bluuebunny/crossref_metadata_2025 huggingface dataset:
Nature of electrical charge carriers in the Earth's lower mantle from laboratory measurements
Authors: Li Xiaoyuan , Jeanloz Raymond
Published: February 2004

Thermoelectric power measurements on a silicate‐perovskite and magnesiowüstite assemblage at lower‐mantle conditions [(Mg0.89Fe0.11)2SiO4 bulk composition at 48 GPa and temperatures up to 2500 K] yield a positive Seebeck coefficient, thus implying that the dominant charge carriers are positive and that electrons in the conduction band (intrinsic carriers) contribute little to the electrical conductivity. The present results suggest that electrical transport is likely dominated by extrinsic charge carriers throughout the entire mantle and, hence, the electrical conductivity can be a powerful tool for characterizing minor phases, impurities and defect states of the Earth's deep interior.
Signatures of the magnetotail neutral sheet
Authors: Wang Zuo‐Ding , Xu R.‐L.
Published: February 2004

The geometry and the magnetic field of the magnetotail neutral sheet at −4RE <X < −21RE are studied with ISEE‐2 magnetometer data. Neutral sheet crossings are determined using a local coordinate system. We show the position of the neutral sheet after the effect of tilt angle is removed, and construct a smooth model to fit it.
Vertical transport rates in the stratosphere in 1993 from observations or CO2, N2O and CH4
Authors: Wofsy Steven C. , Boering Kristie A. , Daube Bruce C. , McElroy Michael B. , Loewenstein Max , Podolske James R. , Elkins James W. , Dutton Geoffrey S. , Fahey David W.
Published: February 2004

Measurements of CO2, N2O and CH4 are analyzed to define hemispheric average vertical exchange rates in the lower stratosphere from November 1992 to October 1993. Effective vertical diffusion coefficients were small in summer, ≤ 1 m²s−1 at altitudes below 25 km; values were similar near the tropopause in winter, but increased markedly with altitude. The analysis suggests possibly longer residence times for exhaust from stratospheric aircraft, and more efficient transport from 20 km to the middle stratosphere, than predicted by many current models. Seasonally‐resolved measurements of stratospheric CO2 and N2O provide significant new constraints on rates for global‐scale vertical transport.
A flux rope followed by recurring encounters with traveling compression regions: GEOTAIL observations
Authors: Kawano H. , Yamamoto T. , Kokubun S. , Tsuruda K. , Lui A. T. Y. , Williams D. J. , Yumoto K. , Hayakawa H. , Nakamura M. , Okada T. , Matsuoka A. , Shiokawa K. , Nishida A.
Published: February 2004

This paper reports a peculiar series of events observed with Geotail on October 24, 1992 at X ≃ −80 RE. On this day a combination of a bipolar perturbation in By and a double‐peaked perturbation in Bz, signature of a flux rope, was observed. Following this flux rope, bipolar Bz events, identifiable as Traveling Compression Regions (TCRs), were recurrently observed. The axis of the flux rope was deduced to be field‐aligned. Energetic ions (electrons) streamed earthward (tailward) in the flux rope. During the TCRs, the E×B flow showed a bipolar north‐then‐south perturbation, consistent with expected lobe plasma motion. The TCRs corresponded to weak ground magnetic disturbances and Pi2 waves. The observations can be explained by a model in which quasi‐stagnant plasmoids (Nishida et al., 1986) are recurrently generated.
Statistical significance and pattern of extratropical QBO in column ozone
Authors: Yang Hu , Tung Ka Kit
Published: February 2004

Statistical tests are performed on 30 years (1957–1986) of Dobson station data. The triple‐period (30, 20, and 8.6 months) extratropical QBO signal in ozone is found to be statistically significant. Earlier tests, based on 9 years of TOMS data, gave ambiguous results. We further suggest an objective method of extracting ozone QBO signal in the extratropics using a linear regression model.
An examination of the total hydrogen budget of the lower stratosphere
Authors: Dessler A. E. , Weinstock E. M. , Hintsa E. J. , Anderson J. G. , Webster C. R. , May R. D. , Elkins J. W. , Dutton G. S.
Published: February 2004

We analyze the hydrogen budget of the lower stratosphere using simultaneous in situ measurements of northern hemispheric water vapor (H2O) and methane (CH4) obtained during the spring Stratospheric Photochemistry, Aerosols, and Dynamics Expedition (SPADE), as well as previously published in situ H2 data. Based on this data, we conclude that approximately two H2O molecules are produced for each CH4 molecule destroyed. This implies that H2 production from CH4 oxidation is balanced by H2 oxidation. The uncertainty in this analysis is greatly reduced by the use of multiple data sets. Additionally, we infer that, on an annual and global average, H2O enters the stratosphere with a mixing ratio of 4.2±0.5 ppmv, and that the quasi‐conserved quantity 2×[CH4] + [H2O] has a value of 7.6±0.6 ppmv in these northern hemisphere air parcels (where [ξ] denotes the mixing ratio of the constituent ξ).
Apparent removal of the transient tracer carbon tetrachloride from anoxic seawater
Authors: Krysell Mikael , Fogelqvist Elisabet , Tanhua Toste
Published: February 2004

Two chlorofluorocarbons (CFC‐11 and carbon tetrachloride, CCl4) widely used as tracers for dating water masses, were measured in the Gotland Basin of the Baltic Sea. At the time of the survey, the bottom water of the basin had remained stagnant for 15 years and anoxic for about the same period of time, and the concentrations of both CFC‐11 and CCl4 decrease dramatically with depth below the mixed layer. Furthermore, the ratio of CFC‐11 to CCl4 increases with depth under the mixed layer along with a steep decrease in oxygen concentration. This is contrary to what would be expected from the atmospheric histories. The most plausible explanation for this is that there is a mechanism whereby the CCl4 is removed from the water mass under anoxic and suboxic conditions.
Scaling of intraplate earthquake recurrence interval with fault length and implications for seismic hazard assessment
Authors: Marrett Randall
Published: February 2004

Consensus indicates that faults follow power‐law scaling, although significant uncertainty remains about the values of important parameters. Combining these scaling relationships with power‐law scaling relationships for earthquakes suggests that intraplate earthquake recurrence interval scales with fault length. Regional scaling data may be locally calibrated to yield a site‐specific seismic hazard assessment tool. Scaling data from small faults (those that do not span the seismogenic layer) suggest that recurrence interval varies as a negative power of fault length. Due to uncertainties regarding the recently recognized changes in scaling for large earthquakes, it is unclear whether recurrence interval varies as a negative or positive power of fault length for large faults (those that span the seismogenic layer). This question is of critical importance for seismic hazard assessment.
Multifractal characteristics of natural fracture apertures
Authors: Belfield William C.
Published: February 2004

Using information acquired from microscanner logs in horizontal boreholes, fracture apertures are shown to be characterized by multifractal scaling. A representative f‐α spectrum can be modeled using a multiplicative cascade based on a two‐scale Cantor set. The resulting cascade can be used to simulate fracture aperture distributions at any scale. When compared to well data, the simulations show good agreement with aperture sizes and reproduce the clustering commonly recognized in fracture networks.
The effects of changes in plate motions on the shape of the Marquesas Fracture Zone
Authors: Kuykendall Martha G. , Kruse Sarah E. , McNutt Marcia K.
Published: February 2004

The Marquesas fracture zone (MFZ), one of the great fracture zones that formed on the Pacific‐Farallon ridge system, shows dramatic variations in morphology along its strike that cannot be explained by models for lithospheric flexure in response to thermal stresses and differential subsidence. Marine geophysical data collected by the R/V Maurice Ewing in fall 1991 show that major structures in the MFZ can be correlated with changes in plate motions as the fracture zone formed. The western MFZ shows two significant changes in trend: at 209°E and at 224°E. The change in strike at 209°E records a reorientation that put the transform fault under compression and created a 100 km‐long sinuous ridge within the fracture zone. The change in plate motions at 224°E induced extension in the transform fault, creating three subparallel fracture zones. These results are in accord with observations of morphological changes observed at active transform faults and other fracture zones, and suggest that even relatively small changes (∼6°) in spreading direction can produce significant structures that are preserved in the fracture zone.
Development of improved space sampling strategies for ocean chemical properties: Total carbon dioxide and dissolved nitrate
Authors: Goyet Catherine , Davis Daniel , Peltzer Edward T. , Brewer Peter G.
Published: February 2004

Large‐scale ocean observing programs such as the Joint Global Ocean Flux Study (JGOFS) and the World Ocean Circulation Experiment (WOCE) today, must face the problem of designing an adequate sampling strategy. For ocean chemical variables, the goals and observing technologies are quite different from ocean physical variables (temperature, salinity, pressure). We have recently acquired data on the ocean CO2 properties on WOCE cruises P16c and P17c that are sufficiently dense to test for sampling redundancy. We use linear and quadratic interpolation methods on the sampled field to investigate what is the minimum number of samples required to define the deep ocean total inorganic carbon (TCO2) field within the limits of experimental accuracy (±4 µmol/kg). Within the limits of current measurements, these lines were oversampled in the deep ocean. Should the precision of the measurement be improved, then a denser sampling pattern may be desirable in the future. This approach rationalizes the efficient use of resources for field work and for estimating gridded TCO2 fields needed to constrain geochemical models.
Freezing temperatures of H2SO4/HNO3/H2O mixtures: Implications for polar stratospheric clouds
Authors: Song Naihui
Published: February 2004

The freezing temperatures of H2SO4/HNO3/H2O mixtures were systematically documented. Nitric acid was found to affect freezing significantly. Measurements show that nitric acid can cause substantial supercooling over a broad composition range. However, some ternary compositions, like to those in polar stratospheric clouds (PSCs), have high freezing temperatures. The freezing of PSC particles could be controlled by the temperature and vapor pressure of both nitric acid and water in a non‐linear way. Formation of polar stratospheric clouds may be forecasted on the basis of conditions of temperature and vapor contents of water and nitric acid.
Rock magnetism of deformed Upper Triassic limestones from the Lagonegro Basin (Southern Apennines, Italy)
Authors: Gialanella P. R. , Heller F. , Incoronato A.
Published: February 2004

The stable component of the natural remanent magnetization (NRM) of the Upper Triassic “Calcari con Selce” limestone formation at Marsico Nuovo (Lagonegro Basin, Southern Italy) has an inclination which is about 45° too steep for the expected paleogeographic position. In order to explain this abnormal magnetization direction, several rock magnetic properties such as the dependence of susceptibility on temperature and alternating field frequency, anisotropy of low field susceptibility, anisotropy of anhysteretic remanent magnetization (ARM) and characteristics of acquisition and thermal decay of isothermal remanent magnetization (IRM) have been investigated. Strong inverse fabrics of both susceptibility and ARM have been recognized, which are due to magnetite in the superparamagnetic state on the one hand and in the stable single domain grain size on the other hand. Although internal deformation in the investigated rocks has not been reported in the geological literature, this may be the cause of the observed anisotropies. The anisotropy is probably responsible for the anomalous NRM directions of these limestones.
The effect of ice particles on Thomson scattering from the polar summer mesopause region
Authors: Klostermeyer J.
Published: February 2004

In the polar summer mesopause, negatively charged ice particles probably occur forming clouds with a thickness of a few kilometers. It is assumed that colliding ice particles and neutral molecules behave like rigid elastic spheres. Then calculated Thomson scatter spectra have a narrow particle line in addition to the ion and electron lines. Least‐squares fits of theoretical autocorrelation functions to autocorrelation functions measured by the EISCAT 933‐MHz radar yield particle radii and concentrations of about 3 nm and 1010 m−3. These results support earlier suggestions that there is a large number of particles producing electron density depletions and a viscous‐convective subrange in the turbulence spectrum of the electrons.
New evidence for ozone depletion in the upper stratosphere
Authors: Claude H. , Schönenborn F. , Steinbrecht W. , Vandersee W.
Published: February 2004

Differential absorption lidar measurements at the Meteorological Observatory Hohenpeißenberg between 1987 and 1993 show a statistically significant ozone decrease between 32 and 42 km, peaking at about −1.7% per year at 39 km altitude. This depletion is higher than reported by SAGE II or SBUV, yet the Hohenpeißenberg data agree very well with the results from Umkehr measurements. The observed ozone trend is in the upper range of predictions from photochemical models (−0.5 to −1.5% per year), whereas SBUV and SAGE II results are close to the lower end of the simulations. The agreement with photochemical models indicates that the depletion is most likely caused by catalytic ozone destruction through anthropogenic chlorine.
Variation of spring climate in lower‐middle Yangtse River Valley and its relation with solar‐cycle length
Authors: Hameed Sultan , Gong Gaofa
Published: February 2004

The relatively large number of historical records originating from the area of the Middle and Lower Yangtse River Valley in the late Ming dynasty and the Qing dynasty allows an estimation of the long term fluctuations of phenological dates. Dates of blossoming of plants, found in personal diaries and other documents, and used in this reconstruction are available, with some gaps, for 1580–1920. Independent estimates of spring conditions during the 18th century using data on last day of snowfall, and during 20th and late 19th centuries using accumulated temperatures in Shanghai are also presented. The results show that the spring weather in this region was colder than present in the 17th century and during 1790–1820 and 1870–1920. Spring temperature warmer than the present prevailed during 1720–1770 and 1840–1860. This variation agrees in its broad outline with that of the solar cycle length presented by Friis‐Christensen and Lassen (1991).
Differences in recent ground surface warming in eastern and western Canada: Evidence from borehole temperatures
Authors: Wang Kelin , Lewis Trevor J. , Belton David S. , Shen Po‐Yu
Published: February 2004

Because of the perturbation caused by a recent climatic warming, most borehole temperature‐depth profiles in Canada show reduced or negative gradients at shallow depths. However, the onset time and magnitude of the warming are different in eastern and western (British Columbia and southern Yukon) Canada. We determined the average subsurface temperature perturbations associated with the recent warming from borehole data for 34 and 51, respectively, well distributed sites in these two regions of Canada. If the ground surface temperature is assumed to have increased linearly since an onset time, the results indicate that the ground surface has warmed by 1.5 K since the mid‐19th century in eastern Canada but only by 0.8 K since the late 19th century in British Columbia and southern Yukon.
On the physics of high altitude lightning
Authors: Milikh G. M , Papadopoulos K. , Chang C. L.
Published: February 2004

Past and recent observations indicate the presence of lightning at altitudes in excess of 30 km. The phenomenon is manifested as a high altitude optical flash, correlated with the presence of giant thunderstorms in the atmosphere below. This letter presents the first physical model of the process. The model is based on low frequency RF breakdown of the upper atmosphere, ignited by the upward propagating electromagnetic pulses due to conventional low altitude lightning. Horizontal intercloud lightning strokes form the optimal configuration. Horizontal lightning discharges with cloud‐to‐cloud moment charge ∼ 6,000–8,000 C‐km account for the observed level of optical emissions.
Near‐field deformation seen on distant broadband seismograms
Authors: Vidale John E. , Goes Saskia , Richards Paul G.
Published: February 2004

Although far‐field body waves and surface waves are widely recognized, the improvements in broadband networks now allow the measurement of “near‐field” deformation of large earthquakes at great distances. Near‐field motions have been recognized previously only in theory and in close‐in recordings of earthquakes. We show examples from two recent events. For the large deep event on June 9, 1994 in Bolivia, there is a clear offset after the arrival of the P wave that has the amplitude expected for the near‐field term. In the shallow September 2, 1992 Nicaragua earthquake, the very long‐period motion observed between the P and S waves has roughly the amplitude expected from near‐field terms. Such near‐field terms are insensitive to earth structure, but supply information on long‐period source processes, and their observation begins to close the gap between long‐period seismology and geodesy.
Preliminary analysis of long‐period basin response in the Los Angeles Region from the 1994 Northridge Earthquake
Authors: Graves Robert W.
Published: February 2004

Long‐period (1–10 sec) ground motions recorded in the Los Angeles basin region during the Northridge earthquake show complex waveforms, extended durations and multiple sets of arrivals which cannot be attributed solely to source processes or wave propagation within a plane‐layered medium. These features suggest a strong interaction between the propagating seismic wave field and the laterally varying subsurface geologic structure of this region. Recorded motions at a hard rock site in the Santa Monica Mountains (scrs) are smaller by nearly a factor of three in peak velocity compared to recordings at more distant sites in the adjacent, northwest portion of the Los Angeles basin. In addition, although the rock site recording has a relatively simple wave shape, the basin site recordings are dominated by late arriving, large amplitude pulses of energy. We interpret these arrivals to be surface waves, which are generated by body waves interacting with the thickening margin of the basin. A preliminary modeling analysis of these data indicates that a combination of both large‐scale (deep basin) and small‐scale (shallow micro‐basin) structures are needed to explain the observed responses.
Rayleigh lidar detection of aerosol echoes from noctilucent cloud altitudes at the Arctic Circle
Authors: Langer M. , Müller K. P. , Fricke K. H.
Published: February 2004

During 3 out of 16 observations runs in July and August 1993 the Rayleigh Lidar at the Andøya Rocket Range (69°N, 16°E) in Northern Norway detected aerosol echoes from noctilucent cloud altitudes on July 28, August 7, and August 9. The geometric elevation of the center of the Sun was from +1.3° to −4.5° during aerosol detection. These three events differed significantly in peak signal strength, altitude, cloud layer shape, altitude integrated signal, and temporal evolution. Aerosol echoes were seen from the altitude range 81 to 87 km. The strongest aerosol event showed a peak backscatter ratio of 240 at 83.2 km altitude equivalent to the molecular (Rayleigh) scattering signal from 41.5 km. The weakest event had a peak backscatter ratio of 7 at 84.8 km with a Rayleigh equivalent altitude of 73.3 km. The zenith optical thickness of the aerosol layers varied by approximately two orders of magnitude. Detection times ranged from longer than 5 hours to as short as 15 minutes. The temporal evolution during the events suggests that single clouds were drifting through the laser beam which has a diameter of approximately 4 m at 85 km altitude. All events occurred before local midnight and the gross temporal evolution is compatible with tidal models for the diurnal variation of the visibility in PMCs and NLCs although there is considerably more structure in the lidar data than predictable by such a model. The estimated zenith optical thickness is within the bounds of microphysical NLC models.
The Davy Crater Chain: Implications for tidal disruption in the Earth‐Moon System and elsewhere
Authors: Wichman R. W. , Wood C. A.
Published: February 2004

Linear crater chains on Ganymede and Callisto apparently provide an impact record of tidally disrupted bodies, like Comet Shoemaker‐Levy 9, at Jupiter. We propose that the Davy crater chain on the Earth's Moon records a similar tidal disruption event in the Earth‐Moon system. Most lunar crater chains result from either volcanism or secondary impacts, but the Davy chain differs in setting and appearance from these crater chains and instead shows morphologic similarities to the Jovian crater chains. While the Davy chain is much smaller than the Jovian crater chains, tidal disruption models indicate that this smaller size is consistent with the Earth's lower mass. The disruption models also indicate that most Earth‐crossing comets and asteroids are moving too fast for fragment dispersion before impact to produce the observed crater chain length. Thus, the Davy and Jovian crater chains apparently result from bodies with different orbital characteristics. In addition, the limited dispersion of high velocity fragments at the Moon suggests that crater chains may not form for all disruption events or on all planetary satellites. Based on modeled fragment dispersions elsewhere in the solar system, we suggest that similar crater chains may be present on Iapetus, and possibly on Titan, Titania or Oberon.
Special collection on the June 1993 volcanic eruption on the CoAxial segment, Juan de Fuca Ridge
Authors: Fox Christopher G.
Published: February 2004

The mid‐ocean ridge system is the primary site of oceanic crustal accretion and a major source of chemical/thermal flux from the Earth's interior to the hydrosphere. Although geological mapping, geophysical exploration, and hydrographie/chemical surveys have provided important insights into accretionary processes, until recently there has been no method of monitoring the dynamics of these systems over long periods and large areas. Insights into spreading center dynamics have depended on serendipitous discoveries of evidence of activity based on water column anomalies [Baker et al., 1987], bathymetric differences [Fox et al., 1992], or direct field observations [Haymon et al., 1993]. In situ instrumentation has been used to monitor dynamics at a few selected sites for long periods, but these instruments are generally unable to telemeter data in real time.
Tropospheric ozone trends over Canada: 1980–1993
Authors: Tarasick D. W. , Wardle D. I. , Kerr J. B. , Bellefleur J. J. , Davies J.
Published: February 2004

An analysis of ozone in the troposphere at five sites in Canada is presented, using ECC sonde data from 1980–1993. The entire data record has been carefully reexamined for quality, and where necessary reevaluated from the raw telemetry. Trend analysis is performed on both the raw and the corrected (normalized to the total ozone measurement) profiles. The correction factors are also examined for trends. Where required, the data are adjusted for diurnal variation introduced by changes in time of launch. We find statistically significant (2σ) decreases in concentration at all stations except Alert, and in most cases, at all levels, including the surface. The tropospheric trends we derive here are compared with corresponding lower stratospheric trends. Although the long‐term trends are similar, stratospheric variations on shorter time scales are not well‐correlated with those in the troposphere.
Analysis of German climatic variations during the period of instrumental record
Authors: Balling Robert C.
Published: February 2004

The purpose of this investigation is to characterize climatic changes that have occurred in Germany based on historical observational records. Analyses show that mean annual temperatures in Germany have warmed by 0.66°C over the past 140 years with most of this warming occurring during the low‐sun seasons and early in this century. Very long‐term records from three German stations, which are similar to long‐term data from surrounding stations, reveal no warming over the past 200+ years. All of the temperature records show the period near 1890 to be anomalously cool. As with many other parts of the world, the diurnal temperature range in Germany has declined slightly while precipitation totals and cloud cover have increased; precipitation and the diurnal temperature range have a strong and negative correlation over the period 1950–1989. Historical climatic variations in Germany generally are consistent with patterns found for other mid‐latitude locations around the world.
Observation of a mass independent oxygen isotopic composition in terrestrial stratospheric CO2, the link to ozone chemistry, and the possible occurrence in the Martian atmosphere
Authors: Thiemens Mark H. , Jackson Teresa L. , Brenninkmeijer Carl A. M.
Published: February 2004

Multi‐isotope (δ17O and δ18O) measurements of stratospheric CO2 and 14CO are reported. Samples were acquired from altitudes in excess of 11.5 km from Christchurch, New Zealand to the South Pole. A mass independent isotopic variation is observed in CO2, the magnitude of which correlates well with 14CO concentration, indicating a stratospheric source of the effect. The component arises from isotopic exchange between the product of O3 photolysis, O(¹D) and CO2 thus providing a unique measure of ozone photolysis and turnover. A similar process may occur in the Martian atmosphere, as suggested by water isotopic measurements from SNC meteorites.
Photoproduction of carbonyl sulfide in South Pacific Ocean waters as a function of irradiation wavelength
Authors: Weiss Peter S. , Andrews Steven S. , Johnson James E. , Zafiriou Oliver C.
Published: February 2004

Carbonyl sulfide (OCS) photoproduction rates were measured at selected wavelengths of ultraviolet light between 297 and 405 nm in sea water samples from the southern Pacific Ocean. Near‐surface and column production rate spectra for natural sunlit waters were calculated using sea‐surface sunlight data measured near the austral summer solstice. These plots show that photoproduction rates are at a maximum at 313 nm in tropical waters and at 336 nm in Antarctic waters. Tropical surface and column rates were found to be 68 pM/day and 360 nmol/m²/day, respectively, and Antarctic surface and column rates were found to be 101 pM/day and 620 nmol/m²/day, respectively. A high degree of variability was observed between photoproduction rates from different ocean regions, with coastal rates being the highest, suggesting that natural environmental variability is an important factor. Photoproduction rates at 297 nm were found to be constant at individual locations with increasing irradiation time. Relative photoproduction rates from this work are compared to previously measured rates from coastal sea water.
Continuous airborne measurements of gaseous formic and acetic acids over the western North Atlantic
Authors: Chapman E. G. , Kenny D. V. , Busness K. M. , Thorp J. M. , Spicer Chester W.
Published: February 2004

A tandem mass spectrometer modified for aircraft applications was used to measure gas‐phase formic and acetic acid mixing ratios over the western North Atlantic during late summer 1992. The sensitive, specific, and essentially real‐time measurements provided by the mass spectrometer allow a true spatial evaluation of these compounds in the study area. Formic and acetic acid mixing ratios showed substantial vertical variation, varying by factors of up to 13 and 6, respectively, within 2‐km profiles extending from the boundary layer into the free troposphere. Substantial horizontal variation was also observed at constant altitudes within both the boundary layer and free troposphere. Mixing ratios of the two acids were correlated (r²>0.70) throughout the study region.
Simulated annealing inversion of teleseismic P‐wave slowness and azimuth for crustal velocity structure at Long Valley Caldera
Authors: Steck Lee K.
Published: February 2004

Simulated annealing, a non‐linear global search algorithm, is used to invert teleseismic P‐wave slowness and azimuth data for crustal velocity structure. Synthetic tests show that simulated annealing is able to locate low P‐wave velocity zones with reasonable accuracy in space, and recovers almost 70% of the target velocity perturbations. Testing suggests that significant results can be obtained with as few as two stations. Inversion of ray direction data from Long Valley caldera finds an asymmetrical low velocity zone beneath the resurgent dome at 8km depth, having a perturbation of −25% from the background. This zone extends to the east and south to depths of at least 24km, with a perturbation of about −10%. These features generally agree with previous results from teleseismic travel‐time inversion and forward modeling of ray direction, and are probably associated with the residual Long Valley caldera magma chamber.
The trapped He flux dynamics observed on the OHZORA satellite during 1984–1987
Authors: Kohno T. , Gusev A. A. , Martin I. M. , Pugacheva G. I.
Published: February 2004

The results of observations of spatial distribution and dynamics of trapped He fluxes with the energy 3.2‐9.2 MeV/nuc obtained by low altitude Japanese OHZORA satellite are reported. Transient trapped He fluxes associated with solar and magnetospheric activity were observed at low altitudes in the region of L=2.0‐3.0. Possible sources of the fluxes including remnants of solar particle population trapped during substorms, acceleration of hot plasma from the outer magnetosphere, and pitch‐angle scattering from the top of the magnetic field line are discussed.
CO2and radon measurements in the Vogtland Area (Germany) ‐ A contribution to earthquake prediction research
Authors: Heinicke J. , Koch U. , Martinelli G.
Published: February 2004

The interpretation of long term radon measure‐ments in a spring located in Vogtland shows a significant relationship to the seismicity of a region close to the sampling point. A statistical check was performed in order to identify the anomaly‐generating area. The cause for this relation is emission of mantle originated gases (including CO2) influenced by tectonic processes in the crust.
Resonant amplification of magnetosheath MHD fluctuations at the magnetopause
Authors: Belmont Gérard , Reberac Fabien , Rezeau Laurence
Published: February 2004

Broad‐band ULF fluctuations are routinely observed upstream of the terrestrial magnetosphere: their amplitude, fairly large in the whole magnetosheath, peaks at the magnetopause, and decays to very small values in the magnetosphere. We test the idea that the source of all these fluctuations is in the magnetosheath and that the high magnetopause level is an amplification effect due to propagation. Starting from given stable magnetosonic waves in the magnetosheath, their behaviour is calculated when, during their propagation, they encounter the magnetopause density gradient. For a certain category of incident waves, a “resonant amplification”, occurring inside the gradient layer, is found.
Teleseismic P‐wave image of crust and upper mantle structure beneath the Valles Caldera, New Mexico: Initial Results from the 1993 JTEX Passive Array
Authors: Lutter William J. , Roberts Peter M. , Thurber Clifford H. , Steck Lee , Fehler Michael C. , Stafford Darrik G. , Baldridge W. Scott , Zeichert Timothy A.
Published: February 2004

Teleseismic P‐wave relative arrival‐time data, collected from a temporary array during the 1993 Jemez Tomography Experiment (JTEX), have been inverted to image velocity anomalies beneath the Valles caldera in northern New Mexico. Instruments were deployed in two 30‐km‐long profiles, one of 8 and one of 9 stations. These profiles crossed the caldera trending at azimuths of N46°W and N60°E, respectively. Two‐dimensional teleseismic relative arrival time inversion of the 1993 data set, supplemented with data from an overlapping 1987 profile, confirms the existence of a mid‐crustal low velocity region (‐30%) beneath the Valles caldera in the depth range of 8 to 13 km (below sea level), with about a 6 km horizontal extent. This feature is interpreted to be the seismic expression of the remnant magma chamber. A shallow low velocity anomaly beneath San Antonio Mountain coincides with the region of highest thermal gradient values in the caldera. A lower crust/upper mantle low velocity anomaly is imaged but is not as well constrained due to the limited length of the profile. We tentatively correlate this anomaly with the thermal effects of basaltic magmas ponded at the crust‐mantle boundary.
Reshaping spectrum estimates by removing periodic noise: Application to seismic spectral ratios
Authors: Lees Jonathan M.
Published: February 2004

An automated method for removing line spectrum elements embedded in colored spectra is presented. Since smooth spectrum estimates are desired, line spectra tend to smear out over an effective smoothing window. This introduces a bias in spectrum estimation that seriously degrades signal‐to‐noise ratios, spectral deconvolution or any other operation where spectrum shape is important. Multi‐taper analysis provides a simple algorithmic solution including a method of determining where spectral peaks are both significant with high power. The method is completely general, and examples include estimation of signal‐to‐noise ratio at the 1990 high frequency array, Pinyon Flat, CA. A comparison of noise spectra line segments and signal spectra line spectra reveals similarities associated with instrument noise and shallow resonances stimulated by incoming seismic signals. Identification and removal of resonances can provide a better means of estimating background noise spectra for modeling earthquake source spectra and path effects associated with attenuation.
Elliptically polarized bursty radio emissions from Jupiter
Authors: Reiner M. J. , Desch M. D. , Kaiser M. L. , Manning R. , Fainberg J. , Stone R. G.
Published: February 2004

We report a new component of Jovian radio emission observed by the Ulysses spacecraft when Ulysses was at high Jovigraphic latitudes (≳30° north or south of the Jovian magnetic equator). This bursty high‐latitude emission is elliptically polarized in the right‐hand sense when observed from northern latitudes and in the left‐hand sense when observed from southern latitudes, consistent with extraordinary mode. The orientation of the polarization ellipse is observed to systematically vary with time relative to the observer. It is argued that the elliptically‐polarized nature of the emission is intrinsic to the source region.
Shear‐wave splitting from local earthquakes at the Geysers Geothermal Field, California
Authors: Evans John R. , Julian Bruce R. , Foulger G. R. , Ross Alwyn
Published: February 2004

Shear‐wave splitting from local microearth‐quakes recorded in The Geysers geothermal field shows that seismic anisotropy is distributed in a complex geographic pattern. At stations within about 2 km of northwest‐striking regional faults, the fast polarization direction is parallel to those faults. The geothermal field, lying between two such faults, has both northwest and northeast fast polarization directions, often at the same station. This pattern suggests at least two causes of splitting: (1) extensive dilatancy anisotropy (EDA) and (2) fault‐produced fractures or rock fabric. The observed anisotropy may derive from the upper 1.5 km of the crust, averaging 4% there, or it may be heterogeneously distributed throughout the upper 5 km. Fast polarization directions coincide with fracture directions inferred from borehole data for one of the youngest rock types in the region, a felsite pluton of about 1 Ma, and with injectate pathways inferred from microseismicity and geochemistry. Including in reservoir models a permeability anisotropy with a pattern similar to seismic anisotropy may help in optimizing fluid injection and steam recovery.
Transient electrical response of San Quintin Dunite as a function of oxygen fugacity changes: Information about charge carriers
Authors: Roberts Jeffery J. , Duba Alfred G.
Published: February 2004

The electrical conductivity (σ) of San Quintin dunite (SQD) measured between 950 and 1150°C at controlled oxygen fugacity (fO2) within the olivine stability field shows transients in response to changes in fO2. Such behavior has not been reported previously for measurements made under similar conditions on either olivine single crystals or polycrystalline samples (dunites and lherzolites) in which olivine is the major phase. In general for olivine, an increase in fO2 results in an increase in σ. The transient is manifested as a change in σ from a stable equilibrium value at a specific fO2 to a quickly established subsequent value, the direction of which is opposite that of the final value that will be attained for the fO2 change. This transient may be caused by a changing population of electrons produced by oxygen vacancies, the grain boundaries, or a short‐lived defect. We postulate that the transient is observed in this particular dunite because of its large surface area to volume ratio. The transient is more pronounced at relatively high fO23 and temperatures between 950 and 1100°C. At relatively low fO2s and temperatures higher than 1100°C, the effect is diminished. The Seebeck coefficient (S), at 1200°C, is slightly smaller than that reported for single‐crystal olivine, and at 1100°C is similar to that reported for single crystal olivine.
Heterogeneous chemistry of bromine species in sulfuric acid under stratospheric conditions
Authors: Hanson D. R. , Ravishankara A. R.
Published: February 2004

The first‐order loss rate coefficients for BrONO2 on 45, 60, and 70 wt% sulfuric acid solutions were measured in a wetted‐wall flow tube reactor. The BrONO2 reactive uptake coefficients were >0.2 and HOBr was the product. When HCl was added to the acid, production of HOBr was still observed but the main product was BrCl. Based on these observations it is concluded that the conversion of BrONO2 to active forms such as HOBr and BrCl on sulfate aerosols in the stratosphere is very rapid. The efficiency of the hydrolysis of BrONO2 suggests that, even for non‐volcanic conditions, much of the BrONO2 in the stratosphere can be converted to HOBr at night.
Energization of ions in near‐Earth current sheet disruptions
Authors: Taktakishvili A. , Lopez R. E. , Goodrich C. C.
Published: February 2004

In this study we examine observations made by AMPTE/CCE of energetic ion bursts during seven substorm periods when the satellite was located near the neutral sheet, and CCE observed the disruption cross‐tail current in situ. We compare ion observations to analytic calculations of particle acceleration. We find that the acceleration region size, which we assume to be essentially the current disruption region, to be on the order of 1 RE. Events exhibiting weak acceleration had either relatively small acceleration regions (apparently associated with pseudobreakup activity on the ground) or relatively small changes in the local magnetic field (suggesting that the magnitude of the local current disruption was limited). These results add additional support for the view that the particle bursts observed during turbulent current sheet disruptions are due to inductive acceleration of ions.
Melting and phase transitions of RbCl to 10 kilobars
Authors: Morse S. A. , Yoder H. S.
Published: February 2004

Melting determinations on spectrographic grade RbCl by differential thermal analysis in an internally‐heated, gas‐media apparatus gave the following constants for the Simon equation, P − Po = A[(T/To)c−1] (bars, Kelvin). For RbClI=L, Po = 1, To = 993.45, A = 8122, c = 5.02, sd = 0.5 K. For RbClII = L, Po = 7750, To = 1131.15, A = 5061, c = 6.40, sd = 1.0 K. The solid‐solid transition RbClI=II determined by DTA is described by P = 4490 + T/0.35. The best‐fit triple point lies on a liquidus cusp at 1134 K, 7790 b. The results for melting are 3–7 K higher than earlier results. The new determinations are useful in the calibration of experimental apparatus at moderate pressure. They confirm that temperature calibration cannot explain divergent liquidus determinations for the system Ab‐H2O.
High‐pressure acoustic wave velocities and equations of state of the alkali chlorides
Authors: Campbell Andrew J. , Heinz Dion L.
Published: February 2004

Acoustic wave velocities have been measured in RbCl and CsCl to 17 GPa. The congressional wave velocities vary with density as VP (km/s) = 3.4143 (84) + 1.368 (11) Δρ for the high‐pressure phase of RbCl and VP (km/s) = 2.8247 (57) + 1.1469 (77) Δρ for CsCl (numbers in parentheses indicate uncertainties on the last digit). The equations of state of RbCl and CsCl have also been determined at room temperature to ∼30 GPa. Eulerian finite strain equation of state parameters are ρ02 = 3.3068 (10) Mg m−3, K0T = 17.9 (10) GPa and K0T′ = 5.23 (29) for RbCl in the B2 structure, and K0T = 17.01 (29) GPa and K0T′ = 5.49 (15) for CsCl. The accumulated set of data for the alkali chlorides under high pressure is used to test several empirical relations between velocity and density. A simple logarithmic relation is shown to allow the most accurate extrapolation from low‐pressure velocity data. Gruneisen's parameters are also calculated from the velocity and density data, allowing a complete thermal equation of state to be developed for the alkali chlorides.
Topography and subduction geometry in the central Andes: Clues to the mechanics of a noncollisional orogen
Authors: Gephart John W.
Published: February 2004

The central Andean orogen between 12° and 32°S latitude exhibits a high degree of spatial order: principally an extraordinary bilateral symmetry that is common to the Earth's surface, the underlying Wadati‐Benioff zone, and the Nazca/South America plate kinematics, which has been stable since the mid‐Tertiary. This spatial order must reflect the physical mechanisms of mountain building in this noncollisional orogen. The shapes of the topography and subduction zone can be reduced to symmetric and antisymmeric components relative to any vertical symmetry plane; the particular plane which minimizes the antisymmetry (and maximizes the symmetry) is well‐resolved and is essentially coincident with the stable Euler equator of Nazca/South America relative motion since the mid‐Tertiary. That the topography, subduction geometry, and persistent mid‐Tertiary plate kinematics share common spatial and geometric elements suggests that the distribution of topography in this orogen depends strongly on the dynamics of subduction. Other factors that might affect the topography and underlying tectonics, such as climate and inherited structural fabric, which have different spatial characteristics, must be of less significance at a continental scale. Furthermore, the small components of asymmetry among the various elements of the orogen appear to be mutually related in a simple way; it is possible that this coupled asymmetry is associated with a late Tertiary change in plate kinematics. These observations suggest that there is a close connection between plate tectonics and the form of the Earth's surface in this noncollisional setting. It follows that the distribution of topography near convergent plate boundaries may provide a powerful constraint for understanding the dynamics of subduction.
Thermal and geochemical evolution of the mantle wedge in the northeast Japan arc: 2. Contribution from geochemistry
Authors: Yamashita Shigeru , Tatsumi Yoshiyuki
Published: February 2004

Compositions of primary basalt magmas were backcalculated from Miocene Mg‐rich basalts in the Japan Sea back arc basin and the NE Japanese volcanic front, in order to assess the spatial variation in physicochemical conditions for magma production during opening of the back arc basin. Chemical compositions of these magmas together with available liquidus experimental data suggest that the primary basalt magmas both in the Japan Sea (BABB magma) and the NE Japanese volcanic front (VFB magma) were equilibrated with harzburgitic mantle materials at almost identical pressure and temperature conditions. The observation that the BABB magma is more depleted in Fe and some incompatibje trace elements and more enriched in Al than the VFB magma then suggests that these magmas may have been derived from source mantle materials with different chemical compositions. An equilibrium melting model further demonstrates that the BABB magma was produced by a smaller degree of partial melting of a more depleted source mantle material (compositional equivalent to abyssal harzburgites) than the VFB magma. Provided that the varying degrees of depletion in the source mantle materials were manifestations of mantle upwelling efficient beneath the back arc side region, the more depleted BABB magma source may have been a plausible geochemical reservoir in the deeper portion of the mantle wedge.
Thermal and geochemical evolution of the mantle wedge in the northeast Japan arc: 1. Contribution from experimental petrology
Authors: Tatsumi Yoshiyuki , Furukawa Yoshitsugu , Yamashita Shigeru
Published: February 2004

Melting phase relations at high pressures have been examined for four Mg‐rich basalts from both the trench and the backarc sides of the Miocene NE Japan arc. All these basalts crystallize olivine and orthopyroxene on the liquidus at pressures lower and higher than the point of multiple saturation with those two phases, respectively. The pressure of multiple saturation is rather constant for all samples (1.0–1.4 GPa), suggesting that (1) there was no across‐arc variation in the depth of magma segregation in the Miocene NE Japan arc, (2) the depth of magma segregation remains constant since 20 Ma in the trench side of the volcanic arc, whereas it has changed from 30–40 km to >60 km beneath the backarc side of the arc. This temporal variation may be caused by increasing thickness of the lithosphere beneath the backarc region associated with cooling of the mantle wedge after the opening of the Japan Sea backarc basin in the early Miocene.