A unified view on convection and field-aligned current patterns in the polar cap

During the last two decades measurements of polar cap ionospheric electric fields and currents, field-aligned currents, and global auroral forms have been made from ground-based and space-based platforms. An attempt is made to unify these observations into a large-scale view of polar phenomena. In this view, plasma convection patterns and the corresponding electrodynamics in the polar region can consistently be ordered by the orientation of the interplanetary magnetic field (IMF). The different patterns of the electric potential and of field-aligned currents depend on where the main interaction between the terrestrial and interplanetary fields occurs, on the morning or evening side of the central polar cap, or on the dayside portion of the ‘closed’ cusp region, or on the nightside portion of the ‘open’ cusp region. One of the essential elements of this unified view is that it is possible to account for various convection patterns ranging from the four-cell pattern (during periods of strong northward IMF and B_y ~ 0), to the three-cell pattern (B_z > 0 and |B_y| 2> 0), to the conventional two-cell pattern (B_z < 0) with its possible deformation into a convection throat near the dayside cusp (during southward IMF). We also discuss the way in which the complicated field-aligned current systems can consistently be accounted for in terms of these convection patterns.     

The spatial coherence of Schumann activity in the polar cap

The spatial coherence of the first two Schumann resonant modes has been studied at two locations in the polar cap separated by 1100 km. Measurements were made at Assistance Bay and Mould Bay, which have geomagnetic latitudes of 83° and 79°, respectively, and satellite time-keeping was employed to accurately synchronise the field stations. The coherence was found to be high, typically 95% for the first Schumann mode, and was unaffected by changes in K_p, a storm sudden commencement or a solar flare event. Polarization rotations were observed between the two stations, which could most likely be attributed to the coastline effect. The results are consistent with a stable propagation of Schumann activity from mid to high latitudes that is relatively unaffected by changes in the polar cap ionosphere.     

Observations of neutral winds in the polar cap during northward IMF

Long term remote observations of neutral winds at F-region altitudes have been performed at Thule Air Base (lat. 76.5°N, long. 69.0°W), Greenland, and Søndre Strømfjord (lat. 67.0°N, long. 50.9°W), Greenland. The former site is very close to the geomagnetic pole, while the latter site is within the polar cap for several hours each night on either side of geomagnetic midnight. Wind data corresponding to clear sky conditions and Kp ⩽ 4 were sorted according to the sign of the IMF B_z component. The averaged maximum poleward flow near midnight LST was reduced by approximately one third during B_z northward conditions. If the magnitude of B_y was less than the magnitude of the northward B_z component, then the averaged poleward flow was further reduced by one half. In addition, if B_z > 5 nT, then sunward directed horizontal neutral winds were observed at the very highest latitudes near noon LST.     

Variations of transport conditions and winter anomaly in the D-ionospheric region

The system of differential equations, describing the behaviour of the concentrations of minor neutral constituents and charged particles within the height range 30–150 km have been numerically solved and the effect of variations in the turbulent diffusion coefficient upon the ion structure of D-region evaluated. Two cases have been analysed. In the first complete mixing of the atmosphere is assumed to 90 km. In the second the effect of rapid transport through the 95–105 km region is considered. In the latter case the concentration of nitric oxide is increased compared with the first in the height interval 70–100 km, i.e. at those altitudes where the winter anomaly phenomenon is localized. The maximum excess is about 19 times. The distribution of concentrations of charged particles in the second case is also in agreement with values observed experimentally during the winter anomaly period.     

Sodium density and atmospheric temperature in the mesopause region in polar summer

Sodium lidar measurements have been performed during three summer seasons at a polar latitude (69°N), yielding profiles of sodium number density and temperature of the 85–100 km altitude region. Density measurements were performed during the months of June–August; temperature measurements only were made in August. The sodium layer was found to be both significantly weaker and more variable in summer than in winter. Measurements in summer 1987 yielded an average maximum Na density of about 900 atoms per cm³. The average maximum Na density during summer 1986 and 1988 was near 2600 atoms per cm³. The observed Na column density in summer varied from 3.10⁸ to 3.10⁹ atoms per cm². Temperature measurements were performed in August of 1986 and 1987. Mesopause temperatures of less than 125 K were observed in early August, rising rapidly throughout the month. The mean altitude of the mesopause was found to be about 87 km.     

Dynamics and the ozone distribution in the winter stratosphere : modelling the inter-hemispheric differences

Results from a two year simulation of a General Circulation Model are used to illustrate the main differences found in the lower stratosphere dynamics and the ozone distribution between the Southern and the Northern Hemispheres in winter.The model extends from ground to mesospheric levels with a spectral horizontal resolution up to isotropic wavenumber 42. It incorporates a fully interactive scheme for the ozone mixing ratio which accounts for photochemical sources and sinks, advection by the model winds and coupling with radiative calculations.The model reproduces the large scale inter hemispheric differences quite well, with a very stable and cold vortex in the Southern Hemisphere and a warmer vortex often distorted in the Northern Hemisphere. It is concluded that due to interactions between dynamics, polar stratospheric cloud formation and chemistry, there is a possibility that some stratospheric ozone depletion could be effective in late winter near the night terminator in the Northern Hemisphere, whereas significant ozone depletion only occurs in early spring in the Southern Hemisphere.The importance of synoptic scale dynamics on the ozone transport between the high latitudes and the equator is also stressed. The model develops tongues of ozone-rich air from the high latitudes which are irreversibly mixed at mid-latitudes with tongues of ozone-poor air from the low latitudes. Similar tongues or filaments are clearly visible in the TOMS satellite data. They result from the activity of medium scale-waves in the Southern Hemisphere, whereas in the Northern Hemisphere the larger scale planetary waves play a major role in their development, and their size and extension are larger. It is concluded that transport of the ozone depletion to the mid-latitudes could be more effective in the Northern than in the Southern Hemisphere.     

Calculations and ground-based observations of pulsed proton events in the dayside aurora

A procedure is established to evaluate the Balmer excitation rates of Hα and Hβ to produce the corresponding volume emission rates versus height, using semi-empirical range relations of protons in air. The calculations are carried out with identified ion-energy particle spectra of the dayside aurora obtained by low altitude satellites. The calculated emission intensities of Hα and Hβ indicate that they are indeed observable by ground-based optical detection. Measurements of the dayside aurora from Nordlysstasjonen in Adventdalen, Svalbard, are discussed in relation to these calculations. Periodic bursts of auroral Hα and Hβ emissions are observed in the dayside aurora by ground-based photometers and spectrometers. The mean period between proton events is found to be 10 min on average. Furthermore, it is found that when the time between successive bursts decreases, the emission ratio of Hα and Hβ fluctuates indicating a step-like behaviour in the primary initial proton energy.     

IMF Bx and By dependencies of the polar cap auroral distribution for northward IMF orientation inferred from observations at Vostok station

The effects of the IMF radial (B_x) and azimuthal (B_y) components on the distribution of polar cap arcs are examined using all-sky camera data from Vostok station for the winter months of 1977–1985. We conclude that three factors control the character of the aurora distribution: the type of the sector structure, the IMF radial component, and the IMF azimuthal component. Based on the experimental results, the following scheme for the auroral distribution in the northern and southern polar caps for different signs of B_x and B_y is put forward. The ‘garden hose’ structure (B_x > 0, B_y < 0 or B_x < 0, B_y > 0) produces symmetric auroral distributions in the morning and evening sectors of both the northern and southern polar caps; the ‘orthogonal garden hose’ structure (B_x > 0, B_y > 0 or B_x < 0, B_y < 0) is evidently inefficient in the production of aurorae. The B_x component determines the intensity of aurorae in that polar cap where geomagnetic field lines are in the opposite direction to the IMF (B_x < 0 in the case of the northern cap, and B_x > 0 for the southern cap) and produces the daytime auroral belt poleward of the auroral oval and parallel to it. The B_y component affects the auroral appearance in the morning or evening sectors of the polar cap, depending on its sign, and acts asymmetrically in the opposite polar cap. The appropriate patterns of plasma filament distributions in the high-latitude tail lobes are proposed. The characteristics of auroral movements affected by the B_y component (such as the direction and speed of the arc motion and the magnitude of displacements) are examined.     

Measurements of odd oxygen in the polar region on 10 February 1984 during MAP/WINE

Abundances of atomic oxygen and ozone have been measured by various techniques over northern Scandinavia during the MAP/WINE campaign in the winter 1983–1984. On 10 February at Kiruna, Sweden, rocket experiments used resonance fluorescence and twin path absorption at 130 nm to measure [O]between 70 and 178 km. Rocket-borne measurements of nightglow at 557.7, 761.9 and 551.1 nm and at 1.27 μm have also been obtained and [O]values derived from the atmospheric band intensities. Ozone abundances between 50 and 90 km have been determined from rocket-borne measurements of the ν₃ 9.6 μm nightglow intensity from Andøya, Norway, and Kiruna. These have been compared with [O₃] measured on the same day from the Solar Mesospheric Explorer satellite, using measurements of dayglow at 1.27 μm, and with results from other rocket launchings in MAP/WINE. The results show evidence of low, perhaps exceedingly low, [O] and below normal [O₃] above the mesopause. Below 75 km at night [O₃] exceeded earlier and subsequent observations in the campaign. The measurements were made during a minor stratospheric warming, characterised by an offset polar vortex centred near the measurement zone.     

On the behaviour of wind systems in the upper mesopause region during the transition from summer to winter conditions

Ionospheric drift measurements in the LF range indicate that the phase of the semidiurnal tidal wind oscillation in the upper mesopause, while being approximately equal in summer and in winter, develops characteristic changes near the equinoxes. These changes may either take the form of a complete rotation or, alternatively, an advance and retardation of the phase. What happens in any one year is not predetermined by the initial conditions alone but depends on random processes the nature of which cannot be deduced from the results of wind measurements only.     

Upper crustal fluid flow in the outboard region of the Southern Alps,New Zealand

The currently active fluid regime within the outboard region of the Southern Alps, New Zealand was investigated using a combination of field observations, carbon‐ and oxygen‐stable isotopes from fault‐hosted calcites and interpretation of magnetotelluric (MT) data. Active faulting in the region is dominated by NE striking and N striking, oppositely dipping thrust fault pairs. Stable isotopic analyses of calcites hosted within these fault zones range from 10 to 25‰δ¹⁸O and from ?33 to 0‰δ¹³C. These values reflect mixing of three parent fluids: meteoric water, carbon‐exchanged groundwater and minor deeper rock‐exchanged fluids, at temperatures of 10–90°C in the upper 3–4 km of the crust. A broad, ‘U‐shaped’ zone of high electrical conductivity (maximum depth c. 28 km) underlies the central Southern Alps. In the ductile region of the crust, the high‐conductivity zone is subhorizontal. Near‐vertical zones of high conductivity extend upward to the surface on both sides of the conductive zone. On the outboard side of the orogen, the conductive zone reaches the surface coincident with the trace of the active Forest Creek Faults. Near‐surface flow is shown to dominate the outboard region. Topographically driven meteoric water interacts, on a kilometre scale, with either carbon‐exchanged groundwater or directly with organic material within Pliocene gravels, resulting in a distinctive low ¹³C signal within fault‐hosted calcites of the outboard region. The high‐strain zone in the lower crust focuses the migration of deeply sourced fluids upward to the base of the brittle–ductile transition. Interconnected fluid is imaged as a narrow vertical zone of high conductivity in the upper crust, implying continuous permeability and possibly buoyancy‐driven flow of deeply sourced fluids to higher levels of the crust where they are detected by the isotopic analysis of the fault‐hosted calcites.     

Factors affecting fluid flow in strike–slip fault systems: coupled deformation and fluid flow modelling with application to the western Mount Isa Inlier, Australia

Deformation and focused fluid flow within a mineralized system are critical in the genesis of hydrothermal ore deposits. Dilation and integrated fluid flux due to coupled deformation and fluid flow in simple strike–slip fault geometries were examined using finite difference analysis in three dimensions. A series of generic fault bend and fault jog geometries consistent with those seen in the western Mount Isa Inlier were modelled in order to understand how fault geometry parameters influence the dilation and integrated fluid flux. Fault dip, fault width, bend/jog angle, and length were varied, and a cross-cutting fault and contrasting rock types were included. The results demonstrate that low fault dips, the presence of contrasts in rock type, and wide faults produce highest dilation and integrated fluid flux values. Increasing fault bend lengths and angles increases dilation and integrated fluid flux, but increasing fault jog length or angle has the opposite effect. There is minimal difference between the outputs from the releasing and restraining fault bend and jog geometries. Model characteristics producing greater fluid flows and/or gradients can be used in a predictive capacity in order to focus exploration on regions with more favorable fault geometries, provided that the mineralized rocks had Mohr–Coulomb rheologies similar to the ones used in the models.     

Numerical modelling of 3D fluid flow and oxygen isotope exchange in fractured media: spatial distribution of isotope patterns

An understanding of fluid flow, mass transport and isotopic exchange in fractured rock is required to understand the origin of several geological processes including hydrothermal mineral deposits. The numerical model HydroGeoSphere simulates 3D advection, molecular diffusion, mechanical dispersion and isotopic exchange in a discretely fractured porous media, and can be used to better understand the processes of mass transport and isotopic exchange in fractured rocks. Study of ¹⁸O isopleth patterns for different types of fractures and fracture networks with a range of structural complexity and hydraulic properties shows that fracture properties and geometry control mass transport and isotopic exchange. The hydraulic properties, as well as the density, spacing, and connectivity of fractures determine the isotopic patterns. Asymmetries in the geometry of oxygen isotope patterns could be used to determine the direction of hydrothermal fluid flow.     

Emergence of a region. Exploring the role of spatial planning in the emergence of high-tech region ELAt using assemblage and actor-network theory

ABSTRACT

Regions or regional development have not only gained importance in spatial planning, but also got fuzzy meanings. Originally regions refer to a specific geographical demarcated area, often with an inductive historic or cultural meaning. In the meantime, in our networked world, the concept also refers to transport regions based on models of daily urban systems, or functional regions based on distinctive urban or social functions. Within the post-industrial era, the concept also gained importance as economic regions. In this paper, we will explore how regional concepts emerge out of specific economic interest concerning technological innovation. We will focus on a cross-border municipal case, for example, the triangle Eindhoven–Leuven–Aachen. With the help of the assemblage and actor-network theory, we will show how the identity of regions is translated by evolving actor-networks, and how these actor-networks are influenced and adapted by those alternating regional identities themselves. From these insights, we will come up with some ideas and propositions how regional planning could play an important role within these co-evolving processes.     

The mid-latitude trough in the electron concentration of the ionospheric F-layer: a review of observations and modelling

Experimental observations and theoretical modelling of the terrestrial mid-latitude trough are reviewed. The mid-latitude trough is considered as an F-layer phenomenon, and its relationships to the lightion trough in the topside ionosphere and to the plasmapause are discussed. The observed morphology of the mid-latitude trough is summarised. Recent evidence on plasma temperatures in the trough is examined. The physical processes that may be important in the trough region are listed. Large-scale computational models that include some of those processes are described and the results compared with observations. Deficiencies in the models and possible future developments are mentioned.     

Multi-isotope fingerprints (O,Sr and Pb) in archaeological animal bone bioapatite: Similarity search and the suitability for provenance analysis in a geologically complex Alpine region

Multi-isotope fingerprints in the bioapatite of archaeological skeletons are mostly superior over single isotope analyses for provenance studies. Gaussian mixture model (GMM) clustering is a novel tool for a similarity search among multidimensional data sets and at the same time permits the evaluation of the structural importance of particular isotopic ratios in the data set. We applied three GMM clustering experiments on multi-isotope fingerprints—stable strontium (Sr), lead (Pb) and oxygen (O) isotopic ratios—established in 217 archaeological animal bones excavated along a specific transect across the European Alps. This reference region had been in use since prehistoric times by humans who crossed the Alps from north to south, and vice versa. The resulting clusters permit a spatial assignment of the specimens with a very high probability, in particular with regard to the geological complexity of the region. A combination of Sr with Pb stable isotopes led to an optimal differentiation between the southern and northern Alpine forelands that cannot be distinguished from each other by ⁸⁷Sr/⁸⁶Sr ratios alone, while the contribution of δ¹⁸O is not particularly high. The isotopic mapping and subsequent cluster analysis is suitable for the analysis of archaeological human finds and the reconstruction of the direction of transalpine mobility and trade.     

Role conceptions,order transition and institutional balancing in the Asia-Pacific: a new theoretical framework

The dawn of the twenty-first century witnessed a new wave of multilateral initiatives in the Asia-Pacific. By integrating institutional balancing theory and role theory, the author proposes a new theoretical framework—‘balance of roles’—to explain the variations in institutional strategies by different states. It is argued that a state’s role conception will shape its institutional balancing strategies in an order transition period. An order defender, like the USA, is more likely to adopt exclusive institutional balancing to exclude its target from its dominated institutions. An order challenger, such as China, will choose both inclusive and exclusive institutional balancing to maximise its own power and legitimacy in a new international order. As a kingmaker, a proactive second-tier state is more likely to pick an inter-institutional balancing strategy to initiate new institutions for competing for influence with existing institutions. An institutionalised order transition might be more peaceful than widely perceived.     

Origin of palaeofluids in a normal fault setting in the Aegean region

The province of Burdur (SW Turkey) is seismically an active region. A structural, geochronological, petrographical, geochemical and fluid inclusion study of extension veins and fault‐related calcite precipitates has been undertaken to reconstruct the palaeofluid flow pattern in this normal fault setting in the Aegean region. A palaeostress analysis and U/Th dating of the precipitates reveals the neotectonic significance of the sampled calcites. Fluid inclusion microthermometry of calcites‐filling extension veins shows final melting temperatures (T_m ice) of 0°C. This indicates pure water, most likely of meteoric origin. The oxygen isotope values (?9.8‰ to ?6.5‰ VPDB) and the carbon isotopic composition (?10.4‰ to ?2.9‰ VPDB) of these calcites also show a near‐surface meteoric origin of the fluid responsible for precipitation. The microstructural characteristics of fault‐related calcites indicate that calcite precipitation was linked with fault activity. Final melting temperature of fault‐related calcites ranges between 0 and ?1.9°C. The oxygen isotope values show a broad range between ?15.0‰ and ?2.2‰ VPDB. Several of these calcites have a δ¹⁸O composition that is higher or lower than the oxygen isotopic composition of meteoric calcites in the area (i.e. between ?10‰ and ?6‰ VPDB). The δ¹³C composition largely falls within the range of the host limestones and reflects a rock‐buffered system. Microthermometry and stable isotopic study indicate a meteoric origin of the fluids with some degree of water–rock interaction or mixing with another fluid. Temperatures deduced from microthermometry and stable isotope analyses indicate precipitation temperatures around 50°C. These higher temperatures and the evidence for water–rock interaction indicate a flow path long enough to equilibrate with the host–rock limestone and to increase the temperature. The combined study of extension vein‐ and fault‐related calcite precipitates enables determining the origin of the fluids responsible for precipitation in a normal fault setting. Meteoric water infiltrated in the limestones to a depth of at least 1 km and underwent water–rock interaction or mixing with a residual fluid. This fluid was, moreover, tapped during fault activity. The extension veins, on the contrary, were passively filled with calcites precipitating from the downwards‐migrating meteoric water.     

Massive dolomitization of a Messinian reef in the Great Bahama Bank: a numerical modelling evaluation of Kohout geothermal convection

The hypothesis that Kohout thermal convection may have induced the massive dolomitization of the 60 m thick lowest more reefal unit in well Unda [top of Great Bahama Bank (GBB)] is evaluated through numerical modelling. A two‐dimensional (2‐D) section, including lithological and petrophysical data, together with datings for the sediments of the GBB, was used in the basin model TEMISPACK to reconstruct the history of the whole platform, with a focus on the reef unit. Simulations showed that during high sea‐level periods, Kohout convection is a valid mechanism in the settings of the GBB, although the convection cell remains flat in most cases because of high permeability anisotropy. This mechanism induces rapid fluid flow in the superficial as well as in the deeper parts of the platform, with velocities of at least two orders of magnitude higher than with compaction alone. Lithology appears as a strong control of fluid circulations at the margin scale through the permeability anisotropy, for which a critical value lies between values of 10 and 100. The reefal unit in Unda is part of a larger area determined by the lithologic distribution, in which flow velocities are significantly higher than in the rest of the platform. These velocities are high enough to bring the magnesium necessary to precipitate the observed amounts of dolomite, within durations in agreement with the available time of post‐reef deposition high sea level(s). However, neither fluid flow pattern nor flow velocities are able to explain the preferential massive dolomitization of the lower reef unit and the complete absence of dolomite in the upper one.