Electrification of volcanic plumes

Volcanic lightning, perhaps the most spectacular consequence of the electrification of volcanic plumes, has been implicated in the origin of life on Earth, and may also exist in other planetary atmospheres. Recent years have seen volcanic lightning detection used as part of a portfolio of developing techniques to monitor volcanic eruptions. Remote sensing measurement techniques have been used to monitor volcanic lightning, but surface observations of the atmospheric electric Potential Gradient (PG) and the charge carried on volcanic ash also show that many volcanic plumes, whilst not sufficiently electrified to produce lightning, have detectable electrification exceeding that of their surrounding environment. Electrification has only been observed associated with ash-rich explosive plumes, but there is little evidence that the composition of the ash is critical to its occurrence. Different conceptual theories for charge generation and separation in volcanic plumes have been developed to explain the disparate observations obtained, but the ash fragmentation mechanism appears to be a key parameter. It is unclear which mechanisms or combinations of electrification mechanisms dominate in different circumstances. Electrostatic forces play an important role in modulating the dry fall-out of ash from a volcanic plume. Beyond the local electrification of plumes, the higher stratospheric particle concentrations following a large explosive eruption may affect the global atmospheric electrical circuit. It is possible that this might present another, if minor, way by which large volcanic eruptions affect global climate. The direct hazard of volcanic lightning to communities is generally low compared to other aspects of volcanic activity.     

Complications for traditional land consolidation in Central Europe

An integral part of post-socialist transformation under the Washington Consensus has been the privatisation of previously state owned and/or co-operative farms. In many instances, there have been attempts at ‘turning back the clock’ to pre-War conditions, including land ownership structures. Frequently, the result has been the division of large, economically efficient units into numerous, small and economically barely viable private plots. Following accession to the European Union, these re-constituted peasant-scale structures pose a major challenge to the Union’s agricultural policy. As this paper demonstrates, a simple transfer of western European practices, such as land consolidation, is not possible. The particular legacies of the communist system have given land ownership particular values, legitimacy and personal identity, and emotional bonds. Simple technocratic solutions, as applied in the West earlier, are thus not feasible. Consequently, the paper points out, new forms and instruments of tackling disadvantageous agricultural structures need to be found.     

Three-dimensional simulations of air flow and momentum transfer in partially harvested forests

In order to predict wind loading on trees (canopy height h) in partially harvested forests, it is necessary to characterize air flow and momentum transfer in progressively more complex patterns where groups of trees (or aggregates) are retained. In this study, we used large-eddy simulation to explore the effects of aggregate size, inter-aggregate spacing, and the ratio between the aggregate size and inter-aggregate spacing on air flow and momentum transfer. Forty-five grid points across an aggregate were needed to achieve an adequate level of turbulence. Using grid sizes of h/15 throughout was too viscous for the smaller aggregates. Vertical and horizontal flow deflection by the leading aggregates sheltered some of the downstream aggregates to varying degrees where turbulence increased for subsequent rows. The number of rows of protected aggregates decreased as aggregate dimensions and the space between aggregates increased. A theoretical treatment of time-dependent wind is presented for the lead aggregate and a simulation case is presented for the case of a gust of reduced wind passing through the aggregate pattern. The leading aggregate responded with decreasing moment for decreasing ambient wind speed as predicted by theory. However, downwind aggregates experienced substantial increases in bending moment. The overall results of the disruptive aspects of time dependence agrees with arguments regarding the role of irrotational (potential) flow to this problem. Our treatment of retention pattern design is only a first step and further research suggestions are presented.     

Euv Spectroscopy of the Sunspot Region Noaa 7981 Using Soho – II. Velocities and Line Profiles

We have studied the dynamics in the sunspot transition region between the chromosphere and the corona and investigated the extension of the flow field into the corona. Based on EUV spectra of a medium size sunspot and its surroundings, NOAA 7981, observed with CDS and SUMER on SOHO, we derive line-of-sight velocities and study the line profiles for a series of emission lines.The flow field in the low corona is found to differ markedly from that in the transition region. In the transition region the relative line-of-sight velocity shows an upflow in the umbra and relatively large areas with downflow that cover part of the penumbra. The spatial extent of these areas with upflow and downflow increases with increasing temperature in the transition region, but the whole flow field changes character as the temperature increases from the upper transition region to the low corona. Based on a calibration of the SUMER wavelength scale we find that the entire sunspot transition zone appears to be moving downwards towards the chromosphere. The relation between this finding and the general tendency for transition-region lines to show a net red shift is discussed.Several of the transition-region spectral line profiles are observed to show two line components with Gaussian shape and line-of-sight velocities that differ markedly. Several of the line profiles that are composed of two spectral line components occur close to the dividing line between up- and downflow. A discussion of this observation is presented. In small regions with spatial extent of a few arc sec we detect enhanced continuum emission underlying explosive events. The similarities between explosive events with continuum emission and the moustaches observed in H close to sunspots are so striking that we are tempted to introduce the notation transition-region moustaches.     

The ortho- to para- ratio of H2 in the starburst of NGC 253

We present measurements of several near-infrared emission lines from the nearby galaxy NGC 253. We have been able to measure four H₂ lines across the circumnuclear starburst, from which we estimate the ortho- to para- ratio of excited H₂ to be ∼2. This indicates that the bulk of the H₂ emission arises from photodissociation regions (PDRs), rather than from shocks. This is the case across the entire region of active star formation.
As the H₂ emission arises from PDRs, it is likely that the ratio of H₂ to Brγ (the bright hydrogen recombination line) is a measure of the relative geometry of O and B stars and PDRs. Towards the nucleus of NGC 253 the geometry is deduced to be tightly clustered O and B stars in a few giant H  II regions that are encompassed by PDRs. Away from the nuclear region, the geometry becomes that of PDRs bathed in a relatively diffuse ultraviolet radiation field.
The rotation curves of 1–0 S(1) and Brγ suggest that the ionized gas is tracing a kinetic system different from that of the molecular gas in NGC 253, particularly away from the nucleus.     

Heavy metal residues in Laysan Duck feathers

The heavy metal data presented herein indicate that the wild Laysan Duck population may not be contaminated with metal-laden industrial wates. It is therefore possible that the food chain which supports the duck population is uncontaminated, with the possible exception of prey taken from pelagic sea bird carcasses. Such a short, geographically isolated food chain, involving a non-migratory avian carnivore, could be an ideal system for the investigation of bio-concentration, bio-accumulation and bio-magnification of naturally occurring heavy metals.     

Minerals produced during cooling and hydrothermal alteration of ash flow tuff from Yellowstone drill hole Y-5

A rhyolitic ash-flow tuff in a hydrothermally active area within the Yellowstone caldera was drilled in 1967, and cores were studied to determine the nature and distribution of primary and secondary mineral phases. The rocks have undergone a complex history of crystallization and hydrothermal alteration since their emplacement 600,000 years ago. During cooling from magmatic temperatures, the glassy groundmass underwent either devitrification to alkali feldspar + α-cristobalite ± tridymite or granophyric crystallization to alkali feldspar + quartz. Associated with the zones of granophyric crystallization are prismatic quartz crystals in cavities similar to those termed miarolitic in plutonic rocks. Vapor-phase alkali feldspar, tridymite, magnetite, and sporadic α-cristobalite were deposited in cavities and in void spaces of pumice fragments. Subsequently, some of the vapor-phase alkali feldspar crystals were replaced by microcrystalline quartz, and the vapor-phase minerals were frosted by a coating of saccharoidal quartz.Hydrothermal minerals occur primarily as linings and fillings of cavities and fractures and as altered mafic phenocrysts. Chalcedony is the dominant mineral related to the present hydrothermal regime and occurs as microcrystalline material mixed with various amounts of hematite and goethite. The chalcedony displays intricate layering and was apparently deposited as opal from silica-rich water. Hematite and goethite also replace both mafic phenocrysts and vapor-phase magnetite. Other conspicuous hydrothermal minerals include montmorillonite, pyrite, mordenite, calcite, and fluorite. Clinoptilolite, erionite, illite, kaolinite, and manganese oxides are sporadic. The hydrothermal minerals show little correlation with temperature, but bladed calcite is restricted to a zone of boiling in the tuff and clearly was deposited when CO₂ was lost during boiling.Fractures and breccias filled with chalcedony are common throughout Y-5 and may have been produced by rapid disruption of rock caused by sudden decrease of fluid pressure in fractures, most likely a result of fracturing during resurgent doming in this part of the Yellowstone caldera. The chalcedony probably was deposited as opal or β-cristobalite from a pre-existing silica floc that moved rapidly into the fractures and breccias immediately after the sudden pressure drop.     

Reconstructions of the Campbell Plateau and the Lord Howe Rise

Reconstructions of the southeastern margin of Gondwanaland require either a separation of East and West Antarctica or movement between the Lord Howe Rise and the Campbell Plateau. Previous plate tectonic reconstructions based on sea-floor spreading data eliminated the Lord Howe Rise-Campbell Plateau separation prior to 36 m.y. ago because of overlap. This conclusion is dependent on the reconstruction of Australia and Antarctica, interpretation of magnetic anomalies between Antarctica and the Campbell Plateau and the nature of the plate boundary in New Zealand. Revised reconstructions of the fit between Australia and Antarctica, and a reinterpretation of the magnetic anomalies between the Campbell Plateau and Antarctica suggest that there is no problem of overlap between the Lord Howe Rise and the Campbell Plateau, and that continued motion between these plates prior to 36 m.y. ago is a more plausible alternative to separation between East and West Antarctica.     

Use of clast shape in determining the sedimentary history of the late devonian keepit conglomerate,Australia

Clasts of the Late Devonian Keepit Conglomerate of northeastern New South Wales, Australia, are predominantly andesites of isotropic nature that lack any apparent initial shape controls. Given adequate time in a particular environment, these clasts could be reasonably expected to develop shapes characteristic of abrasion within that environment.Clasts from both fluvial and marine resedimented conglomerates of the Keepit Conglomerate possess shape characteristics indicative of shaping within a fluvial environment. Maximum projection sphericity, and a plot of sphericity against either the oblate-prolate index or the flatness parameter C/A, were the most useful in indicating fluvial shaping processes. In addition, the $\text{OP}$ Index and the dominant form classes of the Sneed and Folk Sphericity-Form diagram were in support of a fluvial history for the clasts.The occurrence of clasts exhibiting typical fluvial shapes in marine resedimented conglomerates indicates a lack of time and/or insufficient energy in a beach environment for reshaping of the clasts prior to resedimentation into deeper-water submarine-fan environments. This interpretation is consistent with and lends support to the interpretation, based on all other available data, for the Keepit Conglomerate of a history of rapid progradation of fluvial gravels into a relatively low-energy coastline environment, with periodic resedimentation of coarse sediment into deeper water.