bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact of permeable conduits on solute transport in aquitards: Mathematical models and their application
Authors: Harrington Glenn A. , Hendry M. Jim , Robinson Neville I.
Published: May 2007

The migration of contaminants through porous conduits (for example, sand layers) in aquitards, or any preferential flow feature within a low‐permeability matrix, can be significantly retarded via diffusion into the matrix and processes such as sorption and decay. Previous solutions for simulating contaminant transport in these types of environments have been limited to a parallel‐plate approach such as that used in studies of fractured rock aquifers. A major drawback of using these approaches is that they cannot account for the radial component of diffusion that occurs from circular‐ or elliptical‐sectioned conduits. We have developed solutions for both of the latter cases and compared results from generic simulations to those obtained with a conventional parallel‐plate model. The results demonstrated using a circular conduit approach can produce concentration profiles for both the conduit and surrounding matrix that are up to several orders of magnitude lower than those predicted using parallel‐plate models. The solutions for elliptical‐section conduits provide concentration profiles that are bounded by the circular‐ and parallel‐plate models. We also present several generic simulations to demonstrate the effects of conduit radius and average groundwater flow velocity on concentration profiles. Finally, the circular conduit model is applied to a clay‐rich till aquitard in southern Saskatchewan, Canada to provide insight into an anomalous dissolved chloride peak in the vertical pore water profile. The model demonstrates that the source of the high Cl− could be as far as 10–100 km from the site (although this distance may be unrealistic) and allows estimation of the Cl− concentration at the source. We envisage that the solutions for conduit diffusion will have far wider applications than just aquitard studies, and future uses may include tracer tests in karstic and fractured aquifers.
Comparison of Mg/Ca‐ and alkenone‐based sea surface temperature estimates in the fresh water–influenced Gulf of Guinea, eastern equatorial Atlantic
Authors: Weldeab Syee , Schneider Ralph R. , Müller Peter
Published: May 2007

This study presents a comparison of sea surface temperature (SST) estimates based on Mg/Ca ratios of Globigerinoides ruber and alkenone unsaturation index (U37K′) in core sediment recovered from the Gulf of Guinea, eastern equatorial Atlantic. Mg/Ca‐ and U37K′‐based SST estimates yield fairly comparable results for the time interval 21,000–14,500 years and for the late Holocene. The early and middle Holocene, however, are largely characterized by a discrepant trend, with warm Mg/Ca and cold U37K′ based SST estimates. This discrepant SST trend is accompanied by low sea surface salinity estimates (high riverine runoff) and biogenic sediment, which is characterized by high biogenic opal content, low carbonate content, and relatively low alkenone concentration. We hypothesize that the discrepancy in the reconstructed SSTs during the middle and early Holocene presumably suggests a period of elevated riverine input of dissolved silica and dominantly siliceous phytoplankton bloom in a low saline and warm surface water, while alkenone producers were likely prevalent in a season of cold SST and low riverine silica input. This study suggests that changes in the local hydrography and nutrient input have strong influence on the U37K′‐based SST estimate that may be unraveled by combining different SST proxies.
Modeling the sharp compositional interface in the Pu`u `Ō`ō magma reservoir, Kīlauea volcano, Hawai`i
Authors: Mittelstaedt Eric , Garcia Michael O.
Published: May 2007

Lavas from the early episodes of the Pu`u `Ō`ō eruption (1983–1985) of Kīlauea Volcano on the island of Hawai`i display rapid compositional variation over short periods for some episodes, especially the well‐sampled episode 30 with ∼2 wt% MgO variation in <4 hours. Little chemical variation is observed within the episode 30 lavas before or after this abrupt change, suggesting a sharp compositional interface within the Pu`u `Ō`ō dike‐like shallow reservoir. Cooling‐induced crystal fractionation in this reservoir is thought to be the main control on intraepisode compositional variation. Potential explanations for a sharp interface, such as changing reservoir width and wall rock thermal properties, are evaluated using a simple thermal model of a dike‐like body surrounded by wall rock with spatially variable thermal conductivity. The model that best reproduces the compositional data involves a change in wall rock thermal conductivity from 2.7 to 9 W m−1 C−1, which is consistent with deep drill hole data in the east rift zone. The change in thermal conductivity may indicate that fluid flow in the east rift zone is restricted to shallow depths possibly by increasing numbers of dikes acting as aquicludes and/or decreasing pore space due to formation of secondary minerals. Results suggest that wall rock thermal gradients can strongly influence magma chemistry in shallow reservoirs.
Fifth‐generation lithospheric magnetic field model from CHAMP satellite measurements
Authors: Maus Stefan , Lühr Hermann , Rother Martin , Hemant Kumar , Balasis George , Ritter Patricia , Stolle Claudia
Published: May 2007

Six years of low‐orbit CHAMP satellite magnetic measurements have provided an exceptionally high‐quality data resource for lithospheric magnetic field modeling and interpretation. Here we describe the fifth‐generation satellite‐only magnetic field model MF5. The model extends to spherical harmonic degree 100. As a result of careful data selection, extensive corrections, filtering, and line leveling, the model has low noise levels, even if evaluated at the Earth's surface. The model is particularly suited for inferring large‐scale structure and composition of the lithosphere. It is also meant to serve as the long‐wavelength part of continental‐ and global‐scale marine and aeromagnetic anomaly maps.
Coupling of perturbations in the solar wind density to global Pi3 pulsations: A case study
Authors: Han D.‐S. , Yang H.‐G. , Chen Z.‐T. , Araki T. , Dunlop M. W. , Nosé M. , Iyemori T. , Li Q. , Gao Y.‐F. , Yumoto K.
Published: May 2007

A typical Pi3 pulsation is examined by magnetic field measurements from multiple satellites and ground stations. Low‐latitude ground observations with a wide longitudinal span indicate that the amplitude of the Pi3 pulsation peaks on the dayside and is gradually decreasing toward the nightside. This effect and the fact that the wave phase on the dayside leads that on the nightside, imply that the source of the Pi3 lies on the dayside. Variations in solar wind dynamic pressure observed by the GEOTAIL satellite (just outside of the magnetosphere) are highly correlated with these ground magnetic field variations. We argue in this case that the global Pi3 pulsation is directly driven by impulsive variations in the solar wind dynamic pressure. The Pi3 pulsation observed along the latitudinal magnetometer chain at 0930LT shows significant equatorial enhancement and additional observations along a latitudinal chain at 1630LT show that the phase of the Pi3 pulsation at high latitudes lags behind that at low latitudes. The low‐altitude polar orbiting satellite Oersted also observed this pulsation in the dayside inner magnetosphere. The B∥ (northward) component at Oersted is strictly out of phase with the X component observed at the dip equator below the spacecraft path, which indicates that the Pi3 pulsation at the dip equator is caused by oscillation of an ionospheric current. We propose that the Pi3 pulsations at different latitudes are generated by different mechanisms.
Effects of overshoots on electron distributions upstream and downstream of quasi‐perpendicular collisionless shocks
Authors: Yuan Xingqiu , Cairns Iver H. , Robinson P. A. , Kuncic Z.
Published: May 2007

We use test particle simulations to investigate the effect of overshoots on electron distributions upstream and downstream of quasi‐perpendicular collisionless shocks as functions of angle θbn between upstream magnetic field and shock normal. The main results are: (1) The development of overshoots leads to obvious loss cone structures in upstream electron distributions, increases the reflection of upstream electrons, and reduces the leakage of downstream electrons. An electron beam associated with the escape cutoff effect exists in upstream reduced electron distribution functions for large θbn shocks. (2) Overshoots significantly affect the downstream electron distribution, too, preventing the upstream and downstream electrons with high perpendicular speeds from crossing the shock and leading to a loss cone and beam features rather than arc features in downstream distributions. (3) The shock‐reflected electrons conserve their magnetic moments on average. Demagnetized electrons are mainly those transmitted, and most are overadiabatic electrons. The assumption of conservation of magnetic moment is an increasingly good approximation as θbn increases. (4) The major temporal changes in ramp overshoot structure expected from shock nonstationarity should lead to significant changes in electron distributions and associated waves upstream and downstream.
Magnetospheric Convection near a Drainage Plume
Authors: Lin Chin S. , Yeh Huey‐Ching , Sandel Bill R. , Goldstein J. , Rich Frederick J. , Burke William J. , Foster J. C.
Published: May 2007

We report on equatorial convection associated with a plasmaspheric drainage plume using simultaneous observations from five satellites. During the early recovery phase of the July 2000 Bastille Day magnetic storm, the Extreme Ultraviolet sensor on the Magnetopause‐to‐Aurora Global Exploration satellite detected the plume near 16:00–17:00 magnetic local time extending outward to L ≈ 2.8. The plasmaspheric boundary was near L = 2 at other local times. We mapped simultaneously measured ionospheric plasma drifts from ROCSAT‐1 and three Defense Meteorological Satellite Program (DMSP) spacecraft along magnetic field lines to infer equatorial convection velocities in the inner magnetosphere. The zonal component of convection derived from ROCSAT‐1 ion‐drift measurements had a sharp, positive azimuthal gradient near the plume’s boundaries, reversing direction from westward to eastward. The meridional profile of horizontal velocities deduced from DMSP measurements shows a large, westward‐flowing subauroral polarization stream (SAPS) located outside the plasmapause. The peak velocity of the SAPS centered at a radial distance of L ≈ 2.8 with a full width of ∼1 RE. In the inertial frame of reference, equatorial plasmas flowed toward the plume from both its day and evening sides, suggesting a negative gradient in the equatorial azimuthal velocity that was largest near the plume’s outermost boundary. These observations provide new evidence about diversion of SAPS plasma flows and distinctive azimuthal velocity patterns in the vicinity of plasmaspheric plumes.
EL ‐ a possible indicator to monitor the magnetic field stretching at global scale during substorm expansive phase: Statistical study
Authors: Meurant M. , Gérard J.‐C. , Blockx C. , Spanswick E. , Donovan E. F. , Hubert B. , Coumans V. , Connors M.
Published: May 2007

An interesting open question of magnetospheric physics is the understanding of the dynamics of the magnetotail. The question of the field stretching is even more challenging during substorm periods, mainly because of the short time scales involved during such explosive events. In this study, we asses the ability of global scale proton auroral imaging to provide information on the tail stretching during active periods. We base our investigation on more than 250 isolated substorms observed by IMAGE‐SI12 between 2000 and 2002. Applying the algorithm proposed by Donovan et al. (2003) for ground based observations to IMAGE‐SI12 data, we determine the Equatorial Limit (EL) of the oval and propose to use it as an indicator of the tail stretching. Simultaneous comparison with GOES‐8 allows us to estimate how strong is the relationship between the EL position deduced from SI12 and the magnetic field stretching. The EL indicator is shown to be consistent with previous studies (Sergeev and Gvozdevsky (1995) and Blockx et al. (2005)) and is found to be located in average ∼1 degree equatorward of the limit deduced from DMSP measurements. The time evolution of the EL magnetic latitude is also presented for different local times relative to the onset position. This evolution of the EL index presents an asymmetric shape following the time of onset, suggesting a more important stretching of the tail duskward of the onset position. This asymmetric stretching is consistent with GOES‐8 in situ measurements.
Geometry and P and S velocity structure of the “African Anomaly”
Authors: Wang Yi , Wen Lianxing
Published: May 2007

We constrain the geometry and P and S velocity structure of a low‐velocity anomaly in the lower mantle beneath southern Africa (we term it the “African Anomaly”) on the basis of forward traveltime and waveform modeling of seismic data sampling a great arc across the anomaly from the East Pacific Rise to the Japan Sea. Our collected data set consists of direct S, direct P, Sdiff, ScS, PcP, SKS, and SKKS phases recorded by three temporary broadband PASSCAL seismic arrays deployed in Africa between 1994 and 2002, the Tanzania seismic array (1994–1995), the Kaapvaal seismic array (1997–1999), and the Ethiopia/Kenya seismic array (2000–2002) for earthquakes occurring in the East Pacific Rise, Drake Passage, South Sandwich islands, Iran, Hindu Kush, Xinjiang, and the Japan Sea. The seismic data provide excellent sampling of the African Anomaly in the lower mantle along the specific great arc. In order to accurately account for the contributions from the African Anomaly, we relocate all the events using a global seismic shear velocity tomographic model and seismic data recorded by the Global Seismographic Network and correct for the contributions from the seismic heterogeneities outside the African Anomaly. The seismic observations suggest that the African Anomaly locally extends 1300 km above the core‐mantle boundary beneath southern Africa (around −25°N, 27°E) and exhibits a “bell‐like” geometry with both the southwestern and the northeastern flanks dipping toward its center with the lateral dimension of the anomaly increasing with depth. The base is about 4000 km wide extending broadly in both the southwestward and the northeastward directions. The seismic data can best be explained by a shear velocity structure with average velocity decreases of −5% in the base and −2% to −3% in the mid‐lower mantle above the base, and a compressional velocity structure with a uniform S to P velocity perturbation ratio of 3:1 for the entire African Anomaly. These geometric and velocity features suggest that the mid‐lower mantle portion of the African Anomaly is an integral component of the very low velocity province and the African Anomaly is compositionally distinct and geologically stable.
Earthquake mechanics and deformation in the Tonga‐Kermadec subduction zone from fault plane orientations of intermediate‐ and deep‐focus earthquakes
Authors: Warren Linda M. , Hughes Amanda N. , Silver Paul G.
Published: May 2007

We make use of rupture directivity to analyze 82 deep earthquakes (≥100 km depth) in the Tonga‐Kermadec subduction zone. Identifying the fault planes for 25 of them, we are able to place new constraints on both the physical mechanism of intermediate‐ and deep‐focus earthquakes and deformation within the subducting slab. We find that half of deep earthquakes with MW ≥ 6 have detectable directivity. We compare the obtained fault orientations with those expected for the reactivation of outer‐rise normal faults and with those expected for the creation of new faults in response to the ambient stress field. Earthquakes >300 km depth match the patterns expected for the creation of a new system of faults: we observe both subhorizontal and subvertical fault planes consistent with a downdip‐compressional stress field. Slip along these faults causes the slab to thicken. Rupture propagation shows no systematic directional pattern. In contrast, at intermediate depths (100–300 km), all ruptures propagate subhorizontally and all identified fault planes, whether in the upper or lower region of the double seismic zone, are subhorizontal. Rupture propagation tends to be directed away from the top surface of the slab. After accounting for the angle of subduction, the subhorizontal fault plane orientation is inconsistent with the orientation of outer‐rise normal faults, allowing us to rule out mechanisms that require the reactivation of these large surface faults. Subhorizontal faults are consistent with only one of the two failure planes expected from the slab stress field, suggesting that isobaric rupture processes or preexisting slab structures may also influence the fault plane orientation. If all deformation takes place on these subhorizontal faults, it would cause the slab to thin. Assuming the slab is incompressible, this implies that the slab is also lengthening and suggests that slab pull rather than unbending is the primary force controlling slab seismicity at intermediate depths.
Altimetry and drifter data assimilations of loop current and eddies
Authors: Lin X.‐H. , Oey L.‐Y. , Wang D.‐P.
Published: May 2007

The goal is to quantify in an eddy‐rich ocean environment the accuracy of currents obtained from a multi‐level primitive‐equation ocean model that assimilates altimetry sea‐surface height anomaly (SSHA) and surface drifters. The 1999–2000 period in the Gulf of Mexico is chosen for the availability of drifters and Acoustic Doppler Current Profiler (ADCP) measurements in the loop current and eddies during that period. Sequential assimilations of SSHA and/or currents with statistical‐interpolation schemes are used. Experiments initialized with and without altimetry and/or drifter assimilations, including a forecast case (without assimilation) for comparison, are conducted. It is shown that the SSHA + Drifter analysis consistently outperforms the analysis that assimilates only SSHA, especially at smaller scales. Drifter‐assimilation alone also constraints the pressure field, such that the loop and eddies compare quite favorably with altimetry SSH field. When compared against independent ADCP data, the analyses with either SSHA or SSHA + Drifter assimilation yield amplitude and phase of analysis‐to‐observed complex (velocity) correlation of 0.76∼0.86 and 0.3°∼7°, respectively. The mean speed and direction (absolute) errors are 0.4–5 cm s−1 (1∼10% errors) and 10°∼20°, respectively. The correlations of the two dominant empirical orthogonal function (EOF) modes with the corresponding observation modes at a yearlong mooring over the northern slope are: mode‐1 ≈ 0.88∼0.93 and mode‐2 ≈ 0.5∼0.63. Both show vertically coherent but strongly sheared modes 1 and 2 representing propagation eddies and reversing mode‐3 that intensifies for z < −300 m.
Ice Shelf Water plume flow beneath Filchner‐Ronne Ice Shelf, Antarctica
Authors: Holland Paul R. , Feltham Daniel L. , Jenkins Adrian
Published: May 2007

A two‐dimensional plume model is used to study the interaction between Filchner‐Ronne Ice Shelf, Antarctica and its underlying ocean cavity. Ice Shelf Water (ISW) plumes are initiated by the freshwater released from a melting ice shelf and, if they rise, may become supercooled and deposit marine ice due to the pressure increase in the in situ freezing temperature. The aim of this modeling study is to determine the origin of the thick accretions of marine ice at the base of Filchner‐Ronne Ice Shelf and thus improve our understanding of ISW flow paths. The model domain is defined from measurements of ice shelf draft, and from this ISW the model is able to predict plumes that exit the cavity in the correct locations. The modeled plumes also produce basal freezing rates that account for measured marine ice thicknesses in the western part of Ronne Ice Shelf. We find that the freezing rate and plume properties are significantly influenced by the confluence of plumes from different meltwater sources. We are less successful in matching observations of marine ice under the rest of Filchner‐Ronne Ice Shelf, which we attribute primarily to this model’s neglect of circulations in the ocean outside the plume.
A climatological study of evapotranspiration and moisture stress across the continental United States based on thermal remote sensing: 1. Model formulation
Authors: Anderson Martha C. , Norman John M. , Mecikalski John R. , Otkin Jason A. , Kustas William P.
Published: May 2007

Due to the influence of evaporation on land‐surface temperature, thermal remote sensing data provide valuable information regarding the surface moisture status. The Atmosphere‐Land Exchange Inverse (ALEXI) model uses the morning surface temperature rise, as measured from a geostationary satellite platform, to deduce surface energy and water fluxes at 5–10 km resolution over the continental United States. Recent improvements to the ALEXI model are described. Like most thermal remote sensing models, ALEXI is constrained to work under clear‐sky conditions when the surface is visible to the satellite sensor, often leaving large gaps in the model output record. An algorithm for estimating fluxes during cloudy intervals is presented, defining a moisture stress function relating the fraction of potential evapotranspiration obtained from the model on clear days to estimates of the available water fraction in the soil surface layer and root zone. On cloudy days, this stress function is inverted to predict the soil and canopy fluxes. The method is evaluated using flux measurements representative at the watershed scale acquired in central Iowa with a dense flux tower network during the Soil Moisture Experiment of 2002 (SMEX02). The gap‐filling algorithm reproduces observed fluxes with reasonable accuracy, yielding ∼20% errors in ET at the hourly timescale, and 15% errors at daily timesteps. In addition, modeled soil moisture shows reasonable response to major precipitation events. This algorithm is generic enough that it can easily be applied to other thermal energy balance models. With gap‐filling, the ALEXI model can estimate hourly surface fluxes at every grid cell in the U.S. modeling domain in near real‐time. A companion paper presents a climatological evaluation of ALEXI‐derived evapotranspiration and moisture stress fields for the years 2002–2004.
Examinations of ice formation processes in Florida cumuli using ice nuclei measurements of anvil ice crystal particle residues
Authors: Prenni Anthony J. , DeMott Paul J. , Twohy Cynthia , Poellot Michael R. , Kreidenweis Sonia M. , Rogers David C. , Brooks Sarah D. , Richardson Mathews S. , Heymsfield Andrew J.
Published: May 2007

A continuous flow diffusion chamber (CFDC) was used to measure ice formation by cloud particle residuals during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers‐Florida Area Cirrus Experiment. These measurements were directed toward determining the relative contributions of homogeneous nucleation, heterogeneous nucleation, and secondary ice formation processes to the concentrations of ice crystals in anvil cirrus formed from convection. The CFDC sampled residual particles remaining after evaporation of cloud particles initially collected by a counterflow virtual impactor. This allowed, for the first time, determination of the ice nucleation ability of particles that included the presumed nuclei for cloud‐ice formation. The approach proved successful for estimating concentrations of heterogeneous ice nuclei (IN) transported into anvil clouds, but experimental issues limited measurements of homogeneous freezing and, consequently, in determining the role of secondary ice formation. Results suggest agreement within a factor of 2–3 between CFDC heterogeneous IN concentrations and anvil ice crystal concentrations in the size range above ∼30 μm. IN concentrations also correlated with ice concentrations inferred from measurements by the FSSP (Forward Scattering Spectrometer Probe). However, measured IN concentrations were nearly two orders of magnitude lower than FSSP concentrations. This difference may have resulted from homogeneous freezing, secondary ice formation, or other unidentified ice formation processes that were not fully captured by the CFDC. The data suggest that heterogeneous nucleation played a smaller role than homogeneous nucleation in determining anvil ice crystal concentrations, except during periods of strong desert dust ingestion by cumuli. Nevertheless, heterogeneous nucleation may provide the source for larger ice crystals present in anvil regions.
Estimate of radiative forcing of Asian biomass‐burning aerosols during the period of TRACE‐P
Authors: Wang Sheng‐Hsiang , Lin Neng‐Huei , Chou Ming‐Dah , Woo Jung‐Hun
Published: May 2007

The regional radiative impact of biomass‐burning aerosols in Asia is estimated using the new and detailed emission data during the experimental period of Transport and Chemical Evolution over the Pacific (TRACE‐P) in March 2001. Integration of the USA National Oceanic and Atmospheric Administration (NOAA) Hybrid Single‐Particle Lagrangian Integrated Transport model (HYSPLIT) and a solar radiative transfer model (CLIRAD‐SW) allow us to simulate the spatial and temporal distributions of black carbon (BC) and organic carbon (OC) aerosols from biomass burning in the South Asian region. It also allows us to estimate further their aerosol optical properties and radiative forcing. We find that an anticyclone over Bay of Bengal dominates the transport of pollutants of the South Asian region. The monthly mean surface concentration of OC and BC is 1.1 μg m−3 in this region. Western Myanmar has the maximum value, with the concentration reaching 12.5 μg m−3. The monthly mean clear‐sky direct shortwave radiative forcing ranges from −1.9 to 0.4 W m−2 at the top of the atmosphere and from −0.5 to −12.0 W m−2 at surface, resulting in an increase of the atmospheric heating rate from 0.01 to 0.3°C day−1. Owing to the spatial distributions of the aerosol optical depth ratio (OC/BC) and the surface albedo, there is a strong gradient of heating rate near the source regions, which may modify local circulations.
An analysis of the regulation of tropical tropospheric water vapor
Authors: Dessler A. E. , Minschwaner K.
Published: May 2007

We use a simple trajectory model to investigate the mechanisms that regulate mid‐ and upper‐tropospheric humidity. Our model advects water passively and contains no microphysics other than the requirement that water vapor is immediately removed so as to prevent the relative humidity from ever exceeding 100%. We demonstrate that our model accurately reproduces H2O measurements made by the Atmospheric Infrared Sounder onboard NASA's Aqua satellite. Our results show that, given the large‐scale circulation of the troposphere, detailed microphysics need not be included in order to accurately simulate H2O. We have also identified three preferred regions where air parcels in the mid and upper troposphere experience their final dehydration. The first is in the equatorial upper troposphere and is associated with convective outflow at the top of the tropical Hadley circulation. Final dehydration of air that detrains at potential temperature θ above ∼340 K (∼10 km) predominantly occurs here. The other two regions are found at lower altitudes in the midlatitudes of both hemispheres and are associated with dehydration during isentropic excursions to midlatitudes. Final dehydration of air that detrains at θ below ∼340 K predominantly occurs here. Finally, we analyze the water budget of the dry eastern Pacific subtropics and find that dehydration in both the equatorial upper troposphere and the midlatitudes contribute to the dryness there.
Sensitivity of global sulphate aerosol production to changes in oxidant concentrations and climate
Authors: Rae J. G. L. , Johnson C. E. , Bellouin N. , Boucher O. , Haywood J. M. , Jones A.
Published: May 2007

The oxidation of SO2 to sulphate aerosol is an important process to include in climate models, and uncertainties caused by ignoring feedback mechanisms affecting the oxidants concerned need to be investigated. Here we present the results of an investigation into the sensitivity of sulphate concentrations to oxidant changes (from changes in climate and in emissions of oxidant precursors) and to changes in climate, in a version of HadGAM1 (the atmosphere‐only version of HadGEM1) with an improved sulphur cycle scheme. We find that, when oxidants alone are changed, the global total sulphate burden decreases by approximately 3%, due mainly to a reduction in the OH burden. When climate alone is changed, our results show that the global total sulphate burden increases by approximately 9%; we conclude that this is probably attributable to reduced precipitation in regions of high sulphate abundance. When both oxidants and climate are changed simultaneously, we find that the effects of the two changes combine approximately linearly.
Aerosol optical and microphysical properties over the Atlantic Ocean during the 19th cruise of the Research Vessel Akademik Sergey Vavilov
Authors: Sakerin S. M. , Smirnov A. , Kabanov D. M. , Pol'kin V. V. , Panchenko M. V. , Holben B. N. , Kopelevich O. V.
Published: May 2007

This paper presents aerosol optical depths in the total atmospheric column, aerosol size distributions, number concentrations and black carbon mass concentrations at the deck level measured in October–December 2004 on board the R/V Akademik Sergey Vavilov. Aerosol optical depths measured within the spectral range 0.34–4.0 μm were close to background oceanic conditions (∼0.04–0.08) in the high‐latitude southern Atlantic. Angstrom parameters derived within 440–870 nm and 870–2150 nm spectral ranges did not exceed 0.6, yielding averages of 0.34 and 0.12, respectively. The mass concentration of black carbon varied within the range 0.02–0.08 μg/m3 in the 34–55°S latitudinal belt. The average of 0.04 μg/m3 (s.d. ∼0.015) is close to the reported results for the remote areas of the South Indian Ocean. Aerosol volume size distributions measured within the size range of 0.4–10 μm can be characterized by a geometric volume mean radius ∼3 μm. This is consistent with the columnar retrievals reported by the Aerosol Robotic Network (AERONET).
Cloud droplet activation of secondary organic aerosol
Authors: Prenni Anthony J. , Petters Markus D. , Kreidenweis Sonia M. , DeMott Paul J. , Ziemann Paul J.
Published: May 2007

Measurements of hygroscopicity and cloud condensation nuclei (CCN) activity were conducted on secondary organic aerosol (SOA) formed in a smog chamber. SOA precursors included α‐pinene, β‐pinene, Δ3‐carene, and toluene, representative of both naturally and anthropogenically emitted organic species. Measured CCN activation was comparable for all of the species studied and occurred at humidity conditions which are readily attained in the atmosphere. Further, there was little variation in hygroscopic growth between compounds. However, measured droplet activation conditions were inconsistent with hygroscopicity measured below water saturation and Köhler theory expressions based on Raoult’s law for several parameterizations for water activity. In the atmosphere, SOA may compose a large fraction of atmospheric particulate matter and will often exist internally mixed with inorganic species. Using the current results, we compare SOA to insoluble organic species to calculate CCN activation from mixed organic‐sulfate particles for a range of atmospheric conditions. We find that droplet activation behavior of mixed particles containing SOA is the same as that of mixed particles for which the organic component is nonhygroscopic, except for cases in which there are low particle concentrations, low updraft velocities, and the aerosol composition is dominated by organics.
Transience and persistence in the depositional record of continental margins
Authors: Jerolmack Douglas J. , Sadler Peter
Published: May 2007

Continental shelves and coastal plains are large persistent depositional landforms, which are stationary (nonmigrating) at their proximal ends and characterized by relatively steady long‐term growth. In detail, however, their surface form and stratigraphic record is built of transient freely migrating landscape elements. We derive the timescales of crossover from transient to persistent topographic forms using empirical scaling relations for mean sediment accumulation as a function of averaging time, based upon tens of thousands of empirical measurements. A stochastic (noisy) diffusion model with drift predicts all the gross features of the empirical data. It satisfies first‐order goals of describing both the surface morphology and stratigraphic completeness of depositional systems. The model crossover from noise‐dominated to drift‐dominated behavior corresponds to the empirical crossover from transport‐dominated (autogenic) transient behavior to accommodation‐dominated (subsidence) persistent behavior, which begins at timescales of 102–103 years and is complete by scales of 104–105 years. Because the same long‐term scaling behavior emerges for off‐shelf environments, it is not entirely explicable by steady subsidence. Fluctuations in sediment supply and routing probably have significant influence. At short‐term (transient) scales, the exponents of the scaling relations vary with environment, particularly the prevalence of channeled sediment transport. At very small scales, modeling sediment transport as a diffusive process is inappropriate. Our results indicate that some of the timescales of interest for climate interpretation may fall within the transitional interval where neither accommodation nor transport processes are negligible and deconvolution is most challenging.
Future climate of the north Pacific Ocean
Authors: Overland James E. , Wang Muyin
Published: May 2007

Major changes in species distribution and abundance in North Pacific marine ecosystems are often correlated with climatic shifts in the twentieth century. Species affected in the past include halibut in the Gulf of Alaska, sardine near Japan, and various species along the Oregon/California coast [Chen and Hare, 2006; Zhang et al., 2004; Peterson and Schwing, 2003]. Because these changes can affect the fishing industry, we have investigated possible future climate patterns in the North Pacific based on the evaluation of 22 coupled atmosphere‐ocean general circulation models (GCMs). These GCMs were made available to the science community for independent evaluation in preparation for the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC).
West Antarctic ice sheet change since the Last Glacial Period
Authors: Deen Tara , Hillenbrand Claus‐Dieter , Johnson Joanne , Larter Rob , Livermore Roy , Smith James , Eagles Graeme , Gohl Karsten , Kuhn Gerhard , Schenke Hans‐Werner , Uenzelmann‐Neben Gabriele , Nitsche Frank , Pudsey Carol , Dietrich Reinhard , Udintsev Gleb
Published: May 2007

The potential for rapid deglaciation, or collapse, of the 2‐million‐square‐kilometer West Antarctic Ice Sheet (WAIS) in response to climate change is one of the most serious environmental threats facing mankind. The WAIS is a marine ice sheet with large parts of its ice grounded below sea level. Complete collapse would result in a global sea level rise of approximately 5 meters, with immense social, economic, and ecological consequences.

While most experts consider such a collapse unlikely within the next few centuries, the Amundsen Sea sector has been identified as the most likely site for initiation of collapse, and it alone contains the potential to raise sea level by approximately 1.5 meters [Vaughan, 2007]. This would result in devastating flooding in many low‐lying cities (e.g., New Orleans, London), agricultural areas (e.g., Netherlands, Bangladesh) and atolls (e.g., Maldives).
Counting Atlantic tropical cyclones back to 1900
Authors: Landsea Christopher
Published: May 2007

Climate variability and any resulting change in the characteristics of tropical cyclones (tropical storms, subtropical storms, and hurricanes) have become topics of great interest and research within the past 2 years [International Workshop on Tropical Cyclones, 2006].An emerging focus is how the frequency of tropical cyclones has changed over time and whether any changes could be linked to anthropogenic global warming.
Accurate relocation of İzmit earthquake (Mw = 7.4, 1999) aftershocks in Çınarcık Basin using double difference method
Authors: Bulut Fatih , Aktar Mustafa
Published: May 2007

We relocated part of the aftershock activity in Çınarcık Basin and surrounding areas that are associated with the 1999 İzmit earthquake Mw 7.4. Double difference relocation algorithm is used to relocate the aftershocks. The data set was obtained from a temporary seismic network deployed 10 days after the main shock by cooperation between Boğaziçi University Kandilli Observatory and Earthquake Research Institute, LGIT (Grenoble), and IPGP (Paris). For a better station coverage, additional data set was obtained from a network operated by TUBITAK Marmara Research Center. Differential travel times were calculated using both arrival time readings and waveform cross correlation method. We relocated 1145 of the aftershocks and interpreted the results with emphasis on the Yalova and Tuzla cluster located within the Marmara Sea. The results show better focused seismicity patterns for the Yalova cluster, providing clear evidence for the proposed models. We present a revised location of the 1963 Çınarcık earthquake which took place in area of Yalova cluster. Finally we propose that the activity of Tuzla cluster represents a parallel subsidiary fault of the Main Marmara Fault.
Anthropogenic speed‐up of oceanic planetary waves
Authors: Fyfe John C. , Saenko Oleg A.
Published: May 2007

We have analyzed a suite of state‐of‐the‐art climate model simulations, and show that anthropogenic warming of the upper ocean produces a detectable speed‐up of low‐latitude North Pacific oceanic planetary waves by the end of the 20th century. The projected percent increase in propagation speed for the end of the 21st century is about 35% (relative to pre‐industrial) following one of the standard emissions scenarios from the Intergovernmental Panel on Climate Change. This remarkable simulated effect of oceanic warming on planetary wave propagation speed portends important observed change in interannual climate variability.
Mapping the crustal structure under active volcanoes in central Tohoku, Japan using P and PmP data
Authors: Xia Shaohong , Zhao Dapeng , Qiu Xuelin , Nakajima J. , Matsuzawa T. , Hasegawa A.
Published: May 2007

We present high‐resolution tomographic images of the crust under the active arc volcanoes in the central part of Northeast Japan (Tohoku) determined by using arrival times of first P waves and post‐critically reflected waves from the Moho discontinuity (PmP). Results of detailed resolution analyses show that the addition of PmP data can improve significantly the resolution of the lower crustal structure. After the PmP data are included in the tomographic inversion, the low‐velocity (low‐V) anomalies in the lower crust under the active volcanoes can be better imaged. The low‐V zones are clearly visible in the entire crust beneath the volcanoes extending from the surface down to the Moho discontinuity. Arc‐magma related, deep, low‐frequency microearthquakes are located around the low‐V zones in the lower crust under the volcanoes, which occurrence is probably associated with the movement of fluid magma under the volcanoes.
Derivation of the dipole map
Authors: Ali Halima , Punjabi Alkesh , Boozer Allen
Published: May 2007

In our method of maps [Punjabi et al., Phy. Rev. Lett. 69, 3322 (1992), and Punjabi et al., J. Plasma Phys. 52, 91 (1994)], symplectic maps are used to calculate the trajectories of magnetic field lines in divertor tokamaks. Effects of the magnetic perturbations are calculated using the low MN map [Ali et al., Phys. Plasmas 11, 1908 (2004)] and the dipole map [Punjabi et al., Phys. Plasmas 10, 3992 (2003)]. The dipole map is used to calculate the effects of externally located current carrying coils on the trajectories of the field lines, the stochastic layer, the magnetic footprint, and the heat load distribution on the collector plates in divertor tokamaks [Punjabi et al., Phys. Plasmas 10, 3992 (2003)]. Symplectic maps are general, efficient, and preserve and respect the Hamiltonian nature of the dynamics. In this brief communication, a rigorous mathematical derivation of the dipole map is given.
Moderate energy ions for high energy density physics experiments
Authors: Grisham L. R.
Published: May 2007

This paper gives the results of a preliminary exploration of whether moderate energy ions (≈0.3–3 MeV/amu) could be useful as modest-cost drivers for high energy density physics experiments. It is found that if the target thickness is chosen so that the ion beam enters and then leaves the target in the vicinity of the peak of the dE/dX (stopping power) curve, high uniformity of energy deposition may be achievable while also maximizing the amount of energy per beam particle deposited within the target.
The fabrication and characterization of (Pb,Ca)TiO3 pyroelectric thin films with different Ca contents
Authors: Chang C. C. , Lai Y. C.
Published: May 2007

This study uses radio-frequency sputtering methods to deposit lead titanate thin films with different contents of Ca on Pt∕Ti∕SiO2∕Si substrates to form Pb1−xCaxTiO3 (PCT) thin films. The PCT thin films contained different amounts of Ca in order to examine the influence of the Ca content on the properties of thin films. Analysis of the electrical properties of the PCT thin films revealed that their relative permittivities, dissipation factors, and pyroelectric coefficients tend to increase with the Ca content. On the other hand, the coercive field and remnant polarization decreased with an increase in the Ca content. In addition, the measured data indicated that the figure of merit for voltage (Fv) and the figure of merit for detectivity (FD) of a PCT (30) thin film are the highest with values of 0.033m2C−1 and 0.862×10−6(m3J−1)1∕2, respectively. Therefore, the PCT (30) thin film was evaluated as the best composition for manufacturing pyroelectric infrared (PIR) sensors. PCT thin films were also used to fabricate thermal PIR sensors by surface machining technology. The detectivity measurement showed that the PIR sensor with PCT (30) thin films has the highest value of D* (1.29×107cmHz1∕2∕W) at 0.3Hz.
The nano- and mesoscopic cooperative collective mechanisms of inhomogenous elastic-plastic transitions in polycrystalline TiNi shape memory alloys
Authors: Mao S. C. , Han X. D. , Zhang Z. , Wu M. H.
Published: May 2007

The cooperative collective effects of strain-induced martensitic variant accommodation in nano- and micrograined polycrystalline TiNi shape memory alloys were discovered to form macroscopic strain-induced shearing bands—the Lüders-like deformation bands. We use the in situ electron backscattered diffraction technique and the single surface trace analysis method to unambiguously elucidate the formation and propagation of shearing bands derived from the chain effect of intergrain selective martensite habit plane variants. The macroscopic characteristics of shearing bands can be well interpreted by mesoscale crystallographic features using phenomenological crystallographic theory and Schmid’s law with a strong correlation to texture. It was also discovered that the nonlinear elastic feature in the stress-strain curve prior to the stress-strain plateau correlates to lattice/grain rotations other than martensitic variant reorientation.
Deposition conditions and electrical properties of relaxor ferroelectric Pb(Fe1∕2Nb1∕2)O3 thin films prepared by pulsed laser deposition
Authors: Yan Li , Li Jiefang , Viehland D.
Published: May 2007

Epitaxial lead iron niobate thin films with thicknesses of 50nm<t<500nm have been deposited by pulsed laser deposition. We have identified the deposition conditions that result in insulating layers. These critical conditions are essential to (i) prevent semiconducting resistivity characteristics, (ii) achieve higher induced polarizations of 70μC∕cm2 under E=190kV∕mm, and (iii) obtain remanent polarizations of 17.7μC∕cm2, coercive fields of 9.5kV∕mm, and dielectric constants of ∼1200 at room temperature.
Modeling ferroelectric capacitors based on the dipole switching theory
Authors: Wang Longhai , Yu Jun , Wang Yunbo , Peng Gang , Liu Feng , Gao Junxiong
Published: May 2007

In this paper, we derived a compact model for the description of the P–E hysteresis behavior based on the dipole switching theory. Simulation results show good agreement with the experiment for various hysteresis loops, and the mathematical description can be easily combined with an electronic design automation software for circuit simulation. Therefore, the model can be used for both circuit simulation and providing better intuition for the ferroelectric material behavior.
Dielectric and pyroelectric properties of barium strontium titanate films on orthorhombic substrates with (110)//(100) epitaxy
Authors: Akcay G. , Misirlioglu I. B. , Alpay S. P.
Published: May 2007

The role of anisotropic misfit strains on the spontaneous polarization, dielectric properties, and pyroelectric response of (110) oriented Ba0.6Sr0.4TiO3 (BST 60/40) thin films on (100) orthorhombic substrates is analyzed theoretically. The anisotropic in-plane strain state and the rotation of the elastic and the electrostrictive constants of the BST 60/40 films result in strongly directional and unique properties, different from BST 60/40 films on cubic substrates with (100)BST//(100)substrate epitaxy. The thermodynamic formalism also incorporates the thickness dependence of the internal stress state due to the anisotropic relaxation of epitaxial stresses through the formation of misfit dislocations along the two in-plane directions. In particular, the model is applied to (110) BST 60/40 ferroelectric films on (100) NdGaO3 orthorhombic substrates. A more generalized analysis treating the in-plane misfit strains as parameters shows that ferroelectric phases that cannot be observed in single-crystal perovskite ferroelectrics can be stabilized due to the reduction in the symmetry induced by the anisotropic strain state.
Fast-wave multifrequency diagnostic of tokamak plasmas
Authors: LaFonteese D. J. , Morales G. J. , Taylor R. J.
Published: May 2007

An exploratory investigation, both computational and experimental, is made of the diagnostic possibilities of a fast wave-based method for measuring the ion density and temperature profiles of tokamak plasmas. The concept consists of simultaneously launching several discrete frequencies and detecting their amplitude and phase at various toroidal locations. This study focuses on an array of frequencies that match the second harmonic of the ion gyrofrequency at various radial locations in the plasma profile. The method is explored with simple, wave-propagation codes for parameters corresponding to the Electric Tokamak (ET) [R. J. Taylor, et al., Nucl. Fusion 42, 46 (2002)] and ITER [R. Aymar, P. Barabaschi, and Y. Shimomura, Plasma Phys. Controlled Fusion 44, 519 (2002)]. An experimental investigation of the concept has been performed in a large tokamak (ET) in which six frequencies are launched and detected at four toroidal locations. Positive results obtained indicate that the concept and other variants deserve to be pursued in greater depth, using more sophisticated codes.