bluuebunny/crossref_metadata_2025 huggingface dataset:
Radiation due to an infinitely imposed current line source near a dielectric elliptic waveguide: A dyadic Green's function approach
Authors: Li L. W. , Li Z. C. , Leong M. S.
Published: January 2004

In this paper, the dyadic Green's function technique has been employed to characterize electromagnetic radiation of an imposed current line source in the presence of an isotropic dielectric elliptic cylinder. The current density along the infinitely long wire has a constant amplitude but a varying phase. The elliptic cylinder is considered to be infinite in length. In order to analyze the problem, the dyadic Green's functions are expressed in terms of elliptic vector wave functions and the general equations needed to solve for the reflection and transmission coefficients are derived from the boundary conditions. These derived equations are transformed into, and solved using, a linear equation system. Numerically, the radiation patterns of the infinitely long wire are computed, plotted, and shown for various cases where the position and distance of the line source are varied. Both lossy and lossless dielectric media for the elliptic cylinder are considered. The results are believed to be very useful to many practical problems, and especially to characterize cable radiation or transmission line power leakage in tunnels.
Three‐dimensional MHD simulation of a flux rope driven CME
Authors: Manchester Ward B. , Gombosi Tamas I. , Roussev Ilia , De Zeeuw Darren L. , Sokolov I. V. , Powell Kenneth G. , Tóth Gábor , Opher Merav
Published: January 2004

We present a three‐dimensional (3‐D) numerical ideal magnetohydrodynamics (MHD) model, describing the time‐dependent expulsion of plasma and magnetic flux from the solar corona that resembles a coronal mass ejection (CME). We begin by developing a global steady‐state model of the corona and solar wind that gives a reasonable description of the solar wind conditions near solar minimum. The model magnetic field possesses high‐latitude coronal holes and closed field lines at low latitudes in the form of a helmet streamer belt with a current sheet at the solar equator. We further reproduce the fast and slow speed solar wind at high and low latitudes, respectively. Within this steady‐state heliospheric model, conditions for a CME are created by superimposing the magnetic field and plasma density of the 3‐D Gibson‐Low flux rope inside the coronal streamer belt. The CME is launched by initial force imbalance within the flux rope resulting in its rapid acceleration to a speed of over 1000 km/s and then decelerates, asymptotically approaching a final speed near 600 km/s. The CME is characterized by the bulk expulsion of ∼1016 g of plasma from the corona with a maximum of ∼5 × 1031 ergs of kinetic energy. This energy is derived from the free magnetic energy associated with the cross‐field currents, which is released as the flux rope expands. The dynamics of the CME are followed as it interacts with the bimodal solar wind. We also present synthetic white‐light coronagraph images of the model CME, which show a two‐part structure that can be compared with coronagraph observations of CMEs.
Slope‐dependent friction in a barotropic model
Authors: Döös Kristofer , Nycander Jonas , Sigray Peter
Published: January 2004

An evaluation of different bottom friction parameterizations has been performed with a nonlinear barotropic shallow water model. The model was set up for the Baltic Sea and forced with meteorological data during 1 year. The simulations were validated using hourly observations from 38 tide gauge stations around the Baltic. A new parameterization with friction proportional to the scalar product between the flow velocity and the bottom slope was tested and compared with parameterizations using Rayleigh friction, Ekman friction, Laplacian viscosity, or quadratic bottom friction. The new parameterization consistently gave both a smaller error and a better correlation with the observations. The average error with slope friction was 5.0 cm, as compared with 5.2 cm using quadratic bottom friction, the best of the other parameterizations. The correlation using slope friction was 0.92, as compared with 0.91 using quadratic bottom friction. The results were slightly improved by combining slope friction and Rayleigh friction.
On quadrature components of dissimilar statistics and their relevance in antenna error analysis
Authors: Monzon Cesar
Published: January 2004

Statistical analysis of the feed array of a complex antenna revealed distribution functions which cannot be represented by Rayleigh or Rice distribution models. Here we present the analytical description of these distributions, which may be seen as an extension of the Rice distribution. We conclude that statistical processes involving guidance of waves with very significant random content (e.g., near nulls) result in general in quadrature components of different statistical properties.
Magnetic fabrics may proxy as neotectonic stress trajectories, Polis rift, Cyprus
Authors: Borradaile Graham J. , Hamilton Tom
Published: January 2004

The Miocene Polis rift opened along a NNW axis, obviously in response to WSW relative extension and relative tension starting ∼5 Myr ago. However, geologically young plate movements are believed to be closing the rift by sinistral transpression producing minor younger faults since 1 Ma. Modern earthquake solutions give E‐W compression compatible with the younger faults. Magnetic fabrics using anisotropy of low field magnetic susceptibility (AMS) and anisotropy of anhysteretic remanent magnetization are kinematically compatible with stress axes required by the fault and rift geometry and thus were acquired in <5 Ma. However, by different statistical treatments and selecting samples from different subareas it is possible to reveal sedimentary‐depositional fabrics and perhaps also a composite AMS fabric related to young transpression (≤1 Ma).
Numerical modeling of flow processes over gravelly surfaces using structured grids and a numerical porosity treatment
Authors: Lane S. N. , Hardy R. J. , Elliott L. , Ingham D. B.
Published: January 2004

This article describes the development and validation of a method for representing the complex surface topography of gravel bed rivers in high‐resolution three‐dimensional computational fluid dynamic models. This is based on a regular structured grid and the application of a porosity modification to the mass conservation equation in which fully blocked cells are assigned a porosity of zero, fully unblocked cells are assigned a porosity of one, and partly blocked cells are assigned a porosity of between 0 and 1, according to the percentage of the cell volume that is blocked. The model retains an equilibrium wall function and an RNG‐type two‐equation turbulence model. The model is combined with a 0.002 m resolution digital elevation model of a flume‐based, water‐worked, gravel bed surface, acquired using two‐media digital photogrammetry and with surface elevations that are precise to ±0.001 m. The model is validated by comparison with velocity data measured using a three‐component acoustic Doppler velocimeter (ADV). Model validation demonstrates a significantly improved level of agreement than in previous studies, notably in relation to shear at the bed, although the resolution of model predictions was significantly higher than the ADV measurements, making model assessment in the presence of strong shear especially difficult. A series of simulations to assess model sensitivity to bed topographic and roughness representation were undertaken. These demonstrated inherent limitations in the prediction of 3‐D flow fields in gravel bed rivers without high‐resolution topographic representation. They also showed that model predictions of downstream flux were more sensitive to topographic smoothing that to changes in the roughness parameterization, reflecting the importance of both mass conservation (i.e., blockage) and momentum conservation effects at the grain and bed form scale. Model predictions allowed visualization of the structure of form‐flow interactions at high resolution. In particular, the most protruding bed particles exerted a critical control on the turbulent kinetic energy maxima typically observed at about 20% of the flow depth above the bed.
Sorption kinetics during macropore transport of organic contaminants in soils: Laboratory experiments and analytical modeling
Authors: Rahman M. Mokhlesur , Liedl Rudolf , Grathwohl Peter
Published: January 2004

Preferential solute transport coupled with diffusion into the surrounding matrix region has been examined in a silty loam soil by conducting macropore column experiments for various hydrophobic organic compounds (phenanthrene, 1, 2‐DCB, TCE, carbofuran) representing the polycyclic aromatic hydrocarbons, chlorobenzenes, chlorinated solvents, and pesticides. A new and ready‐to‐use analytical solution was developed for this setting to model the breakthrough curves. The model accounts for advection in the macropore region, diffusion into the matrix region, and linear sorption in both regions. In this setting, hydrodynamic dispersion is negligible as proved by a comparison of an advection‐dispersion model of finite pulse input. Conservative tracer experiments were predicted very well with independently determined transport parameters except for the tortuosity factor, which was used as a fitting parameter for the pore diffusion coefficient in the matrix. In case of sorbing solutes the sorption coefficient (Kd) was used as additional fitting parameter. The fitted Kd was 65% smaller for less sorbing compounds, e.g., carbofuran, and 80% less for strongly sorbing compounds, e.g., phenanthrene compared to the independently determined Kd from batch experiments. This indicates that sorption equilibrium was not obtained completely during the matrix diffusion at the timescale of the macropore flow experiment.
Relationship between climatic factors and dust storm frequency in Inner Mongolia of China
Authors: Zhao Chunsheng , Dabu X. , Li Ying
Published: January 2004

Meteorological dust storm frequency data from 37 stations of 40 years (1961–2000) throughout the Midwest Inner Mongolia of China are analyzed together with climatic factors of 40 years in this region. Dust storm frequency in this region has taken on a decline trend during the period of 1961–2000. The main climatic factors controlling dust storm frequency in this region are number of days with gale, intensity index of Asian polar vortex, and area index of the northern hemispheric polar vortex which are good representatives for large‐scale cold air activities. The explanation for the decreasing trend is that it is mainly due to the variation in climatic factors determining dust storm frequency in Inner Mongolia of China.
Top‐down estimates of global CO sources using MOPITT measurements
Authors: Arellano Avelino F. , Kasibhatla Prasad S. , Giglio Louis , van der Werf Guido R. , Randerson James T.
Published: January 2004

We present a synthesis inversion of CO emissions from various geographical regions and for various source categories for the year 2000 using CO retrievals from the MOPITT (Measurements of Pollution in the Troposphere) instrument. We find a large discrepancy between our top‐down estimates and recent bottom‐up estimates of CO emissions from fossil fuel/biofuel (FFBF) use in Asia. A key conclusion of this study is that CO emissions in East Asia (EAS) are about a factor of 1.8–2 higher than recent bottom‐up estimates.
Effects of metamorphic crustal densification on earthquake size in warm slabs
Authors: Wang Kelin , Cassidy John F. , Wada Ikuko , Smith Alex J.
Published: January 2004

Some recent damaging earthquakes occurred in the lower crust or mantle of warm subducting slabs. They are consistent with a theoretical prediction that larger events tend to be deeper inside the slab as a result of mechanical damage to the crust caused by metamorphic rock densification. The densification begins in a thin layer along the slab surface, inducing a stretching force in it. Fracture spacing scales with layer thickness, resulting in a “shattered” upper crust in which earthquake ruptures have limited propagation distance. In contrast, the more uniform untransformed substrata can host larger ruptures. Often, the lack of compression in warm‐slab mantle is also consistent with a shattered crust.
Liquid ternary aerosols of HNO3/H2SO4/H2O in the Arctic tropopause region
Authors: Irie H. , Kondo Y. , Koike M. , Takegawa N. , Tabazadeh A. , Reeves J. M. , Sachse G. W. , Vay S. A. , Anderson B. E. , Mahoney M. J.
Published: January 2004

Measurements of total reactive nitrogen (NOy) concentrations in the gas and aerosol phases were made on board the NASA DC‐8 aircraft within 1 km above the Arctic tropopause in February 2000. As temperatures decreased, NOy was taken up into the background sulfate aerosols. The observed temperature‐dependent NOy uptake agrees well with that calculated from a model of nitric acid (HNO3) uptake to form liquid HNO3/H2O/H2SO4 ternary droplets. The observations reported here provide the first direct evidence for the formation of ternary droplets in the Arctic tropopause region.
Multidecadal fluctuations in the relationship between equatorial Pacific heat content anomalies and ENSO amplitude
Authors: Cai Wenju , McPhaden Michael J. , Collier Mark A.
Published: January 2004

Observations over the past 20 years indicate that equatorial Pacific Ocean heat content variations associated with El Niño‐Southern Oscillation (ENSO) cycles lead sea surface temperature (SST) anomalies in the equatorial cold tongue by about 7 months. However, an asymmetry exists in the relationship between SST and heat content: positive SST anomalies related to El Niño are stronger than negative SST anomalies related to La Niña for the same magnitude (but opposite sign) heat content anomaly. In this study, we analyse a multi‐century simulation using the CSIRO Mark 3 coupled climate model to show that a similar asymmetry exists in some decades but not in others. This non‐stationarity appears to be a consequence of modulations by a mode of multidecadal variability which affects the temperature of upwelled water and the efficiency with which upwelling generates SST anomalies.
Rheological controls on fault loading rates in northern California following the 1906 San Francisco earthquake
Authors: Kenner S. J.
Published: January 2004

To estimate seismic hazard in complex, multiple fault systems, it is necessary to understand how stresses within the system are transferred. Accurate estimates of loading rate due to far‐field tectonic motion and postseismic transients following large earthquakes are required. Using plausible lower crustal rheologies constrained by observations following the 1906 San Francisco earthquake, I show that postseismic relaxation may play a significant role in reloading the coseismic fault, providing 60–80% of the stress released during great earthquakes. Further, postseismic stressing rates along neighboring faults are highly dependent on the geometry and rheology of the lower crust/upper mantle. This implies that tectonic loading rate estimates are also highly dependent on lower crustal/upper mantle structure. Thus, improvement of seismic hazard estimates within complex, multiple fault systems is dependent on a better understanding of structure and rheology at depth.
A detailed description of the solar wind triggers of two dayside transients: Events of 25 July 1997
Authors: Zesta Eftyhia , Sibeck David G.
Published: January 2004

Traveling Convection Vortices (TCVs), a specific type of dayside transient event, offer a good opportunity to study the modes of interaction between the solar wind, bow shock and the magnetosphere/ionosphere system. We study here in detail the solar wind triggers of two TCV events that occurred at 1500 UT and 1835 UT on 25 July 1997. During these two events there was a fortuitous conjunction of four solar wind monitors near the Earth's magnetosphere. We were able to identify the exact solar wind discontinuity that triggered each ground TCV. We found that the 1500 UT TCV was triggered by the density (and thus dynamic pressure) enhancement accompanying a tangential discontinuity. We were able to determine the orientation of the discontinuity plane and thus predict, in good agreement with observations, the propagation of the discontinuity between the four spacecraft as well as the propagation of the transient in the magnetosphere (geosynchronous) and ionosphere. The ground transient was generated in the early afternoon local time and then propagated westward, first toward local noon and then away from noon toward dawn. The 1835 UT TCV, which was stronger, was triggered by a more complicated solar wind discontinuity that exhibited significant spatial structure and an unusual propagation pattern. A detailed analysis of the orientation of the discontinuity fronts explained the propagation of the discontinuity in the solar wind. Even though the discontinuity did not carry a significant dynamic pressure enhancement, it had the properties required to generate a hot flow anomaly (HFA) or a foreshock cavity at the bow shock. The corresponding pressure reduction in the magnetosheath interacted with the magnetosphere to generate the transient near local noon that propagates eastward toward dusk. Geosynchronous observations confirm these conclusions. To strengthen our conclusions, we compared the discontinuity that triggered the ground TCV event with four other discontinuities that occurred in the same 2‐hour window. We found that none of the other four discontinuities carried significant dynamic pressure enhancements or had properties required to create a HFA at the bow shock. They did not trigger detectable transients on the ground. It thus seems that TCVs can be triggered by solar wind discontinuities that either carry dynamic pressure enhancements (or alternatively reductions) or by discontinuities that create HFAs or foreshock cavities at the bow shock.
Plasmaspheric mass loss and refilling as a result of a magnetic storm
Authors: Reinisch B. W. , Huang X. , Song P. , Green J. L. , Fung S. F. , Vasyliunas V. M. , Gallagher D. L. , Sandel B. R.
Published: January 2004

Using the sounding measurements from the radio plasma imager on IMAGE and a plasma density inversion algorithm, we derive the plasma density profiles along the magnetic field in a few L shells every 14 hours at magnetic local noon before, during, and after the 31 March 2001 magnetic storm. An empirical model of the plasmaspheric plasma density distribution is derived as a reference using the measurements before the storm. During the storm the equatorial plasma was substantially depleted in a range of L shells. The flux tubes were refilled after the storm. The filling ratio, the equatorial plasma density normalized by its quiet time value before the storm, is introduced to assess the time evolution of the depletion and refilling processes. The depletion, more than two thirds of the quiet time content, appeared to occur rather quickly after the storm onset, as determined by the limited temporal resolution of the measurements. The refilling proceeded, although more slowly than the depletion process, significantly faster than the theoretical prediction of a 3‐day timescale. Dynamic structures are observed in situ and confirmed by the extreme ultraviolet imager (EUV) measurements.
IMAGE EUV observation of radially bifurcated plasmaspheric features: First observations of a possible standing ULF waveform in the inner magnetosphere
Authors: Adrian M. L. , Gallagher D. L. , Avanov L. A.
Published: January 2004

We present EUV observations of the plasmasphere from 1938 to 2211 UT on 28 June 2000 characterized by the presence of bifurcated radial enhancements of the He+ plasma distribution in the nightside sector. These features remain stable throughout the period of observation and are found to move about the Earth at 67% of the corotation rate. Two‐dimensional simulation of the plasmasphere assuming the presence of an azimuthal standing wave patterns at L = 1.8 and 2.5 suggests that the organization of the outer plasmasphere is the result of convective motion driven by a ULF standing wave. Preliminary analysis of ground‐based magnetometer data provided by the IMAGE magnetometer network during the period of EUV observation indicates the presence of several narrow‐frequency oscillations extending down to 0.68 mHz, consistent with simulation results. Similar narrow‐frequency features are found in preliminary analysis of ACE Solar Wind Electron Proton Alpha Monitor (SWEPAM) bulk solar wind velocity data. We speculate that the observed radial He+ enhancements of the nightside plasmasphere may be the result of a nonresonant oscillation driven by the solar wind.
Solar wind termination shock and heliosheath effects on the modulation of protons and antiprotons
Authors: Langner U. W. , Potgieter M. S.
Published: January 2004

The interest in the role of the solar wind termination shock (TS) and heliosheath in cosmic ray modulation studies has increased significantly as the Voyager 1 and 2 spacecraft approach the estimated position of the TS. For this work the modulation of cosmic ray protons (p) and antiprotons (), and the consequent charge‐sign dependence, is studied with a numerical model including a TS with diffusive shock acceleration, a heliosheath, and drifts. The model allows a comparison of modulation with and without a TS. A more fundamental and comprehensive set of diffusion coefficients is used, applicable to a number of cosmic ray species during both magnetic polarity cycles of the Sun. Newly computed and improved local interstellar spectra for p and are used. The modulation of p with an anomalous component is also done to establish charge‐sign dependence at low energies. The modulation effects of the heliosheath and TS are illustrated for the different species and how they affect the computed /p. We found that the computed modulation for is surprisingly different from p and that the heliosheath is important for cosmic ray modulation. The local proton interstellar spectrum may not be known at energies <∼1 GeV until a spacecraft actually approaches the heliopause because of the strong modulation that occurs in the heliosheath, the effect of the TS, and the presence of anomalous protons. For antiprotons, in contrast, these effects are less pronounced.
The strain path and kinematics of lava domes: An example from Lipari (Aeolian Islands, Southern Tyrrhenian Sea, Italy)
Authors: Ventura Guido
Published: January 2004

A circular dome from Lipari Island consists of latitic enclaves hosted in a rhyolitic magma. A strain analysis of the enclaves has been carried out and the pure shear (α) and simple shear (γ) deformation, the vorticity number Wk and flow kinematics are determined. The axial ratio Rf of the enclaves and the angle ϕ between the long axis of the enclaves and the transport direction are measured in 131 sites concentrated in the axial zone (z1), upper‐distal zone (z2) and basal zone (z3) of the flow. The ϕ values depict a pattern suggesting endogenous growth. In z1, α/γ > 1. In z2, 1 < α < 1.35 and −1.8 < γ < −0.5. In z3, 1 < α < 1.5 and 0.3 < γ < 2.8. In z1, Wk < 0.5. In z2 and z3, Wk > 0.8. Lateral stretching due to the upward motion of magma from the conduit prevails in z1. Here the increase of pure shear strain from the bottom to the top reflects strain accumulation due to endogenous growth. z2 and z3 suffer simple shear deformation. In z3, the sense of shear is consistent with the transport direction. An opposite sense of shear characterizes z2. This is due to velocity gradients located in the lower and upper portions of the flow. The kinematics is viscous spreading in z1 and viscous gliding (hyperbolic flow) in z2–z3. Possible rupturing of the exterior may be important in z1, where lateral stretching occurs, and in z3, where γ is at a maximum. The effusion rate is ∼1.93 m3/s. Strain rates calculated using structural data span a range from 1.9 to 5.8.10−6 s−1.
Comparison of seasonal and spatial variations of leaf area index and fraction of absorbed photosynthetically active radiation from Moderate Resolution Imaging Spectroradiometer (MODIS) and Common Land Model
Authors: Tian Y. , Dickinson R. E. , Zhou L. , Zeng X. , Dai Y. , Myneni R. B. , Knyazikhin Y. , Zhang X. , Friedl M. , Yu H. , Wu W. , Shaikh M.
Published: January 2004

This paper compares by land cover type seasonal and spatial variations of MODIS leaf area index (LAI) and fraction of photosynthetically active radiation (0.4–0.7 μm) absorbed by vegetation (FPAR) from 2.5 years with those from the Common Land Model (CLM) and investigates possible reasons for notable differences. The FPAR value is mainly determined by LAI in MODIS and both LAI and stem area index (SAI) in CLM. On average, the model underestimates FPAR in the Southern Hemisphere and overestimates FPAR over most areas in the Northern Hemisphere compared to MODIS observations during all seasons except northern middle latitude summer. Such overestimation is most significant in winter over northern high latitudes. The MODIS LAI is generally consistent with the model during the snow‐free periods but may be underestimated in the presence of snow, especially for evergreen trees. The positive FPAR bias is mainly attributed to CLM SAI of deciduous canopy and higher LAI than MODIS for evergreen canopy as well. The negative FPAR bias results from several factors, including differences in LAI and soil albedo between CLM and MODIS or limitations of the geometric optics scheme used in the model. Therefore the MODIS algorithm needs to better represent the winter LAI retrievals, while the model needs to better quantify LAI and SAI. Since stems will not have the same single‐scattering albedo as green leaves, it may be inappropriate for the model to treat LAI and SAI the same in the FPAR and albedo parameterizations. If so, the role of SAI in these parameterizations needs reformulation.
Ice‐oxyhydrocarbon interactions in the troposphere
Authors: Huffman William A. , Snider Jefferson R.
Published: January 2004

Both surface and volume uptake can contribute to the removal of tropospheric gases by ice‐phase precipitation and cloud particles. These processes were evaluated by depositing ice in the presence of several gaseous oxyhydrocarbons and analyzing the chemical composition of the deposit. Acetone, methanol, ethanol, n‐propanol, n‐butanol, tert‐butanol, cyclohexanol, and toluene were tested. Volume uptake appears to be the dominant process, and results are presented as temperature‐dependent volume uptake coefficients. When extrapolated to 0°C, the volume uptake coefficients are at least a factor of two smaller than predictions based on gas partitioning into liquid water. Volume uptake coefficients at −10°C are 5–2 mol m−3 Pa−1 for the alkanols (i.e., 5 × 102–2 × 102 mol L−1 atm−1), 0.8 mol m−3 Pa−1 for acetone, and 0.01 mol m−3 Pa−1 for toluene. Further, our analysis indicates that the alkanols weaken water‐water bonding when incorporated into ice. This assertion is based on the positive temperature dependence of the alkanol volume uptake coefficients and is corroborated by indirect estimates of the effect of the alkanols on ice saturation vapor pressure. Since the observed volume uptake coefficients do not exceed the 10 mol m−3 Pa−1 threshold proposed by Crutzen and Lawrence [2000], our results indicate that the incorporation of the studied compounds into vapor‐deposited ice is not a substantial atmospheric removal process.
Relaxation of compensated topography and the evolution of crustal plateaus on Venus
Authors: Nunes Daniel Cahn , Phillips Roger J. , Brown C. David , Dombard Andrew J.
Published: January 2004

Crustal plateaus, dominant physiographic features on Venus, likely originate through dynamic mantle processes, although a debate exists on whether they formed by mantle upwellings or downwellings. Regardless of the mode of formation, several observations led to the hypothesis that viscous relaxation may be the driving force behind the apparent evolutionary sequence from a high‐standing plateau to a low‐standing plateau with elevated margins. We apply analytic and finite element models to test this hypothesis for isostatically compensated topography, as modeling of gravity data suggests that crustal plateaus are presently supported by crustal roots. Geotherm values ≤5 K km−1 combined with a surface temperature of 740 K preclude relaxation within 109 years, while geotherm values ≥20 K km−1 can yield relaxation times of 108 years or less. Hence significant relaxation requires hot conditions in order to occur within the appropriate 1‐Gyr timescale set by crustal plateau ages. We also show that a compensated plateau can either retain its shape as it relaxes or become more domical in appearance. Mantle temperatures <1400 K allow strong crust‐mantle coupling that hinders flow of crustal material from the center of the plateau and produces domical relaxed profiles. Higher temperatures lead to a relatively inviscid mantle and relaxation that is largely insensitive to topographic wavelength, thus preserving the original topographic shape during relaxation. In either case, relaxation of compensated plateaus does not yield elevated rims. We propose that the state of compensation must be considered variable.
Differential subsidence and rebound in response to changes in water loading on Mars: Possible effects on the geometry of ancient shorelines
Authors: Leverington D. W. , Ghent R. R.
Published: January 2004

If large liquid or solid water bodies existed in the past in Martian basins such as Argyre, Hellas, and the northern lowland plains, they would have represented massive surficial loads. Earth analogs suggest that the magnitudes of crustal displacements related to water loading and unloading would have varied spatially within and around affected basins. It is likely that the effects of bathymetric irregularities on lithospheric flexure would have caused shoreline areas proximal to deep regions to be depressed (and, subsequently, to rebound) to a greater extent than shoreline areas located near shallow regions. Crustal and mantle inhomogeneities would have likely further contributed to spatial variation in water‐related subsidence and rebound. Simple two‐dimensional elastic flexure models suggest that Martian shoreline features of common age and formed in association with a large ancient water body could vary in elevation today by hundreds of meters as a result of these differential effects. Examples of similar shoreline offsets on Earth suggest that sets of Martian strandline features will reflect the changing nature of loading through time.
The Syrtis Major volcanic province, Mars: Synthesis from Mars Global Surveyor data
Authors: Hiesinger H. , Head J. W.
Published: January 2004

We investigated the geology, stratigraphy, morphology, and topography of Syrtis Major, one of the large Hesperian‐aged volcanic provinces on Mars. New data from the Mars Global Surveyor (MGS) and Odyssey spacecraft allowed us to study Syrtis Major in unprecedented detail. On the basis of Mars Orbiter Laser Altimeter (MOLA) data we estimated the thickness of Syrtis Major lavas to be on the order of ∼0.5–1.0 km, their volume being ∼1.6–3.2 × 105 km3. MOLA data also show that the calderas of Nili and Meroe Patera are located within a large N‐S elongated central depression and are on the order of 2 km deep. MOLA data further indicate that the slopes of the flanks of the shield are ≪1°. These very gentle slopes are similar to other Martian highland paterae such as Amphitrites, Tyrrhena, and Syria Planum but are much smaller than slopes measured on the flanks of large Martian shield volcanoes such as Olympus, Elysium, Ascraeus, and Arsia Mons. At kilometer‐scale baselines, the surface of the Syrtis Major Formation is smoother than the surrounding highland plains but rougher than the floor of Isidis. We propose that the differences in surface roughness and wrinkle ridge patterns between Isidis Planitia and Syrtis Major are probably caused by additional sedimentation in the impact basin. Both the wrinkle ridge pattern and topography of Syrtis Major are interpreted to be consistent with a gravitational collapse of the southeastern sector of Syrtis Major. Recently a model has been proposed to explain the low elevation of the Isidis rim in the Syrtis Major region [e.g., Tanaka et al., 2002]. This model calls on catastrophic erosion of the rim that is triggered by the emplacement of sills, which interacted with a volatile‐rich substrate. We used MOLA data from nearby terrains of the Isidis rim to investigate the Isidis rim in locations where it has supposedly been eroded. On the basis of our investigation we conclude that the smooth morphology and relatively low topography of the Isidis rim in the Syrtis Major region can be best explained by initial heterogeneities in topography and flooding with lavas, together with some erosion and/or tectonic modification of the original rim. New crater counts show that Syrtis Major is of Early Hesperian age (N(5) = 154), older than in the geologic map of Greeley and Guest [1987]. On the basis of inspection of all available Mars Orbiter Camera (MOC) images we identified several terrain types and developed a stratigraphic sequence for Syrtis Major. Large‐scale erosional modification (e.g., deflation) of the Syrtis Major lavas and/or tephra deposits and redistribution of eolian material are evident in numerous MOC images.
Protecting Intellectual Property
Authors: Lanzerotti Louis J.
Published: January 2004

The increase in business interests in space weather leads almost naturally to tensions between competing interests: between business and business, business and government, and researchers and research entities. It is the policy of Space Weatherand its Editor to strive insofar as possible to identify and take appropriate action on any potential conflicts of interest in the consideration and review of all materials submitted to the publication.
The Silurian to Permian history of a metamorphic core complex in Lofoten, northern Scandinavian Caledonides
Authors: Steltenpohl Mark G. , Hames Willis E. , Andresen Arild
Published: January 2004

The Lofoten archipelago exposes Precambrian Baltic basement and Caledonian allochthonous sequences within a 1000 km long chain of gravity and magnetic highs and structural culminations along the extended, British and Norwegian continental shelf. Previous regional geophysical studies indicate that post‐Caledonian extension and development of the northern Norwegian shelf occurred during broadly defined Carboniferous‐Permian, Cretaceous‐Jurassic, and early Tertiary events. Structures related to these events are known to young westward. We report field, structural, and 40Ar/39Ar thermochronologic data from rocks exposed in Lofoten that further define the history and style of post‐Caledonian extension. The islands of southwest Lofoten also represent the most outboard exposures of Caledonian basement in northern Norway that presumably formed the middle to deep crustal core of the orogen. Metasedimentary rocks and penetratively deformed basement in Lofoten record high‐grade Silurian‐Devonian metamorphism and top‐to‐the‐east (hereinafter tops‐east) thrusting followed by episodes of Late Devonian to Early Carboniferous, tops‐west, ductile extension which progressed into oblique left‐slip movements. The structural style and timing of Silurian contraction in this area are remarkably similar to that determined for the more forelandward areas on the mainland, ∼120 km to the east, supporting the inference that distal parts of the Baltic continental margin that were once deeply subducted are presently exposed in Lofoten. The timings of post‐Devonian structural events that affected rocks in Lofoten are partially constrained by the ages of unconformities and strata known to be preserved in graben flanking the Lofoten culmination. The radiometric age and structural data presented in this study, in combination with stratigraphic constraints, suggest a westward progression through time of extensional deformation over a protracted interval of Silurian to Permian time. The latest, Permian extension in Lofoten is largely characterized by brittle structures that formed at conditions substantially less than 300°C. Compared to the exhumation history of the southern Western Gneiss Region, the depth of Caledonian, continental (A‐type) subduction and subsequent unroofing of Lofoten are of lesser magnitude, and the present erosional level remained in the middle crust for a much longer interval of time. The Permian 40Ar/39Ar mineral ages documented in this study are the youngest such ages yet identified in Scandinavia. These ages relate to episodes of deformation and cooling in response to extensional tectonic events that occurred roughly 100 m.y. after comparable effects identified on the Caledonian mainland. Our preferred explanation for the Carboniferous‐Permian radiometric ages, structural evolution, and stratigraphic data for Lofoten is that they all developed in the context of a long‐lived Cordilleran‐style metamorphic core complex.
Cenozoic denudation of Corsica in response to Ligurian and Tyrrhenian extension: Results from apatite fission track thermochronology
Authors: Zarki‐Jakni Bouchra , van der Beek Peter , Poupeau Gérard , Sosson Marc , Labrin Erika , Rossi Philippe , Ferrandini Jean
Published: January 2004

The island of Corsica (France) occupies a unique position in the western Mediterranean, since it has recorded both the Cenozoic Alpine orogenic history of the area as well as subsequent extensional collapse and oceanic basin formation. We present 41 new apatite fission track (AFT) ages and 23 measurements of track length distributions from Corsica, in order to elucidate its Cenozoic thermal and morphological evolution. AFT ages vary from 10.5 ± 0.8 Ma to 53.8 ± 4.1 Ma and form a clear spatial pattern: oldest ages are encountered in the southwest of the island, with a broad band of ages between 20 and 30 Ma running across the mountainous central area and ages <20 Ma confined to the eastern half of the island. Samples along the western and northwestern coasts record kilometer‐scale erosional denudation linked to rifting in the Ligurian‐Provençal basin, whereas samples from close to the extensionally inverted Alpine deformation front record a later cooling phase related to Tyrrhenian extension. The eastward younging pattern of AFT ages suggests the migration of a “wave” of erosional denudation from west to east across the island, apparently controlled by the migrating locus of extension. Our AFT data therefore support models of Mediterranean extension controlled by slab roll‐back.
Structural characterization of an island aquifer via tidal methods
Authors: Trefry M. G. , Bekele E.
Published: January 2004

A set of water level time series collected along a transect through a sedimentary island aquifer was used to test the utility of various simple models of ocean tidal propagation in bounded one‐dimensional aquifers. Fourier spectra were calculated for the ocean tidal modes and compared with spectra measured in wells along the island transect. Other sources of fluctuation could be neglected. An observed spatial bias in the well responses (attenuations and lags) could not be modeled by a homogeneous aquifer theory. A theory involving composite heterogeneity accounted well for the spatial bias, yielding estimates of aquifer transmissivities and storage coefficients indicating a fivefold difference in hydraulic diffusivity along the transect. A lack of well locations toward one end of the transect reduced the statistical significance of this result, with correlations between regression parameters evident. At the same time, a second bias was seen involving the ratio of signal amplitude and lag with penetration distance into the aquifer, as observed in prior tidal studies. A brief set of numerical experiments showed that horizontal layering in aquifer properties was the most probable cause of this propagation bias. Application of these results to the island data set supported a conceptual stratigraphic model of a highly conductive, sloping stratum underlying a less conductive, superficial sand layer. This model is inconsistent with well logs along the island transect but is supported by additional off‐transect well logs. It was concluded that one‐dimensional tidal propagation models may be useful in inverse characterization of aquifers with macroscale hydrogeological structures, and that the analysis of measured propagation bias has the potential to yield extra information on aquifer properties in the vertical direction.
Improving the worthiness of the Henry problem as a benchmark for density‐dependent groundwater flow models
Authors: Simpson Matthew J. , Clement T. Prabhakar
Published: January 2004

This study considers the worthiness of the Henry saltwater intrusion problem as a test case to benchmark density‐dependent groundwater flow models. Previously published results from a coupled versus uncoupled analysis indicate that the flow patterns associated with the standard Henry problem are largely dictated by the boundary forcing and not necessarily a result of density‐dependent effects [Simpson and Clement, 2003]. Results in this study show that the worthiness of Henry's problem can be improved by decreasing the freshwater recharge. This modification maintains the usual benefits of the standard test case, while at the same time increasing the influence of the density‐dependent effects. The numerical results for the modified Henry problem are rigorously tested against a new set of semianalytical results. The semianalytical result for the modified problem offers an additional improvement over the standard Henry problem that has typically only been tested using intercode comparisons.
Stochastic inverse mapping of hydraulic conductivity and sorption partitioning coefficient fields conditioning on nonreactive and reactive tracer test data
Authors: Huang Hai , Hu Bill X. , Wen Xian‐Huan , Shirley Craig
Published: January 2004

A three‐dimensional geostatistically based iterative inverse method is presented for mapping spatial distributions of the hydraulic conductivity and sorption partitioning coefficient fields by sequential conditioning on both nonreactive and reactive tracer breakthrough data. A streamline‐based semianalytical simulator is adopted to simulate chemical movement in a physically and chemically heterogeneous field and serves as the forward modeling. In this study, both the hydraulic conductivity and sorption coefficient are assumed to be random spatial variables. Within the framework of the streamline‐based simulator an efficient semianalytical method is developed to calculate sensitivity coefficients of the reactive chemical concentration with respect to the changes of conductivity and sorption coefficient. The calculated sensitivities account for spatial correlations between the solute concentration and parameters. The performance of the inverse method is assessed by a synthetic tracer test conducted within an aquifer with distinct spatial features of physical and chemical heterogeneities. The study results indicate that our iterative stochastic inverse method is able to identify and reproduce the large‐scale physical and chemical heterogeneity features. The conditional study on the geostatistical distributions of conductivity and sorption coefficient are expected to significantly reduce prediction uncertainties for solute transport in the medium.
Numerical trajectory calculations for the efficient inversion of transient flow and tracer observations
Authors: Vasco D. W. , Finsterle Stefan
Published: January 2004

We introduce a trajectory‐based method for the inversion of flow and transport observations. The approach operates on the output of a standard numerical simulator and is applicable under very general conditions. Using only head and concentration histories, we efficiently construct the model parameter sensitivities required for solving the inverse problem. A single simulation or forward calculation is required in order to take a step in the inversion. Our formulation, based on asymptotic solutions for flow and transport, partitions the inverse problem into an arrival time and an amplitude‐matching problem. Because the model parameter sensitivities are defined along trajectories, both inverse problems scale very well with respect to model size. At the migration experimental site of the Grimsel Rock Laboratory in Switzerland we utilized transient head and tracer arrival times to constrain the hydraulic conductivity between a suite of boreholes. The squared data misfit is reduced by over an order of magnitude in 30 iterations of our inversion algorithm. Each iteration requires two runs of our numerical simulator TOUGH2, one for each experiment, to construct the trajectories and associated model parameter sensitivities. We find a high‐conductivity channel curving in a roughly east‐west direction, in agreement with two previous studies. Estimates of model parameter resolution indicate that we can image the large‐scale conductivity variations within the array of boreholes.
A note on groundwater flow along a hillslope
Authors: Daly Edoardo , Porporato Amilcare
Published: January 2004

Particular cases of groundwater flow along a hillslope are studied using the groundwater hydraulic theory (e.g., Dupuit approximation) described by the Boussinesq equation. Analytical solutions are found as simple transformations of known similarity solutions. In particular, the expressions for phreatic surface level and volume flux and the corresponding loop‐rating curve for the flow of a groundwater mound as well as the travelling wave solutions of the Boussinesq equation are described in detail.
Multivariate hydrological frequency analysis using copulas
Authors: Favre Anne‐Catherine , El Adlouni Salaheddine , Perreault Luc , Thiémonge Nathalie , Bobée Bernard
Published: January 2004

This article presents the modeling of multivariate extreme values using copulas. Our approach allows us to model the dependence structure independently of the marginal distributions, which is not possible with standard classical methods. The methodology has been applied on two different problems in hydrology. The first application is concerned with the combined risk in the framework of frequency analysis. Four copulas have been tested on peak flows from the watershed of Peribonka in Québec, Canada. The second application relates to the joint modeling of peak flows and volumes. Three copulas have been applied to the watershed of the Rimouski River in Québec, Canada. This approach using copulas is promising since it allows us to take into account a wide range of correlation which can happen in hydrology.