bluuebunny/crossref_metadata_2025 huggingface dataset:
Future changes in the distribution of daily precipitation totals across North America
Authors: Wilby R. L. , Wigley T. M. L.
Published: October 2002

Shape and scale parameters of the two‐parameter gamma distribution were estimated for daily distributions of precipitation at individual grid‐points in two General Circulation Models (HadCM2 and CSM). Maps of changing parameter distributions under anthropogenic forcing show the extent to which future precipitation scenarios for North America are consistent with observed trends in the 20th century. The scale parameter is found to be more variable, both spatially and temporally, than the shape parameter. Patterns of changes in mean wet‐day amounts are strongly correlated with changes in the scale parameter. While the two models show quite different results for the spatial patterns of change, both indicate that the proportion of total precipitation derived from extreme and heavy events will continue to increase relative to moderate and light precipitation events.
Comparison of O+ density from ARGOS LORAAS data analysis and SAMI2 model results
Authors: Huba J. D. , Dymond K. F. , Joyce G. , Budzien S. A. , Thonnard S. E. , Fedder J. A. , McCoy R. P.
Published: October 2002

We report the first results comparing the ionospheric O+ density obtained from the Low Resolution Airglow and Aurora Spectroscopy (LORAAS) experiment aboard the Advanced Research and Global Observation Satellite (ARGOS) with computational modeling results from the NRL ionosphere code “Sami2 is Another Model of the Ionosphere” (SAMI2). We also compare the electron density obtained from SAMI2 with the International Reference Ionosphere (IRI). The O+ density comparison between the LORAAS data analysis and the SAMI2 results is very good considering that the modeled results near the geomagnetic equator are sensitive to the electric field and neutral wind models. For example, we find better agreement with the data using a simple sinusoidal model of the E × B drift instead of the empirical Fejer/Scherliess drift model Scherliess and Fejer [1999]. It is expected that better agreement between data and modeled results will be achieved using more accurate electric field and neutral wind input data. This suggests that the ARGOS data set will be an important test bed to assess the physical processes needed in a comprehensive model of the low‐ to mid‐latitude ionosphere. The comparison of the LORAAS data with the IRI model is also reasonably good, but some details of the ionosphere's morphology is better described by SAMI2.
The initiation of orogenic margin reverse faulting
Authors: Bailey R. C.
Published: October 2002

Laboratory values of rock friction coefficients suggest that reverse faulting should be very difficult to initiate by simple horizontal compression of the crust. Values of stresses required by Andersonian faulting may be an order of magnitude higher than those actually present in orogenic margins. A simple stress balance calculation shows that the effect of the excess lithostatic pressure under an elevated orogen, if transmitted laterally through a crustal ductile layer to the orogenic margin, is to provide sufficient hydraulic lift under the orogen flanks to initiate reverse faulting by direct lift, even with rock friction coefficients of order 0.8. The required orogenic elevation above surrounding “normal” lithosphere is about one fifth of the thickness of the brittle crust of the orogen. This elevation may be as small as 2 km in tectonically active regions. The mechanism works even in the absence of regional lithospheric compressive stresses.
Wind initiation thresholds of the moistened sands
Authors: Dong Zhibao , Liu Xiaoping , Wang Xunming
Published: October 2002

The widely accepted Bagnold‐type function for calculating threshold wind velocity or shear velocity was developed for dry sands, but surface moisture is an extremely important variable controlling the entrainment process of sands by wind because the tensile force between the water molecules and sand grains produces cohesion. Here we report detailed wind tunnel experimental results on the threshold shear velocity of moistened sand of different sizes. The results show that relative threshold shear velocity, which is the ratio of threshold shear velocity of sand in the moistened state to that in the dry state, is better related to moisture content than threshold shear velocity itself. Function, modified after the Bagnold equation has been developed to estimate the threshold shear velocities of moistened sands. For a given grain size, the threshold shear velocity is proportional to (1 + KM)1/2, where, M is the moisture content, and K is a coefficient depending on grain size.
Realtime data filtering models for air temperature measurements
Authors: Hubbard K. G. , Lin X.
Published: October 2002

Air temperature measurement biases caused by solar radiation and ambient wind speed are well‐known. However, realtime air temperature filtering models are essential for generating homogeneous climate data by transforming one air temperature measurement system into another, and correcting in‐situ air temperature biases especially for non‐aspirated radiation shield systems. This study investigated the air temperature biases caused in the commonly used radiation shields in the United States, including the ASOS, MMTS, Gill, CRS, ASP‐ES, and NON‐ASP‐ES shields along with corresponding temperature sensors. The realtime air temperature filtering models developed for each air temperature system are capable of removing the solar radiation and ambient wind speed effects on air temperature measurements taken over comparable vegetation surfaces at any weather station or experimental site.
Validation of MODIS aerosol retrieval over ocean
Authors: Remer L. A. , Tanré D. , Kaufman Y. J. , Ichoku C. , Mattoo S. , Levy R. , Chu D. A. , Holben B. , Dubovik O. , Smirnov A. , Martins J. V. , Li R.‐R. , Ahmad Z.
Published: October 2002

The MODerate resolution Imaging Spectroradiometer (MODIS) algorithm for determining aerosol characteristics over ocean is performing within expected accuracy. A two‐month data set of MODIS retrievals co‐located with observations from the AErosol RObotic NETwork (AERONET) ground‐based sunphotometer network provides the necessary validation. Spectral radiation measured by MODIS (in the range 550–2100 nm) is used to retrieve the aerosol optical thickness, effective particle radius and ratio between the submicron and micron size particles. MODIS‐retrieved aerosol optical thickness at 660 nm and 870 nm fall within the expected uncertainty, with the ensemble average at 660 nm differing by only 2% from the AERONET observations and having virtually no offset. Roughly seventy percent of MODIS retrievals of aerosol effective radius for optical thickness greater than 0.15 agree with AERONET retrievals to within ±0.10 μm.
Validation of MODIS aerosol optical depth retrieval over land
Authors: Chu D. A. , Kaufman Y. J. , Ichoku C. , Remer L. A. , Tanré D. , Holben B. N
Published: October 2002

Aerosol optical depths (τa) are derived operationally for the first time from the MODIS (Moderate Resolution Imaging Spectroradiometer) measurements over vegetated and partially vegetated land at 0.47 and 0.66 μm wavelengths. The extensive validation made during July – September 2000 encompasses 315 co‐located τa in space and time derived by MODIS and AERONET (Aerosol Robotic Network) from more than 30 AERONET sites. The lack of AERONET measurements in East Asia, India and Australia makes this validation unavailable for those regions. The MODIS aerosol retrievals, except in coastal zones, are found within the retrieval errors of Δτa = ±0.05 ±0.2 τa. The root mean square (RMS) errors are ≤ 0.1 in the continental inland regions and up to 0.3 in the coastal regions (attributed mainly to water contaminated signals). With this validation we believe that MODIS aerosol products can be used quantitatively in many applications with caution for possible residual clouds, snow/ice, and water contamination.
A spatio‐temporal approach for global validation and analysis of MODIS aerosol products
Authors: Ichoku Charles , Chu D. Allen , Mattoo Shana , Kaufman Yoram J. , Remer Lorraine A. , Tanré Didier , Slutsker Ilya , Holben Brent N.
Published: October 2002

With the launch of the MODIS sensor on the Terra spacecraft, new data sets of the global distribution and properties of aerosol are being retrieved, and need to be validated and analyzed. A system has been put in place to generate spatial statistics (mean, standard deviation, direction and rate of spatial variation, and spatial correlation coefficient) of the MODIS aerosol parameters over more than 100 validation sites spread around the globe. Corresponding statistics are also computed from temporal subsets of AERONET‐derived aerosol data. The means and standard deviations of identical parameters from MODIS and AERONET are compared. Although, their means compare favorably, their standard deviations reveal some influence of surface effects on the MODIS aerosol retrievals over land, especially at low aerosol loading. The direction and rate of spatial variation from MODIS are used to study the spatial distribution of aerosols at various locations either individually or comparatively. This paper introduces the methodology for generating and analyzing the data sets used by the two MODIS aerosol validation papers in this issue.
Fluid in mineral interfaces—molecular simulations of structure and diffusion
Authors: Dysthe D. K. , Renard F. , Porcheron F. , Rousseau B.
Published: October 2002

We study the effect of burial depth on thermodynamics and transport properties of fluids confined between mineral surfaces. The solvation curve and diffusion coefficients of fluid films confined between mineral surfaces have been obtained for different states of stress and temperature using Grand Canonical Monte Carlo and molecular dynamics simulations. Our results indicate that the mass transport coefficient (film thickness times diffusion coefficient) of the thin films of fluids trapped at grain contacts decrease by a factor 40 from 1 km to 3 km and 10 km. This effect has strong implications on the rates at which mechano‐chemical processes of deformation (e.g. pressure solution) occur in the upper crust.
Evidence of the present relative land stability of Venice, Italy, from land, sea, and space observations
Authors: Tosi Luigi , Carbognin Laura , Teatini Pietro , Strozzi Tazio , Wegmüller Urs
Published: October 2002

The city of Venice is very vulnerable to loss in surface elevation as a result of subsidence and eustacy because of its small elevation above sea level. The alarm of the scientific community related to this persistent problem is increasing because of the forecasts of sea level rise caused by global warming. In order to evaluate the present relative subsidence of Venice, a study has been performed by combining high precision leveling, Satellite Radar Interferometry (SRI) and tide gauge measurements. The analysis of the most recent data points out with an unprecedented detail the present ground stability of the city.
Recent changes in wind chill temperatures at high latitudes in North America
Authors: Keimig Frank T. , Bradley Raymond S.
Published: October 2002

Afternoon wind chill temperatures at fifteen Alaskan and northern Canadian stations in the months October through April have increased in most months and at most stations in the period 1953–1993 (that is, “apparent temperatures” have become warmer). Many monthly means increased by more than 5°C over the period. Though increases in air temperature had a dominant effect on increases in wind chill temperature, decreases in wind speed generally contributed to the wind chill temperature increases. The largest and most persistent positive trends in wind chill temperature were in Alaska and western Canada, with negative and smaller positive trends in central, eastern, and northern Canada. As a result of the trends, humans outdoors in the afternoon have experienced an “apparent” warming even larger than the warming indicated by the air temperature trends.
Seismogenic plane of the northern Andean Subduction Zone from aftershocks of the Antofagasta (Chile) 1995 earthquake
Authors: Patzig Robert , Shapiro Serge , Asch Günter , Giese Peter , Wigger Peter
Published: October 2002

A temporary seismological network, which was located in the Antofagasta (northern Chile) region, recorded a large part of the aftershocks from a MW = 8.0 earthquake in 1995. Results from a tomographic inversion show that the aftershocks were concentrated in a plane, approximately 3 km thick spatial zone. Comparison of our results with earlier processed wide‐angle reflection data, shows clearly that this zone is positioned at the top of the oceanic crust. Therefore, it represents the shearing boundary between the subducting oceanic and the continental plate, and gives an in‐situ estimation of the thickness of the boundary. Outside of this zone, events were detected in the continental crust, as well as within the oceanic mantle.
The electrodynamics of sprites
Authors: Bering E. A. , Benbrook J. R. , Garrett J. A. , Paredes A. M. , Wescott E. M. , Moudry D. R. , Sentman D. D. , Stenbaek‐Nielsen H. C. , Lyons W. A.
Published: October 2002

A balloon campaign was conducted in summer, 1999, to measure the stratospheric electromagnetic fields associated with sprites. The balloon payloads were instrumented with electric field detectors, magnetometers, an upward looking photometer, and other instruments. Ground observations for detection of sprites included low light level TV (LLTV) observations from three sites, Jelm Mt., Wyoming, Bear Mt., South Dakota, and Yucca Ridge, Colorado. Flight 3 of the campaign flew from Ottumwa, Iowa at 00:39:32 UTC to 11:12:00 UTC on 08/21/99. A sprite at 0955:36.980 UTC produced a vertical electric field perturbation of ∼0.275 V/m that was similar in time profile to the light emission. There was also a positive azimuthal magnetic pulse of ∼3 nT.
The tempo of climate change during Dansgaard‐Oeschger interstadials and its potential to affect the manifestation of the 1470‐year climate cycle
Authors: Schulz Michael
Published: October 2002

The oxygen‐isotope record from the GISP2 ice core serves a air‐temperature proxy to estimate cooling rates during Dansgaard‐Oeschger interstadials between 15–53 thousand years before present. The duration of individual Dansgaard‐Oeschger interstadials scales inversely with the cooling rate and high cooling rates are associated with large continental ice volume and vice versa. Cooling rates determine the extent to which the postulated 1470‐year pacing cycle of the Dansgaard‐Oeschger interstadials is visible in paleoclimatological records: Only cooling rates associated with intermediate ice volume (approx. −84 ± 20 m relative sea‐level equivalent) allow the climate system to respond to succeeding trigger events of the 1470‐year cycle and result in stadials/interstadials of nearly the same duration.
Gravity wave characteristics over Tromelin Island during the passage of cyclone Hudah
Authors: Chane‐Ming Fabrice , Roff Greg , Robert Laurent , Leveau Jean
Published: October 2002

The time and spatial evolution of gravity‐wave characteristics are analysed using wavelets in vertical profiles of temperature and winds at Tromelin Island (15.53°S, 54.31°E) during the passage of the intense tropical cyclone Hudah in the Southern Ocean Indian Basin in 2000. Inertia‐gravity waves were observed in the upper troposphere and the lower stratosphere with dominant vertical wavelengths of 1.5–3 km, horizontal wavelengths <2000 km and periods of 0.6–1.6 days. Large amounts of gravity‐wave energy were detected during landfalls of the tropical cyclone. The distribution of total energy indicates that mesoscale convective structures such as tropical cyclones are important gravity‐wave sources in the upper troposphere.
New paleoseismological data from the Gran Sasso d'Italia area (central Apennines)
Authors: Galli P. , Galadini F. , Moro M. , Giraudi C.
Published: October 2002

Paleoseismological analyses along the Campo Imperatore normal fault (CIF) in the Gran Sasso massif, which is an area characterized by the absence of significant historical earthquakes, highlight the occurrence of surface faulting after the 5th–3rd cent. BC and around the 6th–5th millenium BC. These ages agree with those reported byGiraudi and Frezzotti[1995]on the western tip of the CIF, thus suggesting the possible entire rupture of the 30‐km‐long CIF during M∼7 events. These data contribute to the re‐evaluation of the seismic hazard of a large surrounding area, including the city of L'Aquila (∼100.000 inhabitants), which is located 20 km from the CIF, in the hangingwall side.
Upper mantle structure beneath the Hawaiian swell: Constraints from the ocean seismic network pilot experiment
Authors: Collins J. A. , Vernon F. L. , Orcutt J. A. , Stephen R. A.
Published: October 2002

Data from two broadband, ocean‐bottom seismographic stations deployed ∼225 km southwest of Oahu, Hawaii during the Ocean Seismic Network Pilot Experiment provide constraints on upper mantle structure beneath the Hawaiian swell. Receiver functions show that the mantle transition zone is thinned by >50 km relative to reference model PA5, which, in the absence of compositional changes, implies excess temperatures of >350 K in the transition zone. The combination of the measurements reported here and the thickness variations reported by Li et al. [2000] imply that the transition zone is thinned by 30 ± 15 km over an along‐swell dimension of at least 700 km. At ∼80 km depth, P‐to‐S converted phases are identified from the Gutenberg discontinuity marking the lid of the oceanic low‐velocity zone and the base of the lithosphere. Shear‐wave splitting measurements imply that fast‐polarization azimuths are intermediate between the absolute plate‐motion vector and the fossil spreading direction; multi‐event stacked values of ø and δt are −80° and 1.5 s, respectively.
Recent aqueous floods from the Cerberus Fossae, Mars
Authors: Burr Devon M. , McEwen Alfred S. , H. Sakimoto Susan E.
Published: October 2002

Streamlined forms and longitudinal grooving seen in Mars Orbital Camera (MOC) images indicate recent aqueous flooding occurred downslope (south) of the southern‐most Cerberus Fossae fissure. Topography from the Mars Orbital Laser Altimeter (MOLA), in conjunction with the absence of fluvial features in MOC images immediately to the north of the Fossa, substantiate the idea that floods emanated from this fissure. The floodwater flowed southward onto the western Cerberus Plains, where it probably percolated into existing lava flows. Thus, shallow ice may still be extant beneath young lava flows in this equatorial region.
On the interpretation of the VHF radar echoes from the equatorial lower E region
Authors: Patra A. K.
Published: October 2002

Reanalysis of the recent radar observations reported by Tsunoda and Ecklund [1999] has been made to explain the VHF radar echoes from the collision dominated lower E region (< 95 km). It is shown that the lower E region echoes extending down to 90 km can be explained using the gradient drift instability if the neutral wind is taken into consideration. It is also shown that the inclusion of neutral wind in the growth rate of the gradient drift instability is capable of explaining the day‐to‐day variability of the occurrence of the irregularities extending to the lower altitudes. Interpretation is given of the low value of Doppler velocities and the unusual velocity reversal observed by the radar at the lower altitudes that is consistent with the existing theory of the equatorial electrojet.
Wetlands at the Last Glacial Maximum: Distribution and methane emissions
Authors: Kaplan Jed O.
Published: October 2002

The global distribution of potential wetlands and their methane (CH4) emissions at the present‐day and the Last Glacial Maximum (LGM) are estimated using a GCM simulation of LGM climate, a vegetation model, and simple algorithms for determining wetland area based on topography and soil moisture, and CH4 emissions based on ecosystem carbon turnover in wet soils. LGM wetland area was 15% larger than present, but CH4 emissions were 24% less. Extensive wetlands were simulated on the exposed continental shelves. The soil CH4 sink was simulated as 14 Tg now but <0.5 Tg at the LGM. CH4 emissions at LGM were limited by substrate availability, in turn due to low atmospheric CO2. The glacial‐interglacial change in atmospheric CH4 concentration cannot be completely attributed to changes in the wetland source.
A Nonlinear Mechanism for Decadal El NiñO Amplitude Changes
Authors: Timmermann Axel , Jin Fei‐Fei
Published: October 2002

Based on the analysis of a low‐order tropical atmosphere‐ocean model we propose a nonlinear mechanism explaining several features of the observed El Niño‐Southern Oscillation (ENSO) phenomenon: ENSO irregularity, ENSO Amplitude Modulations and decadal tropical climate variability. The mechanism suggested here is based on the idea of homoclinic/heteroclinic orbits, an inherently nonlinear concept. It turns out that this mechanism operates even in the presence of wind noise and is consistent with results from intermediate ENSO model simulations.
Statistics of the mid‐altitude cusp observed by Polar
Authors: Rae I. J. , Lester M. , Davies J. A. , Milan S. E. , Fenrich F. R. , Fritz T. A. , Scudder J. D.
Published: October 2002

The Polar GGS space mission has allowed the northern hemispheric polar cusp region to be probed in a variety of ways to further our understanding and knowledge of the processes that occur within this region. The discovery of pulsed, energy‐dispersed ion injections on newly‐opened field lines (Pulsed Particle Signatures, or PPSs), the magnetospheric plasma signatures of transient reconnection, is one such advancement in our knowledge. Utilising a ∼22 months subset of Polar's mission, we perform a statistical study of the dayside traversals of the cusp region by the spacecraft to determine the extent and location of PPSs as well as the prevailing Interplanetary Magnetic Field (IMF) conditions under which they occur. In this paper we report upon the broad extent of these signatures in latitude and local time regardless of IMF orientation, and show that PPSs occur under both southward and northward IMF conditions in high percentages, although favouring southward directed IMF. These results are discussed in terms of previous statistical studies of reconnection signatures, and in terms of lobe and low latitude reconnection.
Evaluating TERRA‐1 MODIS data for discrimination of tropical secondary forest regeneration stages in the Brazilian Legal Amazon
Authors: Lucas Richard M. , Xiao Xiangming , Hagen Stephen , Frolking Steve
Published: October 2002

We establish the potential of TERRA‐1 Moderate Resolution Imaging Spectrometer (MODIS) data for discriminating and mapping tropical secondary forest regeneration stages in the Brazilian Legal Amazon, in terms of both their age and pathway. In using MODIS data, many difficulties encountered in local to regional scale mapping and discrimination of regeneration stage using NOAA Advanced Very High Resolution Radiometer (AVHRR) and fine spatial resolution Landsat/SPOT sensor data can be largely overcome.
BGK electron solitary waves in 3D magnetized plasma
Authors: Chen Li‐Jen , Parks George K.
Published: October 2002

This paper presents analytical solutions that we obtained in extending the BGK electron solitary wave solutions in 1D to include the 3D electrical interaction (E ∼ 1/r2) of charged particles. Our results indicate that for a single humped electric potential, the parallel cut of the perpendicular component of the electric field (E⟂) is unipolar and that of the parallel component (E∥) bipolar. The multi‐dimensional features of solitary waves have been observed by the FAST satellite. The parallel width‐amplitude relation is found to be an inequality and it depends on the perpendicular scale size of the solitary structure. This feature can be used in conjunction with experimental data to obtain an estimate on the typical perpendicular size of observed solitary waves.
Deformation of convergent plates: Evidence from discrepancies between GPS velocities and rigid‐plate motions
Authors: Yang Youqing , Liu Mian
Published: October 2002

Systematic discrepancies between the Global Positioning System (GPS) site velocities and those predicted by plate‐motion models across the Andes, the Himalayan‐Tibetan plateau, and the Taiwan orogen delineate diffuse plate‐boundary deformation and significant intraplate deformation, even in the presumably rigid oceanic plates. The relationship between the GPS velocities and the predictions of plate‐motion models is illustrated using a simple timescale‐dependent mechanical model of plate convergence. A simple stiffness number (ϕ), based on the difference between the predictions of plate‐motion models and the GPS velocity near plate boundaries, provides a convenient measure of the “plate‐like” behavior of convergent plates and strain partitioning between intraplate and interplate deformation.
Detection of high‐altitude ionospheric irregularities with GPS/MET
Authors: Sokolovskiy Sergey , Schreiner William , Rocken Christian , Hunt Douglas
Published: October 2002

In this study radio occultation data from the GPS/MET experiment are used for detection of high‐altitude ionospheric irregularities. This is done by back propagation of the complex electromagnetic field observed in orbit while accounting for the direction of the Earth's magnetic field. The irregularities are detected mainly in the F region. However, for some occultations they are detected above the F2 peak at altitudes up to 1000 km and higher. Results of numerical simulations, a description of the used algorithm, and examples of the processed GPS/MET data are presented.
Precipitation anomalies in the tropical Indian Ocean and their relation to the initiation of El Niño
Authors: Curtis Scott , Huffman George J. , Adler Robert F.
Published: October 2002

A pattern of intraseasonal to interannual variability in precipitation and surface winds for the eastern equatorial Indian Ocean (EEIO) during 1979 to 1999 is described using combined Empirical Orthogonal Function (EOF) analyses. The main features of the positive phase of the EEIO mode are 1) enhanced precipitation to the south of the island of Sumatra, 2) suppressed precipitation in the central equatorial Indian Ocean, 3) surface westerly wind anomalies directed from the dry toward the wet region, and 4) southeasterly wind anomalies which meet the westerly anomalies in the vicinity of the enhanced precipitation. A relationship was found between the precipitation gradient of the EEIO mode and the five strongest El Niño events since 1979 (1982/83, 1986/87, 1991/92, 1994/95, and 1997/98). For the cases when the interannual component of the gradient reached a positive peak followed by significant power (94%) in the 30–60 day component of the gradient roughly a season later, an El Niño was observed to develop.
Electromagnetic images of a strike‐slip fault: The Tintina fault—Northern Canadian
Authors: Ledo Juanjo , Jones Alan G. , Ferguson Ian J.
Published: October 2002

Wideband magnetotelluric (MT) data were acquired along three profiles crossing the strike‐slip Tintina Fault in northwestern Canada. The MT responses obtained exhibit remarkable similarity from all three profiles, implying similar two‐dimensional (2‐D) electromagnetic behavior of the fault zone over a strike length of at least 350 km. Analyses of the MT responses for dimensionality corroborate the validity of assuming regional 2‐D structures in interpretation. Several high conductivity anomalies at different depth scales are present in the models obtained, and we suggest that both the shallow structures and the deep crustal scale anomalies are caused by electronic conduction mechanisms in interconnected mineralized zones. Intriguingly, the middle and lower crust beneath the surface expression of the Tintina Fault is highly resistive, in contrast to some other large‐scale strike‐slip faults. This implies that fault zone processes that result in interconnected conducting phases are not generic in nature but are controlled by local conditions.
Charge states of energetic (≈0.5 MeV/n) ions in corotating interaction regions at 1 AU and implications on source populations
Authors: Möbius E. , Morris D. , Popecki M. A. , Klecker B. , Kistler L. M. , Galvin A. B.
Published: October 2002

The ionic charge states of He, C, O, Ne, Mg and Fe at ≈0.5 MeV/n have been obtained in several corotating interaction regions (CIRs) in 1999 and 2000 with the Solar Energetic Particle Ionic Charge Analyzer (SEPICA) on the Advanced Composition Explorer (ACE). A large fraction (on average 25%) of He+ is found relative to He2+, indicating a substantial contribution of interstellar pickup ions. The mean charge states of the heavy ions are consistent with those in CME related energetic particle events and in solar wind. A rather low upper limit of <1% is found for singly charged ions for C, O and Mg, while Ne shows a small, but noticeable, fraction (4.7%) of Ne+. These observations are consistent with a contribution from interstellar pickup ions, but seem to eliminate inner source pickup ions as a substantial source for CIRs at and near 1 AU.
Polar mesosphere summer echo observations at HF frequencies using the HAARP Gakona Ionospheric Observatory
Authors: Kelley Michael C. , Huaman Mercedes , Chen Charlie Y. , Ramos Camilo , Djuth Frank , Kennedy Edward
Published: October 2002

We present initial polar mesosphere summer echo (PMSE) observations over Alaska in the HF band. Echoes were detected near 85 km over 50% of the observation time even though it was late in the PMSE season. The signal‐to‐noise ratio sometimes exceeded 25 dB. We also present the effects of different transmitted powers and antenna pointing directions on PMSE strength and occurrence. There is some evidence that using 4.5 MHz electron heating occurred, even at the low duty cycle used.
Influence of coordination number and percolation probability on rock permeability estimation
Authors: Fauzi U. , Hoerdt A. , Neubauer F. M.
Published: October 2002

Estimation of permeability from image sections can be conducted by means of Local Porosity Theory (LPT) and the effective medium approximation (EMA). Using these approaches, the coordination number that is important for rock modeling is included. In this paper, we extend the EMA approach by considering the percolation probability as an additional parameter. Both equations show that permeability will be higher as coordination number as well as percolation probability increases. The permeability increases most rapidly close to the percolation threshold. Several thin sections of sandstone were created by digital image analysis. Two Point Correlation Functions were applied to estimate porosity and specific surface area. Permeability distribution as an input to EMA was created from the local permeability. The effective permeability was then calculated from the EMA equation iteratively. The result shows that considering coordination number and percolation probability will improve permeability estimation.
Slab breakoff depth: A slowdown subduction model
Authors: Li Ligang , Liao Xinhao , Fu Rongshan
Published: October 2002

A slowdown subduction model is presented to estimate slab breakoff depth and initial time when continental lithosphere subducts into mantle. By assuming oceanic lithosphere subducts with uniform velocity (all forces acting on plate are balanced) and noticing that, to leading order, some resistant forces are proportional functions of subduction velocity, a simple dynamic model is proposed to describe the retarded subduction process. Thermal and strength structures within the slab are calculated under this slowdown process. We then compare the integrated strength of transitional zone from continental to oceanic lithosphere within the slab with buoyancy change due to subducted continental crust to assess slab breakoff depth and initial time. Normally, the slab breakoff depth is 65 ∼ 130 km and initial time is 1 ∼ 6 M.yr. after continental lithosphere initiates subduction. The initial subduction velocity is a major factor that affects the breakoff depth and initial time while subduction angle has insignificant influence.
Interseismic strain accumulation in south central Chile from GPS measurements, 1996–1999
Authors: Ruegg J. C. , Campos J. , Madariaga R. , Kausel E. , de Chabalier J. B. , Armijo R. , Dimitrov D. , Georgiev I. , Barrientos S.
Published: October 2002

Two campaigns of Global Positioning System (GPS) measurements were carried out in the Concepción‐Constitución area of Chile in 1996 and 1999. It is very likely that this area is a mature seismic gap, since no subduction earthquake has occurred there since 1835. In 1996, 32 sites were occupied in the range 35°S–37°S, between the Pacific coast of Chile and the Andes near the Chile‐Argentina border. In 1999, the network was extended by the installation of 9 new points in the Arauco region whereas 13 points among the 1996 stations were reoccupied. The analysis of this campaign data set, together with the data recorded at eight continuous GPS sites (mostly IGS stations) in South America and surrounding regions, indicates a velocity of about 40 ± 10 mm/yr in the direction N80–90°S for the coastal sites with respect to stable cratonic South America. This velocity decreases to about 20–25 mm/yr towards the Andes. We interpret this result as reflecting interseismic strain accumulation above the Nazca‐South America subduction zone, due to a locked thrust zone extending down to about 60 km depth.
Effects of rock mechanical properties on local stress field of the Mahanadi basin, India—results from finite element modelling
Authors: Chatterjee Rima , Mukhopadhyay Manoj
Published: October 2002

Two dimensional (2‐D) finite element models (FEM) are generated using two available seismic sections across the Mahanadi Basin (MB) at the east coast of India. This permits to study the interactive effect between applied stress in the direction of maximum horizontal compressive stress (SH) and variations in rock mechanical properties of several litho‐units present in the basin. The SH orientation for six offshore wells in the MB known from our previous studies [Chatterjee and Mukhopadhyay, 2000] have been used as constraints for FEM. Local stress modifications due to contrast in the Young's modulus between sedimentary in‐fill and the crust down to 20 km depth are investigated for two more orthogonal seismic profiles traversing the basin from onland to offshore. FEM‐derived stress vectors clearly respond to variations in elastic properties of rocks corresponding to lithological interfaces in the basin and its underlying crust. Rotation of the principal stress is prominent where the stress concentration is high. Further, the stress concentration reflects the basinal configuration.
Ion‐acoustic resistivity in plasmas with similar ion and electron temperatures
Authors: Watt C. E. J. , Horne R. B. , Freeman M. P.
Published: October 2002

Analytical estimates of resistivity due to electrostatic current‐driven ion‐acoustic waves are compared with Vlasov simulation results. Particular attention is given to the case of similar ion and electron temperatures that is appropriate to the magnetopause and low‐latitude boundary layer (LLBL). It is shown that Vlasov simulation runs of growing ion‐acoustic waves with Te = 2Ti give values of resistivity which are at least three orders of magnitude higher than an existing analytical estimate [Labelle and Treumann, Sp. Sci. Rev., 47, 1988] and exhibit a different dependence on the wave energy density. A particle‐in‐cell code was also run with the same temperature ratio and gave similar resistivity values that back up the Vlasov simulation results. The discrepancy between simulation and analytical estimate arises because the derivation of the analytical estimate assumes that the quasilinear effects of the instability are weak. The simulation results show that this is not the case, since plateau formation is clearly seen in the electron distribution function. These simulation results show that the ion‐acoustic instability may be more important in the magnetopause and LLBL than previously thought.
Land use effects on atmospheric 13C imply a sizable terrestrial CO2 sink in tropical latitudes
Authors: Townsend Alan R. , Asner Gregory P. , White James W. C. , Tans Pieter P.
Published: October 2002

Records of atmospheric CO2 and 13CO2 can be used to distinguish terrestrial vs. oceanic exchanges of CO2 with the atmosphere. However, this approach has proven difficult in the tropics, partly due to extensive land conversion from C3 to C4 vegetation. We estimated the effects of such conversion on biosphere‐atmosphere 13C exchange for 1991–2000, and then explored how this “land‐use disequilibrium” altered the partitioning of net atmospheric CO2 exchanges between ocean and land using NOAA‐CMDL data and a 2D, zonally averaged atmospheric transport model. Our results suggest sizable CO2 uptake in C3‐dominated tropical regions in 8 of the 10 years; 1997 and 1998, which included a strong ENSO event, are near neutral. Since these fluxes include any deforestation source, our findings imply either that such sources are smaller than previously estimated, and/or the existence of a large equatorial terrestrial CO2 sink.
Electroosmotic flow and the validity of the classical Darcy equation in silty shales
Authors: Revil A. , Pessel M.
Published: October 2002

Electroosmotic flow represents the flow of pore water through a porous medium submitted to an electrical field or an electrical current density. A model is developed to describe the coupled electric/hydraulic flow problem in silty shales. The strength of electroosmotic flow is modeled here as a function of porosity, grain shape, pH, and ionic strength of the pore water. In the case of forced flow under a pore fluid pressure gradient, electroosmosis reduces the filtration velocity. This effect can be modeled by introducing an effective or apparent permeability into the classical form of the Darcy equation. This apparent permeability can be much smaller than the intrinsic permeability and becomes very sensitive to the salinity of the pore water.
Tropical Pacific control of intraseasonal oscillations off Chile by way of oceanic and atmospheric pathways
Authors: Hormazabal Samuel , Shaffer Gary , Pizarro Oscar
Published: October 2002

Sea level, current, satellite wind data and a simple model of wind‐forced, low frequency waves are used to study the origins of strong, observed intraseasonal variability in the ocean and atmosphere off Chile. There intraseasonal wind fluctuations are correlated to wind fluctuations in the equatorial Pacific, associated with the Madden‐Julian Oscillation. Results suggest intraseasonal teleconnections via two distinct atmospheric pathways. Very simple model simulations forced by satellite winds from the equator and the South American coast compare well with observed fluctuations of currents and sea level off central Chile. There most of this intraseasonal variability, particularly during summer and during El Niño events, arrives as free, oceanic, coastal trapped waves via oceanic, equatorial Kelvin waves, forced by tropical Pacific winds. South of 20°S, some oceanic intraseasonal variability is forced by local winds associated with the atmospheric teleconnections.
Transient electric phenomena observed during fluid circulation in unsaturated porous media
Authors: Hovhannissian G. M. , Pozzi J.‐P. , Bernard P. , Tabbagh A.
Published: October 2002

We conducted a series of electrokinetic measurements on partially saturated sandstone samples. Both steady and transient electric signals were observed. We recorded transient electric signals with frequencies of 0.5–2Hz and amplitudes 10–100 times smaller than the quasi‐DC streaming potential, which we associate with fluid flow instabilities in the unsaturated porous rocks samples. Some of these electric signals were correlated with fluid pressure variations, delayed by one to a few seconds.
Three‐dimensional S‐wave velocity structure in Southern California
Authors: Tanimoto T. , Prindle Sheldrake K.
Published: October 2002

The three‐dimensional S‐wave velocity structure was constructed from Rayleigh wave phase velocities, measured using teleseismic TriNet data. The S‐wave velocity maps show some features that are much more distinct than previous tomographic results in Southern California. There is a clear seismic velocity contrast across the San Andreas fault. The North American plate side is systematically slower than the Pacific plate side. Under the Eastern California Shear Zone, there are distinct slow velocity anomalies in the crust, suggesting a close connection to lower viscosity crust, previously concluded from observation of the post‐seismic deformation after the Landers earthquake. Major upper mantle features include a fast velocity root under the Transverse Ranges, which is the dominant feature in the upper mantle, and a slow velocity anomaly under the Salton Trough. Our results support that the velocity contrast across the San Andreas fault extends below the Moho.
Geophysical signatures of a basic‐body rock placed in the upper crust of the External Zones of the Betic Cordillera (Southern Spain)
Authors: Serrano Inmaculada , Bohoyo Fernando , Galindo‐Zaldívar Jesús , Morales José , Zhao Dapeng
Published: October 2002

The combined use of different geophysical techniques (seismic tomography, gravity and magnetic research) carried out in the External Zones of the Betic Cordillera (Southern Spain) points to the existence of a controversial set of anomalies. The high resolution seismic tomography clearly indicates a fast anomaly of up to +7% P‐wave velocity, and the surface magnetic and aeromagnetic measurements also show a positive anomaly. The negative anomaly of the dipole is very smooth. However, the estimated Bouguer anomaly values are clearly negative. This set of anomalies has been interpreted as due to a basic‐body rock (gabbros) located in the upper crust. The existence of this body suggests that the Iberian Massif constitutes the basement of the External Zones of the Betic Cordilleras, up to near the boundary with the Internal Zones.
Holocene mass wasting on upper non‐Polar continental slopes—due to post‐Glacial ocean warming and hydrate dissociation?
Authors: Vogt Peter R. , Jung Woo‐Yeol
Published: October 2002

Incorporating both late/post‐Glacial bottom‐water warming and eustatic sealevel rise into a MH (methane hydrate) stability model explains why at least some major submarine landslides (e.g., the Storegga Slide, Norwegian margin) may have been triggered by MH dissociation during the early Holocene (rising sealevels), not during the lowest sealevels of the LGM (Last Glacial Maximum, 18–20 ka). In the case of Storegga, failure may have been initiated either below the upper slope or under the shelf (for fresh pore water, especially with admixed ethane). At water depths below ca. 800m, persistent low bottom water temperatures allowed the sealevel rise to thicken the MH stability zone over time, ruling out Holocene initiation of failure. MH release by Holocene mass wasting cannot have initiated deglaciation.
Rock glacier surface motion in Beacon Valley, Antarctica, from synthetic‐aperture radar interferometry
Authors: Rignot Eric , Hallet Bernard , Fountain Andrew
Published: October 2002

We present radar interferograms of rock glaciers in the Beacon Valley sector of the McMurdo Dry Valleys, in East Antarctica, as part of a comprehensive study of surface processes in the area. Due to the relative absence of net precipitation (snow) in this region and the stability of the surface, the rock glaciers maintain excellent coherence of the radar returns over several years. As a result, we obtain a spatially continuous surface velocity field with a precision of fractions of a millimeter per year. On distinct rock glaciers entering Beacon Valley, we find coherent velocity patterns, with peak velocities approaching 40 mm per year. The ice supply from these rock glaciers nourishes the central portion of Beacon Valley, where velocities are found to be vanishingly small, and partly compensates for mass losses induced by sublimation. This analysis is consistent with the tantalizing notion that Beacon Valley ice is the oldest on Earth.
Enhanced ground motions due to large‐amplitude critical Moho reflections (SmS) in the Sea of Marmara, Turkey
Authors: Boztepe‐Güney Aysun , Horasan Gündüz
Published: October 2002

Aftershocks of the 17 August 1999, Mw = 7.4, Kocaeli earthquake were used to investigate the large‐amplitude SmS arrivals in the Sea of Marmara. We produced the event record sections from the transverse components of S and SmS arrivals at a distance of 10 to 200 km for the data recorded towards the east and west in the Sea of Marmara. For the data recorded towards the west, we observed that the amplitude of SmS phases enhances the ground motion by a factor of 2 to 3. The dipping Moho and/or anisotropy in the upper mantle or deep convex structure or deep lens are possible sources for the large‐amplitude SmS phases. Since the study area has a potential of creating damaging earthquakes in the future, the effect of large‐amplitude SmS phases on the ground motion should be considered in the studies of the seismic hazard of the region.
Experimental and simulated solute transport in a partially‐saturated, variable‐aperture fracture
Authors: Detwiler Russell L. , Rajaram Harihar , Glass Robert J.
Published: October 2002

We compare solute transport experiments to simulations in a partially‐saturated, variable‐aperture fracture in measured fracture aperture and entrapped‐air geometry fields. The computational model tracks particles through a quasi‐three‐dimensional velocity field that is based on the two‐dimensional solution to the Reynolds equation. The model predicts 84% of the relative increase in dispersion caused by the entrapped phase, and reproduces the experimentally observed nonlinear velocity‐dependence of solute dispersion.
Morphology and scaling of ejecta deposits on icy satellites
Authors: Schenk Paul M. , Ridolfi Francis J.
Published: October 2002

Continuous ejecta deposits on Ganymede consist of two major units, or facies: a thick inner hummocky pedestal facies, and a relatively thin outer radially scoured facies defined also by the inner limit of the secondary crater field. Both ejecta facies have a well‐defined power‐law relationship to crater diameter for craters ranging from 15 to ∼600 km across. This relationship can be used to estimate the nominal crater diameter for impact features on icy satellites (such as palimpsests and multiring basins) for which the crater rim is no longer recognizable. Ejecta deposits have also been mapped on 4 other icy satellites. Although morphologically similar to eject deposits on the Moon, ejecta deposits for smaller craters are generally significantly broader in extent on the icy satellites, in apparent defiance of predictions of self‐similarity. A greater degree of rim collapse and enlargement on the Moon may explain the observed difference.
The propagation of traveling atmospheric disturbances observed during the April 6–7, 2000 ionospheric storm
Authors: Lee Chien‐Chih , Liu Jann‐Yenq , Reinisch Bodo W. , Lee Yung‐Po , Liu Libo
Published: October 2002

The great magnetic storm of April 6–7, 2000 generated ionospheric disturbances in the west Pacific region. Two ionosondes at Wuhan (30.6°N, 114.4°E) and Chung‐Li (24.9°N, 121°E) observed the ionosphere during this period. The variations of the ionospheric parameters, NmF2 (plasma density of the F‐peak), hmF2 (height of the F‐peak) and h′F (minimum virtual height of the F‐layer), show that a traveling atmospheric disturbance (TAD) affects the ionosphere at middle and low latitudes in this region. The propagation velocities deduced from the time delay of hmF2 and h′F recorded at the two stations are about 655 and 164 m/s, respectively. Furthermore, a method of deriving the vertical phase and group velocities is applied to the sequences of virtual heights at fixed sounding frequencies. The vertical and associated meridional velocities demonstrate that the upward motions of the ionospheric plasma are caused by a TAD.