bluuebunny/crossref_metadata_2025 huggingface dataset:
Fluctuations associated with sheared velocity regions near auroral arcs
Authors: Basu Bamandas , Coppi Bruno
Published: February 2008

The theory of electrostatic, collisional plasma modes that are driven unstable by a sheared field‐aligned ion flow velocity (i.e., Vio=Vo(x)eˆz, Bo=Boêz) is presented. The threshold condition for the instability is V′o/νin>2 (1+Ti/Te) and the unstable modes are characterized by k∥«k⟂ such that λ∥(=2π/k∥)»λm and 2πρi<λ⟂(=2π/k⟂)≲Lv, where V′o=dVo/dx, νin is the ion‐neutral collision frequency, λm is the electron mean‐free‐path, ρi is the ion gyroradius and Lv is the velocity shear scale length. It is shown that the linear instability provides a direct means of exciting the observed [Basu et al., 1986, 1988] sub‐km scale irregularities in the auroral F‐region. The spectral characteristics of the density and the electric field fluctuations that can be inferred from the theory are found to be consistent with the observations.
Effects of the magnetic field on free oscillations of the Earth
Authors: Mochizuki E.
Published: February 2008

Effects of the magnetic field on seismic waves are reexamined. We define a fourth‐order tensor which is expressed in terms of the magnetic field. Free oscillations are described by the integral which is quadratic form in the spatial derivative of the displacement with coupling by the fourth‐order tensor.
Reply [to “Comment on ‘MHD wave breaking in the outer plasmasphere’”]
Authors: Moore T. E. , Gallagher D. L. , Horwitz J. L. , Comfort R. H.
Published: February 2008

The phenomenon of resonance absorption leads to a secular damping of surface waves propagating parallel to the local magnetic field in a region of strong perpendicular gradient in the local Alfvén speed. This damping results from the growth of other wave modes at the expense of the surface waves. Resonance absorption is an effective dissipation mechanism which may forestall the steepening of MHD waves in such regions, and is probably the dominant mechanism by which widely distributed MHD wave energy becomes concentrated in rather thin, resonant, “energy‐containing” layers coinciding with regions of strong Alfvén wave speed gradients. However, based upon physical consideration of the impulsive radially propagating magnetosonic disturbances associated with substorms, we maintain that nonlinear steepening effects are likely to be important in the dissipation of their energy.
Ilmenite lamellae and stability of magnetization
Authors: Beske‐Diehl S. J.
Published: February 2008

I have analyzed magnetic data from four deep‐sea basalts which have undergone the “exsolution” stage of high‐temperature oxidation, but have not begun the “replacement” stage. Even when ilmenite lamellae development was extensive, coercivities were low with a coercive force (Hc) of 11.7 mT (1 mT=10 Oe) and medium destructive field (MDF) of 9.1 mT. The remanence vector exhibited a directional swing of 30° upon alternating field (AF) demagnetization. Thus, few of the titanomagnetite intergrowths behaved like single‐domain grains. This tentative conclusion is supported by those previous studies of subaerial basalts and synthetic materials which optically identified the degree of oxidation and in which no titanomagnetite granulation was observed. In these studies, MDF's generally did not increase above 15 mT during ilmenite lamellae formation. Those natural and synthetic samples which exhibit features of the “replacement” stage have large natural remanent magnetization (NRM) intensities and high coercivities suggesting that despite intense hematization, single‐domain magnetite may still be present.
The growth of Fe‐Ti oxides: Phase relations in the Fe‐Ti‐B‐O system
Authors: Smith Guy M.
Published: February 2008

It has become apparent during the last few years that some important aspects of rock magnetism require data that can not be provided by studies of natural Fe‐Ti oxides. Accordingly, there have been efforts by several groups to develop techniques to produce synthetic materials suitable for the required studies. This paper presents the preliminary results of an attempt to grow oxides of the magnetite‐ulvospinel series using the flux growth technique with a NaBO4 flux. I focus here on the essential first step in the process, which is the establishment of the temperature and oxygen fugacity conditions necessary to grow the desired phases. The results show that the Fe‐Ti‐B‐O system is complicated by the presence of borate phases as well as the expected oxides. The net effect is to place a upper limit on the ulvospinel concentration that can be achieved which varies with temperature from about 10% at 1200°C to around 60% at 1000°C.
The influence of stress path on thermoremanent magnetization
Authors: Martin Randolph J. , Noel James S.
Published: February 2008

The influence of stress path on thermoremanent magnetization (TRM) was studied experimentally. Specimens with a TRM were cyclically loaded under three different conditions: hydrostatic pressure, uniaxial compression, or uniaxial strain. Initial loading resulted in a large decrease in magnetization at stress and permanent demagnetization at the termination of the stress cycle. The observed magnetic changes were much larger for non‐hydrostatic loading than for hydrostatic compression. With subsequent loading to the same peak stress over the same path, stress induced variations in magnetization were smaller and tended to become reproducible; shear stress produced greater magnetic perturbations.
Limiting depth of magnetization in cratonic lithosphere
Authors: Toft Paul B. , Haggerty Stephen E.
Published: February 2008

Values of magnetic susceptibility and natural remanent magnetization (NRM) of clinopyroxene‐garnet‐plagioclase granulite facies lower crustal xenoliths from a kimberlite in west Africa are correlated to bulk geochemistry and specific gravity. Thermomagnetic and AF demagnetization analyses identify magnetite (Mt) and native iron (Fe) as the dominant magnetic phases (totalling ≤0.1 vol.% of the rocks) along with subsidiary sulfides. Oxidation states of the granulites are ≤MW, observed Mt occurs as rims on coarse (∼1 µm) Fe particles, and inferred SD‐PSD Mt may be a result of oxidation of fine‐grained Fe. The deepest limit of lithospheric ferromagnetism is 95 km, but a limit of 70 km is most reasonable for the West African Craton and for modelling Magsat anomalies over exposed Precambrian shields.
Thermal evolution of the lithosphere beneath fracture zones inferred from geoid anomalies
Authors: Marty Jean C. , Cazenave Anny
Published: February 2008

A global survey of Seasat derived geoid anomalies across fracture zones (FZ) has been conducted to characterize the behaviour of the geoid slope with age of plate in response to lithospheric cooling. We present new results for the geoid slope versus age along six FZ of the Atlantic ocean (Gibbs, Pico, Doldrums, Romanche, Ascension and Agulhas‐Falkland FZ). Including results of a previous study on Pacific FZ (Mendocino, Murray, Clarion and Unditsev FZ), we confirm that the geoid slope does not vary with age as conductive cooling models predict and show that its complex behaviour is a worldwide phenomenum. Two trends are clearly shown up by the data: (1) a sharp initial decrease of the geoid slope at very young ages, (2) a subsequent increase which typically starts at ages around 30‐40 Ma and culminates at ∼60 Ma. In a few cases, the rise of the geoid slope occurs later, beyond 80 Ma. According to the recent models developed by Robinson, Parsons and Driscoll, these trends may result from small scale convection induced by the horizontal thermal gradients underneath the FZ, instabilities developing in a sublithospheric low viscosity layer whose properties vary with age.
Interpretation of bipole pattern in a mesoscale storm
Authors: Hill R. D.
Published: February 2008

Recent observations of bipole patterns of CG lightning strokes at ground level are interpreted in terms of the production of charge centers in a model cell of a Florida thunderstorm, and in the subsequent histories of these centers following collapse of the updraft that generated the centers.
Toward an operational 3 dimensional simulation of the tropical Atlantic Ocean
Authors: Merle Jacques , Morlière Alain
Published: February 2008

Simulations obtained with a three dimensional primitive equation model in the tropical Atlantic ocean are compared with observations made during the FOCAL and SEQUAL experiments in 1984. In many respects the results are encouraging; notably, the most characteristic aspects of the 1984 warm event are correctly represented by the simulations. As part of the TOGA program, it is planned to run such a model operationally in the tropical Atlantic ocean. An improvement in the simulation is expected from a regular reinitialization of the model using observations. The quality of the forcing functions, especially the wind stress, will be improved by using a high frequency wind field provided operationally by the European Center for Medium range Weather Forecasting (ECMWF).
Xe in amorphous silica: A new thermometer in geothermal systems
Authors: Matsubara Kayo , Matsuda Jun‐ichi , Nagao Keisuke , Kita Itsuro , Taguchi Sachihiro
Published: February 2008

We measured noble gases in amorphous silica of geothermal origin. These samples were formed by precipitation from geothermal water in neutral pH, and by the leaching of rocks in acid hot springs. The concentration of 132Xe has a negative correlation with the temperature of geothermal water although 36Ar and 84Kr show no such correlation. The relationship between 132Xe content A (×10−8cm³STP/g) and temperature T(°C) is approximated by the equation A=−(4.5×10−3)T +0.50. The obtained equation should be useful for estimating the silica‐forming temperature that cannot be easily measured by other methods.
Detection of underside P reflections at mantle discontinuities by stacking broadband data
Authors: Wajeman Nathalie
Published: February 2008

Underside P‐reflections at mantle discontinuities are difficult to observe directly on seismograms mainly because of their low amplitude. It is shown that stacking seismograms obtained at several epicentral distances but having their PP bounce points in the same region, enables the identification of such phases. This method is applied to data from Japanese and Taïwan events recorded by the NARS array and other broadband European stations; discontinuities at about 670 and 300 km are revealed beneath Northern Eurasia.
Simultaneous observations of Sun‐aligned polar cap arcs in both hemispheres by Exos‐C and Viking
Authors: Obara Takahiro , Kitayama Masanobu , Mukai Toshifumi , Kaya Nobuyuki , Murphree J. S. , Cogger L. L.
Published: February 2008

On September 25, 1986, the EXOS‐C satellite traversed an intense electron precipitation in the southern polar cap, while the Viking satellite simultaneously obtained image data of the polar cap arc in the northern hemisphere. The energy spectrum of the precipitation, measured by instrumentation aboard EXOS‐C, was very similar to that of adjacent (typical) auroral arcs, and the precipitation in the southern polar cap was observed in the same local time sector in which the arc was found in the northern polar cap. Observations seem to support the view that the polar cap arc occurs on closed field lines and is conjugate in both hemispheres.
A comparison of ozone trends from SME and SBUV satellite observations and model calculations
Authors: Rusch D. W. , Clancy R. T.
Published: February 2008

Trends in the ozone mixing ratio near the stratopause are presented for global observations by the Ultraviolet Spectrometer (UVS) instrument on the Solar Mesosphere Explorer (SME) and the Solar Backscatter Ultraviolet Instrument (SBUV) on NIMBUS‐7. The June, September, and January data are separately analyzed for trends as a function of latitude over the 1982‐1986 period. The SME UVS data indicate trends in the range −0.5±1.3%/yr in ozone for the summer hemisphere at 1.0 mbar for January, June, and for all latitudes in September. The SBUV data show decreases of 2‐5%/yr for all three months. Model calculations of ozone trends at 1.0 mb, including 5%/yr ClX increases, measured solar flux decreases over the 1982‐1986 time period, and measured temperatures, reproduce the SME trends. The solar flux and ClX trends contribute equally to the measured changes at 1.0 mb. The SBUV and UVS data exhibit remarkably similar seasonal and latitudinal variations in ozone trends over the five years. The detailed variations of ozone trends from both data sets are reproduced by photochemical model calculations which include latitude‐dependent NMC temperature trends over the 1982‐1986 period.
Deep mixing in the Gulf of Lions, Revisited
Authors: Schott Friedrich , Leaman Kevin D. , Zika Rod G.
Published: February 2008

The Gulf of Lions, south of France, is a preferred location for deep convection in late winter as documented by the so‐called MEDOC studies during 1969‐73. During 23 January to 5 March 1987 a renewed investigation was carried out in this region to investigate the occurrence of deep convection with new technology. Vertical and horizontal currents were measured over a range of several hundred meters with moored upward‐looking acoustic Doppler current profilers (ADCPs); full‐depth horizontal current profiles were obtained by PEGASUS profiler; and CTD hydrography combined with measurements of some biological and chemical parameters to delineate watermass properties in the convection regime. A deep‐mixed patch had already developed at the beginning of the experiment, following a particularly intense mistral on 10/11 January. During a second mistral, 15‐20 February, vertical current events of 5‐15 cm/s downward were observed. Events were of short duration but large vertical scale.
Polarization anisotropy and fine‐scale structure of the Eurasian Upper Mantle
Authors: Gee Lind S. , Jordan Thomas H.
Published: February 2008

We have observed shear‐wave splitting, with (tSH‐tSV)/tSV up to 1.5%, on long‐period records of multiply reflected S waves bottoming in the upper mantle beneath the Russian and Siberian platforms. The dispersion of Love and Rayleigh waves over these paths shows discrepancies of comparable or larger magnitude with respect to smooth, isotropic (SI) structures, consistent with a model of the uppermost mantle having significant apparent vertical anisotropy. Although the splitting and dispersion data can be fit by smooth, anisotropic (SA) models, we have investigated the apparent anisotropy associated with fine‐scale ("rough") structure beneath stable Eurasia. We fit the data with a rough, isotropic (RI) model having an rms shear velocity fluctuation that varies from 14% in the uppermost mantle to zero at 400‐km depth. These fluctuations are larger than the variation in isotropically averaged parameters expected for even a diverse assemblage of upper‐mantle ultrabasic rocks, which we take to be evidence for some sort of intrinsic (local) anisotropy.
Shear wave properties of marine sediments derived from cepstral analysis of background noise
Authors: Butler Rhett
Published: February 2008

Cepstral analysis of background noise recorded on a horizontal borehole seismometer in the northwest Pacific reveals strong cepstral peaks corresponding to shear wave reverberation in the marine sediments. Shear reverberation intervals in the marine sediments derived from the cepstral analysis are within 10% of results obtained from a detailed analysis of seismic refraction profiling at the site. The close correspondence between the cepstral analysis and seismic profile analysis results are indicative that cepstral analysis is a useful tool in measuring and constraining marine sediment properties.
Heterogeneous interactions of chlorine nitrate, hydrogen chloride, and nitric acid with sulfuric acid surfaces at stratospheric temperatures
Authors: Tolbert Margaret A. , Rossi Michel J. , Golden David M.
Published: February 2008

The heterogeneous interactions of ClONO2, HCl and HNO3 with sulfuric acid surfaces were studied using a Knudsen cell flow reactor. The surfaces studied, chosen to simulate global stratospheric particulate, were composed of 65‐75% H2SO4 solutions at temperatures in the range −63 to −43°C. Heterogeneous loss, but not reaction, of HNO3 and HCl occurred on these surfaces and the measured sticking coefficients are reported. Chlorine nitrate reacted on the cold sulfuric acid surfaces, producing gas‐phase HOCl and condensed HNO3. ClONO2 also reacted with HCl dissolved in the 65% H2SO4 solution at −63°C, forming gaseous Cl2. In all cases studied, the sticking and/or reaction coefficients were much larger for the 65% H2SO4 solution at −63°C than for the 75% solution at −43°C.
Polar atmospheric circulation and chemistry of recent (1957‐1983) south polar precipitation
Authors: Legrand M. , Kirchner S.
Published: February 2008

In this paper, we present a detailed study of Na, Cl, and NO3 concentrations in the south polar snow layers covering the 1957‐1983 time period. Our data point to a trend of the Na winter values which suggest a weaker poleward transport within the troposphere since 1980. The NO3 profiles exhibit generally maxima in summer. However, as an exception to this rule, we observe additional maxima during the springs of 1982, 1975 or 1976, 1973 or 1974, and to a lesser extent in 1959. These unusual patterns of the seasonal NO3 deposition correspond to years during which the lower stratosphere was very cold. This coincidence provides an indirect support for the hypothesis of a denitrified stratosphere by polar stratospheric clouds (PSCs). Due to inherent problems in studying seasonal variations in the south polar snow, these results have to be taken with some caution. Nevertheless, if confirmed by additional measurements and extended to the present, such studies of south polar precipitation will be very useful to examine changes of the southern hemisphere circulation pattern and to provide a long term record of polar stratospheric temperature.
Thermochemical stabilities and vibrational spectra of isomers of the chlorine oxide dimer
Authors: McGrath M. P. , Clemitshaw K. C. , Rowland F. S. , Hehre W. J.
Published: February 2008

Ab initio molecular orbital calculations have been carried out to determine the relative thermochemical stabilities and infrared vibrational spectra of isomers of the ClO. dimer. Two straight‐chain isomers, ClOOCl and ClOClO, and one branched species, ClClO2, have been identified as energy minima on the Cl2O2 potential surface. The highest level calculations show ClOOCl and ClClO2 to be of comparable stability, with ClOClO some 11 kcal mol−1 higher in energy. Intense infrared absorptions for ClOOCl are calculated at 765, 679 and 633 cm−1. These correlate closely with two broad bands (centered at 740 and 653 cm−1) observed by Molina and Molina (1987) to result from the gas‐phase reactions of chlorine atoms with various ClO. precursors. The previous assignment of the 653 cm−1 band to ClOClO [Molina and Molina, 1987] is inconsistent with its calculated infrared spectrum. The calculations also suggest that the two most intense bands in the experimental infrared spectrum, at 1225 and 1057 cm−1 and previously assigned to ClOOCl, correspond instead to antisymmetric and symmetric stretching modes of ClO2 functionality. These bands may indicate the presence of the third Cl2O2 isomer, ClClO2, or an alternative species such as ClOClO2.
Drilling summary, Cajon Pass Scientific Drilling Project: Phase I
Authors: Wicklund A. Percy , Andrews Robert S. , Johnson Robert J.
Published: February 2008

The drill hole for the Cajon Pass Scientific Drilling Project was designed uniquely to accomplish specific science experiments. Special consideration was given to drilling practices for hole size, spot coring, deviation from the vertical, chemical and physical properties of the drilling fluids and pipe lubricants, monitoring mud logging and drilling parameters, and procedures for handling of cores and cuttings samples. Phase I of drilling reached a depth of 2115 m.
Theoretical time‐temperature relationships of magnetization for distributions of single domain magnetite grains
Authors: Worm H. ‐U. , Jackson M.
Published: February 2008

Experimental studies have demonstrated that demagnetization temperatures for removing thermoviscous magnetizations (TVRMs) in rocks are often higher than predicted by Pullaiah et al.'s time‐temperature (t‐T) nomogram based on Néel's single domain (SD) theory. Better agreement has been found for t‐T relationships based on Walton's calculations invoking volume distributions. It has been pointed out, however, that Walton's formula applies for t‐T conditions for acquisition of magnetization only, not to demagnetization. We applied numerical methods for assessing the true influence of distributions in SD volume. As it turns out, for reasonable volume distributions, the differences between our results and Pullaiah et al.'s simpler approach are marginal; the differences in demagnetization temperature are significant only for moderate‐term low‐temperature acquisition. Discrepancies between experiments and theory appear because rocks contain predominantly pseudo‐single and multi‐domain grains to which SD theory does not apply.
Spectral analysis of Canada Basin under‐ice draft distribution as recorded by the USS Queenfish, August 1970
Authors: Key J. R. , McLaren A. S.
Published: February 2008

Spectral analysis has been applied to 940 kilometers of under‐ice thickness data recorded by the USS QUEENFISH in the Canada Basin, August 1970. Periodicities of 50‐150 m most commonly occurred throughout the track, with longer wavelengths common in areas of thicker, more variable ice. While some regional variations could be discerned, unique regional patterns were not apparent, supporting the hypothesis that ice characteristics in this region are relatively homogeneous.
An attempt to remotely sense from space the surface heat budget over the Indian Ocean during the 1979 Monsoon
Authors: Gautier Catherine , Frouin Robert , Simonot Jean‐Yves
Published: February 2008

Satellite data are used to estimate the net surface heat flux (Q) over the Indian Ocean during June 1979. Ten‐day and monthly average fields of Q and its components are produced and analyzed in relation to monsoon dynamics. When compared to ship‐based estimates, the satellite‐derived fluxes exhibit correct orders of magnitude and their temporal evolution is consistent with our monsoon knowledge. This study, which represents a first attempt to remotely sense from space the earth surface net heat flux, demonstrates that current satellite sensor data can be combined to accurately describe net heat flux changes in areas such as the Arabian Sea, where they are large, rapid, and spatially extended, and therefore not fully observed by ships.
Direct measurements of the photolysis rate coefficient of ethyl nitrate
Authors: Luke Winston T. , Dickerson Russell R.
Published: February 2008

We report the direct measurement of the photolysis rate coefficient of ethyl nitrate to NO2 and the ethoxy radical: using a luminol chemiluminescence NO2 detector. The photolysis of ethyl nitrate is slow: at a temperature of 288 K and a zenith angle of 60°, j1 = 0.45 × 10−6 s−1. At a zenith angle of 0°, j1 is estimated to be ca. 1.1 × 10−6 s−1. This implies a photolytic lifetime of about one month in the planetary boundary layer. The photolysis frequency is very temperature dependent, and approximately doubles between 279 and 299 K. Observed photolysis rate coefficients agree, within experimental uncertainty, with coefficients calculated using recently measured absorption cross‐sections and an assumed quantum yield of unity.
Orthorhombic‐tetragonal phase transition in CaGeO³ perovskite at high temperature
Authors: Liu X. , Wang Y. , Liebermann Robert C.
Published: February 2008

CaGeO3 perovskite was synthesized from its wollastonite polymorph at P=8 GPa and T=1000°C in a uniaxial split‐sphere apparatus (USSA‐2000). For recovered specimens heated to less than 500°C at 1 bar, the crystallographic distortion of the orthorhombic (Pbnm) CaGeO3 perovskite, that is the tilting of the [GeO6] octahedra, decreases with increasing temperature in the range 25‐250°C. At temperatures near 250°C, CaGeO3 undergoes a reversible transformation from an orthorhombic to a tetragonal structure, accompanied by an abrupt increase in the mean thermal expansion. Such behavior is typical of other orthorhombic perovskites and may occur for silicate perovskites in the lower mantle.
Balloon‐borne measurements of stratospheric ion density and conductivity at low latitude
Authors: Beig G. , Sidhu J. S. , Das S. R. , Chakrabarty D. K.
Published: February 2008

A new approach has been used to measure the electrical parameters of the stratosphere. In this, two spherical probes were simultaneously flown onboard a balloon. One measured the total density and the other gave the conductivity of ions. Combining the results of the two, the value of mobility has been derived. The values of ion density, conductivity and mobility are given in the altitude range of 20 to 30 km.
Cross‐equatorial air mass exchanges
Authors: Holl Manfred M. , Wolff Paul M. , Bush Yeager A.
Published: February 2008

A method is described to compute atmospheric mass time series from a data base of sea‐level pressure analyses. The short‐term hemispheric mass exchange is used to examine the validity of this method.

A 1/6 degree by 1/6 degree, latitude and longitude, terrain data base, provided by the Fleet Numerical Oceanography Center (FNOC), is used to reduce sea‐level pressure to surface pressure. Surface pressure is converted to mass and summed. The FNOC sea‐level pressure and the European Center for Medium Range Weather Forecasting (ECMWF) 1000‐mb analyses are used to compute the mass and generate time series for the Northern Hemisphere 1946–1987 and the Southern Hemisphere 1981–1987.

The Northern Hemisphere and Southern Hemisphere mass time series are combined to show that exchanges of atmospheric mass occur between hemispheres on the order of several millibars (equivalent mass) on a time scale of days to weeks. The larger exchanges typically occur during the Northern Hemisphere winter.
The altitude coverage of temperature measurements using RASS with wind profiler radars
Authors: May P. T. , Strauch R. G. , Moran K. P.
Published: February 2008

The Radio Acoustic Sounding System (RASS) technique for measuring temperature profiles with good time and height resolution has been applied using wind profiling radars operating at three frequencies (49.8, 404.37 and 915MHz). The performance of the three systems is discussed in terms of the altitude coverage of the temperature measurements and physical processes limiting the coverage. The lower frequencies can probe greater altitudes, but the 49.8MHz wind profilers have a minimum range of about 2.1 km limiting their usefulness for some studies. These preliminary results indicate that the use of RASS in concert with wind profilers has promise for operational meteorology.
Thermal‐mechanical controls on seismicity depth distributions in the San Andreas Fault Zone
Authors: Miller Cynthia K. , Furlong Kevin P.
Published: February 2008

Earthquake depth distributions in continental crust can be related to factors which determine the depth of the transition from brittle to ductile failure. These factors include temperature, strain rate and lithology. The San Andreas Fault Zone of Northern and Central California is an ideal place to test the relative importance of these factors since there is abundant earthquake data and our understanding of the tectonic interaction of the Pacific and North American plates provides constraints for several parameters. In the San Andreas Fault Zone we have found an approximately 3 km increase from Northern to Central California of the median depth of events and the depth above which 90% of events occur. In addition, depth distributions of earthquakes vary systematically from Northern to Central California. Both the maximum depth of earthquakes and the depth of the peak of seismic activity are shallower in Northern California. Utilizing Critical Strength Envelopes we have found that, unlike the oceanic case, this variation is not thermally controlled. Rather, a combination of low strain rate and low stress level cause the seismicity in Northern California to be shallow relative to Central California.
Evidence for multiple boundary faults beneath the northwest moat of Long Valley Caldera: Magnetotelluric results
Authors: Hermance John F. , Neumann Gregory A.
Published: February 2008

The boundaries of Long Valley Caldera, in Eastern California, are sharply delineated by steeply dipping normal faults which, for the most part, are buried and obscured by recent volcanic and sedimentary cover. The only evidence for their presence is from their geophysical signatures on regional gravity, seismic and electromagnetic surveys. Recently, a surge of interest has focused studies in the western moat, where the volcanism is most recent, and where many workers feel that the geothermal potential is highest. A detailed, narrow‐band (20–80 s) magnetotelluric profile in that area has delineated a parallel set of buried high angle normal faults which have virtually no expression at the surface. The outermost fault has a throw of approximately 500 m, while the innermost has a throw of approximately 2 km; neither has an expression in the surface morphology. Moreover, based on a relatively low resistivity contrast between the basement and the basin fill, we infer a relatively high fracture porosity in the Sierran basement, which suggests that there may be considerable lateral and vertical migration of meteoric water; a result which has considerable significance to understanding the regional hydrology.
Raman spectroscopy of diamond in ureilite and implication for the origin of diamond
Authors: Miyamoto Masamichi , Matsuda Jun‐ichi , Ito Keisuke
Published: February 2008

Most ureilite meteorites contain diamonds that are generally thought to have been formed by shock‐induced high pressure that converted carbonaceous material to diamond. We measured Raman spectra of ureilite diamond in order to investigate the origin of such diamonds. The FWHM (full width at half maximum) of the Raman line at 1330 cm−1 from diamond in the ALH‐77257 ureilite is about 10 cm−1 which is narrower than those of artificially shock‐produced diamonds ( >20 cm−1) but within the range of vapor‐growth diamonds measured previously. This result suggests that the vapor‐growth origin of ureilite diamond in an interstellar environment should be considered seriously, although further studies are necessary to characterize vapor‐growth diamonds by measuring the Raman line of diamonds synthesized by various methods.
Background heatflow on hotspot planets: Io and Venus
Authors: Stevenson David J. , McNamara Sean C.
Published: February 2008

On planets where most of the heat is transported to the surface by igneous activity (extrusive volcanism or near‐surface intrusions), the surface heatflow at localities well away from regions of current igneous activity need not be even approximately the conductive heatflow through the entire lithosphere but may instead be dominated by the residual heat leaking out from the last igneous event in that locality. On Io, it is likely that (κτ)1/2 « lithosphere thickness ( κ = thermal diffusivity, τ = typical time between “resurfacing” events) and the background heatflow may be very large, comparable or even larger than the current observational heatflow, which is associated with the hotspots alone. This upward revision of Io's heatflow is compatible with observations and with recent indications of a non‐steady tidal and thermal evolution. On Venus, (κτ)1/2 is probably comparable to the lithosphere thickness and the resulting upward revision of heatflow may be only marginally significant, unless magmatic activity is enormously greater than on Earth.
Simulation of the global air‐sea transfer velocity field of helium
Authors: Erickson David J.
Published: February 2008

Air‐sea exchange is important in constructing a budget of He in the upper oceanic water column. This exchange of He is controlled by the transfer velocity (KwHe) and the air‐sea concentration gradient. Here, the global transfer velocity field of He is computed for January and July with user‐defined derived fields based on control runs of the NCAR (National Center for Atmospheric Research) CCM1 (Community Climate Model), a 12 layer atmospheric general circulation model. The spatial resolution of these calculations is 4.5° × 7.5° latitude‐longitude. The range of KwHe variation over the globe is over an order of magnitude, varying from 5 to 75 cm hr−1. Equatorial values are generally 10‐20 cm hr−1 and high latitude regions experience values in excess of 60 cm hr−1. The annual variability of the transfer velocity in the high‐latitude northern hemisphere is larger than in the high‐latitude southern hemisphere. This work shows that the spatial and temporal variation in the global transfer velocity field of He is significant. This result should be included in future high‐resolution 3‐dimensional coupled ocean‐atmosphere tracer models when attempting to quantitatively deconvolute vertical transport and air‐sea exchange in surface ocean He budgets. This approach may allow high‐resolution global estimates of nitrate flux into the euphotic zone, an important component in oceanic biogeochemical modeling efforts.
Test particle simulation study of whistler wave packets observed near comet Giacobini‐Zinner
Authors: Kaya N. , Matsumoto H. , Tsurutani B. T.
Published: February 2008

In order to study nonlinear interactions of water group ions with large amplitude whistler wave packets detected at the leading edge of steepened magnetosonic waves observed near comet Giacobini‐Zinner, we carried out test particle simulations of water ion interactions with a model wave based on the G‐Z data. As the model wave, we adopted a linearly polarized magnetosonic (MS) wave as the trailing portion of the wave, and circularly polarized whistler waves in the leading edge of the wave. Both the MS and whistler waves are a priori assumed to have large amplitudes. We found that some of the water ions are decelerated in the steepened portion of the magnetosonic wave to the resonance velocity with the whistler wave packets. Through resonance and related nonlinear interaction with the large amplitude whistler waves, the water ions become trapped by the whistler wave packet. An energy balance calculation demonstrates that the trapped ions do lose their kinetic energy during the trapped motion in the whistler wave packet. It is thus demonstrated that the nonlinear trapping motion in the wave structure leads to the effective energy transfer from the water group ions to the whistler wave packets in the leading edge of the steepened MHD waves.
Pore shape deformation by solution transfer: A critical reexamination
Authors: Reuschlé T. , Darot M. , Gueguen Y.
Published: February 2008

We conducted a theoretical and experimental reexamination of the solution transfer experiment proposed by Sprunt and Nur (1977). Limestone parallelepipedic samples with cylindrical holes were submitted to uniaxial load in a fluid which was hydrochloric or acetic acid. A theoretical treatment similar to that of Griffith's crack is proposed, which allows the calculation of the equilibrium shape of the hole by assuming that it deforms into an elliptical cylinder with its major axis perpendicular to the applied stress. Experiments conducted to check the model showed that, when all basic theoretical assumptions are fulfilled, the kinetics of hole shape evolution is too slow to make any hole deformation observable after a two months run. The disagreement between our results and Sprunt and Nur's observations is explained by experimental procedure differences. The model proposed should give a new insight into the solution transfer phenomenon.
Limestones of western Newfoundland that magnetized before Devonian folding but after Middle Ordovician lithification
Authors: Hodych J. P.
Published: February 2008

A positive fold test and a negative conglomerate test help determine when and how stable remanence was acquired in the Middle Ordovician Table Head Group limestones of the Port au Port Peninsula of Newfoundland. The limestones magnetized after lithification and incorporation as clasts into a Middle Ordovician breccia. Hence, the limestones do not carry a detrital or other primary remanence despite their very low conodont colour alteration index of 1. The remanence may be thermoviscous or diagenetic and was acquired before Devonian folding. This suggests the need for caution in interpreting paleomagnetic results from other early Paleozoic limestones whose remanence resides in magnetite of blocking temperature lower than 400°C.
The effect of ballooning modes on thermal transport and magnetic field diffusion in the solar corona
Authors: Strauss H. R.
Published: February 2008

Presently favored mechanisms of coronal heating ‐ current sheet dissipation and Alfvén wave resonant heating ‐ deposit heat in thin layers. Classical thermal conduction cannot explain how heat is transported across the magnetic field. If heating occurs in thin layers, large pressure gradients can be created, which can give rise to ballooning modes. These instabilities are caused by the pressure gradient and the curvature of the magnetic field, and are stabilized by magnetic tension. The modes are broad band in wavelength and should produce turbulence. A mixing length expression for the turbulent heat transport shows that it is more than adequate to rapidly convect heat into much broader layers. Furthermore, the turbulent resistivity implies that heating occurs over most of the width of these broadened layers. The broadening also implies that much shorter time scales are required for heating. The β values in the corona suggest that 1 ‐ 10 turbulent layers are formed in typical loop or arch structures.
The influence of the source on the high‐frequency behavior of the near‐Field acceleration spectrum: A numerical study
Authors: Gariel Jean‐Christophe , Campillo Michel
Published: February 2008

The hypothesis that particular physical properties of the earth at the source can affect the radiation of high‐frequency waves was numerically investigated. Two factors have been considered: a non‐elastic behavior of the material at the crack tip (i.e presence of a cohesive zone) and the kinematics of the rupture front. Using the discrete wave number method, we calculated complete near‐source synthetic spectra radiated by a circular shear crack model. The two processes can explain an exponential decrease of the acceleration spectrum at high frequencies. Moreover, they can be differentiated. In the case of a final smooth deceleration of the rupture front, the rate of decay of the acceleration spectra is equivalent in all the azimuths. A clear azimuthal dependence exists in the presence of a cohesive zone, with the maximum rate of decay being observed in the direction of the fault strike. The parameter fmax varies as the ratio of the rupture velocity over the length of the cohesive zone for the non‐elastic model and as the inverse of the duration of the deceleration of the rupture front when the rupture front stops smoothly. These two models result in a decay of spectral amplitude at high frequency that mimics the effect of the anelastic attenuation.
Formation of the 1988 Antarctic ozone hole
Authors: Krueger Arlin J. , Stolarski Richard S. , Schoeberl Mark R.
Published: February 2008

The 1988 Antarctic ozone hole, as observed with the Nimbus 7 TOMS instrument, formed in August but failed to deepen significantly during September. The structure of the surrounding total ozone maxima also differed from the prior year. The 1987 total ozone pattern was pole centered and symmetrical. During 1988 a persistent strong wavenumber 1 perturbation in total ozone developed in August which resulted in displacement of the polar ozone minimum to the base of the Antarctic Peninsula. Subsequently, a series of transient mesoscale size minima formed within the broader polar minimum. In September the frequency of the transient events diminished and a larger scale decrease in polar total ozone began. The decrease lasted less than two weeks, resulting in a net change of only 25 DU compared with the nearly 100 DU decline observed during the same period in 1987. The minimum values remained roughly constant until October 19, 1988 and then increased rapidly. The 1988 Antarctic ozone hole subsequently drifted off the Antarctic continent in late October and dissipated in mid‐November.
Perturbed ray tracing on a heterogeneous sphere
Authors: Virieux Jean
Published: February 2008

We propose a fast ray tracing method on a laterally heterogeneous Earth. When the square of slowness is expanded into spherical harmonics, an approximate analytical ray tracing can be performed. Using a Hamiltonian formulation, we introduce new coordinates, that have the specific adiabatic invariance of action/angle coordinates. A first‐order solution is constructed in this new coordinate system. Excellent agreement is obtained between numerical and approximate analytical ray tracings, for the global model of Nakanishi and Anderson [1984] with an azimuthal order 6.
Airborne lidar observations of clouds in the Antarctic troposphere
Authors: Morley Bruce M. , Uthe Edward E. , Viezee William
Published: February 2008

In January 1986, SRI International made exploratory airborne observations of Antarctic tropospheric clouds with a downward‐viewing lidar onboard an LC‐130 supply aircraft. Frequency of observations depended upon the schedule of supply missions. Two types of clouds were observed: relatively opaque, midlevel cloud layers 3.0 to 4.0 km below flight level (about 4.0 to 4.5 km MSL); and higher altitude optically transparent cirrus clouds exhibiting long trails or curtains of ice crystals that extended from flight level downward to the top of the midlevel clouds and, frequently, to ground level. The midlevel clouds were often multilayered and, at times, showed wave or cellular structure associated with cloud streets. The ice crystal trails from the cirrus clouds showed evidence of the presence of strong vertical wind shear, and were observed to “seed” the midlevel cloud layers, producing large breaks in the overcast. These exploratory observations attest to the utility of lidar for atmospheric research studies in the Antarctic region.
Note concerning possible mechanisms for non‐double‐couple earthquake sources
Authors: Frohlich Cliff , Riedesel Mark A. , Apperson K. Denise
Published: February 2008

Some earthquake sources are not double couples, i.e, they are not due solely to slip along a simple, planar fault surface. One possible explanation for such sources is that they occur because of source complexity, namely, they consist of simultaneous or time‐separated double‐couple subevents along different fault surfaces. For intermediate depth earthquakes consisting of only two subevents, we illustrate how non‐double‐couple earthquakes might occur (1) near the edges of subducting lithospheric slabs; or (2) in the interior of a slab if an earthquake with a downdip P (or T) axis triggers a “bending” subevent along the inside (outside) of the slab. We can choose between an edge, inside‐bending or outside‐bending interpretation by comparing the downdip direction of the Wadati‐Benioff zone and the orientation of the moment tensor axes. While slip along a curved fault surface can produce a non‐double‐couple source, this can occur only for a limited class of slip and fault geometries. Non‐double‐couple sources can never be produced by double‐couple subevents if (1) the subevents occur along parallel fault planes; (2) the subevents occur on a cylindrical fault surface, with slip due to rotation about the cylinder axis; or (3) the subevents occur on a cylindrical fault surface, with slip parallel to the axis.
Observational determination of the adiabatic index in the quiet time plasma sheet
Authors: Huang C. Y. , Goertz C. K. , Frank L. A. , Rostoker G.
Published: February 2008

We show that in the quiet time (AE<100nT) central plasma sheet the plasma density and temperature are, in general, anticorrelated. This indicates that the adiabatic index is less than 1 and that earthward converting plasma cools as it is compressed. We do not have a satisfactory explanation for this surprising result.
High‐speed flows of H+ and He++ ions at the magnetopause
Authors: Paschmann G. , Fuselier S. A. , Klumpar D. M.
Published: February 2008

During a crossing of the subsolar magnetopause into the boundary layer the Hot Plasma Composition Experiment on AMPTE/CCE has provided the first observations of high‐speed flows of both H+ and He++ ions. Furthermore, the flow velocities of the two species showed good agreement. When considered as a single fluid, the ion flow obeys the MHD momentum balance relation for a rotational discontinuity, and thus is consistent with expectations for magnetic reconnection. This balance test does not, however, predict that the flow speeds of H+ and He++ should be equal. Thus our observations provide information not contained in the fluid description. The observed agreement between the flow velocities of different ion species follows if one considers the motion of individual ions across the magnetopause current sheet. Assuming that the motion conserves the particles' pitch‐angle, or changes it by an equal amount, as for adiabatic motion, all particles will gain the same amount in speed regardless of mass. The particles gain their energy by sliding along the magnetopause in the direction of the tangential electric field intrinsic to the reconnection process. To preserve equality of speed, the He++ ions must move twice the distance of the H+ ions.
IUE Observations of the Jovian dayglow emission
Authors: McGrath M. A. , Feldman P. D. , Ballester G. E. , Moos H. W.
Published: February 2008

IUEssspectra of Jupiter are examined in light of recent models put forward to explain the anomalously bright ultraviolet emissions seen from the upper atmospheres of the outer planets. Chi‐squared fits of the IUE spectra with model spectra produced by two proposed excitation mechanisms, electron impact and fluorescence of solar radiation, result in consistently higher χ² values for the solar fluorescence model. We find no conclusive evidence in the IUE data for the dominance of solar fluorescence over electron excitation in producing the Jovian dayglow emission.
Doppler shifted H Ly α Emission from Jupiter's aurora
Authors: Clarke John T. , Trauger John , Waite J. Hunter
Published: February 2008

IUE observations of the aurora on Jupiter have been performed with high spectral resolution in a search for Doppler shifted H Ly α emission produced through charge exchange by fast precipitating protons, as observed in the Earth's aurora. No emission has been observed corresponding to proton energies greater than 200 eV, placing a strict upper limit on the contribution of KeV ‐ MeV protons to the production of Jupiter's aurora. However, a large fraction of the H Ly α emission has appeared Doppler‐shifted mainly toward the blue by roughly 50 km/sec, corresponding to a kinetic energy of 10–20 eV for a fast proton or H atom, and there are higher velocity wings on the line extending out to equivalent energies of 150–200 eV. The blue shift indicates motion up out of the atmosphere, and we suggest that the emission results from the in situ acceleration of ionospheric protons in Jupiter's auroral ionosphere by analogy to the ionospheric potentials observed in the Earth's auroral zones. These observations demonstrate that the acceleration of ionospheric plasma in an H2 atmosphere can lead to bright Ly α emission, with implications for the production of the outer planet airglow emissions. The observed Doppler shift represents a significant fraction of the escape velocity, and the upflowing protons and H atoms may contribute substantially to the low energy plasma in Jupiter's magnetosphere if the plasma motions are at high altitudes.