bluuebunny/crossref_metadata_2025 huggingface dataset:
The impact of NSCAT winds on predicting the 1997/1998 El Niño: A case study with the Lamont‐Doherty Earth Observatory model
Authors: Chen Dake , Cane Mark A. , Zebiak Stephen E.
Published: September 2002

Using the NASA scatterometer (NSCAT) winds for initialization has greatly improved the Lamont‐Doherty Earth Observatory model forecasts of the 1997/1998 E1 Niño. The improvement is mostly attributed to the better resolved wind field in the southeast tropical Pacific. Because of the simplicity of the model and the short record of the NSCAT data, our model results should be taken as indicative rather than conclusive. Nevertheless, it is crucial to assimilate accurate information into the initial model state to predict the development of E1 Niño. Satellite‐derived wind products certainly have the potential to provide such information for real‐time forecasting.
Can interannual land surface signal be discerned in composite AVHRR data?
Authors: Cihlar J. , Chen J. M. , Li Z. , Huang F. , Latifovic R. , Dixon R.
Published: September 2002

The ability to make repeated measurements of the changing Earth's surface is the principal advantage of satellite remote sensing. To realize its potential, it is necessary that true surface changes be isolated in the satellite signal from other effects which also influence the signal. In this study, we explore the magnitude of such effects in composite NOAA advanced very high resolution radiometer (AVHRR) images with a pixel spacing of 1 km. A compositing procedure is frequently used in the preparation of data sets for land biosphere studies to minimize the effect of clouds. However, the composite images contain residual artifacts which make it difficult to compare measurements at various times. We have employed a 4‐year (1993–1996) AVHRR data set from NOAA 11 and 14 covering the Canadian landmass and corrected these data for the influence of the remaining clouds (full pixel or subpixel), atmospheric attenuation, and bidirectional reflectance. We have found that such corrections are essential for studies of interannual variations. The magnitude of the interannual signal varied with the AVHRR channel, land cover type, and satellite sensor but it was reduced by a factor of 2 to 8 between top of the atmosphere and the normalized surface reflectance. The remaining variations consisted of true interannual signal and the residual noise in the data (including sensor calibration) which was not removed by the correction process. Assuming that barren or sparsely vegetated land in northern Canada has not changed over the 4‐year period, the mean residual uncertainty in surface reflectance of the selected sites was 0.012 for AVHRR channel 1, 0.042 for channel 2, and 0.068 for the normalized difference vegetation index (NDVI). These values decreased to 0.011, 0.024 and 0.038, respectively, when excluding 1994 data because their atmospheric and bidirectional corrections were hampered by high solar zenith angles (mean values above 55° in all 1994 composite periods). The errors could be further reduced by more refined corrections for bidirectional and atmospheric effects. The impact of the uncertainty of channel 1 and 2 measurements is also significantly diminished by using ratio indices such as the NDVI. It is concluded that interannual variability exceeding 0.015–0.038 in NDVI (averaged over multiple pixels) can be detected for similar data sets and conditions, provided that sensor calibration does not introduce additional errors. Since such errors can be large for some conditions and applications, the importance of accurate sensor calibration cannot be overemphasized.
Influence of weather on the stable isotopic ratios of wines: Tools for weather/climate reconstruction?
Authors: Ingraham Neil L. , Caldwell Eric A.
Published: September 2002

Precipitation, local ground water, soil water, atmospheric water vapor, grape leaf and grape berry water just prior to harvest, and grape must during the wine‐making process, from the Napa Valley in northern California were collected for stable isotopic analysis. In addition, 27 red wines and 4 white wines produced in the Napa Valley, and 8 red wines produced in Livermore Valley located over 110 km to the southeast, were analyzed for both oxygen and hydrogen isotopic compositions. The isotopic compositions of the grape leaf water fall on a transpiration line with a slope of 2.1, while those of the grape berry water fall on a transpiration line with a slope of 2.8. The stable isotopic compositions of the 27 red wines from the Napa Valley range from −3 to +20‰ in δD and from +4.6 to + 10.2‰ in δ18O and plot along a line described by δD = 3.4 δ18O − 17.2. The maximum difference in the stable oxygen composition between two wineries 110 km apart is only 1.4‰, while the differences between the vintage years within each winery are 4.8 and 5.8‰ in δ18O. The stable isotopic composition of the grape water is controlled by transpiration in the weeks prior to harvest, overshadowing all other effects. As a result of the timing of harvest, the red wines are some 4 to 5‰ more enriched in δ18O than the white wines.
Performance characteristics of an automated gas chromatograph‐ion trap mass spectrometer system used for the 1995 Southern Oxidants Study field investigation in Nashville, Tennessee
Authors: Daughtrey E. Hunter , Adams Jeffrey R. , Oliver Karen D. , Kronmiller Keith G. , McClenny William A.
Published: September 2002

A trailer‐deployed automated gas chromatograph‐mass spectrometer (autoGC‐MS) system capable of making continuous hourly measurements was used to determine volatile organic compounds (VOCs) in ambient air at New Hendersonville, Tennessee, and Research Triangle Park, North Carolina, in 1995. The system configuration, including the autoGC‐MS, trailer and transfer line, siting, and sampling plan and schedule, is described. The autoGC‐MS system employs a pair of matched sorbent traps to allow simultaneous sampling and desorption. Desorption is followed by Stirling engine cryofocusing and subsequent GC separation and mass spectral identification and quantification. Quality control measurements described include evaluating precision and accuracy of replicate analyses of independently supplied audit and round‐robin canisters and determining the completeness of the data sets taken in Tennessee. Data quality objectives for precision (±10%) and accuracy (±20%) of 10‐ to 20‐ppbv audit canisters and a completeness of >75% data capture were met. Quality assurance measures used in reviewing the data set include retention time stability, calibration checks, frequency distribution checks, and checks of the mass spectra. Special procedures and tests were used to minimize sorbent trap artifacts, to verify the quality of a standard prepared in our laboratory, and to prove the integrity of the insulated, heated transfer line. A rigorous determination of total system blank concentration levels using humidified scientific air spiked with ozone allowed estimation of method detection limits, ranging from 0.01 to 1.0 ppb C, for most of the 100 target compounds, which were a composite list of the target compounds for the Photochemical Assessment Monitoring Station network, those for Environmental Protection Agency method TO‐14, and selected oxygenated VOCs.
A model of ball lightning as a magnetic knot with linked streamers
Authors: Rañada Antonio F. , Soler Mario , Trueba José L.
Published: September 2002

We develop a topological model of ball lightning which explains its stability by the coupling of an air ball to a magnetic knot, a magnetic field with linked magnetic lines. Assuming that currents flow inside the ball, along short‐circuited linked streamers following the lines of ∇ × B, the lifetime, energy, and radiated power of the average ball are correctly accounted for. The model explains why some witnesses do not feel heat, while others are burnt, and why filaments are seen to trail the ball in some cases.
An evaluation of upper troposphere NOx with two models
Authors: Penner Joyce E. , Bergmann Daniel J. , Walton John J. , Kinnison Douglas , Prather Michael J. , Rotman Douglas , Price Colin , Pickering Kenneth E. , Baughcum Steven L.
Published: September 2002

Upper tropospheric NOx controls, in part, the distribution of ozone in this greenhouse sensitive region of the atmosphere. Many factors control NOx in this region. As a result it is difficult to assess uncertainties in anthropogenic perturbations to NO from aircraft, for example, without understanding the role of the other major NOx sources in the upper troposphere. These include in situ sources (lightning, aircraft), convection from the surface (biomass burning, fossil fuels, soils), stratospheric intrusions, and photochemical recycling from HNO3. This work examines the separate contribution to upper tropospheric “primary” NOx from each source category and uses two different chemical transport models (CTMs) to represent a range of possible atmospheric transport. Because aircraft emissions are tied to particular pressure altitudes, it is important to understand whether those emissions are placed in the model stratosphere or troposphere and to assess whether the models can adequately differentiate stratospheric air from tropospheric air. We examine these issues by defining a point‐by‐point “tracer tropopause” in order to differentiate stratosphere from troposphere in terms of NOx perturbations. Both models predict similar zonal average peak enhancements of primary NOx due to aircraft (≈10–20 parts per trillion by volume (pptv) in both January and July); however, the placement of this peak is primarily in a region of large stratospheric influence in one model and centered near the level evaluated as the tracer tropopause in the second. Below the tracer tropopause, both models show negligible NOx derived directly from the stratospheric source. Also, they predict a typically low background of 1‐20 pptv NOx when tropospheric HNO3 is constrained to be 100 pptv of HNO3. The two models calculate large differences in the total background NOx (defined as the source of NOx from lightning + stratosphere + surface + HNO3) when using identical loss frequencies for NOx. This difference is primarily due to differing treatments of vertical transport. An improved diagnosis of this transport that is relevant to NOx requires either measurements of a surface‐based tracer with a substantially shorter lifetime than 222Rn or diagnosis and mapping of tracer correlations with different source signatures. Because of differences in transport by the two models we cannot constrain the source of NOx from lightning through comparison of average model concentrations with observations of NOx.
Influence of springtime weather systems on vertical ozone distributions over three North American sites
Authors: Cooper O. R. , Moody J. L. , Davenport J. C. , Oltmans S. J. , Johnson B. J. , Chen X. , Shepson P. B. , Merrill J. T.
Published: September 2002

The Atmosphere/Ocean Chemistry Experiment (AEROCE) '96 Springtime Intensive was designed to quantify major atmospheric chemical species transported from the United States east coast to the North Atlantic Ocean. During the study ozonesondes were launched almost every day between March 22 and May 3, 1996, from Charlottesville, Virginia; Purdue University, Indiana; and Bermuda. Whenever possible, the Charlottesville sondes were timed to fly behind passing cold fronts into midtropospheric to upper tropospheric bands of dry air. The dry air was hypothesized to contain ozone of stratospheric origin and was detected with color‐enhanced satellite water vapor imagery. Soundings were placed in three categories: sondes launched ahead of an approaching cold front, sondes launched behind a passing cold front, and sondes launched into cutoff lows. This stratification explained much of the vertical ozone variation at each site. Tropospheric mean ozone increased with height at all three sites under postfrontal conditions, with relatively little increase with height under prefrontal conditions. Backward trajectories from Charlottesville indicated that the postfrontal air masses originated at high elevations to the northwest, while prefrontal air masses came from relatively lower elevations to the southwest. Transport also explained the lower tropospheric ozone differences between Charlottesville and Bermuda. The enhanced ozone observed in the upper troposphere over Charlottesville compared with the other sites may be linked to upwind conditions more favorable for tropopause folding. However, we believe that selective launching based on the operational use of satellite water vapor imagery allowed us to sample the full range of tropospheric ozone over Charlottesville.
Electrostatic charging processes of balloon and gondola surfaces in the Earth atmosphere
Authors: Grard Réjean
Published: September 2002

Electrostatic charging of balloons and gondolas is frequently observed, especially during ascents in the atmosphere. Charge buildup modifies the potential distribution of the environment and perturbs the measurements of quasi‐static fields with electric antennas and of atmospheric conductivity with Langmuir probes and relaxation probes. The magnitude of the surface charging is a function of altitude, vertical velocity, body size, and geometry; the polarity of the potential may differ during ascent and descent. An explanation is proposed for the mechanisms responsible for this complex phenomenon, where aerosol, turbulence, loss of negative ions, and downward fair weather electric field play critical roles. This model is supported by experimental results collected during balloon flights dedicated to the investigation of atmospheric electricity. The possible consequences for the measurements to be performed during the descent of the Huygens Probe in the atmosphere of Titan are briefly discussed.
Regional climate model simulation of precipitation in central Asia: Mean and interannual variability
Authors: Small Eric E. , Giorgi Filippo , Sloan Lisa Cirbus
Published: September 2002

We examine how well the National Center for Atmospheric Research (NCAR) regional climate model (RegCM2) simulates the mean and interannual variability of precipitation in a semiarid region to more fully establish the strengths and weaknesses of the model as a tool for studying regional scale climate processes. We compare precipitation observations with RegCM2 output from a 5.5 year long simulation of the climate of central Asia, driven by the European Centre for Medium‐Range Weather Forecasts analyses. RegCM2 simulates well the spatial patterns and annual cycles of precipitation observed in climatically different subregions. The magnitude of simulated precipitation is similar to observations except over the driest part of Central Asia where the simulated precipitation is too high. We calculate precipitation anomalies for each month as the difference between the monthly total and the 5 year average for that month, from both observations and RegCM2 output. The magnitude of simulated interannual variability is similar to observations, although there are differences. RegCM2 tends to underpredict (overpredict) the magnitude of variability in the same combinations of subregion and season for which it underpredicts (overpredicts) mean precipitation. RegCM2 closely reproduces precipitation anomalies observed in specific months, except during summer and during winter in the mountains. There is no correlation between model biases in mean precipitation and how well the model reproduces a series of precipitation anomalies. This suggests that the processes controlling the mean and the variability of precipitation differ. Therefore evaluating the ability of a regional climate model to simulate both quantities is a demanding test of model performance.
Short‐lived alkyl iodides and bromides at Mace Head, Ireland: Links to biogenic sources and halogen oxide production
Authors: Carpenter L. J. , Sturges W. T. , Penkett S. A. , Liss P. S. , Alicke B. , Hebestreit K. , Platt U.
Published: September 2002

Automated in situ gas chromatograph/mass spectrometer (GC/MS) measurements of a range of predominantly biogenic alkyl halides in air, including CHBr3, CHBr2Cl, CH3Br, C2H5Br, CH3I, C2H5I, CH2ICl, CH2I2, and the hitherto unreported CH2IBr were made at Mace Head during a 3‐week period in May 1997. C3H7I and CH3CHICH3 were monitored but not detected. Positive correlations were observed between the polyhalomethane pairs CHBr3/CHBr2Cl and CHBr3/CH2IBr and between the monohalomethane pair CH3I/C2H5I, which are interpreted in terms of common or linked marine sources. During periods when air masses were affected by emissions from local seaweed beds, the concentrations of CHBr3, CH2ICl, and CH2IBr not only showed remarkable correlation but also maximized at low water. These are the first field observations to provide evidence for a link between the tidal cycle, polyhalomethanes in air, and potential marine production. The calculated total flux of iodine atoms into the boundary layer at Mace Head from organic gaseous precursors was dominated by photolytic destruction of CH2I2. Photolysis of CH3I contributed less than 3%. The calculated peak flux of iodine atoms during the campaign coincided with the highest measured levels of iodine oxide radicals, as determined using Differential Optical Absorption Spectrometry (DOAS).
Evidence for periodic modulation of Jupiter's decametric radio emission
Authors: Wilkinson Malcolm H.
Published: September 2002

A plausible explanation for the strong correlation between the occurrence of Jupiter's sporadic decametric radio emission and the orbital position of Io is that the emission is either generated in discrete radio sources located along the instantaneous magnetic flux tube connecting Io with Jupiter or in multiple discrete radio sources associated with other flux tubes excited by ionospheric Alfvén wave reflections downstream from Io. On the assumption that a periodic increase in the probability of receiving radio emission should be observable as the directional emission beams from these multiple discrete radio sources are swept past the observer by Io's orbital motion, a search has been made for periodic modulation of the Jupiter radio emission using a statistical analysis of the data from a total of 34 Io‐B radio noise storms recorded at a wave frequency of 20 MHz during the 1984 and 1996 apparitions of Jupiter. This analysis shows that a weak periodic modulation of the radio emission with a repetition interval near 15 min is present in this source. Assuming that this modulation results from the action of multiple sweeping radio beams, calculations using the O4 model of Jupiter's magnetic field and recently measured emission cone half‐angles give an angular separation between successive Alfvén wave reflections in the Io plasma torus of 7.8±1° (or possibly half this value, depending on assumptions). This estimate is in approximate agreement with theoretical predictions.
Secular and local time dependence of Jovian X ray emissions
Authors: Gladstone G. Randall , Waite J. Hunter , Lewis William S.
Published: September 2002

Jovian soft X rays are believed to be line emissions from energetic oxygen and sulfur ions generated through charge exchange and stripping reactions when the ions enter Jupiter's upper atmosphere. The X rays are brightest in the polar regions (generally about twice as bright in the north as in the south) but also have a large component from low latitudes. Observations of Jupiter's X ray emissions at several epochs by the high‐resolution imager (HRI) instrument on the ROSAT satellite show a general decrease in overall brightness by ∼50% from 1994 to 1996 and reveal an interesting dependence of brightness on local time. The emissions are not of uniform brightness across the disk but are strongly weighted toward one limb of the planet. The X ray limb can be on either the duskside or dawnside of Jupiter, and so far it correlates with position of the subsolar point relative to the sub‐Earth point (i.e., the X ray limb is the bright visible limb). Except during the Shoemaker‐Levy 9 impacts, the total X ray emissions are not strongly correlated with System III central meridian longitude. However, a composite map of the emissions shows that they are generally located in regions of low surface magnetic field strength at low latitudes, and in regions of large horizontal surface magnetic field strength gradients at high latitudes.
Detailed study of FUV Jovian auroral features with the post‐COSTAR HST faint object camera
Authors: Prangé Renée , Rego Daniel , Pallier Laurent , Connerney J. E. P. , Zarka Philippe , Queinnec Julien
Published: September 2002

A set of Hubble Space Telescope faint object camera images taken in the H2 bands near 1550 Å is used to infer the morphological properties of the steady state Jovian FUV aurorae. We focus on issues best addressed using the excellent spatial resolution available after correction of the spherical aberration, i.e., those related to high latitude or small auroral features. A thorough comparison of the emission loci with model ovals highlights the improvement of the VIP4 magnetic field model over previous ones at all latitudes. The north‐south conjugacy of the main oval is now correctly accounted for, and second‐order discrepancies suggest non axially symmetric contributions of external origin. This oval is usually amazingly narrow (down to 80±50 km) and very bright, although quite variable with time (100 kR to 1–2 MR, i.e., peak input flux of ∼10–200 ergs cm−2 s−1). We discuss its structure, in latitude and longitude, and show that it is consistent with precipitation by pitch angle scattering. Fainter concentric narrow ovals are also present on the north polar cap, presumably at the footprint of open field lines. Both polar caps are partly covered by a faint diffuse emission, confined to the afternoon sector in magnetic local time. A bright extended feature, previously identified across the north polar cap along the 160° meridian, might be not a specific auroral feature but rather a region where inner arcs and diffuse polar cap emissions are intensified, maybe by a solar wind driven ionospheric process. Equatorward of the main oval, we identify a belt of moderate emission, attributed to a precipitation process distributed between the Io torus and the distant magnetosphere. Longitudinally confined bright areas lie in the same latitude range and consist of series of short segments of concentric arcs. We also present the discovery of a narrow faint oval at the footprint of Io's orbit. Finally, we confirm that the FUV footprints of the Io flux tube are very small (a few hundreds of kilometers or less), implying an interaction close to Io. The input energy flux in this spots is huge and variable (0.8–5 × 1011W).
The Mars Pathfinder landing site and the Viking control point network
Authors: Zeitler Wolfgang , Oberst Jürgen
Published: September 2002

We recomputed the Viking Mars control point network and derived Mars‐fixed three‐dimensional coordinates of 3739 selected, globally distributed landmarks. Mars Pathfinder and Viking Lander 1 coordinates as well as data from reanalyzed spacecraft occultation measurements are used as fixed control information in the analysis. The network benefits greatly from recently restored Viking orbiter trajectory data and new planet rotational parameters derived from Pathfinder lander tracking. In our attempt to predict the coordinates of the Viking Lander 1 site from given Pathfinder coordinates, we find an offset of ≈4–5 km of this lander location with respect to the previously reported data. We suggest that this probably is explained by erroneous identification of this landing site in the images. Ninety percent of our landmark coordinates have positional errors of less than 1800 m. This network thus removes previously noted severe offsets between Mars‐fixed coordinates and cartographic products.
Hubble Space Telescope observations of the Martian aphelion cloud belt prior to the Pathfinder mission: Seasonal and interannual variations
Authors: Wolff Michael J. , Bell James F. , James Philip B. , Clancy R. Todd , Lee Steven W.
Published: September 2002

The presence of a globally extant equatorial belt of water ice clouds on Mars is quantitatively investigated using data from three seasons of our Hubble Space Telescope synoptic monitoring program (1993–1997). A subset of the 1996–1997 images covers the landing site of the Mars Pathfinder including a set of images taken after touchdown. Using multicolor imaging from the Wide Field Planetary Camera and the Wide Field Planetary Camera 2, we characterize both water ice cloud and dust optical depths as a function of latitude at several local times for each observing epoch. The analysis technique models calibrated data using a multiple scattering radiative transfer code. Our results support the initial results of Clancy et al. [1996a] regarding changes between the aphelion and perihelion climate of Mars and provide a more detailed look at the development and decay of the cloud belt. Comparing our dust optical depths to those of the Viking landers for the same seasons, we note a trend toward lower dust loading in late northern winter and in spring. Our observations of the Pathfinder site in July 1997 reveal a dust opacity in good agreement with that reported by Pathfinder [Smith et al., 1997b]. In addition, the serendipitous occurrence of a dust storm in Valles Marineris in late June 1997 allows us to derive a set of dust single scattering albedos for use in more accurately modeling the dust's radiative properties and effects.
Evidence for Martian electrostatic charging and abrasive wheel wear from the Wheel Abrasion Experiment on the Pathfinder Sojourner rover
Authors: Ferguson Dale C. , Kolecki Joseph C. , Siebert Mark W. , Wilt David M. , Matijevic Jacob R.
Published: September 2002

The Wheel Abrasion Experiment (WAE) on the Mars Pathfinder rover was designed to find out how abrasive the Martian dust would be on strips of pure metals attached to one of the wheels. A specially modified wheel, with 15 thin film samples (five each of three different metals), specularly reflected sunlight to a photovoltaic sensor. When the wheel was rotated to present the different sample surfaces to the sensor, the resulting signal was interpreted in terms of dust adhesion and abrasive wear. Many data sequences were obtained. Ground tests of similar wheels in a simulated Martian environment showed that static charging levels of 100–300 V could be expected. To prevent the possibility of Paschen discharge in the low‐pressure Martian atmosphere, charge dissipation points were added to the Sojourner rover and were shown in ground tests to keep charging levels at 80 V or less. Nevertheless, significant dust accumulations on Sojourner's wheels may be interpreted as evidence for electrostatic charging. Simple considerations of the expected maximum level of charging and electrostatic dust adhesion lead to an estimate for the size of the adhering dust grains. From the WAE data, it is hypothesized that the photoelectric effect is the most important mechanism for slow discharge in Martian daylight. Sensor signals obtained late in the Pathfinder mission show that significant wheel wear was seen on the metal wheel strips, with the most wear on the thinnest aluminum samples and the least on the thickest nickel and platinum samples. An estimate is made of the reflectance of the adhering Martian dust. The depth of dig of the WAE wheel shows that the dust is in some places very loose and in others tightly packed. Finally, comparison of the WAE results with ground test results makes possible a comparison of the Martian soil with mineral grain types and sizes found on Earth and show that the Martian dust is fine‐grained and of limited hardness.
Ionospheric storm forecast for high‐frequency communications
Authors: Hu S. , Bhattacharjee A. , Hou J. , Sun B. , Roesler D. , Frierdich S. , Gibbs N. , Whited J.
Published: September 2002

An improved physical model for ionospheric storm propagation is presented. The model uses the Dst index to monitor storm commencement. It also employs a latitude‐ and storm‐strength‐dependent propagation speed for the pressure disturbance that propagates from the auroral source region, where energy is deposited at storm commencement, to lower latitudes. The new storm forecast code is embedded in PropMan, an ionospheric program developed at Rockwell Avionics and Communications. The predictions of the new code for maximum usable frequencies during storms are compared with radio sounding data. Improvements are reported in the capability of PropMan to predict maximum usable frequencies in the 24 hours following a storm.
Accretion of a rifted passive margin: The Late Paleozoic Rhenohercynian fold and thrust belt (Middle European Variscides)
Authors: Oncken O. , von Winterfeld C. , Dittmar U.
Published: September 2002

In the western Rhenish Massif, the Rhenohercynian fold and thrust belt of the Middle European Varsicides exposes a telescoped complete Devonian to Early Carboniferous passive margin. This permits the analysis of geometry and kinematic processes of passive margin accretion to an erogenic wedge. During Variscan collision (330–300 Ma), the sedimentary cover of the passive margin was shortened by some 50% or 180 km. Crustal scale balancing and restoration reveals a wide, symmetric rift with a central graben. A marginal plateau separated this failed Lower Devonian rift from an Emsian‐Middle Devonian oceanic basin in the south, remnants of which are preserved in the southernmost imbricates and the Giessen‐Harz nappes. The seismically well‐imaged Aachen‐Midi detachment (Faille du Midi) acted as the basal decollement of this thin‐ to thick‐skinned orogenic wedge. It shows a ramp and flat geometry from the blind tip down to middle crustal levels. Owing to its position below the base of the basin fill, the thick synrift sequence and structure controlled structural evolution during contraction by localizing thrust branch lines and by inversion of rift structures, synthetic to the subduction direction, with formation of basement footwall shortcuts. Moreover, the three‐dimensional detachment geometry shows large‐scale oblique ramp‐flat features which control the architecture of the belt and the distribution of metamorphic grade. Rocks and fabrics from the detachment show that the latter was located at the transition into the ductile field at the fossil 300°–400°C isotherm. In the restored section, the detachment trajectory displays a saucershaped geometry rising to the surface at the rear and at the front. This suggests that the basal detachment propagated into the passive margin by ductile failure during lithospheric flexure under the load of an advancing upper plate. The regional pattern of synkinematic metamorphic grade shows varying modes of margin accretion: basal underplating into the orogenic wedge by the shelf slope and marginal plateau with formation of duplex stacks and elongate thrust sheets and frontal accretion of the remaining thicker failed rift in the north into the propagating wedge with formation of several imbricate fans. Cyclical changes in accretion history and/or critical taper are suggested by spaced domains of out‐of‐sequence thickening. These are also related to internal domainal kinematic partitioning of the wedge, controlled by oblique collision.
Microwave remote sensing of temporal variations of brightness temperature and near‐surface soil water content during a watershed‐scale field experiment, and its application to the estimation of soil physical properties
Authors: Mattikalli Nandish M. , Engman Edwin T. , Jackson Thomas J. , Ahuja Laj R.
Published: September 2002

Passive microwave airborne remote sensing was employed to collect daily brightness temperature (TB) and near‐surface (0–5 cm depth) soil water content (referred to as “soil water content”) data during June 10–18, 1992, in the Little Washita watershed, Oklahoma. A comparison of multitemporal data with the soils data revealed a direct correlation between changes in TB and soil water content, and soil texture. Regression relationships were developed for the ratio of percent sand to percent clay (RSC) and effective saturated hydraulic conductivity (Ksat) in terms of TB and soil water content change. Validation of results indicated that both RSC and Ksat can be estimated with adequate accuracy. The relationships are valid for the region with small variation of soil organic matter content, soils with fewer macropores, and limiting experimental conditions. However, the findings have potential to employ microwave remote sensing for obtaining quick estimates of soil properties over large areas.
A numerical three‐dimensional conditioned/unconditioned stochastic facies type model applied to a remediation well system
Authors: Rauber Martin , Stauffer Fritz , Huggenberger Peter , Dracos Themistocles
Published: September 2002

In this study a three‐dimensional stochastic facies‐based aquifer model was developed. The model can be used to numerically simulate flow and solute transport in heterogeneous groundwater aquifers. The stochastic generation process can be conditioned by using available facies information in one vertical plane or two orthogonal vertical ones. In this study the information was obtained from a facies interpretation of a vertical georadar profile in a natural gravel formation in Switzerland. In the domain outside the known profile, unconditioned lenses and layers were generated at random according to statistical information on coherent sedimentary structures based on observations in adjacent gravel pits [Jussel et al., 1994a]. The method was applied to a single extraction well designed to capture an initially block‐shaped contaminant plume. A total of 80 conditioned and unconditioned synthetic aquifers was generated. The flow and transport simulations were performed using a finite element flow model and a random walk transport model. The results are presented as the ensemble of integral solute mass recovery curves of single realizations. One would expect conditioning to reduce the bandwidth of the recovery curves representing the uncertainty, but the results show that the bandwidth even increased. This effect was attributed to a discrepancy in the mean volumetric fraction of the different facies types in the conditioned and the unconditioned cases. Moreover, a simulation using a homogeneous model with constant equivalent flow and transport parameters overestimated the remediation efficiency. The influence of a linear, reversible equilibrium sorption on the remediation well efficiency was taken into account by an uncorrelated random field of the retardation factor based on values from the literature. However, the impact of the variability in hydraulic conductivity clearly exceeded the effect of the variability in the retardation factor.
Response of the Ha! Ha! River to the flood of July 1996 in the Saguenay region of Quebec: Large‐scale avulsion in a glaciated valley
Authors: Lapointe M. F. , Secretan Y. , Driscoll S. N. , Bergeron N. , Leclerc M.
Published: September 2002

Modifications to valley form due to extreme flooding in the lower 34 km of the Ha! Ha! River were analyzed. Heavy regional precipitation in July 1996 triggered extreme runoff and the catastrophic drainage of Ha! Ha! Lake, producing discharges of 1100 m3/s, 8 times the 100‐year flood. Dominant valley modifications, revealed by comparing preflood and postflood topographies derived photogrammetrically, were related to two large‐scale avulsions; in particular, a deep retrogressive incision which bypassed the 30‐m‐high Perron Falls, exporting 6 × 106 m3 of glacial stratified drift from a 2‐km section of valley and producing massive sedimentation in the reach downstream. Reconstructed maximum flow power values support the existence of a 300 W/m2 threshold for major scouring of the alluvial valley bottom. The evidence highlights the potential for massive scour and fill and reorganization of the long profile, with potentially catastrophic effects on infrastructure, during extreme floods in glaciated valley settings.
Stochastic determination of well capture zones
Authors: van Leeuwen Matthijs , te Stroet Chris B. M. , Butler Adrian P. , Tompkins Jacob A.
Published: September 2002

A stochastic approach is adopted for characterizing the uncertainty in well capture zones in heterogeneous formations. Transmissivity is modeled as a random space function and a Monte Carlo approach is used to infer the probability distribution of the resulting stochastic capture zones. Through several numerical experiments, the influence of the statistical parameters of transmissivity variation on the extent of uncertainty in the location of the capture zone is investigated. Two aquifer models are considered: a fully confined aquifer and a leaky‐confined aquifer receiving recharge from above. A connection is made with previous work on transport theory, and the statistical parameters of the capture zone probability distribution are compared with those of a solute concentration plume.
A hybrid global optimization method for inverse estimation of hydraulic parameters: Annealing‐Simplex Method
Authors: Pan Lehua , Wu Laosheng
Published: September 2002

Inverse estimation of unsaturated hydraulic parameters is often a highly nonlinear optimization problem with multiple parameters. The objective functions involved are often topographically complex and may contain many local minima. Because of these reasons, the inverse solutions are commonly very sensitive to the initial guess of the parameters when conventional optimizers are used. This paper presents an annealing‐simplex method that incorporates simulated annealing strategies into a classical downhill simplex method. An upward infiltration experiment was used as an example of inverse estimation to test the method. Numerical experiments of both minimizing an algebraic function and inversion of upward infiltration data showed that the new method successfully converged to the global minimum in all cases, irrespective of the initial hydraulic parameter estimates, while the classical downhill method often converged to unfavorable local minima. The CPU times needed for the annealing‐simplex method to estimate 5 and 7 hydraulic parameters simultaneously are about a half hour and 1 hour on a PC, respectively. Additionally, no special requirements are imposed on the objective function, and the method is independent of the details of the simulation submodel. Therefore the proposed method should be applicable to other optimization problems in water resources when it is important to have a robust global search capability.
Concentration fluctuations in transport by groundwater: Comparison between theory and field experiments
Authors: Fiori Aldo , Dagan Gedeon
Published: September 2002

In a recent work [Dagan and Fion, 1997] we developed a Lagrangian theoretical framework to compute the concentration variance in transport of a conservative solute in a heterogeneous formation of random stationary structure. This variance, a measure of concentration fluctuations in the plume, depends on the spreading effect of advection and on the mixing effect of pore‐scale dispersion. Comparison between theory and the numerical simulations of Graham and McLaughlin [1989] showed very good agreement. Here we compare the same theoretical formulae with the field measurements at Borden Site and Cape Cod. We rely on the analysis of these experiments carried out by Fitts [1996], who characterized the concentration fluctuations by a global measure. The latter is the standard deviation of the logarithm of the ratio between measured and modeled concentrations over the entire plume and at different times. The theoretical relationships require computing the two particles trajectories' covariances. We simplify the computations considerably by taking advantage of the anisotropy of the heterogeneous structures of the two aquifers. Thus the major effect of advection is in the shearing of the plume in the longitudinal direction, whereas pore‐scale dispersion acts mainly through its transverse effect in the vertical direction. We found a good agreement between theory and experiments by using parameter values determined independently in the past, provided that the values of transverse pore‐scale dispersivities were 0.5 mm for Cape Cod and 0.44 mm for Borden Site. These values are somewhat smaller than the vertical macrodispersivities inferred from measurements.
AWIPS in place
Authors: Showstack Randy
Published: September 2002

After a decade‐long effort, the U.S. Commerce Department announced on July 28 that it has completed installing high‐tech, interactive weather computer and communications system units at 152 National Oceanic and Atmospheric Administration (NOAA) sites across the country.

The Advanced Weather Interactive Processing System (AWIPS) significantly improves weather and flood‐related services of the National Weather Service (NWS), according to NOAA, a division of the Commerce Department that includes NWS.
AGU Candidates for Office, 2000–2002
Authors: Anonymous
Published: September 2002

Robert E. Dickinson. AGU member since 1960, Regents Professor, University of Arizona. Joint appointments at the University of Arizona in Department of Atmospheric Sciences, Institute of Atmospheric Physics, Department of Hydrology and Water Resources, and Tree Ring Laboratory Major areas of interest are global change, climate modeling, remote sensing, tropical deforestation, drought, and the interaction of terrestrial and atmospheric hydrological processes. B.A., 1961, chemistry and physics, Harvard University; M.S., 1962, Ph.D., 1966, meteorology, Massachusetts Institute of Technology. Professor, University of Arizona since 1990, National Center for Atmospheric Research. Member, National Academy of Science; Fellow, AGU; Fellow, American Meteorological Society. Authored 167 refereed publications, 36 in AGU journals, as well as 22 book chapters and one book. Recipient of the Rossby Award (AMS), 1996; Roger Revelle Medal, 1996; Vetlesen Medal, 1995. AGU service as President, Atmospheric Sciences Section, 1988–1992; Committee on Earth as a System, 1987–1989; William Bowie Medal Committee, 1996–1998; Roger Revelle Medal Committee, 1998–2000.
UN head calls for “culture of prevention” in addressing natural disasters
Authors: Showstack Randy
Published: September 2002

Citing war and natural disasters as “the major threats to the security of individuals and human communities worldwide,” United Nations Secretary General Kofi Annan, in his September 9 annual report on the UN, urged nations to focus on preventing these threats instead of simply reacting after the fact with relief.

With hurricanes, cyclones, floods, and fires wreaking havoc last year, the United Nations head called 1998 the worst year on record for weather‐related natural disasters, which killed tens of thousands of people and displaced millions more. Earthquakes in Afghanistan, Turkey, and elsewhere, he said, added to the destructive toll from natural disasters.
Effects of changing immunosuppressive regimen on the incidence, duration, and viral load of cytomegalovirus infection in renal transplantation: a single center report
Authors: De Maar E.F. , Verschuuren E.A.M. , Homan vd Heide J.J. , Kas‐Deelen D.M. , Jagernath D. , The T.H. , Ploeg R.J. , Van Son W.J. , De Maar E.F. , Verschuuren E.A.M. , Homan vd Heide J.J. , Kas‐Deelen D.M. , Jagernath D. , The T.H. , Ploeg R.J. , Van Son W.J.
Published: September 2002

Abstract: Background. In this retrospective single center study we have evaluated the relation between the immunosuppressive regimen and the incidence and characteristics of cytomegalovirus (CMV) infection in the setting without CMV prophylaxis from 1989 through 1998. Methods. All (470) first cadaveric renal transplantations in nonsensitized (PRA < 60%) patients were analyzed. Immunosuppression consisted of cyclosporine A (Sandimmune) and prednisolone from 1989 through 2‐1993 (S; 189 patients), of cyclosporine microemulsion (Neoral) and prednisolone from 3‐1993 through 5‐1997 (N; 200 patients) and of mycophenolate mofetil, Neoral and prednisolone from 5‐1997 until 1998 (M; 81 patients). The CMV pp65‐antigenemia was measured routinely at least once weekly from day 10 till 12 weeks after transplantation or until pp65‐antigenemia became negative. No CMV‐prophylaxis was given. Results. By changing from Sandimmune to Neoral and by adding mycophenolate mofetil, respectively, we observed a higher frequency of especially secondary CMV infections (S vs. N vs. M, respectively, 28 vs. 50 vs. 63%, P = 0.026; S vs. N, P = 0.027; S vs. M, P = 0.015; and N vs. M, n.s). The CMV infections lasted longer (median duration antigenemia S vs. N vs. M, respectively, 3 vs. 5 vs. 7 weeks, P = 0.0003; S vs. N, P < 0.002; S vs. M, P < 0.001; and N vs. M, P < 0.05). Viral load was higher in M (median maximal pp65‐antigenemia S vs. N vs. M, respectively, 19 vs. 14.5 vs. 73, P < 0.01; S vs. N, n.s.; S vs. M, P < 0.001 and N vs. M, P < 0.01). Conclusions. The use of Neoral and the addition of mycophenolate mofetil caused significant changes in the incidence, duration and viral load of CMV infections.
Antiviral prophylaxis may prevent human herpesvirus‐6 reactivation in bone marrow transplant recipients
Authors: Rapaport D. , Engelhard D. , Tagger G. , Or R. , Frenkel N.
Published: September 2002

Abstract: Human herpesvirus‐6 (HHV‐6) infects the majority of children under the age of 2 years causing roseola infantum. Following short self‐limited disease, the virus enters into a latency phase in peripheral blood lymphocytes (PBL). It has been previously reported that HHV‐6 reactivation from latency, in immunocompromised patients undergoing bone marrow transplantation (BMT), could result in febrile illness, pneumonitis, meningitis, and/or encephalitis. In our study, 14 BMT patients received two different antiviral prophylactic therapies: 8 patients received acyclovir, whereas 6 patients received ganciclovir. Clinical manifestations and virus recovery were monitored pre‐ and post‐BMT by polymerase chain reaction tests of cord blood cells cultured with the patients' PBL. No HHV‐6 recovery was shown in the 6 patients treated with ganciclovir, whereas 3 of the 8 acyclovir‐treated patients experienced virus reactivation 20–21 days post‐BMT. One of the 3 patients was asymptomatic but had late engraftment; the second patient had prolonged fever, skin rash, and hemorrhage; the third patient experienced prolonged fever, pneumonitis, marrow rejection, and fatal encephalitis. It is concluded that viral reactivation may be prevented by prophylactic treatment with ganciclovir. Our observation awaits further documentation in prospective randomized trials in high‐risk BMT recipients.