bluuebunny/crossref_metadata_2025 huggingface dataset:
Worldwide character of the 1991 geomagnetic jerk
Authors: De Michelis P. , Cafarella L. , Meloni A.
Published: February 2004

A recent examination of the geomagnetic element annual mean values for the European magnetic observatories, has shown the existence of a sudden change in the secular acceleration at about 1991. In this work the space time character of the 1991 impulse is investigated and its worldwide character is evidenced; an evaluation of the amplitude spatial distribution is given for the Y component, analysing data relative to 74 magnetic observatories. The external effects were removed from the annual mean data and successively the Y secular variation has been evaluated from the corrected annual means. Moreover the worldwide character of the intensity of the step in the second time derivative is compared with the character of the previous well known jerk events of 1969 and 1978.
Thermal stress evolution in cooling pluton environments of different geometries
Authors: Bergbauer Stephan , Martel Stephen J. , Hieronymus Christoph F.
Published: February 2004

Thermoelastic displacement potentials and fast Fourier transforms can be combined to rapidly calculate the thermal stresses in 2‐D for plutons that cool by conduction. First, temperature distributions over time are computed by solving the diffusion equation. Thermal stresses are then obtained using thermoelastic stress potentials. This method can be applied to a broad range of pluton geometries and initial conditions, and requires far less computation time than finite difference or finite element analyses. Results of 2‐D analyses show that pluton geometry strongly influences the thermal stresses that occur in a cooling pluton. Thermal stresses of several tens of MPa arise during cooling and are highest at the corners or where the intrusion is thin. The most tensile stress is greater inside a pluton than in the host rock. Moreover, the orientation of the most tensile stress in a cooling pluton generally changes over time. This could result in multiple fracture sets, which would significantly affect the mechanical and hydraulic behavior of a pluton.
Apportionment of light scattering and hygroscopic growth to aerosol composition
Authors: McInnes Lynn , Bergin Mike , Ogren John , Schwartz Stephen
Published: February 2004

During a recent campaign at the NOAA CMDL monitoring station on Sable Island, Canada (43.93° N, 60.01° W) a dual‐nephelometer humidigraph measured the hygroscopic growth factor of aerosol scattering, fRH(σsp), one of the key parameters necessary for estimating short‐wave aerosol radiative forcing. Measurements revealed less growth for anthropogenically influenced aerosols than for marine, fRH(σsp) of 1.7 ±0.1 vs. 2.7 ± 0.4, where fRH(σsp) = σsp(85%)/ σsp(40%). A combined measurement‐modeling approach was used to estimate σsp; and its RH‐dependence, based on the measured particle size distribution and composition. The model suggested that differences in the particle size distribution, assuming the same aerosol composition, could not explain the observed differences in fRH(σsp). We have confirmed with individual particle analysis, that aerosol composition was indeed responsible for the difference in fRH(σsp). As well, the scattering contribution of organic carbon for the influenced case is at least as much as sulfate aerosol.
Continuous GPS measurements of contemporary deformation across the Northern Basin and Range Province
Authors: Bennett R. A. , Wernicke B. P. , Davis J. L.
Published: February 2004

We have acquired and analyzed data from the northern Basin and Range (NBAR) continuous GPS network since July 1996. The RMS residual with respect to the best fitting lines through the individual station position estimates is 2–3 mm in the horizontal and 6–10 mm in the vertical. After the first 395 days of operation, uncertainties in horizontal velocity estimates are 1–2 mm/yr (1‐σ). Relative motion among NBAR sites located in eastern Nevada and in Utah is small, but east‐west extension is significant assuming uniform strain accumulation across the whole network. The relative motion observed across the Wasatch fault zone is 2 ±2 mm/yr, east‐west. Relative motions among stations in western Nevada and California, in contrast, are dominated by northwest, right‐lateral shear. We infer an integrated deformation across the northern Basin and Range of 11 ± 2 mm/yr, northwest. These rates are consistent with previous geodetic measurements. Our GPS velocity estimates, however, reveal a possibly abrupt transition from east‐west extension in eastern Nevada and Utah to right‐lateral shear in western Nevada. This transition is roughly coincident with the central Nevada seismic belt and is consistent with the right‐oblique focal mechanisms of the 1954 Dixie Valley and Fairview Peak earthquakes. The transition also appears to correlate spatially with a transition in upper mantle structure.
Evidence for an anisotropic lower mantle beneath eastern Asia: Comparison of shear‐wave splitting data of SKS and P660s
Authors: Iidaka Takashi , Niu Fenglin
Published: February 2004

Anisotropy in the lower mantle is studied by measuring the difference of the splitting parameter τ (the delay time between two split shear‐waves) between the two phases SKS and P660s. These two phases are the P‐to‐S conversion waves at the CMB and the 660‐km discontinuity, and therefore are affected by the accumulated anisotropy of whole and upper mantle, respectively. An approximately 0.4 sec time difference of τ value between SKS and P660s is observed at the station HIA, a CDSN broadband seismic station located in central China. This difference is supposed to be caused by the accumulated anisotropy in the lower mantle beneath the eastern Asia region. If the anisotropy is assumed to be distributed uniformly in the whole lower mantle or a lowermost 300‐km D” layer, the resulted anisotropy will be 0.08% and 0.5%, respectively. However, the real intensity of the existing anisotropy in the studied region may be much larger than the above values, depending on its size and location in the lower mantle.
Open system behavior of helium in case of the HIMU source area
Authors: Hanyu Takeshi , Kaneoka Ichiro
Published: February 2004

Lower ³He/4He than that of mid‐ocean ridge basalts (MORBs) observed in HIMU‐ocean island basalts (OIBs) has been considered to be the evidence that the HIMU source is related to recycled materials. However, typical ³He/4He value of Polynesian HIMU‐OIBs (∼6.8 RA) is too high to be explained by addition of in situ radiogenic 4He in the recycled oceanic crust. Mixing of the upper mantle material with the recycled oceanic crust cannot explain ³He/4He of HIMU‐OIBs as revealed from mixing calculation in the He‐Pb isotope system. As another possibility, if we assume that large mobility of helium affects ³He/4He of recycled materials, the model calculation indicates that the balance between radiogenic 4He production in the recycled oceanic crust and diffusive loss of 4He to the surrounding mantle accounts for ³He/4He of HIMU. The model suggests the thickness of HIMU source body to be in the order of 1 km.
Comparison of AKR simultaneously observed by the GEOTAIL and WIND spacecraft
Authors: Hashimoto K. , Matsumoto H. , Murata T. , Kaiser M. L. , Bougeret J.‐L.
Published: February 2004

AKR dynamic spectra observed with the GEOTAIL Plasma Wave Instrument (PWI) and the WIND WAVES investigation are compared. GEOTAIL was in the near earth orbit of 10 ‐ 50 RE until February and 10 ‐ 30 RE after March 1995. WIND was in near‐earth orbits of a few to 75 RE in November–December 1994, and was mainly in a ‘halo’ orbit of about 200 RE between Earth and the sun in 1995. The comparison is made for the following two cases, (a) both satellites are in the near‐earth orbits, and (b) when GEOTAIL was in the near‐earth orbits and WIND was in the ‘halo’ orbit. The observations are compared with ray tracing to explain the results. Most observations are explained in terms of AKR source locations around 21‐22 MLT, but some cannot be explained unless the source locations are assumed to be extended to around 19 MLT during substorms.
Model of field aligned potential drops near Io
Authors: Cheng A. F. , Paranicas C.
Published: February 2004

The Galileo spacecraft passed through an unexpectedly dense plasma and mass loading region near Io closest approach. This paper shows how the prodigious mass loading observed in this region can produce field‐aligned potential drops. For parameters appropriate to Io and consistent with Galileo measurements, this mechanism is shown to support up to two hundred volt, field‐aligned potential drops near Io and field‐aligned electron beams. The total power in these electron beams is less than ∼4×108 W, a small fraction of the total energy requirement for maintaining torus ultraviolet emissions. This mechanism may nevertheless be important for the Jupiter‐Io interaction, because it injects a seed population of energized electrons and ions into the Io flux tube with hundred volt parallel energies. A two step acceleration process may operate in the Io flux tube, in which a seed population of electrons with parallel energies above an eV is created, followed by field‐aligned acceleration in the Alfven wings.
Thickness of a submarine lava flow determined from near‐bottom magnetic field mapping by autonomous underwater vehicle
Authors: Tivey Maurice A. , Johnson H. Paul , Bradley Albert , Yoerger Dana
Published: February 2004

Magnetic field surveys obtained near the seafloor can map the boundaries of recent volcanic eruptions and can provide thickness estimates of these lava flow units independent of bathymetry differencing methods. Magnetic thickness estimation requires knowledge of the intensity of magnetization of the new lava and surrounding terrain, but this can be satisfactorily obtained by representative sampling of the various volcanic units. While bathymetry differencing requires pre‐existing data to assess the thickness of new lava eruptions, magnetic surveys can be obtained after an eruption has occurred. In this study, near‐bottom magnetic surveys were obtained using an autonomous underwater vehicle (AUV), which operates without a tether or human intervention. AUV technology offers rapid deployment and an efficient surveying approach for remotely mapping recent lava eruption sites on the seafloor.
Distribution of Atlantic and Pacific waters in the upper Arctic Ocean: Implications for circulation
Authors: Jones E. Peter , Anderson Leif G. , Swift James H.
Published: February 2004

The Atlantic and Pacific oceans provide source waters for the Arctic Ocean that can be distinguished by their differing nitrate and phosphate concentration relationships. Using these relationships, we estimate the amount of Atlantic and Pacific waters in the surface layer (top 30 m) of the Arctic Ocean. Atlantic source water is dominant in most of the Eurasian Basin and is present in significant amounts in the Makarov Basin north of the East Siberian Sea. Pacific source water is dominant in most of the Canadian Basin and is present in significant amounts in the Amundsen Basin north of Greenland. We deduce circulation patterns from the distributions of Atlantic and Pacific source waters in the surface layer of the Arctic Ocean and conclude that the flow within the surface layer differs from ice drift along the North American and European boundaries of the Polar Basin.
Non‐resonant firehose instability: Consequences for the theory of cosmic ray acceleration
Authors: Shapiro V. D. , Quest K. B. , Okolicsanyi M.
Published: February 2004

Upstream from the supernova quasiparallel shock wave, the hot component representing cosmic rays is locked at the shock front due to scattering by magnetic field fluctuations, and is accelerated by the diffusive shock acceleration mechanism. The cosmic ray population, isotropic in the shock frame and drifting with the shock velocity relative to the interstellar plasma, is shown to be unstable with respect to a nonresonant beam type electromagnetic instability similar to a firehose mode. Solution of the dispersion relation for this instability is obtained using both analytical and numerical methods. For a power‐like distribution of the cosmic ray particles, f(ε) ∼ ε−2, an expected consequence of diffusive shock acceleration, the maximum growth rate of the magnetic fluctuations corresponds to wavelengths that are significantly greater than the gyroradius at the upper edge of the energy spectrum. Because such extremely long fluctuations tangle magnetic field lines, diffusion of the cosmic ray particles increases significantly, resulting in an essential extension of the energy range for diffusive shock acceleration.
Ionospheric response to magnetic forcing: Magnetic cloud passage of October 18–20, 1995
Authors: Huang C. Y. , Burke W. J. , Gussenhoven M. S. , Hardy D. A. , Gentile L. C.
Published: February 2004

On October 18–20, 1995 a magnetic cloud was observed, first by the WIND spacecraft upstream in the solar wind, then at the Earth. Inside the cloud, plasma density, velocity and temperature, and magnetic field strength were relatively steady for almost 24 hrs. However, the magnetic field direction rotated slowly from −Z to −Y and finally to +Z (GSE coordinates). This magnetic cloud passage allows us to study the solar wind‐magnetosphere‐ionosphere interaction under nearly ideal slowly‐varying conditions. This paper reports on the nightside ionospheric response to a long interval with Bz <0 in the interplanetary medium. Temporal variations in the integrated energy deposited in the nightside auroral zone within 3 hrs of local midnight are similar to variations in ϵ, the energy coupling function, and dissimilar to auroral magnetograms. While substorm effects are observed in the ionospheric electron flux, the integrated energy is dominated by diffuse precipitation at low latitudes. We also find that the integrated energy curve lags the ϵ parameter by 1–2 hrs. This delay represents the time required for convective electric fields to heat particles adiabatically in the plasma sheet.
Mineral aerosol production by wind erosion: Aerosol particle sizes and binding energies
Authors: Alfaro Stéphane C. , Gaudichet Annie , Gomes Laurent , Maillé Michel
Published: February 2004

Size distributions of mineral aerosols released by wind‐erosion from arid areas are of primary importance to model their transport patterns as well as their effect on climate. Wind tunnel experiments meant to test the influence of wind strength and soil characteristics are carried out with two natural soils differing both in texture and in mineral composition. In all cases, the aerosols can be considered as mixtures, in proportions depending on wind speed, of the same three lognormally distributed particle populations. By using appropriate binding energies for these populations, a sandblasting model previously developed allows retrieval of the size distributions of the aerosols produced by the two soils at any wind speed. A major implication of this study is that the size distributions of mineral aerosols greatly depend on the wind conditions prevailing during their generation. Aerosols optical properties being size dependent, this should clearly be taken into account in climate modeling.
Seasonal variations of the diurnal tide induced by gravity wave filtering
Authors: Mayr H. G. , Mengel J. G. , Chan K. L. , Porter H. S.
Published: February 2004

Wind measurements with the UARS spacecraft show that between 90 and 100 km altitude the fundamental diurnal tide is modulated semi‐annually with peak amplitudes of almost 100 m/s near equinox, more than a factor of two larger than during solstice. Applying Hines' Doppler‐Spread Parameterization (DSP) for small scale gravity waves (GW), we present results from a Numerical Spectral Model (NSM) to describe the seasonal variations in the mean zonal circulation interacting self consistently with the diurnal tide. With the DSP, the GW momentum source increases the amplitude of the tide at altitudes above 70 km, in contrast to the Rayleigh friction parameterization that causes damping. Since the tide absorbs GW momentum, it reduces the wave‐generated semi‐annual oscillations (SAO) in the mean zonal winds at equatorial latitudes. Outside the tropics, GW momentum is absorbed by the mean zonal winds that peak near the summer and winter solstices. As a result, the GW reach the upper mesosphere with more momentum during equinox periods and thus cause a seasonal modulation of the tide that is predominately semi‐annual.
GPS measurements across the Northern Caribbean Plate Boundary Zone: Impact of postseismic relaxation following historic earthquakes
Authors: Pollitz Fred F. , Dixon Timothy H.
Published: February 2004

GPS measurements in the northern Caribbean suggest that the rate of Caribbean plate motion relative to North America is about 10 mm/yr faster than predicted by global plate motion model NUVEL‐1A. Several of the key sites used in the GPS study are located in the Dominican Republic, near the rupture zones of large earthquakes in 1946 and in the previous two centuries. Postseismic relaxation of the crust and upper mantle is a possible explanation for the plate velocity discrepancy. We explore a range of fault mechanisms and crustal and mantle rheology to place an upper bound on postseismic relaxation effects. The upper bound velocity contribution in the southern Dominican Republic is 5–6 mm/yr, and the most plausible contribution is 1–2 mm/yr, suggesting that postseismic effects cannot account for the discrepancy. This implies that the NUVEL‐1A model underestimates the rate of motion of the Caribbean plate.
Quasi‐periodic radar echoes from midlatitude sporadic E and role of the 5‐day planetary wave
Authors: Tsunoda Roland T. , Yamamoto Mamoru , Igarashi Kiyoshi , Hocke Klemens , Fukao Shoichiro
Published: February 2004

Using measurements of magnetic‐aspect‐sensitive radar echoes from midlatitude sporadic E collected over a two‐month period from Tanegashima, Japan, we show that while their occurrence duration from night to night did not exhibit any systematic variation, that of the so‐called quasi‐periodic (QP) echoes varied sinusoidally with a period of 5 days. We have interpreted this behavior in terms of effects produced by a planetary wave and identified its presence through neutral‐wind measurements made with a partial‐reflection drift radar located nearby at Yamagawa. We propose that the occurrence of QP echoes is affected both by a contribution of the wind to the dynamo electric field and by the direction of the neutral wind. We argue that because the wind vector of the planetary wave is elliptically polarized at midlatitudes, a preferred wind direction conducive to the generation of QP echoes occurs once every 5 days. On the other hand, this wave is linearly polarized and directed zonally over the geographic equator. The fact that QP echoes are most fully developed at midlatitudes and less so at lower latitudes suggests that zonal flow is not particularly favorable for QP echo production.
Radiation belt electron observations following the January 1997 magnetic cloud event
Authors: Selesnick R. S. , Blake J. B.
Published: February 2004

Relativistic electrons in the outer radiation belt associated with the January 1997 magnetic cloud event were observed by the HIST instrument on POLAR at kinetic energies from 0.7 to 7 MeV and L shells from 3 to 9. The electron enhancement occurred on a time scale of hours or less throughout the outer radiation belt, except for a more gradual rise in the higher energy electrons at the lower L values indicative of local acceleration and inward radial diffusion. At the higher L values, variations on a time scale of several days following the initial injection on January 10 are consistent with data from geosynchronous orbit and may be an adiabatic response.
Geomagnetic storms caused by coronal mass ejections (CMEs): March 1996 through June 1997
Authors: Brueckner G. E. , Delaboudiniere J.‐P. , Howard R. A. , Paswaters S. E. , St. Cyr O. C. , Schwenn R. , Lamy P. , Simnett G. M. , Thompson B. , Wang D.
Published: February 2004

(1) All but two geomagnetic storms with Kp ≥ 6 during the operating period (March 1996 through June 1997) of the Large Angle Spectroscopic Coronagraph (LASCO) experiment on the Solar and Heliospheric Observatory (SOHO) spacecraft can be traced to Coronal Mass Ejections (CMEs). (2) These geomagnetic storms are not related to high speed solar wind streams. (3) The CMEs which cause geomagnetic effects, can be classified into two categories: Halo events and toroidal CMEs. (4) The CMEs are accompanied by Coronal Shock Waves as seen in the Extreme Ultraviolet Imaging Telescope (EIT) Fe XII images. (5) Some CMEs are related to flares, others are not. (6) In many cases, the travel time between the explosion on the Sun and the maximum geomagnetic activity is about 80 hours.
Type II radio emissions in the frequency range from 1–14 MHz associated with the April 7, 1997 solar event
Authors: Kaiser M. L. , Reiner M. J. , Gopalswamy N. , Howard R. A. , St. Cyr O. C. , Thompson B. J. , Bougeret J.‐L.
Published: February 2004

We present an analysis of radio emissions associated with the April 7, 1997 solar eruptive event. The event consisted of a filament disappearance, a complex two‐phase coronal mass ejection (CME), and a C6.9, 2N flare. At the same time, intermittent type II radio emissions in the frequency range 1‐10 MHz, corresponding to an altitude range of 2‐15 Ro, were observed by the Wind/WAVES radio receiver. Using the onset times and inferred heights and speeds of the radio bursts, we considered both a CME‐driven shock and a flare‐associated blast wave shock as possible causes of the type II radio emissions. We conclude that some of the radio emissions in the WAVES data are associated with each shock. The type II radio emissions associated with the blast wave shock were farther from the sun than any emission of this type that has been reported previously.
Preferred VGP paths during geomagnetic polarity reversals: Symmetry considerations
Authors: Gubbins David , Love J. J.
Published: February 2004

The reversing geomagnetic field has been said to have virtual geomagnetic poles (VGPs) confined to a pair of longitudes close to where magnetic flux is concentrated at the core surface today, at approximately 90°W and 110°E. This can be explained if flux remains concentrated on the same longitudes throughout the transition. The VGP path then depends on site position, reversal sense (R→N or N→R), and sense of flux migration (pole‐ or equator‐ward). For transitional fields which remain antisymmetric about the equator, N→R transitions with poleward flux migration give western longitude VGP paths for sites in the NE and SW quadrants and eastern longitude VGP paths for sites in the NW and SE quadrants. Sites on quadrant boundaries record rapid, variable VGP positions. Data from the last (Matuyama‐Brunhes) reversal are broadly consistent with poleward flux migration.
Mass fluxes and dynamics of Moreno Glacier, Southern Patagonia Icefield
Authors: Rott Helmut , Stuefer Martin , Siegel Andreas , Skvarca Pedro , Eckstaller Alfons
Published: February 2004

Accumulation, ablation, calving, and flow dynamics of Moreno Glacier, one of the main outlet glaciers of the Southern Patagonia Icefield, were studied based on field campaigns and on spaceborne radar imagery acquired by SIR‐C/X‐SAR. Ice velocities and ablation were measured through two summers and one winter. The ice depth was sounded seismically at a transect 8 km above the calving front, showing a maximum depth of 720 m. The velocity field of the terminus was derived from SIR‐C/X‐SAR data by means of interferometry and amplitude correlation. The average specific annual net accumulation is 5540±500 mm water equivalent. The bottom topography of the lake and the high ratio of calving flux to net accumulation explain the remarkable stability of Moreno Glacier throughout this century which is in contrast to the retreat of other glaciers in this region.
Influence of the diurnal tide and thermospheric heat sources on the formation of mesospheric temperature inversion layers
Authors: States Robert J. , Gardner Chester S.
Published: February 2004

One hundred eighty nine hours of mesopause region temperature, meridional wind, and Na density measurements were made at the Urbana Atmospheric Observatory (40°N, 88°W) during both day and night in Sep/Oct 1996. The data are used to study tidal oscillations and their relationship to mesospheric temperature inversion layers. The observations show that thermospheric forcing by UV and EUV absorption plays an important role in establishing the tidal characteristics in the upper mesosphere. Because of the large tidal amplitudes and strong thermospheric heating during the day, the general characteristics of the background temperature structure can only be established by measuring temperature throughout the diurnal cycle. When the temperature profile is averaged over the complete diurnal cycle, the mesopause is considerably warmer (196 K compared to 190 K) and lower (96 km compared to 101 km) than that observed at night. Furthermore, there is little evidence of the prominent inversion layers frequently reported in nighttime measurements. These features appear to be artifacts associated with incomplete sampling of the strong diurnal tide.
Electric field measurements above and within a sporadic‐E layer
Authors: Pfaff R. , Yamamoto M. , Marionni P. , Mori H. , Fukao S.
Published: February 2004

In‐situ DC and wave electric fields were detected above and within a sporadic‐E layer by sounding rocket‐borne instruments in the presence of quasi‐periodic backscatter radar echoes. When analyzed in conjunction with plasma density measurements, the in‐situ data reveal complex electrodynamics associated with the sporadic‐E layer. The electric field data show: (1) a sinusoidal variation of ±3 mV/m between 130–170 km which may be associated with a gravity wave with a horizontal wavelength of ∼20 km; (2) localized DC electric fields of ∼20 mV/m associated with narrow (few km) plasma density depletions near 125 km altitude; and (3) a broad spectrum of plasma irregularities, including long wavelength (km‐scale) and meter‐scale waves. No short‐scale plasma waves were observed in‐situ above 115 km, despite the fact that simultaneous radar data show echoes originating from altitudes as high as 135 km.
Initial FAST observations of acceleration processes in the cusp
Authors: Pfaff R. , Clemmons J. , Carlson C. , Ergun R. , McFadden J. , Mozer F. , Temerin M. , Klumpar D. , Peterson W. , Shelley E. , Mœbius E. , Kistler L. , Strangeway R. , Elphic R. , Cattell C.
Published: February 2004

FAST satellite observations during two encounters with the Earth's cusps near 4000 km are presented. In addition to precipitating magnetosheath particles with isotropic pitch angle distributions, the energetic particle data reveal upgoing ion beams, ion conics, downgoing “inverted‐V” electron distributions, and very narrow, intense upgoing electron beams. A rich assortment of DC‐coupled electric fields and plasma waves accompany these acceleration processes. In one example, step‐like injections of magnetosheath ions are correlated with bursts of upgoing ion beams and downgoing electrons, suggesting that the currents associated with these injections set up local electric potential structures that subsequently drive the acceleration processes. The observations underscore the fact that the cusp is not merely a conduit for the passage of magnetosheath particles and fields, but contains a dynamic internal electrical structure that accelerates particles locally and may alter the precipitating magnetosheath particle populations themselves.
Evidence of old carbon in the deep water column of the Panama Basin from natural radiocarbon measurements
Authors: Druffel Ellen R. M. , Griffin Sheila , Honjo Susumu , Manganini Steven J.
Published: February 2004

Radiocarbon (Δ14C) analyses were performed on sinking and suspended particulate matter, dissolved inorganic carbon (DIC), sediment and sediment fluff from a deep‐water station in the Panama Basin. Δ14C signatures for sinking particulate inorganic and organic carbon (PIC, FOC) collected at 3354 meters depth were lower than surface DIC Δ14C values, and higher than the inorganic and organic carbon from the sediment (SIC, SOC). We compare these data with those obtained for other Pacific and Atlantic sites and show that the gradient between surface DIC Δ14C and deep suspended POC Δ14C is the same irrespective of distance from the coast. This indicates that: 1) resuspended SOC is an equally important contributor to deep POC at locations close to and far from continental slopes, and/or 2) DOC sorption is a significant contributor for causing low Δ14C values of deep POC.
Earth's continuous oscillations observed on seismically quiet days
Authors: Tanimoto Toshiro , Um Junho , Nishida Kiwamu , Kobayashi Naoki
Published: February 2004

Analysis of IDA gravimeter data between 1983 and 1994 and GEOSCOPE data between 1988 and 1994 show that fundamental modes of the Earth, for frequencies between 2 and 7 mHz, are excited even on seismically quiet days. Amplitudes of acceleration are slightly less than one ngal(10−9gal). Examination of a sequence of shorter time interval records suggests that the Earth is oscillating continuously. Currently, both atmospheric excitation and tectonic motions are possible cause(s) of these oscillations.
Spatial structure of sprites
Authors: Pasko Victor P. , Inan Umran S. , Bell Timothy F.
Published: February 2004

A theory of the electrical breakdown (EB) above thunderstorms is developed. The streamer type of the EB is proposed for the explanation of recent observations of fine spatial structures and bursts of blue optical emissions associated with sprites.
Ice foot development at temperate tidewater margins in Alaska
Authors: Hunter Lewis E. , Powell Ross D.
Published: February 2004

The presence of an ice foot at the base of temperate tidewater ice cliffs has been debated for nearly 100 years. This paper presents evidence demonstrating ice feet at tidewater margins in Glacier Bay, Alaska. Ice feet are likely sources of many submarine icebergs originating at the ice margin. The cause of ice foot development is unclear, but may represent a change in fracture behavior near the bed where higher debris concentrations affect fracture propagation and calving. Ice foot formation can be favored by englacial discharge and sediment ramps along the glacier margin that can cause differential melting of the ice cliff. The presence of ice feet is important to understanding ice‐proximal sediment dynamics because they are a primary source of debris‐rich icebergs and their calving affects sediment redistribution patterns.
VLF chorus emissions observed by Polar during the January 10, 1997, magnetic cloud
Authors: Lauben D. S. , Inan U. S. , Bell T. F. , Kirchner D. L. , Hospodarsky G. B. , Pickett J. S.
Published: February 2004

VLF chorus emissions occur near the dawn meridian in fast response (<60 s) to magnetospheric perturbations caused by sudden fluctuations in solar wind dynamic pressure and southward turnings of the interplanetary magnetic field (IMF) at the arrival of the Jan. 10, 1997 magnetic cloud. Raytracing analysis indicates the likely chorus source region to be near the magnetic equator with rays launched at oblique wave normal angles, for which likely resonant electron energies are in the range E∼14–30 keV, consistent with observed particle data.
A pan‐Atlantic decadal climate oscillation
Authors: Xie Shang‐Ping , Tanimoto Youichi
Published: February 2004

Sea surface temperature (SST) variabilities on time scales of 10–14 years have been documented in various parts of the Atlantic Ocean. Here we present observational evidence that these regional variabilities are part of a coherent pan‐Atlantic decadal oscillation (PADO) characterized by zonal bands of SST and wind anomalies stacked in the meridional direction with alternate polarities from the South Atlantic all the way to Greenland. We propose that the interaction of wind, evaporation and SST is key to establishing this interhemispherical PADO, based on results from a new ocean‐atmosphere coupling model. Forced by extratropical wind forcing, the model successfully reproduces the observed decadal oscillation in both SST and wind velocity over the Tropics. This decadal extratropical forcing of the Tropics is in sharp contrast to the well‐known Tropics‐to‐extratropics teleconnection that operates on interannual time scales in association with El Nino/Southern Oscillation (ENSO).
Quartz and Cristobalite: high‐temperature cell parameters and volumes of fusion
Authors: Bourova Ekatarina , Richet Pascal
Published: February 2004

The cell parameters of quartz and cristobalite have been measured up to their melting points from X‐ray diffraction experiments with synchrotron radiation. After a smooth increase up to 1300 K, the volume of β‐cristobalite decreases continuously up to the melting temperature of 2000 K where it is back to the 750 K value of 27.4 cm³/mol. A slightly negative thermal expansion coefficient is also observed for quartz above 1400 K, resulting in a volume of 23.45 cm³/mol at 1673 K. From these results and the molar volume of SiO2 liquid, the volumes of fusion of β‐cristobalite and quartz are −0.1 and 3.85 cm³/mol, respectively. With these values and the known entropies of fusion, only a slight adjustment to 1673 K of the melting temperature of quartz has been found necessary to ensure consistency with available phase equilibria data.
Spectroscopic observation of HCl degassing from Soufriere Hills Volcano, Montserrat
Authors: Oppenheimer Clive , Francis Peter , Maciejewski Adam J. H.
Published: February 2004

Open‐path Fourier transform infrared (FTIR) spectroscopic techniques were employed to study gas emissions from Soufriere Hills volcano in July–August 1996. Observations were made using both volcanic and artificial sources of infrared energy. Column amounts of HCl fall in the range 1–100 ppmv m but other species expected in the gas phase, notably SO2, are not apparent in the spectra. The minimum detection limit for SO2 in these data indicates that the HCl/SO2 molecular ratio exceeded 10. Scaled against measured fluxes of SO2, the HCl emission rate during this period exceeded 15 kg s−1 (1300 t d−1). Comparison of our results with other geochemical measurements of Soufriere Hills emissions is complicated by inherent differences between the analytical methods employed. While the ability to measure atmospheric concentrations of reactive trace gases at high temporal resolution is of clear use in environmental and medical studies of volcanic effluents, a better understanding of the kinetics of plume chemistry is needed to resolve ambiguities in interpretation of time‐series FTIR observations.
Stratospheric cooling and arctic ozone recovery
Authors: Danilin Michael Y. , Sze Nien‐Dak , Ko Malcolm K. W. , Rodriguez Jose M. , Tabazadeh Azadeh
Published: February 2004

We present sensitivity studies using the AER box model for an idealized parcel in the lower stratosphere at 70°N during winter/spring with different assumed stratospheric coolings and chlorine loadings. Our calculations show that stratospheric cooling could further deplete ozone via increased polar stratospheric cloud (PSC) formation and retard its expected recovery even with the projected chlorine loading decrease. We introduce the concept of chlorine‐cooling equivalent and show that a 1 K cooling could provide the same local ozone depletion as an increase of chlorine by 0.4–0.7 ppbv for the scenarios considered. Thus, sustained stratospheric cooling could further reduce Arctic ozone content and delay the anticipated ozone recovery in the Northern Hemisphere even with the realization of the Montreal Protocol and its Amendments.
Slow rock fracture as eruption precursor at Soufriere Hills Volcano, Montserrat
Authors: Kilburn Christopher R. J. , Voight Barry
Published: February 2004

Breakout of magmatic activity at Soufriere Hills volcano, Montserrat, was preceded by a tenfold increase in rate of earthquake occurrence. A new model of subcritical rock failure shows that this increase is consistent with the growth, possibly episodic, of the magma conduit at a rate controlled by progressive weakening of the host country rock. The preferred weakening mechanism is stress corrosion, by which circulating juvenile and hydrothermal fluids chemically attack the country rock and promote failure at stresses smaller than the rock's theoretical strength. The results illuminate the potential for slow‐cracking models to enhance eruption forecasts using the inverse‐rate technique combined with traditional monitoring methods.
Broadband recording of Strombolian explosions and associated very‐long‐period seismic signals on Mount Erebus Volcano, Ross Island, Antarctica
Authors: Rowe C. A. , Aster R. C. , Kyle P. R. , Schlue J. W. , Dibble R. R.
Published: February 2004

In December 1996 and January 1997, broadband seismometers were deployed on the summit plateau of Mount Erebus at radial distances of 0.7, 1.4 and 1.9 km from the central crater and lava lake. Strombolian explosions at Erebus previously have been observed to produce seismic and acoustic energy between 1 and 6 Hz. New observations document significant energy with spectral peaks as grave as 20 s. Nearly identical very‐long‐period (VLP) signals begin ∼1.5 s prior to explosions, have dilatational onsets and persist for up to 150 s. Similar VLP waveforms were recorded at all three stations, indicating that the seismograms are essentially source‐dominated. Particle motions suggest an initial depth for the VLP source of up to several hundred meters, migrating deeper in the course of ∼15 s. Such explosion‐associated VLP signals may indicate a nondestructive lossy resonance or nonlinear fluid‐flow excitation within the shallow magmatic system.
IMF‐controlled configuration of the reverse convection in the dayside polar ionosphere
Authors: Taguchi S. , Warashina M.
Published: February 2004

Northward interplanetary magnetic field (IMF) causes a “reverse” convection in the dayside polar ionosphere, i.e., flow having a sunward component at the highest latitudes and anti‐sunward flow on both sides of the sunward flow region. Previous studies have shown that this sunward flow region is shifted in the dawn‐dusk direction depending on IMF BY. This paper reports another new mode of the IMF controlled configuration of the sunward flow region. Seventy‐two reverse convection events identified in the Dynamics Explorers 2 dawn‐dusk passes were analyzed. Results of statistical analyses show that the sunward flow region expands in the dawn‐dusk direction as the magnitude of IMF in the Y‐Z plane becomes large. This result can be interpreted by a model which predicts that the dawn‐dusk dimension of the high‐latitude magnetopause reconnection region from which sunward flow is created extends with the increase of the magnitude of IMF in the Y‐Z plane.
Non‐linear rate dependent deformation under compression due to state variable friction
Authors: Renshaw Carl E. , Schulson Erland M.
Published: February 2004

Observations of strain‐rate effects in brittle failure under compression have been interpreted as suggesting that sub‐critical crack growth plays an important role in the deformation process. We suggest an alternate interpretation in which strain‐rate effects are attributed to rate‐ and state‐dependent friction along parent cracks. Using independently measured friction law parameters we demonstrate that a wing crack model incorporating state variable friction replicates the observed dependence of the stress‐strain curve on applied strain rate. Model results are essentially equivalent to those of an earlier model incorporating sub‐critical crack growth, suggesting that despite their different conceptual foundations, the validity of either model can not be determined on the basis of the observed strain‐rate effects. However, only the rate‐dependent friction model reproduces the observed unsteady growth of wing cracks.
Effects of D″ anisotropy on seismic velocity models of the outermost core
Authors: Garnero Edward J. , Lay Thorne
Published: February 2004

We explore effects of shear wave anisotropy in D″ on seismic waves utilized in constructing models of the outermost core. Reflectivity synthetic seismograms approximating transverse isotropy (TI) in D″ yield absolute and differential time perturbations of S, SKS, and SKKS of up to several seconds, especially if laterally varying anisotropy is considered. Several studies have used anomalies of this magnitude to infer a 0.5–2.5% P velocity reduction in the outermost 50–150 km of the core, suggesting a stably stratified layer just beneath the core‐mantle boundary. Our data samples the mantle and core beneath Alaska and northern Pacific, a region with strong lateral variations in D″ anisotropy. TI models that predict the magnitude of shear wave splitting seen in the data can account for much (but not all) of the anomalies that isotropic models attribute to outermost core velocity reductions. Future outermost core seismic studies should address such D″ anisotropy effects.
Nitrogen recycling in subduction zones
Authors: Sano Yuji , Takahata Naoto , Nishio Yoshiro , Marty Bernard
Published: February 2004

The isotopic composition of nitrogen bears important information concerning the fate of this volatile in the mantle‐crust‐atmosphere system. Based on the isotopic compositions of mid‐ocean ridge basalts and pristine diamonds, a δ15N value of about ‐ 5±2‰ (where δ15N = [( 15N/ 14)sample/ ( 15N/ 14N)air − 1] × 1000) is assigned to the upper mantle. In contrast, the origin of nitrogen has not been well documented in subduction zones. We report here δ15N values, N2/36Ar, and 40Ar/ 36Ar ratios of a comprehensive suite of samples from along convergent plate boundaries measured using a newly developed static mass spectrometry method. The δ15N values and the N2/ 36Ar ratios vary significantly from −2.7‰ to 5.0‰ and from 2.28×104 to 7.15×l05, respectively. Taking a typical δ 15N value for sediments, assuming that the N2/ 36Ar ratio of mid‐ocean ridge basalts is representative of the upper mantle, and that later isotopic and elemental fractionation are not significant, it is possible to deconvolve each fraction of nitrogen on the basis of simple mixing equations. About 50% of nitrogen in back‐arc basin basalts originated from the upper mantle, whereas island arc samples contain only about 15% of the mantle‐derived nitrogen, the major fraction being derived from recycled sedimentary nitrogen.
Nonlinear evolution of Alfvénic wave packets
Authors: Buti B. , Jayanti V. , Viñas A. F. , Ghosh S. , Goldstein M. L. , Roberts D. A. , Lakhina G. S. , Tsurutani B. T.
Published: February 2004

Alfvén waves are a ubiquitous feature of the solar wind. One approach to studying the evolution of such waves has been to study exact solutions to approximate evolution equations. Here we compare soliton solutions of the Derivative Nonlinear Schrödinger evolution equation (DNLS) to solutions of the compressible MHD equations. We find that the soliton solutions of the DNLS equation are not stable solutions of Hall‐MHD—they evolve and dissipate with time. Although such solitons may serve as approximate initial conditions to the Hall‐MHD equations, they are not stationary solutions. This may account for the absence of soliton‐like wave forms in the free‐flowing solar wind.
Possible causes for the seismic activity observed in Cotopaxi Volcano, Ecuador
Authors: Ruiz Mario , Guillier Bertrand , Chatelain Jean‐Luc , Yepes Hugo , Hall Minard , Ramon Patricio
Published: February 2004

Continuous monitoring of Cotopaxi volcano from January 1989 to September 1997 shows that it is subject to a steady shallow Long Period (LP) activity. LP events are concentrated in a column with a diameter of about 3 km and a height of about 12 km, between an elevation of 4 km and 8 km depth. They do not occur in swarms, nor have there been periods of complete calm. High frequency volcano‐tectonic (VT) events are mostly located on the northeastern side of the LP column, with the maximum activity of both types of events coinciding in depth. LP activity cannot be related to unrest of the volcano. The most likely explanation for the continuous occurrence of LP events beneath Cotopaxi is that they are produced by the interaction of glacier thaw water and hot material at shallow depths. The relative spatial distribution of both type of events in two adjacent zones suggest that VT and LP activities are interconnected.
Inferring spatial correlation of hydraulic conductivity from sediment cores and outcrops
Authors: Eggleston Jack , Rojstaczer Stuart
Published: February 2004

Spatial variation of hydraulic conductivity is often assumed to follow patterns of sediment texture. This study examines whether sediment texture observed in cores and outcrops can be used to infer spatial correlation of hydraulic conductivity. The measures of spatial correlation that we consider, correlation length and Hurst coefficient, are commonly used for interpolating conductivity at unmeasured locations and making stochastic estimates of dispersivity. Results indicate that, when comparing hydraulic conductivity values derived from sediment texture to those measured by pumping tests, horizontal correlation lengths are approximately the same but vertical correlation does not correspond well. The results also suggest that sediment information may be useful for setting spatial limits to scaling behavior that is assumed with fractal interpretation of hydraulic conductivity variability.
A study of the large‐scale dynamics of the Jovian magnetosphere using the Galileo Plasma Wave Experiment
Authors: Louarn Philippe , Roux A. , Perraut S. , Kurth W. , Gurnett D.
Published: February 2004

Using observations of the Galileo PWS experiment, we show that energetic phenomena recurrently occur in the jovian magnetosphere. They are characterized by intensifications of the auroral radio emissions and the creation of new sources of radiations in the outer regions of the Io torus. Simultaneously, modifications of the structure of the plasmasheet are observed at large distance (more than 60 Rj) from Jupiter. These large‐scale processes, presenting a periodicity of 50 to 80 hours, could be linked to global instabilities of the jovian magnetosphere.
Troposphere‐to‐stratosphere transport in the lowermost stratosphere from measurements of H2O, CO2, N2O and O3
Authors: Hintsa E. J. , Boering K. A. , Weinstock E. M. , Anderson J. G. , Gary B. L. , Pfister L. , Daube B. C. , Wofsy S. C. , Loewenstein M. , Podolske J. R. , Margitan J. J. , Bui T. P.
Published: February 2004

The origin of air in the lowermost stratosphere is investigated with measurements from the NASA ER‐2 aircraft. Air with high water vapor mixing ratios was observed in the stratosphere at θ∼330–380 K near 40 N in May 1995, indicating the influence of intrusions of tropospheric air. Assuming that observed tracer‐tracer relationships reflect mixing lines between tropospheric and stratospheric air masses, we calculate mixing ratios of H2O (12–24 ppmv) and CO2 for the admixed tropospheric air at θ=352–364 K. Temperatures on the 355 K surface at 20–40 N were low enough to dehydrate air to these values. While most ER‐2 CO2 data in both hemispheres are consistent with tropical or subtropical air entering the lowermost stratosphere, measurements from May 1995 for θ<362 K suggest that entry of air from the midlatitude upper troposphere can occur in conjunction with mixing processes near the tropopause.