bluuebunny/crossref_metadata_2025 huggingface dataset:
3D structures of steady flow of ideal compressible fluid in MHD: a new model of primordial solar nebula
Authors: Salmin Vladimir V.
Published: April 2009

Stereographic projection of Hopf field on the 3-sphere into Euclidean 3-space is used as a model of 3D steady flow of ideal compressible fluid in MHD. In such case, flow lines are Villarceau circles lying on tori corresponding to the levels of Bernoulli function. Existence of an optimal torus with minimal relative surface free energy is shown. Optimal tori are considered as precursors of planetary orbits.
Stellar magnetic fields across the H-R diagram: observational evidence
Authors: Berdyugina Svetlana V.
Published: April 2009

This review presents most recent measurements of magnetic fields in various types of stars and substellar objects across the H-R diagram with the emphasis on measurement methods, observational and modeling biases, and the role of magnetic fields in stellar evolution.
Magnetic field observations of low-mass stars
Authors: Reiners Ansgar
Published: April 2009

Direct measurements of magnetic fields in low-mass stars of spectral class M have become available during the last years. This contribution summarizes the data available on direct magnetic measurements in M dwarfs from Zeeman analysis in integrated and polarized light. Strong magnetic fields at kilo-Gauss strength are found throughout the whole M spectral range, and so far all field M dwarfs of spectral type M6 and later show strong magnetic fields. Zeeman Doppler images from polarized light find weaker fields, which may carry important information on magnetic field generation in partially and fully convective stars.
Magnetic fields in O-type stars measured with FORS 1 at the VLT
Authors: Hubrig Swetlana , Schöller M. , Schnerr R. S. , Ilyin I. , Henrichs H. F. , Ignace R. , González J. F.
Published: April 2009

The presence of magnetic fields in O-type stars has been suspected for a long time. The discovery of such fields would explain a wide range of well documented enigmatic phenomena in massive stars, in particular cyclical wind variability, Hα emission variations, chemical peculiarity, narrow X-ray emission lines and non-thermal radio/X-ray emission. Here we present the results of our studies of magnetic fields in O-type stars, carried out over the last years.
The magnetic field of the B3V star 16 Pegasi
Authors: Henrichs Huib F. , Neiner C. , Schnerr R. S. , Verdugo E. , Alecian A. , Catala C. , Cochard F. , Gutiérrez J. , Huat A.-L. , Silvester J. , Thizy O.
Published: April 2009

The slowly pulsating B3V star 16 Pegasi was discovered by Hubrig et al. (2006) to be magnetic, based on low-resolution spectropolarimetric observations with FORS1 at the VLT. We have confirmed the presence of a magnetic field with new measurements with the spectropolarimeters Narval at TBL, France and Espadons at CFHT, Hawaii during 2007. The most likely period is about 1.44 d for the modulation of the field, but this could not be firmly established with the available data set. No variability has been found in the UV stellar wind lines. Although the star was reported once to show Hα in emission, there exists at present no confirmation that the star is a Be star.
Analysis of magnetic pressure effects in atmospheres of CP stars
Authors: Shulyak Denis , Valyavin G. , Kochukhov O. , Burlakova T.
Published: April 2009

Several dynamical processes may induce considerable Lorentz forces in atmospheres of mCP stars, thus modifying the hydrostatic structure of their atmospheres. This modification can be seen as characteristic rotational variability of certain spectral features such as hydrogen Balmer lines. In this work we present the first results of modeling the magnetic pressure effects in atmospheres of mCP stars in the framework of model atmosphere analysis with accurate treatment of microscopic properties of atmospheric plasma. We show that at least part of the rotational variability of hydrogen lines seen in high-resolution spectra of mCP stars could be attributed to the non-zero electrical currents flowing along stellar surfaces.
Simulations of magneto-hydrodynamic waves in atmospheres of roAp stars
Authors: Khomenko Elena , Kochukhov Oleg
Published: April 2009

We report 2D time-dependent non-linear magneto-hydrodynamical simulations of waves in the atmospheres of roAp stars. We explore a grid of simulations in a wide parameter space. The aim of our study is to understand the influence of the atmosphere and the magnetic field on the propagation and reflection properties of magneto-acoustic waves, formation of shocks and node layers.
Gradient of the stellar magnetic field in measurements of hydrogen line cores
Authors: Kudryavtsev Dimitry O. , Romanyuk Iosif I.
Published: April 2009

We report the observed systematic differences in longitudinal magnetic field values, obtained from measurements of metal lines and the core of the Hβ line for a number of Ap stars, having strong global magnetic fields. In overwhelming majority of cases the magnetic field values, obtained from measurements of hydrogen lines cores, is smaller then the ones obtained from metal lines. We discuss some possible explanations of this effect, the most probable of which is the existence of the gradient of the magnetic field in stellar atmospheres.
Angular momentum loss and stellar spin-down in magnetic massive stars
Authors: ud-Doula Asif , Owocki Stanley P. , Townsend Richard H.D.
Published: April 2009

We examine the angular momentum loss and associated rotational spin-down for magnetic hot stars with a line-driven stellar wind and a rotation-aligned dipole magnetic field. Our analysis here is based on our previous 2-D numerical MHD simulation study that examines the interplay among wind, field, and rotation as a function of two dimensionless parameters, W(=Vrot/Vorb) and ‘wind magnetic confinement’, η∗ defined below. We compare and contrast the 2-D, time variable angular momentum loss of this dipole model of a hot-star wind with the classical 1-D steady-state analysis by Weber and Davis (WD), who used an idealized monopole field to model the angular momentum loss in the solar wind. Despite the differences, we find that the total angular momentum loss averaged over both solid angle and time follows closely the general WD scaling ~ ṀΩR2A. The key distinction is that for a dipole field Alfvèn radius RA is significantly smaller than for the monopole field WD used in their analyses. This leads to a slower stellar spin-down for the dipole field with typical spin-down times of order 1 Myr for several known magnetic massive stars.
Polarized hydrogen emission lines in Mira stars: a mystery behind the shock
Authors: Fabas Nicolas , Lèbre Agnès , Gillet Denis
Published: April 2009

We present a full spectropolarimetric study (in the Stokes parameters I, Q, U and V) on omicron Ceti (the prototype of Mira stars), and focus on the strong polarization detected in Balmer emission lines. This study is made with observations from NARVAL instrument at TBL (Telescope Bernard Lyot) in Pic du Midi Observatory, France.
Dynamo-generated magnetic fields in fast rotating single giants
Authors: Konstantinova-Antova Renada , Aurière Michel , Schröder Klaus-Peter , Petit Pascal
Published: April 2009

Red giants offer a good opportunity to study the interplay of magnetic fields and stellar evolution. Using the spectro-polarimeter NARVAL of the Telescope Bernard Lyot (TBL), Pic du Midi, France and the LSD technique we began a survey of magnetic fields in single G-K-M giants. Early results include 6 MF-detections with fast rotating giants, and for the first time a magnetic field was detected directly in an evolved M-giant: EK Boo. Our results could be explained in the terms of α–ω dynamo operating in these giants.
The magnetic structure of our Galaxy: a review of observations
Authors: Han JinLin
Published: April 2009

The magnetic structure in the Galactic disk, the Galactic center and the Galactic halo can be delineated more clearly than ever before. In the Galactic disk, the magnetic structure has been revealed by starlight polarization within 2 or 3 kpc of the Solar vicinity, by the distribution of the Zeeman splitting of OH masers in two or three nearby spiral arms, and by pulsar dispersion measures and rotation measures in nearly half of the disk. The polarized thermal dust emission of clouds at infrared, mm and submm wavelengths and the diffuse synchrotron emission are also related to the large-scale magnetic field in the disk. The rotation measures of extragalactic radio sources at low Galactic latitudes can be modeled by electron distributions and large-scale magnetic fields. The statistical properties of the magnetized interstellar medium at various scales have been studied using rotation measure data and polarization data. In the Galactic center, the non-thermal filaments indicate poloidal fields. There is no consensus on the field strength, maybe mG, maybe tens of μG. The polarized dust emission and much enhanced rotation measures of background radio sources are probably related to toroidal fields. In the Galactic halo, the antisymmetric RM sky reveals large-scale toroidal fields with reversed directions above and below the Galactic plane. Magnetic fields from all parts of our Galaxy are connected to form a global field structure. More observations are needed to explore the untouched regions and delineate how fields in different parts are connected.
Galactic dynamo simulations
Authors: Elstner Detlef , Gressel Oliver , Rüdiger Günther
Published: April 2009

Recent simulations of supernova-driven turbulence within the ISM support the existence of a large-scale dynamo. With a growth time of about two hundred million years, the dynamo is quite fast – in contradiction to many assertions in the literature. We here present details on the scaling of the dynamo effect within the simulations and discuss global mean-field models based on the adopted turbulence coefficients. The results are compared to global simulations of the magneto-rotational instability.
The magnetic field in luminous star-forming galaxies
Authors: Robishaw Timothy , Heiles Carl
Published: April 2009

An ongoing search for Zeeman splitting in the 1667 MHz OH megamaser emission from luminous star-forming galaxies has yielded numerous detections. These results, in addition to being the first extragalactic measurement of the Zeeman effect in an emission line, suggest that OH megamasers are excellent extragalactic magnetometers. We review the progress of our survey and discuss future observations.
Magnetic field transport from AGN cores to jets, lobes, and the IGM
Authors: Kronberg Philipp P.
Published: April 2009

I describe various stages of energy flow along an extragalactic jet, which subsequently evolves into an extended lobe which is visible in radio and X-rays. The sizes of the lobes vary from kpc scales to several megaparsec, so that the largest lobes are clearly injecting back hole energy into the IGM on scales comparable with a galaxy-galaxy separation. This is sometimes loosely referred to as Black hole-IGM “feedback”. My talk begins with a well-formed jet, and avoids the complex and unclarified physics at less than a few Schwarzschild radii that cause the initial launching the jet.

This presentation focuses on recent thinking and supercomputer simulations that appear to clarify the fundamental nature of these remarkable jets and lobes. The energy transport process appears to be electrodynamic, rather than particle beam–driven. A new observational verification of a 1018 Ampère current in an actual jet is concordant with the predictions and simulations of poynting flux-dominated electromagnetic jets. In this model the current is tightly related to the BH mass and angular energy.

The magneto-plasma properties of the lobes must obviously match to the jets which feed them. The “energy sink” phase is when BH energy is ultimately deposited on supra-galactic scales. The process from the BH to the lobe production happens with remarkable efficiency. The presence or absence of a galaxy cluster environment creates laboratory conditions that help to calibrate the energy flow paths, and the magnetic rigidity of these jet-lobe systems.

I conclude by describing recent, sensitive radio observations on supra-cluster scales that test for final magnetic energy deposition - the “sink” phase - into the intergalactic medium.
The polarized emission from the galactic plane at arcminute angular resolution
Authors: Landecker Tom L. , Reich W. , Reid R. I. , Reich P. , Wolleben M. , Kothes R. , Del Rizzo D. , Uyanıker B. , Gray A. D. , Fürst E. , Taylor A. R. , Wielebinski R.
Published: April 2009

As part of the Canadian Galactic Plane Survey (CGPS) we have imaged the polarized emission from the plane of the Milky Way at 1420 MHz, covering 1200 square degrees with arc-minute resolution. Structure on all scales is represented by combining aperture-synthesis data with single-antenna data. The survey depicts the Magneto-Ionic Medium at a resolution that matches images of other components of the Interstellar Medium within the CGPS database (http://www4.cadc.hia.nrc.gc.ca).
Global simulations of a galactic dynamo driven by cosmic-rays and exploding magnetized stars
Authors: Hanasz Michał , Wóltański Dominik , Kowalik Kacper , Pawłaszek Rafał
Published: April 2009

We conduct global galactic–scale magnetohydrodynamical (MHD) simulations of the cosmic–ray driven dynamo. We assume that exploding stars deposit small–scale, randomly oriented, dipolar magnetic fields into the differentially rotating ISM, together with a portion of cosmic rays, accelerated in supernova shocks. Our simulations are performed with the aid of a new parallel MHD code PIERNIK. We demonstrate that dipolar magnetic fields supplied on small SN–remnant scales, can be amplified exponentially by the CR–driven dynamo to the present equipartition values, and transformed simultaneously to large galactic–scales by an inverse cascade promoted by resistive processes.
Evolution of magnetic fields in the IGM: kinetic MHD turbulence
Authors: de Lima Reinaldo S. , de Gouveia Dal Pino E. M. , Lazarian A. , Falceta-Gonçalves D.
Published: April 2009

In this work, we present 3D MHD simulations of non-helical, forced turbulence, with an anisotropic thermal pressure with respect to the orientation of the local magnetic field. Such anisotropy arises when the plasma is weakly collisional, i.e., when the Larmor frequency is much greater than the ion-ion collision frequency. In this Kinetic MHD regime (KMHD), there are instabilities that give rise to fast growing magnetic fluctuations in the smallest scales. The plasma that fills the intergalactic and intracluster media has small density (n ~ 10−3cm−3), hence the effects of these instabilities could be important in the turbulent amplification of the magnetic fields there. In order to study the KMHD turbulence, we have performed 3D numerical simulations employing a godunov-MHD code (e.g., Kowal, Lazarian & Beresnyak 2007; Falceta-Gonçalves, Lazarian & Kowal 2008). The power spectrum of the velocity and magnetic fields were calculated for two cases: when there is a pre-existing mean magnetic field, and when there is only an initial weak magnetic field.
Cosmic magnetic fields in galaxies, groups and clusters
Authors: Geisbuesch Joern , Alexander Paul
Published: April 2009

The distribution of the Faraday depth induced by galaxies, groups and clusters on a patch of sky is investigated. For instance, we utilise a halo model approach to obtain synthetic Faraday skies. Moreover, our modelling includes cluster physical as well as cosmological aspects. A SKA sky survey will provide a large sample of rotation measures of polarised sources. Hence, we examine to what extent statistics of rotation measures of these sources can yield information about cosmic magnetic fields and cosmology.
Cosmic magnetic fields in clusters of galaxies and their analysis
Authors: Geisbuesch Joern , Alexander Paul
Published: April 2009

We discuss how measurements of linear polarisation of cluster background and embedded sources can be used to study cluster magnetic fields via Faraday rotation. We make forecasts for up-coming radio instruments on the basis of synthetic radio sky observations. Our mock polarised sky is modelled to agree with the sparse available data. By applying Bayesian statistical analysis methods, such as Markov Chain Monte Carlo and nested sampling techniques, we investigate which constraints can be placed on cluster magnetic field properties.
A study of the regular structure of the galactic magnetic field using WMAP5 polarization data at 22 GHz
Authors: Ruiz-Granados Beatriz , Rubiño-Martín J. A. , Battaner E.
Published: April 2009

We study the spatial structure of the 3-dimensional large-scale pattern of the Galactic Magnetic Field using the polarization maps obtained by the WMAP satellite at 22 GHz. By using five different models of the large-scale magnetic field of the Milky Way and a model for the cosmic rays distribution, we predict the expected polarized synchrotron emission. Those maps are compared to the observed 22 GHz polarization data using a Maximum Likelihood method. For each model, we obtain the parameter values which better reproduce the data and obtain their marginal probability distribution functions. We find that the model that best reproduces the observed polarization maps is an “axisymmetric” model.
The Faraday rotation measure synthesis technique
Authors: Heald George
Published: April 2009

We discuss practical aspects of the novel Faraday Rotation Measure Synthesis technique, first described by Burn (1966), and recently extended and implemented by Brentjens & de Bruyn (2005). The method takes advantage of the excellent spectral coverage provided by modern radio telescopes to reconstruct the intrinsic polarization properties along a line of sight, using a Fourier relationship between the observed polarization products and a function describing the intrinsic polarization (the Faraday dispersion function). An important consequence of the Fourier relationship and discrete frequency sampling is the need, in some cases, to deconvolve the sampling response from the reconstructed Faraday dispersion function. Practical aspects of the deconvolution procedure are discussed. We illustrate the use of the technique by summarizing a recent investigation carried out with the WSRT. We conclude by briefly describing the applicability to future programs which will be carried out with the next generation of radio telescopes such as LOFAR.
Diagnostic methods based on scattering polarization and the joint action of the Hanle and Zeeman effects
Authors: Bueno Javier Trujillo
Published: April 2009

Polarized light provides the most reliable source of information at our disposal for diagnosing the physical properties of astrophysical plasmas, including the magnetic fields of the solar atmosphere. The interaction between radiation and hydrogen plus free electrons through Rayleigh and Thomson scattering gives rise to the polarization of the stellar continuous spectrum, which is very sensitive to the medium's thermal and density structure. Anisotropic radiative pumping processes induce population imbalances and quantum coherences among the sublevels of degenerate energy levels (that is, atomic level polarization), which produce polarization in spectral lines without the need of a magnetic field. The Hanle effect caused by the presence of relatively weak magnetic fields modifies the atomic polarization of the upper and lower levels of the spectral lines under consideration, allowing us to detect magnetic fields to which the Zeeman effect is blind. After discussing the physical origin of the polarized radiation in stellar atmospheres, this paper highlights some recent developments in polarized radiation diagnostic methods and a few examples of their application in solar physics.
Spectropolarimetry with PEPSI at the LBT: accuracy vs. precision in magnetic field measurements
Authors: Ilyin Ilya , Strassmeier Klaus G. , Woche Manfred , Hofmann Axel
Published: April 2009

We present the design of the new PEPSI spectropolarimeter to be installed at the Large Binocular Telescope (LBT) in Arizona to measure the full set of Stokes parameters in spectral lines and outline its precision and the accuracy limiting factors.
Formelles und informelles Aufgabenprofil in der ambulanten psychiatrischen Pflege aus Sicht von Pflegenden: Eine Meta-Synthese
Authors: Richter Dirk , Hahn Sabine
Published: April 2009

Die ambulante psychiatrische Pflege gewinnt in der aktuellen psychiatrischen Versorgung eine zunehmende Bedeutung. Es mangelt jedoch an Material für die Aus- und Weiterbildung von psychiatrisch Pflegenden in diesem Sektor. Anhand einer Meta-Synthese qualitativer Originalarbeiten sind zentrale Bestandteile der Tätigkeit psychiatrisch Pflegender im ambulanten Bereich aus Sicht der Pflegenden identifiziert worden. Die Literaturrecherche ergab 12 Arbeiten, die den Einschlusskriterien (qualitative Studien bei ambulant psychiatrisch Pflegenden) genügten. Als zentrale Bestandteile wurden Tätigkeiten wie die Einschätzung des Gesundheitszustands und das Medikationsmanagement sowie pflegerisch-therapeutische Inhalte wie die Beziehungsgestaltung zu den Patienten identifiziert. Deutlich wurde dabei die Ambivalenz zwischen der mitmenschlichen Beziehung einerseits und den überwachenden pflegerischen Tätigkeiten andererseits. Es wird geschlussfolgert, dass sich die Ausbildung von Pflegenden im Bereich der ambulanten Psychiatrie nicht allein auf formelle Tätigkeiten konzentrieren darf, sondern informelle Verhaltensweisen sowie Schwierigkeiten und Problemfelder ebenfalls in die Curricula integriert werden sollten.
Leben mit chronischer Herzinsuffizienz – Eine qualitative Studie in Anlehnung an die Grounded Theory
Authors: Kolbe Nina , Schnepp Wilfried , Zegelin Angelika
Published: April 2009

Die Zahl der Menschen, die an einer Herzinsuffizienz erkranken steigt stetig. Die Versorgungssituation dieser komplexen Patientengruppe wird in Deutschland als unzureichend beschrieben. Um erfolgreich intervenieren zu können ist es unabdingbar, die Situation der Menschen mit chronischer Herzinsuffizienz aus deren Sicht zu betrachten. Darauf aufbauend kann ein Teil des Beitrags identifiziert werden, den die professionelle Pflege in der Betreuung leisten kann. Bei der Betrachtung des Forschungsstands zum Erleben von Menschen mit chronischer Herzinsuffizienz konnte keine deutsche Studie gefunden werden. Entsprechend wird in der vorliegenden Arbeit das Erleben von Menschen mit chronischer Herzinsuffizienz in Deutschland untersucht. Methodisch wird ein qualitativer Ansatz in Anlehnung an die Grounded Theory gewählt. Die Daten setzen sich aus neun Interviews mit Betroffenen und einem Erlebnisbericht zusammen, die nach dem Kodierparadigma analysiert wurden. Die Ergebnisse zeigten das Erleben von Einschränkungen als zentrales Phänomen. Auf diese Einschränkungen reagieren die Betroffenen entweder durch Ignorieren dieser, um ihr altes Leben zu erhalten, oder sie nehmen die Einschränkungen an und passen ihr Leben an die Situation an. Daraus resultieren Auswirkungen unterschiedlichster Art auf die bisherige Rolle der Betroffenen, auf die Emotionen, auf das Weiterleben an sich und die Familie. Die Resultate dieser Arbeit unterstützen bestehende Modelle zu chronischen Krankheiten sowie Ergebnisse anderer Studien. Sie ermöglicht einen ersten Einblick in die Erlebenswelt von Menschen mit Herzinsuffizienz, doch bleiben viele Fragen ungeklärt.
Spatiotemporal variation in nonagricultural open fire emissions in China from 2000 to 2007
Authors: Song Yu , Liu Bing , Miao Weijie , Chang Di , Zhang Yuanhang
Published: April 2009

Open fires such as those within forests and grasslands, as well as crop residue burning in fields, contribute considerable amounts of trace gases and particulate matter to the atmosphere and therefore play an important role in climate change and atmospheric chemistry. Emissions from open fires in China are estimated at a medium resolution of 1 km2from April 2000 to March 2007 (seven fire years). Burned areas and land use types at 1 km spatial resolution are defined using the L3JRC product from the Systeme Probatoire pour l'Observation de la Terre (SPOT) satellite and the Global Land Cover 2000 data sets for China, respectively. The 500‐m burned area product (MCD45A1) from the Moderate Resolution Imaging Spectroradiometer (MODIS) is compared with the L3JRC burned area product in China. On an average, the total burned areas from L3JRC product are 16 times those from MCD45A1 product. Interannual changes of burned area are in accordance with the records reported in official statistics. Aboveground biomass densities are characterized by vegetation type and province. Fuel moisture content is considered to calculate the combustion factors by using time series of normalized difference vegetation index (MOD13A3). Crop residue burning accounts for the most biomass burning in China, but we find that it is not detected efficiently by the available burned area algorithms. Both burned area and emission data reveal significant spatial patterns and seasonal variation during the seven fire years. Total nonagricultural fire emissions are concentrated in north and southwest China, especially in the spring and autumn. Forest fires are determined to be the primary contributor to nonagricultural fire emissions. The annual emissions are estimated as follows for China during the seven study years: 137.8 (range from 108.8 to 172.9) Tg a−1CO2, 7.0 (5.5–8.7) Tg a−1CO, 0.25 (0.22–0.34) Tg a−1NOx, 0.90 (0.71–1.1) Tg a−1PM2.5, 0.06 (0.05–0.07) Tg a−1BC, and 0.56 (0.44–0.7) Tg a−1OC.
Comparison of AMIE‐modeled and Sondrestrom‐measured Joule heating: A study in model resolution and electric field–conductivity correlation
Authors: Cosgrove R. B. , Lu G. , Bahcivan H. , Matsuo T. , Heinselman C. J. , McCready M. A.
Published: April 2009

Joule heating by high‐latitude ionospheric electric fields is thought to be underestimated by models, and it has been conjectured that the source of the underestimation is “electric field variability,” which is often defined as electric field structure below the resolution of the model. We investigate this and related issues by (1) comparing the Joule heating measured by the Sondrestrom incoherent scatter radar during a 40 h period containing a storm with that modeled by the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure and (2) employing an magnetosphere‐ionosphere (M‐I) coupling model to analyze the theoretical dependence of Joule heating estimates on the spatial resolution of the inputs. We find that as compared with Sondrestrom measurements, a much larger contribution from correlation between conductance and squared electric field (positive for AMIE and negative for Sondrestrom) partially compensates for a much smaller mean‐squared electric field, such that the overall average Joule heating rate modeled by AMIE is 29% less than measured by Sondrestrom. The underestimation of the mean‐squared electric field was not associated with small‐temporal‐scale variability. Surprisingly, the M‐I coupling model finds that coarse spatial resolution causes overestimation of the Joule heating rate, owing to the finding that the subresolution‐scale spatial fluctuations in conductance and squared electric field are anticorrelated. When comparing estimates of the total Joule heating over a period of time, the increased Joule heating arises as a larger contribution from temporal correlation between conductance and squared electric field, which overcompensates for the reduced mean‐squared electric field. Therefore, the difference in the Sondrestrom and AMIE correlation contributions might be explained by a difference in spatial resolution.
Quiescent current sheets in the solar wind and origins of slow wind
Authors: Suess S. T. , Ko Y.‐K. , von Steiger R. , Moore R. L.
Published: April 2009

Solar wind near the heliospheric current sheet is investigated using Ulysses and ACE data in a superposed epoch analysis for several days on either side of the current sheets. Only data near sunspot minima are used, minimizing the influence of transients. New results are shown for composition and ionization state. Existing results showing a ∼2 day wide depletion in He/H (He++/H+) at the current sheet are confirmed, although the depletion is generally more narrow. A recent finding of a broad 5–10 day wide reduction in He/H around the current sheet is also confirmed. An important result is that the narrow depletion is not a real phenomenon but is instead a statistical consequence of the superposition of transient depletions that also create the broad reduction in the averages. These transient depletions last from a few hours up to several days, come from the core of streamers, and are embedded in a quasi‐steady flow from streamers' legs. Most depletions contain a current sheet just inside one edge, leading to the apparent narrow depletion at the current sheet in the superposed epoch analysis. These results lead us to a hypothesis for how the He/H depletions form with a current sheet just inside one edge. Fe/O fluctuations associated with the He/H fluctuations further show that mixing of plasma from coronal holes adjacent to streamer brightness boundaries into outflow inside the brightness boundary is not an important process.
Numerical models of caldera deformation: Effects of multiphase and multicomponent hydrothermal fluid flow
Authors: Hutnak M. , Hurwitz S. , Ingebritsen S. E. , Hsieh P. A.
Published: April 2009

Ground surface displacement (GSD) in large calderas is often interpreted as resulting from magma intrusion at depth. Recent advances in geodetic measurements of GSD, notably interferometric synthetic aperture radar, reveal complex and multifaceted deformation patterns that often require complex source models to explain the observed GSD. Although hydrothermal fluids have been discussed as a possible deformation agent, very few quantitative studies addressing the effects of multiphase flow on crustal mechanics have been attempted. Recent increases in the power and availability of computing resources allow robust quantitative assessment of the complex time‐variant thermal interplay between aqueous fluid flow and crustal deformation. We carry out numerical simulations of multiphase (liquid‐gas), multicomponent (H2O–CO2) hydrothermal fluid flow and poroelastic deformation using a range of realistic physical parameters and processes. Hydrothermal fluid injection, circulation, and gas formation can generate complex, temporally and spatially varying patterns of GSD, with deformation rates, magnitudes, and geometries (including subsidence) similar to those observed in several large calderas. The potential for both rapid and gradual deformation resulting from magma‐derived fluids suggests that hydrothermal fluid circulation may help explain deformation episodes at calderas that have not culminated in magmatic eruption.
Lidar studies of particulates in the UTLS region at a tropical station over the Indian subcontinent
Authors: Thampi Bijoy V. , Sunilkumar S. V. , Parameswaran K.
Published: April 2009

Characteristics of particulate matter in the upper troposphere and lower stratosphere (UTLS) region during the volcanic quiescent period of 1998–2003 are studied using dual polarization lidar observations at the tropical station Gadanki (13.5°N, 79.2°E). This study revealed a pronounced summer‐winter contrast of the particulate backscatter coefficient (βa) in the LS region with relatively high values during winter and low values during summer. High values of βa (>10−6 m−1 sr−1) in the UT region during summer are closely associated with the manifestation of semitransparent cirrus clouds in this region. High values of volume depolarization ratio (VDR) exceeding 0.04 and increasing up to 0.6 usually encountered in the UT region during this period could be due to the presence of relatively large nonspherical ice particles. These values in the LS region, which are relatively small (<0.04), indicate that the particles in this region are relatively small and more or less spherical in nature. The present study shows that convective activity prevailing in the troposphere significantly influences the microphysical properties of particulates in the UTLS region. Convective available potential energy and outgoing longwave radiation, which are good representative indices for tropospheric convection, show good correlation with VDR in the lower stratosphere during summer and weak correlation during winter. The role of vertical transport from troposphere to stratosphere is also investigated using the vertical wind obtained from mesosphere‐stratosphere‐troposphere (MST) radar data. This study shows that the seasonal variation of mean backscatter coefficient matches well with the corresponding variation in mean vertical mass flux. These results suggest that highly nonspherical particles associated with cirrus clouds forming in the upper troposphere and subsequent uplift across the tropopause aided by strong convection in the troposphere during the summer monsoon period are responsible for the increased VDR observed in the upper troposphere and lower stratosphere region, while the transport of air from troposphere to stratosphere, which is more pronounced during winter, is responsible for the increase in backscatter coefficient in the lower stratosphere.
Assessing the performance of the International Monitoring System's infrasound network: Geographical coverage and temporal variabilities
Authors: Le Pichon A. , Vergoz J. , Blanc E. , Guilbert J. , Ceranna L. , Evers L. , Brachet N.
Published: April 2009

A global‐scale analysis of detections made at all 36 currently operating International Monitoring System (IMS) infrasound arrays confirms that the primary factor controlling signal detectability is the seasonal variability of the stratospheric zonal wind. At most arrays, ∼80% of the detections in the 0.2‐ to 2‐Hz bandpass are associated with propagation downwind of the dominant stratospheric wind direction. Previous IMS infrasound network performance models neglect the time‐ and site‐dependent effects of both stratospheric meteorological variability and ambient noise models. In this study both effects are incorporated; we compare empirical and improved specifications of the stratospheric wind and include station‐dependent wind noise models. Using a deterministic approach, the influence of individual model parameters on the network performance is systematically assessed. At frequencies of interest for detecting atmospheric explosions (0.2–2 Hz), the simulations predict that explosions equivalent to ∼500 t of TNT would be detected by at least two stations at any time of the year. The detection capability is best around January and July when stratospheric winds are strongest, compared to the equinox periods when zonal winds reduce and reverse. The model predicts that temporal fluctuations in the ground‐to‐stratosphere meteorological variables generate detection threshold variations on daily and seasonal timescales of ∼50 and ∼500 t, respectively. While the strong zonal winds lead to an improvement in detection capability, their highly directional nature leads to an increase in the location uncertainty owing to the decreased azimuthal separation of the detecting stations.
A size‐resolved model for below‐cloud scavenging of aerosols by snowfall
Authors: Feng Jian
Published: April 2009

A size‐resolved model of below‐cloud scavenging is required in air quality and atmospheric dispersion modeling. Explicit calculation of the below‐cloud snow scavenging coefficient requires determinations of (1) cross section, (2) terminal velocity, and (3) number size distribution of snow particles; and (4) spectral collision efficiency of aerosol particles with snow particles. In this study, we present a size‐resolved model for below‐cloud snow scavenging, based on current knowledge of each element of the above. In particular, a new scheme is proposed to specify the spectral collision efficiency of aerosol particles for the whole size range of snow particles. The proposed scheme specifies the collision efficiencies for planar and columnar ice crystals until their specific critical sizes, according to the theoretical calculations by Martin et al. (1980) and Miller and Wang (1989), respectively; uses the parameterization of Murakami et al. (1985a) to calculate the spectral collision efficiency for snow particles with maximum dimension Dm equal to 5 mm; and then determines the collision efficiency for Dm between the critical size and 5 mm through exponential interpolation. For Dm greater than 5 mm, the collision efficiency is set to be equal to that for Dm = 5 mm. Compared with the measured one in the literature, the current model generally captures well the trend and the variation range of the scavenging coefficient.
High‐resolution simulations of convective cold pools over the northwestern Sahara
Authors: Knippertz P. , Trentmann J. , Seifert A.
Published: April 2009

Cooling by evaporation of convective precipitation in the deep and dry subcloud layer over desert regions can generate intense downdrafts and long‐lived and extensive atmospheric density currents. The strong gusts at their leading edges can cause so‐called haboob dust storms. Despite their importance for the dust cycle, the ability of state‐of‐the‐art numerical weather prediction models to realistically simulate the associated convective cold pools has been investigated very little to date. During the first field campaign of the Saharan Mineral Dust Experiment in southern Morocco in May/June 2006, several density currents were observed. They were triggered by deep moist convection over the Atlas Mountains during the afternoon and propagated into the foothills in the course of the evening. Here we present numerical simulations of three of these density currents using the nonhydrostatic Consortium for Small‐Scale Modelling model with 2.8‐km horizontal grid spacing, which allows an explicit treatment of deep convection. The model is capable of simulating the timely initiation of convective cells over the Atlas Mountains and the subsequent formation of long‐lived, extensive cold pools with a realistic three‐dimensional structure. Deviations from available surface and satellite observations are closely related to model deficiencies in simulating precipitating convection over the Algerian Sahara. Sensitivity studies with modified microphysics reveal a large influence of raindrop size distributions on evaporation and surface rainfall but a rather moderate influence on the cold pool evolution. Decreasing the length scale for turbulent vertical mixing in the boundary layer leads to more widespread but weaker precipitation, more evaporation, and a faster and more extended cold pool.
Decadal changes in shortwave irradiance at the surface in the period from 1960 to 2000 estimated from Global Energy Balance Archive Data
Authors: Gilgen H. , Roesch A. , Wild M. , Ohmura A.
Published: April 2009

Decadal changes in shortwave irradiance at the Earth's surface are estimated for the period from approximately 1960 through to 2000 from pyranometer records stored in the Global Energy Balance Archive. For this observational period, estimates could be calculated for a total of 140 cells of the International Satellite Cloud Climatology Project grid (an equal area 2.5° × 2.5° grid at the equator) using regression models allowing for station effects. In large regions worldwide, shortwave irradiance decreases in the first half of the observational period, recovers from the decrease in the 1980s, and thereafter increases, in line with previous reports. Years of trend reversals are determined for the grid cells which are best described with a second‐order polynomial model. This reversal of the trend is observed in the majority of the grid cells in the interior of Europe and in Japan. In China, shortwave irradiance recovers during the 1990s in the majority of the grid cells in the southeast and northeast from the decrease observed in the period from 1960 through to 1990. A reversal of the trend in the 1980s or early 1990s is also observed for two grid cells in North America, and for the grid cells containing the Kuala Lumpur (Malaysia), Singapore, Casablanca (Morocco), Valparaiso (Chile) sites, and, noticeably, the remote South Pole and American Samoa sites. Negative trends persist, i.e., shortwave radiation decreases, for the observational period 1960 through to 2000 at the European coasts, in central and northwest China, and for three grid cells in India and two in Africa.
New Maps of California to Improve Tsunami Preparedness
Authors: Barberopoulou Aggeliki , Borrero Jose C. , Uslu Burak , Kalligeris Nikos , Goltz James D. , Wilson Rick I. , Synolakis Costas E.
Published: April 2009

On 25 April 1992, an M 7.1 earthquake shook the coast of Cape Mendocino near Petrolia, Calif., followed by two large aftershocks (both M ∼6.6) the next day. Although no lives were lost in these temblors, 98 people were injured. These earthquakes heavily damaged older structures within this sparsely populated, mountainous region, causing more than US$66 million in losses.
Spatiotemporal gravity changes on volcanoes: Assessing the importance of topography
Authors: Charco María , Camacho Antonio G. , Tiampo Kristy F. , Fernández José
Published: April 2009

Mass redistribution and deformation cause spatiotemporal gravity changes in active volcano areas. The ability of the gravity measurements to detect subsurface magma movement as a precursor to volcanic eruptions is greatly enhanced if gravity changes are analyzed and modeled jointly with ground deformation data. One effective tool for this analysis is provided by the gravity and elevation change ratio. The proposed numerical formulation allows to simulate a wide range of pressures and mass loads. However, the assessment of gravity changes is especially important when they occur without measurable ground deformation. In such a case it is very difficult to relate the gravity/uplift ratio to changes in subsurface mass movements by using classical models. In this work, we study the role played by pressure and mass sources in the interpretation of observed gravity/uplift ratio when deformation is negligible in volcanic areas associated with rough topographic relief.
Sensitivity of the Late Saalian (140 kyrs BP) and LGM (21 kyrs BP) Eurasian ice sheet surface mass balance to vegetation feedbacks
Authors: Colleoni F. , Krinner G. , Jakobsson M.
Published: April 2009

This work uses an atmospheric general circulation model (AGCM) asynchronously coupled to an equilibrium vegetation model to investigate whether vegetation feedbacks could be one of the reasons why the Late Saalian ice sheet (140 kyrs BP) in Eurasia was substantially larger than the Last Glacial Maximum (LGM, 21 kyrs BP) Eurasian ice sheet. The modeled vegetation changes induce a regional cooling for the Late Saalian while they cause a slight regional warming for LGM. As a result, ablation along the margins of the Late Saalian ice sheet is significantly reduced, leading to an increased surface mass balance, while there are no significant mass balance changes observed from vegetation feedbacks at LGM.
Plume ionosphere of Enceladus as seen by the Cassini ion and neutral mass spectrometer
Authors: Cravens T. E. , McNutt R. L. , Waite J. H. , Robertson I. P. , Luhmann J. G. , Kasprzak W. , Ip W.‐H.
Published: April 2009

The Cassini spacecraft passed within 168 km of the surface of Enceladus on 14 July 2005 during the E2 flyby and passed closer (50 km) during the E3 encounter on 13 March 2008. During both flybys the ion and neutral mass spectrometer (INMS) detected a plume atmosphere mainly composed of water. During the E3 flyby, the INMS measured an ion mass spectrum with a large peak at mass number of 19 Daltons (interpreted as H3O+ ions) but not at the mass numbers of other water group ion species (including H2O+, OH+, O+). In addition, the INMS observed ion species at mass numbers 36 and 37 ‐ possibly the water cluster ion species H2O+ ‐ H2O and H3O+ ‐ H2O. The INMS detection of cold H3O+ in the plume combined with the almost complete absence of cold H2O+ ions is attributed to an active ion‐neutral chemistry operating in a plume “ionosphere.”
Bacteria, not archaea, restore nitrification in a zinc-contaminated soil
Authors: Mertens Jelle , Broos Kris , Wakelin Steven A , Kowalchuk George A , Springael Dirk , Smolders Erik
Published: April 2009

Biological ammonia oxidation had long been thought to be mediated solely by discrete clades of β- and γ-proteobacteria (ammonia-oxidizing bacteria; AOB). However, ammonia-oxidizing Crenarchaeota (ammonia-oxidizing archaea; AOA) have recently been identified and proposed to be the dominant agents of ammonia oxidation in soils. Nevertheless, the dynamics of AOB versus AOA, and their relative contribution to soil ammonia oxidation and ecosystem functioning on stress and environmental perturbation, remain unknown. Using a 3-year longitudinal field study and the amoA gene as a molecular marker, we demonstrate that AOB, but not AOA, mediate recovery of nitrification after zinc (Zn) contamination. Pristine soils showed approximately equal amoA gene copy numbers and transcript levels for AOB and AOA. At an intermediate Zn dose (33.7 mmol Zn per kg), ammonia oxidation was completely inhibited, and the numbers of AOB and AOA amoA gene copies and gene transcripts were reduced. After 2 years, ammonia oxidation in the field soils was fully restored to preexposure levels, and this restoration of function was concomitant with an increase of AOB amoA gene copy and gene transcript numbers. Analysis of the restored community revealed domination by a phylogenetically distinct Zn-tolerant Nitrosospira sp. community. In contrast, the numbers of AOA amoA gene copies and gene transcripts remained 3- and 104-fold lower than recovered AOB values, respectively. Thus, although recent findings have emphasized a dominant role of archaea in soil-borne ammonia oxidation, we demonstrate that a phylogenetic shift within the AOB community drives recovery of nitrification from Zn contamination in this soil.
Rumen-like methanogens identified from the crop of the folivorous South American bird, the hoatzin (Opisthocomus hoazin)
Authors: Wright André-Denis G , Northwood Korinne S , Obispo Nestor E
Published: April 2009

The hoatzin is the only known avian species with foregut fermentation. It is a primarily folivorous feeder and has a distended crop and lower/distal esophagus, which has evolved for the microbial fermentation of ingested feed. Crop samples collected from 10 individual animals from the Apure River area, Apure State, Venezuela were examined for the presence and density of methanogens using 16S rRNA gene clone libraries and real-time PCR prepared from pooled and individual PCR products. A total of 197 clones were examined, revealing 24 different methanogen 16S rRNA sequences, or phylotypes. Of the 24 unique phylotypes, 16 (171 of 197 clones) formed five unique clades within the genus Methanobrevibacter with the largest group of clones (118 clones) 98.7% similar to Methanobrevibacter ruminantium. The remaining eight phylotypes (26 clones) formed four unique clades that had only 94.0–96.7% identity to Methanosphaera stadtmanae. Based upon 98% sequence identity, we identified 17 of the 24 methanogen phylotypes from the hoatzin as possible new species and strains, with three phylotypes representing possible new genera (<94.5% sequence identity). Although none of the hoatzin methanogen phylotypes had 100% sequence identity to any other archaeal sequences in the GenBank database, the hoatzin crop methanogen sequences formed sister groups with known rumen methanogens. Mean population densities (numbers per gram wet weight) of methanogenic archaea, rumen bacteria and ciliate protozoa, estimated using real-time PCR, were 5.80 × 109, 7.93 × 1012 and 3.31 × 105, respectively. The crop microbial data presented here provide an excellent example of convergent evolution of foregut fermentation in the hoatzin, similar to that of ruminants.