bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling of air sparging in a layered soil: Numerical and analytical approximations
Authors: van Dijke M. I. J. , van der Zee S. E. A. T. M.
Published: February 2004

Air sparging in an aquifer below a less permeable horizontal layer is modeled using a two‐phase flow approach. Supported by numerical simulations, we show that a steady state situation is reached. For an analysis of the steady state, we distinguish three different flow regimes, which occur between the well screen and the unsaturated zone. Just below the interface that separates the high and the low permeable layers a regime with almost hydrostatic capillary pressures develops. We use this observation to derive an ordinary differential equation for the pressure at the interface, which leads to an approximation of the air flow pattern just below and within the low permeable layer. The approximation provides an estimate for the radius of influence as a function of the physical parameters. The agreement between the analytical approximation and the numerical steady state results is almost perfect when heterogeneity is increased. With a few modifications the analysis applies also to a dense non‐aqueous phase liquid (DNAPL) spill above a less permeable layer. Comparison with an illustrative numerical simulation shows that the analytical approximation provides a good estimate of the radial spreading of the DNAPL flow on top of and within the low permeable layer.
Analytical decomposition of the nonlinear unsaturated flow equation
Authors: Serrano Sergio E.
Published: February 2004

An analytical procedure for the solution of the nonlinear unsaturated flow equation is proposed. The horizontal and vertical flow equations subject to constant boundary conditions and continuous wetting are approximated using analytical decomposition series. The results are verified with the Philip [1955] and the Parlange [1971] classical solutions and with experimental data. A convergence theorem with proof and discussion on the numerical accuracy of decomposition series are included. Applications to the modeling of infiltration subject to hysteresis in the soil‐water functional relationships, soil heterogeneity, and time variable point rainfall are also discussed. Other potential applications in water management models under more realistic conditions are possible. The methodology offers advantages over the common small‐perturbation solutions: the possibility to study nonstationarity in the random quantities; statistical separability from the physics of the problem (i.e., independence between the system parameters and the input quantities), rather than forced through closure approximations; and the construction of an analytical series solution that converges uniformly to the true nonlinear solution. Finally, because of stability and computational economy with respect to linearized numerical solutions, an analytical solution appears promising.
Seasonal variations in the boron isotopic composition of coral: A productivity signal?
Authors: Hemming N. G. , Guilderson T. P. , Fairbanks R. G.
Published: February 2004

Micro‐analysis of a western equatorial Pacific coral across two annual cycles reveals seasonal variation in the boron isotope composition. A heavy boron isotope spike is found coincident with a heavy carbon isotope spike in samples collected from the high density bands in the coral head. The heavy isotope values in both carbon and boron are consistent with high productivity of coral symbionts during periods of high insolation. During these high productivity periods, the symbionts fix carbon and thus produce a residual heavy carbon pool and CO2 depletion. Calcification from the resulting high pH pool results in heavier boron isotope compositions in the coral as the isotopic composition of the aqueous boron species that is incorporated in the coral skeleton (BOH4−) increases with pH. This study suggests that coupled carbon and boron isotope studies may lead to a better understanding of coral calcification processes and a more lucid understanding of coral δ13C records.
Rapid deformation rates along the Wasatch Fault Zone, Utah, from first GPS measurements with implications for earthquake hazard
Authors: Martinez Linda J. , Meertens Charles M. , Smith Robert B.
Published: February 2004

Anomalously high rates of crustal deformation have been measured at the Basin‐Range transition to the Rocky Mountains along the Wasatch fault zone, Utah, by repeated Global Positioning System (GPS) measurements. Four GPS field campaigns (1992–1995) and comparisons with older (1962–1991) geodetic data have revealed east‐west extensional strain at a rate of 0.05 ± 0.02 µstrain/yr corresponding to a 2.7 ±1.3 mm/yr rate of horizontal displacement across a 55‐km wide area. This rate is more than 20% of the total ∼12 mm/yr extension rate across of the ∼800‐km wide Basin and Range province. It is also two to three times larger than the average Late Quaternary fault slip rate on the Wasatch fault and tens of times larger than the displacement rates inferred from the cumulative seismic moments of historic earthquakes. While we do not yet know the source of this unexpected contemporary deformation, possible mechanisms include homogeneous crustal extension, loading of the Wasatch and adjacent faults, and pressure solution creep. If the Wasatch fault is being loaded by this high strain rate, it increases the expected peak ground acceleration significantly from standard values. These new findings demonstrate the importance of GPS in earthquake hazard assessment.
Reconnection event at the dayside magnetopause on January 10, 1997
Authors: Nakamura Masato , Seki Kanako , Kawano Hideaki , Obara Takahiro , Mukai Toshifumi
Published: February 2004

Geotail was at the magnetopause near the sub‐solar point when the magnetic cloud struck the earth's magnetosphere on January 10, 1997. Reeonnection between the southward IMF and the magnetospheric field lines occurred at the dayside magnetopause as observed by Geotail. The signatures of the reconnection were, i) accelerated plasma flow from the reconnection site which reached up to 500km/s, ii) ion heating through the reconnection process, and iii) a velocity filter effect seen in the ion distribution function in the magnetosheath boundary layer. This reconnection may be related to the large substorm onset observed at geosynchronous orbit.
A new source of tropospheric aerosols: Ion‐ion recombination
Authors: Turco Richard P. , Zhao Jing‐Xia , Yu Fangqun
Published: February 2004

We propose a new source of aerosol particles in the lower atmosphere that is based on the formation, growth, and recombination of ubiquitous cosmogenically‐generated ions. This mechanism provides a uniform, continuous fine‐particle generator in the presence of precursor vapors, such as sulfuric acid, or certain organic compounds. Thus, for example, aqueous sulfate aerosols can form at sulfuric acid vapor partial pressures well below the supersaturations required for homogeneous nucleation. Detailed microphysical modeling shows that the highly nonlinear chemical/physical system comprising ions, vapors, and aerosols produces ultrafine and accumulation mode particles having characteristics similar to those detected in the lower troposphere. Accordingly, this mechanism may explain the presence of a stable boundary layer aerosol population of several hundred particles/ cm³. The theory of nucleation by ion‐ion recombination (NIIR) is roughly calibrated here using observed ultrafine particle measurements, and is applied to interpret tropospheric aerosol observations.
Ice nucleation processes in upper tropospheric wave‐clouds observed during SUCCESS
Authors: Jensen E. J. , Toon O. B. , Tabazadeh A. , Sachse G. W. , Anderson B. E. , Chan K. R. , Twohy C. W. , Gandrud B. , Aulenbach S. M. , Heymsfield A. , Hallett J. , Gary B.
Published: February 2004

We have compared in situ measurements near the leading‐edges of wave‐clouds observed during the SUCCESS experiment with numerical simulations. Observations of high supersaturations with respect to ice (>50%) near the leading edge of a very cold wave cloud (T <−60°C) are approximately consistent with recent theoretical and laboratory studies suggesting that large supersaturations are required to homogeneously freeze sulfate aerosols. Also, the peak ice crystal number densities observed in this cloud (about 4 cm−3) are consistent with the number densities calculated in our model. In the warmer wave‐cloud (T ≃−37°C) relatively large ice number densities were observed (20–40 cm−3). Our model calculations suggest that these large number densities are probably caused by activation of sulfate aerosols into liquid droplets followed by subsequent homogeneous freezing. If moderate numbers of effective heterogeneous freezing nuclei (0.5–1 cm−3) had been present in either of these clouds, then the number densities of ice crystals and the peak relative humidities should have been lower than the observed values.
FAST observations of preferentially accelerated He+ in association with auroral electromagnetic ion cyclotron waves
Authors: Lund E. J. , Möbius E. , Tang L. , Kistler L. M. , Popecki M. A. , Klumpar D. M. , Peterson W. K. , Shelley E. G. , Klecker B. , Hovestadt D. , Temerin M. , Ergun R. E. , McFadden J. P. , Carlson C. W. , Mozer F. S. , Elphic R. C. , Strangeway R. J. , Cattell C. A. , Pfaff R. F.
Published: February 2004

The TEAMS instrument on the FAST satellite has detected events in which He+ ions are resonantly accelerated perpendicular to the magnetic field to energies of several keV. The events occur in association with electromagnetic ion cyclotron (EMIC) waves and conic distributions of up to a few hundred eV in H+ and a few keV in O+. Concentrations of He+ can be significantly elevated during the events. Our interpretation is that the He+ ions are accelerated through a cyclotron resonance with the waves. This acceleration is similar to a proposed mechanism for selective ion acceleration in impulsive solar flares.
Auroral kilometric radiation and the auroral electrojet index for the January 1997 magnetic cloud event
Authors: Kurth W. S. , Murata T. , Lu G. , Gurnett D. A. , Matusmoto H.
Published: February 2004

Auroral kilometric radiation (AKR) observations by Polar and Geotail are compared with the auroral electrojet index for the January 1997 magnetic cloud event. These two‐spacecraft measurements are complementary in covering the AKR emission cones throughout the event and, together, reasonably represent the auroral electrojet AE index. We point out, however, limitations of both the AKR index and the AE index in providing truly global measurements of substorm activity.
Strong flow bursts in the nightside ionosphere during extremely quiet solar wind conditions
Authors: Walker A. D. M. , Pinnock M. , Baker K. B. , Dudeney J. R. , Rash J. P. S.
Published: February 2004

Results of an HF radar study of convection during an extended quiet solar wind interval on March 10 1997 are presented. After thirty hours during which the solar wind met the criteria for quiet conditions the HF radars at Sanae and Halley in Antarctica showed strong activity on the night side. Flow bursts with velocities of more than 2000 m s−1, corresponding to electric fields exceeding 100 m V m−1 were observed. These occurred quasi‐periodically for almost two hours on the night‐side with a repetition time of several minutes. It is concluded that they map to a region well inside the magnetotail. It is suggested that they are associated with sporadic energy release during reconfiguration of the tail magnetic field, and that this can occur even during an extended quiet solar wind period.
Spatial variations in the frequency‐magnitude distribution of earthquakes at Soufriere Hills Volcano, Montserrat, West Indies
Authors: Power John A. , Wyss Max , Latchman Joan L.
Published: February 2004

The frequency‐magnitude distribution of earthquakes measured by the b‐value is determined as a function of space beneath Soufriere Hills Volcano, Montserrat, from data recorded between August 1, 1995 and March 31, 1996. A volume of anomalously high b‐values (b > 3.0) with a 1.5 km radius is imaged at depths of 0 and 1.5 km beneath English's Crater and Chance's Peak. This high b‐value anomaly extends southwest to Gage's Soufriere. At depths greater than 2.5 km volumes of comparatively low b‐values (b∼1) are found beneath St. George's Hill, Windy Hill, and below 2.5 km depth and to the south of English's Crater. We speculate the depth of high b‐value anomalies under volcanoes may be a function of silica content, modified by some additional factors, with the most siliceous having these volumes that are highly fractured or contain high pore pressure at the shallowest depths.
Dynamic deformation of Etna Volcano observed by satellite radar interferometry
Authors: Lanari Riccardo , Lundgren Paul , Sansosti Eugenio
Published: February 2004

Satellite radar interferometry of Mt. Etna volcano, Sicily, Italy, reveals a sequence of deformation characterized by deflation during the end of the 1993 eruption, inflation from 1993–1995 with an increase in the inflation rate immediately before its resumed eruptive activity in late 1995. This was followed by very low deformation levels during the following year. The source of the deformation changed from a depth of 9 km during deflation to more than 11–14 km during the subsequent inflation, consistent with a model in which deflation at shallower levels is followed by inflation at greater depth as the volcano system recharges from below before its next eruption. This study demonstrates that radar interferometry provides an important contribution towards understanding the dynamic deformation of volcanoes. By revealing large scale changes in their pre‐eruption deformation rates, radar interferometry could play an important role in volcano eruption monitoring.
Shear wave anisotropy in the Mariana Subduction Zone
Authors: Fouch Matthew J. , Fischer Karen M.
Published: February 2004

To determine the location, strength, and orientation of seismic anisotropy in the Mariana subduction zone beneath Guam, we evaluated shear wave splitting in local S, regional S and ScS, and teleseismic core phases such as SKS recorded at station GUMO. Fast directions from the local S phases have an average azimuth of −45°, and splitting times range from 0.1 s to 0.4 s. For local S phases from events within the southeastern half of the subducting slab, splitting parameters manifest minimal frequency dependence in both fast direction and splitting time. However, for the remaining local S phases in the data set, fast directions vary with frequency content. No well‐constrained splitting parameters were obtained for the regional and teleseismic phases, but the particle motions of these unsplit phases are consistent with an average anisotropic fast direction of ∼−45°. Anisotropy due solely to olivine oriented by slab‐entrained flow in the mantle wedge would produce local S fast directions at ∼−66°, and anisotropy due solely to fossil seafloor spreading in the subducting slab would yield fast directions at −20° to −30°. Neither of these predictions is consistent with the observed fast directions. However, the observed splitting, including the frequency‐dependent fast directions, can be explained by models containing anisotropy in both the slab and wedge, and possibly (although not necessarily) anisotropy due to recent extension in the overriding Philippine sea plate.
Determination of linear filters for predicting Ap during Jan. 1997
Authors: McPherron R. L.
Published: February 2004

The Ap index is a daily average of the range of magnetic disturbance in each three‐hour UT interval. It is the only global magnetic index routinely forecast. Predictions of Ap are subjective estimates made on the basis of past behavior of Ap and events at the Sun. The predicted variance in present forecasts is only 30%. Here we develop a set of linear filters for Ap forecasting. We show that auto regressive filters with constant coefficients do as well as human forecasters. Filters with time varying coefficients predict 37% of the variance. If we assume Ap is driven by solar wind velocity through an auto regressive moving average we predict 47% of the variance. However, this filter requires today's average solar wind velocity to predict today's Ap. Only with remote sensing of the solar wind a day in advance would it be possible to implement this model. We apply our filters to data for January 1997 determining whether effects of the January 6–11 magnetic cloud can be predicted. The filters do not predict CME related activity, but they do predict activity later in January obtaining a monthly average prediction efficiency of 59% that should be compared SEC results of 40%.
Climatic variability in upper ocean ventilation rates diagnosed using chlorofluorocarbons
Authors: Doney Scott C. , Bullister John L. , Wanninkhof Rik
Published: February 2004

The chlorofluorocarbon CFC‐12 (CCl2F2) distributions from two occupations of a meridional hydrographic section in the eastern North Atlantic are used to describe the oceanic penetration of CFCs and change in the integrated ventilation patterns over the five years from 1988 to 1993. The CFC‐12 water‐column inventories increased by 30–40%, despite a slowing atmospheric growth rate (14%), because of continuing uptake by undersaturated subsurface water masses whose response is lagged by the ventilation time‐scales. After removing the long‐term CFC temporal trend using a tracer age based normalization technique, we observe a distinct dipole pattern in upper ocean ventilation, with reduced convection in the subpolar gyre and enhanced production of saline subtropical underwater in 1993. These differences are discussed in relation to interannual variability in atmospheric surface forcing, upper ocean anomalies, and convection patterns associated with the North Atlantic Oscillation.
Quasi‐periodic modulations of the Jovian magnetotail
Authors: Woch J. , Krupp N. , Lagg A. , Wilken B. , Livi S. , Williams D. J.
Published: February 2004

Measurements with the Energetic Particles Detector (EPD) on Galileo orbit C9 in the Jovian magnetotail revealed the existence of distinct quasi‐periodic variations of energetic ion intensities which are superimposed on the well‐known 10‐hour modulations due to the planetary rotation. The intensity variations are associated with changes of the particle energy spectra and the plasma flow pattern. They are clearly of temporal nature and not the consequence of the spacecraft passing through periodically separated spatial structures. The modulation period is about 3 days. The oscillations are most pronounced throughout the middle magnetotail regime (20 to 80 RJ), however, seem to persist even in the deep tail region. The amplitude of the modulation is dependent on the particle energy. The highest energies measured (about 1 MeV) show the strongest variations. Energetic particle features with similar periodicity are observed on other Galileo orbits as well. The cause of these modulations is unclear; however, it may be speculated that they correspond to a quasi‐periodic transition between two basic states of the Jovian magnetotail which occur with a time constant inherent to the Jovian magnetosphere.
Energetic particle bursts in the predawn Jovian magnetotail
Authors: Krupp N. , Woch J. , Lagg A. , Wilken B. , Livi S. , Williams D. J.
Published: February 2004

From September to October 1996 the Galileo spacecraft crossed through the distant predawn tail region of the Jovian magnetosphere. The Energetic Particles Detector (EPD) onboard Galileo recorded a series of energetic particle flow bursts in the region beyond 80 RJ to the apojove at 113 RJ. The events are similar in nature to an event observed with the hot plasma instrument (LECP) onboard Voyager 2. The individual events last for several hours and cover the whole energy range from 15 keV to 55 MeV. The majority of them show considerable intensity increases which are most prominent for heavy ions. The events exhibit high radially outward directed anisotropies suggesting strongly collimated radial outflowing ion beams. The Voyager event was observed beyond the corotation boundary within a magnetospheric boundary layer termed the magnetospheric wind region and consequently it was assumed that the underlying process is connected with a boundary layer instability. However, the Galileo observations show the bursts being embedded in a general corotation flow. It is thus suggested that the flow bursts are driven by an internal plasma sheet process possibly associated with a major re‐configuration of the Jovian magnetotail. A series of five very prominent flow bursts observed near apojove of the orbit occurred quasi‐periodically with a repetition period of about 2.6±0.2 days which is presumably related to an internal time constant of the Jovian magnetotail.
Observation of near‐zero ozone concentrations in the upper troposphere at mid‐latitudes
Authors: Davies W. E. , Vaughan G. , O'Connor F. M.
Published: February 2004

Measurements by an ECC ozonesonde launched from Aberystwyth (52.4°N, −4.1°E) in July show ozone concentrations decreasing steadily from a warm frontal surface to the tropopause, cumulating in a layer ∼0.5 km deep with near‐zero ozone concentrations at 12 km. Such features have previously been detected by lidar but have not been reported in ozonesonde data at mid‐latitudes; they have, however, been found in ozonesonde profiles above the equatorial Pacific. We examine three possible hypotheses for the origin of the ozone‐free air: in situ destruction by cirrus clouds, rapid transport from the marine boundary layer in the extratropics and long‐range transport from the tropics. We conclude that the ozone‐poor air observed on this day could only have resulted from long‐range transport from the tropics.
Petrologic determination of ascent rates for the 1995–1997 Soufriere Hills Volcano andesitic magma
Authors: Devine J. D. , Rutherford M. J. , Gardner J. E.
Published: February 2004

The recent eruption of the Soufriere Hills Volcano in Montserrat (July, 1995, to present; October, 1997) has produced a hornblende‐bearing, andesitic lava dome. It is possible to petrologically estimate changes in ascent rates of amphibole‐bearing magmas. For certain rates of decompression, a breakdown rim of fine‐grained, anhydrous reaction products forms where amphibole is in contact with melt. The thickness of the rim varies with ascent rate. Most of the amphibole phenocrysts in the magma storage region lack breakdown rims. About 10% have 200–400 µm‐thick, coarse‐grained breakdown rims that are interpreted to be relicts of a past heating event. Study of a time series of new dome andesites showed that ascent rate increased from December, 1995 (∼0.001 m/s), to July, 1996 (∼0.008 m/s), while eruptive style remained extrusive. Ascent rate increased to >0.012 m/s in August, 1996, and the first major explosive eruption occurred on 17–18 September, 1996.
Freshening of the upper ocean in the Arctic: Is perennial sea ice disappearing?
Authors: McPhee Miles G. , Stanton Timothy P. , Morison James H. , Martinson Douglas G.
Published: February 2004

During the Surface Heat Budget of the Arctic (SHEBA) deployment in October, 1997, multiyear ice near the center of the Beaufort Gyre was anomalously thin. The upper ocean was both warmer and less saline than in previous years. The salinity deficit in the upper 100 m, compared with the same region during the Arctic Ice Dynamics Joint Experiment (AIDJEX) in 1975, is equivalent to surface input of about 2.4 m of fresh water. Heat content has increased by 67 MJ m−2. During AIDJEX the change in salinity over the melt season implied melt equivalent to about 0.8 m of fresh water. As much as 2 m of freshwater input may have occurred during the 1997 summer, possibly resulting from decreased ice concentration from changes in atmospheric circulation early in the summer , in the classic albedo‐feedback scenario. Unchecked, the pattern could lead to a significantly different sea‐ice regime in the central Arctic.
Observation of the 40 keV field‐aligned ion beams
Authors: Sheldon R. B. , Spence H. E. , Fennell J. F.
Published: February 2004

Recent observations by CEPPAD/IPS from the new perspective of the POLAR orbit reveal a close association of field‐aligned ionospheric beams with convecting plasmasheet “nose” ions. April 15, 1996 was marked by a large southward BZ accompanying a fast solar wind shock. This event triggered a strong cross‐tail convection electric field that pushed plasmasheet ions deep into the magnetosphere. When the POLAR spacecraft passed through the inner magnetosphere, it observed both an unusually energetic plasmasheet nose ion injection at ∼90 keV, as well as a peculiar field‐aligned beam at ∼40 keV. These beams appear to be enriched in oxygen ions (as inferred from other instruments), which would place their origin in the ionosphere. Both populations existed from L=7–3, for a duration of at least 2 hours. We speculate that the nose ions create a parallel electric field that is responsible for the extended ionospheric beam signature.
Dissolved organic carbon of infiltration within the autogenic Karst Hydrosystem
Authors: Emblanch Christophe , Blavoux Bernard , Puig Jean‐Michel , Mudry Jacques
Published: February 2004

This work aims at using the Dissolved Organic Carbon (DOC) as a tracer of infiltration in karstic aquifers with only diffuse recharge. Regular measurements of DOC have been carried out in three karstic systems located in South‐eastern France during an hydrogeological cycle. Considering that the DOC is mainly located in the soil, it might be used as a tracer of the infiltration. The behavior of the tracer considerably varies between the high and low flow periods.

The low concentrations of DOC occur when the flow is mainly due to a long residence time of the water in the saturated zone, whereas the concentration of DOC increases with the contribution of recent waters during the flood period. So the DOC can be used as a tracer of the infiltration. A comparison between the magnesium and the DOC allows to demonstrate the ability of using the DOC as a tracer of the water residence time.
Do coronal mass ejections implode in the solar wind?
Authors: Riley Pete , Gosling J. T.
Published: February 2004

Ulysses observations show that many coronal mass ejections observed at high heliographic latitudes expand because they initially have higher internal pressures than that of the surrounding solar wind. This expansion commonly drives a shock wave into the ambient wind in all directions. In the analogous process of an explosion in the Earth's atmosphere, the expansion is followed by an implosion at the center of the disturbance. Ulysses observations to date, however, suggest that these “over‐expanding” CMEs do not implode, at least within 5.4 AU, in spite of the fact that many have central pressures at large heliocentric distances that are considerably lower than that of the surrounding solar wind. We use fluid simulations to investigate whether these CMEs might eventually collapse at larger heliocentric distances. We find that for a wide range of initial perturbations close to the Sun the CMEs do not implode at any heliocentric distance. Implosion does not occur because of the overall reduction in pressure associated with the spherical expansion of the solar wind.
Upper‐tropospheric relative humidity observations and implications for cirrus ice nucleation
Authors: Heymsfield Andrew J. , Miloshevich Larry M. , Twohy Cynthia , Sachse Glen , Oltmans Samuel
Published: February 2004

Relative humidity (RH) measurements acquired in orographic wave cloud and cirrus environments are used to investigate the temperature‐dependent RH required to nucleate ice crystals in the upper troposphere, RHnuc(T). High ice‐supersaturations in clear air—conducive to the maintenance of aircraft contrails yet below RHnuc and therefore insufficient for cirrus formation—are not uncommon. Earlier findings are supported that RHnuc in mid‐latitude, continental environments decreases from water‐saturation at temperatures above −39°C to 75% RH at −55°C. Uncertainty in determining RHnuc below −55°C results in part from size detection limitations of the microphysical instrumentation, but analysis of data from the SUCCESS experiment indicates that RHnuc below −55°C is between 70 and 88%. A small amount of data acquired off‐shore suggests the possibility that RHnuc may also depend on properties of the aerosols.
Imaging P‐wave scatterer distribution in the focal area of the 1995 M7.2 Hyogo‐ken Nanbu (Kobe) Earthquake
Authors: Matsumoto Satoshi , Obara Kazushige , Hasegawa Akira
Published: February 2004

Spatial distribution of P‐wave scatterers in and around the focal area of the 1995 Hyogo‐ken Nanbu Earthquake (M7.2) has been estimated by using dense seismic array data. Waveforms of 12 explosions were analyzed in a frequency band of 6–10Hz range. It is difficult to estimate the inhomogeneous structure in this wavelength range from the ordinary travel time tomography, in spite of its importance for understanding earthquake‐generating process. Observed waveforms were slant stacked into various directions from the array and then AGC and diffraction curve summation are applied in order to image scatterer distribution. Spatial distribution of scattering strength thus imaged shows that higher strengths are distributed beneath the hypocenter, the initiation point of the mainshock rupture, and in the southwestern part of the fault plane of the event.
An overview of the impact of the January 10–11 1997 magnetic cloud on the magnetosphere via global MHD simulation
Authors: Goodrich C. C. , Lyon J. G. , Wiltberger M. , Lopez R. E. , Papadopoulos K.
Published: February 2004

The results of a 3D MHD simulation of the January 10–11, 1997 geomagnetic storm are presented. The simulation results agree well with ground‐based and geosynchronous observations. The 28 hours modeled by the simulation include the magnetic cloud responsible for the storm, the shock preceding the cloud, and the dense plasma filament following it. The simulation shows that during the period of southward IMF ionospheric activity was strongly correlated to the solar wind density. The arrival of the plasma filament during northward IMF pushed the dayside magnetopause well within geosynchronous orbit, but generated little ionospheric activity. It appears that nsw as well as the orientation of Bsw plays a role in controlling the intensity of ionospheric and magnetospheric activity.
Little Ice Age clearly recorded in northern Greenland ice cores
Authors: Fischer H. , Werner M. , Wagenbach D. , Schwager M. , Thorsteinnson T. , Wilhelms F. , Kipfstuhl J. , Sommer S.
Published: February 2004

Four ice cores drilled in the little investigated area of northern and northeastern Greenland were evaluated for their isotopic (δ18O) and chemical content. From these rather uniform records a stable isotope temperature time series covering the last 500 years has been deduced, which reveals distinct climate cooling during the 17th and the first half of the 19th century. Timing of the preindustrial temperature deviations agrees well with other northern hemisphere temperature reconstructions, however, their extent (∼1°C) significantly exceeds both continental records as well as previous southern and central Greenland ice core time series. A 20–30% increase in the sea salt aerosol load during these periods supports accompanying circulation changes over the North Atlantic. Comparison with records of potential natural climate driving forces points to an important role of the long‐term solar influence but to only episodically relevant cooling during years directly following major volcano eruptions.
Analysis of auroral morphology: Substorm precursor and onset on January 10, 1997
Authors: Germany G. A. , Parks G. K. , Ranganath H. , Elsen R. , Richards P. G. , Swift W. , Spann J. F. , Brittnacher M.
Published: February 2004

We study the dynamics of the poleward and equatorward boundaries of the auroral oval in response to the solar wind IMF on January 10, 1997 using global auroral images obtained by the Ultraviolet Imager (UVI) on Polar. A neural network algorithm is used to perform an automated morphological analysis. Poleward and equatorward boundaries identified by the algorithm exhibit clear equatorward motion during the substorm growth phase associated with the southward turning of the IMF. At substorm expansive phase onset, the high latitude edge of the oval expands poleward while the low latitude edge in the midnight sector shows continued expansion for several minutes after onset.
Electric potential changes prior to shear fracture in dry and saturated rocks
Authors: Yoshida Shingo , Clint Oswald C. , Sammonds Peter R.
Published: February 2004

Electric potential changes before shear rupture were measured using Darley Dale sandstone (quartz‐rich) and Icelandic basalt (quartz‐free) on both dry specimens and in the presence of pore fluid. We find that electric potential changed markedly just prior to dynamic rupture in dry and saturated sandstones and saturated basalt but we did not detect precursory signals in dry basalt. The absence of signals in dry basalt provides strong evidence that the piezoelectric effect and electrokinetic effect are dominant sources for precursory signals. Moreover we find that the amplitude of the precursory signals due to electrokinetic effect in saturated sandstone were as large as the coseismic signals. We propose that this signal is caused by accelerating evolution of dilatancy as cracks grow in the rock before rupture, resulting in water flow into the dilatant region with an electric current produced concurrently.
Diffraction effects upon finite‐frequency travel times: A simple 2‐D example
Authors: Tong Jun , Dahlen F. A. , Nolet Guust , Marquering Henk
Published: February 2004

The widespread availability of broad‐band digital seismic data makes it possible to measure travel‐time anomalies by cross‐correlation with spherical‐earth synthetic seismograms. Finite‐frequency diffraction effects render such measurements sensitive to wave‐speed perturbations off of the infinite‐frequency geometrical ray path. We show, by consideration of a simple 2‐D example, that the Born approximation provides an excellent description of these off‐path sensitivity effects, in the absence of caustics and for travel‐time shifts that are small compared to the wave period. Remarkably, an isolated low‐velocity anomaly may produce fringing fast travel‐time anomalies, as measured by cross‐correlation.
Solar cycle evolution of the structure of magnetic clouds in the inner heliosphere
Authors: Mulligan T. , Russell C. T. , Luhmann J. G.
Published: February 2004

Nearly ten years of continuous magnetic field observations by the Pioneer Venus spacecraft allows us to study the correlation between the structure of magnetic clouds in the inner heliosphere and the phase of the solar cycle. Fifty‐six magnetic clouds have been identified in the PVO data at .7AU during 1979–1988. As this period spans nearly two solar maxima and one solar minimum we can study the evolution of the structure of these magnetic clouds through varying solar activity and under various orientations of the coronal streamer belt. Until shortly after the 1979 solar maximum the majority of clouds had an initially southward magnetic field which turned northward as the cloud was traversed, while in the period leading up to the 1988 solar maximum the majority had a northward field that turned southward. In the declining phase of solar activity magnetic clouds continued to occur, but only a minority can be classified as having south‐to‐north and north‐to‐south rotations. The majority of these clouds occurred with the field remaining entirely north or south relative to the solar equator. These results confirm observations using Helios and ISEE data indicating that the structure of magnetic clouds varies in response to changes in the magnetic structure of the source region. By interpreting these observations to imply that the leading magnetic field in magnetic clouds is controlled by the polarity of the sun's global field and that the inclination of the coronal streamer belt controls the axis of symmetry of the clouds, we can predict preferred magnetic cloud structure and orientation during varying phases of the solar cycle. The helicity of the observations does not seem to be ordered by the solar cycle.
On supersaturation spectrum and size distributions of cloud condensation nuclei
Authors: Ji Qiang , Shaw Glenn E.
Published: February 2004

The supersaturation spectra of cloud condensation nuclei (CCN) are sometimes S‐shaped and always asymptotically approach a limiting value as supersaturation becomes more than several percent. Such a complex shape can correspond to a bell‐shaped size distribution of sub‐micron aerosols. We found that an exponential expression N = N0 (1‐exp[−B SK]) fits measured supersaturation spectra better than the commonly used power law expression N = C SK, where N is the number concentration of CCN at the supersaturation S, N0 is the total number concentration of CCN, B, C and K are empirical coefficients. The exponential expression and the power law are related. For example, at S ∼ 0%, the exponential expression reduces to the power law, with C ∼ N0B. The derived size distribution from the exponential expression agrees closely with measured size distributions for laboratory salts, but not for aerosols in polluted airmasses. The disagreement in polluted airmasses suggests that CCN have complex physiochemistry.
Simulation of water waves generated by a potential debris avalanche in Montserrat, Lesser Antilles
Authors: Heinrich Philippe , Mangeney Anne , Guibourg Sandrine , Roche Roger , Boudon Georges , Cheminée Jean‐Louis
Published: February 2004

The evolution of the volcano activity in Montserrat could lead to the collapse of a portion of the lava dome in the Tar River Valley and to a sudden entry of debris avalanche into the Caribbean Sea. The impact of a debris avalanche with a volume of 40 × 106 m³ into the sea and the generated tsunami have been simulated numerically by a mixture model solving the 3D Euler's equations. The mixture is composed of sediments considered as an homogeneous fluid of density 2 and of water. Numerical tests show that the generated waves are sensitive to both initial impact velocities and avalanche fronts of the landslide. The water surface and velocities calculated by the 3D mixture model are used as input data in a non‐linear shallow water model, to calculate tsunami propagation along the coasts of Montserrat. The hydraulic risks in Montserrat are roughly assessed for a tsunami generated by a mass of 40 × 106 m³ entering the sea.
Observations of methyl nitrate in the lower stratosphere during STRAT: Implications for its gas phase production mechanisms
Authors: Flocke F. , Atlas E. , Madronich S. , Schauffler S. M. , Aikin K. , Margitan J. J. , Bui T. P.
Published: February 2004

Methyl nitrate has been measured for the first time in the lower stratosphere at altitudes to 20.5 km during the December 1996 NASA Stratospheric Tracers of Atmospheric Transport (STRAT) deployment. Whole air samples were taken on board the NASA ER2 aircraft and analyzed using gas chromatography/mass spectrometry. Methyl nitrate was present at measurable levels throughout the entire altitude range covered. Taking advantage of the rather simple chemistry in the lower stratosphere compared to the troposphere, and considering the known in‐situ photochemical sources for methyl nitrate, the yield of methyl nitrate from the reaction of methyl peroxy radicals with NO was estimated.
Seismic evidence of flow at the base of the upper mantle
Authors: Vinnik Lev , Chevrot Sebastien , Montagner Jean‐Paul
Published: February 2004

A combined analysis of SKS, SKKS and P660s seismic phases detected in the records of BCAO/BNG seismic station in central Africa reveals that the waveform and amplitude of the T component of P660s deviate significantly from those predicted from the observations of shear wave splitting in SKS and SKKS. The inverse problem is investigated by using the anisotropic Thomson‐Haskell code and a genetic algorithm. The discrepancy between SKS/SKKS and P660S can be explained by P‐SH conversion at the boundaries of a weakly anisotropic layer 30–40 km thick lying atop 660 km discontinuity beneath BCAO/BNG. This anisotropy is probably induced by horizontal flow at the bottom of the upper mantle, in the transition zone.
Results from the Broadband Seismic Network on Montserrat
Authors: Neuberg Jürgen , Baptie Brian , Luckett Richard , Stewart Rod
Published: February 2004

A digital broadband seismic network has been installed around Soufriere Hills Volcano on Montserrat. While several distinctive types of seismic events with frequencies ranging from 0.5Hz to 30Hz could be identified, the emphasis is on two types of low‐frequency events which indicate the involvement of a fluid phase in the source mechanism: the so‐called long‐period events and the hybrid events. The latter occur in swarms with distinct periodicities of 4 to 12 hours and preceed major dome collapses and explosions. The swarms correlate very well with the tilt observed at the flanks of the volcanic edifice and, hence, can be linked to the pressurization of the magmatic system. Occasionally separate hybrid events merge and form harmonic tremor, which sometimes has a shifting spectral content. This reveals temporary changes in the source parameters. Low‐frequency seismic signals on Montserrat are considered to be key parameters for the monitoring of the internal dynamics of the volcano.
The Fast Auroral SnapshoT (FAST) Mission
Authors: Carlson C. W. , Pfaff R. F. , Watzin J. G.
Published: February 2004

The FAST satellite mission investigates plasma processes occurring in the low altitude auroral acceleration region, where magnetic field‐aligned currents couple global magnetospheric current systems to the high latitude ionosphere. In the transition region between the hot tenuous magnetospheric plasma and the cold, dense ionosphere, these currents give rise to parallel electric fields, particle beams, plasma heating, and a host of wave‐particle interactions. FAST instruments provide observations of plasma particles and fields in this region, with excellent temporal and spatial resolution combined with high quantitative accuracy. The spacecraft data system performs on‐board evaluation of the measurements to select data “snapshots” that are stored for later transmission to the ground. New measurements from FAST show that upward and downward current regions in the auroral zone have complementary field and particle features defined by upward and downward directed parallel electric field structures and corresponding electron and ion beams. Direct measurements of wave particle interactions have led to several discoveries, including Debye‐scale electric solitary waves associated with the acceleration of upgoing electron beams and ion heating, and the identification of electrons modulated by ion cyclotron waves as the source of flickering aurora. Detailed quantitative measurements of plasma density, plasma waves, and electron distributions associated with auroral kilometric radiation source regions yield a consistent explanation for AKR wave generation.
Potential new atmospheric sources and sinks of odd nitrogen: Sources involving the excited O2, and the N2O•O3 species
Authors: Prasad Sheo S.
Published: February 2004

The NO and NO2 radicals play important roles in atmospheric chemistry. This paper, therefore, theoretically discusses the following speculations: (1) the O2 (B³Σ) + N2 → 2NO reaction, and perhaps the photoexcitation of the N2•O2 dimers (or collision complexes) by Herzberg band photons as well, may be potentially important atmospheric sources of odd‐nitrogen, (2) there is a tantalizing potential for a substantive NOx production of the order of 1200 NOx cm−3 s−1 in the upper troposphere subject to certain condition, and (3) photodissociation of the possible N2O•O3 species in the 320 to 430 nm may be a non‐trivial source of NOx in the upper troposphere. Experimental studies of these ideas are needed, due to their relevance in regional pollution and global change issues.
Cradle to grave tracking of the January 6–11,1997 Sun‐Earth connection event
Authors: Fox N. J. , Peredo M. , Thompson B. J.
Published: February 2004

During the interval January 6–11, 1997, the satellites and ground facilities of the International Solar‐Terrestrial Physics (ISTP) “Observatory” tracked a solar eruption from the Sun to the Earth. The resulting Coronal Mass Ejection (CME) took four days to travel through interplanetary space before arriving at Earth, where it caused electromagnetic disturbances and spectacular aurorae. The initial expulsion lifted off the Sun on January 6, the resulting magnetic cloud arrived on January 10, and its effects lasted over 24 hours. The initial solar observations from SOHO were reported on January 7, during an ISTP Science Workshop on Sun‐Earth Connection events. This alerted the community to the impending arrival of the CME thereby allowing the event to be monitored in ‘realtime’ using the wide variety of ISTP instruments. This event provided the first ever end to end tracking of a space storm. Further, it provided a strong pressure pulse of extremely high density resulting in the compression of the magnetopause to within geosynchronous orbit during northward IMF conditions. Here we present an overview of the event and available observations.
Current‐voltage relationship in the downward auroral current region
Authors: Temerin M. , Carlson C. W.
Published: February 2004

In the auroral zone of the earth currents flow along magnetic field lines. In the downward current region currents are mainly carried by upflowing electrons from the ionosphere. Because of the low plasma density along auroral field lines, substantial currents in the range of microamps per square meter require substantial potential drops parallel to the magnetic field in the range of a few hundred to a few thousand volts. The current‐voltage relation along such magnetic field lines can be determined for simple profiles of the background ion density by invoking the condition of charge neutrality. For typical parameters, the current density is found to be a few times larger in the downward current region compared to currents in the upward current region for similar potential drops. Thus potential drops up to a few thousand volts and the consequent acceleration of ionospheric electrons up to keV energies, such as has been observed by the FAST satellite, are a necessary consequence of the observed current densities in the downward auroral current region.
Rapid conversion of elastic energy into plastic shear heating during incipient necking of the lithosphere
Authors: Regenauer‐Lieb Klaus , Yuen David A.
Published: February 2004

An important and novel mechanism for ductile failure of the lithosphere is identified here, which is intrinsic to the thermal‐mechanical feedback in a temperature dependent plastic body with coupled elastic fields. Both a temperature‐dependent power‐law visco‐elasto‐plastic rheology and a temperature‐dependent elasto‐plastic rheology are employed to study in a self‐consistent fashion the deformation of the lithosphere subject to extension by means of a two‐dimensional, finite‐element code. A structural perturbation initially localizes elasto‐plastic deformation only in its immediate vicinity. However, after 800,000 years have elapsed the localized zone of deformation takes off in a ‘crack‐like’ fashion and travels to the bottom of the lithosphere in about 50,000 years time. When the plate is severed, thermal runaway is caused by mechanical heating triggered by the rapid energy transfer of the globally stored elastic energy into localized plastic dissipation in the ductile fault.