bluuebunny/crossref_metadata_2025 huggingface dataset:
Using artificial neural networks to assess wolf distribution patterns in Portugal
Authors: Bessa‐Gomes Carmen , Petrucci‐Fonseca Francisco
Published: September 2003

Although the conservation of endangered species often implies the definition of priority areas for conservation, detailed information on their distribution patterns is seldom available over a large geographic range. The present paper explores the performance of an alternative data analysis approach, artificial neural networks, for assessing distribution patterns of endangered mammals when data are scarce and noisy. This approach was applied to identify wolf occupancy in Portugal based on information on wolf depredation and inquiries. Artificial neural networks were able to discriminate successfully between areas sporadically used by vagrant individuals and areas occupied by resident wolves, with a low estimated prediction error (around 1%). Only 33% of the wolf range is regularly occupied, being fragmented in five nuclei. These nuclei are surrounded by more disturbed marginal areas, with a source‐sink dynamic between nucleus and marginal areas. Selection of priority areas for wolf conservation in the context of the Natura 2000 Network increased twofold the proportion of wolf regular range within protected areas. The good performance of artificial neural networks in assessing wolf distribution patterns suggests that this approach may be applied to other species where detailed records of distribution are limited.
Viability of a diminishing roan antelope population: predation is the threat
Authors: McLoughlin Craig A. , Owen‐Smith Norman
Published: September 2003

The roan antelope (Hippotragus equinus) population inhabiting the Kruger National Park, South Africa, declined from 450 animals in 1986 to around 25 free‐ranging animals subsequent to 1994. A computer simulation model was developed to: (1) evaluate likely contributions of low rainfall, habitat deterioration, population fragmentation and predation to the observed population decline; (2) project future likelihood of persistence of the population remnant, under various scenarios. Direct consequences of severe drought and habitat deterioration alone were inadequate to explain the observed decline, unless effects were more severe than assumed in the model. An increased predation loss to around 30% per year was needed. Persistence probability over 50 years was less than 0.5 if the predation loss remained above 20% per year. Models that take into account only stochastic uncertainty in demography and environmental variability are of limited reliability if potential changes in predation risk are not also accommodated.
A recent bottleneck in the warthog and elephant populations of Queen Elizabeth National Park, revealed by a comparative study of four mammalian species in Uganda national parks
Authors: Muwanika Vincent B. , Siegismund Hans R. , Okello John Bosco A. , Masembe Charles , Arctander Peter , Nyakaana Silvester
Published: September 2003

Until 1972, Uganda's national parks boasted of large numbers of large mammal species. Following the breakdown of law and order between 1972 and 1985, large‐scale poaching led to an unprecedented decline in numbers of most large mammals in Uganda's national parks. However, the extent of decline varied in the different parks across different animal species. We have investigated the genetic effects of these reductions in four mammalian species (the common warthog, African savannah elephant, savannah buffalo and common river hippopotamus) from the three major parks of Uganda using both microsatellite loci (for elephant and warthog populations) and mitochondrial control sequence variation in the warthogs, elephants, buffaloes and hippopotamuses. Queen Elizabeth National Park showed extreme reduction in nucleotide diversity for two species, the common warthog (π= 0.0%) and African elephant (π= 0.4%); no such decrease was found for the two other species, the buffalo (π= 3.7–5.4%) and hippopotamus (π= 1.7–1.9%), in the three parks. Nuclear microsatellite markers on the other hand showed high gene diversity in all populations in the common warthog (mean He 0.66–0.78) and the African savannah elephant (mean He 0.68–0.72). We interpret these results in terms of varying poaching pressure in the different parks, susceptibility of different species to poaching and differences in effective population sizes at the mitochondrial and nuclear loci.
Impact of fire management on the ecology of collared lizard (Crotaphytus collaris) populations living on the Ozark Plateau
Authors: Brisson Jennifer A. , Strasburg Jared L. , Templeton Alan R.
Published: September 2003

Eastern collared lizards (Crotaphytus collaris collaris) on the Ozark Plateau of southern Missouri are restricted to islands of rocky glade habitat located throughout the oak‐hickory forests of the region. Human mediated suppression of fire negatively impacts collared lizard populations by permitting the overgrowth and consequent disappearance of this glade habitat and also leads to a dense forest understorey that impedes movement of lizards between glades. We present data examining the effects of a fire management regime on collared lizard populations we monitored via mark/recapture from 1998 to 2001. We demonstrate increased glade‐to‐glade dispersal, colonization of previously unoccupied glades, and a significant increase in population size in the burned area. In addition, we show that populations within burned areas exhibit body sizes similar to those reported for populations living on healthy habitat as compared to those living on habitat that has deteriorated because of fire suppression. We conclude that managed forest fires positively impact collared lizard populations in the Ozarks, promoting factors that increase the long‐term sustainability of the species.
The role of local adaptation in metapopulation restorations
Authors: Robert Alexandre , Couvet Denis , Sarrazin François
Published: September 2003

We propose an original approach to model the effect of the initial spatial distribution of a reintroduced metapopulation (one‐patch release versus multi‐patch release) on local adaptation. Genetic and demographic processes are considered to investigate how the different patterns of adaptation resulting from initial conditions affect metapopulation viability. In agreement with classical interpretations in the fields of population biology and evolutionary genetics, we observe an influence of the degree of environmental correlation among patches on demographic processes and an influence of inter‐patch connection on genetic processes. However, our results uncover some further effects of the environment, owing to positive feedback interactions among demographic and genetic processes. When considering the one‐patch release, demographic stochasticity engenders a delay in the colonization of initially empty patches. This delay enhances the genetic asymmetry among patches (in terms of local adaptation), which in turn increases demographic asymmetry. In contrast, the multi‐patch release produces similar levels of adaptation among patches. Metapopulation dynamics is strongly influenced by these differences, with contrasting effects under different environments. The pattern of adaptation produced by the one‐patch release strategy is optimal under a regime of recurrent slight perturbations or environmental stochasticity, while the multi‐release strategy is optimal in the presence of rare and severe perturbations.
Genetic identification of wild Asian water buffalo in Nepal
Authors: Flamand J. R. B. , Vankan D. , Gairhe K. P. , Duong H. , Barker J. S. F.
Published: September 2003

The wild water buffalo is highly endangered, with the few remaining populations already affected or likely to be increasingly affected by hybridization with domestic buffalo. The work described here was done to evaluate a genetic method to discriminate wild from mixed ancestry (hybrid) and domestic animals, and to identify with high probability those most likely to be purebred wild. Samples from 45 animals (phenotypically classified into three groups ‐ ten wild, 28 domestic and seven hybrid) were genotyped for ten microsatellite loci. Although genetic distances among the three groups were small, an assignment test identified two of the ‘wild’ and seven of the ‘domestic’ as hybrids. However, sample sizes also are small, indicating the need for a conservative approach in the first instance in using these results. As more animals are genotyped, assignments will become more accurate, and a translocation programme to establish a second Nepalese wild population in a protected area could be undertaken.
The influence of scale on salmon habitat restoration priorities
Authors: Feist Blake E. , Steel E. Ashley , Pess George R. , Bilby Robert E.
Published: September 2003

Habitat loss and alteration is the leading cause of species' declines world‐wide, therefore habitat restoration and protection is a prominent conservation strategy. Despite obvious connections between habitat and threatened or endangered species, conservationists have been hard pressed explicitly to link abundance or population health with habitat attributes. Given that habitat relationships with species are often characterized at a spatial scale that does not account for the functional relationships between habitat and populations, it is not surprising that the habitat‐population conundrum persists. In order to explore the influence of spatial scale on the apparent relationship between habitat and populations, we examined the relationship between GIS‐based habitat data and spring/summer chinook salmon (Oncorhynchus tshawytscha) redd (spawning nests built by females) densities in the Salmon River basin, Idaho, at two very different spatial scales: stream reach and watershed. Redd density was strongly correlated with climate, geology, wetlands and terrain. However, our stream‐reach scale models provided poor predictive power compared with the watershed scale models. Based on these results, we conclude that our perception of which habitat attributes were important was clearly a function of our scale of observation, and that restoration efforts should focus on conditions at the watershed or landscape scale when attempting to do local or reach scale restoration projects.
Movement and survival parameters of translocated and resident swift foxes Vulpes velox
Authors: Moehrenschlager Axel , Macdonald David W.
Published: September 2003

Conservation programmes increasingly involve the translocation of animals to reinforce failing populations or establish new ones. To help guide translocation programmes of swift foxes (Vulpes velox) or other imperilled species, we aimed to discern factors affecting translocation success among reintroduced swift foxes in Canada. Post‐release movements characterized three stages. In the initial acclimation phase, foxes moved erratically and quickly distanced themselves from release sites. During the establishment phase, distances from the release site did not change significantly but daily movements were more wide‐ranging than those of concurrently tracked, resident swift foxes. In the final settlement phase, movements of translocated foxes reflected those of resident individuals. Radio‐telemetry showed that survival and reproductive success were highest for swift foxes with small dispersal distances, suggesting that measures should be taken to acclimatize animals to release sites. Since females had lower survival rates than males, translocations should also use a greater proportion of females to establish balanced sex ratios in the population. Translocated juveniles dispersed less far but survived and reproduced as well as translocated adults, suggesting that juveniles can be used to establish translocated foxes in small, protected areas, while minimizing demographic effects on source populations. The fact that survival rates and litter sizes of translocated foxes were similar to those of resident animals indicates that translocation can be an effective reintroduction tool for this endangered species, and possibly other foxes.
An experimental investigation of the diffusive infiltration of alkalis into partially molten peridotite: Implications for mantle melting processes
Authors: Lundstrom C. C.
Published: September 2003

When a silica‐undersaturated melt is juxtaposed with partially molten peridotite, alkali elements rapidly diffuse into the peridotite in a process referred to as the diffusive infiltration of alkalis (DIA). Four types of piston cylinder experiments were performed providing constraints on the DIA process: (1) simple phase relation experiments, (2) melt‐melt diffusion couples, (3) experiments examining the reaction between powders of basanite and spinel lherzolite (direct mixture experiments), and (4) diffusive infiltration‐reaction couples between basanite and partially molten peridotite. Melt‐melt diffusion couples constrain effective binary diffusion coefficients (EBDC) for all major elements except Na to be in the 10−6 to 10−7 cm2/s range at 1450°C and 0.9 GPa. The Na concentration profile is not binary being coupled to gradients in SiO2. EBDCs for Cl, Li, Rb, Sr, Ba, and La are in the 10−6 cm2/s range while Nb and Zr are in the 10−7 cm2/s range. A time series of direct mixture experiments shows that basanite reacts with lherzolite to reduce the orthopyroxene mode to a constant value within 15 min at 1300°C and 0.9 GPa. Quench modified melts in the direct mixture experiments have 50–51 wt.%. SiO2, independent of the basanite/lherzolite ratio. In contrast, infiltration‐reaction experiments show that sodium diffuses from basanite into partially molten peridotite in 10–30 min, resulting in quench modified melt pools with up to 64 wt.% SiO2 within the peridotite. Modal analysis shows that addition of alkalis causes orthopyroxene to incongruently break down to olivine plus silica rich melt. In experiments using a basanite with enriched Cl concentrations, a distinct boundary zone appears between the basalt‐peridotite interface and the peak in SiO2 concentration. Melts within this boundary zone have elevated CaO and Cl concentrations relative to both the basanite and melts within the peridotite beyond the boundary zone. The repeated formation of this boundary zone may indicate an important aspect of the DIA process, possibly responsible for the formation of anorthitic plagioclase and CaO rich melts.
Historical relative gravity observations and the time rate of change of gravity due to postglacial rebound and other tectonic movements in Canada
Authors: Pagiatakis Spiros D. , Salib Philip
Published: September 2003

A major re‐adjustment of the primary Canadian Gravity Standardization Network (CGSN) is carried out based on relative gravity measurements spanning over 40 years. Anticipating that secular variations of gravity, dominated primarily by the continuing process of glacial isostatic adjustment could be detected, we parameterize the time rate of change of gravity () into the observation equation and estimate it directly from a generalised least squares solution. Time rates of change of gravity () from repeated absolute gravity observations, as well as absolute gravity values at selected sites are used as weighted constraints. The results are presented in form of a map and demonstrate that the primary CGSN, with its over 40‐year‐long history, can provide us with useful constraints for the evaluation/verification and refinement of post‐glacial rebound models.
Io's auroral limb glow: Hubble Space Telescope FUV observations
Authors: Retherford K. D. , Moos H. W. , Strobel D. F.
Published: August 2003

Observations of Io's FUV aurora were obtained using the Space Telescope Imaging Spectrograph (STIS) on several occasions between 1997 and 2000. The STIS first‐order long‐slit spectroscopy mode and 2″ wide slit were used to produce nearly monochromatic images of Io. These images reveal several distinct auroral features, including limb brightened emissions at the poles, designated “limb glow”. A detailed study of the limb glow brightness in OI] 1356 Å images is reported. The limb glow on the hemisphere facing the plasma torus centrifugal equator is consistently brighter than on the other hemisphere, and is brighter by a factor of ∼2 when Io is farthest from the plasma torus centrifugal equator. We determine that this behavior is consistent with there being more electrons and more electron energy in the part of an intersecting plasma torus flux tube located above the brighter hemisphere. Since most of the electrons in an intersecting flux tube have time to travel along the field line and collide with Io before the flux tube moves downstream across Io's poles, more torus electron energy is transferred into the polar hemisphere with brighter aurora. We demonstrate that a Kappa distribution model of the plasma torus electron column density above each hemisphere predicts to first order the ratio of north and south limb glow brightnesses as a function of Io's distance from the plasma torus centrifugal equator. This finding illustrates the importance of field‐aligned torus electron energy transport for producing Io's aurora.
Shear and normal load perturbations on a two‐dimensional continuous fault: 1. Static triggering
Authors: Perfettini H. , Schmittbuhl J. , Cochard A.
Published: September 2003

The influence of normal and shear stress static perturbations on a strike‐slip fault is addressed on the basis of a two‐dimensional continuous and quasi‐dynamic model. Friction along the fault plane is described using a rate‐and‐state friction law with depth variable properties. Normal and shear stress perturbations result in similar effects in terms of earthquake triggering if Δτ − μ*Δσ is constant, Δτ and Δσ being the amplitude of the shear and normal stress fluctuations, respectively, and μ* being a constant which can be interpreted as the static friction coefficient on the fault in a Coulomb failure model. Therefore the Coulomb stress change ΔCFF = Δτ − μ*Δσ is a useful tool to account simultaneously for normal and shear stress variations in our model. We also show that when estimating the clock advance or clock delay of an earthquake, the simple Coulomb failure model is at first order in good agreement with our results during the first 90% of the earthquake cycle. However, it differs significantly during the last 10% due to the sharp velocity increase predicted by the rate‐and‐state friction law before rupture. This suggests that as long as static variations of stress are concerned, realistic fault models using rich, laboratory‐based, friction laws like rate‐and‐state friction laws may lead to predictions fairly close to the ones made using one of the simplest failure model, i.e., the Coulomb failure model. This may explain why Coulomb stress change computations, although often based on drastic approximations, have been able in many occasions to explain earthquake triggering sequences.
Shear and normal load perturbations on a two‐dimensional continuous fault: 2. Dynamic triggering
Authors: Perfettini H. , Schmittbuhl J. , Cochard A.
Published: September 2003

We study the consequences of temporal stress perturbations on earthquake nucleation in a continuous fault model. Using a two‐dimensional (2‐D) quasi‐dynamic model of a strike‐slip fault governed by a rate‐and‐state friction law with depth variable properties, we show that dynamic triggering (due to stress pulses or wave packets), although allowed by our results, is an exception rather than a rule and should be limited to understressed areas such as areas of high pore pressures or to faults at the very end of their earthquake cycle. When periodic stress perturbations are sensitive, the response of the fault is frequency‐independent for periods lower than a period T0 but strongly depends on the frequency for periods larger than T0. We demonstrate that the crossover period T0 is equal to the time left until the earthquake instability. According to our model, high frequencies are demonstrated to have a higher triggering potential than low ones, which makes tidal triggering very unlikely before the end of the cycle due to the very low amplitudes of the stress perturbations involved.
On the scaling of the slip weakening rate of heterogeneous faults
Authors: Perfettini H. , Campillo M. , Ionescu I.
Published: September 2003

We present an attempt to describe the scaling law of the slip weakening rate at the onset of instability using a two‐dimensional fault model. A fault consists of a series of weak patches under slip weakening friction, separated by unbreakable barriers. A first group of faults contains an even distribution of patches of different scales conserving the same total slipping length, while a second group consists of various fractal Cantor sets. The global behavior of rupture is described by the exponential growth rate λ. For an infinite homogeneous fault, the coefficient λ is governed by the weakening rate of the friction law. We estimate the weakening rate of each individual fault in an heterogeneous fault system such that the rate of exponential growth λ of this fault network is identical to that of a single homogeneous fault. Using this homogenization procedure, we compute the weakening rate on the weak patches for faults with different scales of heterogeneity and a given λ. At large scales, the weakening rate is scale‐independent, the initiation process on a long patch being similar to the case of an infinite fault. At small scales and for all the different geometries considered here, the weakening rate varies as α = β*0/a, where a is the scale or half length of each elementary fault and β*0 ≃ 1.158. We discuss the physical implications of our results on the value of the slip weakening distance Dc and give a possible explanation of the scale dependence of this parameter.
Anisotropy of electrical conductivity record of initial strain at the toe of the Nankai accretionary wedge
Authors: Henry Pierre , Jouniaux Laurence , Screaton Elizabeth J. , Hunze Sabine , Saffer Demian M.
Published: September 2003

An approach based on March's theory is applied to measurements of the anisotropy of electrical conductivity on samples and is used to quantify initial strain at the toe of the Nankai accretionary wedge. A quantitative determination of strain is possible from simple assumptions: passive reorientation of flat pores forming the porous network and existence of a linear relationship between fabric tensor and electrical conductivity tensor. We show that this simple model correctly accounts for the increase of anisotropy with compaction at a reference site located in the trench (Ocean Drilling Program drill Site 1173). At the toe of the accretionary wedge (Site 1174), development of anisotropy in the horizontal plane and concurrent reduction of vertical plane anisotropy are observed. This can be explained by 12% horizontal ductile shortening, occurring after decollement initiation but before slip on imbricate thrust faults. Anisotropy in the underthrust sequence is correctly described by vertical compaction, consistent with decoupled stress states across the decollement. At Site 1174 the magnitude of ductile strain implies at least 75 m slip on the decollement. Ductile shortening is associated with porosity loss, implying partly drained conditions above the decollement.
The front on the Northern Flank of Georges Bank in spring: 1. Tidal and subtidal variability
Authors: Dale Andrew C. , Ullman David S. , Barth John A. , Hebert Dave
Published: September 2003

During March–April 1999, 2 weeks of undulating CTD and shipboard acoustic Doppler current profiler surveys revealed the variability of the intense internal tide on the northern edge of Georges Bank. The nature of the internal tide was modulated by episodic surface intrusions of cool, fresh Scotian Shelf Water (SSW), stratifying the otherwise vertically well‐mixed outer bank. The introduction of SSW created a system analogous to that in summer, when the outer bank is thermally stratified and separated from well‐mixed regions by a tidal mixing front. During SSW intrusions, internal tidal behavior is characterized by tidal advection that is significantly faster than internal wave propagation speeds on the bank (supercritical flow) and slower than the lowest internal modes in deeper water to the north (subcritical flow). A large‐amplitude internal lee wave develops over the slope during off‐bank tidal flow. This stalled energy is released to propagate on‐bank as a high‐frequency internal wave when the tide reverses. It is suggested, by analogy with the summer case, that a portion of this energy is used by mixing at the on‐bank limit of SSW. The presence of SSW thus modifies the internal tidal response, enabling a mechanism that contributes to its assimilation with ambient bank water. The off‐bank‐propagating internal tide is dominated by a mode 1 internal wave at the M2 frequency, with cross‐bank velocities comparable to the barotropic tide.
The front on the Northern Flank of Georges Bank in spring: 2. Cross‐frontal fluxes and mixing
Authors: Ullman David S. , Dale Andrew C. , Hebert Dave , Barth John A.
Published: September 2003

Hydrographic observations made with an undulating vehicle carrying a CTD and concurrent shipboard ADCP velocity observations over a 12‐day period are combined to investigate vertical mixing and cross‐frontal fluxes on the Northern Flank of Georges Bank. The CTD density time series is analyzed to detect the presence of vertical overturns, the statistics of which are used to infer vertical mixing parameters. Vertical turbulent buoyancy fluxes are downward and most intense, reaching values of 5 × 10−7 W/kg, near the bottom at the edge of the bank and decrease both on‐ and off‐bank. Horizontal, cross‐bank buoyancy fluxes are partitioned into mean, tidal pumping, and nontidal eddy components and are computed as a function of cross‐isobath/vertical position by averaging in the along‐isobath direction. The tidal pumping component is dominant over most of the cross‐bank section with a peak value of ∼1 × 10−4 W/kg, directed off‐bank near the bank edge. A diagnosed tidal vertical velocity field is used with mean buoyancy gradients to compute the along‐isopycnal skew flux. The horizontal component of this skew flux has similar spatial structure and magnitude to that of the observed tidal pumping flux. The divergent component of the skew flux, at depths above the bottom boundary layer, appears to be convergent north of the bank edge and divergent at the bank edge, suggesting that tidally driven advective processes drive buoyant bank water downward and off‐bank at mid‐depth and force the upwelling of deep, dense water near the bottom at the bank edge.
Coccolithophorid distribution in the Ionian Sea and its relationship to eastern Mediterranean circulation during late fall to early winter 1997
Authors: Malinverno Elisa , Ziveri Patrizia , Corselli Cesare
Published: September 2003

The distribution of coccolithophorid assemblages is analyzed from water samples collected in the photic zone of the middle Ionian Sea during a cruise of R/V Urania in November–December 1997. Coccolithophorids are an important phytoplankton group in the oligotrophic eastern Mediterranean, and their coccoliths make an important contribution to the sediments of this area, being also widely used for paleoclimatic and paleoceanographic reconstructions. Nevertheless, studies on extant coccolithophorids ecology and distribution in the eastern Mediterranean are limited and mostly related to surface waters: this study, even if restricted to a single period of the year, provides the first detailed analysis of species distribution throughout the photic zone, with relation to the main local physicochemical parameters. During the investigated period, the area is characterized by the presence of a surface mixed layer, reaching a depth of 25 to 90 m. Below this layer, a marked thermo‐ and halocline is developed. Coccolithophorids are the dominant phytoplankton group in the investigated samples and reach concentrations up to 2 × 104 coccospheres per liter of seawater. The species assemblage is that typical of the subtropical latitude, with a general high species diversity and a well‐defined depth distribution. It is in fact possible to recognize an upper photic zone assemblage, dominated by E. huxleyi and characterized by higher concentration and species diversity and a lower photic zone where typically deep‐living species (i.e., F. profunda, G. flabellatus) are present. These two zones are separated by a transition layer, where species of both zones are represented and new ones appear. Such vertical distribution appears to be strictly related to the local hydrology, with the zone boundaries rising and falling as a function of the location of the isotherms. In particular the first significant occurrence of F. profunda from surface to the deep photic zone corresponds with the start of the thermocline. Comparison of present plankton data with the surface sediment record, although displaying a consistent pattern of species assemblage, shows some differences in the presence and relative abundance of some species (G. oceanica): this can be related to seasonal as well as interannual variations in the pattern and intensity of surface circulation in the investigated area.
Subsurface structure of interannual temperature anomalies in the Australian sector of the Southern Ocean
Authors: Sokolov Serguei , Rintoul Stephen R.
Published: September 2003

A 7 year time series of austral summer expendable bathythermograph (XBT) sections between Tasmania and Antarctica is used to describe the subsurface structure of Southern Ocean interannual temperature anomalies. Comparison of the discontinuous XBT record with a continuous (weekly average) satellite‐based SST data set confirms that the XBT sampling is adequate to resolve interannual variability. Significant correlations are found between changes in surface and subsurface temperature along much of the section. In the Subantarctic zone, surface and subsurface changes are coherent because deep convection in winter homogenizes the upper 600 m, and the summer mixed layer temperature reflects the preconditioning of the previous winter. At other latitudes the regions of high correlation generally extend well beyond the depth of direct atmospheric influence (i.e., the depth of the winter mixed layer). Negative (positive) temperature anomalies at interannual timescales are coherent with poleward (equatorward) displacements of fronts. The simplest explanation for the correspondence between deep, vertically coherent temperature anomalies and the location of ACC fronts is that the observed features reflect meridional shifts of temperature gradients associated with the fronts. The link between temperature anomalies and front displacements suggests Southern Ocean sea surface temperature (SST) anomalies primarily reflect a dynamical response of the ocean to wind or other forcing rather than surface‐trapped features produced by anomalous air‐sea heat flux. The XBT record contains both interannual and longer (unresolved) period signals, which cannot be isolated in the short discontinuous XBT time series. Spectral analysis of the 17 year SST data set reveals roughly equal variability in 2–7 year and >7 year bands.
Synoptic‐scale transport of reactive nitrogen over the western Pacific in spring
Authors: Miyazaki Y. , Kondo Y. , Koike M. , Fuelberg H. E. , Kiley C. M. , Kita K. , Takegawa N. , Sachse G. W. , Flocke F. , Weinheimer A. J. , Singh H. B. , Eisele F. L. , Zondlo M. , Talbot R. W. , Sandholm S. T. , Avery M. A. , Blake D. R.
Published: September 2003

Pathways of synoptic‐scale uplifted transport of pollutants from East Asia and their effects on chemical distributions of NOy species are investigated based on a subset of the aircraft data obtained during the NASA Transport and Chemical Evolution over the Pacific (TRACE‐P) experiment, conducted in February–April 2001. Meteorological and chemical analyses indicate that 73% of the uplifted transport was associated with warm conveyor belts (WCBs) and convective outflow (COF), which transported air masses strongly impacted by biomass burning over Southeast Asia. The rest (27%) of the uplifted air masses originated over coastal regions of northeast China, where fossil fuel combustion was a dominant source of pollutants. Both WCB associated with a midlatitude cyclone and COF associated with a stationary front over southeast China are examined in detail for the April 4 case. During the TRACE‐P period, low NOx(= NO + NO2)/NOy ratios in the WCB and COF indicate that a significant part of the NOx was oxidized to nitric acid (HNO3) and peroxyacetyl nitrate (PAN) during transport. Low HNO3/NOy ratios in the WCB and COF airstreams indicate that a large amount of HNO3 was removed during transport on timescales within 1–3 days. PAN was found to be the dominant form of NOy in air masses transported by the WCB and COF, likely due to the production of PAN in regions of biomass burning and industrial emissions, as well as due to the rapid removal of HNO3 during transport. For emissions that were transported to the free troposphere by WCBs and COF, about 10–20% of the NOy remained after transport to the free troposphere, and 30% of the NOy surviving in the boundary layer in limited cases. The results indicate that the WCB and COF provide both an efficient sink for HNO3 and an efficient mechanism for the transport of PAN from the boundary layer to the free troposphere over the western Pacific.
Large‐scale ozone and aerosol distributions, air mass characteristics, and ozone fluxes over the western Pacific Ocean in late winter/early spring
Authors: Browell Edward V. , Fenn Marta A. , Butler Carolyn F. , Grant William B. , Brackett Vincent G. , Hair Johnathan W. , Avery Melody A. , Newell Reginald E. , Hu Yuanlong , Fuelberg Henry E. , Jacob Daniel J. , Anderson Bruce E. , Atlas Elliot L. , Blake Donald R. , Brune William H. , Dibb Jack E. , Fried Alan , Heikes Brian G. , Sachse Glen W. , Sandholm Scott T. , Singh Hanwant B. , Talbot Robert W. , Vay Stephanie A. , Weber Rodney J. , Bartlett Karen B.
Published: September 2003

Large‐scale measurements of ozone (O3) and aerosol distributions were made from the NASA DC‐8 aircraft during the Transport and Chemical Evolution over the Pacific (TRACE‐P) field experiment conducted in February–April 2001. Remote measurements were made with an airborne lidar to provide O3 and multiple‐wavelength aerosol backscatter profiles from near the surface to above the tropopause along the flight track. In situ measurements of O3, aerosols, and a wide range of trace gases were made onboard the DC‐8. Five‐day backward trajectories were used in conjunction with the O3 and aerosol distributions on each flight to indicate the possible origin of observed air masses, such as from biomass burning regions, continental pollution, desert regions, and oceanic regions. Average latitudinal O3 and aerosol scattering ratio distributions were derived from all flights west of 150°E, and these distributions showed the average latitude and altitude dependence of different dynamical and chemical processes in determining the atmospheric composition over the western Pacific. TRACE‐P (TP) showed an increase in the average latitudinal distributions of both O3 and aerosols compared to PEM‐West B (PWB), which was conducted in February–March 1994. O3, aerosol, and potential vorticity levels were used to identify nine air mass types and quantify their frequency of occurrence as a function of altitude. This paper discusses the characteristics of the different air mass types encountered during TP and compares them to PWB. These results confirmed that most of the O3 increase in TP was due to photochemistry. The average latitudinal eastward O3 flux in the western Pacific during TP was found to peak near 32°N with a total average O3 flux between 14 and 46°N of 5.2 Tg/day. The eastward total CO flux was calculated to be 2.2 Tg‐C/day with ∼6% estimated from Asia. The Asian flux of CO2 and CH4 was estimated at 4.9 and 0.06 Tg‐C/day.
Are faults preferential flow paths through semiarid and arid vadose zones?
Authors: Sigda John M. , Wilson John L.
Published: August 2003

Numerous faults crosscut the poorly lithified, basin‐fill sands found in New Mexico's Rio Grande rift and in other extensional regimes. The deformational processes that created these faults sharply reduced both fault porosity and fault saturated hydraulic conductivity by altering grains and pores, particularly in structures referred to as deformation bands. The resulting pore distribution changes, which create barriers to saturated flow, should enhance fault unsaturated flow relative to parent sand under the relatively dry conditions of the semiarid southwest. We report the first measurements of unsaturated hydraulic properties for undisturbed fault materials, using samples from a small‐displacement normal fault and parent sands in the Bosque del Apache Wildlife Refuge, central New Mexico. Fault samples were taken from a narrow zone of deformation bands. The unsaturated flow apparatus (UFA) centrifuge system was used to measure both relative permeability and moisture retention curves. We compared these relations and fitted hydraulic conductivity‐matric potential models to test whether the fault has significantly different unsaturated hydraulic properties than its parent sand. Saturated conductivity is 3 orders of magnitude less in the fault than the undeformed sand. As matric potential decreases from 0 to −200 cm, unsaturated conductivity decreases roughly 1 order of magnitude in the fault but 5–6 orders of magnitude in undeformed sands. Fault conductivity is greater by 2–6 orders of magnitude at matric potentials between −200 and −1000 cm, which are typical potentials for semiarid and arid vadose zones. Fault deformation bands have much higher air‐entry matric potential values than parent sands and remain close to saturation well after the parent sands have begun to approach residual moisture content. Under steady state, one‐dimensional, gravity‐driven flow conditions, moisture transport and solute advection is 102–106 times larger in the fault material than parent sands. Faults are sufficiently conductive to hasten the downward movement of water and solutes through vadose‐zone sands under semiarid and arid conditions like those in the Rio Grande rift, thereby potentially enhancing recharge, contaminant migration, and diagenesis.
Differential effective medium schemes for investigating the relationship between high‐frequency relative dielectric permittivity and water content of soils
Authors: Cosenza Philippe , Camerlynck Christian , Tabbagh Alain
Published: September 2003

Differential effective medium (DEM) theory is presented and used to calculate the effective HF dielectric permittivity κ of unsaturated soils considered as mixtures of solid and two fluid phases. In the case of coarse‐grained soils for which dielectric losses are negligible, a good agreement with the empirical equation of Topp et al. [1980] is obtained using only a spherical grain shape. Moreover, results of DEM schemes have shown that ohmic losses induced by salinity modify significantly the relationship between the apparent dielectric permittivity at 120 MHz and the volumetric water content θ, for NaCl concentration greater than 0.045 mol/L. In the case of clayey soils, simulations based on the same theoretical approach show that the available data can not be modeled by considering only the geometrical effect associated with the “platy” units and the ohmic losses associated with the surface conductivity.
Magnetic field draping enhancement at Venus: Evidence for a magnetic pileup boundary
Authors: Bertucci C. , Mazelle C. , Slavin J. A. , Russell C. T. , Acuña M. H.
Published: September 2003

The absence of a global‐scale dynamo‐generated magnetic field and the existence of an ionosphere at Venus and Mars caused many to predict that their solar wind interaction would be similar. After Pioneer Venus Orbiter (PVO) observations, it was concluded that the global aspects of the Venusian interaction could be well described by single‐fluid models. According to these models, the magnetic field draping should develop progressively from the shock down to the ionopause. A recent study at Mars, where a “Venus‐like” interaction was expected, showed that draping is prominent only inside the magnetic pileup boundary (MPB), a well‐defined plasma boundary located between the shock and the ionopause first reported at comets, but never at Venus. From an identical analysis on PVO magnetometer data, we report a dramatic enhancement of draping on the dayside of Venus. Then, we deduce the existence of a Venusian counterpart of the Martian and cometary MPB.
Guadalupe Island, Mexico as a new constraint for Pacific plate motion
Authors: Gonzalez‐Garcia J. J. , Prawirodirdjo L. , Bock Y. , Agnew D.
Published: August 2003

We use GPS data collected on Isla de Guadalupe and in northern Baja California, Mexico, to estimate site velocities relative to Pacific plate motion. The velocities of all three geodetic monuments on Guadalupe fit a rigid Pacific plate model with residuals of 1 mm/yr. Using the Guadalupe data and data from five IGS stations on the Pacific plate (CHAT, KOKB, KWJ1, MKEA, and THTI) we estimate an angular velocity for this plate that is consistent with other recently‐published estimates. Our results indicate that Isla de Guadalupe lies on the Pacific plate, and that GPS data collection on the island usefully constrains Pacific plate motion and rigidity.
Vertical dimensions of seasonal trends in the diurnal temperature range across the central United States
Authors: Balling Robert C. , Cerveny Randall S.
Published: September 2003

Many investigators have used near‐surface air temperature measurements to document a downward global trend in the diurnal temperature range (DTR). In this paper, we use radiosonde‐based tropospheric measurements to examine vertical dimensions in trends in the DTR over the central United States. We find declining trends in DTR only at 85 kPa and the surface in the high‐sun season, with the absolute trend at 85 kPa being greater than the trend at the surface suggesting that the trend in DTR is far more than an urban artifact in the data. There are no significant trends in DTR from 70 kPa to 25 kPa in any season. These results suggest that DTR trends in the low troposphere are likely influenced by near‐surface processes such as variations in cloudiness, vegetation, or precipitation but not dominated by urban effects.
Narrow Bipolar Events as indicators of thunderstorm convective strength
Authors: Suszcynsky D. M. , Heavner M. J.
Published: September 2003

Narrow Bipolar Events (NBEs) are impulsive in‐cloud lightning discharges that are commonly detected by both ground‐based and satellite‐based radio‐frequency sensors. In this paper, NBE flash rates are shown to be statistically correlated to cloud‐to‐ground (CG) lightning flash rates as recorded by an array of electric‐field‐change sensors located in Florida. In addition, NBE source heights are found to generally increase with increasing NBE flash rates. The inference is that NBE flash rates and source heights are generally driven by the intensity/strength of the convective updraft in thunderstorms. As a consequence, NBEs represent a meteorologically important type of lightning and provide an excellent target of opportunity for future satellite‐based very high frequency (VHF) global lightning monitors.
Solar wind and magnetospheric ion impact on Mercury's surface
Authors: Kallio E. , Janhunen P.
Published: September 2003

The impact of the solar wind protons on the surface of Mercury is studied by a global hybrid model. In the three‐dimensional self‐consistent quasi‐neutral hybrid (ions are particles, electrons are a fluid) model ions can hit the surface of the planet. The response of the impact to several solar wind conditions is studied by analyzing four upstream cases: pure northward interplanetary magnetic field (IMF), pure southward IMF, the Parker spiral IMF, and atypically high solar wind speed. Three different high impact regions on the surface can be identified: (1) “auroral” impact on the equatorward side of the open/closed field line boundary, (2) “cusp” impact on the dayside in the noon midnight meridian plane, and (3) “nose” impact around the subsolar point when the solar wind dynamic pressure is high. The particle flux also has North‐South and dawn‐dusk asymmetries.
Boundary conditions of the heliosphere
Authors: Frisch P. C.
Published: September 2003

Radiative transfer equilibrium models of nearby interstellar matter (ISM) are required to determine the boundary conditions of the heliosphere from astronomical observations of nearby stars. These models are also constrained by data on the ISM inside of the solar system, including pickup ion, anomalous cosmic rays, and in situ Heo data. The two best ISM models give semiempirical filtration factors for H (0.41–0.52), He (0.86–1.16), N (0.74–1.11), O (0.55–0.77), Ne (1.41–2.80), and Ar (0.61–1.76) when observational uncertainties are included. Uncertainties in the Ne filtration factor may result from poorly known interstellar abundances. These models predict the characteristics of the ISM outside of the solar system: n(Ho) = 0.20–0.21 cm−3, n(e−) = 0.10 cm−3, H+/H = 0.29–0.30, and He+/He = 0.47–0.51. However, if the isotropic 2 kHz emission observed by Voyager [Kurth and Gurnett, 2003] is formed in the surrounding ISM, an alternate model (Model 25) is indicated. The weakly polarized starlight of nearby stars suggests that the local galactic magnetic field is parallel to the galactic plane and the strongest polarization is toward the upstream direction of the ISM flow and also (coincidently) near the ecliptic plane. Observations of nearby ISM, the radiative transfer models, and historical 10Be records provide information on past variations in the galactic environment of the Sun.