bluuebunny/crossref_metadata_2025 huggingface dataset:
Mantle viscosity from the simultaneous inversion of multiple data sets pertaining to postglacial rebound
Authors: Peltier W. R. , Jiang Xianhua
Published: February 2004

We employ the formalism of Bayesian inference to invert three distinct data sets related to the phenomenon of glacial isostatic adjustment. These data consist, respectively, of the wavenumber spectrum of relaxation times for Fennoscandian rebound inferred by McConnell (1968), the characteristic relaxation times for a large collection of distinct 14C dated relative sea level curves from both Canada and Fennoscandia, and two data related to the rotational response of the Earth to the glaciation‐deglaciation cycle of the late Pleistocene ice age. Our analyses show that the spherically symmetric viscosity structure objectively inferred on the basis of these data from the once glaciated regions of the Northern Hemisphere allows a fully satisfactory reconciliation of both US East Coast relative sea level observations as well as providing a close fit to the requirements of aspherical geoid anomalies.
Long term trends in sporadic E layers and electric fields over Fortaleza, Brazil
Authors: Abdu M. A. , Batista I. S. , Muralikrishna P. , Sobral J. H. A
Published: February 2004

Long term trends in the sporadic E‐layer occurrences and associated electric fields over the equatorial station, Fortaleza are analysed using 16 years (1975–1990) of ionosonde data. The secular drift of the magnetic equator and hence that of the equatorial electrojet current (EEJ) to northward of Fortaleza has resulted in marked long term changes in the occurrence characteristics of the different types of Es layers: the q‐type (arising from electrojet instability processes) and the 1, f, c and h types (resulting from wind/wind shear mechanisms). Systematic decrease in the occurrence rates of the q‐type Es, accompanied with increases in the remaining types of Es, was registered from 1975 to 1990, during which period the magnetic equator drifted to north of Fortaleza by ∼400km. The long term trend manifests competing roles of the equatorial electric field and wind systems, in the generation of the different types of Es layers as a function of the distance from the electrojet center. The F‐layer dynamo electric field is seen to exercise strong control of Es layer formation near sunset. Solar cycle variations, represented by the Fl0.7cm flux, seems to be present in elctrojet intensity and the lower thermospheric wind system.
Large‐scale properties and solar connection of the heliospheric current and plasma sheets: WIND observations
Authors: Lepping Ronald P. , Szabo Adam , Peredo Mauricio , Hoeksema J. T.
Published: February 2004

This letter presents the results of interplanetary magnetic field (IMF) analyses performed on WIND magnetometer data covering the first five months of the mission. It discusses the timing of the large scale (1–2 AU) IMF polarity changes at 1 AU and compares it to predictions that are based on a potential field solar source surface model [Hoeksema, 1989], with excellent results. General statistical properties of locally observed heliospheric current sheets, from 212 selectively chosen individual crossings, are estimated from variance analysis of their field transitions. Some of the properties discussed are: current sheet normal direction, relative BN‐component, and the rotation angle of the field in the current sheet‐plane. When a related plasma sheet is present it has a complex, and difficult to characterize, magnetic field magnitude‐profile. When the plasma sheet's presence is most apparent, the directional discontinuity of the field (the embedded current sheet) appears to be most abrupt, based on preliminary results from about 1/2 of the 212 cases.
Observations of a very thin collisionless shock
Authors: Newbury J. A. , Russell C. T.
Published: February 2004

The structure of collisionless shocks is governed by the upstream plasma conditions. The laminar collisionless shock is well studied and has been found to have a ramp thickness on the order of an ion inertial length. The behavior of the shock at higher Mach number and β is not as thoroughly studied. However, it has been speculated that an exactly perpendicular shock behaves like the soliton wave solution from classic plasma theory. This would result in a much thinner shock ramp with a thickness on the order of electron inertial lengths. No such thin shock has been observed in the laminar regime. In this study of ISEE‐1 and ‐2 crossings of supercritical, nearly‐perpendicular bow shocks (θBn > 80°), we find that the shock velocity is highly variable between spacecraft crossings and during observations. The fine structure of high velocity shocks is poorly resolved by the ISEE‐1 and ‐2 magnetometers due to filters used to prevent aliasing of the digitized data. When we restrict our attention to slowly moving shocks, we find one example of a very thin shock with a ramp thickness of only two electron inertial lengths. We suggest that this thin structure arises when the nearly perpendicular shock moves into the perpendicular regime, but cannot confirm this conjecture because of the uncertainty and temporal variability of the normal.
A seafloor gravity profile across the TAG Hydrothermal Mound
Authors: Evans Rob L.
Published: February 2004

A series of on‐bottom gravity stations were completed across the TAG hydrothermal mound during a dive program with the Japanese Shinkai 6500 submersible. The mound appears as a gravity high (∼2 mGal) with respect to the surrounding seafloor, reflecting the high density sulfides of which it is comprised. Three‐dimensional modeling of the data shows no evidence of a dense sulfide root extending deep into the seafloor below the mound, which would be associated with a broad, highly altered, stockwork zone. Sulfide thickness appears to be greatest (∼50m) to the north of the mound. The thickness decreases sharply to the south, reaching a steady value of about 10m just to the south of the Kremlin area. The mass of sulfides within the mound is estimated at 3 million tonnes. The surrounding basaltic seafloor appears to have a density of 2400±100 kgm−3, indicating a surficial porosity of between 20–30%.
Precursory localization and development of microfractures along the ultimate fracture plane in amphibolite under triaxial creep
Authors: Satoh Takashi , Shivakumar Karekal , Nishizawa Osamu , Kusunose Kinichiro
Published: February 2004

In a triaxial creep experiment in amphibolite, we clearly found a precursory localization and development of microfractures along the final fracture plane using an AE (acoustic emission) source location technique. The precursory localization of AE hypocenters first nucleated near a pre‐existing macroscopic defect and then extended gradually along the final fracture plane prior to failure On the other hand, no significant precursory localization of AE hypocenters on the final fracture plane before failure has been reported in rock samples free of pre‐existing macroscopic defects. This difference in AE occurrence patterns before failure could be explained by the difference in the degree of damage in the portion of the rock surrounding the localization zone when it nucleates.
NOy correlation with N2O and CH4 in the midlatitude stratosphere
Authors: Kondo Y. , Schmidt U. , Sugita T. , Engel A. , Koike M. , Aimedieu P. , Gunson M. R. , Rodriguez J.
Published: February 2004

Total reactive nitrogen (NOy), nitrous oxide (N2O), methane (CH4), and ozone (O3) were measured on board a balloon launched from Aire sur l'Adour (44°N, 0°W), France on October 12, 1994. Generally, NOy was highly anti‐correlated with N2O and CH4 at altitudes between 15 and 32 km. The linear NOy‐N2O and NOy‐CH4 relationships obtained by the present observations are very similar to those obtained on board ER‐2 and DC‐8 aircraft previously at altitude below 20 km in the northern hemisphere. They also agree well with the data obtained by the Atmospheric Trace Molecule Spectroscopy (ATMOS) instrument at 41°N in November 1994. Slight departures from linear correlations occurred around 29 km, where N2O and CH4 mixing ratios were larger than typical midlatitude values, suggesting horizontal transport of tropical airmasses to northern midlatitudes in a confined altitude region.
Monte Carlo slip inversion in the frequency domain∷ Application to the 1992 Nicaragua Slow Earthquake
Authors: Ihmlé Pierre F.
Published: February 2004

The spatio‐temporal complexity of moment release of the 1992 Nicaragua slow earthquake (Mw=7.7) is estimated by simulated annealing. Contrary to linearized inversions, Monte Carlo techniques do not make assumptions about a priori features of the model, in particular, large variations in rupture velocities can be imaged. Relative spectra between the main shock and an empirical Green's function were obtained from 4–44 mHz using first and second orbit fundamental mode Rayleigh waves. The spectra were inverted for the moment distribution on a 2D horizontal fault, under the physical constraints of slip positivity and causality. The non‐linear inversion revealed two main regions of slip. One centered 20 km to the NW of the epicenter, the other 160 km to the SE, but delayed by 70 s. Rupture velocities in the slipping patches were found to be low, around 1 km/s. Large amount of slip occurred trench ward of the epicenter, accounting for the large tsunami excitation. Analysis of the slip distribution suggests that the slow and smooth nature of the 1992 Nicaragua event may be related to the frictional properties at the plate interface.
Micron‐sized particles detected in the vicinity of Jupiter by the Voyager plasma wave instruments
Authors: Tsintikidis D. , Gurnett D. A. , Kurth W. S. , Granroth L. J.
Published: February 2004

Wideband waveform data obtained by the plasma wave instruments onboard the Voyager 1 and 2 spacecraft have been used to study micron‐sized dust particles in the vicinity of Jupiter. The technique used was developed during the fly by s of Saturn, Uranus, and Neptune, and makes use of the fact that a particle striking the spacecraft at 10–20 km/s causes a voltage pulse in the plasma wave receiver. The waveform of the voltage pulse is much different than the waveform of plasma waves and provides a highly reliable method of detecting micron‐sized dust particles. Although the dust impact rate observed in the vicinity of Jupiter is much lower than the rates at Saturn, Uranus, and Neptune, the particles are easily detectable. Approximately 1200 48‐second frames of wideband waveform data were examined in the vicinity of Jupiter. Dust impact signatures were found in approximately 20% of these frames. The peak impact rates are about 1 impact per second, and the peak number densities are about 10−5 m−3. Most of the impacts occurred near the equatorial plane at radial distances less than about 35 RJ from Jupiter. Analysis of the detection threshold indicates that the particles have masses greater than 10−11 g, which corresponds to particles with diameters of a few micrometers or larger.
Multifractal analysis of Vesuvius volcano eruptions
Authors: Godano Cataldo , Civetta Lucia
Published: February 2004

The standard statistical analysis of volcanic eruptions could be not very useful tools to describe temporal variations of the volcanic events clustering due to the shortness of the catalogues. A more appropriate approach is the multifractal analysis. If interevent times between eruptions are fractally distributed, they have a scale invariant structure and the behaviour of the catalogue can be described in terms of Poissonian or stationary clustered distribution. On the contrary, if a multifractal distribution is observed, the clustering cannot be considered constant. We analyse the catalogue of occurrence times of Vesuvius eruptions from 1631 to 1944 that can be considered complete. We find a multifractal distribution. Such a result implies a clustering degree that varies in time. At small scales a weak clustering is observed, while at large scale the catalogue can be considered Poissonian. This implies that the correlation between the events of the volcanic activity cycles is very weak and that the dynamics evolves at the same time scales within a given cycle and between cycles.
Conductive heat flow at the TAG Active Hydrothermal Mound: Results from 1993–1995 submersible surveys
Authors: Becker K. , Von Herzen R. , Kirklin J. , Evans R. , Kadko D. , Kinoshita M. , Matsubayashi O. , Mills R. , Schultz A. , Rona P.
Published: February 2004

We report 70 measurements of conductive heat flow at the 50‐m‐high, 200‐m‐diameter TAG active hydrothermal mound, made during submersible surveys with Alvin in 1993 and 1995 and Shinkai 6500 in 1994. The stations were all measured with 5‐thermistor, 0.6‐ or 1‐m‐long Alvin heat flow probes, which are capable of determining both gradient and thermal conductivity, and were transponder‐navigated to an estimated accuracy of ±5–10 m relative to the 10‐m‐diameter central complex of black smokers. Within 20 m of this complex, conductive heat flow values are extremely variable (0.1‐ > 100 W/m²), which can only be due to local spatial and possible temporal variability in the immediate vicinity of the vigorous discharge sites. A similar local variability is suggested in the “Kremlin” area of white smokers to the southeast of the black smoker complex. On the south and southeast side of the mound, there is very high heat flow (3.7‐ > 25 W/m²) on the sedimented terraces that slope down from the Kremlin area. Heat flow is also high (0.3–3 W/m²) in the pelagic carbonate sediments on the surrounding seafloor within a few tens of meters of the southwest, northwest, and northeast sides of the mound. On the west side of the sulfide rubble plateau that surrounds the central black smoker peak, there is a coherent belt of very low heat flow (<20 mW/m²) 20–50 m west of the smokers, suggestive of local, shallow recharge of bottom water. The three submersible surveys spanned nearly two years, but showed no indication of any temporal variability in conductive heat flow over this time scale, whether natural or induced by ODP drilling in 1994.
Downward trends in the frequency of intense at Atlantic Hurricanes during the past five decades
Authors: Landsea Christopher W. , Nicholls Neville , Gray William M. , Avila Lixion A.
Published: February 2004

There is concern that the enhanced greenhouse effect may be affecting extreme weather events such as tropical cyclones. The North Atlantic basin offers a reliable, long‐term record of tropical cyclone activity, though it may not be representative of tropical cyclones throughout the rest of the tropics. The most recent years of 1991 through 1994 have experienced the quietest tropical cyclone activity on record in terms of frequency of tropical storms, hurricanes, and intense hurricanes. This was followed by the 1995 hurricane season, one of the busiest in the past 50 years. Despite 1995's activity, a long‐term (five decade) downward trend continues to be evident primarily in the frequency of intense hurricanes. In addition, the mean maximum intensity (i.e., averaged over all cyclones in a season) has decreased, while the maximum intensity attained by the strongest hurricane each year has not shown a significant change.
The SCIFER Experiment
Authors: Kintner Paul M. , Bonnell John , Arnoldy Roger , Lynch Kristina , Pollock Craig , Moore Tom , Holtet Jan , Deehr Charles , Stenbaek‐Nielsen Hans , Smith Roger , Olson John , Moen Jøran
Published: February 2004

The Sounding of the Cleft Ion Fountain Energization Region (SCIFER) experiment was conducted to investigate the ionospheric origin of the Cleft Ion Fountain (CIF). In the previous decade several high altitude spacecraft studies concluded that the CIF is the principal source of mass for the magnetosphere, especially O+. Yet the ionospheric cleft in the altitude range between 1000 km and 2000 km had not been explored since the ISIS spacecraft experiments in the 1970s. SCIFER was designed to fill that gap with instrumentation that provided continuous spatial/temporal resolution two orders of magnitude better than that achieved by previous orbiting spacecraft.
Volcanic Ash Model verification using a Klyuchevskoi Eruption
Authors: Heffter Jerome L.
Published: February 2004

Satellite imagery of volcanic ash is used to verify the Air Resources Laboratory (ARL) time dependent three‐dimensional Volcanic Ash Forecast Transport And Dispersion (VAFTAD) model. VAFTAD forecasts are included in volcano hazards alert messages issued as an aid to aircraft operations for ash clouds that reach flight levels of 6 km or higher and may drift hundreds to thousands of kilometers from an explosive volcanic eruption. VAFTAD is run by users connected through Internet to a workstation at ARL using screen‐prompted input, and is applicable globally. Model output gives charts of the forecast ash cloud which are phone‐faxed back to the user and made available for public distribution over various weather information distribution systems and Internet. Volcanic ash model verification is essential for interpreting ash cloud forecasts and applying them for decision‐making. The VAFTAD model verification is detailed using a September 1994 eruption of the Klyuchevskoi Volcano on Kamchatka Peninsula in eastern Russia. Both the downwind extent of the ash cloud along the main flow axis and the ash cloud width perpendicular to the main flow axis, seen on satellite imagery, compared remarkably well with the VAFTAD calculations that used eruption source information and archived meteorological analyses as model input.
Magnetic cloud‐bow shock interaction: WIND and IMP‐8 observations
Authors: Lepping R. P. , Szabo A. , Ogilvie K. W. , Fitzenreiter R. J. , Lazarus A. J. , Steinberg J. T.
Published: February 2004

An interplanetary magnetic cloud of typical magnetic field flux rope structure and of diameter 0.23 AU was observed in WIND magnetic field and plasma data of February 8, 1995. Starting at about 1 hour later it was also observed at IMP 8, where the bow shock reached at least 39 RE from Earth, on the dusk side, for brief periods within the cloud. This expanded bow shock changed from a perpendicular to pulsation type at IMP‐8 as a result of the magnetic field smoothly changing direction within the passing cloud, and its surface normal was nearly, and unexpectedly, invariant during the expansion. It is inferred that, within measurement error, the bow shock's shape expanded almost ‘isotropicly’ and that the magnetosheath became unusually wide.
Cyclic fluid effusion accompanied by pressure change: Implication for volcanic eruptions and tremor
Authors: Ida Yoshiaki
Published: February 2004

Magma effusion and tremor sometimes occur in quite regular intervals with periodic pressure changes, as observed in volcanic eruptions at Kilauea Volcano, lava dome growth at Unzen Volcano, and tremor episodes at Izu‐Oshima Volcano. These events have more or less asymmetric pressure change of quasi‐sinusoidal to saw‐toothed shape with longer time elapsing in build‐up of the fluid pressure than in its relaxation. Such cyclic fluid effusion can be explained systematically by a simple model in which fluid is supplied at a constant rate, accumulates in an elastic chamber, and flows out in a cylindrical vent that may widen or narrow due to viscous deformation of the surrounding country rock.
The lunar wake at 6.8 RL: WIND magnetic field observations
Authors: Owen C. J. , Lepping R. P. , Ogilvie K. W. , Slavin J. A. , Farrell W. M. , Byrnes J. B.
Published: February 2004

We report on WIND magnetic field observations at ∼6.8 RL downstream of the moon on 27th December 1994. The moon was in the solar wind during the encounter. IMP‐8 observations are used to determine baseline IMF conditions, and therefore determine those features in the WIND data which are related to its proximity to the moon. Previous Explorer 35 observations suggest that the lunar wake is not detectable beyond a downstream distance of ∼4 RL. However, despite the distance of WIND from the moon, we observe a slight decrease in field intensity just prior to the spacecraft entering the optical shadow, a slight field strength enhancement whilst in shadow, and perhaps a weak depression once the spacecraft reemerges into sunlight. These signatures closely resemble, but are weaker than, the previous observations. We conclude that a lunar wake did extend to these distances at the time of this encounter. We also note a rotation in field direction some distance outside of the wake signature which may be attributed to the crossing of the lunar mach cone boundary. We discuss the observations in terms of simple models of the solar wind interaction with an insulating body.
Tetrachloroethylene as an indicator of low Cl atom concentrations in the troposphere
Authors: Singh H. B. , Thakur A. N. , Chen Y. E. , Kanakidou M.
Published: February 2004

Tetrachloroethylene (C2Cl4), a largely man‐made chemical pollutant, is known to react with Cl atoms at a rate that is some 300 times faster than with OH radicals (kCl/kOH = 365 at 275 K). Analysis of C2Cl4 data, with the help of a global 2‐D model and in conjunction with the OH field derived from CH3CCl3 observations, has been used to provide a sensitive means for evaluating Cl atom abundance in the troposphere. In the “mean case” scenario, that employs best available measurements, emissions and kinetic parameters, it is found that OH oxidation is adequate to balance the C2Cl4 budget and significant removal by Cl is not indicated (Cl ≤10² molec. cm−3). An “upper limit” analysis that takes into account possible uncertainties in measurements, source emissions (man‐made and natural), and reaction rates, is performed to estimate that annually averaged Cl atom concentrations in the troposphere are <5–10×10² molec. cm−3. If we assume that nearly all (80–100%) of the Cl atoms reside in the marine boundary layer (MBL), mean MBL concentrations are estimated to be <5–15×10³ molec. cm−3. This analysis implies that mean Cl concentrations in the MBL are below or near the lower end of the values inferred in recent studies (104‐106 molec. cm−3). We conclude that despite their high reactivity, Cl atoms are too few to compete with OH radicals (≈ 106 molec. cm−3) in influencing the oxidizing capacity of the global troposphere.
A note on the transport of the Brazil Current
Authors: Garraffo Zulema D. , Kamenkovich Vladimir M.
Published: February 2004

Stommel's hypothesis on the influence of the thermohaline circulation on the transport of the Brazil Current is illustrated using the product of Semtner and Chervin's model. The velocity distribution along specifically chosen zonal sections is analyzed. A procedure of singling out the thermohaline component of the circulation is suggested and the significance of the component is proved.
Seismic and electrical anisotropies in the lithosphere across the Grenville Front, Canada
Authors: Sénéchal G. , Rondenay S. , Mareschal M. , Guilbert J. , Poupinet G.
Published: February 2004

The Grenville Front is a prominent tectonic feature of the Canadian Shield which has been the focus of a LITHOPROBE transect. A strong electrical anisotropy has been detected in a frequency range of 0.1–0.01 Hz (≈ 50 to 150 km), the most conductive direction being oriented N80E. In order to compare electrical and seismic anisotropies, ten seismometers have been deployed across the Grenville Front to record teleseismic events. S‐wave splitting measurements show an average delay of 1.54±0.21 s between the fast and the slow components. The fast axis direction is approximately E‐W at all stations, showing a strong coherence between the stations along the complete transect. This azimuth correlates well with that of the electrical anisotropy. The electrical anisotropy originates in the subcrustal lithosphere between 50 and 150 km. The similarity of the magnetotelluric and seismic anisotropy directions across the Grenville Front is an argument in favor of an origin of the seismic anisotropy in the subcrustal lithosphere as advocated by Silver and Kaneshima (1993).
How to include magnetostriction in micromagnetic models of titanomagnetite grains
Authors: Fabian Karl , Heider Franz
Published: February 2004

Numerical models of the micromagnetic structure of titanomagnetite particles require the consideration of magnetostriction. A new technique for calculating magnetostrictive self energies in finite element models is introduced. The method is based on the continuum theory of defects [Kröner, 1958]. By solving the biharmonic equation for the second order stress function tensor in an infinite elastically homogeneous medium the treatment of the magnetostrictive energy becomes similar to the treatment of demagnetizing energy. Fast Fourier Transformation can therefore be applied to the calculation of both, demagnetizing and magnetostrictive energies.
Reply to “A note on evaluating VAN earthquake predictions,” by G‐Akis Tselentis and Nicos S. Melis
Authors: Varotsos P. , Lazaridou M.
Published: February 2004

The intriguing suggestion by Tselentis and Melis [1996], that the tolerance limit in predicting the epicentral location should depend on earthquake magnitude, is discussed.

Tselentis and Melis applied the procedure of Mulargia and Gasperini [1992] to an ideally perfect earthquake prediction method, which achieved to predict successfully all the seventeen earthquakes with Ms ≥ 5.3 that occurred within the area 36–41°N, 19–25°E during the three years period 1983–1985, and found that these ideal predictions can be ascribed to chance. Their application clearly demonstrates that the procedure of Mulargia and Gasperini [1992] is questionable. In this Reply we also give a precise example of statistics, which indicates how Mulargia and Gasperini's [1992] procedure strongly violates Poisson restrictions, and hence leads to unacceptable results.
Fast impulsive reconnection and current sheet intensification due to electron pressure gradients in semi‐collisional plasmas
Authors: Ma Z. W. , Bhattacharjee A.
Published: February 2004

A numerical simulation of forced reconnection and current sheet growth due to inward boundary flows in semi‐collisional plasmas is presented, and contrasted with the results of an incompressible resistive MHD simulation in the high‐Lundquist‐number regime. Due to the presence of electron pressure (or Hall currents) in the generalized Ohm's law, the reconnection dynamics makes an impulsive transition from a slow linear regime to a nonlinear regime characterized by fast reconnection and current sheet intensification at a near‐Alfvénic rate. The current sheet spanning Y‐points in the early nonlinear regime shrinks and approaches an X‐point geometry. The spatial scale of the collisionless parallel electric field is the ion skin depth, and decoupled from the spatial scale of the parallel current which is much narrower and determined by the Lundquist number.
Heavy ozone enrichments from ATMOS infrared solar spectra
Authors: Irion F. W. , Gunson M. R. , Rinsland C. P. , Yung Y. L. , Abrams M. C. , Chang A. Y. , Goldman A.
Published: February 2004

Vertical enrichment profiles of stratospheric 16O16Ol8O and 16O18O16O (hereafter referred to as 668O3 and 686O3 respectively) have been derived from space‐based solar occultation spectra recorded at 0.01 cm−1 resolution by the ATMOS (Atmospheric Trace MOlecule Spectroscopy) Fourier‐transform infrared (FTIR) spectrometer. The observations, made during the Spacelab 3 and ATLAS‐1, ‐2, and ‐3 shuttle missions, cover polar, mid‐latitude and tropical regions between 26 to 2.6 mb inclusive (≈ 25 to 41 km). Average enrichments, weighted by molecular 48O3 density, of (15±6)% were found for 668O3 and (10±7)% for 686O3. Defining the mixing ratio of 50O3 as the sum of those for 668O3 and 686O3, an enrichment of (13±5)% was found for 50O3 (1σ standard deviation). No latitudinal or vertical gradients were found outside this standard deviation. From a series of ground‐based measurements by the ATMOS instrument at Table Mountain, California (34.4°N), an average total column 668O3 enrichment of (17±4)% (1σ standard deviation) was determined, with no significant seasonal variation discernable. Possible biases in the spectral intensities that affect the determination of absolute enrichments are discussed.
A Neural Network Approach for blocking recognition
Authors: Verdecchia Marco , Visconti Guido , D'Andrea Fabio , Tibaldi Stefano
Published: February 2004

We propose to use an Artificial Neural Network (ANN) for meteorological blocking recognition. The network output is presented as a number which ranges between 0 (absence of blocking) and 1 (blocked situation). This output is then compared with the step function obtained with a blocking index used in meteorological analysis and in the recognition of synoptic maps. We show that the ANN can pick events which are disregarded by the TM index and that ANN performances are equivalent and in some cases better than those indicated by an analytically computed blocking index.
Interstellar pickup H+ Ions at 8.3 AU: Pioneer 10 plasma and magnetic field analyses
Authors: Intriligator Devrie S. , Siscoe George L. , Miller W. David
Published: February 2004

Analysis of Pioneer 10 plasma and magnetic field observations at 8.3 AU in 1975 provides new evidence for the presence of interstellar pickup hydrogen (H+) ions. Use of plasma sensors that look far from the solar wind direction confirms the spherical shell distribution of the pickup ions in velocity space. Phase space density and flux estimates are closely consistent with those from Ulysses measured under similar conditions. Power spectral analyses of the magnetic field data show a distinct signal a little above the proton gyrofrequency, consistent with the presence of Doppler‐shifted ion‐cyclotron waves generated by H+ pickup ions. These results show that the Pioneer data set has the potential for systematic studies of the global properties of interstellar pickup ions.
Mantle convection behavior with segregation in the core‐mantle boundary
Authors: Nauheimer Günter , Fradkov Anatoly S. , Neugebauer Horst J.
Published: February 2004

Dynamical effects at the core‐mantle boundary have so far been modeled in the frame of thermal as well as double‐diffusive convection, yet accumulating evidence supports the idea that the mantle material looses part of its heavy component at the CMB due to combined chemical and physical processes. The segregation of the heavy FeO component from the lowermost mantle to the top of the core occurs inside the lower thermal boundary layer and leads to a new kind of boundary layer instability. A mathematical description of mantle convection including segregation of FeO into the core is developed and the relevant model parameters are estimated. The numerical investigation of the flow structure shows the forming and up‐welling of thermo‐compositionally driven plumes, as well as downwelling of pure thermally driven plumes even for conditions where the simple thermal convection case has a steady behavior. Periods of quasi‐stable plume activity interchange with periods of chaotic reorganization of the flow structure connected with strongly time dependent Nusselt.
Directivity analysis of the December 28, 1994 Sanriku‐Oki Earthquake (Mw=7.7), Japan
Authors: Hartog J. Renate , Schwartz Susan Y.
Published: February 2004

On December 28, 1994 a segment along the northern Japan trench failed in a Mw=7.7 underthrusting earthquake, the Sanriku‐oki earthquake. Less than 30 years earlier, the great Tokachi‐oki underthrusting earthquake of May 16, 1968 (Mw=8.2) occurred in the same region. We examine the rupture process of the recent event, using teleseismic body and surface wave data, and compare our results to the rupture characteristics of the Tokachi‐oki earthquake, as estimated by various authors in previous studies. We use an empirical Green’ function technique to obtain relative source time functions spanning a large range of the directivity parameter. The strong azimuthal dependence of the durations of these source time functions indicates a significant unilateral component of rupture in a down‐dip direction (west‐northwest). The main rupture initiated about 35 km southwest of the epicenter approximately 20 seconds after the onset of a low energy precursor. The main Tokachi‐oki rupture was also preceded by low moment release. However, it is unclear whether the low moment release preceding both earthquakes represents part of the rupture process or a distinct foreshock. The main rupture areas (asperities) of the Sanriku‐oki and the Tokachi‐oki earthquakes do not significantly overlap.
Depletion of atmospheric nitrate and chloride as a consequence of the Toba Volcanic Eruption
Authors: Yang Q. , Mayewski P. A. , Zielinski G. A. , Twickler M. , Taylor K. C.
Published: February 2004

Continuous measurements of SO42− and electrical conductivity (ECM) along the GISP2 ice core record the Toba mega‐eruption at a depth 2590.95 to 2091.25 m (71,000±5000 years ago). Major chemical species were analyzed at a resolution of 1 cm per sample for this section. An ∼6‐year long period with extremely high volcanic SO42− coincident with a 94% depletion of nitrate and 63% depletion of chloride is observed at the depth of the Toba horizon. Such a reduction of chloride in a volcanic layer preserved in an ice core has not been observed in any previous studies. The nearly complete depletion of nitrate (to 5 ppb) encountered at the Toba level is the lowest value in the entire ∼250,000 years of the GISP2 ice core record. We propose possible mechanisms to explain the depletion of nitrate and chloride resulting from this mega‐eruption.
X‐ray evidence for the new phase β‐iron at high temperature and high pressure
Authors: Saxena S. K. , Dubrovinsky L. S. , Häggkvist P.
Published: February 2004

X‐ray synchrotron study of iron heated between 1400 to 2200 K over a pressure range of 40 to 60 gigapascals confirms previous reports of the transformation of the hexagonal closest packed (HCP) phase of iron (ε) to the double HCP Iron (β). The study extends the stability range of the new phase β to the highest pressure range yet achieved for such transformation.
Time scales in atmospheric chemistry: Theory, GWPs for CH4 and CO, and runaway growth
Authors: Prather Michael J.
Published: February 2004

Atmospheric CH4 perturbations, caused directly by CH4 emissions or indirectly by those of CO are enhanced by chemical feedbacks. They can be diagnosed in terms of the natural modes of atmospheric chemistry that are general solutions of the continuity equations. Each mode is a pattern in the global distribution of all chemical species, and each has a single time‐constant that accurately describes its exponential decay about a given atmospheric state. This mathematical theory extends earlier work and is general for 2‐D and 3‐D chemistry‐transport models. A formal proof relates the steady‐state distribution and its lifetime to the integral of the true time‐dependent response (properly included in the recent IPCC assessment). Changes in CO are also known to perturb CH4; however, the impact of CO emissions on climate has not been formally assessed in part because the short lifetime of CO (months) relative to that of CH4 (decade) was believed to limit the integrated impact. Using the IPCC model studies, this theory predicts that adding 5 CO molecules to today's atmosphere is equivalent to adding 1 CH4 molecule with the same decadal duration as direct CH4 addition. Extrapolating these results, CH4 sources would have to triple before runaway growth, wherein CH4 emissions exceed the oxidizing capacity of the troposphere.
Further evidence for a global correlation of the Earth‐ionosphere cavity resonances
Authors: Füllekrug M. , Fraser‐Smith A. C.
Published: February 2004

The Stanford ELF/VLF Radio Noise Survey provides digital time series in the ELF range and VLF analog recordings of one horizontal magnetic field component at different locations around the globe. Three sites, Arrival Heights in Antarctica, Søndrestrømfjord in Greenland and Stanford in California, are chosen to investigate the natural magnetic noise in the frequency range of the Earth‐ionosphere cavity resonances (6–60 Hz). The resonances are interpreted as pure resonance phenomena and the associated parameters are derived in a robust manner by use of the complex exponential algorithm. The resulting amplitudes of the first and second resonances exhibit a pronounced diurnal variation and a distinct day to day variability of the same order during the time interval from January to April 1990. The day to day variability is well correlated between all of the three different sites. They also exhibit a 20–30 day variation that is related to the solar rotation period, expressed by means of sunspot numbers.
The AMICIST auroral sounding rocket: A comparison of transverse ion acceleration mechanisms
Authors: Lynch K. A. , Arnoldy R. L. , Kintner P. M. , Bonnell J.
Published: February 2004

Recent auroral sounding rocket data illustrate the relative significance of two transverse acceleration of ion (TAI) mechanisms for initiating nightside auroral ion outflow. First, the new data from this two payload mission show clearly that for lower hybrid solitary wave events, a) these individual events are spatially localized to scales approximately 100 m wide perpendicular to B, and b) the probability of occurrence of the events is greatest at times of maximum VLF wave intensity. Second, ion acceleration by broadband, low frequency electrostatic waves is observed in a 30 km wide region at the poleward edge of the arc. The fluxes from this and other sounding rockets are shown to be consistent with DE‐1 and Freja outflow measurements, indicating that the AMICIST observations show the low altitude, microphysical signatures of nightside auroral outflow from TAI.
Microscopic anharmonicity and equation of state of MgSiO3‐perovskite
Authors: Gillet Philippe , Guyot François , Wang Yanbin
Published: February 2004

The effect of temperature on the Raman spectrum of MgSiO3‐perovskite is investigated between 77 and 300 K. The data, combined with those obtained at high pressure, are used to infer microscopic anharmonic parameters (ai). It is shown that only two low‐frequency Raman modes are significantly anharmonic. The small volume dependency of the ai parameters allows a quasi‐harmonic calculation of the thermal pressure from a simplified density of states of the vibrational modes without other a priori informations. The calculated high‐temperature EOS reproduces to within ±0.4% the experimental molar volume obtained in the 0.1 MPa‐36 GPa and 77–2000 K range. A softening of a low‐frequency mode with decreasing temperature is also observed.
A comparison of self‐consistent kinetic and quasi‐MHD simulations: Application to a dipolarizing field reversal
Authors: Chapman Sandra C. , Mouikis Chris G.
Published: February 2004

Self consistent one dimensional hybrid code (particle ions, massless electron fluid) simulations are used to examine the possible structure and evolution of a dipolarizing field reversal in the near earth geotail. Here, we run the simulations in both the ion kinetic (hybrid) limit, where the ion moments and the electromagnetic fields are all well resolved on ion Larmor scales, and the quasi‐ MHD limit, where all ion trajectories are still fully resolved but the ion moments are taken, and the electromagnetic fields are advanced on spatial scales larger than the gyroradii of the ions. One simulation selfconsistently includes the ion current and density resolved on ion Larmor scales whereas the other does not; both simulations have sufficient bandwidth to well resolve all the low frequency wave modes expected from kinetic (in the hybrid case) or 2 fluid (in the quasi‐MHD case) theory. It is shown that the evolution of the electromagnetic field and ion pressure tensor are markedly different in the two cases. The results suggest that the selfconsistent quasi‐ MHD solution obtained in this way cannot be obtained from a coarse graining of the full kinetic (hybrid) selfconsistent solution.
Slow dynamics in the nonlinear elastic response of Berea sandstone
Authors: Ten Cate James A. , Shankland Thomas J.
Published: February 2004

A typical resonance curve—measured acceleration versus drive frequency—made on a thin bar of rock shows peak bending with a softening (nonlinear) modulus as drive levels are increased. The shapes of these nonlinear resonance curves were found in earlier work to depend somewhat on sweep rate; these “slow dynamics” are now examined and quantified. We have measured slow dynamics in a 0.3 m long, 50 mm diameter bar of Berea sandstone under ambient conditions. Peak strain levels during the experiments ranged from 10−11 to 10−5 at driving frequencies near 4 kHz, the fundamental longitudinal resonance frequency of the bar. Slow dynamics begin to manifest themselves at strain amplitudes above 10−6 at ambient conditions and at the onset of nonlinear peak bending. Strains above this value condition the rock, altering its response for minutes to hours after the drive has been turned off.
Attenuation of coda waves in southern Tibet
Authors: Reese C. C. , Ni J. F.
Published: February 2004

The alternation characteristics of the crust in the southernmost Tibetan plateau are determined from analysis of S‐wave coda recorded at a temporary broadband station deployed during the 1994 INDEPTH‐II experiment. A method for determiningQcis developed which utilizes the coda spectrogram observed at a single station. The average S‐wave coda quality factor for this continent‐continent collision zone isQc(f) = (160 ± 69) (f/f0)1.11±0.19, 1 < (f/f0) < 4, wheref0= 1Hz. The results are consistent with other measurements ofQc(f) in continental collisional environments which typically exhibit low values ofQc(f) at 1 Hz and a strong dependence on frequency. In particular, the attenuation characteristics obtained for the Arabian‐Eurasian continental collisional boundary in western Turkey are quite similar to the results reported here for the southern Tibetan plateau.
Monochromatic body waves excited by great subduction zone earthquakes
Authors: Ihmlé Pierre F. , Madariaga Raúl
Published: February 2004

Large quasi‐monochromatic body waves were excited by the 1995 Chile Mw=8.1 and by the 1994 Kurile Mw=8.3 events. They are observed on vertical/radial component seismograms following the direct P and Pdiff arrivals, at all azimuths. We devise a slant stack algorithm to characterize the source of the oscillations. This technique aims at locating near‐source isotropic scatterers using broadband data from global networks. For both events, we find that the oscillations emanate from the trench. We show that these monochromatic waves are due to localized oscillations of the water column. Their period corresponds to the gravest ID mode of a water layer for vertically traveling compressional waves. We suggest that these monochromatic body waves may yield additional constraints on the source process of great subduction zone earthquakes.
The southern California uplift and associated earthquakes
Authors: Castle Robert O. , Bernknopf Richard L.
Published: February 2004

Southern California earthquakes ≥ M5.5 during the period 1955/01/01–1994/01/17 were concentrated along or adjacent to the south flank of the southern California uplift, as defined both at its culmination and following its partial collapse. Spatial clustering of these earthquakes within three more‐or‐less distinct groups suggests either gaps along the south flank that were previously filled or are yet to be filled. Nearly all of the indicated earthquakes accompanied or followed partial collapse of the uplift, and seismic activity within this regime seems to have been increasing through at least 1994/01/17.
Possible role of atmosphere‐biosphere interactions in triggering the Last Glaciation
Authors: de Noblet Nathalie I. , Prentice I. Colin , Joussaume Sylvie , Texier Delphine , Botta Aurélie , Haxeltine Alex
Published: February 2004

We coupled a global biome model iteratively with an atmospheric general circulation model to study the possible role of vegetation in the climate system, at the time of glacial inception 115,000 years ago. Orbital forcing alone was not sufficient to initiate glaciation when other components of the climate system were kept as present (atmospheric composition, oceans, biosphere and cryosphere). Summers were however cold enough to induce major vegetation shifts in high northern latitudes. Southward migration of the boreal forest/tundra limit helped to create favourable conditions for continental ice‐sheet growth, with increasing snow depth and duration in Labrador, Arctic Canada and northern/western Fennoscandia. These results support a role for biogeophysical feedback in initiating glaciations.
The lithosphere‐asthenosphere boundary of the Valencia Trough (western Mediterranean) deduced from 2D Geoid and Gravity Modelling
Authors: Ayala C. , Pous J. , Torné M.
Published: February 2004

The lithosphere‐asthenosphere boundary in the Valencia trough has been investigated by integrated geoid and gravity forward modelling along five regional profiles across the Trough. Our results show that the base of the lithosphere maintains an almost constant depth of about 60 km along the axis of the basin whereas the crust thickens in a NE‐SW direction from 12–13 km to 19 km. These results suggest that a non homogeneous lithospheric stretching mechanism with a greater extension of the lithospheric mantle was responsible for the opening of the Trough, particularly in the southern area.
Depth‐dependent crustal anisotropy at Midwestern Honshu, Japan
Authors: Nakamura Mamoru , Ando Masataka , Kusunose Kinichiro , Sato Takashi
Published: February 2004

Aligned cracks, possibly induced by tectonic stress, produce anisotropy in the Earth's crust. Permeability and state of stress at several depths in the crust can be estimated from the state of crack distribution. We present clear evidence that crustal anisotropy changes with depth at the Inagawa earthquake swarm area, mid‐western Honshu, Japan. The observed fast shear‐wave directions are parallel to the maximum horizontal compressional axes obtained from a hydro‐fracturing test at a depth of 0.80 km and focal mechanism solution at depths 4–8 km in the same area. These observations provide us the evidence that the crustal anisotropy in this region is controlled by the tectonic stress. We estimated the degree of anisotropy, that is, the ratio of the difference between fast and slow S‐wave velocities, as a function of depth using the layer‐stripping method. The obtained value is 2% or less at most depths but anisotropy of 11% is observed at depths 6–8 km. This high‐anisotropy layer has a local gradient in seismicity rates. We infer that vertical fluid flow from the high‐anisotropy layer would be trapped in the low‐anisotropy layer above, pore pressure would increase, and it could generate earthquakes. This correspondence suggests that the degree of anisotropy in the upper crust changes with depth and has some relation to seismicity.
The excess temperature of plumes rising from the core‐mantle boundary
Authors: Albers Michael , Christensen Ulrich R.
Published: February 2004

We study the rise of conduit‐type thermal plumes from the core‐mantle boundary (CMB) in a simplified numerical model. Viscosity is a strong function of temperature and pressure. Assuming that all plumes start with the same excess temperature at the CMB, we find that their temperature in the upper mantle is controlled by the plume flux and is insensitive to variations in viscosity or other material parameters or to the kind of flow law (Newtonian or non‐linear). The reduction of excess temperature with height is stronger for weaker plumes. Plumes with a buoyancy flux of less than 1000 kg/s should have cooled so much that they would not melt beneath old lithosphere. The existence of such hot‐spots possibly indicates that not all plumes rise from the CMB.