A multipoint study of a substorm occurring on 7 December, 1992, and its theoretical implications

On 7 December 1992, a moderate substorm was observed by a variety of satellites and ground-based instruments. Ionospheric flows were monitored near dusk by the Goose Bay HF radar and near midnight by the EISCAT radar. The observed flows are compared here with magnetometer observations by the IMAGE array in Scandinavia and the two Greenland chains, the auroral distribution observed by Freja and the substorm cycle observations by the SABRE radar, the SAMNET magnetometer array and LANL geosynchronous satellites. Data from Galileo Earth-encounter II are used to estimate the IMF B_z component. The data presented show that the substorm onset electrojet at midnight was confined to closed field lines equatorward of the pre-existing convection reversal boundaries observed in the dusk and midnight regions. No evidence of substantial closure of open flux was detected following this substorm onset. Indeed the convection reversal boundary on the duskside continued to expand equatorward after onset due to the continued presence of strong southward IMF, such that growth and expansion phase features were simultaneously present. Clear indications of closure of open flux were not observed until a subsequent substorm intensification 25 min after the initial onset. After this time, the substorm auroral bulge in the nightside hours propagated well poleward of the pre-existing convection reversal boundary, and strong flow perturbations were observed by the Goose Bay radar, indicative of flows driven by reconnection in the tail.     

Evidence for an ionized disc in the narrow-line Seyfert 1 galaxy Ark 564

We present simultaneous ASCA and RXTE observations of Ark 564, the brightest known 'narrow-line' Seyfert 1 in the 2–10 keV band. The measured X-ray spectrum is dominated by a steep (Γ≈2.7) power-law continuum extending to at least 20 keV, with imprinted Fe K-line and edge features and an additional 'soft excess' below ∼1.5 keV. The energy of the iron K-edge indicates the presence of highly ionized material, which we identify in terms of reflection from a strongly irradiated accretion disc. The high reflectivity of this putative disc, together with its strong intrinsic O  viii Ly α and O  viii recombination emission, can also explain much of the observed soft excess flux. Furthermore, the same spectral model also provides a reasonable match to the very steep 0.1–2 keV spectrum deduced from ROSAT data. The source is much more rapidly variable than 'normal' Seyfert 1s of comparable luminosity, increasing by a factor of ∼50 per cent in 1.6 h, with no measurable lag between the 0.5–2 keV and 3–12 keV bands, consistent with much of the soft excess flux arising from reprocessing of the primary power-law component in the inner region of the accretion disc. We note, finally, that if the unusually steep power-law component is a result of Compton cooling of a disc corona by an intense soft photon flux, then the implication is that the bulk of these soft photons lie in the unobserved extreme ultraviolet.     

X-ray spectral complexity in narrow-line Seyfert 1 galaxies

We present a systematic analysis of the X-ray spectral properties of a sample of 22 'narrow-line' Seyfert 1 galaxies for which data are available from the ASCA public archive. Many of these sources, which were selected on the basis of their relatively narrow H β linewidth (FWHM ≤2000 km s⁻¹), show significant spectral complexity in the X-ray band. Their measured hard power-law continua have photon indices spanning the range 1.6–2.5 with a mean of 2.1, which is only slightly steeper than the norm for 'broad-line' Seyfert 1s. All but four of the sources exhibit a soft excess, which can be modelled as blackbody emission ( T _bb≈100–300 eV) superposed on the underlying power law. This soft component is often so strong that, even in the relatively hard bandpass of ASCA , it contains a significant fraction, if not the bulk, of the X-ray luminosity, apparently ruling out models in which the soft excess is produced entirely through reprocessing of the hard continuum.
Most notably, six of the 22 objects show evidence for a broad absorption feature centred in the energy range 1.1–1.4 keV , which could be the signature of resonance absorption in highly ionized material. A further three sources exhibit 'warm absorption' edges in the 0.7–0.9 keV bandpass. Remarkably, all nine 'absorbed' sources have H β linewidths below 1000 km s⁻¹, which is less than the median value for the sample taken as a whole. This tendency for very narrow linewidths to correlate with the presence of ionized absorption features in the soft X-ray spectra of NLS1s, if confirmed in larger samples, may provide a further clue in the puzzle of active galactic nuclei.     

Rare earth element abundances in hydrothermal fluids from the Manus Basin, Papua New Guinea: Indicators of sub-seafloor hydrothermal processes in back-arc basins

Rare earth element (REE) concentrations are reported for a large suite of seafloor vent fluids from four hydrothermal systems in the Manus back-arc basin (Vienna Woods, PACMANUS, DESMOS and SuSu Knolls vent areas). Sampled vent fluids show a wide range of absolute REE concentrations and chondrite-normalized (REE_N) distribution patterns (La_N/Sm_N ∼ 0.6-11; La_N/Yb_N ∼ 0.6 - 71; ). REE_N distribution patterns in different vent fluids range from light-REE enriched, to mid- and heavy-REE enriched, to flat, and have a range of positive Eu-anomalies. This heterogeneity contrasts markedly with relatively uniform REE_N distribution patterns of mid-ocean ridge hydrothermal fluids. In Manus Basin fluids, aqueous REE compositions do not inherit directly or show a clear relationship with the REE compositions of primary crustal rocks with which hydrothermal fluids interact. These results suggest that the REEs are less sensitive indicators of primary crustal rock composition despite crustal rocks being the dominant source of REEs in submarine hydrothermal fluids. In contrast, differences in aqueous REE compositions are consistently correlated with differences in fluid pH and ligand (chloride, fluoride and sulfate) concentrations. Our results suggest that the REEs can be used as an indicator of the type of magmatic acid volatile (i.e., presence of HF, SO₂) degassing in submarine hydrothermal systems. Additional fluid data suggest that near-seafloor mixing between high-temperature hydrothermal fluid and locally entrained seawater at many vent areas in the Manus Basin causes anhydrite precipitation. Anhydrite effectively incorporates REE and likely affects measured fluid REE concentrations, but does not affect their relative distributions.     

Efficient conditional modeling for geotechnical uncertainty evaluation

A first‐order Taylor series method including direct derivative coding (DDC) is presented as a computationally efficient method for producing the probability distribution associated with calculated geotechnical performance. The probability distribution is employed in reliability analyses to calculate the probability of failure, valuable information that is not typically associated with deterministic analyses. The probability distribution also is used to identify important input parameters and to direct sampling efforts. Another approach to generate the probability distribution is the Monte Carlo (MC) method, however, Taylor series results generally are calculated in less time than the MC approach. One key to the implementation of the Taylor series approach is efficient approximation of the sensitivities required by the Taylor series calculation. DDC provides the technique to produce an efficient Taylor series algorithm. Directly coding the sensitivity analysis into the engineering model is accomplished by automatic and hand programming of derivatives. ADIFOR 2.0 was employed to automatically add derivatives to an existing engineering analysis model. For this paper a meshing program and 3D FEM for soil deformation is used to demonstrate the DDC approach. Although DDC requires a large up‐front programming effort, it is not site or data specific. Therefore, once the derivative programming has been performed, the numerical model can be applied to a wide variety of problems without additional user intervention. Copyright © 2001 John Wiley & Sons, Ltd.     

Coronal-Temperature-Diagnostic Capability of the Hinode/X-Ray Telescope Based on Self-consistent Calibration. II. Calibration with On-Orbit Data

The X-Ray Telescope (XRT) onboard the Hinode satellite is an X-ray imager that observes the solar corona with the capability of diagnosing coronal temperatures from less than 1 MK to more than 10 MK. To make full use of this capability, Narukage et al. (Solar Phys. 269, 169, 2011) determined the thickness of each of the X-ray focal-plane analysis filters based on calibration measurements from the ground-based end-to-end test. However, in their paper, the calibration of the thicker filters for observations of active regions and flares, namely the med-Be, med-Al, thick-Al and thick-Be filters, was insufficient due to the insufficient X-ray flux used in the measurements. In this work, we recalibrate those thicker filters using quiescent active region data taken with multiple filters of XRT. On the basis of our updated calibration results, we present the revised coronal-temperature-diagnostic capability of XRT.     

Distributed velocity method of solving the convective-dispersion equation: 2. Error analysis and comparison with other methods

This is the second part of a two-part paper presenting a new method for treating convective-dispersive transport. The motivation for developing this technique arises from the demands of performing a risk assessment for a nuclear waste repository. These demands include computational efficiency over a relatively large range of Peclet numbers, the ability to handle chains of decaying radionuclides with rather extreme contrasts in both solution velocities and half lives and the ability to treat leach- or solubitity-limited sources. To the extent it has been tested to date, the distributed velocity method (DVM) appears to satisfy these demands. This part presents an error analysis employing statistical sampling and regression analysis techniques, and comparisons of DVM with other methods for convective-dispersive transport.