bluuebunny/crossref_metadata_2025 huggingface dataset:
Radiative forcing of the Earth's climate system due to tropical tropospheric ozone production
Authors: Portmann R. W. , Solomon S. , Fishman J. , Olson J. R. , Kiehl J. T. , Briegleb B.
Published: February 2004

The radiative forcing of the Earth's climate system due to tropical tropospheric ozone is estimated using ozonesonde profiles and maps of the tropospheric ozone column derived from satellite data. The forcing is estimated using several different techniques in order to place bounds on its likely magnitude and to elucidate the role of biomass burning in producing the observed forcing. The results suggest that a widespread radiative forcing of at least 0.5 to 1 W m−2 exists over large areas in the tropics for much of the year. This radiative forcing is comparable in magnitude, but opposite in sign, to estimates of the aerosol forcing from tropical biomass burning. However, the burning contribution to ozone forcing is present over a larger geographic area than the aerosol forcing. The majority of the burning and thus these radiative forcings have likely been present only in the past century. These enhancements in tropical ozone are also estimated to be responsible for a radiative forcing of between 0.1 and 0.4 W m−2 when globally averaged. Comparison of these regional and global forcings due to tropical ozone changes to the estimates of forcing due to carbon dioxide and other trace gas increases since preindustrial times (about 2.45 W m−2) suggests that the effects of tropical ozone changes could be significant for evaluation of both regional and global anthropogenic forcing of climate.
System design of a mission to detect Earth‐sized planets in the inner orbits of solar‐like stars
Authors: Koch David , Borucki William , Cullers Kent , Dunham Edward , Webster Larry , Miers Tom , Reitsema Harold
Published: February 2004

A point design for a mission to detect Earth‐sized planets in the inner orbits of solar‐like stars is described. The observing technique is based upon continuously and simultaneously monitoring 5000 solar‐like stars for brightness changes that would be caused by planets transiting their star. Detection of periodic transits of the same amplitude and duration provides for a robust method of discovery. The instrument would consist of a 1‐m Schmidt telescope with an array of charge‐coupled devices (CCDs) filling the 12° field of view. The instrument would be placed in a halo orbit about the L2 Lagrange point, where its viewing would not be obscured at any time by the Sun, Earth, or Moon.
A search technique for planets in nearby binary stars using a ground‐based interferometer
Authors: Traub W. A. , Carleton N. P. , Porro I. L.
Published: February 2004

A search for Jovian‐type planets in 100 nearby binary stars could be carried out with the existing ground‐based infrared‐optical telescope array (IOTA) interferometer. We would study binaries with sufficiently great separation (25–50 AU; typical separation around 0.4 arcsec) that such a planet could be in a stable orbit about one member of the pair. The method is to measure the angular separation of stars in each binary, with a single‐measurement accuracy sufficient to detect the amplitude of a Uranus orbiting one of the stars. The technique is based on an auxiliary device, the pupil‐splitting interferometer (PSI), which substantially reduces systematic and random errors by converting a measurement of angular separation into a measurement of the differential optical delay between the two components of the binary. The program would be relatively economical, and could begin soon.
Partitioning of H and C between the mantle and core during the core formation in the Earth: Its implications for the atmospheric evolution and redox state of early mantle
Authors: Kuramoto Kiyoshi , Matsui Takafumi
Published: February 2004

Partitioning of H and C among fluid, silicate melt, and molten metallic iron within a growing Earth at temperatures 2000–2500 K and pressures 0.2–5 GPa is estimated by using a thermodynamic model based on the recent knowledge on gas solubility into silicate melts and molten metallic iron. The repulsive interactions among H, C, and S dissolved in molten metallic iron are taken into account. It is shown that partition coefficient of H between molten metallic iron and silicate melt increases with pressure and temperature. Under the presence of Fe‐rich metal, CO2content in silicate melt is suggested to be very low because of low oxygen fugacity under such condition. Assuming a homogeneous accretion of planetesimals with the composition given by the two‐component model slightly modified fromRingwood[1977] andWäanke[1981], it is shown that C is preferentially partitioned to molten metallic iron and quite less to silicate melt, whereas a substantial proportion of H is partitioned to silicate melt as H2O and also to molten metallic iron as interstitial atoms. For such concentrations of H, C, and S, the effect of thermodynamic interaction among them in molten metallic iron is not strong enough to cause the oversaturation of graphite. H and C partitioned to molten metallic iron may account for a significant portion of the density deficit in Earth's core. The estimated amount of H2O partitioned to silicate melt is possibly large enough to explain the sources for (1) H2O in the hydrosphere and mantle, (2) oxygen which partially oxidizes ferrous iron to ferric iron in the mantle, and (3) oxidant for metals which may fail to segregate to the core and act as the source of the highly siderophile elements in the mantle of the present Earth. The higher H/C and the lower C/36Ar ratios in the silicate Earth including the hydrosphere compared to various classes of meteorites are possibly explained if these elements are derived from the early mantle material after the H and C partitioning to molten metallic iron and core segregation. Accretion of the late veneer material such as the highly oxidized, CI chondrite‐like material seems difficult to explain such elemental abundance pattern without invoking unknown large volatile reservoir in the mantle.
Quantification of extraterrestrial lava flow effusion rates through laboratory simulations
Authors: Gregg Tracy K. P. , Fink Jonathan H.
Published: February 2004

We have used carefully controlled laboratory simulations to develop a model which relates lava flow morphology to effusion rate and rheology. Through comparisons with measured and estimated eruption rates on Earth, this approach allows us to constrain eruptive styles and compositions of extraterrestrial lava flows. By applying this model to lava flows on the Moon, Mars and Venus, we have determined that all the common flow morphologies (domes, folds and levees) on these planets could have been produced by basalt‐like or andesite‐like lavas through either continuous or episodic emplacement. The presence of more evolved magma compositions on other planets is not required to explain any of the observed lava flow morphologies.
The distribution of hot hydrogen atoms produced by electron and proton precipitation in the Jovian aurora
Authors: Bisikalo D. V. , Shematovich V. I. , Gérard J.‐C. , Gladstone G. R. , Waite J. H.
Published: February 2004

The energy distribution functions of nonthermal thermospheric hydrogen atoms are calculated for electron and proton precipitation in the Jovian aurora. A numerical model taking into account the production, elastic and inelastic relaxation and transport processes for hot H atoms is developed. This model is based on a Monte Carlo solution of the nonlinear Boltzmann equation for hot H atoms produced by electron and proton impact on H and H2 and exothermic chemical reactions. The distribution functions show a much higher energy tail for proton than electron precipitation. It is shown that the steady state flux of hot atoms (E ≥ 2 eV) is essentially isotropic. The peak and column hot H densities are about 3 × 105 cm−3 and 1 × 1014 cm−3 for a 100 erg cm−2 s−1 precipitation combining hard (22 keV) and soft (0.2 keV) electrons mixed with a 10 erg cm−2 s−1 flux of soft (0.3 keV) protons. These column densities, coupled with the wide range of hot H atom energies, may play an important role in the formation of the Lyman α line profile. Multiple scattering in the wings of the Ly α line by the fast H atoms is shown to partly account for the broad Ly α profile observed in the Jovian aurora with the Hubble space telescope.
Mars dynamics from Earth‐based tracking of the Mars Pathfinder lander
Authors: Folkner W. M. , Kahn R. D. , Preston R. A. , Yoder C. F. , Standish E. M. , Williams J. G. , Edwards C. D. , Hellings R. W. , Eubanks T. M. , Bills B. G.
Published: February 2004

Measurements of Mars' rotational variations can be conducted via Earth‐based radio tracking observations of the Mars Pathfinder lander during an extended mission. Two‐way range measurements between an Earth tracking station and the lander will enable precise monitoring of the planet's orientation, allowing details of Mars' internal structure and global surface/atmosphere interactions to be determined. An analysis has been performed to investigate the accuracy with which key physical parameters of Mars can be determined using the Earth‐based radio tracking measurements. Acquisition of such measurements over one Martian year should enable determination of Mars' polar moment of inertia to 1% or better, providing a strong constraint on radial density profiles (and hence on the iron content of the core and mantle) and on long‐term variations of the obliquity, which influences the climate. Variations in Mars length of day and polar motion should also be detectable, and will yield information on the seasonal cycling of carbon dioxide between the atmosphere and the surface.
Constraints on the solid‐state greenhouse effect on the icy Galilean satellites
Authors: Urquhart Mary L. , Jakosky Bruce M.
Published: February 2004

Surface temperature data from the Voyager spacecraft provide a constraint on the magnitude of a possible solid‐state greenhouse effect on the icy Galilean satellites. A solid‐state greenhouse effect will occur if the regoliths of Europa, Ganymede, and Callisto are optically thin in the visible and opaque in the thermal infrared, which would be consistent with particulate water ice. We examine in detail the effects of using different values for light penetration depth and regolith thermal properties on the diurnal variation of surface temperature. We then compare model results with surface temperature measurements for all three satellites. We conclude that the solid‐state greenhouse effect is limited to the approximate range of 0 cm ≤ ζ ≤ 2.2 cm on Europa, where ζ is the characteristic e‐folding insolation absorption length; this magnitude of greenhouse effect produces an increase in subsurface temperatures of approximately 10 K or less. Similarly, Ganymede and Callisto both have allowable ranges for ζ of 0 to 0.5 cm based on Voyager surface temperature, with no significant heating of the subsurface layers. The amount of subsurface heating is strongly dependent on the assumed thermal properties of the regolith.
Mare Tranquillitatis: Basalt emplacement history and relation to lunar samples
Authors: Staid Matthew I. , Pieters Carlé M. , Head James W.
Published: February 2004

Galileo and Clementine multispectral data of the Mare Tranquillitatis region have been analyzed to investigate the stratigraphy of basaltic units and the effects of lateral and vertical mixing processes within the mare. The distribution of compositionally distinct mare units is observed to be correlated with previous UV/VIS ratio images, although estimates of soil titanium contents are low in some areas as a result of mixing of local basalts with nonmare feldspathic materials. Basalt units identified by their spectral properties and spectral mixture analysis are compared with groups of Apollo 11 samples defined by previous workers on the basis of age and chemistry. Spectral studies presented here indicate that the Apollo 11 site lies at the edge of a localized western mare unit which includes the youngest and most titanium‐rich basalts in Tranquillitatis (Apollo 11 high‐K, high‐Ti samples). In southern Tranquillitatis, these basalts have been contaminated by a large degree of mixing with nonmare feldspathic materials. Nonmare materials near the Apollo 11 site are attributed largely to crater rays from Theophilus (100 km in diameter), which is located approximately 300 km to the south. A more extensive and stratigraphically older unit exposed near Apollo 11 is related to the low‐K, high‐Ti Apollo 11 samples and appears to extend as a coherent surface unit as far north as the Apollo 17 site in southern Serenitatis. The distribution of this spectrally identified basalt unit supports petrologic and geochemical evidence for the grouping of the high‐Ti, low‐K Apollo 11 and 17 basalt samples into the same regional volcanic events. Multispectral analysis of Tranquillitatis deposits also identify low‐titanium basalts in the northeastern and southeastern portions of the basin that are older than the high‐Ti basalts and are believed to be unsampled by Apollo 11. Several lines of evidence suggest that the Cayley Formation along the western Tranquillitatis margin may indeed lie on top of an ancient mare deposit buried by Imbrium basin ejecta (e.g., a cryptomare deposit). The distribution of vertically excavated feldspathic premare material within the mare provides information on the depth of the mare units and the proximity of the underlying basin topography. Compositional stratigraphy observed in both sets of multispectral data supports an asymmetric premare‐fill basin topography containing thicker basalts in the northwestern portion of the basin than previously predicted by crater flooding data.
Cross sections for the production of cations by electron impact on methanol
Authors: Srivastava S. K. , Krishnakumar E. , Fucaloro A. F. , van Note Tatia
Published: February 2004

Utilizing a crossed electron beam and a molecular beam collision geometry and the single particle counting technique, cross sections for the production of positive ions by electron impact on methanol have been measured for electron impact energies ranging from 0 to 500 eV. Appearance potentials for the various ionic fragments have also been obtained. These potentials are compared with values calculated from the heats of formation for methanol and for neutral and cationic products in order to identify the various channels of dissociation at threshold energies.
Observation of expanding vapor cloud generated by hypervelocity impact
Authors: Kadono Toshihiko , Fujiwara Akira
Published: February 2004

Observations of the expanding vapor cloud generated by the hypervelocity impact have been carried out. Under usual laboratory conditions, rock or ice materials cannot be vaporized completely. In order to investigate the expansion of a large amount of the vapor by complete vaporization caused by hypervelocity impact, we used a nylon projectile and measured the fundamental quantities of the vapor, that is, the expansion velocity, the shape of the vapor cloud, the temperature, and the light energy, by observing the light radiating from the vapor. The expansion velocity of the leading edge of the vapor is almost constant with time and is about twice that of the isothermal sound velocity, which is defined from the pressure and the density of the nylon projectile after passing of the shock wave. The shape of the cloud is not always hemispherical but depends on the combination of the material of the projectile and target, and impact velocity and angle. Inside the vapor cloud are not only the vapor but also the solid ejecta, which travel with the same velocity as the leading edge of the cloud. The temperature of the cloud in the case of nylon impacting on nylon decreases with the power law exponent of time of −0.04 to −0.2. The light energy radiating from the cloud is about 10−4 to 10−5 times the initial projectile kinetic energy.
Mobilization of dust on the Mars surface by the impact of small cosmic bodies
Authors: Rybakov V. A. , Nemtchinov I. V. , Shuvalov V. V. , Artemiev V. I. , Medveduk S. A.
Published: February 2004

The Impact of small cosmic bodies on the Martian surface may be the cause of local sand storms. The interaction of the shock waves with the thermal layer (created by the action of thermal radiation to the surface) leads to the formation of a high‐velocity jet moving along the surface. A reverse vortex in the precursor facilitates dust lifting. This and other factors lead to the dust rising: outgassing of the surface layer due to heating by the radiation impulse; intrusion of the high‐pressure atmospheric gas behind the shock wave into the regolith and dust layer and subsequent blow off in the rarefaction wave; and formation of jets moving along the surface due to interaction of the ballistic wave with the blast wave and due to erosion by high‐velocity impulsive winds behind the shock wave of the explosion. The results of preliminary theoretical simulations and laboratory modeling are presented.
Faunal and alkenone reconstructions of subtropical North Atlantic surface hydrography and paleotemperature over the last 28 kyr
Authors: Chapman M. R. , Shackleton N. J. , Zhao M. , Eglinton G.
Published: February 2004

Two techniques for estimating past variations in sea surface temperature (SST) have been used to investigate climatic change in Biogeochemical Oceanic Flux Study (BOFS) core 31K (19°N, 20°W) from the eastern subtropical Atlantic. High‐resolution SST records for the last 28 kyr have been produced using planktonic foraminiferal assemblages, based on the Imbrie‐Kipp transfer function technique, and the UK′37 index derived from abundances of C37 alkenones biosynthesized by prymnesiophyte algae. Modern observations suggest that these indices reflect particular hydrographic conditions in the upper ocean: the UK′37 index corresponds to the temperature at the time of maximum coccolith productivity, typically late spring‐early summer in the study area today, whereas the faunal transfer function is calibrated for seasonal maximum and minimum temperatures. In general, the faunal and biomarker paleotemperature records display comparable SST variations during the last glacial and deglacial, but although the overall trends are similar, differences exist in the magnitude and timing of these temperature changes. Most notably, the faunal Twarm and UK′37 SST estimates diverge by 3°C between 8 ka and 6 ka, and this offset persists through the late Holocene. This difference cannot be adequately explained by uncertainties associated with either the calibration data sets or fluctuating preservation levels. We therefore propose that the deviation in SST estimates is linked to a switch in the seasonal timing of maximum coccolith production from the summer in the glacial ocean to the late spring‐early summer in the modern ocean. Our results suggest that a dual approach to SST estimation based on faunal and biomarker proxies can provide a valuable means of evaluating mixed layer and productivity changes associated with the movement of oceanographic frontal zones during the late Quaternary.
Origin of the first global meltwater pulse following the Last Glacial Maximum
Authors: Clark Peter U. , Alley Richard B. , Keigwin Lloyd D. , Licciardi Joseph M. , Johnsen Sigfus J. , Wang Huaxiao
Published: February 2004

Well‐dated sea level records show that the glacioeustatic rise following the last glacial maximum was characterized by two or possibly three brief intervals of rapid sea level rise separating periods with much lower rates. These very high rates of sea level rise indicate periods of exceptionally rapid deglaciation of remaining ice sheets. The Laurentide Ice Sheet is commonly targeted as the source of the first, and largest, of the meltwater pulses (mwp‐IA between ∼14,200 (12,200 14C years B.P.) and 13,700 years ago (11,700 14C years B.P.)). In all oceanic records of deglaciation of the former northern hemisphere ice sheets that we review, only those from the Gulf of Mexico and the Bermuda Rise show evidence of low δ18O values at the time of mwp‐IA, identifying the southern Laurentide Ice Sheet as a potential source for mwp‐IA. We question this source for mwp‐IA, however, because (1) ice sheet models suggest that this sector of the ice sheet contributed only a fraction (<10%) of the sea level needed for mwp‐IA, (2) melting this sector of the ice sheet at the necessary rate to explain mwp‐IA is physically implausible, and (3) ocean models predict a much stronger thermohaline response to the inferred freshwater pulse out of the Mississippi River into the North Atlantic than is recorded. This leaves the Antarctic Ice Sheet as the only other ice sheet capable of delivering enough sea level to explain mwp‐IA, but there are currently no well‐dated high‐resolution records to document this hypothesis. These conclusions suggest that reconstructions of the Laurentide Ice Sheet in the ICE‐4G model, which are constrained to match the sea level record, may be too low for time periods younger than 15,000 years ago. Furthermore, δ18O records from the Gulf of Mexico show variable fluxes of meltwater from the southern margin of the Laurentide Ice Sheet which can be traced to the opening and closing of eastward draining glacial‐lake outlets associated with surging ice sheet behavior. These variable fluxes through eastern outlets were apparently sufficient to affect formation of North Atlantic Deep Water, thus underscoring the sensitivity of this process to changes in freshwater forcing.
Simulated ocean circulation and sediment transport in the North Atlantic during the Last Glacial Maximum and today
Authors: Seidov Dan , Haupt Bernd J.
Published: February 2004

Paleocirculation of the North Atlantic Ocean at the last glacial maximum (LGM) is simulated using a large‐scale ocean general circulation model (OGCM). The model is driven by glacial sea surface thermohaline conditions and wind stress. For comparison of past and present circulation patterns, a separate run provides the Holocene/modern circulation patterns based on the present day sea surface climatology. The output of the OGCM is then used in a sedimentation model and in a model to trace water parcel trajectories. The sedimentation model reveals the differences in sediment deposition in the North Atlantic linked to past and present circulation regimes. The trajectory‐tracing model facilitates a better understanding of the thermocline and deep ocean ventilation, the actual three‐dimensional conveying of water, and the role of convection in maintaining the meridional thermohaline overturning. The results of the trajectory‐tracing technique indicate stronger subtropical thermocline ventilation during the LGM. For the deep ocean currents, we find severe alteration of three‐dimensional water motion in response to weakening of the LGM convection and its retreat to the southwest from its present locations. Ocean circulation models can provide sedimentation studies with information on the circulation regime that proxy data used alone cannot. These is because such models furnish both circulation patterns and the ventilating convection depths.
Biogenic sedimentation beneath the California Current System for the past 30 kyr and its paleoceanographic significance
Authors: Gardner James V. , Dean Walter E. , Dartnell Peter
Published: February 2004

A north‐south transect of 17 cores was constructed along the eastern boundary of the California Current system from 33° to 42°N to investigate the changes in biogenic sedimentation over the past 30 kyr. Percentages and mass accumulation rates of CaCO3, Corg, and biogenic opal were assembled at 500 to 1000 years/sample to provide relatively high resolution. Time‐space maps reveal a complex pattern of changes that do not follow a simple glacial‐interglacial two‐mode model. Biogenic sedimentation shows responses that are sometimes time‐transgressive and sometimes coeval, and most of the responses show more consistency within a limited geographic area than any temporal consistency. Reconstructed conditions during late oxygen isotope stage 3 were more like early Holocene conditions than any other time during the last 30 kyr. Coastal upwelling and productivity during oxygen isotope stage 3 were relatively strong along the central California margin but were weak along the northern California margin. Precipitation increased during the last glacial interval in the central California region, and the waters of the southern California margin had relatively low productivity. Productivity on the southern Oregon margin was relatively low at the beginning of the last glacial interval, but by about 20 ka, productivity in this area significantly increased. This change suggests that the center of the divergence of the West Wind Drift shifted south at this time. The end of the last glacial interval was characterized by increased productivity in the southern California margin and increased upwelling along the central California margin but upwelling remained weak along the northern California margin. A sudden (<300 years) decrease in CaCO3, Corg, and biogenic opal occurred at 13 ka. The changes suggest a major reorientation of the atmospheric circulation in the North Pacific and western North America and the establishment of a strong seasonality in the central California region. A carbonate preservation event occurred at 10 ka that appears to reflect the uptake of CO2 by the terrestrial biosphere as the northern latitudes were reforested following retreat of the glaciers. The Holocene has been a period of relatively high productivity in the southern California margin, relatively strong coastal upwelling along the central California margin, relatively weak upwelling along the northern California margin, and the northward migration of the divergence zone of the West Wind Drift.
Coupled ocean‐atmosphere model response to freshwater input: Comparison to Younger Dryas Event
Authors: Manabe Syukuro , Stouffer Ronald J.
Published: February 2004

This study explores the responses of a coupled ocean‐atmosphere model to the discharge of freshwater into the North Atlantic Ocean. In the first numerical experiment in which freshwater is discharged into high North Atlantic latitudes over a period of 500 years, the thermohaline circulation (THC) in the Atlantic Ocean weakens, reducing surface air temperature over the northern North Atlantic Ocean and Greenland and, to a lesser degree, over the Arctic Ocean, the Scandinavian peninsula, and the Circumpolar Ocean and the Antarctic continent of the southern hemisphere. Upon the termination of the water discharge at the 500th year, the THC begins to intensify, regaining its original intensity in a few hundred years. With the exception of the Pacific sector of the Circumpolar Ocean of the southern hemisphere, where the surface air temperature recovery is delayed, the climate of the northern North Atlantic and surrounding regions rapidly resumes its original distribution. The evolution of the ocean‐atmosphere system described above resembles the Younger Dryas event as inferred from the comprehensive analysis of ice cores and deep‐sea and lake sediments. In the second experiment, in which the same amount of freshwater is discharged into the subtropical North Atlantic again over a period of 500 years, the THC and climate evolve in a manner qualitatively similar to the first experiment. However, the magnitude of the THC response is 4–5 times smaller. It appears that freshwater is much less effective in weakening the THC if it were discharged outside high North Atlantic latitudes.
Subpicosecond electrodynamics of distributed Bragg reflector microlasers: Results from finite difference time domain simulations
Authors: Hagness Susan C. , Joseph Rose M. , Taflove Allen
Published: February 2004

With advances in nanofabrication techniques leading to ever smaller and more intricate semiconductor laser structures, a detailed understanding of the electrodynamics of these micron‐scale devices is required in order to optimize their design. The finite difference time domain (FD‐TD) Maxwell's equations solver holds much promise for providing highly realistic simulations of novel microcavity lasers. We have extended the FD‐TD algorithm to include the effects of frequency‐dependent gain and gain saturation. This approach and its application to the modeling of distributed Bragg reflector microlasers is presented.
Modeling the formation of polar cap patches using large plasma flows
Authors: Valladares C. E. , Decker D. T. , Sheehan R. , Anderson D. N.
Published: February 2004

Recent measurements made with the Sondrestrom incoherent scatter radar have indicated that the formation of polar cap patches can be closely associated with the flow of a large plasma jet. In this paper, we report the results of a numerical study to investigate the role of plasma jets on patch formation, to determine the temporal evolution of the density structure, and to assess the importance of O+ loss rate and transport mechanisms. We have used a time‐dependent model of the high‐latitude F region ionosphere and model inputs guided by data collected by radar and ground‐based magnetometers. We have studied several different scenarios of patch formation. Rather than mix the effects of a complex of variations that could occur during a transient event, we limit ourselves here to simulations of three types to focus on a few key elements. The first attempt employed a Heelis‐type pattern to represent the global convection and two stationary vortices to characterize the localized velocity structure. No discrete isolated patches were evident in this simulation. The second modeling study allowed the vortices to travel according to the background convection. Discrete density patches were seen in the polar cap for this case. The third case involved the use of a Heppner and Maynard pattern of polar cap potential. Like the second case, patches were seen only when traveling vortices were used in the simulation. The shapes of the patches in the two cases of moving vortices were defined by the geometrical aspect of the vortices, i.e. elliptical vortices generated elongated patches. When we “artificially” removed the Joule frictional heating, and hence any enhanced O+ loss rate, it was found that transport of low density plasma from earlier local times can contribute to ∼60% of the depletion. We also found that patches can be created only when the vortices are located in a narrow local time sector, between 1000 and 1200 LT and at latitudes close to the tongue of ionization.
Modal expansion analysis of monopole antennas driven from a coaxial line
Authors: Shen Zhongxiang , MacPhie Robert H.
Published: February 2004

A rigorous modal expansion analysis is presented for a monopole antenna fed through an infinite perfectly conducting ground plane by a coaxial transmission line. An infinite perfectly conducting plate is introduced to facilitate the use of the modal expansion method. The surface current and input impedance of the monopole antenna result from finding the expansion coefficients of the electromagnetic field expressions by enforcing boundary conditions at conducting surfaces and regional interfaces. Numerical results for the current distribution and input admittance of a parallel plate antenna and a monopole fed by a coaxial line are presented and compared with available data in the literature. Very good agreement is observed. Also examined is the effect of the junction between the feed line and the monopole on the antenna's admittance.
Scattering and absorption of E‐ and H‐polarized plane waves by a circularly curved resistive strip
Authors: Nosich A. I. , Okuno Y. , Shiraishi T.
Published: February 2004

An analytical‐numerical method of analysis is presented for two‐dimensional wave diffraction by an open circular resistive strip. The method is based on the dual series equations regularization approach and results in algorithms with accuracy limited only by a computer's digital precision. Scattering and absorption cross sections are computed as functions of frequency for lossless and lossy strips.
Directional VLF antenna for communicating with submarines
Authors: King Ronold W. P.
Published: February 2004

High‐power, very low frequency transmitters for communicating with submarines use electrically short, top‐loaded, vertical monopoles. These are efficient radiators of the lateral surface wave, but since they are omnidirectional, they expose residents of neighboring urban areas to possibly harmful effects. A possible alternative, the horizontal traveling‐wave antenna of the Beverage type, is analyzed, and the design for the frequency range from 10 to 30 kHz is described. The antenna is highly directive in the horizontal plane. Although the field of the unit horizontal dipole over the earth is much smaller than that of the unit vertical dipole, the large effective length of the traveling‐wave antenna makes its field comparable to that of the electrically short vertical monopole. Furthermore, since the radiated field in all directions except within a 30° to 60° angle out to sea is small, there is no exposure risk when the electrically long horizontal antenna is located near inhabited areas.
Sub‐Fresnel‐scale vertical resolution in atmospheric profiles from radio occultation
Authors: Karayel E. Tuna , Hinson David P.
Published: February 2004

We have investigated the vertical resolution that can be achieved in atmospheric profiles retrieved from radio occultation measurements. The results are based on forward simulations of radio wave propagation through model atmospheres using the multiple phase‐screen method. We find that profiles retrieved through Abel inversion, the standard algorithm derived from geometrical optics, have a vertical resolution that is diffraction‐limited, as expected. To overcome this limitation, we have developed an advanced retrieval algorithm, which is based on scalar diffraction theory and properly accounts for diffraction effects. We demonstrate that the method is capable of retrieving accurate refractivity profiles at sub‐Fresnel‐scale resolution for Mars‐ and Earth‐like atmospheres. It also provides a natural means for deciphering multipath propagation effects. The method seems capable of enhancing resolution by a factor of 10 beyond the diffraction limit. In one simulation involving an Earth‐like model atmosphere the algorithm successfully retrieved a profile in which the refractive index changed by 10−5 over a vertical scale of 250 m. The maximum vertical gradient of refractive index within this small‐scale feature was about 0.8×10−7 m−1. For comparison, critical refraction occurs for a gradient of about 1.6×10−7 m−1. The feature was embedded in a smooth refractive index profile at the level where the pressure and mean refractive index were 42 kPa and 1.00013, respectively. Total refractive bending for a ray that grazed this level was 0.01–0.02 rad.
Intracrustal extension of an Archean orogen revealed using single‐grain U‐Pb zircon geochronology
Authors: Moser D. E. , Heaman L. M. , Krogh T. E. , Hanes J. A.
Published: February 2004

The metaplutonic Wawa gneiss domain in the southern Superior Province is part of an uplifted block that was exhumed during the Proterozoic, exposing the lower‐crustal (∼30 km) levels of the late Archean (2720 to 2670 Ma) Abitibi‐Wawa orogen. Previous structural and geophysical studies of the midcrustal Wawa gneiss domain reveal subhorizontal shear zones that formed during orogen‐parallel extension and correspond to gently dipping seismic reflectors, present at depth elsewhere in the orogen. In order to bracket the age of this extensional deformation, the ages of metre‐scale igneous bodies that crystallized before and after extension have been determined in four outcrops using single‐grain U‐Pb zircon dating techniques. The results constrain the time of extension to the interval between 2660 and 2645 Ma and show that deformation was coeval with pegmatite emplacement, partial melting of tonalite gneisses as old as 2925±35 Ma, and regional circa 2660 Ma granulite‐facies metamorphism of adjacent, more deeply eroded crust. This extension and associated high‐grade metamorphism in the Wawa gneiss domain occurred 10 to 25 m.y. after the cessation of regional compression, major transcurrent fault movement, and sediment deposition in the upper structural levels of the orogen. The middle and lower crust was therefore mechanically decoupled from the upper crust during this period of orogen‐parallel extension. This intracrustal style of deformation is interpreted to be the consequence of gravitational forces working on a thermally softened middle crust. The detachment of lithosphere from the orogen base is the favored mechanism for generating these forces and for introducing the heat that caused synextension metamorphism. Cyclic construction and delamination of orogen lithosphere could account for even younger metamorphic/strain events evident in nearby exposures of lower crust.
Shallow and deep rotations in the Miocene Alps
Authors: Laubscher H.
Published: February 2004

Mapping and the construction of balanced cross‐sections reveal dextral rotation in addition to N‐S contraction during the late middle to late Miocene Jura phase both at the northern and the southern front of the Central Alps (Jura and Lombardic Southern Alps, respectively). These rotations may be ascribed to one and the same shallow domain or sublid, rotated clockwise around a pivot somewhere at the southwestern end of the Aar massif. In a crude first approximation model the sublid may be considered rigid, although the data indicate differential rotations and longitudinal stretching within the lid. The eastern boundary of the sublid crosses the Alps at the Giudicarie‐Brenner line, which, according to very recent data, in the Jura phase formed a kinematically linked system, whereas from Innsbruck to the northwest it is postulated to join, as a diffuse or accommodation zone, the eastern tip of the Jura. In the southwest, the Lombardic thrusts enter into the interior of the Western Alps. From there to the southwestern end of the Jura the lid boundary is tentatively chosen arbitrarily to pass somewhere near the northern end of the Belledonne Massif. A similar sublid, though less well substantiated, may comprise the Tauern and the Venetian Southern Alps. The rotational components are superimposed on elements of internal strain, particularly transverse contraction and longitudinal stretching due to simple dextral shear and lateral escape. The model of dextrally rotating sublids pulls together a number of hitherto unexplained structures and opens new perspectives on such recalcitrant problems as the eastward disappearance of the Jura and the Adige embayment in the Southern Alps. Dextral rotation of such shallow sublids may be considered to constitute “mode 1” of the dextral component at the Europa‐Adria plate boundary. There is also a “mode 2” that affects its deep parts. At the surface, its manifestation is a dextral belt of en échelon folds and pull‐apart domains that crosses the sublids diagonally. It consists of the Massifs line in the west and the Neo‐Pustertal line in the east. They approximately join in the Brenner area, where they cross and interfere with the sublid boundaries. The combined Massifs‐Pustertal line describes an arcuate partial northern boundary of the Adriatic plate with an apparent center of sinistral rotation in central Italy. This sinistral rotation may be responsible for the contractional features in the southern part of the western Alps which cannot be accounted for by SE‐NW Adria‐Europa convergence. It could have caused the development of the fold and thrust belts of Sisteron, Castellane and Nice. These arcs, in turn, suggest the action of more or less independent shallow sublids also in this part of the Alps.
Far‐field effects of Late Miocene subduction in the Eastern Carpathians: E‐W compression and inversion of structures in the Alpine‐Carpathian‐Pannonian region
Authors: Peresson Herwig , Decker Kurt
Published: February 2004

Kinematic and paleostress data constrain a Late Miocene E‐W compressional event that affected the entire Alpine‐Carpathian‐Pannonian system after 9 Ma and prior to 5.3 Ma. The maximum horizontal compression directions obtained from 110 stations show a mean σ1 orientation of 083°. Deformation is mainly strike‐slip. E‐W directed compression followed Early to Middle Miocene upper plate extension in the Pannonian Basin which was caused by the retreating subduction boundary in the outer Carpathians. This compressional event terminated Early to Middle Miocene eastward lateral extrusion of the Eastern Alps and reverted strike‐slip faults which bounded earlier extruded wedges such as the Salzachtal‐Ennstal fault, the Periadriatic fault, the Mur‐Mürz‐Vienna Basin fault system, and strike‐slip faults in the Western Carpathians. E‐W compression caused the reorientation of the extension direction of the Alpine crustal stack. East‐directed tectonic unroofing of the metamorphic domes in the central Eastern Alps terminated between 9 and 6 Ma and Early to Middle Miocene orogen‐parallel E‐W extension switched to Late Miocene N‐S extension which parallels modern topographic slopes. In the Pannonian Basin the change from synrift extension to Late Miocene compression during the postrift phase caused the pronounced postrift subsidence by stress induced downward flexure of the loaded lithosphere.

We relate Late Miocene E‐W compression to coeval late‐stage west‐ directed subduction of the European plate below the Eastern Carpathians. Slab pull of the subducted plate caused subduction roll back and upper plate extension of the Pannonian area up to the Middle Miocene. Subduction slowed down and ceased when up to 60‐km‐thick buoyant continental crust entered the subduction zone. During the short period of continued convergence E‐W ‐directed compressive stress was transmitted across the subduction boundary into the upper plate. Compressive stress was transferred through the uppermost brittle crust of the earlier extended Pannonian region into the Eastern Alps, up to 1400 km behind the subduction zone. E‐W compression terminated during the Pliocene when the Pliocene to recent NNW‐SSE compressive stress field was established in Central Europe.
The deep structure of the Carmel fault zone, northern Israel, from gravity field analysis
Authors: Achmon Moshe , Ben‐Avraham Zvi
Published: February 2004

The Carmel‐Yizre'el‐Jordan fault system is a major structural feature in the geology of Israel. There is a great difference in topographical features, structural style, seismic activity, crustal structure, and other geological characteristics to the north and south of this fault system. We examine the gravity field of the region around the fault system by combining the techniques of upward continuation and horizontal gradient analysis. The results suggest the existence of a system of deep seated, N‐S trending faults that are probably related to the continental breakup of the region in the Triassic‐Jurassic. The present complex deformation of the area is the result of interaction between the older faults system and the younger stresses resulting from the formation of the Dead Sea rift.
Hydrogeologic Controls on the Groundwater Interactions with an Acidic Lake in Karst Terrain, Lake Barco, Florida
Authors: Lee T. M.
Published: February 2004

Transient groundwater interactions and lake stage were simulated for Lake Barco, an acidic seepage lake in the mantled karst of north central Florida. Karst subsidence features affected groundwater flow patterns in the basin and groundwater fluxes to and from the lake. Subsidence features peripheral to the lake intercepted potential groundwater inflow and increased leakage from the shallow perimeter of the lake bed. Simulated groundwater fluxes were checked against net groundwater flow derived from a detailed lake hydrologic budget with short‐term lake evaporation computed by the energy budget method. Discrepancies between modeled and budget‐derived net groundwater flows indicated that the model underestimated groundwater inflow, possibly contributed to by transient water table mounding near the lake. Recharge from rainfall reduced lake leakage by 10 to 15 times more than it increased groundwater inflow. As a result of the karst setting, the contributing groundwater basin to the lake was 2.4 ha for simulated average rainfall conditions, compared to the topographically derived drainage basin area of 81 ha. Short groundwater inflow path lines and rapid travel times limit the contribution of acid‐neutralizing solutes from the basin, making Lake Barco susceptible to increased acidification by acid rain.
Estimation of “Effective” Soil Hydraulic Properties by Top Soil Moisture and Evaporation Modeling Applied to an Arable Site in Central Spain
Authors: Gouweleeuw Ben T. , van de Griend Adriaan A. , Owe Manfred
Published: February 2004

A surface moisture model for large‐scale semiarid land application has been extended with a moisture flow routine for capillary flow. The model has been applied to a field‐scale data set of topsoil moisture and latent heat flux of an arable site in central Spain. A comparison of the soil hydraulic properties, determined by model simulations and measurements in the field, demonstrates the capability of the model to determine these properties out of a range of soil classes as defined according to the parameterization by Clapp and Hornberger [1978]. Estimation of area average or “effective” soil physical parameters according to this approach requires time series of topsoil moisture and actual evapotranspiration on a patch or regional scale. Therefore this approach has potential for use with remotely sensed data.
Estimating the upper tail of flood‐peak frequency distributions using hydrometeorological information
Authors: Naghettini Mauro , Potter Kenneth W. , Illangasekare Tissa
Published: February 2004

In its 1988 report, the National Research Council Committee on Estimating the Probabilities of Extreme Floods identified principles for improving the estimation of floods with annual exceedance probabilities of the order of 10−3 or smaller. This paper presents a methodology for estimating the probability of extreme floods which makes use of these principles. Its core is the “peak‐to‐volume” method [Bradley and Potter, 1992], which is based on separately estimating the probability distributions of flood volumes and flood peaks conditioned on volumes. In its original form it relies on extrapolating a conventionally estimated probability distribution, the distribution of flood volumes. To strengthen this step, we propose use of the gradient of extreme values (GRADEX) method [Guillot and Duband, 1967], in which the upper tail of the flood volume distribution is deduced from that Of precipitation. We enhance the GRADEX method by exploiting the work of Smith [1989], who developed a regional model for estimating the upper tail of a frequency distribution based on extreme order statistics. An example illustrates the proposed method.