bluuebunny/crossref_metadata_2025 huggingface dataset:
Earthquake locations and three‐dimensional fault zone structure along the creeping section of the San Andreas fault near Parkfield, CA: Preparing for SAFOD
Authors: Thurber C. , Roecker S. , Roberts K. , Gold M. , Powell L. , Rittger K.
Published: May 2003

Arrival‐time data from 453 local earthquakes and 6 explosions at Parkfield, CA, are inverted for earthquake locations and three‐dimensional Vp and Vp/Vs structure. The structure is dominated by the velocity contrast across the SAF, with the southwest side about 20–25% faster, consistent with previous studies. Nearly all the earthquakes occur almost directly beneath the fault trace. We find high‐Vp/Vs anomalies that correlate with low‐resistivity features in a magnetotelluric model that are interpreted to represent fluids. We locate a magnitude 2 earthquake that is a potential target event for the final stage of SAFOD drilling, yielding a depth of 3.1 km below surface and an epicenter 100 m southwest of the fault trace. Nonlinear analyses indicate 95%‐confidence relative and absolute uncertainties on the order of 500–700 m vertically and 200–300 m horizontally for this target earthquake.
What high altitude observations tell us about the auroral acceleration: A Cluster/DMSP conjunction
Authors: Vaivads A. , André M. , Buchert S. , Eriksson A. I. , Olsson A. , Wahlund J.‐E. , Janhunen P. , Marklund G. , Kistler L. M. , Mouikis C. , Winningham D. , Fazakerley A. , Newell P.
Published: May 2003

Magnetic conjugate observations by Cluster and DMSP F14 satellites are used to study the field lines of auroral arc. Cluster is well above the acceleration region and observes upward keV ion beams and bipolar electric structures. The integrated potential at Cluster altitudes shows a dip that is consistent with the keV electron acceleration energy at low altitude. The earthward Poynting flux at Cluster altitudes is comparable to the electron energy flux at low altitudes. Thus, for this event the auroral acceleration can be described as a quasi‐stationary potential structure with equipotential lines reaching the Cluster altitudes. The arc forms at the outer edge of the plasma sheet at a density gradient. Multiple Cluster satellite measurements allow us to study the density increase associated with the development of the arc, and to estimate the velocity of the structure. The quasi‐potential structure itself may be part of an Alfvén wave.
Empirical plasmapause models from magnetic indices
Authors: O'Brien T. P. , Moldwin M. B.
Published: May 2003

We use a database of CRRES in situ observations of plasmapause crossings to build empirical models of the plasmapause location as a function of geomagnetic indices. Previous models used the maximum value in Kp during the hours to days leading up to the plasmapause crossing. We find that a recent maximum in AE or minimum in Dst provides a better model of the plasmapause radius than does maximum Kp. AE and Dst measure specific current systems (the auroral electrojet and ring current, respectively). The AE model suggests that substorms may be involved in the erosion of the plasmapause. The Dst model suggests that ring current may be formed by the same electric field that erodes the plasmapause. In more complex models, Kp and AE can describe local time structure in the plasmapause, with the furthest plasmapause before dawn at quiet times, premidnight at active times.
A comparative analysis of lightning data from lightning networks and LIS sensor in the North and Southeast of Brazil
Authors: Pinto O. , Pinto I. R. C. A. , de Faria H. H.
Published: May 2003

Intracloud and cloud‐to‐ground (CG) lightning data in the North and Southeast regions of Brazil are compared based on observations from 01 October 1999 to 13 April 2000. The observations were made by ground networks and the Lightning Imaging Sensor (LIS) on board the TRMM satellite. For the whole period of observation, a detailed comparative analysis indicates that the cloud‐to‐ground lightning activity in the North region is about 20% higher than that in the Southeast for a similar size area, while the percentage of intracloud flashes is almost the same in both regions (∼60–65%). On a 49‐day basis (to avoid the local time bias in the LIS data), the same analysis indicates that the lightning activity recorded by LIS is representative of the CG lightning activity detected by the lightning networks, either in the same time and space seen by the satellite sensor, or in the area of the study. It was also found that the percentage of positive CG flashes in the North region is correlated to the percentage of intracloud flashes.
Dolomite‐II: A high‐pressure polymorph of CaMg(CO3)2
Authors: Santillán Javier , Williams Quentin , Knittle Elise
Published: May 2003

We have measured the infrared spectra and x‐ray diffraction of CaMg(CO3)2‐dolomite to pressures of 50 GPa at 300 K. We observe both splittings and disappearances of x‐ray diffraction peaks initiating near 20 GPa, as well as new bands in the infrared spectrum of dolomite. The onset of the changes in both the x‐ray and infrared data appears to be gradual, and thus kinetically impeded: this is consistent with previous shock results. The infrared and x‐ray data are consistent with dolomite adopting a calcite‐III‐like structure. Our results indicate that high‐pressure polymorphism in dolomite could stabilize CaMg(CO3)2 in the deep mantle, and thus that high‐pressure polymorphs of dolomite could represent the main reservoir for carbon storage within Earth's lower mantle.
Using ScP precursors to search for mantle structures beneath 1800 km depth
Authors: Castle John C. , van der Hilst Rob D.
Published: May 2003

If either two stratified geochemical reservoirs or a mineralogical phase change in perovskite exist in the mantle, the boundary between the geochemical layers or mineralogical phases may lie at a depth between 1800 km and the core‐mantle boundary (CMB). We searched for the ScP precursors (S‐to‐P reflections) that would be generated at the boundary by stacking hundreds of short‐period, vertical component teleseismic waveforms from the dense Pacific Northwest Seismic Network (PNSN). PNSN recorded clean ScP phases and saved the P to ScP time window for four earthquakes. We estimate our detection threshold to be impedance contrast >4%. None of the data show evidence of sharp structure between 1800 km and the CMB, suggesting that a sharp seismic discontinuity does not exist between 1800 km and the CMB under the Gulf of Alaska and Mexico: any discontinuity would need to be diffuse, have large topography, or have a small impedance change. While not conclusive, this observation is consistent with an Earth model lacking a global boundary separating geochemical reservoirs and lacking a phase change in this depth range.
Jupiter's polar ionospheric flows: Measured intensity and velocity variations poleward of the main auroral oval
Authors: Stallard T. S. , Miller S. , Cowley S. W. H. , Bunce E. J.
Published: May 2003

Recent analysis of high‐resolution spectra of Doppler‐shifted H3+ emission from the auroral/polar regions of Jupiter revealed a complex wind system, with a persistent auroral electrojet and strong anti‐sunward flows in a region of lesser intensity centred around the magnetic pole [Stallard et al., 2001]. This region, which we have called the Dark Polar Region (DPR), is re‐investigated, transforming the observed line‐of‐sight velocities into a frame of reference fixed with respect to the magnetic pole. The DPR is shown to include a region essentially stagnant in this frame of reference (the f‐DPR). We identify it as a region coupled to open magnetotail field lines. There is also a transition region in which the ion velocity returns to corotation (the r‐DPR).
Ephemeral lakes and desert dust sources
Authors: Mahowald Natalie M. , Bryant Robert G. , del Corral John , Steinberger Linda
Published: May 2003

The processes that determine which areas are strong sources of mineral aerosols are not well known. In this study we consider the role of ephemeral lakes in modulating emissions of atmospheric mineral aerosols. We focus on two ephemeral lake regions that have been identified as source regions: the zone of Chotts in Tunisia and Algeria, and Etosha Pan in Namibia. Comparisons of satellite retrieved inundation data and the TOMS absorbing aerosol index suggest that during some periods of inundation, desert dust loadings are reduced. There is some indication that after flooded areas have dried there is increased dust loading. However, the role of the inundated ephemeral lake compared with nearby regions in modulating desert dust sources is unclear, in addition, problems with interpreting the TOMS AI make conclusions difficult. More research is required to understand the small‐scale sources of atmospheric desert dust in dry, unvegetated, topographic lows.
Shortwave radiative forcing by stratospheric water vapor
Authors: Zhong Wenyi , Haigh Joanna D.
Published: May 2003

It is shown that most previous estimates of radiative forcing due to increased stratospheric water vapor have been overestimates because most broad‐band radiation schemes underestimate the (negative) shortwave component. This paper compares line‐by‐line calculations of shortwave forcing with those of five broad and multiple band radiation schemes, including a new parameterization of water vapor absorption which reduces the errors to within 3%. The results of two‐dimensional model experiments indicate that the magnitude of the shortwave forcing should be approximately doubled, relative to previous estimates. As a result, estimates of global average net radiative forcing due to stratospheric water vapor increase should be decreased by approximately 10%.
Interannual variability of air‐sea O2 fluxes and the determination of CO2 sinks using atmospheric O2/N2
Authors: McKinley Galen A. , Follows Michael J. , Marshall John , Fan Song‐Miao
Published: May 2003

Motivated by the use of atmospheric O2/N2 to determine CO2 sinks under the assumption of negligible interannual variability in air‐sea O2 fluxes, we examine interannual fluctuations of the global air‐sea flux of O2 during the period 1980–1998 using a global ocean circulation and biogeochemistry model along with an atmospheric transport model. It is found that both the El Niño/Southern Oscillation (ENSO) cycle and wintertime convection in the North Atlantic are primary drivers of global air‐sea oxygen flux interannual variability. Model estimated extremes of O2 flux variability are −70/+100 × 1012 mol/yr (Tmol/yr), where positive fluxes are to the atmosphere. O2/N2 variability could cause an up to ±1.0 PgC/yr error in estimates of interannual variability in land and ocean CO2 sinks derived from atmospheric O2/N2 observations.
Evidence for correlation of electrical resistivity and seismic velocity in heterogeneous near‐surface materials
Authors: Meju Max A. , Gallardo Luis A. , Mohamed Adel K.
Published: May 2003

The electrical resistivity and seismic velocity distributions over a buried hillside have been obtained using non‐invasive controlled experiments on coincident profiles and 2D image reconstructions. The optimal images are in structural agreement and allow the deduction of two opposite resistivity‐velocity trends in the near‐surface materials. For both trends, the resistivity (ρ) and p‐wave velocity (Vp) are related in the form Log10 ρ = mLog10Vp + c with the respective constants m and c having different signs in unconsolidated and consolidated materials.
Quality of wind stress fields measured by the skill of a barotropic ocean model: Importance of stability of the Marine Atmospheric Boundary Layer
Authors: Ali Ahmed Haider , Zlotnicki Victor
Published: May 2003

The stability of the Marine Atmospheric Boundary Layer (MABL) plays an important role in the air‐sea exchange of momentum. Hence MABL's stability has an impact on the performance of numerical ocean models, which are driven by wind stress (along with other forcings). Here we investigate the effect of three wind stress parameterizations on the ability of a barotropic model to fit sea‐level measurements from the US‐French satellite TOPEX/POSEIDON (TP). We show that the wind stress parameterization that takes into account the stability of MABL enhances the model's skill to fit the TP data. Because the ocean shows a barotropic response primarily in high latitudes, the model's gain in skill is also in the high latitudes, where the probability of the MABL being unstable is in the 50% to 70% range.
Nonlinear saturation of high‐m Alfvén‐ballooning modes in magnetospheric plasmas
Authors: Chen Liu
Published: May 2003

A theoretical model is proposed for the nonlinear saturation of high‐m Alfvén‐ballooning instabilities in magnetospheric plasmas. Here, m is the azimuthal wave number. In the present model, a broad spectrum of Alfvén waves nonlinearly generate ion‐sound density perturbations; which, in turn, scatter the Alfvén turbulence toward lower frequencies. Balancing the linear instability growth rate with the nonlinear scattering (Landau damping) rate then yield the corresponding saturated spectrum, which tends to peak near the bottom of the eigenmode frequencies. The theory also gives estimates of wave amplitudes at saturation in reasonable agreement with satellite observations.
Introducing sub‐seasonal spatial and temporal resolution to winter climate prediction
Authors: Cohen Judah
Published: May 2003

The dominant Northern Hemisphere winter mode of variability is characterized by a same‐signed sea level pressure anomaly at high latitudes with an opposite‐signed anomaly stretching across mid‐latitudes. The surface temperature pattern associated with this mode is a same‐signed temperature anomaly across the major continents and an opposite‐signed anomaly across the major oceans. We demonstrate that this temperature pattern is mostly an artifact of multi‐year averaging, which results in the super positioning of two distinctive patterns. Separation of the two patterns allows for more accurate seasonal predictions and introduces a spatial and temporal resolution in forecasts previously not possible.
Intermittency of magnetospheric dynamics through non‐Gaussian distribution function of PC‐index fluctuations
Authors: Stepanova M. V. , Antonova E. E. , Troshichev O.
Published: May 2003

Dynamical behavior of the one minute resolution Polar Cap (PC) index was studied by using the 1995–2000 data sets. It was found that the probability distribution functions (PDFs) of the PC‐index increments display a strong non‐Gaussian shape in both positive and negative time intervals, depending on the time of an increment. This indicates that PC‐index is not characterized by a global time self‐similarity but rather exhibits an intermittency, previously detected in solar wind and auroral electrojet index time series. The PDFs for the PC index increments are fitted by the functional form proposed by Castaing et al. [1990] to describe intermittency phenomena in an ordinary turbulent fluid flow. The parameters that characterize the PC index increments PDF are very close to those reported before for solar wind magnetic field probability distribution functions. This indicates that the PC index adequately reflects the solar wind effects on the high‐latitude magnetosphere.
Solar cycle induced variations of the outer heliospheric structures
Authors: Scherer K. , Fahr H. J.
Published: May 2003

The solar wind undergoes complicated but typical changes during the solar activity cycle which are especially strongly pronounced in the inner heliosphere. In the outer heliosphere, as the main surviving solar cycle feature, a periodic variation of the solar wind dynamical pressure has been recognized by the VOYAGER‐1/2 spacecraft. We model this long‐periodic variation of the solar wind dynamical pressure with time‐dependent inner boundary conditions in our two‐dimensional 5‐fluids code. Only after running more than 8 activity cycles do the interface boundary layers start carrying out periodic breathings in constant phase lags with respect to the solar activity cycle. Especially the pick‐up ions and the anomalous cosmic rays, which are dynamically coupled to the low energy H‐atom and proton fluids, activate new interaction modes and store a longtime history of the past 2–3 solar cycles. This memory effect influences the analysis of energetic neutral atoms (ENA's) from the heliospheric interface regions.
Helium in solubility equilibrium with quartz and porefluids in rocks: A new approach in hydrology
Authors: Lehmann Bernhard E. , Waber H. Niklaus , Tolstikhin Igor , Kamensky Igor , Gannibal Maria , Kalashnikov Evgenii , Pevzner Boris
Published: May 2003

Quartz crystals in sandstones at depths of 1200 m–1400 m below the surface appear to reach a solubility equilibrium with the 4He‐concentration in the surrounding pore‐ or groundwater after some time. A rather high 4He‐concentration of 4.5 · 10−3 cc STP 4He/cm3 of water measured in a groundwater sample would for instance maintain a He pressure of 0.47 atm in a related volume. This value is equal within analytical error to the pressure deduced from the measured helium content of the quartz and its internal helium‐accessible volume. To determine this volume, quartz crystals of 0.1 to 1 mm were separated from sandstones and exposed to a helium gas pressure of 32 atm at a temperature of 290°C for up to 2 months. By crushing, melting or isothermal heating the helium was then extracted from the helium saturated samples. A volume on the order of 0.1% of the crystal volume is only accessible to helium atoms but not to argon atoms or water molecules. By monitoring the diffusive loss of He from the crystals at 350°C an effective diffusion constant on the order of 10−9 cm2/s is estimated. Extrapolation to the temperature of 70°C in the sediments at a depth of 1400 m gives a typical time of about 100 000 years to reach equilibrium between helium in porewaters and the internal He‐accessible volume of quartz crystals. In a geologic situation with stagnant pore‐ or groundwaters in sediments it therefore appears to be possible with this new method to deduce a 4He depth profile for porewaters in impermeable rocks based on their mineral record.
Geomagnetic and climatic variability reflected by 10Be during the Quaternary and late Pliocene
Authors: Aldahan A. , Possnert G.
Published: May 2003

We present continuous 10Be data extending to 3.5 Ma that show strong response to the Earth's magnetic field shielding. We find a prominent enhancement in 10Be at geomagnetic reversals and in particular at the Brunhes/Matuyama geomagnetic boundary and several geomagnetic excursions during the Brunhes Chron. Similarity in 10Be fluxes of Holocene to Eemian period occurs during oxygen isotope stages 11 through 13. According to our data, climatic patterns of these periods may likely represent exception rather than the rule during the last million years. We suggest that the interplay between the geomagnetic field shielding and solar activity had effectively regulated paleoclimatic attenuation.
A semi‐global reference model for electrical conductivity in the mid‐mantle beneath the north Pacific region
Authors: Utada H. , Koyama T. , Shimizu H. , Chave A. D.
Published: May 2003

One‐dimensional electrical conductivity structure in the mid‐mantle of the one‐fourth of the Earth beneath the north Pacific Ocean was obtained by a semi‐global electromagnetic induction study. Electromagnetic response functions estimated from electric field variations measured by submarine cables and geomagnetic field variations obtained by magnetic observatories and long‐term observations sites were inverted into radially symmetric conductivity distribution by taking the distribution of land and ocean at the surface into account. As a most preferred model, a smooth conductivity‐depth profile was obtained with two abrupt increases that possibly correspond to the seismic discontinuities at 410 and 660 km.
Magnetic zenith enhancement of HF radio‐induced airglow production at HAARP
Authors: Pedersen T. R. , McCarrick M. , Gerken E. , Selcher C. , Sentman D. , Carlson H. C. , Gurevich A.
Published: May 2003

Airglow production at various beam positions relative to the magnetic field was investigated as part of an optics campaign at HAARP in February 2002. Strong emissions up to several hundred Rayleigh at 630.0 nm and more than 50 R at 557.7 nm were produced in a small spot approximately 6° in diameter located near the magnetic zenith when the transmitter beam was directed up the magnetic field. This effect was observed hundreds of times over a wide range of frequencies and ionospheric conditions. The spot at HAARP appears on average just equatorward of the nominal magnetic field direction, deflects somewhat toward the beam center when the beam is scanned, and varies slightly in size with transmitter frequency. Red‐to‐green ratios as low as 3 were observed, with both wavelengths showing significant onset delay. Identifiable enhancements in red‐line emission were produced down to 2 MW ERP in a power ramp experiment.
Radiative forcing of climate by historical land cover change
Authors: Matthews H. Damon , Weaver Andrew J. , Eby Michael , Meissner Katrin J.
Published: May 2003

The radiative effect of changing human land‐use patterns on the climate of the past 300 years is discussed through analysis of a series of equilibrium and transient climate simulations using the UVic Earth System Climate Model. Land‐surface changes are prescribed through varying land cover type, representing the replacement of natural vegetation by human agricultural systems from 1700 to 1992. All land cover simulations show a cooling in the range of 0.09 to 0.22°C with larger regional changes caused by local positive feedbacks.
Isostatic response and anisotropy of the Eastern Himalayan‐Tibetan Plateau: A reappraisal using multitaper spectral analysis
Authors: Rajesh R. S. , Stephen Jimmy , Mishra D. C.
Published: May 2003

We estimate the variation in strength of the Eastern Himalayan‐Tibetan lithosphere from 2D gravity and topography coherence functions calculated with the Thomson‐Slepian multitaper technique. The coherence shows evidence of structural weakness of the plate in the N‐S direction, aligned with the direction of maximum compression. The Tibetan plateau is characterized by an effective elastic thickness (Te) that is much lower than would be expected from its large crustal thickness and the additional strength contributed by a coherently folded mantle inferred from shear wave splitting. The seismogenic thickness indicates that only the upper crust is contributing to the elastic strength and not the mantle. The predominant weakness of the lithosphere in the N‐S direction revealed from the anisotropy in the coherence function suggests that the mantle may not be directly coupled to crustal deformation beneath the Tibetan plateau.
Variation of CO2/SO2 ratio in volcanic plumes of Miyakejima: Stable degassing deduced from heliborne measurements
Authors: Shinohara H. , Kazahaya K. , Saito G. , Fukui K. , Odai M.
Published: May 2003

Heliborne measurements of CO2/SO2 ratio in a volcanic plume were performed at Miyakejima volcano, which has degassed intensively since September, 2000. The repeated measurements started in October, 2000 and showed constant molar CO2/SO2 ratio at 0.75 ± 0.25 despite decreased SO2 emission rate from 42 kt/d in late 2000 to 16 kt/d in late 2001. The CO2 emission rate also decreased from 21 kt/d in late 2000 to 8 kt/d in late 2001. The CO2 content in the magma is estimated to be 1200 ppm based on the mole ratio and S content in melt inclusions (1300 ppm). The estimated CO2 content corresponds to a saturation pressure of 280 MPa suggesting the presence of CO2‐rich bubbles in the magma chamber located at 4 km. The constant CO2/SO2 ratio over the year implies a stable magma degassing process without a change in the composition of the degassing magma.
Upper mantle P velocity structure beneath the Baikal Rift from modeling regional seismic data
Authors: Brazier Richard A. , Nyblade Andrew A.
Published: May 2003

Uppermost mantle P wave velocity structure beneath the Baikal rift and southern margin of the Siberian Platform has been investigated by using a grid search method to model Pnl waveforms from two moderate earthquakes recorded by station TLY at the southwestern end of Lake Baikal. The results yielded a limited number of successful models which indicate the presence of upper mantle P wave velocities beneath the rift axis and the margin of the platform that are 2–5% lower than expected. The magnitude of the velocity anomalies and their location support the presence of a thermal anomaly that extends laterally beyond the rift proper, possibly created by small‐scale convection or a plume‐like, thermal upwelling.
Upstream magnetospheric ion flux tube within a magnetic cloud: Wind/STICS
Authors: Posner Arik , Liemohn Michael W. , Zurbuchen Thomas H.
Published: May 2003

We present a case study of a remarkable upstream O+ and N+ ion outflow event. We present observational evidence for spatially structured outflow of these Low Charge State Heavy Ions (LCSHIs) of magnetospheric origin along a small reconnected field line region within the framework of a magnetic cloud of an ICME. From the particles' in situ 3D distribution function we conclude that in this case the interaction of the outflow with the bow shock is small. We conclude further that the gyrophases of outflowing ions at the reconnection point are randomly distributed. This leads to the formation of a flux tube with a specific geometry. In particular, the outflow reveals spatial dispersion and non‐gyrotropy. This result has implications for the size of the dayside reconnection site.
A comparison of wind products in the context of ENSO prediction
Authors: Chen Dake
Published: May 2003

Four different wind products are evaluated in terms of their application to ENSO prediction. These wind products have been used to initialize an intermediate ocean‐atmosphere coupled model for monthly retrospective forecasts from 1980 to 2002. The wind product that includes satellite scatterometer data has the highest scores, with the NCEP reanalysis and the new FSU objective analysis closely behind. The latter is a major improvement over the old FSU subjective analysis which has some serious problems in recent years. It seems that the wind products from remote sensing, in‐situ observation and model reanalysis are all useful for ENSO prediction. At present, an ensemble of forecasts initialized with various wind data sets is probably our best bet.
Water yield responses to high and low spatial resolution climate change scenarios in the Missouri River Basin
Authors: Stone Mark C. , Hotchkiss Rollin H. , Mearns Linda O.
Published: May 2003

Water yield responses to two climate change scenarios of different spatial scales were compared for the Missouri River Basin. A coarse‐resolution climate change scenario was created from runs of the Commonwealth Scientific and Industrial Research Organization General Circulation Model (CSIRO GCM). The high‐resolution climate change scenario was developed using runs of the Regional Climate Model RegCM, for which the GCM provided the initial and lateral boundary conditions. Water yield responses to the high‐ and low‐resolution climate change scenarios were investigated using the Soil and Water Assessment Tool (SWAT). Basin‐wide water yield increased for both GCM and RegCM scenarios but with an overall greater increase for the RegCM scenario. Significant differences in water yields were found between the GCM and RegCM climate scenarios.
When will Voyager 1 and 2 cross the termination shock?
Authors: Izmodenov Vlad , Gloeckler George , Malama Yuri
Published: May 2003

Our Solar System moves through a warm (∼6,500 K), partly ionized local interstellar cloud (LIC) with a relative speed of ∼26 km/s. The solar wind interacts with the LIC to form a cavity around the Sun called the heliosphere. The solar wind meets the interstellar charged component at the heliopause, where solar wind pressure balances the pressure of the LIC. Before reaching the heliopause, the supersonic solar wind is decelerated at an extended shock wave, the heliospheric termination shock (TS). The two Voyager spacecraft are cruising away from the Sun and approaching the termination shock. Here we present predictions of when the Voyagers will encounter the termination shock by calculating the position of the TS using a numerical multi‐component model of the heliospheric interface and improved measurements of interstellar H atoms. Interstellar atoms penetrate into the heliosphere where they are ionized and detected as pickup ions by the SWICS instrument on Ulysses. We conclude that the most probable crossing of the termination shock by Voyager 1 will occur between 2007 and 2012.
Climate change during 1985–1999: Cloud interactions determined from satellite measurements
Authors: Cess Robert D. , Udelhofen Petra M.
Published: May 2003

We have extended two recent studies that present evidence for significant decadal variability in the top‐of‐atmosphere (TOA) tropical radiative energy budget by combining satellite measurements of the TOA energy budget and cloud cover with measurements of the Earth's surface temperature. The domain studied is from 40°S to 40°N. As in the prior studies, which were restricted to lower latitudes, there is a significant increase in the TOA outgoing longwave radiation during the period 1985 to 1999 together with an increase in solar (shortwave) radiation absorbed by the climate system. It is suggested that these changes are related to an observed reduction in cloud cover.
Deformation in transcurrent and extensional environments with widely spaced weak zones
Authors: Choi Eun‐seo , Gurnis Michael
Published: May 2003

Previous mechanical models of the western U.S. have concluded that plate boundary forces cannot generate far‐field deformation. Such models have ignored preexisting large‐scale lithospheric strength variations, an assumption that appears to be inconsistent with seismically determined variations in lithospheric structure. We have formulated a three‐dimensional viscous flow model with imposed plate motions, but include lateral zones of low viscosity. These models show that strain rates are concentrated in weak zones with adjacent blocks experiencing little deformation. Deformation can extend far inboard of plate boundaries, contrary to the result of previous studies with rheologically homogeneous plates, and apparently compatible with the variation is seismic velocity and GPS determined deformations in western U.S. These results suggest that plate boundary forces cannot be neglected in the deformation of the western U.S., including the Cenozoic extension of the Basin and Range Province.
Roles apparent resistivity amplitude and phase play in an aquifer's electrical‐hydraulic conductivity correlation
Authors: Purvance David T.
Published: May 2003

This paper argues how the spectral characteristics of two borehole apparent resistivity traces further corroborate two statistically significant electrical‐hydraulic (eh) conductivity correlations previously reported in Nevada's fractured welded tuffs. Even though the eh conductivity correlation is positive in one borehole and negative in the other, as explained by low pore water electrical conductivity and the absence or presence of alteration minerals, both apparent resistivity amplitude spectra are identically power‐law structured. This is interpreted to mean that eh flow is occurring along rock fractures of a common regional fractal dimension. Furthermore, both apparent resistivity phase spectra are strikingly linear, as mandated by the condition of incompressible fluids. Linear phase implies a groundwater flow that is geostatistically nonstationary in the wide sense, a complication normally not considered by hydrogeologists.
Cluster observation of a bifurcated current sheet
Authors: Runov A. , Nakamura R. , Baumjohann W. , Zhang T. L. , Volwerk M. , Eichelberger H.‐U. , Balogh A.
Published: May 2003

The current sheet structure and motion at XGSM = −19.5 RE, observed by Cluster/FGM during 1055–1107 UT on 29 August 2001, is examined. It is found that during the interval 1055–1102 UT the current sheet moves vertically up and down with a velocity of about 60 km/s. During this interval the current sheet has a bifurcated structure: electric current is concentrated in two sheets with an extended layer of weak nearly uniform magnetic field in between. In the interval 1103–1107 UT the current sheet moves slowly upward and the current sheet has a Harris‐type structure. By using four‐spacecraft timing analysis, it is shown that the fast motion and bifurcation of the current sheet are associated with a wave‐like transient propagating in the dawn‐to‐dusk direction.
A substorm‐associated drift echo of energetic protons observed by Geotail: Radial density gradient structure
Authors: Hori T. , Ohtani S. , Lui A. T. Y. , McEntire R. W. , Maezawa K. , Saito Y. , Mukai T.
Published: May 2003

We found a drifting population with a fairly long (∼several tens of minutes) dispersion at a geocentric distance >9 RE, indicating that energetic particles can lie on a closed drift path around the Earth much farther than the geosynchronous distance. In this event, Geotail was situated in the plasma sheet in the post‐midnight sector at a distance of ∼10 RE and observed a drift echo of energetic protons with energies of several tens to hundreds of keV. This drifting population showed an azimuthal sector anisotropy in particle distribution as it passed by the spacecraft. The drift echo showed a lack of duskward‐directed particle fluxes in its leading portion, became isotropic in the middle of the event, and finally showed enhanced duskward‐directed fluxes in its trailing portion. Since the magnetic field was dominated by the Bz component during this event, this sequence of anisotropy can be considered in terms of a density gradient structure of the drifting population with a scale of the order of proton gyroradius (∼0.5 RE) in the equatorial plane. Because the duskward‐directed flux at the spacecraft can be attributed to protons with their guiding centers sunward of the observation point, it is suggested that the drifting proton echo has a spatial structure such that protons are localized tailward of the spacecraft at the leading portion, while a sunward density gradient exists around the trailing portion. Thus the present study shows that a drift echo is not an uniform population but has a complicated structure with a sharp density gradient in the radial direction, which may reflect some characteristics of its source site as well as its drift path.
Increase of monoterpene emissions from a pine plantation as a result of mechanical disturbances
Authors: Schade Gunnar W. , Goldstein Allen H.
Published: May 2003

Mixing ratios and emission rates of monoterpenes were measured above a ponderosa pine plantation in the Sierra Nevada mountains before, during and after a pre‐commercial thinning in spring 2000. The thinning removed and left onsite approximately one half of the plantations biomass. Monoterpene fluxes increased tenfold during the thinning and pinene mixing ratios in excess of 3 ppb were observed, possibly altering regional atmospheric chemistry. The increase was mostly because of higher basal emission rates, but small changes in the temperature‐dependence were also found. Using an emission‐model based on these responses, the additional monoterpene emissions due to the thinning were estimated to increase emissions by a factor of forty, and yearly emissions by a factor of five. Using US tables of absolute timber removal and on site residue volumes from logging and thinning activities, we calculate that current US monoterpene emissions may be underestimated by several percent.
Saturation, pore pressure and effective stress from sandstone acoustic properties
Authors: Siggins Anthony F. , Dewhurst David N.
Published: May 2003

Acoustic velocity and Vp/Vs ratio show different responses in saturated and dry rocks under increasing differential pressures. Velocity is also shown to be sensitive to pore pressure, not just differential pressure. Under identical low differential pressure conditions, velocity is higher in sandstones when pore pressure is high during simulation of inflationary overpressure conditions. Vp/Vs ratios of sandstones with high fluid pressures are shown to lie between dry conditions and saturated conditions with constant and low pore pressure. Thus the velocity‐differential pressure relationship is not unique. However, the use of the measured Biot effective stress coefficient results in a unique relationship. It is postulated that higher velocity and different Vp/Vs ratios are caused by loss of compliance in microfractures due to stiffening by increasing fluid pressure.
Isotopic study of lead transfer at the interface soil‐plants‐atmosphere
Authors: Freydier Rémi , Viers Jérôme
Published: May 2003

Soil, rock, plant and rainwater samples have been collected in the evergreen forest of Cameroon and analyzed for their 206Pb/207Pb and 208Pb/207Pb ratios and Pb concentrations. Plant isotopic ratios exhibit the same values than the rains collected at the same site and higher values than the ones observed for surface soils (litter and 20 cm deep). The isotopic composition of rains and plants is in agreement with a mixing model between an anthropogenic end‐member and a Saharan particle end‐member. This indicates that the enrichment of lead in rainwaters is anthropogenic in origin and that the presence of lead in plants is essentially due to the assimilation of atmospheric lead directly from their leaves and/or from their bark.
Antiproton radiation belt produced by cosmic rays in the Earth magnetosphere
Authors: Gusev Anatoly A. , Jayanthi Udaya B. , Choque Kenny T. , Pugacheva Galina I. , Schuch Nelson , Spjeldvik Walther N.
Published: May 2003

The possible existence of noticeable fluxes of antiparticles in the Earth magnetosphere has been predicted on theoretical considerations in this article. The antiprotons expected at several hundred kilometers of altitudes, we do not believe are of direct extraterrestrial origin, but are the natural products of nuclear reactions of the high‐energy primary cosmic rays (CR) with the constituents of the terrestrial atmosphere. Extraterrestrial, galactic antiprotons are themselves of secondary in origin, i.e. they are born in nuclear reactions of the same CR particles passing through 5–7 g/cm2 of interstellar matter encountered during their lifetime in the Galaxy. We expect that the fluxes of magnetospheric antiprotons to be higher compared to the interstellar fluxes because the fluxes get accumulated due to confinement by the magnetic field of the Earth. We present the results of the computations of the antiproton fluxes at 50 MeV to several GeV energies due to the CR particle interactions with the matter in the interstellar space, and also with the residual atmosphere at altitudes of ∼1000 km over the Earth's surface. The estimates show that the magnetospheric antiproton fluxes are two orders of magnitude greater compared to the interstellar fluxes measured at energies < 1 GeV.
Exploring linkages between coastal progradation rates and the El Niño Southern Oscillation, Southwest Washington, USA
Authors: Moore L. J. , Kaminsky G. M. , Jol H. M.
Published: May 2003

Climate oscillations such as the El Niño‐Southern Oscillation (ENSO) affect storm tracks, wave climate, precipitation and sea level in the U.S. Pacific Northwest. The impacts of these changes on coastal behavior have not been investigated in detail beyond the study of recent El Niño events, largely because existing historical records of coastal behavior are not of sufficient resolution to study annual responses to climatic forcing. We compare a newly developed annual record of coastal progradation for a location on the Washington coast, generated using high‐resolution subsurface ground penetrating radar (GPR), with ENSO indices. This analysis reveals higher rates of seaward coastal growth following the warm, El Niño, ENSO phase and lower rates of coastal growth following the cold, La Niña, ENSO phase. The observed relationship between ENSO and progradation, although weak, is hypothesized to result from differences in sediment transport patterns and beach recovery rates following El Niño and La Niña events.
Diurnal variations in vertical strain observed in a temperate valley glacier
Authors: Sugiyama Shin , Gudmundsson G. Hilmar
Published: May 2003

During a period of diurnal fluctuations in glacial flow speed, vertical strain was measured with sub‐daily temporal resolution on Unteraargletscher, Switzerland. Mean vertical strain in boreholes up to 300‐m deep in 400‐m‐thick ice was found to fluctuate diurnally. Vertical strain rates were tensile in the daytime and compressive at night, with a magnitude of up to 10−3 day−1. Horizontal surface strain was observed to fluctuate in a manner consistent with the vertical deformation. Diurnal surface flow speed variations correlated well with basal water pressure suggesting a basal control on temporal flow variations. Nevertheless, the strain rate measurements indicated that changes in surface flow speed are affected by internal ice deformation and not a direct measure of local basal motion. Basal conditions in the surrounding neighborhood and their temporal variations take an important role in short‐term glacial flow fluctuations.
Experimentally induced root mortality increased nitrous oxide emission from tropical forest soils
Authors: Varner Ruth K. , Keller Michael , Robertson Jillana R. , Dias Jadson D. , Silva Hudson , Crill Patrick M. , McGroddy Megan , Silver Whendee L.
Published: May 2003

We conducted an experiment on sand and clay tropical forest soils to test the short‐term effect of root mortality on the soil‐atmosphere flux of nitrous oxide, nitric oxide, methane, and carbon dioxide. We induced root mortality by isolating blocks of land to 1 m using trenching and root exclusion screening. Gas fluxes were measured weekly for ten weeks following the trenching treatment. For nitrous oxide there was a highly significant increase in soil‐atmosphere flux over the ten weeks following treatment for trenched plots compared to control plots. N2O flux averaged 37.5 and 18.5 ng N cm−2 h−1 from clay trenched and control plots and 4.7 and 1.5 ng N cm−2 h−1 from sand trenched and control plots. In contrast, there was no effect for soil‐atmosphere flux of nitric oxide, carbon dioxide, or methane.
Transverse dimensions of chorus in the source region
Authors: Santolík O. , Gurnett D. A.
Published: May 2003

We report measurement of whistler‐mode chorus by the four Cluster spacecraft at close separations. We focus our analysis on the generation region close to the magnetic equatorial plane at a radial distance of 4.4 Earth's radii. We use both linear and rank correlation analysis to define perpendicular dimensions of the sources of chorus elements below one half of the electron cyclotron frequency. Correlation is significant throughout the range of separation distances of 60–260 km parallel to the field line and 7–100 km in the perpendicular plane. At these scales, the correlation coefficient is independent for parallel separations, and decreases with perpendicular separation. The observations are consistent with a statistical model of the source region assuming individual sources as gaussian peaks of radiated power with a common half‐width of 35 km perpendicular to the magnetic field. This characteristic scale is comparable to the wavelength of observed waves.
Permanent shadow in simple craters near the lunar poles
Authors: Bussey D. Ben J. , Lucey Paul G. , Steutel Donovan , Robinson Mark S. , Spudis Paul D. , Edwards Kay D.
Published: May 2003

An analysis of simple craters in the lunar polar regions has produced new values for the minimum amount of permanent shadow in these areas, 7500 km2 and 6500 km2, for the north and south pole respectively. These values were obtained by conducting illumination simulations of realistically shaped simple craters, <20 km in diameter, to investigate the size and latitudinal extent of permanently shadowed regions near the lunar poles. Craters as far as 20° from the pole still contain significant amounts of permanent shadow. Larger simple craters have slightly more relative permanent shadow than smaller craters. Seasonal effects are independent of crater size and latitude, with a crater having 15% more of its interior shadowed during a lunar day in winter than in summer.
Tidal observations on floating ice using a single GPS receiver
Authors: King Matt , Aoki Shigeru
Published: May 2003

We measure ocean tides as experienced by sea ice or ice shelves using a single GPS receiver. Such a method allows for tidal measurements to be made with the same precision regardless of its distance from a GPS base station, since such a base station is not required. Single epoch observations are shown to be accurate to about 50 mm when compared with concurrent Bottom Pressure Gauge (BPG) observations. The differences between the GPS and BPG observations are largely free from power at tidal frequencies. Furthermore, harmonic tidal analyses show that these GPS observations allow the correct determination of diurnal and semi‐diurnal tidal constituents, meaning that observations of this type can be assimilated into numerical tide models.
Vapor pressure above ice at temperatures below 170 K
Authors: Mauersberger Konrad , Krankowsky Dieter
Published: May 2003

Ice clouds in the earth's atmosphere and the presence of ices in comets and on planetary surfaces have raised the interest in the formation and existence of ice particles and of ice in bulk matter. Of special importance are the saturated vapor pressures well below 200 K. Marti and Mauersberger [1993] published a simple, experimentally derived equation that covers the temperature range from 273 to 170 K. Measurements have been extended toward 165 K and they show a clear departure in saturated vapor pressures when compared to a single‐fit Clausius‐Clapeyron expression over the entire temperature range. The equation derived for temperatures below169 K, log P = −3059/T + 14.88 (P in Pa and T in K), is significant for extrapolations of ice vapor pressures to temperatures in the mesosphere where clouds form well below 160 K.
Combined use of satellite and surface observations to infer the imaginary part of refractive index of Saharan dust
Authors: Sinyuk Alexander , Torres Omar , Dubovik Oleg
Published: May 2003

We present a method for the retrieval of the imaginary part of refractive index of desert dust aerosol at near UV wavelengths. The method uses observations of radiances at 331 and 360 nm by the Total Ozone Mapping Spectrometer, and aerosol optical depth measurements by the Aerosol Robotic Network. The derived values of imaginary part of refractive index of Saharan dust aerosol at 360 nm are significantly lower than previously reported values. The average retrieved values vary between 0.0054 and 0.0066 for different geographical locations. The results reported in this work are in good agreement with the results of several recent investigations.
Nonlinear evolution of dust waves driven by cross‐field electron currents
Authors: Scales Wayne A. , Chae Gyoo Soo
Published: May 2003

The nonlinear evolution of dust waves generated by a low‐frequency Hall current instability in a magnetized collisional dusty plasma is investigated with theory and nonlinear numerical simulations. This instability is believed to have broad applications to irregularity production in regions where dust is present in the earth's ionosphere such as noctilucent clouds and meteor trails. The instability is driven by an electron current and is an analog, in the dust acoustic type wave regime, of the well‐known Farley‐Buneman instability. The results indicate that the instability nonlinearly saturates with dust heating and the production of secondary waves that propagate in a direction perpendicular to the primary dust acoustic type waves.