bluuebunny/crossref_metadata_2025 huggingface dataset:
Gas at the inner disk edge
Authors: Carr John S.
Published: November 2007

Infrared molecular spectroscopy is a key tool for the observation of gas in the innermost region of disks around T Tauri stars. In this contribution, we examine how infrared spectroscopy of CO can be used to study the inner truncation region of disks around T Tauri stars. The inferred inner gas radii for T Tauri star disks are compared to the inner dust radii of disks, to the expectations of models for disk truncation, and to the orbital distribution of short-period extra-solar planets.
Observational constraints on disk photoevaporation by the central star
Authors: Herczeg Gregory J.
Published: November 2007

We apply results from FUV and X-ray spectroscopy to evaluate the role of photoevaporation in dispersing the disk around TW Hya. Accretion produces bright EUV emission that may be smothered by the accretion column. Solar-like magnetic activity produces fewer ionizing photons, which may be absorbed by an accretion-powered neutral wind. We estimate a photoevaporation rate of ∼ 5 × 10−11M⊙ yr−1 for the disk around TW Hya. These models can be tested by detecting gas in the ionized disk surface, including emission in the [Ne II] 12.8μm line. Photoevaporation is likely a minor process in disk dispersal during the accretion phase, but could remove ∼ 1 MJ of remnant gas around a solar-mass star after accretion ceases.
Accretion and outflow-related X-rays in T Tauri stars
Authors: Güdel Manuel , Briggs Kevin , Arzner Kaspar , Audard Marc , Bouvier Jérôme , Dougados Catherine , Feigelson Eric , Franciosini Elena , Glauser Adrian , Grosso Nicolas , Guieu Sylvain , Ménard François , Micela Giusi , Monin Jean-Louis , Montmerle Thierry , Padgett Deborah , Palla Francesco , Pillitteri Ignazio , Preibisch Thomas , Rebull Luisa , Scelsi Luigi , Silva Bruno , Skinner Stephen , Stelzer Beate , Telleschi Alessandra
Published: November 2007

We report on accretion- and outflow-related X-rays from T Tauri stars, based on results from the “XMM-Newton Extended Survey of the Taurus Molecular Cloud.” X-rays potentially form in shocks of accretion streams near the stellar surface, although we hypothesize that direct interactions between the streams and magnetic coronae may occur as well. We report on the discovery of a “soft excess” in accreting T Tauri stars supporting these scenarios. We further discuss a new type of X-ray source in jet-driving T Tauri stars. It shows a strongly absorbed coronal component and a very soft, weakly absorbed component probably related to shocks in microjets. The excessive coronal absorption points to dust-depletion in the accretion streams.
Why are accreting T Tauri stars less luminous in X-rays than non-accretors?
Authors: Gregory S. G. , Wood K. , Jardine M.
Published: November 2007

Accreting T Tauri stars are observed to be less luminous in X-rays than non-accretors, an effect that has been detected in various star forming regions. To explain this we have combined, for the first time, a radiative transfer code with an accretion model that considers magnetic fields extrapolated from surface magnetograms obtained from Zeeman-Doppler imaging. Such fields consist of compact magnetic regions close to the stellar surface, with extended field lines interacting with the disk. We study the propagation of coronal X-rays through the magnetosphere and demonstrate that they are strongly absorbed by the dense gas in accretion columns.
Spectroscopic diagnostics of T Tauri inner winds
Authors: Edwards Suzan
Published: November 2007

The role of the star-disk interaction region in launching the high velocity component of accretion-driven outflows is examined. Spectroscopic indicators of high velocity inner winds have been recognized in T Tauri stars for decades, but identifying the wind launch site and the accompanying mass loss rates has remained elusive. A promising new diagnostic is He I λ10830, whose metastable lower level results in a powerful probe of the geometry of the outflowing gas in the interaction region. This, together with other atomic and molecular spectral diagnostics covering a wide range of excitation and ionization states, suggests that more than one launch site of the innermost wind is operational in most accreting stars.
The generation of jets from young stars: an observational perspective
Authors: Ray T. P.
Published: November 2007

The birth of a young star is accompanied not only by accretion but by the expulsion of matter as well in the form of a collimated outflow. These outflows are seen at various wavelengths from X-rays to the radio band, but ultimately the driving mechanism appears to be a highly collimated supersonic jet that contains not only atomic but molecular components as well. These jets may also play a key role in the star formation process itself since they could be one of the primary mechanism for removing angular momentum from the accretion disk thereby allowing accretion to occur. Whereas much is known about their propagation on large-scales (i.e., hundreds of AU to several parsecs) from both observations and simulations, we must explore the “central engine” in order to understand how they are generated. While this is particularly challenging, high spatial resolution studies are beginning to reveal interesting data from which we can confront the various models. In this review, I will summarise what these studies suggest and note how they already favour certain models over others. I will also describe some of the results from spectro-astrometry and interferometry that are revealing details of outflows on milliarcsecond scales from the source.
The role of thermal pressure in jet launching
Authors: Soker Noam
Published: November 2007

I present and discuss a unified scheme for jet launching that is based on stochastic dissipation of the accretion disk kinetic energy, mainly via shock waves. In this scheme, termed thermally-launched jet model, the kinetic energy of the accreted mass is transferred to internal energy, e.g., heat or magnetic energy. The internal energy accelerates a small fraction of the accreted mass to high speeds and form jets. For example, thermal energy forms a pressure gradient that accelerates the gas. A second acceleration stage is possible wherein the primary outflow stretches magnetic field lines. The field lines then reconnect and accelerate small amount of mass to very high speeds. This double-stage acceleration process might form highly relativistic jets from black holes and neutron stars. The model predicts that detail analysis of accreting brown dwarfs that launch jets will show the mass accretion rate to beṀBD≳ 10−9− 10−8M⊙yr−1, which is higher than present claims in the literature.
The accretion-ejection connexion in T Tauri stars: jet models vs. observations
Authors: Cabrit S.
Published: November 2007

Key observational constraints for jet models in T Tauri stars are outlined, including the jet collimation scale, kinematic structure, and ejection/accretion ratio. It is shown that MHD self-collimation is most likely required. The four possible MHD ejection sites (stellar surface, inner disk edge, extended disk region, magnetosphere-disk reconnexion line) are then critically examined against observational constraints, and open issues are discussed.
The structure accompanying young star formation
Authors: Demichev Vasily A. , Matveyenko L. I.
Published: November 2007

We studied the structure of the H2O super maser region in Orion with VLBI angular resolution of 0.1 mas or 0.05 AU. The maser emission (F ∼ 8 MJy) was determined by highly organized structure: accretion disk, bipolar outflow, torus and surrounding shell. The accretion disk, divided into protoplanetary rings, is viewed edge-on. The disk rotates as a rigid body with velocities V ∼ ΩR and the rotation period is ∼ 170 yrs. The highly collimated bipolar outflow has a size of 9×0.7 AU, a velocity of ∼ 10 km/s. In the center a bright compact (≤0.05 AU) source – ejector is located, surrounded by a torus 0.6 AU in diameter. The outflow has a helix structure, which is determined by precession with a period of T ∼ 10 yrs. Comet-like bullets were observed on distances up to 80 AU.
Last gasp of V1647 Ori: a brief post-outburst warm, molecular wind
Authors: Brittain Sean D. , Simon Theodore , Rettig Terrence W. , Gibb Erika L. , Balsara Dinshaw , Tilley David , Hinkle Kenneth H.
Published: November 2007

Followup infrared spectroscopy is reported for V1647 Ori, a young star whose recent eruption illuminated McNeil's Nebula. Lines of HI, H2, and CO are compared to previous observations. We find that the accretion rate fell two orders of magnitude and the CO bandheads disappeared at the end of the outburst. We also report a striking metamorphosis of the fundamental CO spectrum from centrally peaked profiles to emission lines with superimposed blue-shifted absorption lines and back again one year later. This remarkable change in spectral appearance indicates that the system did not return to equilibrium immediately following the outburst. In this paper we propose a mechanism to explain the emergence of a transient post-outburst outflow.
The rotational evolution of young low mass stars
Authors: Bouvier Jérôme
Published: November 2007

Star-disk interaction is thought to drive the angular momentum evolution of young stars. In this review, I present the latest results obtained on the rotational properties of low mass and very low mass pre-main sequence stars. I discuss the evidence for extremely efficient angular momentum removal over the first few Myr of pre-main sequence evolution and describe recent results that support an accretion-driven braking mechanism. Angular momentum evolution models are presented and their implication for accretion disk lifetimes discussed.
The rotation of very low-mass stars and brown dwarfs
Authors: Eislöffel Jochen , Scholz Alexander
Published: November 2007

The evolution of angular momentum is a key to our understanding of star formation and stellar evolution. The rotational evolution of solar-mass stars is mostly controlled by magnetic interaction with the circumstellar disc and angular momentum loss through stellar winds. Major differences in the internal structure of very low-mass stars and brown dwarfs – they are believed to be fully convective throughout their lives, and thus should not operate a solar-type dynamo – may lead to major differences in the rotation and activity of these objects. Here, we report on observational studies to understand the rotational evolution of the very low-mass stars and brown dwarfs.
Magnetization, accretion, and outflows in young stellar objects
Authors: Shu Frank H. , Galli Daniele , Lizano Susana , Cai Mike J.
Published: November 2007

We review the theory of the formation and gravitational collapse of magnetized molecular cloud cores, leading to the birth of T Tauri stars surrounded by quasi-Keplerian disks whose accretion is driven by the magnetorotational instability (MRI). Some loss of magnetic flux during the collapse results typically in a dimensionless mass-to-flux ratio for the star plus disk of λ0≈ 4. Most of the mass ends up in the star, while almost all of the flux and the angular momentum ends up in the disk; therefore, a known mass for the central star implies a computable flux in the surrounding disk. A self-contained theory of the MRI that drives the viscous/resistive spreading in such circumstances then yields the disk radius needed to contain the flux trapped in the disk as a function of the aget. This theory yields analytic predictions of the distributions with distance ϖ from the central star of the surface density Σ(ϖ), the vertical magnetic fieldBz(ϖ), and the (sub-Keplerian) angular rotation rate Ω (ϖ). We discuss the implications of this picture for disk-winds, X-winds, and funnel flows, and we summarize the global situation by giving the energy and angular-momentum budget for the overall problem.
MHD simulations of star-disk magnetospheres and the formation of outflows and jets
Authors: Fendt Christian
Published: November 2007

In this review the recent development concerning the large-scale evolution of stellar magnetospheres in interaction with the accretion disk is discussed. I put emphasis on the generation of outflows and jets from the disk and/or the star. In fact, tremendous progress has occurred over the last decade in the numerical simulation of the star-disk interaction. The role of numerical simulations is essential in this area because the processes involved are complex, strongly interrelated, and often highly time-dependent. Recent MHD simulations suggest that outflows launched from a very concentrated region tend to be un-collimated. I present preliminary results of simulations of large-scale star-disk magnetospheres loaded with matter from the stellar, resp. the disk surface demonstrating how a disk jet collimates the wind from the star and also how the stellar wind lowers the collimation degree of the disk outflow.
MHD simulations of disk-star interaction
Authors: Romanova Marina M. , Long M. , Kulkarni A. K. , Kurosawa R. , Ustyugova G. V. , Koldoba A. K. , Lovelace R. V. E.
Published: November 2007

We discuss a number of topics relevant to disk-magnetosphere interaction and how numerical simulations illuminate them. The topics include: (1) disk-magnetosphere interaction and the problem of disk-locking; (2) the wind problem; (3) structure of the magnetospheric flow, hot spots at the star's surface, and the inner disk region; (4) modeling of spectra from 3D funnel streams; (5) accretion to a star with a complex magnetic field; (6) accretion through 3D instabilities; (7) magnetospheric gap and survival of protoplanets. Results of both 2D and 3D simulations are discussed.
MHD instabilities at the disk-magnetosphere boundary: 3D simulations
Authors: Kulkarni Akshay K. , Romanova Marina M.
Published: November 2007

We present results of 3D simulations of MHD instabilities at the accretion disk-magnetosphere boundary. The instability is Rayleigh-Taylor, and develops for a large range of parameter values. It manifests itself in the form of tall, thin tongues of plasma that reach the star by penetrating through the magnetosphere in the equatorial plane. The tongues rotate around the star in the equatorial plane, and their shape and number changes with time on inner-disk dynamical timescales. In contrast with funnel flows, which deposit matter mainly in the polar region, the tongues deposit matter much closer to the stellar equator.
The nature of stellar winds in the star-disk interaction
Authors: Matt Sean , Pudritz Ralph E.
Published: November 2007

Stellar winds may be important for angular momentum transport from accreting T Tauri stars, but the nature of these winds is still not well-constrained. We present some simulation results for hypothetical, hot (∼ 106 K) coronal winds from T Tauri stars, and we calculate the expected emission properties. For the high mass loss rates required to solve the angular momentum problem, we find that the radiative losses will be much greater than can be powered by the accretion process. We place an upper limit to the mass loss rate from accretion-powered coronal winds of ∼ 10−11M yr−1. We conclude that accretion powered stellar winds are still a promising scenario for solving the stellar angular momentum problem, but the winds must be cool (e.g., 104 K) and thus are not driven by thermal pressure.
Large scale magnetic fields in discs: jets and reconnection X-winds
Authors: Ferreira Jonathan , Bessolaz Nicolas , Zanni Claudio , Combet Céline
Published: November 2007

In this contribution we first briefly review our current knowledge on the physics of accretion discs driving self-confined jets. It will be shown that a large scale magnetic field is expected to thread the innermost disc regions, giving rise to a transition from an outer standard accretion disc to an inner jet emitting disc. We then report new progresses on the theory of star-disc interaction, allowing to explain the formation of accretion funnel flows with stellar dipole fields consistent with observational constraints. Such a connection is now not only probed by modern observations but it is also requested for spinning down protostars, which are known to be both actively accreting and contracting. This spin down most probably relies on the angular momentum removal by ejection. Two such scenarios will be addressed here, namely “accretion-powered stellar winds” (Matt & Pudritz 2005) and “Reconnection X-winds” (Ferreira, Pelletier & Appl 2000). The latter can slow down a protostar on time scales shorter or comparable to the embedded phase. It will be shown that these two scenarios are not incompatible and that transitions from one to another may even occur as they mainly depend on the stellar dynamo.
The implications of close binary stars for star-disk interactions
Authors: Mathieu Robert D.
Published: November 2007

The presence of close (≲ 0.1 AU) stellar companions must greatly alter the circumstellar environment of classical T Tauri stars, including severe truncation if not elimination of circumstellar disks. It is thus remarkable how little impact the presence of a close companion has on our observable diagnostics for accretion and outflow. Emission line shapes, degrees of continuum veiling, and spectral energy distributions are all indistinguishable between single classical T Tauri stars and classical T Tauri close binaries. Some of the most classical T Tauri stars that laid the foundation for our single-star accretion-disk paradigm have turned out to have close companions. Periodicities in spectral signatures are suggestive of the presence of accretion flows from circumbinary disks to the circumstellar regions; the subsequent flow of material through the circumstellar region to the stellar surface in the presence of a stellar magnetosphere is unstudied. Observations of stellar rotation distributions in close binaries suggest that inner disk regions may act to regulate stellar angular momentum.
Disc–magnetosphere interactions in cataclysmic variable stars
Authors: Hellier Coel
Published: November 2007

I review, from an observational perspective, the interactions of accretion discs with magnetic fields in cataclysmic variable stars. I start with systems where the accretion flows via a stream, and discuss the circumstances in which the stream forms into an accretion disc, pointing to stars which are close to this transition. I then turn to disc-fed systems and discuss what we know about how material threads on to field lines, as deduced from the pattern of accretion footprints on the white dwarf. I discuss whether distortions of the field lines are related to accretion torques and the changing spin periods of the white dwarfs. I also review the effect on the disc–magnetosphere interaction of disc-instability outbursts. Lastly, I discuss the temporary, dynamo-driven magnetospheres thought to occur in dwarf-nova outbursts, and whether slow-moving waves are excited at the inner edges of the disc.
Star-disk interaction in brown dwarfs: implications for substellar formation
Authors: Mohanty Subhanjoy
Published: November 2007

I review the current state of knowledge regarding disk accretion in young brown dwarfs (BDs), and the interaction of the disk with the central object. In particular, I discuss (1) observations of accretion/outflow phenomena in BDs; (2) techniques for measuring accretion rates (Ṁacc); (3) the dependence of Ṁacc on the central mass from stars to brown dwarfs; (4) the temporal evolution of Ṁacc; and (5) observations of variability in the accretion line profiles. I then examine the implications of these issues for the formation mechanism of BDs, and discuss new observations that can further constrain substellar origins.
Outflow activity in brown dwarfs
Authors: Whelan Emma T. , Ray Thomas P. , Bacciotti Francesca , Randich Sofia , Jayawardhana Ray , Natta Antonella , Testi Leonardo , Mohanty Subu
Published: November 2007

While numerous studies have been aimed at understanding the properties of young brown dwarfs relatively little exploration of their potential as drivers of outflows has occurred. Forbidden emission lines are important probes of outflows from young stellar objects, as they trace the shocks which form as an outflow interacts with the ambient medium of its driving source. While forbidden emission was identified in the spectra of young brown dwarfs, indicating the presence of outflows, these lines were weak and confined to the brown dwarf continuum position. Hence their origin in an outflow could not be confirmed. Our approach to this problem, is to analyse the forbidden line regions of brown dwarfs using spectro-astrometry. Spectro-astrometry is a novel technique which allows the user to recover spatial information from a spectrum beyond the limitations of the seeing of the observation. Using this technique we have found two brown dwarf outflows to date. In this chapter we outline this technique, describe our results for the brown dwarfs ρ-Oph 102 and 2MASS1207-3932 and discuss our future plans.
Summary and concluding remarks
Authors: Appenzeller Immo
Published: November 2007

This symposium was characterized by an intense exchange of new information and by lively discussions on many aspects of the formation and early evolution of low-mass stars. The observational data presented at this meeting, obtained in spectral regions ranging from X-rays to submm waves, were found to be remarkably consistent with the current magnetospheric disc-accretion paradigm for young stellar objects. But there remain open questions, and a full understanding of the star-formation process will require much additional work.
Why did they not take on the disputes? Law, power and politics in the decision-making of Chinese courts
Authors: He Xin
Published: November 2007

Chinese courts’ recent refusal to take on some disputes raises questions on the extent to which they are controlled by superior political powers in their region. Through a close examination of the handling process of ‘Married Out Women’ disputes, this article shows that lower courts in Guangdong Province, China, have effectively resisted pressure to solve the disputes. Arguing legal barriers and enforcement difficulties, the courts ultimately referred the disputes to the governments but agreed to review the governments’ decisions in administrative litigation. In so doing, the courts retain an advantageous position in the power relationship with the governments. The article argues that Chinese courts are capable of deliberating about and transforming their situation by strategically interpreting the law and negotiating with superior powers. It suggests that judicial independence in China is far more complicated than is often recognised, and that judicial behaviour cannot be adequately explained without thick descriptions and understanding of the legal arguments, resource constraints and strategic interpretations open to the courts, in context.
Corruption, legal solutions and limits of law
Authors: Carr Indira
Published: November 2007

Since the mid-1990s there has been intense activity in terms of anti-corruption initiatives. Section 1 of this paper (Regulatory measures: the conventions) focuses on the frameworks of these conventions and in the course of their assessment argues (a) that the lack of a unified approach is unlikely to further the fight against corruption in any meaningful way, (b) that regulation is unlikely to be effective in terms of results unless there are robust enforcement mechanisms in place, and (c) that anti-corruption legislation provides only a partial answer and that we need to engage in what I call a process of re-socialisation. Section 2 (Enforcement and informers) highlights the difficulties associated with enforcing the conventions and explores whether the antiquatedqui tamaction might serve a useful purpose in addressing the problem of enforcement deficit. Section 3 (Fighting corruption through re-socialisation) asks whether greater social awareness through education provides a possible solution. Guided by a humanistic philosophy of society the view is put forward that part of the answer for effectively tackling corruption lies in making people aware of its long-term effects.
Theorising law and legitimacy in international criminal justice
Authors: Henham Ralph
Published: November 2007

This paper seeks to explore the relationship between law and morality and its relevance for establishing the legitimacy of international criminal justice (ICJ) within the context of international trials. At present, imperatives for peace and reconstruction in conflict societies are divorced both conceptually and practically from the process of punishment in international criminal trials. It argues that, in order for international trial justice to move beyond partial forms of retributivism requires a profound re-alignment of the rationales underpinning international penality and a merging of retributive and restorative justice forms. The paper suggests that the resolution of ‘truth’ must go further than this by implicating penal law and process as crucial determinants of ‘legitimate’ strategies for intervention, thereby enabling a wider choice of consequent resolutions. The paper suggests that the intrinsic value of international criminal process lies in its capacity to confront the relativism of ICJ by providing the means to engage with its plurality and so increase its legitimacy for all victims and communities affected by social conflict and war. In so doing it considers how law may be transformed into normative guides to conduct and examines the relationship between the processes of legal reasoning and sentence decision-making in international criminal trials.
Modeling the soil consumption of atmospheric methane at the global scale
Authors: Curry Charles L.
Published: November 2007

A simple scheme for the soil consumption of atmospheric methane, based on an exact solution of the one‐dimensional diffusion‐reaction equation in the near‐surface soil layer, is described. The model includes a parameterization of biological oxidation that is sensitive to soil temperature, moisture content, and land cultivation fraction. The scheme was incorporated in the Canadian Land Surface Scheme (CLASS), with forcing provided by a 21‐a, global land meteorological data set, and was calibrated using multiyear field measurements. Application of the scheme on the global scale gives an annual mean sink strength of 28 Tg CH4 a−1, with an estimated uncertainty range of 9–47 Tg CH4 a−1. A strong seasonality is present at Northern Hemisphere high latitudes, with enhanced uptake during the summer months. Under the specified surface forcings, the oxidation parameterization is more sensitive to soil moisture than to temperature. Compared to the previous work of Ridgwell et al. (1999), our empirically based water stress parameterization reduces uptake more rapidly with decreasing soil moisture, resulting in a decrease of ∼50% in the potential global sink strength. Analysis of the geographical distribution of methane consumption shows that subtropical and dry tropical ecosystems account for over half of the global uptake.
Young volcanism and related hydrothermal activity at 5°S on the slow‐spreading southern Mid‐Atlantic Ridge
Authors: Haase K. M. , Petersen S. , Koschinsky A. , Seifert R. , Devey C. W. , Keir R. , Lackschewitz K. S. , Melchert B. , Perner M. , Schmale O. , Süling J. , Dubilier N. , Zielinski F. , Fretzdorff S. , Garbe‐Schönberg D. , Westernströer U. , German C. R. , Shank T. M. , Yoerger D. , Giere O. , Kuever J. , Marbler H. , Mawick J. , Mertens C. , Stöber U. , Walter M. , Ostertag‐Henning C. , Paulick H. , Peters M. , Strauss H. , Sander S. , Stecher J. , Warmuth M. , Weber S.
Published: November 2007

The effect of volcanic activity on submarine hydrothermal systems has been well documented along fast‐ and intermediate‐spreading centers but not from slow‐spreading ridges. Indeed, volcanic eruptions are expected to be rare on slow‐spreading axes. Here we report the presence of hydrothermal venting associated with extremely fresh lava flows at an elevated, apparently magmatically robust segment center on the slow‐spreading southern Mid‐Atlantic Ridge near 5°S. Three high‐temperature vent fields have been recognized so far over a strike length of less than 2 km with two fields venting phase‐separated, vapor‐type fluids. Exit temperatures at one of the fields reach up to 407°C, at conditions of the critical point of seawater, the highest temperatures ever recorded from the seafloor. Fluid and vent field characteristics show a large variability between the vent fields, a variation that is not expected within such a limited area. We conclude from mineralogical investigations of hydrothermal precipitates that vent‐fluid compositions have evolved recently from relatively oxidizing to more reducing conditions, a shift that could also be related to renewed magmatic activity in the area. Current high exit temperatures, reducing conditions, low silica contents, and high hydrogen contents in the fluids of two vent sites are consistent with a shallow magmatic source, probably related to a young volcanic eruption event nearby, in which basaltic magma is actively crystallizing. This is the first reported evidence for direct magmatic‐hydrothermal interaction on a slow‐spreading mid‐ocean ridge.
Planetary waves and intraseasonal oscillations at Davis, Antarctica, from undersampled time series
Authors: Stockwell R. G. , Riggin D. M. , French W. J. R. , Burns G. B. , Murphy D. J.
Published: November 2007

Nine years (1997 to 2005) of nighttime hydroxyl (6‐2) band rotational temperatures were measured with a scanning spectrometer over Davis station, Antarctica (68.6°S, 78.0°E). A novel time series analysis technique is employed to create continuous long‐term time series, and local spectral analysis of these temperature time series was performed to search for planetary wave and intraseasonal oscillations. Many significant wave signatures were observed. Coincident observations are found in a comparison between these temperature wave signatures and horizontal wind measurements made from a collocated MF radar. Several very long term wave signatures (30 to 50 days) are seen in the OH temperatures which are absent from the MF radar winds. An increase in wave activity is seen in the late winter season. Interannual variations are also shown indicating a peak in 2002; the year of the Southern Hemisphere Stratospheric Warming Event.
Deep water variability on the southern Agulhas Plateau: Interhemispheric links over the past 170 ka
Authors: Molyneux Elizabeth G. , Hall Ian R. , Zahn Rainer , Diz Paula
Published: November 2007

Sortable silt mean grain sizes together with oxygen and carbon isotopic data produced on the benthic foraminiferal species Fontbotia wuellerstorfi are used to construct high‐resolution records of near‐bottom flow vigour and deep water ventilation at a core site MD02‐2589 located at 2660 m water depth on the southern Agulhas Plateau. The results suggest that during glacial periods (marine oxygen isotope stages 2 and 6, MIS 2 and MIS 6, respectively), there was a persistent contribution of a well‐ventilated water mass within the Atlantic to Indian oceanic gateway with a δ13C signature similar to present‐day Northern Component Water (NCW), e.g., North Atlantic Deep Water (NADW). The records of chemical ventilation and near‐bottom flow vigor reflect changes in the advection of northern source waters and meridional variability in the location of the Antarctic Circumpolar Current and its associated fronts. We suggest that during Termination II (TII), changes in chemical ventilation are largely decoupled from near‐bottom physical flow speeds. A mid‐TII climate optimum is associated with a low‐flow speed plateau concurrent with a period of increased ventilation shown in the benthic δ13C of other Southern Ocean records but not in our benthic δ13C of MD02‐2589. The climate optimum is followed by a period of southern cooling around 128 ka coincident with a stronger influence of NCW to interglacial levels at around 124 ka. All proxy records show a near synchronous and rapid shift during the transition from MIS 5a‐4 (73 ka). This large event is attributed to a rapid decrease in NADW influence and replacement over the Agulhas Plateau by southern source waters.
Focal waveform of a prolate‐spheroidal impulse‐radiating antenna
Authors: Baum Carl E.
Published: November 2007

This paper develops some analytical approximations for the transient focal waveform produced at the second focus of a prolate‐spheroidal reflector due to a pulse TEM wave launched from the first focus. This is extended to consider the spot size of the peak field near the second focus.
Variations in stratospheric inorganic chlorine between 1991 and 2006
Authors: Lary D. J. , Waugh D. W. , Douglass A. R. , Stolarski R. S. , Newman P. A. , Mussa H.
Published: November 2007

A consistent time series of stratospheric inorganic chlorine Cly from 1991 to present is formed using space‐borne observations together with neural networks. A neural network is first used to account for inter‐instrument biases in HCl observations. A second neural network is used to learn the abundance of Cly as a function of HCl and CH4, and to form a time series using available HCl and CH4 measurements. The estimates of Cly are broadly consistent with calculations based on tracer fractional releases and previous estimates of stratospheric age of air. These new estimates of Cly provide a critical test for global models, which exhibit significant differences in predicted Cly and ozone recovery.
Real‐time simultaneous detection of volcanic Hg and SO2 at La Fossa Crater, Vulcano (Aeolian Islands, Sicily)
Authors: Aiuppa A. , Bagnato E. , Witt M. L. I. , Mather T. A. , Parello F. , Pyle D. M. , Martin R. S.
Published: November 2007

Measuring Hg/SO2 ratios in volcanic emissions is essential for better apportioning the volcanic contribution to the global Hg atmospheric cycle. Here, we report the first real‐time simultaneous measurement of Hg and SO2 in a volcanic plume, based on Lumex and MultiGAS techniques, respectively. We demonstrate that the use of these novel techniques allows the measurements of Hg/SO2 ratios with a far better time resolution than possible with more conventional methods. The Hg/SO2 ratio in the plume of F0 fumarole on La Fossa Crater, Vulcano Island spanned an order of magnitude over a 30 minute monitoring period, but was on average in qualitative agreement with the Hg/SO2 ratio directly measured in the fumarole (mean plume and fumarole ratios being 1.09 × 10−6 and 2.9 × 10−6, respectively). The factor 2 difference between plume and fumarole compositions provides evidence for fast Hg chemical processing the plume.
Interannual salinification of the Mediterranean inflow
Authors: Millot Claude
Published: November 2007

Hydrological decadal trends of Mediterranean waters (MWs, e.g., salinification of ∼0.01/decade) have been imputed to local environmental changes, hence assuming unchanged inflowing Atlantic water (AW), which is an unchecked hypothesis. To better understand the long‐term changes in the sea, an autonomous CTD has been moored, among others, on the Moroccan shelf in the strait of Gibraltar. We show that the inflowing AW salinity displays a marked seasonal variability, due to mixing conditions, and a huge interannual variability, having continuously increased by ∼0.05/year in 2003–2007; the AW yearly trend is dozens times larger than the MWs decadal one. The ∼0.20 overall salinification being associated with a ∼0.12 kg/m3 densification, reliable data analyses and numerical models dealing with the sea functioning must definitely consider the interannual variability of the inflow. Autonomous CTDs are efficient instruments and the variance criterion is a valuable data selection technique.
Formation of secondary light‐absorbing “fulvic‐like” oligomers: A common process in aqueous and ionic atmospheric particles?
Authors: Nozière Barbara , Dziedzic Pawel , Córdova Armando
Published: November 2007

Light‐absorbing “humic‐like” compounds of secondary origin have been consistently reported in partly inorganic aerosols and in fog waters but their formation could not be explained until now. In this work, we demonstrate that amino acid‐ and ammonium sulfate‐catalyzed reactions in water and ionic solutions produce compounds of identical molecular and optical properties and account well for the quantities found in atmospheric particles. For typical aerosol concentrations of amino acids or ammonium sulfate the rate constants of reaction are found to be identical to the one in concentrated sulfuric acid (10–15 M), clearly demonstrating the efficiency of these catalysts. Our results also show that these reactions should be common in aqueous and ionic aerosols, as confirmed by the observations, and significantly impact their absorption index. In particular, previous radiative calculations indicate that they should substantially reduce current estimates of the cooling contribution of sulfate aerosols on climate.
Linear mixture modeling of Europa's non‐ice material based on cryogenic laboratory spectroscopy
Authors: Dalton J. Brad
Published: November 2007

Linear mixture modeling has been applied to Galileo Near Infrared Mapping Spectrometer (NIMS) spectra of Europa's dark, non‐water‐ice terrain using cryogenic laboratory spectra of hydrated compounds. Water ice alone could not account for the distorted and asymmetric spectral features attributed to water of hydration in the Europa spectrum. The modeling was conducted using cryogenic reference spectra of hexahydrite, epsomite, bloedite, sodium sulfide nonahydrate, mirabilite, magnesium sulfate dodecahydrate, sulfuric acid hydrate, and saturated brines of magnesium sulfate, sodium carbonate, and sodium sulfate. All were measured between 77 and 130K. The best model fit was attained using abundances of 14% hexahydrite, 11% bloedite, 12% mirabilite, and 62% sulfuric acid hydrate. Results indicate that sulfuric acid hydrate and hydrated sulfate salts, taken together, produce a better spectral match than either class of compound considered alone.
Three‐dimensional measurements of traveling ionospheric disturbances with the Poker Flat Incoherent Scatter Radar
Authors: Nicolls Michael J. , Heinselman Craig J.
Published: November 2007

In this paper, we present results from the Advanced Modular Incoherent Scatter Radar (AMISR) installed at the Poker Flat Research Range near Fairbanks, Alaska, the Poker Flat Incoherent Scatter Radar (PFISR), that focus on the ability of the system to make three‐dimensional, simultaneous measurements of ionospheric parameters. We present observations from PFISR where we were able to resolve the three components of the k vector of a traveling ionospheric disturbance (TID), as well as the period. These measurements give insight into the atmospheric gravity wave (AGW)‐TID relationship, allowing us to apply a recently developed dispersion relation for AGWs that includes the role of kinematic viscosity and thermal diffusivity, important effects in the upper atmosphere, without assumptions about horizontal wavelengths. The analysis indicates that for this particular case, the wave must have been propagating against a background wind of ∼125 m/s. PFISR will be a powerful tool for studying the sources and propagation of waves in the upper atmosphere.
Effect of melt squeezing rate on shear stress along a simulated fault in gabbro during frictional melting
Authors: Tsutsumi Akito , Mizoguchi Kazuo
Published: November 2007

High‐velocity friction experiments were performed on gabbro at an initial constant slip rate of 1.32 m/s and normal stress of 1.2 MPa. Under these conditions, the sliding surfaces melted due to frictional heating. Once steady‐state conditions (shear strength and shortening rate of the sample) in the presence of melt were achieved, normal stress was increased gradually up to 4.5 MPa to simulate enhanced squeezing of melt from the slipping zone. At low normal stress, shear stress increased only slightly with increasing normal stress. When normal stress increased above 2.5 MPa, however, shear stress showed a linear increase with increasing normal stress. We propose that the deformation mechanism changes from melt‐separated viscous shear to a mixed lubrication (solid‐solid contact + frictional melting) due to a reduction in the thickness of the melt layer associated with an increase in the melt squeezing rate at high normal stresses.
Pore‐scale spectral induced polarization signatures associated with FeS biomineral transformations
Authors: Slater Lee , Ntarlagiannis Dimitrios , Personna Yves R. , Hubbard Susan
Published: November 2007

We measured spectral induced polarization (SIP) signatures in sand columns during (1) FeS biomineralization produced by sulfate reducing bacteria (Desulfovibrio vulgaris) under anaerobic conditions, and (2) subsequent biomineral dissolution upon return to an aerobic state. The low‐frequency (0.1–10 Hz peak) relaxations produced during biomineralization can be modeled with a Cole‐Cole formulation, from which the evolution of the polarization magnitude and relaxation length scale can be estimated. We find that the modeled time constant is consistent with the polarizable elements being biomineral encrusted pores. Evolution of the model parameters is consistent with FeS surface area increases and pore‐size reduction during biomineral growth, and subsequent biomineral dissolution (FeS surface area decreases and pore expansion) upon return to the aerobic state. We conclude that SIP signatures are diagnostic of pore‐scale geometrical changes associated with FeS biomineralization by sulfate reducing bacteria.
Simultaneous observations of fluctuating cusp aurora and low‐latitude magnetopause reconnection
Authors: Fuselier S. A. , Petrinec S. M. , Trattner K. J. , Fujimoto M. , Hasegawa H.
Published: November 2007

The location and variability of magnetic reconnection are investigated using simultaneous in situ observations of boundary layer flows at the dayside magnetopause and remote sensing of proton cusp aurora in the ionosphere. Two events when the Geotail spacecraft was at the magnetopause and the Imager for Magnetopause to Aurora Global Exploration (IMAGE) spacecraft was observing cusp proton precipitation are used in this investigation. The directions of high‐speed flows observed in the boundary layer by the Geotail spacecraft are compared to predicted directions from the antiparallel reconnection model and from two component reconnection models. The IMAGE cusp proton aurora observations provide additional information on the type of reconnection and on variability in the reconnection rate. For the first event, antiparallel reconnection may be occurring at the magnetopause and there is a long‐duration (10 s of minutes) decrease in the proton aurora intensity. For the second event, component reconnection is occurring and variability in the cusp emissions on a timescale of several minutes appears to indicate variability in the reconnection rate.
Aspect angle dependence of the E region irregularity velocity at large flow angles
Authors: Makarevich R. A. , Koustov A. V. , Senior A. , Uspensky M. , Honary F. , Dyson P. L.
Published: November 2007

We present the Doppler velocity observations of 1‐m plasma waves in the auroral E region by the Scandinavian Twin Auroral Radar Experiment (STARE) Norway VHF coherent radar in the context of simultaneous and coincident measurements of electron and ion drift velocities determined by the European Incoherent Scatter (EISCAT) tristatic radar facility. The measurements were performed in the afternoon sector (1500–2000 MLT) at seven locations along the STARE radar beam 2 with different values of the magnetic off‐perpendicular (aspect) angle α between 0.48° and 2.63° and at large angles with respect to the electron background drift (θ = 55°–90°). It is demonstrated that the STARE line‐of‐sight velocity, normalized to the EISCAT‐derived electron drift speed at large flow angles, exhibits a decrease with increasing aspect angle, and the rate of decrease is investigated as a function of the flow angle. We also compare the STARE velocity with the electron and ion drift velocity components along the STARE radar beam look direction and show that, at large aspect angles, the E region velocity is correlated (anticorrelated) with the ion (electron) drift velocity component. The results are discussed in the contexts of the linear fluid theory of the modified two‐stream plasma instability and the theory of anomalous collisions.
Correlative variations of the neutral atom emission in the high‐altitude cusp and the fast anti‐sunward convection in the low‐altitude cusp
Authors: Murata Y. , Taguchi S. , Hosokawa K. , Nakao A. , Collier M. R. , Moore T. E. , Sato N. , Yamagishi H. , Yukimatu A. S.
Published: November 2007

Recent studies have shown that the Low Energy Neutral Atom (LENA) imager on the IMAGE spacecraft in the magnetosphere detects neutral atoms coming from the direction of the high‐altitude cusp. The primary source of the neutral atoms has been reported to be the entry of the ions in the cusp, but the evidence for this remains limited. Therefore we herein report the correlative variations of the neutral atom signal in the direction of the high‐altitude cusp and the fast anti‐sunward convection in the ionospheric cusp from an event of simultaneous observations from IMAGE/LENA and SuperDARN radar. During a period of IMF BZ of −40 to −10 nT on 11 April 2001, LENA on IMAGE at (XGSM, YGSM, ZGSM) ∼ (4 RE, 0 RE, 4 RE) observed significant enhancements of neutral atom signals in the direction of the high‐altitude cusp. In concurrence with these enhancements, SuperDARN radars observed an increase in anti‐sunward flow accompanied by equatorward shift of the polar cap boundary. Detailed analyses of the SuperDARN velocity data reveal that the fast anti‐sunward flow region widens and shrinks longitudinally in correlation with the increase and decrease of the LENA signal, respectively. This correlation shows that the neutral atom emission in the direction of the high‐altitude cusp for southward IMF is due to the ion entry caused by enhanced reconnection on the dayside magnetopause. Hence the present study provides evidence of the cusp ion injection being the primary source of the LENA high‐altitude cusp signal for the southward IMF.
Numerous small magnetic field discontinuities of Bartels rotation 2286 and the potential role of Alfvénic turbulence
Authors: Vasquez Bernard J. , Abramenko Valentyna I. , Haggerty Dennis K. , Smith Charles W.
Published: November 2007

Magnetic field data at 1/3 s resolution are used from the ACE spacecraft for days 7 to 33 in 2001 (Bartels rotation 2286) to characterize the statistical properties of discontinuities during this period. A method is developed for finding discontinuities independent of spread angle between magnetic fields across the discontinuity. This was viewed as necessary since larger spread angle discontinuities can occur in close proximity with smaller ones, and the smaller ones are numerous. Discontinuities are found to occur in groupings, and the separation between successive discontinuities has a distribution which is lognormal. With the expectation that most discontinuities have normals across or nearly across the magnetic field, the cross‐product method is used to find the normal. Combining normal direction and plasma data from the ACE spacecraft, we find that the most probable width for discontinuities is 4 to 8 proton inertial lengths or gyroradii. For small β(≡ratio of proton gas and magnetic pressure), the widths scale better with proton inertial length while for large β with proton gyroradius. Most discontinuities have small changes in the total magnetic intensity and are ramp‐like. The statistical properties of the discontinuities appear to come from a single population. To identify this population, rotational and tangential discontinuities and also discontinuities associated with Alfvénic turbulence are considered. The population is most consistent with turbulence.