower on the flanks are likely to vent more fluid mafic lavas.
Evidence for 600 year‐old basalt and magma mixing at Inyo Craters Volcanic Chain, Long Valley Caldera, California
Authors: Varga Robert J. , Bailey Roy A. , Suemnicht Gene A.
Published: February 2008

Andesite inclusions are found within the vent areas of two 600‐year‐old rhyolite domes in the Inyo Craters volcanic chain, eastern California. Both domes lie within the present northwestern sector of 0.73 Ma Long Valley caldera. Inclusion morphology indicates that they were partially molten and ductile during incorporation within coarsely porphyritic rhyolite. The xenocryst assemblage within the inclusions (plagioclase + hornblende + biotite + quartz ± sanidine) is identical to the phenocryst assemblage within the host rhyolite. Microprobe analyses of xenocrysts within the andesite inclusions show that they have compositions similar to phenocrysts in the host rhyolite. These data suggest that the andesite inclusions are the result of mixing of the coarsely porphyritic rhyolite with a more mafic end member. Whole rock geochemistry of the inclusions generally supports a simple mixing model between the coarsely porphyritic rhyolite of the Inyo domes and typical postcaldera mafic lavas found throughout the western caldera moat. The inclusions provide the first evidence for involvement of basaltic magma in the 600‐year‐old rhyolite eruptions of the Inyo Craters volcanic chain and suggest the possibility that the rhyolitic eruptions were initiated by injection of basalt into the lower part of the silicic magma system. Periodic thermal replenishment of the magmatic system through basaltic injection may explain the relatively high temperatures encountered in drill holes within the western caldera moat. The inclusions further suggest that although rhyolite eruptions are statistically more likely from the Inyo Craters volcanic chain, future basaltic eruptions cannot be ruled out.
Stability of the body‐centered cubic phase of iron: A thermodynamic analysis
Authors: Bassett William A. , Weathers Maura S.
Published: February 2008

The boundary separating the body‐centered cubic (bcc) and face‐centered cubic (fee) phases in the phase diagram of iron has an exceptionally large curvature, especially if the two bcc‐fcc boundaries are connected through negative pressure. This curvature can be shown to result from the Curie transition from the ferromagnetic (spin ordered) to paramagnetic (spin disordered) state in the bcc phase. An analysis of the thermodynamics of the magnetic properties indicates that they have little effect on the curvature of the metastable bcc‐fcc boundary at pressures and temperatures above the δ‐γ‐melt triple point at 52 kbar and 1990 K. Thus the metastable bcc‐fcc boundary is expected to continue as a straight line with a slope of approximately 6.25°/kbar in the stability field of the melt. This boundary will not intersect the melt curve at 1.5 Mbar and 4000 K to produce a stability field of bcc as proposed by Ross et al. (this issue) unless the lattice instability mechanism proposed by them affects the thermodynamic properties of the phases to cause a substantial increase in entropy change (ΔS) or decrease in volume change (ΔV) of the bcc‐close packed boundary with increasing temperature and pressure.
Theory of the iron phase diagram at Earth core conditions
Authors: Ross Marvin , Young David A. , Grover Richard
Published: February 2008

Theoretical calculations, together with diamond anvil measurements on the iron γ‐ε phase boundary to high pressure, suggest that a new bcc phase appears in iron at high pressures and temperatures. This bcc phase may be responsible for the shock anomaly observed in iron at 2.0 Mbar, and the solid inner core of the Earth may be in this phase.
An equation of state of γ‐Fe and some insights about magnetoelastic effects on measurements of the α‐γ‐ε triple point and other transitions
Authors: Besson J. M. , Nicol M.
Published: February 2008

Several aspects of the phase diagram of iron near the α‐γ‐ε triple point are uncertain. Although many investigators agree about the position of the γ‐ε boundary, a wide range of values have been reported for the α‐γ‐ε triple point. There is disagreement about even the sign of the slope of the α‐ε boundary. Analysis of new P‐V‐T data for γ‐Fe, known features of the α‐β phase boundary at lower pressures, the magnetic properties of several iron phases, and nonhydrostatic stresses in various high‐pressure cells suggest that magnetoelastic effects in α‐Fe contribute to these apparent discrepancies. Experiments which control these effects are needed to define the equilibrium values of the α‐γ‐ε triple point and the α‐ε boundary. Uncertainties about these magnetic contributions to published thermodynamic properties of iron must be carefully taken into account when measurements made near α‐γ‐ε triple point are extrapolated to estimate properties at higher pressures.
Issues concerning shock temperature measurements of iron and other metals
Authors: Nellis W. J. , Yoo C. S.
Published: February 2008

Determining the melting temperature of iron at the Earth's inner and outer boundary near 3 Mbar is an important problem in geophysics. A knowledge of the pressure, volume, temperature, and internal energy of solid and molten iron at megabar pressures and several thousand degrees provides a critical constraint for modeling the Earth's core. An optical method measuring the thermal radiation from the thin metal film deposited on an optically transparent window material is described. Issues which need to be addressed to obtain accurate thermodynamic shock temperatures of metals from the thermal radiation measured are discussed. These issues include characteristics of metal films, thermal conduction occurring at the metal/window interface, optical and thermal properties of metal and window material, and characteristics of the radiation measured.
The development and analysis of geopotential coefficient models to spherical harmonic degree 360
Authors: Rapp Richard H. , Pavlis Nikolaos K.
Published: February 2008

The GEM‐T2 potential coefficient model (incomplete to degree 50) has been combined, in a least squares sense, with 30 arc min mean anomalies, to obtain an adjusted set of coefficients and gravity anomalies. The adjusted anomalies were then harmonically analyzed to yield a set of potential coefficients to degree 360. The 30 arc min mean anomalies were estimated from terrestrial gravity data, from altimeter‐derived anomalies, and from 1°×1° terrestrial anomalies where such data were available. For areas devoid of gravity information, the anomalies were computed in two ways: (1) from the GEM‐T2 coefficients and (2) from the GEM‐T2 coefficients to degree 36 plus coefficients implied by a topographic/isostatic model. These “fill‐in” anomalies led to two potential coefficient models: OSU89A and OSU89B. The new models were checked in several ways including satellite orbit residual analysis, Geosat undulation comparisons, and Global Positioning System (GPS)/leveling undulation differences. The orbit fits (carried out by NASA) showed improvement over GEM‐T2. After correction for sea surface topography, orbit error, and permanent tidal effects, the geoid undulations from the OSU89B model have an RMS discrepancy with the Geosat‐implied undulation of ±59 cm over a complete 17‐day exact repeat cycle. The comparisons with GPS information indicate the accuracy of the computation of a relative undulation is of the order of 3–4 ppm of the distance between stations. The new models represent a substantial improvement over previous high‐degree expansions.
Analysis of the Socorro hydrogeothermal system: Central New Mexico
Authors: Barroll M. W. , Reiter M.
Published: February 2008

Analysis of new geothermal subsurface hydrogeologic data from the Socorro area provides new insight into both the geothermal regime and groundwater flow system. Geothermal data from the Socorro area, originally obtained by industry investigators, further delineate a known geothermal high in the Socorro mountain block and reveal a profound geothermal low west of the mountain block in La Jencia Basin. Anomalously low heat flows in La Jencia Basin suggest hydrologic downflow, but hydrologic and geothermal evidence indicates that no infiltration of surface recharge occurs in this area. We conclude that eastward flowing groundwater is forced to flow down beneath a claystone aquitard in eastern La Jencia Basin, reducing near‐surface heat flows. High heat flows in the Socorro mountain block occur in areas where relatively permeable volcanic rocks crop out at the surface. We conclude that groundwater flows upward in these areas from beneath the claystone aquitard, enhanced by subsurface barriers to horizontal flow, elevating near‐surface heat flows. Upper crustal magma in the Socorro area (suggested by seismic evidence) may also contribute heat to the system. Finite difference modeling demonstrates that the hydrogeology of the Socorro area could indeed produce the hydrologic phenomena we postulate, which in turn, could produce the geothermal anomalies observed in the Socorro area. We find that forced convection alone, without anomalous heat sources, could produce the observed geothermal anomalies. Analysis of the heat balance of the Socorro system is also consistent with the hypothesis that anomalous crustal heat sources need not play a substantial roll in the Socorro geothermal system in order to produce the flux of heat observed at the surface.
Tectonic motion and deformation from satellite laser ranging to LAGEOS
Authors: Smith David E. , Kolenkiewicz Ronald , Dunn Peter J. , Robbins John W. , Torrence Mark H. , Klosko Steve M. , Williamson Ronald G. , Pavlis Erricos C. , Douglas Nancy B. , Fricke Susan K.
Published: February 2008

Satellite laser ranging (SLR) to LAGEOS acquired during the period 1978–1988 has been analyzed to yield estimates of tectonic motion for 22 laser tracking stations situated on seven major plates. The analysis is based on the precise modeling of the orbit dynamics of LAGEOS and includes the determination of other geodynamic and nonconservative force model parameters involved in the orbit determination problem at the centimeter level. Site velocities were recovered from station positions determined each calendar quarter using a network adjustment procedure which maintains the reference frame. Within the stable interior of tectonic plates, the recovered motions indicate good agreement with existing estimates of stress fields, particularly across northern Europe, the eastern Pacific, and in the Basin and Range province of North America. A comparison of the intersite motions for stations centrally located on separate plates between SLR and those implied by the NUVEL 1 geologic motion model yield a strong positive correlation of 0.989 and a 3–7% scale difference which may be attributable to recent changes in relative velocities or geologic time scale uncertainties. Sites located at or within 250 km of convergent plate boundaries have additional components of motion, indicating a need for further tectonic modeling beyond that provided by simple rigid plate motions. For lines crossing the north Atlantic, the San Andreas fault, and within the Basin and Range province, the geodesic rates determined by SLR are in good agreement with those determined by very long baseline interferometry, an alternative space geodetic technique.
Electromagnetic fluctuations induced by wind waves on the deep‐sea floor
Authors: Cox Charles , Kroll Norman , Pistek Pavel , Watson Kenneth
Published: February 2008

Recent measurements of naturally occurring electromagnetic (em) fields on the sea floor have demonstrated a prominent spectral peak at about 0.2 Hz. The fields associated with this peak are not correlated with natural em signals measured on land adjacent to the oceanic observing station but seem to be related to ocean surface waves having a frequency one half that of the spectral peak. It is proposed that the nonlinear interaction of opposed trains of surface waves (similar to the mechanism thought to be responsible for microseisms) generating fluid motion across the geomagnetic field causes the observed signal. Calculations are presented to substantiate this proposed mechanism.
Inversion of second‐order radar echoes from the Sea
Authors: Lipa Belinda
Published: February 2008

The Doppler spectrum of high‐frequency radar echoes from the sea consists of dominant peaks due to first‐order Bragg scatter surrounded by a higher‐order continuum. Most applications to date have been based on the first‐order lines, requiring multiple observations and large or moving antennas. In contrast, inversion of the second‐order structure can yield the complete directional ocean wave spectrum from a single radar observation. In this report we describe the first inversion of measured second‐order echo spectra from a 21.75‐MHz narrow‐beam radar looking in a single direction. Estimates of the directional ocean wave spectrum are compared with surface truth provided by tilt buoy and weather station, and fair agreement is found. This initial success is indicative of the potential of this technique for remote sensing of the sea surface.
An average geopotential sea level series for the United States
Authors: Hicks Steacy D.
Published: February 2008

For climate monitoring purposes an average sea level series for the United States, from which a representative curve and a single‐value rate were derived, is presented. In addition, the use of dynamic height is introduced in order to take into account the greatly differing latitudes of the tide stations used in the study. The series was obtained by averaging common length uninterrupted sea level elevations reduced from the tide gage measurements of each station. The averaging was by coastal area. The curve, with amplitudes of the averaged meteorological and oceanographic oscillations of periods of less than 5⅓yr attenuated more than 90%, shows the relative apparent secular trend and its changes for the United States as a whole. During the 36‐yr period, 1940–1975, sea level rose along the coast of the United States at the average rate of 1.5 dynamic mm/yr.
Southern hemisphere stratospheric aerosol measurements 1. Simultaneous impactor and in situ single‐particle (light scatter) detection
Authors: Gras J. L. , Laby Jean E.
Published: February 2008

Stratospheric aerosol concentrations obtained on seven balloon soundings by in situ photoelectric counting of individual particles and jet impaction with later electron microscope analysis have been compared. The potential error sources in the two sizing techniques appear sufficient to explain the observed differences in concentration. This implies an underestimate in the impactor‐derived precollection radius (for sulfuric acid aerosol) of about 25% relative to the photoelectrically determined radius in the two ranges r > 0.15 μm and r > 0.25 μm. The variance in impactor‐derived column loadings is determined by comparison of the impactor and photoelectric detector loadings; over the 10‐ to 28‐km altitude range, for example, this gives an error estimate of ≈ ± 18% for a 95% confidence level. An estimate of the flight‐to‐flight accuracy of the impactor sizing models is also determined from the loading comparison.
The inclination of intracloud lightning discharges
Authors: Wong C. M. , Lim K. K.
Published: February 2008

An intracloud discharge can often be modeled in terms of the neutralization of an inclined electric dipole by using a set of parameters specifying the height, orientation, and electric charge of the dipole. This paper describes a new method of determining one of the main parameters involved which is the inclination of the dipole axis. The method is based on the measurement of magnetic fields produced during intracloud discharges. Data from two tropical thunderstorms are presented, and a statistical analysis shows that the median inclination of the dipole axis is 13°, the average inclination being 20°.
Transfers across an air‐water interface at high wind speeds: The effect of spray
Authors: Wang Chen Sheng , Street Robert L.
Published: February 2008

The generation of spray under high wind speed conditions has been investigated in a laboratory wind, water wave research facility. An electrostatic capacitance wire probe system was used to measure spray. Mean energy transfers were determined by a standard boundary layer integral technique. For a given wind velocity the spray concentration decreases logarithmically with increased distance from the mean water surface. The spray concentration and distribution results of this study are consistent with field and other laboratory studies (with one exception). While wave breaking, whitecapping, and bubble bursting during spray formation contribute to increased interface roughness, calculations based on the laboratory data show that the latent and sensible heat transfers from the spray drops make a negligible contribution to the energy transfer observed. The marked increase in measured energy transport under spray conditions is due almost entirely to increased transfer from the roughened interface (there is a linear correlation between the latent and total heat transfers and the root‐mean‐square water surface displacement).However, extrapolation of the laboratory results suggests strongly that spray drops make a significant contribution to the energy transfer in field situations with wind, temperature, and humidity conditions equivalent to those in the laboratory because of greatly increased droplet boundary layer thicknesses in the field.
Fine structure in the Antarctic Polar Front zone: Its characteristics and possible relationship to internal waves
Authors: Georgi Daniel T.
Published: February 2008

Temperature and salinity data from a repeated salinity‐temperature‐depth station and temperature profiles from three expendable bathythermograph experiments are used to investigate both the spatial and the temporal characteristics of fine structure observed in the Antarctic Polar Front Zone. The fine structure was found to evolve considerably on time scales of 1 hour and less. From an experiment designed to elucidate the spatial scales of the fine structure, a marked anisotropy was revealed, suggesting that the temperature structures were elongated filaments aligned with the front. The data were also used to investigate the possibility that internal waves generate the observed fine structure. On the basis of the temperature‐salinity correlation of the fine structure and the extremely large required vertical displacements the vertical motions of internal waves can be ruled out as the primary cause of the fine structure. Because the Antarctic Polar Front Zone is a region of high horizontal temperature and salinity gradients and because there is an observed increase at one‐half inertial period in drop‐lagged coherences, it is hypothesized that the low‐frequency nearly horizontal internal wave motions are generating the observed fine structure. However, in the particular case where direct observations of the vertical motions of internal waves are available, assuming that the relationship between vertical and horizontal displacements prescribed by the Garrett and Munk (1975) model holds, horizontal displacements are also ruled out as the sole source of the observed fine structure, yielding neither enough total variance nor the expected spectral shape; thus much of the observed variability may be attributed to temperature fine structure of noninternal wave origin.
On the stability of the shelf water/slope water front south of New England
Authors: Flagg Charles N. , Beardsley Robert C.
Published: February 2008

The baroclinic stability of a Margules front over steep topography is studied in an attempt to explain some wavelike features observed on the shelf water/slope water front south of New England. During winter this front extends from the bottom near the 85‐m isobath to the surface with a typical mean slope of 2 × 10−3, with a corresponding geostrophic shear of about 10 cm/s. A quasi‐synoptic hydrographic survey of the New England shelf made during March 1974 resolved a wavelike distortion of the front characterized by a 80‐km alongshelf wavelength. The associated Rossby number based upon the alongshelf wave number and the vertical shear (Ro = k(ΔU)/2ƒ) is <0.05, so that a perturbation analysis using the semigeostrophic approximation is possible. This approach allows the resulting equations to be cast into an ordinary eigenvalue problem which can be easily solved numerically. The effect of increasing the bottom slope is to destabilize some neutral modes and to stabilize other modes that had been unstable over flat topography. In general, however, the characteristic e folding times of the unstable modes increase dramatically from 2–5 days for flat topography to greater than 50 days for realistically steep topography. This rapid decrease in growth rates with increasing bottom slope implies that the observed wavelike features on the front must be generated by some mechanism other than local baroclinic instability. Once they are generated, the observed features may propagate as essentially stable frontal wave modes. We note, however, that the front would be quite unstable if it was located over flat topography. This may help explain why persistent fronts of this type appear to be found near the shelf break.
Frontal circulation due to cabbeling and double diffusion
Authors: Garrett Christopher , Horne Edward
Published: February 2008

We analyze the circulation induced by cabbeling at the boundary between two stratified water masses of equal density but different temperature and salinity at any depth. Scale analysis of the dynamical equations shows that the isopycnals remain flat to a very good approximation, the result being that a simple expression for the vertical velocity can be obtained from the density equation. For parameters typical of a subsurface front in the slope water the estimated vertical velocity is about 1 m day−1. Larger speeds are possible in regions of small vertical density gradient, but we show that for the convergence associated with cabbeling to maintain a T‐S front against diffusion typically requires a rather large temperature jump. Our analysis breaks down if the parent water masses are so weakly stratified that a mixture is heavier than the sources at any level. In this case an estimate of vertical circulation can be obtained by analogy with the thermal bar of dimictic lakes and the convection at a heated vertical wall. We also argue that the vertical density flux associated with double diffusion in the interleaving region of a T‐S front should cause some net vertical motion, and we estimate 1 m day−1 for a particular front. While this value is small, it is not much less than a rough estimate of the vertical velocity associated with internal friction at a front across which a density jump occurs.
Seasonal differences in low‐frequency current fluctuations over the Oregon continental shelf
Authors: Huyer Adriana , Smith Robert L. , Sobey Edwin J. C.
Published: February 2008

Current observations over three isobaths (50, 100, and 200 m) on the Oregon continental shelf are available for winter and spring 1975 and summer 1973. In each season there are low‐frequency current fluctuations with periods of several days, predominantly alongshore, that are correlated with the along‐shore wind stress and sea level at Newport. The amplitude of the current fluctuations is greatest in winter and least in summer, but the ratio between current and wind stress fluctuations does not change appreciably. In each season the alongshore fluctuations have the same sign throughout the water column, and they are nearly in phase across the shelf. The vertical and offshore structure of the fluctuations was examined by means of empirical orthogonal functions. In winter the amplitude decreases with depth at each location; in summer it is nearly constant at all locations. The near‐bottom shear is consistent with Ekman veering. Away from the bottom the shear is in approximate geostrophic balance. The fluctuations have a significant baroclinic component in winter but not in summer. In each season the amplitude of the fluctuations decreases with distance from shore, but the offshore length scale is about twice as great in winter as it is in spring.
On estimating velocity from hydrographic data
Authors: Davis Russ E.
Published: February 2008

Methods for inferring absolute velocity from hydrographic observations recently advanced by Stommel and Schott and by Wunsch are compared and found to be based on equivalent dynamical sophistication. The differences in the methods are shown to result from differing assumptions about the scales of the quasi‐steady large‐scale signal and the variability or noise. An objective method of accounting for the noise is advanced.
A comparison between the Düing profiling current meter and the White Horse acoustic profiler
Authors: Evans Robert H. , Leaman Kevin
Published: February 2008

A series of high vertical resolution profiling current meter (PCM) relative profiles was obtained in the Indian Ocean during May–June 1976, along with a series of White Horse (WH) profiles. We present results of a comparison between PCM and WH profiles from stations at 53°E on the equator and at 0°45′N, north of the Seychelles. Estimated rms differences of velocity components obtained by these two techniques range from ±5 to ±10 cm/s. The larger value coincides with periods when vertical structure with large amplitudes (∼20 cm/s) and short vertical scales (∼ 100 m or less) was detected by the PCM.
Near‐bottom sediment concentration and fluid velocity measurements on the inner continental shelf, New York
Authors: Lavelle J. W. , Young R. A. , Swift D. J. P. , Clarke T. L.
Published: February 2008

Prototype instrumentation designed to measure light scattering and transmission and the horizontal components of fluid velocity at a point 100 cm off the sea floor was deployed on the Long Island inner shelf for a 27‐day period in October and November of 1976. Depth at the point of deployment was 10.5 m. Data were taken from sensors in hourly bursts consisting of 468 consecutive 1‐s samples. Measurements taken with the electromagnetic current sensor were converted to absolute units by using a laboratory calibration, while absolute calibration of the turbidimeter in terms of suspended matter concentration was accomplished by using a combination of laboratory and field measurements. The results from the deployment show the effects of water motions at both wave and subtidal frequencies on sediment concentrations. Although burst mean fluid motions during the observation interval were primarily of tidal frequency, a single wind‐forced event caused burst mean currents in excess of 38 cm/s. During that same event, suspended particulate concentrations rose to a burst mean of 79 mg/l from a prestorm level of 5 mg/l, an order of magnitude increase occurring over a period of approximately 12 hours. During the storm event, individual burst records show that fluid motions at surface wave frequencies and with amplitudes of over 100 cm/s occurred at the experimental site. The near‐bottom suspended matter field at that time was found to have appreciable energy at surface wave frequencies as well. Changes in suspended matter concentration of the order of 130 mg/l were observed to occur in a period of 3–5 s. Increased burst mean concentration was seen to accompany increased wave activity, although increased mean flow with declining wave activity also led to increased suspended particulate concentration. When storm conditions (wave activity and mean flow much above deployment interval ambients) abated, concentrations returned to ambient levels in approximately 12 hours. Coherence between suspended matter concentration and horizontal fluid velocity was found to be statistically significant during four intervals of the deployment. In most cases the significance was centered around a broad frequency band near 0.1 Hz. Vertical near‐bottom wave velocities were inferred from the current measurements. The analysis of coherence and phase between the vertical velocity and concentration supports the hypothesis that part of the measured concentration signal was due to the vertical oscillatory advection of the mean concentration field past the turbidimeter during the passage of surface waves.
Wave‐current interaction models for rip currents
Authors: Dalrymple Robert A. , Lozano Carlos J.
Published: February 2008

Two analytic models are developed to describe rip current cells on an open coastline with sloping planar foreshore and flat offshore bathymetry. Both models extend the work of LeBlond and Tang (1974) to include the refraction of the normally incident wave field by the nearshore circulation. The first model includes the effect of the currents on the incident wavelength, but no change in wave direction, and shows that no rip currents are possible. The second, more complete model considers the refraction of the waves as well and predicts rip current cells. The spacing of the rip currents and their associated variables are shown to be a function of one dimensionless parameter. Comparison of the predicted spacing with some published field data as well as with measurements obtained on the Isle of Sylt, West Germany, shows reasonable agreement with the second model.
An estimate of the upwelling rate in the equatorial Atlantic based on the distribution of bomb radiocarbon
Authors: Broecker W. S. , Peng T.‐H. , Stuiver M.
Published: February 2008

As shown by the Geosecs results the equatorial Atlantic Ocean has both a lower water column inventory and a lower surface water concentration of bomb‐produced radiocarbon than do the temperate waters to the north and south. This anomaly can only be explained by equatorial upwelling. For the equatorial zone as a whole this rate must be about 17 sverdrups.
Calcite as a source of excess calcium in rainwater
Authors: Ichikuni Masami
Published: February 2008

Snow and rain samples collected in Sendai, Japan, were analyzed for sodium, potassium, magnesium, calcium, and strontium. The chemical composition of the samples can be fairly explained by adding some calcium to diluted seawater. A low Sr/Ca ratio in most of the samples showed that the excess calcium over seawater contribution may be derived from calcite contained in soil dust transported by wind from North China.
Characteristics of Port Moresby ground flashes
Authors: Thomson E. M.
Published: February 2008

An investigation into the characteristic features of lightning flashes to ground in Port Moresby, Papua New Guinea (latitude 9°S, longitude 147°E), has been carried out. A scheme is presented for the identification of discharge features from simultaneous records of optical radiation, electric field change, and HF radiation. Data were obtained from records of 80 identified ground flashes comprising 282 strokes, 202 interstroke intervals, 223 continuing currents, and 53 stepped leaders. Flash durations are log normally distributed with a geometrical mean of 604 ms and a standard deviation of 0.25 decade. Sixty‐eight per cent of pre‐first‐stroke processes had durations exceeding 100 ms, the mean being 240 ms. Of 59 flashes outside the reversal distance electric field, records of 80% indicated that negative charge was raised before the first return stroke. The distribution of stepped leader durations is normal with a mean of 21 ms and standard deviation of 8 ms. Interstroke intervals are approximately log normally distributed, with a geometrical mean of 61 ms and a standard deviation of 0.36 decade. The geometrical mean value of continuing current duration is 5.5 ms and the standard deviation 0.70 decade, but the distribution is neither normal nor log normal. Of 34 multiple stroke flashes, 47% have at least one long continuing current. The form of the frequency distribution of continuing current duration may reflect a fundamental distinction between long and short continuing currents: however, it is probably the result of differences between the 1976 and 1977 distributions.
Narrow‐band nonlinear sea waves
Authors: Tayfun M. Aziz
Published: February 2008

Probabilistic description of nonlinear waves with a narrow‐band spectrum is simplified to a form in which each realization of the surface displacement becomes an amplitude‐modulated Stokes wave with a mean frequency and random phase. Under appropriate conditions this simplification provides a convenient yet rigorous means of describing nonlinear effects on sea surface properties in a semiclosed or closed form. In particular, it is shown that surface displacements are non‐Gaussian and skewed, as was previously predicted by the Gram‐Charlier approximation; that wave heights are Rayleigh distributed, just as in the linear case; and that crests are non‐Rayleigh.
The fate of the hydroxyl radical in the Earth's primitive atmosphere and implications for the production of molecular oxygen
Authors: Vander Wood Tim B. , Thiemens Mark H.
Published: February 2008

We have examined the possible fates of the hydroxyl radical produced by the photolysis of water vapor in the earth's early atmosphere. Because of the substantial OH radical reactivity with trace species (CO, HCl, SO2, H2S, NH2, and CH2) the formation of molecular oxygen may be prevented, even at a trace species mixing ratio as low as 10−10. The photolysis rate of H2O, with corrections for hydrogen exospheric escape, is capable of describing the oxidation of the atmosphere and crust but may not be used to determine the rate of molecular oxygen generation without consideration of the various OH‐trace species reactions.
The variability of temperature gradient microstructure observed in the Denmark Strait
Authors: Oakey N. S. , Elliott J. A.
Published: February 2008

Extensive temperature microstructure measurements were obtained in August–September 1973 in the Denmark Strait between Iceland and Greenland during the experiment called Overflow '73. We have examined the average properties of the microstructure, such as variance and derived quantities (e.g., vertical eddy diffusivity kz) to establish typical levels of structure with respect to larger‐scale oceanographic features in this area. The measurements were obtained by using the vertical profiler Octuprobe with thin film thermometers to measure temperature gradient. This is an area with levels of microstructure 2 or 3 orders of magnitude higher than in other oceanic areas. It is a region of large horizontal variability and one where interleaving and frontal processes may be important. In our measurements we found no tendency for increased levels of structure to occur where double diffusion is possible. In comparison to bulk models, our measurements of vertical heat flux Q, using the Osborn‐Cox model, suggest that diffusive processes may be important in the formation of Norwegian Sea water. On the other hand, diffusion processes appear to be negligible in comparison with entrainment in the Overflow stream.
Quantitative interpretation of Great Lakes remote sensing data
Authors: Shook D. F. , Salzman J. , Svehla R. A. , Gedney R. T.
Published: February 2008

Remote sensing has been applied in the past to the surveillance of Great Lakes water quality, but it has been only partially successful because of the completely empirical approach taken in relating the multispectral scanning data at visible and near‐infrared wavelengths to water parameters. Any remote sensing approach using water color information must take into account (1) the existence of many different organic and inorganic species throughout the Great Lakes, (2) the occurrence of a mixture of species in most locations, and (3) spatial (inter‐ and intralake as well as vertical) variations in types and concentrations of species. The radiative transfer model provides a potential method for an orderly analysis of remote sensing data and a physical basis for developing quantitative algorithms. Predictions and field measurements of volume reflectances are presented which clearly show the advantage of using a radiative transfer model. Spectral absorptance and backscattering coefficients for two inorganic sediments are reported.
An arc tangent model of irradiance in the sea
Authors: Zaneveld J. Ronald V. , Spinrad Richard W.
Published: February 2008

The solar energy flux as a function of depth (the irradiance profile) in the ocean is an important function. It influences the dynamics of the mixed layer via the heat budget as well as the biology of the euphotic zone. The following three‐parameter model can take into account the very rapid decrease near the surface due to absorption of long‐wavelength radiation by water as well as the eventual exponential decrease at great depths. , where E(z) is the irradiance at depth z and K1, K2, and K3 are constants that depend on the optical properties of the water. The constants are determined for Jerlov's water types. The constants can readily be calculated from any irradiance profile.
Sensitivity of a global climate model to an increase of CO2concentration in the atmosphere
Authors: Manabe Syukuro , Stouffer Ronald J.
Published: February 2008

This study investigates the response of a global model of the climate to the quadrupling of the CO2concentration in the atmosphere. The model consists of (1) a general circulation model of the atmosphere, (2) a heat and water balance model of the continents, and (3) a simple mixed layer model of the oceans. It has a global computational domain and realistic geography. For the computation of radiative transfer, the seasonal variation of insolation is imposed at the top of the model atmosphere, and the fixed distribution of cloud cover is prescribed as a function of latitude and of height. It is found that with some exceptions, the model succeeds in reproducing the large‐scale characteristics of seasonal and geographical variation of the observed atmospheric temperature. The climatic effect of a CO2increase is determined by comparing statistical equilibrium states of the model atmosphere with a normal concentration and with a 4 times the normal concentration of CO2in the air. It is found that the warming of the model atmosphere resulting from the CO2increase has significant seasonal and latitudinal variation. Because of the absence of an albedo feedback mechanism, the warming over the Antarctic continent is somewhat less than the warming in high latitudes of the northern hemisphere. Over the Arctic Ocean and its surroundings, the warming is much larger in winter than summer, thereby reducing the amplitude of seasonal temperature variation. It is concluded that this seasonal asymmetry in the warming results from the reduction in the coverage and thickness of the sea ice. The warming of the model atmosphere results in an enrichment of the moisture content in the air and an increase in the poleward moisture transport. The additional moisture is picked up from the tropical ocean and is brought to high latitudes where both precipitation and runoff increase throughout the year. Further, the time of rapid snowmelt and maximum runoff becomes earlier.