bluuebunny/crossref_metadata_2025 huggingface dataset:
Upstream and magnetosheath energetic ions with energies to ≈2 MeV
Authors: Skoug R. M. , Winglee R. M. , McCarthy M. P. , Parks G. K. , Lin R. P. , Anderson K. A. , Carlson C. , Ergun R. , Larson D. , McFadden J. , Rème H. , Bosqued J. , d'Uston C. , Sanderson T. R. , Wenzel K.‐P. , Lepping R. P. , Szabo A.
Published: February 2004

We present the first observations of ≈2 MeV ion bursts detected in the upstream region and the magnetosheath by the three‐dimensional (3D) plasma and energetic particles instrument on the WIND spacecraft. This instrument measures the full 3D distribution of particles from a few eV to several MeV, and allows characterization of the upstream ions in both pitch angle and energy. The new feature observed is the presence of bursts of ions at energies extending up to ≈2 MeV, both upstream and in the magnetosheath. The observation of MeV ions has strong implications for the ion source and acceleration mechanisms.
Modeling boundary blobs using time varying convection
Authors: Anderson David N. , Decker Dwight T. , Valladares Cesar E.
Published: February 2004

The Global Theoretical Ionospheric Model (GTIM) has been used to study a mechanism which generates F‐region electron density enhancements known as boundary blobs. The model calculates the O+ density as a function of altitude, latitude, and local time. It includes the effects of production of ionization by solar extreme ultraviolet radiation and electron precipitation; loss through charge exchange with N2 and O2; and transport by diffusion, neutral winds, and E×B convection drifts. Using time‐dependent convection patterns that previously were used to study polar cap patch formation, it was found that patches can be convected out of the polar cap and swept sunward by the dusk convection cell. The resulting structures have many of the features associated with boundary blobs: extended in local time and altitude, narrow in latitude, located in the return flow region of the aurora, and densities up to a factor of 8 over background. These results are the first quantitative, first principles_verification and extension of the trajectory modeling of Robinson et al., (1985).
Creep in pelagic sediments and potential for morphologic dating of marine fault scarps
Authors: Mitchell Neil C.
Published: February 2004

Cores from the flanks of the Galapagos spreading centre show that the top 25 cm of pelagic sediments is highly bioturbated. Kenyan and Turcotte [1985] have proposed that bioturbation may cause down‐slope creep of the sediment surface and bioturbation may therefore smooth sediment topography in a similar way to hillslope creep on land. Assuming this produces movement consistent with the diffusion transport model, sediment topography across scarp crests, digitised from Deep Tow profiler records, is modelled with a simple analytic solution to the diffusion equation and with a mean diffusion constant k of ∼0.007 m²/yr. This small value suggests creep rates are modest, for example, 2 cm/yr for a 30° slope, and is an upper bound since sediment avalanching and bottom currents probably also remove sediment from scarp crests. Although requiring further work, these results suggest that morphologic dating methods may be applicable to marine fault scarps and could be useful in relatively sediment‐free areas, such as mid‐ocean ridges, where it is commonly not possible to use datable offset seismic horizons.
Some additional hysteresis parameters for a natural (titano)magnetite with known grain size
Authors: Vlag P. , Rochette P. , Dekkers M. J.
Published: February 2004

The grain‐size dependence (250 down to <5 µm) of the hysteresis properties of a natural magnetite and a natural titanomagnetite were determined with an Alternating Gradient Magnetometer. In addition to the classical hysteresis parameters (Mr/Ms, Hc, Hcr, Hcr/Hc) three additional hysteresis parameters (MDFhys, MIFhys and χhys) were obtained from the loops (von Dobeneck, 1993). The classical hysteresis parameters agree well with data of Hartstra (1982), indicating that the small sample size of the AGM specimens does not hinder acquisition of meaningful data. The additional hysteresis parameters seem to depend on mineralogical composition but show little grain‐size dependence. χhys/χlf is ∼1.6 for coarse grain‐size fractions and decreases with grain size in fine fractions. The onset of the decrease corresponds to the PSD‐MD transition.
Potential atmospheric impact of the Toba Mega‐Eruption ∼71,000 years ago
Authors: Zielinski G. A. , Mayewski P. A. , Meeker L. D. , Whitlow S. , Twickler M. S. , Taylor K.
Published: February 2004

An ∼6‐year long period of volcanic sulfate recorded in the GISP2 ice core about 71,100 ± 5000 years ago may provide detailed information on the atmospheric and climatic impact of the Toba mega‐eruption. Deposition of these aerosols occur at the beginning of an ∼1000‐year long stadial event, but not immediately before the longer glacial period beginning ∼67,500 years ago. Total stratospheric loading estimates over this ∼6‐year period range from 2200 to 4400 Mt of H2SO4 aerosols. The range in values is given to compensate for uncertainties in aerosol transport. Magnitude and longevity of the atmospheric loading may have led directly to enhanced cooling during the initial two centuries of this ∼1000‐year cooling event.
Comparison of infrared and Dobson total ozone columns measured from Lauder, New Zealand
Authors: Rinsland Curtis P. , Connor Brian J. , Jones Nicholas B. , Boyd Ian , Matthews W. Andrew , Goldman Aaron , Murcray Frank J. , Murcray David G. , David Shelle J. , Pougatchev Nikita S.
Published: February 2004

Ozone total columns have been derived from 13 spectral intervals in 5 infrared bands and compared with values deduced from correlative measurements with a Dobson spectrophotometer. The observations were recorded on 10 days in 1994 at the Network for the Detection of Stratospheric Change station in Lauder, New Zealand. The infrared total columns were derived from spectral fittings of unblended, temperature‐insensitive ozone lines in high resolution solar absorption spectra. The line parameters on the 1992 HITRAN compilation were assumed with the O3 H2O relative volume mixing ratio and temperature profiles specified from correlative balloon ozonesonde, microwave O3, and radiosonde measurements. The retrieved IR/Dobson total column ratios ranged from 0.96 to 1.02 with the lower wavenumber bands yielding lower ratios. The results do not support the revised O3 intensity scale currently used to process O3 infrared measurements from 2 instruments on the Upper Atmosphere Research Satellite.
Multifractal analysis of the 1992 Erzincan Aftershock Sequence
Authors: Legrand D. , Cisternas A. , Dorbath L.
Published: February 2004

The set of aftershocks of the Erzincan (Turkey) earthquake of March 13, 1992 (Ms=6.9) is shown to be multifractal, and characterized by a spectrum of generalized fractal dimensions Dq varying from D2=2.1 to D∞=1.35. It is shown that dimensions Dq decrease and then increase until coming back to there initial values few days before the large aftershock of April 20 (magnitude Ms=4.6), for all values of q. Variation of fractal dimensions have yet been observed by other authors (Hirata and Imoto, 1991, Dongsheng et al., 1994, De Rubeis et al., 1993, Hirabayashi, 1992).
Tsunami generation by horizontal displacement of ocean bottom
Authors: Tanioka Yuichiro , Satake Kenji
Published: February 2004

Tsunami generation by an earthquake is generally modeled by water surface displacement identical to the vertical deformation of ocean bottom due to faulting. The effect of horizontal deformation is usually neglected. However, when the tsunami source is on a steep slope and the horizontal displacement is large relative to the vertical displacement, the effect becomes significant. We show this for two recent earthquakes which generated much larger tsunamis than expected from seismic waves. In the case of the 1994 June 2 Java, Indonesia, earthquake, the focal mechanism was a very shallow dipping thrust and the source was near a very steep trench slope. In the case of the 1994 Nov. 14 Mindoro, Philippines, earthquake, strike‐slip faulting extended from ocean to land perpendicular to the coast line. In both cases, we found that the horizontal motion of slope had an important contribution to the tsunami generation.
Debate on evaluation of the VAN Method: Editor's introduction
Authors: Geller Robert J.
Published: February 2004

This special section presents a debate on the statistical significance of the results obtained by the VAN method of earthquake prediction. Other topics related to the VAN method are also discussed by some of the papers in this section. This introduction explains the background that led to this debate. Tables of seismicity data are also included in this introduction. These tables are cited in some of the other papers in this special section.
Surface deformation caused by pressure changes in the fluid core
Authors: Fang Ming , Hager Bradford H. , Herring Thomas A.
Published: February 2004

Pressure load Love numbers are presented for calculating the mantle deformation induced by the variation of the pressure field at the core mantle boundary (CMB). We find that the CMB geostrophic pressure fields, derived from “frozen‐flux” core surface flow estimates at epochs 1965 and 1975, produce a relative radial velocity (RRV) field in the range of 3 mm/decade with uplift near the equator and subsidence near the poles. The contribution of this mechanism to the change in the length of day (l.o.d) is small—about 2.3×10−2 ms/decade. The contribution to the time variation of the ellipticity coefficient
is more important—about −1.3×10−11 /yr.
Scaling of field‐line random walk in model solar wind fluctuations
Authors: Gray P. C. , Pontius D. H. , Matthaeus W. H.
Published: February 2004

The diffusion coefficient associated with random walk of magnetic field lines is computed by direct calculation of a large number of field lines from a specified statistical ensemble. Two‐component magnetic field models are examined, consisting of a mixture of slab and two‐dimensional fluctuations. The scaling of the diffusion coefficient with magnetic field strength is established numerically for a wide range of relative fluctuation amplitudes ( δb/B0). The results confirm the recent nonperturbative theory of field line random walk (Phys. Rev. Lett., 75, 2136, 1995), but depart considerably from the quasilinear B0−2scaling, for models thought to be appropriate to the solar wind.
The cleft ion plasma environment at low solar activity
Authors: Moore T. E. , Pollock C. J. , Adrian M. L. , Kintner P. M. , Arnoldy R. L. , Lynch K. A. , Holtet J. A.
Published: February 2004

Low energy (0.3–25 eV) ion plasma composition and three‐dimensional differential velocity distribution measurements have been made from the Sounding of the Cleft Ion Fountain Energization Region (SCIFER) mission. SCIFER traveled poleward into the dayside prenoon cleft region under conditions of low solar activity. Upleg measurements show that the subcleft topside had a rapid density fall‐off with altitude (ne ≤ 300 cm−3 at 1400 km altitude), and that the payload floating potential changed from typical ionospheric negative values of about a volt, to zero or positive values consistent with ne ≤ 1000 cm−3 in sunlight. As the payload moved poleward and approached apogee, the ion plasma flux abruptly increased. Observations of Langmuir waves at the electron plasma frequency show the plasma density increased by a factor of 6 over a scale length of ∼1 km. The plasma density boundary coincided with passage into the cleft region, as judged from the appearance of field‐perpendicular ion heating to T⟂∼1 eV, with upward bulk flows of several km/s for H+, and 1–2 km/s for O+, and warm superthermal tails in the core H+ with characteristic energy ∼4 eV. An inverse association was observed between ion temperature and plasma density, consistent with heating by current‐driven waves. The heated cleft plasma was H+‐dominated in this region, in stark contrast to the O+ domination observed from 3000–6000 km altitude by DE‐1 and Akebono near solar maximum.
Decay of O2(a¹Δg) in the evening twilight airglow: Implications for the radiative lifetime
Authors: Pendleton W. R. , Baker D. J. , Reese R. J. , O'Neil R. R.
Published: February 2004

Time‐resolved spectra of the decay of the O2 infrared atmospheric ( a¹Δg → X³Σg−) ( 0,0) band emission in the evening twilight at 41.7°N have been obtained using the Fourier transform infrared (FTIR) technique. The measurements were made during a two‐month summer‐fall period which included the autumnal equinox. The late twilight variations were well described by single exponentials with decay time constants which ranged from (44.4±1.6) min in early August to (61.1±2.1) min near the equinox. In this connection, a strong positive trend in the time constant was observed during late August and early September. When combined with available data for collisional quenching and for fall‐winter, upper‐mesospheric altitude distributions of O2 (a¹Δg, ν=0) in the late twilight, these observations support a radiative lifetime of about one hour.
Structure, binding energy, and equilibrium constant of the nitric acid‐Water complex
Authors: Tao Fu‐Ming , Higgins Kelly , Klemperer William , Nelson David D.
Published: February 2004

The nitric acid‐water complex is studied by high level ab initio calculations. The equilibrium structure of the complex has an asymmetric doubly hydrogen‐bonded ring. A strong hydrogen bond is donated by the hydroxyl group of nitric acid to the oxygen atom of water, and a much weaker hydrogen bond is donated by an OH bond of water to a second oxygen of nitric acid. The HNO3 unit in the complex is considerably distorted with the OH stretching frequency red‐shifted by over 300 cm−1 from the isolated molecule and the infrared intensity enhanced by an order of magnitude. The binding energy of the complex is calculated as De = −9.5 kcal/mol. The equilibrium fraction of nitric acid complexed with water is predicted to be near 1% at the Earth's surface and falls with the increase of altitude.
Climatology of tropopause folds at midlatitudes
Authors: Van Haver Philippe , De Muer Dirk , Beekmann Matthias , Mancier Christelle
Published: February 2004

A statistical analysis of a 25 years time series of routine ozone soundings at Uccle (51°48′N, 4°21′E) reveals that the frequency of tropopause folds is, within the limits of uncertainty, similar for all seasons. On the average, 4.8% of the ozone profiles show the presence of a fold whereas a shorter time series of soundings (1985–1993) obtained at the Observatoire de Haute Provence (43°54′N, 5°45′E) yields only a 2% fraction of folds. The difference between both stations is however riot entirely statistically significant. The average wet and dry β artificial radioactivity deposition in the sixties and early seventies was at a maximum at Uccle around June, in good agreement with global Sr‐90 wet deposition measurements (Volchok and Kleinman, 1971) suggesting that stratosphere‐troposphere exchange is more important during spring compared to the rest of the year. This leads to the hypothesis that, if tropopause folds are the major agent of stratosphere‐troposphere exchange (STE), they may be more efficient in spring than in autumn.
Increase of stratospheric carbon tetrafluoride (CF4) based on ATMOS observations from space
Authors: Zander R. , Solomon S. , Mahieu E. , Goldman A. , Rinsland C. P. , Gunson M. R. , Abrams M. C. , Chang A. Y. , Salawitch R. J. , Michelsen H. A. , Newchurch M. J. , Stiller G. P.
Published: February 2004

Stratospheric volume mixing ratio profiles of carbon tetrafluoride, CF4, obtained with the Atmospheric Trace Molecule Spectroscopy (ATMOS) instrument during the ATLAS (Atmospheric Laboratory for Applications and Science) −3 mission of 1994 are reported. Overall the profiles are nearly constant over the altitude range 20 to 50 km, indicative of the very long lifetime of CF4 in the atmosphere. In comparison to the stratospheric values of CF4 inferred from the ATMOS/Spacelab 3 mission of 1985, the 1994 concentrations are consistent with an exponential increase of (1.6±0.6) %/yr. This increase is discussed with regard to previous results and likely sources of CF4 at the ground. Further, it is shown that simultaneous measurements of N2O and CF4 provide a means of constraining the lower limit of the atmospheric lifetime of CF4 at least 2,300 years, two sigma.
Analysis of the relationship between seismic moment and fault length for large crustal strike‐slip earthquakes between 1977–92
Authors: Pegler G. , Das S.
Published: February 2004

We have used an uniform data set to determine the scaling relation between seismic moment M0 and fault length L for 34 large, crustal, strike‐slip earthquakes in the period 1977–92. The seismic moments used were obtained by the centroid‐moment tensor analysis. The aftershocks of each event were relocated in this study and the fault length estimated from their spatial extent. For large events, we find that in spite of some scatter in the data, the trend of this uniform data set indicates that M0 ∝L². Our data set does not show any obvious change of slope around M0 ≈ (.6–.8)× 1020 N m as was seen in a previous non‐uniform data set in Romanowicz [1992].
Anomalous crust of the Bolivian Altiplano, central Andes: Constraints from broadband regional seismic waveforms
Authors: Zandt G. , Beck S. L. , Ruppert S. R. , Ammon C. J. , Rock D. , Minaya E. , Wallace T. C. , Silver P. G.
Published: February 2004

A one‐year deployment of broadband seismographs in the Bolivian Altiplano recorded numerous intermediate‐depth earthquakes at near‐regional distances. We modeled the associated broadband waveforms of two earthquakes to estimate an average crustal structure for the Altiplano. The resulting model is characterized by an anomalously low mean P velocity of 6.0 km/s, a low Poisson's ratio of 0.25, and a crustal thickness of 65 km. The combination of the low mean velocity and low Poisson's ratio can be explained only by a predominantly quartz‐rich, felsic bulk composition. This constraint precludes significant volumes of magmatic addition from the mantle contributing to the great thickness of the Altiplano crust, but is consistent with thickening by compressive shortening concentrated in a weak felsic layer.
Highly accurate P‐SV complete synthetic seismograms using modified DSM operators
Authors: Takeuchi Nozomu , Geller Robert J. , Cummins Phil R.
Published: February 2004

In previous papers [Cummins et al., 1994ab] (hereafter referred to as DSMI and DSMII respectively), we presented accurate methods for computing complete synthetic seismograms for SH and P‐SV respectively in a spherical earth model. The SH calculations used computationally efficient modified matrix operators, but the P‐SV synthetics were computationally intensive. Geller and Takeuchi [1995] (hereafter referred to as GT95) presented a general theory for deriving modified operators and gave the explicit form of the modified operators for the P‐SV case in cylindrical or cartesian coordinates. In this paper we extend GT95's results to derive modified operators for the P‐SV case in spherical coordinates. The use of the modified operators reduces the CPU time by a factor of about 5 without a loss of accuracy. 10 CPU min on a SPARC‐20 workstation with one CPU are required to compute a profile of synthetic seismograms from DC to 20 sec period.
Energetic heavy ions observed upstream of the Earth's bow shock by the STEP/EPACT instrument on WIND
Authors: Mason G. M. , Mazur J. E. , von Rosenvinge T. T.
Published: February 2004

The Supra‐Thermal through Energetic Particle (STEP) subsystem of the EPACT experiment on the WIND spacecraft observed numerous short duration heavy ion enhancements during the ∼9 month period Nov. 1994–Sept. 1995. These enhancements were most frequent and intense when WIND was close to the magnetosphere, but were often observed also during the period when the spacecraft was >100 RE upstream. The events occur in association with high speed solar wind streams that are signatures of corotating interaction regions (CIRs). A typical event observed on January 31, 1995 when WIND was 195 RE upstream showed strong field aligned anisotropies and rapid time variations. Heavy ion abundances near 45 keV/nucleon (nuc) were He:C:O:Fe = 86 : 1.46 : ≡1 ∶ 0.12, similar to those observed at higher energies in CIRs, and distinctly different from magnetospheric ring current abundances measured on the AMPTE spacecraft. We suggest that the CIRs provide the seed population for these heavy ion events, that are then further accelerated in association with the Earth's bow shock.
Recent climate anomalies and their impact on snow chemistry at South Pole, 1987‐1994
Authors: Dibb Jack E. , Whitlow Sallie I.
Published: February 2004

Three 2‐m deep snowpits sampled at South Pole in 1994 provide detailed (2‐cm resolution) profiles of the concentrations of soluble ionic species for the period 1987–1994. The most prominent feature is a large concentration spike of SO4= in snow deposited in 1992 reflecting fallout from the eruptions of Pinatubo and Hudson in 1991. Concentrations of MSA and values of the MSA/(non‐sea‐salt SO4=) ratio are elevated for about three years centered on the prominent volcanic signal. These changes appear to be due to the extended 1991–1993 El Nino. The overlapping effects of the volcanic eruptions and El Nino circulation preclude partitioning the enhanced deposition of SO4= into volcanic and biogenic fractions. Nitrate concentration profiles show no relation to the severity of O3 depletion in the Antarctic stratosphere during the period of record. Rather, the profiles show a progressive decline of the annual peak concentrations over the top 0.5–1.0 m of each pit. This behavior is attributed to post‐deposition loss of NO3−, presumably by reemission of HNO3 into the atmosphere.
Emulation of the results from a coupled general circulation model using a simple climate model
Authors: Raper S. C. B. , Cubasch U.
Published: February 2004

An upwelling diffusion (UD) model has been fitted to the results of a globally coupled ocean atmosphere general circulation model (O/AGCM). In order to adequately simulate the results of the O/AGCM, the differential heating over land and ocean, the change of the upwelling rate with rising mixed‐layer temperature and the climate adjustment of the O/AGCM evident in the control simulation had to be taken into account.

Comparisons using the results of four O/AGCM perturbation experiments show that the timing of the adjustment in the O/AGCM control run differs from that in the perturbed runs. The UD model simulates the global mean temperature evolution, as calculated by the O/AGCM reasonably well. However, when time dependent upwelling is included, the UD model substantially overestimates the thermal expansion compared to this O/AGCM. Possible reasons for this overestimation have been identified.
Stratospheric NO and NO2 abundances from ATMOS Solar‐Occultation Measurements
Authors: Newchurch M. J. , Allen M. , Gunson M. R. , Salawitch R. J. , Collins G. B. , Huston K. H. , Abbas M. M. , Abrams M. C. , Chang A. Y. , Fahey D. W. , Gao R. S. , Irion F. W. , Loewenstein M. , Manney G. L. , Michelsen H. A. , Podolske J. R. , Rinsland C. P. , Zander R.
Published: February 2004

Using results from a time‐dependent photochemical model to calculate the diurnal variation of NO and NO2, we have corrected Atmospheric Trace MOlecule Spectroscopy (ATMOS) solar‐occultation retrievals of the NO and NO2 abundances at 90° solar zenith angle. Neglecting to adjust for the rapid variation of these gases across the terminator results in potential errors in retrieved profiles of ∼20% for NO2 and greater than 100% for NO at altitudes below 25 km. Sensitivity analysis indicates that knowledge of the local O3 and temperature profiles, rather than zonal mean or climatological conditions of these quantities, is required to obtain reliable retrievals of NO and NO2 in the lower stratosphere. Extremely inaccurate O3 or temperature values at 20 km can result in 50% errors in retrieved NO or NO2. Mixing ratios of NO in the mid‐latitude, lower stratosphere measured by ATMOS during the November 1994 ATLAS‐3 mission compare favorably with in situ ER‐2 observations, providing strong corroboration of the reliability of the adjusted space‐borne measurements.
Pleistocene sea levels and tectonic uplift based on dating of corals from Sumba Island, Indonesia
Authors: Bard E. , Jouannic C. , Hamelin B. , Pirazzoli P. , Arnold M. , Faure G. , Sumosusastro P. , Syaefudin
Published: February 2004

We collected and dated fossil corals from the uplifted reef tracts of Sumba Island. Mass spectrometry (TIMS and AMS) was used to obtain reliable and precise radiochronological results. It is possible to identify outcrops corresponding to major sea level high stands: isotope stage 1 (starting at 7.1 kyr BP), 5a (c.a. 86 kyr BP), 5c (c.a. 105 kyr BP), 5e (between 119 and 132 kyr BP) and 9 (c.a. 305 kyr BP). The radiochronological data are thus broadly consistent with the timing of sea level fluctuations predicted by the astronomical theory of paleoclimates. Comparison with similar data from other terrace sequences and from benthic δ18O records indicates that the average tectonic uplift rate at Cape Laundi, Sumba, is on the order of 0.2–0.5m/kyr. The lowest values (<0.3m/kyr) lead to the build‐up of polycyclic topographic terraces in which it is possible to find corals grown during different interstadial or even interglacial times.
Ground‐based measurements of OClO and HCl in austral spring 1993 at Arrival Heights, Antarctica
Authors: Kreher K. , Keys J. G. , Johnston P. V. , Platt U. , Liu X.
Published: February 2004

Ground‐based measurements of stratospheric OClO and HCl total columns are reported. The data were obtained during the spring season of 1993 at Arrival Heights (77.8°S/166.7°E), Antarctica, using zenith sky and direct sun absorption spectroscopy in the visible and infrared spectral regions. Together these data sets represent complementary measurements of chlorine species in Antarctica over an extended period in spring. To illustrate aspects of Antarctic stratospheric chemistry and dynamics that are significant in current studies of ozone depletion, the OClO and HCl data are supplemented by simultaneously measured NO2 data as well as ancillary data from other sources.

Observations of OClO, HCl and NO2 provide an indication of the degree of the perturbed chemistry that is operating in the spring stratosphere. The measurements illustrate the repartitioning of active chlorine into the less reactive HCl reservoir as spring progresses. Comparison of the data with total ozone and stratospheric temperature records shows that the springtime chlorine variations are in agreement with currently accepted models of Antarctic ozone depletion chemistry.
Failure stress change caused by the 1992 Erzincan Earthquake (Ms=6.8)
Authors: Nalbant Süleyman S. , Barka A. Aykut , Alptekin Ömer
Published: February 2004

We calculated Coulomb failure stress change caused by the March 13, 1992 Erzincan, Turkey, earthquake, and explored the relationship between failure stress and the aftershock distribution which includes the Pülümür earthquake (Ms=5.8) that occurred two days later. One of the most significant features of the Erzincan earthquake was the location of aftershocks, which did not correspond with either the eastern segment of the North Anatolian fault zone or the Ovacik fault. This feature can be explained by mapping the failure stress due to the Erzincan earthquake. The map revealed that there is a significant correlation between the aftershock distribution and the areas where static stress was raised by ≥0.3 bar. The 1992 Erzincan earthquake raised the Coulomb failure stress about 1.4 bar at the site of the Pülümür event. This stress rise and optimum orientation of the Pülümür fault favoured its occurrence.
A difficulty with using the Frozen Flux Hypothesis to find steady core motions
Authors: Gubbins David , Kelly Peter
Published: February 2004

Many studies have used the frozen flux hypothesis to estimate core flow from geomagnetic secular variation (SV). Part of the flow remains indeterminate without some additional constraint. A theorem of Voorhies and Backus states that steady flows can be determined uniquely. Frozen flux requires the time scale of SV, τB, to be much shorter than the diffusion time, τD, and the steady motion theorem requires the time scale for change in flow, τV, be much longer than τB. Here we argue we must also have τV ≪ τD because truly steady flow will eventually lead to a steady equilibrium magnetic field and no SV. We illustrate the difficulty by a numerical example with a prescribed steady flow at the top of the core for which frozen flux inversions never yield the correct velocity. Core motions derived using the steady motions theorem may be grossly in error.
Balloon observations of organic and inorganic chlorine in the stratosphere: The role of HClO4 production on sulfate aerosols
Authors: Jaeglé Lyatt , Yung Yuk L. , Toon Geoffrey C. , Sen Bhaswar , Blavier Jean‐François
Published: February 2004

Simultaneous observations of stratospheric organic and inorganic chlorine were made in September 1993 out of Fort Sumner, New Mexico, using the JPL balloon‐borne MkIV interferometer. Between 15 and 20 km, a significant fraction (20–60%) of the inorganic chlorine could not be accounted for by the sum of measured HCl, ClONO2, and HOCl. Laboratory measurements of the reaction of ClO radicals on sulfuric acid solutions have indicated that, along with HCl, small amounts of perchloric acid, HClO4, were formed. Very little is known about the fate of HClO4 in the stratosphere and we use a photochemical box model to determine the impact of this new species on the partitioning of inorganic chlorine in the stratosphere. Assuming that HClO4 is photochemically stable, it is shown that in the enhanced aerosol loading conditions resulting from Mt. Pinatubo's eruption, HClO4 could represent a significant reservoir of chlorine in the lower stratosphere, sequestering up to 0.2 ppbv (or 50%) of the total inorganic chlorine at 16 km. The occurrence of this new species could bring to closure the inorganic chlorine budget deficiency made apparent by recent ER‐2 aircraft in situ measurements of HCl.
Crater Lake heat losses estimated by remote sensing
Authors: Oppenheimer Clive
Published: February 2004

Volcanic crater lakes represent the uppermost parts of magmatic‐hydrothermal systems, and can be regarded as calorimeters in order to estimate subsurface heat fluxes. Here, thermal infrared images recorded by the Landsat Thematic Mapper (TM) are employed to map surface temperatures across Poás (Costa Rica), Ruapehu (New Zealand), and Kawah Ijen and Kelut (Indonesia) volcano lakes. First, lake areas are constrained by inspection of the nonthermal bands. These estimates are used to define “lake” pixels in the thermal band, and the temperature of each flagged pixel is calculated. Alternatively, the “hottest” pixel can be assumed to represent the temperature of the whole lake surface, mitigating the effects of mixed land/water pixels. Taking appropriate values for air temperature, humidity and windspeed, surface heat flux densities and power outputs are then derived from bulk aerodynamic or other formulae. Improved capabilities for monitoring crater lakes will be provided by forthcoming satellite missions, notably the Enhanced Thematic Mapper (ETM+) and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER).
Rheological control of oceanic crust separation in the transition zone
Authors: van Keken P. E. , Karato S. , Yuen D. A.
Published: February 2004

Mineral physics observations suggest that distinct density and rheological differences exist between the crustal component of oceanic lithosphere and the underlying mantle. We have conducted numerical experiments to investigate the influence of both density and viscosity on the effectiveness of recycling of oceanic crust into the lower mantle. Confirming previous results, the density inversion at 670 km depth alone is not sufficient to prevent crustal recycling. However, a soft layer may exist between the strong garnet crust and cold slab interior. Models employing a simplified Newtonian sandwich model show that this thin, weak layer can effectively decouple the crust and slab. Once entrained into the lower mantle, the then lighter crust can rise sufficiently fast as a Rayleigh‐Taylor instability to avoid further entrainment. These results suggest that the crustal component of slabs may be trapped at 670 km depth, leading to a garnet enriched transition zone.
Coastal uplift on active normal faults: The Eliki Fault, Greece
Authors: Stewart Iain , Vita‐Finzi Claudio
Published: February 2004

The Eliki Fault forms part of a system of major normal fault segments that borders the southern margin of the Gulf of Corinth half graben. Radiocarbon dating of elevated marine fossils reveals broadly uniform Holocene coastal uplift, at a time‐averaged rate of 1.5 mm/yr, both along the Eliki Fault and in the transfer zone that separates it from the neighbouring fault segment. Coseismic uplift increments are considered to account for only a minor part of the 6 m of emergence recorded here in the last 3000 years. Reappraisal of shoreline data from the Perachora Peninsula at the eastern end of the Gulf of Corinth indicates a similar, though less rapid (0.7 mm/yr), pattern of uniform Holocene emergence. As these Holocene coastal records embody both coseismic and interseismic deformation they can be used to characterise long‐term tectonic strain.
Resolving diversely polarized, superimposed signals in three‐component seismic array data
Authors: Wagner Gregory S.
Published: February 2004

I present a novel processing approach for three‐component seismic array data that entails a succession of principal component analysis, factor analysis, and principal component analysis. This formulation represents an effort to conduct principal‐component polarization analysis on isolated signals whose propagation direction and apparent propagation direction have been estimateda prioriusing high‐resolution wave‐front analysis. A comparison of the signal parameter estimates realized using single‐site three‐component, vertical‐component array, and three‐component array data is provided.
Influence of the electrical diffuse layer and microgeometry on the effective ionic diffusion coefficient in porous media
Authors: Revil A. , Darot M. , Pezard P. A.
Published: February 2004

This study models the effect of the electrical diffuse layer at the pore matrix interface on ionic diffusion processes in a porous medium in presence of a concentration gradient. We find that the equation D = Df/Fø usually used to compute in steady state conditions the effective diffusion coefficient, D, of a porous medium as a function of the salt diffusion coefficient, Df, the electrical formation factor, F, and the porosity, ø, should be replaced by: D = ( Df/Fø)ξ, in the presence of an electrical diffuse layer at the pore‐matrix interface. The correction factor, ξ arises from the cross‐coupling of ionic fluxes due to electroneutrality requirement.
The regime of decreased OH vertical column abundances at Fritz Peak Observatory, CO: 1991–1995
Authors: Burnett Clyde R. , Burnett Elizabeth B.
Published: February 2004

The 18‐year data base for vertical column abundance measurements of atmospheric OH at Fritz Peak Observatory, Colorado (40°N, 105°W), exhibits a relatively abrupt change in seasonal behavior during 1991 through 1995. Late summer through early fall abundances, especially, for each year of the 1991–1995 period are significantly below the comparable seasonal average for 1980–1990. Early morning abundances for August through October at solar zenith angles greater than 45° exibit an average reduction of about 0.8 × 1013/cm², which at a solar zenith angle of 60° is a 15% column decrease.
Contact discontinuities in collisionless plasmas: A comparison of hybrid and kinetic simulations
Authors: Lapenta G. , Brackbill J. U.
Published: February 2004

A comparison of full kinetic and hybrid simulations for Te/Ti> 1, where Te(Ti) is the electron (ion) temperature, indicates that contact discontinuities cannot persist in collisionless plasmas. A simple analysis suggests that the potential barrier to ion mass and thermal transport identified by Wu et al. [1994] in their hybrid calculations can preserve the contact discontinuity if the contributions of electron thermal transport are small. When Te/Ti> 1, electron energy transport in kinetic calculations results in large potentials which reduce the effectiveness of the potential barrier. Thus, contact discontinuities are unlikely to be observed in spacecraft observations.
On the difference between the average values of Br² in the Atlantic and Pacific hemispheres
Authors: Walker Andrew D. , Backus George E.
Published: February 2004

Recent work on reversals of the earth's magnetic field [Clement, 1991; Constable, 1992; Laj et al., 1991; Runcorn, 1992] and work on low rates of change of the radial magnetic field, Br, in the Pacific hemisphere (see Jacobs [1994] page 8, for a summary) suggest that the statistics of Br differ between the Pacific and Atlantic hemispheres. The question of statistical invariance of the magnetic field is interesting in its own right [Courtillot et al, 1992], and we study this hypothesis by investigating the statistical significance of the difference between the average value of Br² in the Atlantic and Pacific hemispheres at three different radii. The differences between the average value of Br² in the Atlantic hemisphere and the average value of Br² in the Pacific hemisphere at all three radii are incompatibly large with two statistical models of Br. The differences are incompatibly large at two of three radii when a third statistical model is used. The results suggest that further work on the statistical properties of Br is warranted and provide another test for normality of spherical harmonic coefficients.
Analytic minimum information deconvolution and its application to ocean bottom seismometer data
Authors: Kim Han‐Joon , Marillier François
Published: February 2004

Seismic refraction/wide angle reflection data for the study of the earth's crust generally lack resolution due to the low frequency wavelets from seismic sources. Standard deconvolution techniques to improve resolution of the data are limited by phase‐shifted waveforms such as supercritical reflections from the Moho as well as various refraction phases from the crust. We extended the minimum information deconvolution technique to the analytic formulation to deconvolve seismic data that contain phase‐shifted wavelets. When applied to a seismogram, analytic deconvolution yields the amplitude of the earth's impulse response function in the form of the signal envelope. An application example with ocean bottom seismometer data acquired along the Canadian continental margin of the Atlantic shows a remarkable improvement in resolution by compressing the wavelets effectively.
Broadband electrons observed by the DMSP satellites during storm‐time substorms
Authors: Shiokawa K. , Yumoto K. , Meng C.‐I. , Reeves G.
Published: February 2004

Electrons that have intense broadband spectra are found to precipitate in the equatorward part of the auroral oval. The electrons are observed by the DMSP satellites in association with particular substorms during the main phase of magnetic storms. Electron fluxes are drastically enhanced after the substorm onset at all the energies measured (32 eV to 30 keV) at magnetic latitudes lower than 60° (L < 4). The energy flux of the electrons exceeds 1.0 × 1013 eV cm−2 s−1 sr−1. The intense electron precipitation lasts less than 1 h. These characteristics are significantly different from those seen in the central plasma sheet region. We suggest that an unknown energization mechanism of these electrons exists at the inner part of the plasma sheet at L < 4 during these particular storm‐time substorms.
Blue starters∷ Brief upward discharges from an intense Arkansas thunderstorm
Authors: Wescott E. M. , Sentman D. D. , Heavner M. J. , Hampton D. L. , Osborne D. L. , Vaughan O. H.
Published: February 2004

This paper documents the first observations of a new stratospheric electrical phenomenon associated with thunderstorms. On the night of 30 June (UT 1 July) 1994, 30 examples of these events, which we have called “blue starters,” were observed in a 6 m 44 s interval above the very energetic Arkansas thunderstorm where blue jets were first observed. The blue starters are distinguished from blue jets by a much lower terminal altitude. They are bright and blue in color, and protrude upward from the cloud top (17–18 km) to a maximum 25.5 km (83,655 ft.) in altitude. All blue starters events were recorded from two small areas near Texarkana, Texas/Arkansas where hail 7.0 cm in diameter was falling. Comparison to cloud‐to‐ground (CG) lightning flashes revealed: 1. Blue starters were not observed to be coincident with either positive or negative CG flashes, but they do occur in the same general area as negative CG flashes; 2. Cumulative distributions of the negative CG flashes in ±5 s before and after the starter and within a radius of 50 km shows a significant reduction for about 3 s following the event in the two cells where starters and jets were observed. The energy deficit is approximately 109 J. It is possible that blue starters are a short‐lived streamer phenomenon.
Surface manifestation of internal tides generated near Hawaii
Authors: Ray Richard D. , Mitchum Gary T.
Published: February 2004

Analysis of Topex/Poseidon satellite altimetry reveals short‐wavelength fluctuations in the ocean surface tide that are attributable to internal tides. A significant fraction of the semidiurnal internal tide generated at the Hawaiian Ridge is evidently phase‐locked to the astronomical potential and can modulate the amplitude of the surface tide by ∼5 cm. The internal tide is thus easily mapped along satellite groundtracks, and it is found to be spatially coherent over great distances, with waves propagating well over 1000 km from the Hawaiian Ridge before decaying below noise level. Both first and second baroclinic modes are observed in both the M2 (lunar) and S2 (solar) tides. The high space‐time coherence is in sharp contrast to what is often inferred from current‐meter observations, but it confirms recent speculations from an acoustic experiment north of Hawaii.
Flow mechanism and viscosity in basaltic magma chambers
Authors: Nicolas A. , Ildefonse B.
Published: February 2004

Magmatic flow in the dense suspension of crystallizing gabbros below the free surface of basaltic magma chambers is considered from the point of view of flow mechanisms and rheology. Hyperdense suspensions (∼20% melt fraction) may arise if flat plagioclase crystals develop a strong preferred orientation induced by magmatic flow. With the help of Nomarski differential interference contrast and back scattered electron figures, we show that suspension flow is possible even for smaller melt fractions if impingements between moving crystals are reduced by chemical dissolution at their contact points. This dissolution process is rate controlling. With strain rates near 10−9 s−1 and viscosities near 1014–16 Pa.s, such crystalline mushes should be closer to plastically deforming solids than to the overlying basaltic suspension. If we characterize magma chambers by suspension flow, no matter how small the melt fraction, magma chambers below oceanic fast spreading centers should not be restricted to a perched melt lens, but should extend to the Moho and comprise the entire volume of observed strong seismic attenuation.
Gravitational oscillations in the length of day
Authors: Buffett Bruce A.
Published: February 2004

Gravitational interactions between mass anomalies in the core and the mantle cause rotational oscillations of the Earth that can be detected as fluctuations in the length of day. A simple theoretical expression for the frequency of these oscillations is derived using a Lagrangian formulation. The value of the frequency depends on the aspherical distribution of mass, providing a useful constraint on the structure of the Earth. Numerical estimates are obtained using two different models of density, both of which are based on seismically inferred density anomalies. The predicted period of the gravitational oscillation is 2 to 3 years, depending on the choice of density model. Longer period modes of oscillation can also arise from the smaller convective fluctuations in the core about the hydrostatic state. Qualitative estimates for these low frequency oscillations depend on the size of the density fluctuations, but typical values yield a period of several hundred years.
Changes in orientation of near‐surface stress field as constraints to mantle viscosity and horizontal stress differences in eastern Canada
Authors: Wu Patrick
Published: February 2004

Observations indicate that the orientation of the stress field in Eastern Canada has changed significantly during the last 9,000 years. If this temporal rotation of stress orientation is due to changes of the dominant stress component from rebound stress 9,000 years ago to tectonic stress at the present, then this rotation in stress orientation can be used to constrain mantle viscosity and the difference between the horizontal tectonic (principal) stresses. Rebound stress in a Maxwell earth due to the application of a realistic ice load is calculated with the Finite Element method and is superposed on tectonic stress to give the total stress. It is demonstrated that large tectonic stress differences (>10 MPa) or high viscosity (≥ 1022 Pa‐s) in the lower‐mantle cannot explain this temporal stress rotation because in the former case, stress orientation is determined by the static tectonic stress while for the latter case, rebound stress continues to dominate the current stress orientation.
Evidence for anisotropy in the deep mantle beneath Alaska
Authors: Matzel Eric , Sen Mrinal K. , Grand Stephen P.
Published: February 2004

We consider the possibility that the velocity structure of D″ is anisotropic. The data we examined consist of seismograms from 9 deep Japanese earthquakes recorded at WWSSN receiver stations in North America. The source‐receiver combinations span distances of 70°–106° with associated S waves passing through D″ beneath Alaska. Differential travel times of the S, Scd, ScS and SKS phases are used to constrain the velocity structure in D″. Shear waves refracted by D″ are observed beyond 72.2° and provide a sensitive measurement of the velocity structure in D″. Beyond 93°, the vertically polarized (SV) and horizontally polarized (SH) shear waves often appear distinctly split, although, at distances less than 89° the components are more nearly synchronous. Near 94°, SH occurs as a double arrival. SV in this range, however, remains a single arrival roughly synchronous with the second SH arrival. We have been unable to reproduce these effects in isotropic model synthetics. Synthetics for transversely isotropic models have been computed that do match these waveforms. The anisotropy was constrained to be only within D″, with a vertical symmetry axis. We conclude that these observations may be explained by an anisotropic D″ layer. The D″ discontinuity may be due to a transition to anisotropic mantle a few hundred kilometers above the core‐mantle boundary.