bluuebunny/crossref_metadata_2025 huggingface dataset:
Cosmic evolution of black holes and galaxies to z=0.4
Authors: Woo J.-H. , Treu T. , Malkan M. A. , Blanford R. D.
Published: May 2007

We test the evolution of the correlation between black hole mass and bulge properties, using a carefully selected sample of 20 Seyfert 1 galaxies at z=0.36 ±0.01. We estimate black hole mass from the Hβ line width and the optical luminosity at 5100 Å, based on the empirically calibrated photo-ionization method. Velocity dispersion are measured from stellar absorption lines around Mgb (5175 Å) and Fe (5270 Å) using high S/N Keck spectra, and bulge properties (luminosity and effective radius) are measured from HST images by fitting surface brightness. We find a significant offset from the local relations, in the sense that bulge sizes were smaller for given black hole masses at z=0.36 than locally. The measured offset is Δ M•=0.62 ± 0.10, 0.45 ±0.13, 0.59 ±0.19, respectively for M•–σ, M•–Lbulge, and M•–Mbulge relations. At face value, this result implies a substantial growth of bulges in the last 4 Gyr, assuming that the local M•–bulge property relation is the universal evolutionary end-point. This result is consistent with the growth of black holes predating the final growth of bulges at these mass scales (〈σ〉=170 km s−1).
Monte Carlo simulations of dusty gas discs around supermassive black holes
Authors: Baes Maarten , Piasecki Sławomir
Published: May 2007

Using detailed Monte Carlo radiative transfer simulations in realistic models for galactic nuclei, we critically investigate the influence of interstellar dust in ionised gas discs on the rotation curves and the resulting black hole mass measurements. We find that absorption and scattering by interstellar dust leaves the shape of the rotation curves basically unaltered, but slightly decreases the central slope of the rotation curves. As a result, the “observed” black hole masses are systematically underestimated by some 10 to 20% for realistic optical depths.
Black hole masses in type II AGNs from the Sloan Digital Sky Survey
Authors: Bian W. , Gu Q. , Zhao Y.
Published: May 2007

The stellar population synthesis method is used to model the stellar contribution for a sample of 209 type II AGNs at 0.3>z>0.83 from the Sloan Digital Sky Survey. The reliable stellar velocity dispersions are obtained for 33 type II AGNs with significant stellar absorption features. We use the formula of Greene & Ho to obtain the corrected stellar velocity dispersions (σ*c). 20 of which can be classified as type II quasars. The SMBHs masses and the Eddington ratios are calculated. We measure the gas velocity dispersion (σg) from NLRs, and find that the relation between σg and σ*c becomes much weaker at higher redshifts than at smaller redshifts. We find that the deviation of σg from σ*c is correlated with the Eddington ratio.
Accretion in the broad line region of active galactic nuclei
Authors: Bon E. , Popović L. Č. , Ilić D.
Published: May 2007

We modeled the single-peaked Broad Emission Lines (BELs) with two-component model (accretion disk, with surrounding spherical region), comparing it with observational line profiles for a number of Active Galactic Nuclei (AGN). We find that the accretion in the Broad Line Region (BLR) can be present even if the profiles of BELs are single-peaked.
Triaxial orbit-based model of NGC 4365
Authors: van den Bosch Remco C. E. , van de Ven Glenn , Cappellari Michele , de Zeeuw P. Tim
Published: May 2007

We have developed an orbit-based method for constructing triaxial models of elliptical galaxies, which fit their observed surface brightness and kinematics (van den Bosch et al). We have tested this extended Schwarzschild method (1979) against analytical models with general distribution functions (DF) and find that we can recover the DF (van de Ven et al). Here, we present a model of NGC 4365.
Evolution of black-hole intermediate-mass X-ray binaries
Authors: Chen Wen-Cong , Li Xiang-Dong
Published: May 2007

We propose a plausible mechanism for orbital angular momentum loss in black-hole intermediate-mass X-ray binaries, assuming that a small fraction of the transferred mass form a circumbinary disc. The disc can effectively drain orbital angular momentum from the binary, leading to the formation of compact black-hole low-mass X-ray binaries. This scenario also suggests the possible existence of luminous, persistent black hole low-mass X-ray binaries.
Upper limits on the mass of supermassive black holes from HST/STIS archival data
Authors: Corsini E. M. , Beifiori A. , Bontà E. Dalla , Pizzella A. , Coccato L. , Sarzi M. , Bertola F.
Published: May 2007

The growth of supermassive black holes (SBHs) appears to be closely linked with the formation of spheroids. There is a pressing need to acquire better statistics on SBH masses, since the existing samples are preferentially weighted toward early-type galaxies with very massive SBHs. With this motivation we started a project aimed at measuring upper limits on the mass of the SBHs in the center of all the nearby galaxies (D < 100 Mpc) for which STIS/G750M spectra are available in the HST archive. These upper limits will be derived by modeling the central emission-line widths observed in the Hα region over an aperture of ∼0.1″. Here we present our results for a subsample of 22 S0-Sb galaxies within 20 Mpc.
The nuclear properties of early-type galaxies in the Virgo and Fornax clusters
Authors: Côté Patrick
Published: May 2007

We summarize findings from imaging surveys of 143 early-type galaxies in the Virgo and Fornax Clusters. Using deep HST images in the F475W (g) and F850LP (z) band-passes obtained with the Advanced Camera for Surveys (ACS), we have examined the central structure of the program galaxies, finding clear evidence for a compact stellar nucleus in ∼ 75% of the sample. The formation of early-type galaxies of low- and intermediate-mass is often – but not always – accompanied by the formation of a compact stellar nucleus.
Accreting corona model of the X-ray variability in soft state GBH and AGN
Authors: Czerny Bożena , Janiuk Agnieszka
Published: May 2007

We develop a two-flow model of accretion onto a black hole which incorporates the effect of the local magneto-rotational instability. The flow consists of an accretion disk and an accreting corona, and the local dynamo affects the disk/corona mass exchange. The model is aimed to explain the power spectra of the sources in their soft, disk-dominated states. The local perturbations of the magnetic field in the disk are described as in King et al. (2004) and Mayer & Pringle (2006), but the time-dependent local magnetic field is assumed to affect the local supply of the material to the corona. The accreting corona model can reproduce the broad power spectra of Soft State X-ray binaries and AGN. The model, however, predicts that (i) sources undergoing radiation pressure instability (GRS 1915+105) should have systematically steeper power spectra than other sources, (ii) AGN should have systematically steeper power spectra than GBH. More measurements of power spectra of Soft State sources are clearly needed.
Supermassive black holes in BCGs
Authors: Bontà E. Dalla , Ferrarese L. , Miralda-Escudé J. , Coccato L. , Corsini E. M. , Pizzella A.
Published: May 2007

We observed a sample of three Brightest Cluster Galaxies (BCGs), Abell 1836-BCG, Abell 2052-BCG, and Abell 3565-BCG, with the Advanced Camera for Surveys (ACS) and the Imaging Spectrograph (STIS) on board the Space Telescope. For each target galaxy we obtained high-resolution spectroscopy of the Hα and [N II] λ6583 emission lines at three slit positions, to measure the central ionized-gas kinematics. ACS images in three different filters (F435W, F625W, and FR656N) have been used to determine the optical depth of the dust, stellar mass distribution near the nucleus, and intensity map. We present supermassive black hole (SBH) mass estimates for two galaxies which show regular rotation curves and strong central velocity gradients, and an upper limit on the SBH mass of the third one. For the SBHs of Abell 1836-BCG and Abell 3565-BCG, we derived M• = 4.8+0.8−0.7 × 109 M⊙ and M• = 1.3+0.3−0.4 × 109 M⊙ at 1 σ confidence level, respectively. For the SBH of Abell 2052-BCG, we found M• ≤ 7.3 × 109 M⊙.
The VSOP Survey: final aggregate results
Authors: Dodson R. , Horiuchi S. , Scott W. , Fomalont E. , Paragi Z. , Frey S. , Wiik K. , Hirabayashi H. , Edwards P. , Murata Y. , Moellenbrock G , Gurvits L. , Shen Z. , Lovell J.
Published: May 2007

In February 1997 the Japanese radio astronomy satellite HALCA was launched to provide the space-borne element for the VSOP mission. HALCA provided linear baselines three-times greater than that of ground arrays, thus providing higher resolution and higher AGN brightness temperature measurements and limits. Twenty-five percent of the scientific time of the mission was devoted to the “VSOP survey” of bright, compact, extra-galactic radio sources at 5 GHz. A complete list of 294 survey targets were selected from pre-launch surveys, 91% of which were observed during the satellite's lifetime.

The major goals of the VSOP Survey are statistical in nature: to determine the brightness temperature and approximate structure, to provide a source list for use with future space VLBI missions, and to compare radio properties with other data throughout the electro-magnetic spectrum. All the data collected have now been analysed and is being prepared for the final image Survey paper. In this paper we present details of the mission, and some statistics of the images and brightness temperatures.
Generation of shocked hot regions in black hole magnetosphere
Authors: Fukumura Keigo , Takahashi Masaaki , Tsuruta Sachiko
Published: May 2007

We study magnetohydrodynamic (MHD) standing shocks in ingoing plasmas in a black hole (BH) magnetosphere. We find that low or mid latitude (non-equatorial) standing MHD shocks are both physically possible, creating very hot and/or magnetized plasma regions close to the event horizon. We also investigate the effects of the poloidal magnetic field and the BH spin on the properties of shocks and show that both effects can quantitatively affect the MHD shock solutions. MHD shock formation can be a plausible mechanism for creating high energy radiation region above an accretion disk in AGNs.
Evidence for the AGN nature of LINERs
Authors: González-Martín O. , Masegosa J. , Márquez I. , Jiménez-Bailón E.
Published: May 2007

We report the analysis of the X-ray data for a sample of 48 LINER nuclei with available X-ray Chandra imaging. In González-Martín et al. 2006 21 objects had enough count rate to make the spectral analysis. Here we enlarge the sample performing the spectral analysis of the XMM-Newton observations of 7 additional galaxies. Our aim is to investigate the physical mechanisms which power the nuclear activity of LINERs. The use of multiwavelength information at radio, UV, optical HST and X-ray lead us to conclude that at least 60% of the LINERs are hosting a low luminosity AGN in their nuclei.
The entropy increase during the black hole formation
Authors: Hara Tetsuya , Sakai Keita , Kunitomo Shuhei , Kajiura Daigo
Published: May 2007

The entropy increases enormously when a star collapses into a black hole. For the radiation dominated star, the temperature has decreased from the almost gravitational equilibrium one to the so-called black hole temperature. If we interpret this temperature decrease as the volume increase of the black hole, the entropy increase could be understood as the free expansion of radiation throughthe increased volume. The expected volume size is tentatively estimated. Under this interpretation, it is derived that the entropy is proportional to the horizon surface area and the microscopic states of the black hole entropy could be understood as the statistical states of the enlarged phase space.
Observational manifestations of accretion onto isolated black holes of different masses
Authors: Karpov Sergey , Beskin Gregory
Published: May 2007

The process of accretion onto the isolated black holes under the various conditions of the ISM and its observational manifestations are discussed. For the majority of the Galaxy volume the accretion rate is as low as 10−6–10−9 of Eddington one, and the accretion is spherically-symmetric. Such objects manifest itself as a weak optical and x-ray sources with featureless spectra and the significant variability of the emission.

For the BH located inside the dense molecular cloud the regime of accretion depends on its massand velocity. A massive (100–1000M⊙) BH born in the cloud or having low relative velocity, may manifest itself as a ultra-luminous x-ray source (ULX).
AGN types as different states of massive black holes
Authors: Komberg Boris V.
Published: May 2007

After discovering microquasars – active stellar systems with relativistic outflows (Mirabel et al. 1992) – many papers bringing the observational arguments on similar nature of accreting systems with different BH masses (from stellar to galactic nuclei) have appeared. It became clear that a level of activity in such systems could depend on few parameters: BH mass and angular momentum; accretion rate and magnetization parameter of accretion disk (AD); relative orientation of BH and AD angular momentum. The bolometric luminosity and characteristic variation time in such systems is proportional to BH masses, which span an interval in 5–8 decades.
Relativistic jets and non-thermal radiation from collapse of stars to black holes
Authors: Kryvdyk V. , Agapitov A.
Published: May 2007

The formation of the relativistic jets and a non-thermal emission from the collapsing magnetized stars with dipole magnetic fields and the heterogeneous particles distribution are investigated. These polar jets are formed when the stellar magnetosphere compress during collapse its magnetic field increases considerable. The electric field is produced in magnetosphere, which the charged particles will be accelerated. As follow from the calculation, the jets can be formed from collapsing stars already the explosion of supernova stars without shock waves. These jets will generate the non-thermal radiation. The radiation flux depends on the distance to the star, its magnetic field and the particle spectrum in the magnetosphere. This flux can be observed near Earth by means of modern telescopes in the form of the radiation pulse with duration equal to time collapse.
Rotation curves, dark matter and general relativity
Authors: Letelier Patricio S.
Published: May 2007

We study the possibility of pure general relativistic models without exotic matter to describe the observed flattening of the rotation curves for stars moving in circular orbits in a galaxy disk. In particular we consider the dragging of inertial frames (rotation of the source) and the presence of a Taub–NUT (Newman–Unti–Tamburino) “charge”, the gravitational equivalent to a magnetic monopole in electrodynamics.
The orbiting spot model gives constraints on the parameters of the supermassive black hole in the Galactic Center
Authors: Meyer Leonhard , Eckart Andreas , Schödel Rainer , Dovčiak Michal , Karas Vladimír , Duschl Wolfgang J.
Published: May 2007

We report on recent polarimetric observations of the 18± 3 min quasi-periodicity present in near-infrared flares from Sagittarius A*. Observations in the K-band allow us a detailed investigation of the flares and their interpretation within the hot spot model. The interplay of relativistic effects plays a major role. By simultaneous fitting of the lightcurve fluctuations and the time-variable polarization angle, we give constraints to the parameters of the hot spot model, in particular, the dimensionless spin parameter of the black hole and its inclination. We consider all general relativistic effects that influence the polarization lightcurves. The synchrotron mechanism is most likely responsible for the intrinsic polarization. We consider two different magnetic field configurations as approximations to the complex structure of the magnetic field in the accretion flow. Considering the quality of the fit, we suggest that the spot model is a good description of the origin for the QPOs in NIR flares.
Two-dimensional MHD simulations of accretion disk evaporation
Authors: Nakamura Kenji E.
Published: May 2007

We simulate the accretion disk evaporation to study the changes of accretion disk structure during the state transition from the soft state to the hard state. We performed 2 dimensional MHD simulations by including the heat conduction process. We assume the axisymmetric accretion and put a cold rotating gas torus in a hot halo in hydrostatic equilibrium initially. Weak magnetic fields are threaded vertically. Heat conduction equation and MHD equations are solved separately according to the time splitting method. We obtained the result that accretion disk is heated by the hot corona and the hot gas evaporates from the accretion disk surface. We found that magnetic fields lines bended by disk rotation restrict the energy transport vertically and make disk evaporation ineffective.
Steady models of optically thin, magnetically supported two-temperature accretion disks around a black hole
Authors: Oda H. , Nakamura K. E. , Machida M. , Matsumoto R.
Published: May 2007

We obtained steady solutions of optically thin two-temperature magnetized accretion disks around a black hole. We included relativistic bremsstrahlung cooling, synchrotron cooling and inverse Compton effects and assumed that the disk is threaded by toroidal magnetic field. We found that a magnetic pressure dominated new branch, which we call a ‘low-β branch’, appears in the thermal equilibrium curves. The luminosity of the optically thin, magnetically supported disk can exceed 10% of the Eddington luminosity (0.1 LEdd).
Power spectra from spotted accretion discs
Authors: Pecháček Tomáš , Dovčiak Michal , Karas Vladimír
Published: May 2007

Some aspects of power-spectral densities (PSD) of active galactic nuclei are similar to those of galactic black hole X-ray binary systems (McHardy et al. 2005). The signal originates near a black hole and its modulation by general-relativistic effects should be taken into account (Życki & Nedźwiecki 2005). We modified the previous calculations of these effects, assuming a model of spots which occur on the disc surface and decay with a certain lifetime.
Brownian motion of black holes in stellar systems with non-Maxwellian distribution of the field stars
Authors: Pedron Isabel Tamara , Coimbra-Araújo Carlos H.
Published: May 2007

A massive black hole at the center of a dense stellar system, such as a globular cluster or a galactic nucleus, is subject to a random walk due gravitational encounters with nearby stars. It behaves as a Brownian particle, since it is much more massive than the surrounding stars and moves much more slowly than they do. If the distribution function for the stellar velocities is Maxwellian, there is a exact equipartition of kinetic energy between the black hole and the stars in the stationary state. However, if the distribution function deviates from a Maxwellian form, the strict equipartition cannot be achieved.

The deviation from equipartition is quantified in this work by applying the Tsallis q-distribution for the stellar velocities in a q-isothermal stellar system and in a generalized King model.
Detection of IMBHs from microlensing in globular clusters
Authors: Safonova Margarita , Rahvar Sohrab
Published: May 2007

Globular clusters have been long predicted to host intermediate-mass black holes (IMBHs) in their centres. The growing evidence that some/all Galactic globular clusters (GCs) could harbour middle range (102 – 104M⊙) black holes, just as galaxies do, stimulates the searches and the development of new methods for proving their existence. Here we propose another method of detection – the microlensing of the cluster stars by the central BH.
Color variations of gravitationally lensed quasars as a tool for accretion disk size estimation
Authors: Shalyapin V. N.
Published: May 2007

Since the amplitude of microlensing variability depends on a source size the monitoring of gravitationally lensed quasars can produce the valuable information about the accretion disk size. Comparison of standard deviations in two wavebands yields useful constraints from quite moderate number of multicolor observations.

Existing optical VRI monitoring data for the quadruple gravitationally lensed quasar Q2237+ 0305 allow to obtain the source size ratio in two bands, V and R or V and I, as a function of size in the V band. Agreement with the standard accretion disk theory which predicts the dependency of a source size on wavelength ∼ λ4/3 can be achieved only if the quasar size in V band is comparable with the Einstein radius (≃ 1017 cm).
An f(R) gravitation for galactic environments
Authors: Sobouti Yousef
Published: May 2007

We propose an action-based f(R) modification of Einstein's gravity which admits of a modified Schwarzschild-deSitter metric. In the weak field limit this amounts to adding a small logarithmic correction to the Newtonian potential. A test star moving in such a spacetime acquires a constant asymptotic speed at large distances. This speed turns out to be proportional to the fourth root of the mass of the central body in compliance with the Tully-Fisher relation. A variance of MOND's gravity emerges as an inevitable consequence of the proposed formalism.
Peculiar outbursts of a black hole X-ray transient, V4641 Sgr
Authors: Uemura M. , Kato T. , Nogami D. , Imada A. , Ishioka R.
Published: May 2007

We have kept optical monitoring of a peculiar black hole X-ray binary, V4641 Sgr. Based on our observations, we show that its unprecedented activity can be divided into 5 phases. In this paper, we report their observational properties.
Self-gravitating warped disks around nuclear black holes
Authors: Ulubay-Siddiki Ayse , Gerhard Ortwin , Arnaboldi Magda
Published: May 2007

Many galactic nuclei contain disks of gas and possibly stars surrounding a supermassive black hole. These disks may play a key role in the evolution of galactic centers. Here we address the problem of finding stable warped equilibrium configurations for such disks, considering the attraction by the black hole and the disk self-gravity as the only acting forces. We model these disks as a collection of concentric, circular rings.

We find the equilibria of such systems of rings, and determine how they scale with the ring parameters and the mass of the central black hole. We show that in some cases these disk equilibria may be highly warped. We then analyze the stability of these disks, using both direct time integration and linear stability analysis. This shows that the warped disks are stable for a range of disk-to-black hole mass ratios, when the rings extend over a limited range of radii.
The modelling of the line-locking effect in broad absorption line QSOs
Authors: Vilkoviskij Emmanuil Y. , Yefimov Sergey N.
Published: May 2007

We present a unification model of the matter outflow from AGN. The model includes calculations of the hot gas dynamics, the dynamics of the cold clouds in the hot gas flow, and the radiation transfer in this two-phase medium. We used the model for calculation of the ultraviolet spectrum of the quasar q1303+308. The spectrum of this object is a well-know example of the line-locking effect. Our model calculations permits for the first time to obtain some thin details seen in the observed absorption spectrum, which confirms the validity of the main issues of our theory and model.
The relation between the properties of the NLR in narrow-line Seyfert 1 galaxies and the accretion rate
Authors: Xu Dawei , Komossa Stefanie
Published: May 2007

We present a systematic study of the properties of the narrow-line region (NLR) of narrow-line Seyfert 1 galaxies (NLS1s) using Sloan Digital Sky Survey (SDSS) spectroscopy. Various correlations between the observed parameters and physical properties of NLS1s and broad-line Seyfert 1 galaxies (BLS1s) are detected. We search for possible origins of these trends by employing correlation analyses. We further investigate the relationship between black hole mass, Eddington ratio (L/LEdd) and physical parameters of the NLR.
Doppler boosting and de-boosting effects in relativistic jets of AGNs and GRBs
Authors: Zhou Jianfeng , Su Yan
Published: May 2007

It is widely accepted that the Doppler de-boosting effects exist in counter relativistic jets. However, people often neglect another important fact that both Doppler boosting and de-boosting effects could happen in forward relativistic jets. Such effects might be used to explain some strange phenomena, such as the invisible gaps between the inner and outer jets of AGNs, and the rapid initial decays and re-brightening bumps in the light curves of GRBs.
Field distributions and shapes of Langmuir wave packets observed by Ulysses in an interplanetary type III burst source region
Authors: Nulsen A. L. , Cairns Iver H. , Robinson P. A.
Published: May 2007

There is no consensus on the mechanisms producing the intense bursty Langmuir wave packets routinely observed in source regions of interplanetary type III radio bursts. Using data from the Ulysses Fast Envelope Sampler (FES) near 4 AU, new analyses of the distributions of wavefields clearly separate the Langmuir waves into “intense localized structures” (ILSs) and “other waves”. The wave amplitude distributions also show that the observed ILSs, but not the other waves, are inconsistent with pure stochastic growth theory (SGT). Furthermore, it is shown that the ILSs are unlikely to be driven thermal waves or generated by pure exponential growth and damping. The wave distributions, structure, and spacing of the ILSs are compared to predictions for collapsing Langmuir wave packets described by the Zakharov equations, in isolated density depressions and in fully developed strong turbulence, either beam driven or driven at long wavelengths. The results show that the observed ILSs are very unlikely to be collapsing wave packets in any of the cases considered. The observed ILSs are inconsistent with the predictions of self‐organized criticality, electron holes, and refractive focusing of waves. Most are also inconsistent with the predictions of kinetic localization, but this mechanism cannot be eliminated for all ILSs. Other mechanisms not eliminated include trapping of Langmuir waves in density depressions at levels below the collapse threshold, superposition of such trapped waves and “free” Langmuir waves, and superposition of trapped waves with a wave packet formed by beam‐driven Langmuir waves beating with products of electrostatic decay.
The source and propagation of the interplanetary disturbance associated with the full‐halo coronal mass ejection on 28 October 2003
Authors: Tokumaru Munetoshi , Kojima Masayoshi , Fujiki Ken’ichi , Yamashita Masahiro , Jackson Bernard V.
Published: May 2007

Observations of interplanetary scintillations made with the 327‐MHz four‐station system of the Solar‐Terrestrial Environment Laboratory of Nagoya University were analyzed to study the three‐dimensional properties of a transient solar wind stream associated with the 28 October 2003 full‐halo coronal mass ejection (CME). A loop‐shaped high‐density regionregion propagating at a significantly slower speed than the CME‐driven shock was identified. This feature appeared approximately the same as the structure seen in white‐light observations made simultaneously. The orientation of the loop structure was found in general agreement with the inclination of the magnetic flux rope observed at 1 AU. Therefore we propose that the origin of this loop structure included the high‐density plasma ejected from the corona in association with the 28 October 2003 CME. By comparing this loop structure with solar wind speed data, we find that the loop structure had a solar source aligned with a slow‐speed solar wind regionregion.
Spontaneous axisymmetry breaking of the external magnetic field at Saturn
Authors: Goldreich Peter , Farmer Alison J.
Published: May 2007

Saturn’s magnetic field is remarkably axisymmetric. Early evidence for nonaxisymmetry came from the periodicity of Saturn’s kilometric radio bursts (SKR). Subsequently, percent‐level variations of the SKR period were found to occur on timescales of years. A recent breakthrough has been the direct detection of a nonaxisymmetric component of the field that rotates with a period close to that of the SKR and whose magnitude varies only weakly with distance from Saturn. The latter implies that it must be supported by currents external to the planet. We explore the hypothesis that centrifugally driven convection spontaneously breaks the axisymmetry of the external magnetic field at Saturn. The density of the outflowing plasma close to its source is assumed to contain a substantial part that varies as cos and rotates uniformly. We demonstrate that the plasma stream must narrow with distance from the planet, while the field‐aligned currents joining stream to ionosphere increase rapidly. These currents produce a nonaxisymmetric component of magnetic field whose magnitude varies inversely with radial distance in the planet’s equatorial plane. For a rate of plasma outflow 104 ≲ ≲ 105g s−1, this component’s strength is compatible with that observed. Additionally, we postulate that the SKR is associated with the narrow range of longitudes over which large currents flow along magnetic field lines connecting the tip of the outflow to the auroral ionosphere.
Upper mantle seismic velocities and anisotropy in China determined through Pn and Sn tomography
Authors: Pei Shunping , Zhao Junmeng , Sun Youshun , Xu Zhonghuai , Wang Suyun , Liu Hongbing , Rowe Charlotte A. , Toksöz M. Nafi , Gao Xing
Published: May 2007

We have obtained velocity images of the uppermost mantle beneath China by performing tomographic inversion of both Pn and Sn traveltimes. From the Annual Bulletin of Chinese Earthquakes, 99,139 Pn arrivals and 43,646 Sn arrivals were selected. Pn anisotropy was also obtained simultaneously with Pn velocity. Average Pn and Sn velocities are 8.05 and 4.55 km/s, respectively, and maximum velocity perturbations are about 3–4%. The Pn and Sn velocities are low in eastern China and high in western China. Particularly high velocities are associated with old basins (for example, Tarim, Junggar, Turpan‐Hami, Qaidam, and Sichuan) and stable craton (for example, Ordos). Low Sn velocities are found mainly throughout North China. In addition, velocities are relatively low beneath the central Tibetan Plateau and the North‐South Seismic Zone (along 103°E). In Tarim and central China where we observe strong anisotropy, the fast Pn velocity directions are consistent with the directions of maximum principal compressive stress as well as directions of crustal movement determined from Global Positioning System. Beneath the India‐Eurasia collision zone, the Pn anisotropy direction is parallel to the collision arc and nearly perpendicular to both the direction of maximum compression and crustal movement resulting from pure shear deformation. Both the velocity variations and anisotropy indicate that the Tibetan Plateau was extruded, and the mantle material beneath the plateau has flowed around the East Himalaya Syntax, while the remaining material has diverted northwestward beneath the Tarim Basin.
Sensitivities and uncertainties in a coupled regional atmosphere‐ocean‐ice model with respect to the simulation of Arctic sea ice
Authors: Dorn W. , Dethloff K. , Rinke A. , Frickenhaus S. , Gerdes R. , Karcher M. , Kauker F.
Published: May 2007

A series of sensitivity experiments using a coupled regional atmosphere‐ocean‐ice model of the Arctic has been conducted in order to identify the requirements needed to reproduce observed sea‐ice conditions and to address uncertainties in the description of Arctic processes. The ability of the coupled model to reproduce observed summer ice retreat depends largely on a quasi‐realistic ice volume at the beginning of the melting period, determined by the relationship between winter growth and summer decay of ice. While summer ice decay is strongly affected by the parameterization of the sea‐ice albedo, winter ice growth depends significantly on the parameterization of lateral freezing. Reciprocal model biases due to uncertainties in the atmospheric energy fluxes can be compensated to a certain extent. However, potential underlying weaknesses of the model cannot be eliminated that way. Since lateral freezing also determines the ice concentration during winter, and thus the heat loss of the ocean and the near‐surface air temperature, the model tuning possibilities are limited. A large uncertainty in the model relates to the simulation of long‐wave radiation most likely as a result of overestimated cloud cover. The results suggest that uncertainties in the descriptions for Arctic clouds, snow, and sea‐ice albedo, and lateral freezing and melting of sea ice, including the treatment of snow, are responsible for large deviations in the simulation of Arctic sea ice in coupled models. Improved descriptions of these processes are needed to reduce model biases and to enhance the credibility of future climate change projections.
Stratospheric gravity wave simulation over Greenland during 24 January 2005
Authors: Limpasuvan Varavut , Wu Dong L. , Joan Alexander M. , Xue Ming , Hu Ming , Pawson Steven , Perkins James R.
Published: May 2007

The “Advanced Regional Prediction System” forecast model is extended up to the stratopause and over the entire hemisphere to simulate gravity waves during 24 January 2005. With a 15‐km horizontal resolution, the simulation produces dominant gravity wave features near Eastern Greenland that are associated mainly with orographic forcing by the Greenland terrain. The simulated wave temperature perturbations compare favorably with radiance perturbations from NASA Atmospheric Infrared Sounder observations. In the upper stratosphere (40–50 km), vertical overturning of the isentropes suggests the occurrence of wave breaking just east of Greenland that leads to a tremendous reduction of wave amplitudes. The associated flux divergence produces horizontal flow deceleration of 12–120 m s−1 day−1 and coincides with areas of depleted stratospheric wind speed, suggesting strong interactions between orographic gravity waves and the polar vortex. A simulation using the coarser 50‐km horizontal resolution produces gravity waves of significantly weaker amplitudes.
High‐resolution ensemble surface insolation estimates through assimilation of coarse‐scale retrievals into a simple physical model: 2. Ensemble implementation and Shortwave Radiation Budget data assimilation
Authors: Lee Songweon , Margulis Steven A.
Published: May 2007

A simple surface insolation model was used in conjunction with the Ensemble Kalman Filter (EnKF) to ultimately derive an ensemble of high‐resolution posterior insolation fields conditioned on the GEWEX Continental Scale International Project and GEWEX Americas Prediction Project (GCIP/GAPP) Shortwave Radiation Budget (SRB) product. When compared to ground‐based observations, the ensemble of prior estimates was shown to reasonably capture the space‐time variability and uncertainty in surface insolation except in cases where the Visible Infrared Solar‐Infrared Split Window Technique (VISST) product did not properly detect clouds. The EnKF was chosen to provide a systematic framework for merging the insolation information contained in the prior estimates with the well‐validated SRB product. When compared to independent ground‐based observations, the posterior ensemble mean estimate showed a significant reduction in error relative to the prior. The resulting posterior ensemble mean error statistics are of similar magnitude to other recent studies at similar spatial resolution. The reduction in error is highest in cloudy‐sky conditions (where prior uncertainty is largest) and lowest in clear‐sky conditions (where insolation is much easier to predict). A significant value added through application of the data assimilation scheme is a posterior estimate that provides an ensemble that captures the complex space‐, time‐, and state‐dependent uncertainty that would otherwise be very difficult to obtain using a more traditional forward modeling approach.
Effects of topographic structure on salt marsh currents
Authors: Torres Raymond , Styles Richard
Published: May 2007

The purpose of this study was to assess the spatial and temporal variability in overmarsh and in‐channel currents, and to assess that variability in the context of salt marsh topographic structure. We created a high accuracy digital elevation model of a salt marsh island using a real time kinematic Global Positioning System. We measured currents with two velocimeters at the heads of adjacent first order creeks of two separate intertidal creek networks, 30 m apart. We also monitored in‐channel currents with one current profiler. All measurements were taken during a 5‐day period with spring, mixed tides. Observations reveal that during the high‐high tides three current reversals occurred, one during flood, one near peak tide, and another during ebb, as opposed to the usual single reversal near peak tide. These reversals took place in shallow overmarsh flows and in deeper in‐channel flows. This current complexity appears to be related to tide elevation and the submergence or emergence of salt marsh topography, and it likely reflects interactions between local topographic forcing and larger scale barotrophic pressure gradients. Moreover, when the marsh platform was inundated but under ebb conditions the major components in overmarsh flow patterns between creek heads indicated a regular exchange of water between tidal creek systems. Hence the characterization of overmarsh flows as having flow divides between intertidal creek networks deserves greater scrutiny. Taken together, these observations show that the subtle topography of a salt marsh landscape exerts important control on the temporal and spatial variability on currents at centimeter‐ to creek network‐scales. More research is needed to characterize marsh topography, overmarsh circulation, and their combined effect on material transport and sediment accretion.
Organized flow from the South Pole to the Filchner‐Ronne ice shelf: An assessment of balance velocities in interior East Antarctica using radio echo sounding data
Authors: Bingham Robert G. , Siegert Martin J. , Young Duncan A. , Blankenship Donald D.
Published: May 2007

Ice flow through central Antarctica has the potential to transmit accumulation changes from deep‐interior East Antarctica rapidly to the shelf, but it is poorly constrained owing to a dearth of ice‐velocity observations. We use parameters derived from airborne radio echo sounding (RES) data to examine the onset, areal extent, and englacial conditions of an organized flow network (tributaries feeding an ice stream) draining from the South Pole to the Filchner‐Ronne Ice Shelf. We classified RES flight tracks covering the region according to whether englacial stratigraphy was disrupted (i.e., internal layers diverged significantly from the surface and bed echoes) or undisrupted (i.e., internal layers closely parallel surface and basal topography), and we calculated subglacial roughness along basal reflectors. Where satellite‐measured surface ice‐flow speeds are available (covering 39% of the study region), regions of fast and tributary flow correspond with RES flight tracks that exhibit more disrupted internal layers and smoother subglacial topography than their counterparts in regions of slow flow. This suggests that disrupted internal layering and smooth subglacial topography identified from RES profiles can be treated as indicators of past or present enhanced‐flow tributaries where neither satellite nor ground‐based ice‐flow measurements are available. We therefore use these RES‐derived parameters to assess the balance‐flux‐modeled steady state flow regime between the South Pole and Filchner‐Ronne Ice Shelf. The RES analysis confirms that an organized flow network drains a wide region around the South Pole into the Filchner‐Ronne Ice Shelf. However, the spatial extent of this network, as delineated by the RES data, diverges from that predicted by currently available balance‐flux models.
Up to 1‐hour forecasting of radiation hazards from solar energetic ion events with relativistic electrons
Authors: Posner Arik
Published: May 2007

The sudden and prompt occurrence of solar energetic particle events poses a hazard to manned space activities and interferes with robotic space science missions. This study demonstrates the possibility of short‐term forecasting of the appearance and intensity of solar ion events by means of relativistic, near–light speed electrons. A list of the most severe proton events measured by GOES 8 in the years 1996–2002 serves as a basis to derive the fundamentals of the forecasting method with statistical and superposed epoch techniques. The Comprehensive Suprathermal and Energetic Particle Analyzer (COSTEP) on SOHO provides relativistic electron and <50 MeV proton observations at 1 AU. With a subset of solar particle events (SPEs) where the location of the associated flare on the Sun has been determined, we find that (1) relativistic electrons always arrive at 1 AU ahead of nonrelativistic SPEs allowing their forecasting; (2) the intensity increase of both, electrons and protons alike, depends on the magnetic connection, i.e., the magnetic longitude difference between the observer and the flare; and (3) as coming from one source under near‐identical propagation conditions, significant correlations exist that show that the early electron intensity and increase can be utilized as a matrix to forecast the upcoming proton intensity. The study demonstrates one initial empirical forecasting technique with electron and proton observations in 2003.
Climate change already altering Earth, IPCC Says
Authors: Zielinski Sarah
Published: May 2007

The Intergovernmental Panel on Climate Change has confirmed what many scientists had suspected: anthropogenic climate change is already altering the Earth. Ice is melting, water patterns are changing, and a host of organisms are being affected in a variety of ways. More changes are expected as temperatures rise, and the world's poor will be affected the most.

The report from IPCC Working Group II, I “Climate Change 2007: Impacts, Adaptation and Vulnerability,” is the second of three parts of the IPCC Fourth Assessment Report (see Eos 88(6) and 88(7), 2007). The full 1572‐page report, which will be published in book format in September, was compiled over the last few years by 174 lead authors and 222 contributing authors and included the participation of 1183 experts. A 23‐page Summary for Policymakers, which was negotiated by government representatives during a plenary held in Brussels, Belgium, was finalized and released on 6 April (see http://www.ipcc.ch).
Arctic Alpine Ecosystems and People in a Changing Environment
Authors: Körner Christian
Published: May 2007

Because of my own interest in this topic, Arctic Alpine Ecosystems and People in a Changing Environment immediately caught my attention. However, upon opening the book and reviewing the contents, I felt somewhat misguided by the title (as most potential buyers would be), given the actual topics addressed.
Harrison receives 2006 William Gilbert Award
Authors: McEnroe Suzanne A. , Harrison Richard J.
Published: May 2007

Richard J. Harrison received the William Gilbert Award at the 2006 AGU Fall Meeting. The award recognizes outstanding and unselfish work in magnetism of Earth materials and of the Earth and planets.

This year the Gilbert Award is given to an outstanding young scientist under the age of 35. Richard Harrison easily fulfills the first criterion and just makes the second. He is now 34. As I reviewed Richard's accomplishments, I was once again impressed with his scope and level of research. He has 50 papers published, or in press, and all of them are of the same high scientific caliber. Many of you know Richard's cutting‐edge research with electron holography showing magnetic interactions across magnetite‐ulvospinel intergrowths, and are familiar with his groundbreaking research on lamellar magnetism. His TEM observations, combined with extensive Monte Carlo simulations of atomic interactions in hematite‐ilmenite interfaces, which took both electrostatic and magnetic interactions into consideration, have developed the idea of contact layers as a magnetic substructure of defect moments at the interfaces. This was followed by work that showed that contact layers reduce charge imbalance at the interfaces.
‘Rotators’ in the National Science Foundation's Geosciences Directorate
Authors: Mueller‐Parker Giselle
Published: May 2007

More than half of the program directors at the U.S. National Science Foundation are ‘rotators,’ either on loan from their host institutions as visiting scientists, engineers, and educators, or employed through grants to their home institutions. What are the benefits of being a rotator at NSR and should you apply for a rotator position? This forum summarizes the reflections of 17 rotators from the divisions of Atmospheric, Earth, and Ocean Sciences in NSF's Directorate for Geosciences who responded to an informal survey I sent out after completing a 2‐year position in the Division of Ocean Sciences. My aim here is to describe how rotators in the geosciences view their experiences at NSF with respect to their own science and career paths, to help you decide whether to consider applying for a rotator position in the directorate.
Dry snow slab shear fracture speeds
Authors: McClung D. M.
Published: May 2007

Dry snow slab avalanches release by propagating shear fractures within thin weak layers underneath thicker, stronger planar slabs. In this paper, measured shear fracture speeds from small scale snow slabs are compared with theoretical estimates compatible with dynamic fracture mechanics. Given the important physical quantities including density and elastic shear modulus, it is concluded that estimated snow slab shear fracture speeds scale with the shear wave speed similar to estimates in other geophysical applications including shear fractures from earthquakes and in engineering materials. However, the constant of proportionality is much lower than for alpine snow than for earthquakes and engineering materials. The lower constant of proportionality may indicate the possibility of important energy dissipation mechanisms in snow avalanche fracture propagation.
Interdecadal variability of the early summer surface heat flux in the Kuroshio region and its impact on the Baiu frontal activity
Authors: Tomita Tomohiko , Sato Hiroyasu , Nonaka Masami , Hara Masayuki
Published: May 2007

In the Kuroshio region (KR), the early summer surface heat flux (SHF) exhibits a rapid increase around 1990 as a climate shift, which is rooted in the oceanic interdecadal variability in the North Pacific. The sea surface temperature (SST) in the KR, where SST is largely controlled by subsurface ocean circulations, is positively correlated with the local upward SHF. The positive SHF anomalies in the 1990s reinforced the Baiu frontal activity with an atmospheric large‐scale meridional dipole in the western North Pacific. As such, the oceanic interdecadal variability has an impact on the atmospheric circulation through coherent SST and SHF variations even in early summer in the KR.