bluuebunny/crossref_metadata_2025 huggingface dataset:
Homeless street children in Nepal: Use of allostatic load to assess the burden of childhood adversity
Authors: Worthman Carol M. , Panter-Brick Catherine
Published: January 2008

As challenges to child well-being through economic disadvantage, family disruption, and migration or displacement escalate world wide, the need for cross-culturally robust understanding of childhood adversity proportionately increases. Toward this end, developmental risk was assessed in four contrasting groups of 107 Nepali children ages 10–14 years that represent distinctive, common conditions in which contemporary children grow up. Relative cumulative burden (allostatic load) indexed by multiple dimensions of physical and psychosocial stress was ascertained among homeless street boys and three family-based groups, from poor urban squatter settlements, urban middle class, and a remote rural village. Biomarkers of stress and vulnerability to stress included growth status, salivary cortisol, antibodies to Epstein–Barr virus, acute phase inflammatory responses (alpha1-antichymotrypsin), and cardiovascular fitness and reactivity (flex heart rate and pressor response). Individual biomarkers of risk and allostatic load differed markedly among groups, were highest in villagers, and varied by components of allostatic load. Such data suggest a need for critical appraisal of homelessness and migration as a risk factor to youth, given prevailing local conditions such as rural poverty, and represents the only multidimensional study of childhood allostatic load and developmental risk in non-Western settings.
A model-based cluster analysis approach to adolescent problem behaviors and young adult outcomes
Authors: Mun Eun Young , Windle Michael , Schainker Lisa M.
Published: January 2008

Data from a community-based sample of 1,126 10th- and 11th-grade adolescents were analyzed using a model-based cluster analysis approach to empirically identify heterogeneous adolescent subpopulations from the person-oriented and pattern-oriented perspectives. The model-based cluster analysis is a new clustering procedure to investigate population heterogeneity utilizing finite mixture multivariate normal densities and accordingly to classify subpopulations using more rigorous statistical procedures for the comparison of alternative models. Four cluster groups were identified and labeled multiproblem high-risk, smoking high-risk, normative, and low-risk groups. The multiproblem high risk exhibited a constellation of high levels of problem behaviors, including delinquent and sexual behaviors, multiple illicit substance use, and depressive symptoms at age 16. They had risky temperamental attributes and lower academic functioning and educational expectations at age 15.5 and, subsequently, at age 24 completed fewer years of education, and reported lower levels of physical health and higher levels of continued involvement in substance use and abuse. The smoking high-risk group was also found to be at risk for poorer functioning in young adulthood, compared to the low-risk group. The normative and the low risk groups were, by and large, similar in their adolescent and young adult functioning. The continuity and comorbidity path from middle adolescence to young adulthood may be aided and abetted by chronic as well as episodic substance use by adolescents.
Accelerating the development of emotion competence in Head Start children: Effects on adaptive and maladaptive behavior
Authors: Izard Carroll E. , King Kristen A. , Trentacosta Christopher J. , Morgan Judith K. , Laurenceau Jean-Philippe , Krauthamer-Ewing E. Stephanie , Finlon Kristy J.
Published: January 2008

Separate studies of rural and urban Head Start systems tested the hypothesis that an emotion-based prevention program (EBP) would accelerate the development of emotion and social competence and decrease agonistic behavior and potential precursors of psychopathology. In both studies, Head Start centers were randomly assigned to treatment and control/comparison group conditions. In Study 1 (rural community), results of hierarchical linear modeling analyses showed that compared to the control condition (Head Start as usual), EBP produced greater increases in emotion knowledge and emotion regulation and greater decreases in children's negative emotion expressions, aggression, anxious/depressed behavior, and negative peer and adult interactions. In Study 2 (inner city), compared to the established prevention program I Can Problem Solve, EBP led to greater increases in emotion knowledge, emotion regulation, positive emotion expression, and social competence. In Study 2, emotion knowledge mediated the effects of EBP on emotion regulation, and emotion competence (an aggregate of emotion knowledge and emotion regulation) mediated the effects of EBP on social competence.
Twenty‐four hour predictions of f0F2 using time delay neural networks
Authors: Wintoft Peter , Cander Ljiljana R.
Published: February 2008

The use of time delay feed‐forward neural networks to predict the hourly values of the ionospheric F2 layer critical frequency, f0F2, 24 hours ahead, have been examined. The 24 measurements of f0F2 per day are reduced to five coefficients with principal component analysis. A time delay line of these coefficients is then used as input to a feed‐forward neural network. Also included in the input are the 10.7 cm solar flux and the geomagnetic index Ap. The network is trained to predict measured f0F2 data from 1965 to 1985 at Slough ionospheric station and validated on an independent validation set from the same station for the periods 1987–1990 and 1992–1994. The results are compared with two different autocorrelation methods for the years 1986 and 1991, which correspond to low and high solar activity, respectively.
Deep low‐frequency tremor that correlates with passing surface waves
Authors: Miyazawa Masatoshi , Brodsky Emily E.
Published: January 2008

The large surface waves from the 2004 Sumatra‐Andaman earthquake dynamically perturbed the upper mantle structure in Japan and triggered periodic deep low‐frequency seismic tremor in eastern and western Shikoku, western and central Tokai, and the Kii peninsula. We use the relationship between the amplitude of the triggered tremor and the stresses of the seismic waves to investigate the mechanism of deep low‐frequency seismic tremor. Volumetric strain changes from the 15–30 s Rayleigh waves play an important role in the strong triggering, likely via Coulomb failure stress changes. Building on previous results that the tremor signals become increasingly strong with increasing dilatation, we observe a clear increase in the triggered tremor with an increase in the dilatation due to the Rayleigh waves at the 30 km depth source regions. We also observe a correlation with the Coulomb failure stress change resolved on an appropriate plane. There is an exponential relationship between the signal amplitude from triggered tremor and both the dilatation and the Coulomb shear stress at the source region. This combined with the shape of the tremor packets implies that the tremor amplitude is predictable based on the amplitude of the incoming waves. The amplitude variations can be explained by a distribution of sources in the tremor source region.
Effect of the Emperor seamounts on trans‐oceanic propagation of the 2006 Kuril Island earthquake tsunami
Authors: Koshimura S. , Hayashi Y. , Munemoto K. , Imamura F.
Published: January 2008

The effect of tsunami wave scattering by the Emperor seamounts on the propagation of the 2006 Kuril Island earthquake tsunami is demonstrated, using the finite difference method. The model results indicate that the contribution of the Emperor seamounts on the maximum tsunami energy along the Pacific coast of Japan is found to be as much as 50% or more. Also, analysis of the spectral evolution of observed tsunami records in Japan suggests that the scattering waves from the Emperor seamounts possibly dominate the wave components at periods of 4 to 17 minutes.
Decadal growth of black carbon emissions in India
Authors: Sahu S. K. , Beig G. , Sharma C.
Published: January 2008

A Geographical Information System (GIS) based methodology has been used to construct the black carbon (BC) emission inventory for the Indian geographical region. The distribution of emissions from a broader level to a spatial resolution of 1° × 1° grid has been carried out by considering micro level details and activity data of fossil fuels and bio‐fuels. Our calculated total BC emissions were 1343.78 Gg and 835.50 Gg for the base years 2001 and 1991 respectively with a decadal growth of around 61%, which is highly significant. The district level analysis shows a diverse spatial distribution with the top 10% emitting districts contributing nearly 50% of total BC emission. Coal contributes more than 50% of total BC emission. All the metropolitan cities show high BC emissions due to high population density giving rise to high vehicular emissions and more demand of energy.
Use of a standardized runoff index for characterizing hydrologic drought
Authors: Shukla Shraddhanand , Wood Andrew W.
Published: January 2008

Many current metrics of drought are derived solely from analyses of climate variables such as precipitation and temperature. Drought is clearly a consequence of climate anomalies, as well as of human water use practices, but many impacts to society are more directly related to hydrologic conditions resulting from these two factors. Modern hydrology models can provide a valuable counterpart to existing climate‐based drought indices by simulating hydrologic variables such as land surface runoff. We contrast the behavior of a standardized runoff index (SRI) with that of the well‐known standardized precipitation index (SPI) during drought events in a snowmelt region. Although the SRI and SPI are similar when based on long accumulation periods, the SRI incorporates hydrologic processes that determine seasonal lags in the influence of climate on streamflow. As a result, on monthly to seasonal time scales, the SRI is a useful complement to the SPI for depicting hydrologic aspects of drought.
Magnetic properties of anorthosites: A forgotten source for planetary magnetic anomalies?
Authors: Brown Laurie L. , McEnroe Suzanne A.
Published: January 2008

Anorthosites, igneous rocks very rich in plagioclase, rarely considered to be strongly magnetic, are common on Earth, and the Moon, and inferred to be on other planets. Magnetic properties of anorthosites could be important in investigating associated mineral deposits and in studying magnetic anomalies, especially on Mars. Here we investigate three late Proterozoic anorthosites in Rogaland, Norway, for magnetic and petrographic properties. Two of the anorthosites have large natural remanent magnetization (NRM), with intensities comparable to Tertiary basalts. Susceptibility, NRM and hysteresis properties provide information about the magnetic minerals present and their response to inducing fields. Microscopic observations show ubiquitous hemo‐ilmenite in the anorthosites, whereas magnetite is common in the Håland‐Helleren, but rare in the Åna‐Sira and Egersund‐Ogna bodies. This study illustrates that anorthosites can be important sources of magnetic anomalies, and can retain a remanent field over geologic time. It also supports the recently described property of ‘lamellar magnetization’.
Pc1–Pc2 waves and energetic particle precipitation during and after magnetic storms: Superposed epoch analysis and case studies
Authors: Engebretson M. J. , Lessard M. R. , Bortnik J. , Green J. C. , Horne R. B. , Detrick D. L. , Weatherwax A. T. , Manninen J. , Petit N. J. , Posch J. L. , Rose M. C.
Published: January 2008

Magnetic pulsations in the Pc1–Pc2 frequency range (0.1–5 Hz) are often observed on the ground and in the Earth's magnetosphere during the aftermath of geomagnetic storms. Numerous studies have suggested that they may play a role in reducing the fluxes of energetic ions in the ring current; more recent studies suggest they may interact parasitically with radiation belt electrons as well. We report here on observations during 2005 from search coil magnetometers and riometers installed at three Antarctic stations, Halley (−61.84° magnetic latitude, MLAT), South Pole (−74.18° MLAT), and McMurdo (−79.96° MLAT), and from energetic ion detectors on the NOAA Polar‐orbiting Operational Environment Satellites (POES). A superposed epoch analysis based on 13 magnetic storms between April and September 2005 as well as case studies confirm several earlier studies that show that narrowband Pc1–Pc2 waves are rarely if ever observed on the ground during the main and early recovery phases of magnetic storms. However, intense broadband Pi1–Pi2 ULF noise, accompanied by strong riometer absorption signatures, does occur during these times. As storm recovery progresses, the occurrence of Pc1–Pc2 waves increases, at first in the daytime and especially afternoon sectors but at essentially all local times later in the recovery phase (typically by days 3 or 4). During the early storm recovery phase the propagation of Pc1–Pc2 waves through the ionospheric waveguide to higher latitudes was more severely attenuated. These observations are consistent with suggestions that Pc1–Pc2 waves occurring during the early recovery phase of magnetic storms are generated in association with plasmaspheric plumes in the noon‐to‐dusk sector, and these observations provide additional evidence that the propagation of waves to ground stations is inhibited during the early phases of such storms. Analysis of 30‐ to 250‐keV proton data from four POES satellites during the 24–27 August and 18–19 July 2005 storm intervals showed that the location of the inner edge of the ring current matched well with the plasmapause model of O'Brien and Moldwin (2003). However, the POES data showed no evidence of the consequences of electromagnetic ion cyclotron waves (localized proton precipitation) during main and early recovery phase. During later stages of the recovery phase, when such precipitation was observed, it was coincident with intense wave events at Halley, and it occurred at L shells near or up to 1 RE outside the modeled plasmapause but well equatorward of the isotropy boundary.
Satellite and ground‐based observations of auroral energy deposition and the effects on thermospheric composition during large geomagnetic storms: 1. Great geomagnetic storm of 20 November 2003
Authors: Hecht J. H. , Mulligan T. , Strickland D. J. , Kochenash A. J. , Murayama Y. , Tanaka Y.‐M. , Evans D. S. , Conde M. G. , Donovan E. F. , Rich F. J. , Morrison D.
Published: January 2008

This report describes thermospheric composition and particle precipitation changes that occurred during the period of the great geomagnetic storm of 20–21 November 2003, an event that was associated with the passage of a magnetic cloud past the Earth. These changes are compared to those observed during geomagnetic activity on 17 November 2003 and during the intervening quieter period. The data used are obtained from (1) ground‐based magnetometers, an imaging riometer, a scanning Doppler imaging Fabry‐Perot, and photometers from stations in Alaska, (2) photometers from Canadian sites, (3) NOAA POES and DMSP particle sensors, and (4) the TIMED Global Ultraviolet Imager far UV sensor. The composition changes associated with the input of auroral particle and Joule energy showed larger depletions in atomic oxygen on 20 November than on the other nights and greater changes than are seen in the Naval Research Laboratory Mass Spectrometer and Incoherent Scatter (NRLMSIS) model atmosphere. NRLMSIS does better in reproducing the changes during the great magnetic storm with its long duration auroral energy input than during the shorter time duration geomagnetic activity that occurred on 17 November. During the nights with the largest changes in composition the input of Joule energy dominates over auroral particle energy. It is shown that the particle energy distributions associated with the 20–21 November storm in the period around and after the passage of the magnetic cloud had lower average energies and were enhanced at energies below 0.1 keV than those that caused auroral displays on the preceding days.
Longitudinal variability of low‐latitude total electron content: Tidal influences
Authors: Scherliess L. , Thompson D. C. , Schunk R. W.
Published: January 2008

Recently, nighttime ultraviolet (UV) observations obtained by IMAGE FUV and TIMED GUVI instruments have revealed a longitudinal wave number four pattern in the nighttime airglow intensity and in the position of the equatorial anomalies during equinox and high solar flux conditions. In the present study, we have extended this work and determined the longitudinal variability of the low‐latitude total electron content (TEC) climatology during different geophysical conditions with a special emphasis on the longitudinal wave number four structure in the low‐latitude ionosphere. We have used more than 5 million low‐latitude TOPEX TEC observations covering the entire 13 years of TOPEX TEC data from August 1992 until October 2005. This data set was used to determine the local time, seasonal, solar cycle, and geomagnetic activity dependence of the longitudinal variability of TEC at equatorial and low latitudes, and in particular, to address the existence and evolution of the wave number four longitudinal pattern under these conditions. Our study shows that the wave number four pattern is created during the daytime hours at equinox and June solstice but is absent, or washed out by other processes, during December solstice. During equinox the wave number four pattern is created around noon with well‐defined longitudinal enhancements in the low‐latitude TEC. These enhancements, which are symmetric about the geomagnetic equator during this season, last for many hours and can be clearly seen past midnight. The longitudinal patterns are found to be nearly identical between the vernal (March/April) and autumnal (September/October) equinoxes and largely independent of the solar cycle conditions. The wave number four pattern is also observed during geomagnetically active conditions, indicating that the processes that create this pattern are also present during active times. The variations between the well‐defined longitudinal maxima and minima are of the order of 20%. During June solstice, the wave number four pattern is also observed in the afternoon hours but, in contrast to the equinox cases, it exhibits a strong hemispheric asymmetry and is not observed during the night. The low‐latitude TEC exhibits clear longitudinal variations during December solstice, with large daytime enhancements over the east Asian and Pacific regions and a third enhancement emerging in the afternoon over the Atlantic Ocean, but a clear wave number four pattern is not observed during this season. Although the equatorial and low‐latitude TEC values exhibit clear longitudinal patterns during all seasons, a significant amount of scatter remains in the TEC data that is not accounted for by changes in the solar cycle, the season, or the local time or by the longitudinal variability. This remaining scatter is largest near the poleward edges of the anomalies and is of the order of 40%.
Radiation Belt Environment model: Application to space weather nowcasting
Authors: Fok Mei‐Ching , Horne Richard B. , Meredith Nigel P. , Glauert Sarah A.
Published: January 2008

A data‐driven physical model of the energetic electrons in the Earth's radiation belts, called the Radiation Belt Environment (RBE) model, has been developed to understand Earth's radiation belt dynamics and to predict the radiation conditions found there. This model calculates radiation belt electron fluxes from 10 keV to 6 MeV in the inner magnetosphere. It takes into account the realistic, time‐varying magnetic field and considers effects of wave‐particle interactions with whistler mode chorus waves. The storm on 23–27 October 2002 is simulated and the temporal evolutions of the radial and pitch angle distributions of energetic electrons are examined. The calculated electron fluxes agree very well with particle data from the low‐orbit SAMPEX and LANL geosynchronous satellites, when the wave‐particle interactions are taken into account during storm recovery. Flux increases begin near the plasmapause and then diffuse outward to higher L shells, consistent with previous findings from statistical studies. A simplified version of the RBE model is now running in real time to provide nowcasting of the radiation belt environment. With further improvements and refinements, this model will have important value in both scientific and space weather applications.
Track analysis of energetic neutral atom blobs at Saturn
Authors: Carbary J. F. , Mitchell D. G. , Brandt P. , Roelof E. C. , Krimigis S. M.
Published: January 2008

A statistical analysis of observations of the Magnetospheric Imaging Instrument (MIMI) on the Cassini spacecraft at Saturn reveals the morphology and dynamics of energetic neutral atoms (ENA). The ENA (20–50 keV hydrogens) images are smoothed and projected onto Saturn's equatorial plane, and the intensities are slant‐corrected using a thin‐disk approximation. The resulting images exhibit intensity “blobs” that move in a prograde (corotational) sense about Saturn. Blob centroids are determined and tracked for as long as they persist as recognizable objects. The radial distribution of the centroids maximizes near the orbit of Rhea (∼9 RS, 1 RS = 60,268 km). The angular speeds of all blobs lasting longer than 5 h vary from near zero to nearly twice the rigid corotation speed. However, the longer‐lived blobs (those lasting longer than 10 h) exhibit a sharp cutoff at the corotation speed. Inside the orbit of Rhea, the angular speeds decrease linearly with radial distance with a slope of −11.4°/h/RS, while outside the orbit of Rhea, the speeds are essentially constant at 13.1 ± 1.6°/h. Generally, the angular speeds differ from corotation (33.4°/h). The angular speeds tend to be somewhat slower near midnight than at other local times. The radial speed distribution peaks at the slightly inward value of −0.26 RS/h. Radial speeds exhibit a slight outflow from 6 to 10 h local time and a slight inflow from 16 to 20 h.
Spatiospectral localization of global geopotential fields from the Gravity Recovery and Climate Experiment (GRACE) reveals the coseismic gravity change owing to the 2004 Sumatra‐Andaman earthquake
Authors: Han Shin‐Chan , Simons Frederik J.
Published: January 2008

Regional mass fluxes owing to transport and adjustment within the Earth system that are implicitly contained in the monthly Gravity Recovery and Climate Experiment (GRACE) global geopotential coefficients are revealed by localizing global spectra using spatiospectrally concentrated window functions. We have analyzed 45 monthly global GRACE harmonic coefficient series in order to find the coseismic signature associated with the 2004 great Sumatra‐Andaman earthquake. A significant gravity change after the earthquake is found in the time series of the GRACE coefficients after localization with a single band‐limited window centered near the north of the island of Sumatra. This change is undetectable from the original global coefficients or from coefficients localized elsewhere on the globe. A step function with its discontinuity at 26 December 2004 usefully models the coseismic gravity change. The localized GRACE coefficients contain the jumps (associated with the earthquake) up to degree and order 55, although not all of them within this band produce changes that are statistically significant. The gravity change calculated from the localized GRACE coefficients displays 30 μGal peak‐to‐peak variations that are very well correlated with an independently derived seismic model based on elastic dislocation theory.
Human contribution to rapidly increasing frequency of very warm Northern Hemisphere summers
Authors: Jones Gareth S. , Stott Peter A. , Christidis Nikolaos
Published: January 2008

The European summer of 2003 was exceptionally warm, and there is evidence that human influence has at least doubled the risk of such a hot summer. It is possible that by the 2040s, summers over southern Europe will be as warm or warmer 50% of the time. Because of the related socioeconomic impacts, there is growing interest in investigating changes in climate extremes across the world and how they may change in the future. We examine observed and simulated summer temperatures over a set of regions covering the Northern Hemisphere. Simulated changes are consistent with observed changes over the vast majority of regions when the climate simulation includes changes in anthropogenic and natural influences. We detect the dominant influence of anthropogenic factors on observed warming in almost every region, which has led to a rapidly increasing risk of hot summers. We show that hot summers which were infrequent 20–40 years ago are now much more common and that our projections indicate that the current sharp rise in incidence of hot summers is likely to continue.
Isotopic exchange between carbon dioxide and ozone via O(1D) in the stratosphere
Authors: Yung Yuk L. , DeMore W. B. , Pinto Joseph P.
Published: February 2008

We propose a novel mechanism for isotopic exchange between CO2 and O3 via O(1D) + CO2 → CO3* followed by CO3* → CO2 + O(3P). A one‐dimensional model calculation shows that this mechanism can account for the enrichment in 18O in the stratospheric CO2 observed by Gamo et al. [1989], using the heavy O3 profile observed by Mauersberger [1981]. The implications of this mechanism for other stratospheric species and as a source of isotopically heavy CO2 in the troposphere are briefly discussed.
Ionospheric storm effects at subauroral latitudes: A case study
Authors: Prölss G. W. , Brace L. H. , Mayr H. G. , Carignan G. R. , Killeen T. L. , Klobuchar J. A.
Published: February 2008

An attempt is made to classify ionospheric storm effects at subauroral latitudes according to their presumed origin. The storm of December 7/8, 1982, serves as an example. It is investigated using ionosonde, electron content, and DE 2 satellite data. The following effects are distinguished: (1) positive storm effects caused by traveling atmospheric disturbances, (2) positive storm effects caused by changes in the large‐scale thermospheric wind circulation, (3) positive storm effects caused by the expansion of the polar ionization enhancement, (4) negative storm effects caused by perturbations of the neutral gas composition, and (5) negative storm effects caused by the equatorward displacement of the trough region.
Fast and accurate ray tracing by Hamiltonian perturbation
Authors: Virieux Jean
Published: February 2008

Fast and accurate ray tracing in heterogeneous isotropic media is required in many applications of seismology. We propose two analytical techniques of perturbation, the “variation of coordinates” method and the “variation of constants” method, which are faster than an entirely numerical procedure. From a local polynomial expansion of the square of slowness, we explicitly write perturbed analytical expressions for rays, paraxial rays, polarization vectors and travel times. These expressions are in a form suitable for computer programming. Based on these expressions, a finite element approach is proposed where the medium is divided in rectangles for two‐dimensional media and in parallelepipeds for three‐dimensional media. The “variation of coordinates” method is well adapted for cardinal b spline interpolations of the square of slowness in each cell. We have found that b splines of order 4 give a good compromise between the number of elements for describing the heterogeneity of the medium and the efficiency of computing perturbed analytical expressions for rays in each element.
Experimental determination of element partitioning and calculation of phase relations in the MgO‐FeO‐SiO2 system at high pressure and high temperature
Authors: Fei Yingwei , Mao Ho‐Kwang , Mysen Bjorn O.
Published: February 2008

Mg‐Fe partitioning between coexisting phases, magnesiowüstite (Mw) and olivine (α), Mw and β‐phase, Mw and spinel (γ), and Mw and perovskite (Pv), has been determined experimentally with piston‐cylinder apparatus, the multianvil device and the diamond anvil cell technique at pressures between 2 and 28 GPa and temperatures between 1473 and 1773 K. The solution parameters of each solid solution were obtained by fitting the experimental data simultaneously using the Margules formulation. The optimized solution parameters (in J/mol) are WMwMg‐Fe = 16100, WMwFe‐Mg = 26300 − 5.56T; WαMg‐Fe = 4500 + 130P, WαFe‐Mg = 6500 + 130P; WβMg‐Fe = 1000, WβFe‐Mg = 2000; WγMg‐Fe = 900 − 1.10T WγFe‐Mg = 3900; and WPvMg‐Fe = 4130 −1.37T + 110P, WPvFe‐Mg = −4050 − 2.45T + 150 P where P is in GPa and T in K. These parameters are consistent with solution calorimetry and phase equilibrium data. Phase relations in the MgO‐FeO‐SiO2 system were calculated by using the Margules solution model combined with internally consistent thermodynamic data of the pure phases. The computation provides independent constraints for phase relations in the system, in addition to those directly determined in P‐T‐Xi space.
Fluid flow along a decollement layer: A Model applied to the 16°N section of the Barbados Accretionary Wedge
Authors: Henry Pierre , Le Pichon Xavier
Published: February 2008

A seismic section across the whole Barbados accretionary complex at 16°N recently published by Westbrook et al. (1988) shows that the reflection marking the decollement fades between 40 and 60 km arcward of the deformation front but is present again further inland. This interruption appears to be related to a thrust cutting through the wedge. One‐dimensional steady state models of water flow along the decollement suggest a mechanism responsible for decollement disruption: a local increase of the slope either of the wedge, or of the decollement, causes the subducted layer to compact, and locally increases the friction along the decollement. If the thrust is used as a conduit for fluids to escape from the decollement, the friction along the decollement toeward of the thrust is further increased. The model also shows that the permeability of the decollement should be of the order of 10−14 m2, but may be higher near the deformation front for short periods if fluid expulsion mainly occurs in transient bursts associated with hydraulic fracturing. As a consequence of the non‐linearity of the compaction equation, pore pressure at depth in the decollement depends on the water flux, on the lithostatic pressure gradient along the decollement and on the parameters from which the physical properties of the sediment are calculated. However, it is almost independent on the pore pressure below the toe.
Diagnostic calculation for circulation and water mass movement in the deep Pacific
Authors: Fujio Shinzou , Imasato Norihisa
Published: February 2008

The steady circulation of the deep Pacific is estimated with a robust diagnostic model, which is internally constrained by hydrographic data. It is shown that the input data should be modified to fit the model in inverse proportion to the Coriolis parameter because a density field inconsistent with the model generates unrealistic geostrophic flows. The model reproduces most of the deep currents previously reported, such as the deep western boundary current east of New Zealand. In addition, as a new feature, the present model diagnoses an anticyclonic circulation around the East Pacific Rise. This circulation is discovered to be associated with a rise of isopycnals at middepth. Tracking of many particles in the diagnosed velocity field reveals that two water masses enter the Southwest Pacific Basin. One is the deep water of the South Indian Basin which enters through a gap to the south of New Zealand. The other is the upper water of the Antarctic Circumpolar Current; this water becomes dense near the Ross Sea and sinks into the deep Southeastern Pacific Basin. The anticyclonic circulation around the East Pacific Rise transports it to the Southwest Pacific Basin. These waters supply comparable volumes to the Southwest Pacific Basin; the residence time is estimated to be 86 years. The deep water in the Southwest Pacific Basin is brought northward rapidly by the deep western boundary current east of New Zealand; it takes only a few decades to move from the east of New Zealand to the North Pacific.
The WOCE model in the western equatorial Atlantic: Upper layer circulation
Authors: Schott Friedrich A. , Böning Claus W.
Published: February 2008

A high‐resolution general circulation model of the North Atlantic, first developed at the National Center for Atmospheric Research and then run at the Institut für Meereskunde in Kiel for two different wind climatologies and reduced vertical friction, is evaluated in the upper 500 m for the western tropical Atlantic, 5°S to 15°N. Although the general features of the vigorous seasonal circulation changes documented in previous studies and in the earlier high‐resolution model of Philander and Pacanowski (1986a) are reproduced, there are some interesting differences. Lack of eastward penetration of the Equatorial Undercurrent (EUC) and a thermocline that is too diffuse are model deficiencies due to the constant vertical eddy diffusion coefficient. In the lower friction case the undercurrent partially surfaces in the west, causing an eastward surface current on the equator, which is not apparent in the earlier model studies. Further, the zonal currents, in the low‐friction version, have high‐velocity bands, resulting, e.g., in two separate current cores in the North Equatorial Countercurrent (NECC) region; and an eastward surface core just south of the equator, connected to the EUC. Particularly interesting are equatorward undercurrents along the western boundary, one of which has already been confirmed in recent measurements off French Guyana. In winter it connects with the EUC in the model, in summer with the NECC. A northward undercurrent in the model exists off Brazil, between 5° and 10°S, but that is already close to the southern boundary of the model domain. The annual mean throughflow from the southern hemisphere into the Caribbean along the western boundary is small in the model, and in particular, there is no enhanced throughflow in winter, when the cross‐equatorial North Brazil Current transport is not taken up by the NECC.
Computation of atmospheric cooling rates by exact and approximate methods
Authors: Ridgway William L. , Harshvardhan  , Arking Albert
Published: February 2008

Infrared fluxes and cooling rates for several standard model atmospheres, with and without water vapor, carbon dioxide, and ozone, have been calculated using a line‐by‐line method at 0.01 cm−1 resolution. This study was conducted as part of the Intercomparison of Radiation Codes Used in Climate Models (ICRCCM) where line‐by‐line calculations are intended to serve as a benchmark for comparing practical codes used in climate models. The sensitivity of the results to the vertical integration scheme and to the model for water vapor continuum absorption is shown. Comparison with similar calculations performed at NOAA/GFDL shows agreement to within 0.5 W m−2 in fluxes at various levels and 0.05 K d−1 in cooling rates. Comparison with a fast, parameterized radiation code used in climate models reveals a worst case difference, when all gases are included, of 3.7 W m−2 in flux; cooling rate differences are 0.1 K d−1 or less when integrated over a substantial layer with point differences as large as 0.3 K d−1.
Rainwater and throughfall chemistry in a “terra firme” rain forest: Central Amazonia
Authors: Forti M. Cristina , Moreira‐Nordemann L. M.
Published: February 2008

During the Global Tropospheric Experiment (GTE)‐Amazon Boundary Layer Experiment (ABLE) 2B campaign in the Amazon basin, samples of rainwater and throughfall were obtained in a “terra firme” (nonflooded forest) rain forest at the Ducke Reserve (2°57'S, 59°58'W). The samples were collected during one wet period (April 1 to May 13, 1987) and one dry period (August 1 to October 1, 1987). All samples were analyzed for Na+, K+, Mg2+, Ca2+, NH4+, Cl− and SO42−, and pH. The rainwater was acidic, with a volume‐weighted mean pH of 4.6 for the two periods. Rainwater input from the dry period was 2 times greater for Na+, Mg2+, NH4+ and SO42− and about 4 times greater for K− than from the wet period. The ionic concentrations in throughfall were higher than those in rainwater, except for NH4+ during the dry period. This enrichment of throughfall is attributed to the interaction of precipitation with the forest canopy.
Carbon 13 in Pacific Deep and Intermediate Waters, 0‐370 ka: Implications for Ocean Circulation and Pleistocene CO2
Authors: Mix A. C. , Pisias N. G. , Zahn R. , Rugh W. , Lopez C. , Nelson K.
Published: February 2008

Stable isotopes in benthic foraminifera from Pacific sediments are used to assess hypotheses of systematic shifts in the depth distribution of oceanic nutrients and carbon during the ice ages. The carbon isotope differences between ∼1400 and ∼3200 m depth in the eastern Pacific are consistently greater in glacial than interglacial maxima over the last ∼370 kyr. This phenomenon of “bottom heavy” glacial nutrient distributions, which Boyle proposed as a cause of Pleistocene CO2 change, occurs primarily in the 1/100 and 1/41 kyr−1 “Milankovitch” orbital frequency bands but appears to lack a coherent 1/23 kyr−1 band related to orbital precession. Averaged over oxygen‐isotope stages, glacial δ13C gradients from ∼1400 to ∼3200 m depth are 0.1‰ greater than interglacial gradients. The range of extreme shifts is somewhat larger, 0.2 to 0.5‰. In both cases, these changes in Pacific δ13C distributions are much smaller than observed in shorter records from the North Atlantic. This may be too small to be a dominant cause of atmospheric pCO2 change, unless current models underestimate the sensitivity of pCO2 to nutrient redistributions. This dampening of Pacific relative to Atlantic δ13C depth gradient favors a North Atlantic origin of the phenomenon, although local variations of Pacific intermediate water masses can not be excluded at present.
does ion tearing exist?
Authors: Pellat R. , Coroniti F. V. , Pritchett P. L.
Published: February 2008

In a quasi‐neutral sheet the tearing mode is strongly stabilized by electron compressibility. We demonstrate that previous attempts to remove the compressibility by wave turbulent pitch‐angle scattering or by non‐adiabatic stochastic first invariant diffusion are incorrect since these processes do not change the perturbed number of particles on a flux tube. Only spatial diffusion of electrons across magnetic flux surfaces can remove the stabilizing effect of compressibility; in this case, the electron, but not the ion, tearing mode may exist.
A note on the frictional strength of laumontite from Cajon Pass, California
Authors: Morrow C. A. , Byerlee J. D.
Published: February 2008

Laumontite mineralization is pervasive in joints and shear zones encountered in the Cajon Pass drillhole in southern California. In order to determine whether a gouge composed of this hydrated mineral affects shear strength in a manner similar to low‐strength, day‐rich fault gouges, frictional sliding experiments were performed under dry, saturated and high pore pressure conditions at effective pressures up to 450 MPa. Coefficients of friction ranged between 0.66 and 0.84, consistent with most crustal rocks and well above the values typical of clay‐rich San Andreas fault gouges. Saturation state had no effect on strength or sliding stability. These results suggest that the presence of laumontite in shear zones at Cajon Pass will not affect the shear strength of the rock in a way that can account for the inferred low ambient shear stresses.
Temperature trends in the lower mesosphere
Authors: Aikin A. C. , Chanin M. L. , Nash J. , Kendig D. J.
Published: February 2008

The largest atmospheric temperature changes due to the increase of greenhouse gases are expected in the 40 to 60 km altitude region, where enhanced infrared cooling decreases the temperature. Ten‐year (1980–1990) temperature trends at 55 km and 0.4 mb, derived using data from the ground‐based lidar at Haute Provence, 44°N 6°E, and the SSU channel 47X on several satellites, are presented. These data show temperature decreases that are as large and in some cases exceed predictions based on current models. At 44°N, the ground‐based lidar and satellite techniques give a negative trend of −0.10±0.04% per year and −0.14 ± 0.02% per year, respectively. Agreement between these two data sets based on different measurement techniques gives confidence in the detected trends at this latitude. Further analysis of the SSU 47X satellite data between 45°S and 45°N indicates a maximum decline of 0.16% per year near 30°N. A minimum trend decrease of 0.07% per year is detected between 20° and 30°S. Based on NOAA satellite radiance observations, these long‐term temperature changes are larger than changes at any of the other stratospheric levels below 55 km monitored during this period.
Is the extent of glaciation limited by marine gas‐hydrates?
Authors: Paull Charles K. , Ussler William , Dillon William P.
Published: February 2008

Methane may have been released to the atmosphere during the Quaternary from Arctic shelf gas‐hydrates as a result of thermal decomposition caused by climatic warming and rising sea‐level; this release of methane (a greenhouse gas) may represent a positive feedback on global warming [Revelle, 1983; Kvenvolden, 1988a; Nisbet, 1990]. We consider the response to sea‐level changes by the immense amount of gas‐hydrate that exists in continental rise sediments, and suggest that the reverse situation may apply—that release of methane trapped in the deep‐sea sediments as gas‐hydrates may provide a negative feedback to advancing glaciation. Methane is likely to be released from deep‐sea gas‐hydrates as sea‐level falls because methane gas‐hydrates decompose with pressure decrease. Methane would be released to sediment pore space at shallow sub‐bottom depths (100's of meters beneath the seafloor, commonly at water depths of 500 to 4,000 m) producing zones of markedly decreased sediment strength, leading to slumping [Carpenter, 1981; Kayen, 1988] and abrupt release of the gas. Methane is likely to be released to the atmosphere in spikes that become larger and more frequent as glaciation progresses. Because addition of methane to the atmosphere warms the planet, this process provides a negative feedback to glaciation, and could trigger deglaciation.
Generation of long wavelength heterogeneity in the mantle by the dynamic interaction between plates and convection
Authors: Gurnis Michael , Zhong Shijie
Published: February 2008

Lateral variations in seismic velocity (through its dependence on temperature) can easily be generated at the gravest harmonics, including degrees one and two, by the dynamic interaction between plates and convection. Models of thermal convection with a single non‐subducting plate have been formulated in a cylindrical geometry. Plates of width one to four times times the thickness of the convecting region strongly modulate the flow by being pushed over cold downwellings and inhibiting cooling of the fluid beneath. During rapid motion off of hot regions, a large‐scale pattern of shear is developed causing small uprising limbs to be swept into the largest upwellings. Both insulation and plume‐plume collisions pump energy into the lower wavenumber harmonics.
Daily variations of ELF data observed by a low‐altitude satellite
Authors: Parrot M. , Molchanov O. A. , Mogilevski M. M. , Lefeuvre F.
Published: February 2008

Data from a low‐orbiting satellite with a quasipolar orbit have been studied to determine if man‐made waves, such as the Power Line Harmonic Radiations (PLHR), can affect the intensity of the ELF waves observed in the ionosphere. The signals coming from two electric components were processed with a system of 6 filters (from 10 Hz up to 1000 Hz), and recorded on‐board all around the Earth. Most ELF waves derive from electrostatic turbulence. It is shown that the signal recorded by the electric component that is parallel to the Earth's magnetic field has a modulation depending of the days of the week. The amplitude is maximum on Monday and decreases until Saturday. The largest difference between Monday and Saturday (93%) occurs with the filter centered around 72 Hz. The interpretation of the experimental results supposes that the intensity of the ELF waves is connected to the PLHR influence on the ionospheric plasma. A theory is presented to explain this variation: the PLHR emitted from the ground during weekdays are different from those of the weekend, not only because power consumption is lower, but also because the ground configuration of their sources is changed.
Relationship between field line resonance at low geomagnetic latitudes and solar wind structures
Authors: Vellante M. , Villante U.
Published: February 2008

The link between the pulsation activity in the local resonant band at a low latitude station and the macroscale structure of the interplanetary medium has been investigated. The experimental results show a clear dependence of the amplitude of the local resonant events on the interplanetary magnetic field magnitude and a preferable occurrence in correspondence of the compression regions preceding the high velocity solar wind streams. These features appear consistent with an upstream wave source for these events.
An assessment of a magnetospheric model by tracing the energetic particle trapping boundary
Authors: Popielawska B. , Zwolakowska D.
Published: February 2008

We use the two most recent empirical magnetosphere models of Tsyganenko [1987; 1989] to find the energy dependent boundary of isotropic precipitation due to the nonadiabatic particle motion in the nightside current sheet. Model predictions are compared with the earlier published satellite observations of this boundary at low altitudes. A dramatic difference has been found between the predicted position of the isotropy boundary based on T87 and T89 model. The most recent magnetosphere model of Tsyganenko featuring the warped current sheet with thickness dependent both on XGSM and YGSM predicts that the isotropy boundary is situated at much lower latitudes than inferred from the previous models. This is in agreement with observations. However, even this model with very stretched tail magnetic field lines has difficulties in explaining the frequently observed very steep profile of critical rigidity vs L.
Intensity variation and coherence of 3–6 day equatorial waves
Authors: Dunkerton Timothy J.
Published: February 2008

Meridional wind oscillations of 3–6 day period are common in the equatorial lower stratosphere. Upper air data obtained from 32 equatorial stations, 1973–87, show that 70 mb wave intensity over the Maritime continent varied annually with largest amplitude in NH late winter and spring, but the seasonal cycle of intensity was not uniform in the tropics. Time series of meridional velocity and its spatial coherence suggest that 70 mb wave packets were local in longitude and episodic in time.
Regular and chaotic aspects of charged particle motion in a magnetotail‐like field with a neutral line
Authors: Savenkov Boris V. , Zelenyi Lev M. , Ashour‐Abdalla Maha , Büchner Jorg
Published: February 2008

The motion of charged particles is studied numerically and analytically using a test particle approach. Acceleration near the X‐type neutral line is described in terms of adiabatic invariants and separatrix crossings. The relation between regular and chaotic properties of the process is discussed for a realistic source in the plasma mantle.