bluuebunny/crossref_metadata_2025 huggingface dataset:
A fundamental magnetosphere‐Ionosphere coupling mode involving field‐aligned currents as deduced from DE‐2 observations
Authors: Sugiura Masahisa
Published: February 2008

From the magnetic and electric field observations on the DE‐2 satellite it is deduced that the perturbation magnetic field and the electric field in the field‐aligned current regions are, as a rule, orthogonal to each other and are highly correlated. This deduction is equivalent to the statement that the Poynting vector calculated from these magnetic and electric field components is equal to the ionospheric energy dissipation and that the height‐integrated Hall current is divergence free. The state described is interpreted as a frequently prevailing mode of the magnetosphere‐ionosphere coupling involving field‐aligned currents.
Coarse particle soil dust in Arctic aerosols, spring 1983
Authors: Winchester John W. , Li Shao‐meng , Fan Song‐miao , Schnell Russell C. , Bodhaine Barry A. , Naegele S. Stuart
Published: February 2008

Eleven AGASP research flights during March‐April 1983 collected particle size fractions by cascade impactors. Concentrations of elemental constituents of soil dust—Al, Si, K, Ca, Ti, and Fe—primarily in the coarsest particles, >16 µm aerodynamic diameter (µmad), were much greater in samples from six of the flights than in the samples of the remaining five flights. The relative concentrations of these elements were approximately those in geochemical average shale. They differed from concentrations in the average earth's crust by a several‐fold depletion of Si. The composition of stratospheric samples of El Chichon volcanic dust had relatively higher K and Ti than did the high dust aerosols. The results suggest two possible sources for high dust content particles: (1) finely divided clay minerals generated at lower latitudes, e.g., in Asia during late winter, which are transported northward, and under suitable atmospheric conditions before sampling, may grow or coalesce as ice crystals into much larger sizes; and (2) a local Arctic source of soil dust particles.
The long range transport of polyclorinated hydrocarbons to the Arctic
Authors: Oehme M. , Ottar B.
Published: February 2008

The concentration of polychlorinated hydrocarbons has been measured in air samples from 4 Arctic stations in 1980‐83. The measurements show that elevated concentrations are found during episodes of long range transport, and an accumulation of polychlorinated hydrocarbons seems to take place.
DE‐1 observations of ordinary mode and extraordinary mode auroral kilometric radiation
Authors: Mellott M. M. , Calvert W. , Huff R. L. , Gurnett D. A. , Shawhan S. D.
Published: February 2008

Observations of auroral kilometric radiation (AKR) made with DE‐1 indicate the presence of both ordinary and extraordinary wave modes. Although the two modes usually occur separately, they are sometimes observed together. When both modes are present, the ordinary‐mode component tends to occur at lower frequencies and with lower amplitudes than those of the accompanying extraordinary‐mode component. On the other hand, the local electron gyrofrequency is an absolute lower frequency cutoff for both modes. Ordinary mode intensities are proportional to extraordinary mode intensities but less by roughly a factor of 50. Extraordinary mode ray paths are generally confined to a cone within 50° of the source magnetic field direction and ordinary mode emissions are typically observed outside of this cone. This behavior suggests that both components are produced within the same source region but are then refracted differently as they escape.
Rock anelasticity measurements at high pressure, low strain amplitude and seismic frequency
Authors: Jackson I. , Paterson M. S. , Niesler H. , Waterford R. M.
Published: February 2008

A new apparatus has been constructed which will ultimately facilitate the study of rock anelasticity under conditions which closely approach those of teleseismic wave propagation: simultaneous high pressure and temperature, low frequency and strain amplitude, and controlled pore pressure of volatiles. Its performance has been tested in a series of preliminary experiments conducted at room temperature. Measurements on a steel standard demonstrate the sensitivity of the apparatus to very small departures from ideal elasticity (Q>1000). Experimental data for a fine‐grained granitic rock show that both the shear modulus G and quality factor Q increase sharply with increasing pressure below ∼100 MPa, beyond which pressure both parameters become markedly less pressure sensitive. These observations are in accord with those of previous studies at higher frequencies and larger strains, and are consistent with the view that the anelasticity of rocks at ambient pressure is dominated by mechanisms operative at open cracks and grain boundaries.
Resonant ULF waves: A new interpretation
Authors: Kivelson Margaret G. , Southwood David J.
Published: February 2008

Many important properties of ultra‐low frequency (ULF) magnetic pulsations (∼1 to 10 minute periods) observed in the magnetosphere and by ground‐based magnetometers have been interpreted successfully in terms of resonant field line models. These models describe the pulsations as transverse hydromagnetic waves standing on dipole flux tubes with fixed ends in the ionosphere. Signal structure and frequency are consistently explained, but the models fail to provide convincing explanations of the discrete spectra often observed. In this letter we propose that the spectrum of excitations is dominated by frequencies that correspond to eigenfrequencies of the fast (compressional) mode in the outer magnetosphere. In the presence of plasma inhomogeneities, the eigenmodes of the fast mode damp, even in the absence of dissipation, through coupling to transverse waves. We discuss the properties of a damped eigenmode, pointing out the analogy to the properties of damped surface eigenmodes. The coupled waves exhibit field line resonance behavior on the magnetic shell where the transverse mode dispersion relation is satisfied, but the spectrum is dominated by fast mode eigenfrequencies.
Regional stress field of the Indian Plate
Authors: Cloetingh Sierd , Wortel Rinus
Published: February 2008

We have calculated the regional stress field in the Indian plate, implementing dependence of slab pull and ridge push on the age of the oceanic lithosphere in the finite element procedure. The high level of the calculated stress field (order of a few kbar) and the dominance of compression in the plate are consequences of the unique dynamic situation of the present‐day Indian plate. The calculated stress field explains the concentration of intraplate deformation in the region of the Ninetyeast Ridge and yields insight into the variations in stress directions in the Australian continent.
New paleomagnetic data from carboniferous volcanics and red beds from central New Brunswick
Authors: Seguin Maurice K. , Singh A. , Fyffe L.
Published: February 2008

It has long been argued, on the basis of paleomagnetic data derived from Devonian, Carboniferous and Permian lithological units from eastern North America that a sinistral megashear of Carboniferous age parallels and lies within the faults delimiting the Appalachian‐Caledonian chains. Recent paleomagnetic studies in the northern Appalachians have cast doubt on the models of a Carboniferous offset. The geologic evidence suggests that only a small amount of dextral (and not sinistral) strike slip has occurred on faults which are parallel with pre‐Acadian paleogeographic realms. The purpose of this paleomagnetic study is to test the validity of the proposed left‐lateral motion at one of the sites of its presumed passage in central New Brunswick. Six sites (80 oriented specimens) in Carboniferous red beds and volcanics were collected on both sides of the Fredericton Fault and other parallel faults. After AF and thermal cleaning, the mean direction of magnetization is 158° + 38°; the fold test is indecisive. The corresponding paleopole is 135°E, 21°N and the paleolatitude 20°S. The paleopole positions and paleolatitudes are not significantly different on either side of the Fredericton fault and no left‐lateral motion was detected by paleomagnetic means. As no such motion was detected in south‐central New Brunswick and Newfoundland, it is possible but unlikely that it took place in northern New Brunswick and in the western Gaspé Peninsula. This contribution is useful in discussing possible motions of Acadia.
Sonic and ultrasonic velocities: Theory Versus experiment
Authors: Murphy William F.
Published: February 2008

Longitudinal and shear wave velocities have been measured at 2 kHz and 200 kHz. The measurements were made in a granite as a continuous function of partial water saturation and effective pressure. The pore space of the granite consists of micro‐cracks. The low frequency results compare favorably to the low frequency limit of poroelastic theory. Poroelastic theory assumes that the pore space is connected. On the other hand, the ultrasonic results are better described by effective medium scattering theories: the self‐consistent and the average T‐matrix approximations. Each of these theories assume that the microcracks are not connected.
A theory of magnetic flux transfer at the Earth's magnetopause
Authors: Lee L. C. , Fu Z. F.
Published: February 2008

It is suggested that the flux transfer events (FTE's) observed by ISEE satellites can be the result of multiple X‐line reconnection at the dayside magnetopause, which may be caused by the development of a tearing instability. In the presence of the y‐component of the magnetic field (By) in the transition region of the magnetopause, the tearing instability leads to the interconnection of the geomagnetic field lines and the interplanetary field lines, and hence to the occurrence of FTE's. Twisted field lines and field‐aligned currents are formed as a consequence of the tearing instability. The flow direction of the field‐aligned currents depends on By and the results are found to be consistent with satellite observations.
Magnetostratigraphy of the Red Sandstone Creek section ‐ Vail, Colorado
Authors: Miller John D. , Opdyke Neil D.
Published: February 2008

Samples for paleomagnetic study were collected from the area of Red Sandstone Creek (Lat. 39.73°N, Long. 253.6) near Vail, Colorado, in hopes of locating the stratigraphic base of the Kiaman Reversed Interval to within a few meters. Previous workers had sampled the same upper Pennsylvanian and Permian Minturn and Maroon Formations in this section and had placed the base of the Kiaman at 91m to 213m above the Minturn Formation. The interval from 276m below to 420m above the Maroon/Minturn contact was sampled in the present study at one meter intervals where possible. Of the 171 samples collected, only 2 had near normal components. The 2 were not consecutive and the normal components were removed easily by thermal cleaning or were shown to be a viscous overprint of the present field. The previous workers were apparently misled by a lack of magnetic cleaning of their samples. The conclusion of this study is that the base of the Kiaman must be stratigraphically lower in this section. The pole position from the sampled section is Lat. 42.6°N, Long. 115.4°E, A95=2.75 for N=145 samples.
Configuration of the high‐latitude thermosphere neutral circulation for IMF By negative and positive
Authors: McCormac F. G. , Killeen T. L. , Gombosi E. , Hays P. B. , Spencer N. W.
Published: February 2008

Measurements of the neutral wind in the polar F‐region from Dynamics Explorer‐2 (DE‐2) have been used to illustrate asymmetries in the Northern hemisphere neutral circulation that are dependent on the sign of the By (East‐West) component of the interplanetary magnetic field (IMF). Individual DE‐2 orbits and averaged data sets from different Universal times are presented. The data are categorized according to the sign of the hourly averaged IMF By component measured by ISEE‐3 for the hour preceding the DE‐2 measurement. The major features observed are: 1), an asymmetry in the polar cap neutral flow velocity with the region of most rapid anti‐sunward flow shifting from the dawn‐side to the dusk‐side of the polar cap as By changes from positive to negative; 2), a shift in magnetic local time of the region of entry of neutral gas into the polar cap from a location on the dawn‐side of the noon‐midnight meridian for By positive to one more biased towards the dusk‐side for By negative; 3), an enhancement in the velocities associated with the dawn, anti‐clockwise neutral vortex for By negative relative to those observed for By positive. The By neutral wind asymmetries can be explained by similar asymmetries, previously observed, in the polar ion convection pattern. They imply a direct causal relationship between solar wind/magnetosphere coupling and neutral thermospheric dynamics.
Aftershock area expansion and mechanical heterogeneity of fault zone within subduction zones
Authors: Tajima Fumiko , Kanamori Hiroo
Published: February 2008

We investigate global variations in the pattern of aftershock area expansion associated with large subduction zone earthquakes. The expansion of aftershock areas with time is relatively small in the subduction zones of Alaska, the Aleutians, Mexico, and parts of the Kuriles and South America. These subduction zones are interpreted to be characterized by moderate to strong interplate coupling. In contrast, the extent of aftershock expansion is greater for events within the subduction zones of northeast Japan and western and south Pacific where interplate coupling is inferred to be weak. These results are interpreted in terms of an asperity model where a fault zone is represented by a distribution of strong spots (asperities) and weaker zones. The immediate aftershock area is assumed to extend over an area occupied by asperities, and the subsequent expansion to occur into the surrounding weaker zones. If large asperities abut each other on a fault plane, interplate coupling is strong and little expansion of aftershock area occurs. Smaller and more sparsely distributed asperities cause weak interplate coupling and significant expansion of aftershock area. Small and densely distributed asperities result in moderate interplate coupling and little aftershock expansion.
Significant unreported earthquakes in “aseismic” regions of the western Pacific
Authors: Walker Daniel A. , McCreery Charles S.
Published: February 2008

With data recorded by a deep‐ocean hydrophone array centrally located in the Northwestern Pacific Basin near Wake Island, significantly large earthquakes were found to have their epicenters within the interior of the Pacific plate. The signal/noise ratio of the largest is about 40/1 at a distance of 2268 km. Although all of these earthquakes were unreported in National Earthquake Information Service (NEIS) listings, comparisons with the Po/So phases of other earthquakes reported by NEIS indicate that these earthquakes could have body‐wave magnitudes in excess of 5.0.
Use of the PP phase to study the earthquake source
Authors: Lynnes Christopher S. , Ruff Larry J.
Published: February 2008

The space‐time history of the rupture process of a large earthquake can be determined from directivity analysis of source time functions deconvolved from long‐period P waves. However, such analysis requires a good azimuthal distribution of stations, which is often difficult to obtain. We have developed a method for deconvolution of long‐period PP waves which is useful for a distance range of 70° ‐ 123° and 145° ‐ 165°, thus increasing both the available data and the ray parameter aperture. The PP waveform is Hilbert transformed to remove the effect of the PP caustic and then deconvolved in the time domain. We have tested the method on the 2 July 1974 Kermadec event (Ms=7.2) and obtained nearly identical source time functions from P and PP waves.
The Black Mountain asperity: Seismic hazard of the southern San Francisco Peninsula, California
Authors: Scholz C. H.
Published: February 2008

Black Mountain, a 860 m high wedge of Franciscan formation mostly comprising basic‐ultrabasic rock SW of Palo Alto and just NE of the San Andreas fault, marks an abrupt bend in the fault at the northern end of a 100 km long segment of the fault that strikes 9° more E‐W than the fault to the north or south. It also bounds a marked change in the physiographic setting of the fault, which to the north follows a well developed linear fault valley and to the south follows a poorly defined topographic trace that traverses the rugged Santa Cruz Mountains. The bend at Black Mountain had a profound effect on the 1906 rupture: the 75 km section to the SE of this point slipped only 1‐1.4 m, as compared to the 2.5‐4 m typical of the rupture on the San Francisco Peninsula to the NW. This 75 km long slip deficit region from Black Mountain to San Juan Bautista, if ruptured in its entirety would produce a Ms=6.9 earthquake: the conditional probability of this rupturing in the near future is the highest of any section of the San Andreas fault except Parkfield. This earthquake would rupture 30 km farther northwest and be about 3 times larger than that previously proposed by others and this constitutes a greater risk to the southern San Francisco Peninsula than previously expected.
Discriminating intrinsic and apparent attenuation in layered rock
Authors: Menke William , Dubendorff Bruce
Published: February 2008

The spectra of normal incidence transmitted compressional and shear waves are inverted to yield intrinsic (frictional) and apparent (scattering) attenuation factors as a function of frequency. This inversion is made possible by the observation that, to a first approximation, scattering and intrinsic attenuation are additive [Spencer, 1982 and Richards and Menke, 1983]. Two additional assumptions are needed; that poisson's ratio is constant and that intrinsic attenuation is mainly due to shear. The technique is tested against numerical calculations, and is shown to work at least for wavelengths larger than the scale length of the layering. The inversion requires wide‐band observations and is quite sensitive to noise in the data.
Polyhedral modeling of the elastic properties of corundum (α‐Al2O3) and chrysoberyl (Al2BeO4)
Authors: Au Andrew Y. , Hazen Robert M.
Published: February 2008

Coordination polyhedra in a crystal structure are considered to be the structural units in a modified rigid‐ion model. In the polyhedral model the elastic constants of coordination polyhedra are used as input parameters to calculate the single‐crystal elastic constants of corundum and chrysoberyl. The average deviation of the calculated elastic constants from the measured elastic constants is within 6% for corundum and within 1% for chrysoberyl.

The corundum crystal structure is composed entirely of AlO6 octahedra, which are also major polyhedral constituents of the chrysoberyl crystal structure. The nonelectrostatic contribution of the bulk compressibility of an ideal (regular) AlO6 octahedron is found to be 10.5 ± 0.2 Mbar, an invariant in these two crystal structures. The polyhedral elastic constants and the associated perturbational parameters are not universal, however, as demonstrated in the two crystal structures studied.
Supersonic ion outflows in the polar magnetosphere via the geomagnetic spectrometer
Authors: Horwitz J. L. , Waite J. H. , Moore T. E.
Published: February 2008

Observations of ‘supersonic’ O+ outflows by DE‐1 in the polar magnetosphere are interpreted as a velocity‐filter effect resulting from the transport of these low‐energy ions from a horizontally narrow source associated with the polar cleft topside ionosphere into the polar cap magnetosphere. Under certain simplifying circumstances it is shown that the ‘Mach number’ for the flow is essentially a geometrically determined quantitity, approximately the ratio of the horizontal distance of the observation location to the source over the horizontal width of the source. A recently developed two‐dimensional kinetic model of ion transport in the polar magnetosphere is used to calculate distribution functions and the associated bulk flow parameters, and these calculated quantities are compared with measured flow parameters from DE‐1.
Measurements of formate and acetate in precipitation at Niwot Ridge and Boulder, Colorado
Authors: Norton Richard B.
Published: February 2008

Formate and acetate as well as other organic and inorganic anions have been measured in precipitation collected in Colorado at Niwot Ridge (a rural site) and Boulder (a suburban site). At both sites, the organic anion concentration is usually at least 20% of the nitrate concentration and occasionally exceeds the nitrate. Formate is the dominant organic anion measured with concentrations as large as 9 × 10−5 M occurring in summer rain showers. A variety of dicarboxylic anions are observed but their concentration is generally much less than formate. Correlation with nitrate suggests that the large values found for the organic anions results from anthropogenic pollution.
An analysis of earthquake focal depths in the southeastern U. S.
Authors: Bollinger G. A. , Chapman M. C. , Sibol M. S. , Costain J. K.
Published: February 2008

Seven years (1977‐84) of seismic network monitoring in the southeastern U. S. have resulted in a catalog of 255 earthquakes (0 ≤ M ≤ 4.2) with ERZ ≤ 5 km. Focal depths from the Valley & Ridge and Blue Ridge provinces (mean depth 12 km) were combined for analysis as were those for the Piedmont and Coastal Plain provinces (mean depth 8 km). The mean focal depths between these two regions are shown to be statistically different. The 90% depths of earthquakes are also very different between the regions, implying a difference in the depth to the brittle‐ductile transition. First order models of crustal rheology based on estimates of composition, temperature and strain‐rate, indicate that the observed differences in earthquake focal depths may reflect differences in strain‐rate and/or composition.
Ab initio structural and thermoelastic properties of orthorhombic MgSiO3 perovskite
Authors: Wolf George H. , Bukowinski Mark S. T.
Published: February 2008

We present results of an ab initio study of the structural and thermoelastic properties of orthorhombic (Pbnm) MgSiO3 perovskite as a function of temperature and pressure. Self‐consistent free energies are computed using quasiharmonic lattice dynamics with interatomic potentials derived from an electron‐gas formulation. At high temperatures the orthorhombic phase undergoes successive second‐order transitions to tetragonal and cubic phases. The transition temperatures increase with pressure such that the orthorhombic phase is stable throughout most of the lower mantle although the higher symmetry phases could occur near the top of the lower mantle. At zero pressure the calculated bulk modulus and thermal expansion are in excellent agreement with the available data. We find that for high‐temperature isotherms, a finite‐strain decompression of the high‐pressure equation of state of perovskite substantially overestimates its zero‐pressure density and bulk modulus; hence, constraints on the chemical composition of the lower mantle, based on a comparison of the decompressed seismological properties with zero‐pressure laboratory data may significantly overestimate the proportion of perovskite in the lower mantle.
Partial derivatives of the eigenfrequencies of a laterally heterogeneous Earth model
Authors: Tsuboi Seiji , Geller Robert J. , Morris Sandra P.
Published: February 2008

We present a scheme for calculating the partial derivatives of the earth's free oscillation eigenfrequencies with respect to changes in an arbitrary laterally heterogeneous starting model. Such partial derivatives have previously been calculated only with respect to laterally homogeneous models. Numerical tests of the accuracy of the partial derivatives are presented. By means of the scheme presented in this paper it now is possible to apply linearized inverse theory to data such as singlet frequencies or waveforms to obtain a new laterally heterogeneous model, recalculate the forward solution, determine a new set of partial derivatives and residuals, and repeat this cycle until convergence is obtained. It also becomes possible to use a variety of laterally heterogeneous starting models to eliminate possible artifacts due to the choice of the initial model.
An upper limit for the absorption cross section of the oxygen transition
Authors: Simonaitis R. , Leu M. T.
Published: February 2008

A search was made for absorption by O2(a¹Δg) in the wavelength region 190–290 nm. Measurements were done at 10 nm intervals with a grating spectrometer having a bandwidth of 9.0 nm. No absorption above the detection limit of 0.02–0.03% absorption could be observed for O2(a¹Δg) concentrations of (4–7) × 1015 cm−3. An upper limit of 8×10−22 cm² for the absorption cross section of O2(a¹Δg) in this wavelength region was calculated.
Further observations of space shuttle plasma‐electrodynamic effects from OSS‐1/STS‐3
Authors: Stone N. H. , Wright K. H. , Hwang K. S. , Samir U. , Murphy G. B. , Shawhan S. D.
Published: February 2008

Recent analyses of ion measurements obtained from the Differential Ion Flux Probe (DIFP) on the deployed Plasma Diagnostics Package (PDP) during the OSS‐1/STS‐3 mission have provided an additional insight into the plasma‐electrodynamics of the Space Shuttle Orbiter: (1) Measured ion flow directions and energies suggest that the disturbance created in the ionospheric plasma by the Shuttle Orbiter may be confined to an interaction region that extends on the order of 10 m in the forward direction and has a boundary thickness of about 2 m. (2) A correlation between the DIFP and pressure gauge measurements indicates a direct, local proportionality between the neutral gas and ion densities. (3) Preliminary results from a theoretical model of the possible interaction between measured secondary, high inclination ion streams and the ambient plasma indicate the generation of broad‐band electrostatic noise such as that observed by wave instruments on the PDP.
Comment on “Electric field evidence on the viscous interaction at the magnetopause”, by F. S. Mozer
Authors: Heikkila Walter J.
Published: February 2008

Mozer [1984] has published some ISEE‐1 data on the electric field in the magnetospheric equatorial plane which show a polarization of the low latitude boundary layer, consistent with tailward plasma flow. A reinterpretation of these data suggests that the potential difference may be typically 30 kV for the combined dawn and dusk layers, out of a total of 50‐60 kV across the polar cap. Therefore, the LLBL is at least as important as the competing process of magnetic reconnection.
Large amplitude, low frequency plasma fluctuations at comet Giacobini‐Zinner
Authors: Gosling J. T. , Asbridge J. R. , Bame S. J. , Thomsen M. F. , Zwickl R. D.
Published: February 2008

Very large amplitude fluctuations in electron density, temperature, and flow velocity were a prominent aspect of the solar wind interaction with comet Giacobini‐Zinner during the ICE encounter in September 1985. These fluctuations were detected at a distance of at least 9 × 105 km and grew in amplitude as ICE approached the comet, peaking in amplitude 6 × 104 km from closest approach. A typical period associated with the fluctuations was ∼2 min, which corresponds to a scale length in the solar wind frame of ∼5 × 104 km. For the most part these fluctuations appear to be a product of one or more plasma instabilities associated with the solar wind pick up of cometary ions.
Gas ionization induced by a high speed plasma injection in space
Authors: Sasaki S. , Kawashima N. , Kuriki K. , Yanagisawa M. , Obayashi T. , Roberts W. T. , Reasoner D. L. , Taylor W. W. L. , Williamson P. R. , Banks P. M. , Burch J. L.
Published: February 2008

Gas ionization induced by a fast plasma injection has been observed with the Space Experiments with Particle Accelerators (SEPAC) Experiment on Spacelab‐1. When an impulsive high‐density plasma was injected from the orbiter, waves near the lower‐hybrid frequency were enhanced, and the surrounding gas drifting with the orbiter was ionized for several tens of milliseconds after the plasma injection. The long‐duration gas ionization was observed only when the plasma flux incoming to the orbiter cargo bay and the orbital velocity perpendicular to the magnetic field were relatively large. This effect has been explained by the concept of critical velocity ionization (CVI) for the gas drifting with the orbiter, although the gas velocity perpendicular to the magnetic field was less than the Alfvén critical velocity.
The collisionless rings of Uranus
Authors: Michel F. Curtis
Published: February 2008

In light of the Voyager 2 mission, the ringlets of Uranus seem unlikely to be accompanied by the swarm of 10 to 18 "shepherding" satellites generally supposed. Consequently, coherent motion (i.e., bulk circulation) in the ringlets again deserves serious consideration. Moreover the radio occultation data show the rings to be composed of larger boulders but few of the small particles one would expect if these boulders bumped and ground against one another as they would have to if the motions were incoherent. Recent evidence that Neptune's ringlets may be incomplete arcs further points in this direction. Dense (‘liquid’) rings have been proposed by Borderies, Goldreich and Tremaine. We point out here that such rings would be essentially viscosity free if executing coherent circulation and hence endure for geologically long time scales.
Sea level time series in the equatorial Pacific from satellite altimetry
Authors: Miller Laury , Cheney Robert , Milbert Dennis
Published: February 2008

Geosat, a Navy satellite launched in March 1985, will provide the first long‐term, global altimeter data set. These observations will enable construction of monthly sea level maps of the equatorial Pacific, much like those presently derived from island tide gauges, but with greatly improved spatial resolution and coverage. During the first half of the Geosat mission, the satellite ground track will not repeat, requiring time series analyses to be based on altimetric height differences at crossover points. We have used the 3‐month Seasat data set in the equatorial Pacific to test the feasibility and accuracy of this procedure. Crossover differences were sorted into diamond‐shaped areas with zonal and meridional dimensions of 200 and 400 km, respectively. The sea level time series in each of these areas was then determined using objective analysis. These computations show agreement within 5 cm between altimeter and island tide gauge observations on time scales greater than 1 month. Using this technique, we propose to construct monthly maps of sea level variability in the equatorial Pacific for the duration of the Geosat mission (approximately 3 years).
Carrier mobility in the presence of dislocations?
Authors: Hirsch L. M. , Wang C.‐Y.
Published: February 2008

The influence of dislocations upon carrier mobility and diffusivity is studied through measurements of the electrical conductance of single crystals of olivine during creep deformation in the temperature range 1610‐1725 K, under controlled oxygen fugacity and under uniaxial stresses of 60 to 140 MPa. The results presented indicate that under the conditions examined here the generation and movement of dislocations and other defects associated with plastic deformation does not significantly affect the carrier concentration in olivine. One possible explanation of this conclusion may be that dislocation climb in our creep experiments is controlled by the diffusion of electrically neutral defects. In addition, the results indicate that the mobility of the defect responsible for conduction is not significantly perturbed by dislocation effects or that these effects do not exist.
A deep structural ridge beneath central India
Authors: Agrawal P. K. , Thakur N. K. , Negi J. G.
Published: February 2008

A joint‐inversion of magnetic satellite (MAGSAT) and free air gravity data has been conducted to quantitatively investigate the cause for Bouguer gravity anomaly over Central Indian plateaus and possible fold consequences beside Himalayan zone in the Indian sub‐continent due to collision between Indian and Eurasian plates. The appropriate inversion with 40 km crustal depth model has delineated after discriminating high density and magnetisation models, for the first time, about 1500 km long hidden ridge structure trending NW‐SE. The structure is parallel to Himalayan fold axis and the Indian Ocean ridge in the Arabian Sea. A quantitative relief model across a representative anomaly profile confirms the ridge structure with its highest point nearly 6 km higher than the surrounding crustal level in peninsular India. The ridge structure finds visible support from the astro‐geoidal contours.
Source characteristics of the 1985 Michoacan, Mexico Earthquake at periods of 1 to 30 seconds
Authors: Houston Heidi , Kanamori Hiroo
Published: February 2008

Source characteristics of the Sept. 19, 1985 Michoacan, Mexico earthquake and its aftershock on Sept. 21 were inferred from broadband and short‐period teleseismic GDSN records. We Fourier‐transformed the P waves, corrected for instrument response, attenuation, geometrical spreading, and radiation pattern (including the depth phases), and then averaged to obtain the teleseismic source spectrum from 1 to 30 s. The Michoacan source spectrum is enriched at 30 s and depleted at 1 to 10 s relative to an average source spectrum of large interplate subduction events. Source spectra for the Sept. 21 aftershock, 1981 Playa Azul, 1979 Petatlan, and 1978 Oaxaca events follow a trend similar to that of the 1985 Michoacan event. This spectral trend may characterize the Mexican subduction zone.

A station‐by‐station least‐squares inversion of the Michoacan earthquake records for the source time function yielded three source pulses, which we interpreted as events on the fault plane. The first two are similar in moment, and the third contains only 20% of the moment of the first. Directivity is evident in the timing. At each station, we measured the time differences between the pulses, and performed a least‐squares nonlinear estimation of the strike, distance, and time separation between the events to locate them relative to one another. The second event occurred 26 s after the first, and 82 km southeast of it, indicating southeastward rupture along the trench. The third event occurred 21 s after the second, and about 40 km seaward of it. The two large events are also seen in the near‐field strong motions.

The mainshock records, spectrum, and time functions contain less high frequency radiation than those of the 1985 Valparaiso, Chile earthquake. Apparently, the Michoacan earthquake ruptured two relatively smooth, strong patches which generated large 30 s waves, but small 1 to 10 s waves. Such behavior contrasts with the Valparaiso event which had a more complex rupture process and generated more 1 to 5 s energy. This difference is consistent with the higher near‐field accelerations recorded for the Valparaiso event.
Transverse acceleration of oxygen ions by electromagnetic ion cyclotron resonance with broad band left‐hand polarized waves
Authors: Chang Tom , Crew G. B. , Hershkowitz N. , Jasperse J. R. , Retterer J. M. , Winningham J. D.
Published: February 2008

Central plasma sheet (CPS) ion conies are oxygen dominated with peak energies ranging from tens to hundreds of eV centered around pitch‐angles between 115 and 130 degrees. Because of the lack of correlation between the CPS conics and the observed currents and/or electron beam‐like structures, it is not likely that all of these conies are generated by interactions with electrostatic ion cyclotron waves or lower hybrid waves. Instead, we suggest that the observed intense broad band electric field fluctuations in the frequency range between zero and a hundred Hz can be responsible for the transverse energization of the ions through cyclotron resonance heating with the left‐hand polarized electromagnetic waves. This process is much more efficient for heating the oxygen ions than hydrogen ions, thus providing a plausible explanation of the oxygen dominance in CPS conies. Simple algebraic expressions are given from which estimates of conic energy and pitch angle can be easily calculated. This suggested mechanism can also provide some preheating of the oxygen ions in the boundary plasma sheet (BPS) where discrete aurorae form.
Superparamagnetism in volcanic glasses of the KBS Tuff: Transmission electron microscopy and magnetic behavior
Authors: Schlinger Charles M. , Smith Rebecca M.
Published: February 2008

Volcanic glass separates (colorless to dark brown) from the KBS tuff of northern Kenya have been studied with a combination of transmission electron microscopy and low‐temperature ac susceptibility and dc magnetization experiments. The darker of these glasses exhibit classic superparamagnetic behavior, the origin of which lies in a spatially‐uniform precipitate of magnetite, which is present as ∼1% by weight in glass shards with the highest susceptibility. In any given glass separate (obtained by magnetic separation) this precipitate has a surprisingly narrow size distribution. A theory for the origin of the precipitate is nucleatation and growth in quenched glasses at temperatures of ∼1000‐1300°K; an experiment demonstrates the feasibility of this idea. These glasses provide us with a sample for experimental investigations of physical properties of naturally‐occurring dispersed magnetic phases at the lower limit of physical dimension that can be attained in the crystalline state.
Evidence for a latitudinal gradient of the cosmic ray intensity associated with a change in the tilt of the heliospheric current sheet
Authors: Christon S. P. , Stone E. C. , Hoeksema J. T.
Published: February 2008

Since mid‐1985, the average flux of >70 MeV/nucleon cosmic rays at Voyager 2 (r2∼17 AU, Θ2∼0°) has been ∼3‐5% greater than that at Voyager 1 (r1∼24 AU, Θ1∼26°N). This is the first direct observation over such a large radial range in which the galactic cosmic ray flux closer to the sun is higher than the flux farther from the sun for an extended period of time. This observation is consistent with the presence of a negative latitudinal gradient GΘ=−0.36 ± 0.05 (or −0.60 ± 0.08) %/deg, assuming a coexistent radial gradient Gr of 1 (or 2) %/AU. We suggest that the appearance of this persistent negative latitudinal gradient may be due to the abrupt, large decrease of the heliospheric current sheet tilt to ∼20° in early 1985.
Interplanetary field control of the location of the Venus bow shock: Evidence for comet‐like ion pickup
Authors: Alexander C. J. , Luhmann J. G. , Russell C. T.
Published: February 2008

The location of the Venus bow shock is found to be sensitive to both the angle of the interplanetary magnetic field (IMF) to the solar wind flow and the phase of the solar cycle. We attribute the former dependence to the effect of planetary ion pickup by the magnetosheath convection electric field analogous to cometary ion pickup by the solar wind electric field. We attribute the latter dependence to the solar‐cycle variation in the density of exospheric neutrals in the magnetosheath analogous to the cometary response to distance from the sun. We also find both a north‐south and a pole‐equator asymmetry in the location of the bow shock, controlled by the direction of the IMF in the plane perpendicular to the solar wind flow, for those data where the perpendicular component dominates. These observations suggest how the comet‐solar wind interaction should also respond to the combination of the IMF orientation and the intensity of the ionizing solar radiation.
Further evidence for lightning on Venus
Authors: Singh R. N. , Russell C. T.
Published: February 2008

Impulsive electrical signals at all frequencies recorded by the plasma wave instrument on Pioneer Venus are found to cluster around periapsis. The signals are strongest at 100 Hz and have a secondary peak at 5.4 kHz. These characteristics are consistent with generation by lightning in the Venus atmosphere and the direct propagation of whistler mode signals below the electron gyro frequency and the partial transmission of electromagnetic waves in the presence of electron density inhomogeneities above the electron gyro frequency. The scattering by electron density inhomogeneities may also weaken any correlation with surface topographical features. Thus, the source of these signals may either be intercloud lightning at high altitudes or lightning in volcanic plumes near the ground, despite the large scatter in inferred source locations.
Possible evidence of flux transfer events in the polar ionosphere
Authors: Lanzerotti L. J. , Lee L. C. , Maclennan C. G. , Wolfe A. , Medford L. V.
Published: February 2008

We present magnetic field data from the cusp‐latitude South Pole station that exhibit, under appropriate local time and interplanetary magnetic field conditions, the signature expected in the ionosphere from a flux transfer event (FTE) at the magnetopause. In particular, the model of multiple X‐line reconnection at the magnetopause predicts field‐aligned currents in helical flux tubes, with transverse magnetic fields propagating as Alfvén waves toward the ionosphere. The distinctive magnetic signature at a polar cap magnetic station, particularly in the vertical component, can be used to infer the signs of the Byand Bzcomponents of the interplanetary magnetic field.
Electromagnetic fluctuations in the vicinity of the magnetopause
Authors: Rezeau L. , Perraut S. , Roux A.
Published: February 2008

A detailed analysis of electromagnetic fluctuations recorded during several magnetopause and boundary layer crossings by the ESA GEOS‐2 geostationary spacecraft is presented. A high level of electromagnetic (δE/ δB ∼ VA) fluctuations in the ULF (0 ‐ 10 Hz) range is observed for each such crossing. The obtained frequency spectra are shown to fit with a power law B² ∼ f−α. The distribution of these α indexes is found to be narrow (standard deviation ≲ 0.25 for 0.5 ≤ f ≤ 11 Hz), with a peak value α ∼ 2.5 which does not depend on the direction with respect to the magnetic field. Data suggest that the magnetopause boundary layer is the source of these intense fluctuations.
Density fluctuations in the middle atmosphere over Fukuoka observed by an XeF Rayleigh lidar
Authors: Shibata Takashi , Fukuda Terunobu , Maeda Mitsuo
Published: February 2008

Rayleigh lidar observations of the molecule density in the upper stratosphere and the lower mesosphere using an XeF laser (351 and 353 nm) were made from April 1985 through March 1986, at Fukuoka, Japan (33.6°N, 130.4°E). The observed density profiles show the existence of waves with wavelengths around 10 km and downward phase velocities between about 0 and 1.2 km/h. In more than half of the cases, the induced wave periods are longer than the inertial period. Analysis shows that the zonal phase velocities of the waves go in the direction opposite to that of the background flow, at least in these cases. The phase velocity and amplitude of the waves show a semiannual variation. The height dependence of the averaged fluctuation amplitude indicates that the energy dissipation of the waves occurs in the observed altitude range.
October Antarctic temperature and total ozone trends from 1979‐1985
Authors: Newman Paul A. , Schoeberl Mark R.
Published: February 2008

The morphology of temperature trends in the south polar stratosphere from 1979‐1985 is detailed. A significant cooling has occurred in the stratosphere over this period. South polar October mean temperatures have declined 18°K at 24 km over the seven year period. A large fraction of this decline occurs as a result of including 1979 temperatures in the trend. The years 1979 and 1982 differ from other years in that they include large mid‐October wave events which produce significantly warmer polar temperatures. Nevertheless, a significant temperature decline has still occurred in the stratosphere even when the dynamically active years are not included. Comparing two relatively dynamically quiet years, 1980 and 1985, the largest temperature decrease in the 30 mb temperature field occurs not at the pole but in the sub‐polar temperature maximum centered near 60°S. The changes in temperature of both the maximum and the polar low regions correlate fairly well with total ozone changes observed by TOMS.
Some observations on the role of planetary waves in determining the spring time ozone distribution in the Antarctic
Authors: Chandra S. , McPeters R. D.
Published: February 2008

Ozone measurements from 1970 to 1984 from the Nimbus 4 backscattered ultraviolet (BUV) and the Nimbus 7 solar backscattered ultraviolet (SBUV) spectrometers show significant decrease in total ozone only after 1979. The downward trend is most apparent in October south of 70°S in the longitude zone 0° to 30°W where planetary wave activity is weak. Outside this longitude region, the trend in total Ozone is much smaller due to strong interannual variability of wave activity. This paper gives a phenomenological description of ozone depletion in the Antarctic region based on vertical advection and transient planetary waves.
Terrace width variations in complex lunar craters
Authors: Pearce Steven J. , Melosh H. J.
Published: February 2008

The widths of terrace structures in complex craters on the moon are compared to existing theoretical models of their origin. Terrace widths in an individual crater increase monotonically outward toward the crater rim. Similarly, the width W of the terraces lying closest to the rim of a crater of diameter D increases monotonically, obeying a least squares power law relation W(km) = 0.09D0.87(km). A simple model of slumping that ignores inertial forces and assumes a constant bedrock yield strength is in good agreement with the observations.
Normal amplitude brunhes paleosecular variation at low‐latitudes: A paleomagnetic record from the Trans‐Mexican Volcanic Belt
Authors: Herrero‐Bervera Emilio , Fucugauchi Jaime Urrutia , Del Pozzo Ana Lillian Martin , Böhnel Harald , Guerrero José
Published: February 2008

Ancient secular variation in Central Mexico was determined from paleomagnetic measurements on 45 independent lava flows ranging in age (14C and K‐Ar dates) from 2,500 to 580,000 years B.P. All the analyzed flows are characterized by a normal polarity placing them within the Brunhes Chron. The paleosecular variation analysis yielded an angular standard deviation from the field of an axial dipole of 15.3° with 95% confidence limits of 13.4° and 17.9°, and that of the corresponding Virtual Geomagnetic Poles (VGPs) of 13.9° with confidence limits of 12.1° and 16.1°. These values are in agreement with those predicted by most statistical models of secular variation, but divergent from those obtained from low latitudes (19°N) such as Hawaii and Pagan Is.
Stirring and mixing in the mantle by plate‐scale flow: Large persistent blobs and long tendrils coexist
Authors: Gurnis Michael
Published: February 2008

The stirring of a small, passive heterogeneity in an unsteady circulation is investigated by following the boundary of the heterogeneity; the circulation mimics features of plate‐scale flow. After initial release, the heterogeneity is stirred and subsequently consists of at least one large "blob" connected to long, but thin tendrils. Tendrils exponentially lengthen and exponentially thin with time, as predicted by a turbulent mixing law, but the width of blobs decays about 100 times more slowly. The blobs mix slowly because they are smaller than the scale of flow and are sheared and occasionally unmixed by the laminar flow within the interiors of convection cells. The decay time of 1 to 100 km sized heterogeneities is on the order of billions of years for whole‐mantle convection and thus is in accord with isotopic observations which indicate the mantle has chemical heterogeneities persisting for billions of years.