First results from the hot plasma instrument PROMICS-3 on Interball-2

The PROMICS-3 instrument on Interball-2 is nominally identical to the PROMICS-3 instrument on Interball-1. It performs three-dimensional measurements of ions in the energy range 4 eV–70 keV with mass separation and of electrons in the energy range 300 eV–35 keV. Interball-2 was launched on August 29, 1996, into an orbit with the same inclination as that of Interball-1, 63°, but with apogee at 20 000 km. In this study the PROMICS-3 instrument on Interball-2 is briefly described and examples of the first results are presented. Firstly, we report observations of upward moving molecular ions with energies of up to 700 eV at the poleward edge of the auroral oval. Previous observations of outflowing molecular ions have been at lower altitudes and lower energies. Secondly, we show observations of dawnside magnetosheath plasma injections. Using conjugate data from both PROMICS-3 instruments we have found dispersion structures above the morningside auroral oval, which occurred simultaneously with isolated “pockets” of magnetosheath plasma at a distance of X_GSM = −14 to −12 R_E, which had been injected into the inner part of the low-latitude boundary layer. These isolated plasma structures were sites of strong field-aligned currents and are proposed to be the magnetospheric counterparts of the dispersion structures.     

Model Computations of the Impact of Climatic Change on the Windthrow Risk of Trees

The more humid, warmer weather pattern predicted for the future is expected to increase the windthrow risk of trees through reduced tree anchorage due to a decrease in soil freezing between late autumn and early spring, i.e during the most windy months of the year. In this context, the present study aimed at calculating how a potential increase of up to 4°C in mean annual temperature might modify the duration of soil frost and the depth of frozen soil in forests and consequently increase the risk of windthrow. The risk was evaluated by combining the simulated critical windspeeds needed to uproot Scots pines (Pinus sylvestris L.) under unfrozen soil conditions with the possible change in the frequency of these winds during the unfrozen period. The evaluation of the impacts of elevated temperature on the frequency of these winds at times of unfrozen and frozen soil conditions was based on monthly wind speed statistics for the years 1961–1990 (Meteorological Yearbooks of Finland, 1961–1990). Frost simulations in a Scots pine stand growing on a moraine sandy soil (height 20 m, stand density 800 stems ha–1) showed that the duration of soil frost will decrease from 4–5 months to 2–3 months per year in southern Finland and from 5–6 months to 4–5 months in northern Finland given a temperature elevation of 4°C. In addition, it could decrease substantially more in the deeper soil layers (40–60 cm) than near the surface (0–20 cm), particularly in southern Finland. Consequently, tree anchorage may lose much of the additional support gained at present from the frozen soil in winter, making Scots pines more liable to windthrow during winter and spring storms. Critical wind-speed simulations showed mean winds of 11–15 m s–1 to be enough to uproot Scots pines under unfrozen soil conditions, i.e. especially slender trees with a high height to breast height diameter ratio (taper of 1:120 and 1:100). In the future, as many as 80% of these mean winds of 11–15 m s–1 would occur during months when the soil is unfrozen in southern Finland, whereas the corresponding proportion at present is about 55%. In northern Finland, the percentage is 40% today and is expected to be 50% in the future. Thus, as the strongest winds usually occur between late autumn and early spring, climate change could increase the loss of standing timber through windthrow, especially in southern Finland.     

Study of laser heated iron using third generation synchrotron X-ray radiation facility with imaging plate at high pressures

Iron pressurized to 60 gigapascal (GPa) was heated with laser up to temperatures of over 2200 K. The structural changes were determined in-situ using third generation synchrotron X-ray source; the changes were recorded on an imaging plate with a monochromatic beam. The results strongly support the existence of a phase transformation of the hexagonal close-packed (hcp) structure to the new polymorph (β-phase of iron) at high pressure and temperature. We interpret the X-ray data as belonging to the double hexagonal close-packed (dhcp) structure distorted by stress due to laser heating. Received: 2 February 1998 / Accepted: 23 August 1998     

Dating mafic–ultramafic intrusions by ion-microprobing contact-melt zircon: examples from SW Sweden

Zircons from anatectic melts of the country rocks of three Proterozoic mafic–ultramafic intrusions from the Sveconorwegian Province in SW Sweden were microanalyzed for U–Th–Pb and rare earth elements. Melting and interaction of the wall rocks with the intrusions gave rise to new magmas that crystallized zircon as new grains and overgrowths on xenocrysts. The ages of the intrusions can be determined by dating this newly crystallized zircon. The method is applied to three intrusions that present different degrees of complexity, related to age differences between intrusion and country rocks, and the effects of post-intrusive metamorphism. By careful study of cathodoluminescent images and selection of ion probe spots in zircon grains, we show that this approach is a powerful tool for obtaining accurate and precise ages. In the contact melts around the 916?±?11?Ma Hakefjorden Complex, Pb-loss occurred in some U-rich parts of xenocrystic zircon due to the heat from the intrusion. In back-veins of the 1624?±?6?Ma Olstorp intrusion we succeeded in geochemically distinguishing new magmatic from xenocrystic zircon despite small age differences. At Borås the mafic intrusion mixed with country rock granite to form a tonalite in which new zircon grew at 1674?±?8?Ma. Reworking of zircon occurred during 930+33/–34?Ma upper amphibolite facies Sveconorwegian metamorphism. Pb-loss was the result of re-equilibration with metamorphic fluids. REE-profiles show consistent differences between xenocrystic, magmatic, and metamorphic zircon in all cases. They typically differ in Lu/La_N, Ce/Ce*, and Eu/Eu*, and igneous zircon with marked positive Ce/Ce* and negative Eu/Eu* lost its anomalies during metamorphism.     

Mesoscale Wind Field Modifications over the Baltic Sea

For two consecutive days during spring 1997, the windfield over the Baltic Sea has been studied. Thestrength of the geostrophic wind speed is the majordifference in synoptic conditions between these twodays. During both days, the mesoscale wind field overmost of the Baltic Sea is quite heterogeneous; themodifications primarily being caused by the land-seacontrasts. On the day with the weaker wind speed,sea-breeze circulations develop. As a consequence, thewind direction at lower levels is more or lessopposite to the geostrophic over large areas of theBaltic Sea and the surface wind speed decreases withoffshore distance. Wind speed maxima caused by the seabreezes are found along the east coasts in the studiedarea. For the other day, the slow growth of a stableinternal boundary layer over the sea also gives asurface wind speed decrease with offshore distancefrom the coast.     

The Mysterious X-Ray Emission from Late-B Type Stars: the Lindroos Sample

We present a study of the X-ray emission coming from B-type stars in binary systems. The sample has been extracted from the Lindroos catalogue (Lindroos, 1986) and consists of six visual pairs comprised of a B-type star and a later-type companion. Surprisingly, we have detected X-ray emission coming from the late-B primaries, suggesting the presence of a third unresolved late-type star or an unknown mechanism which generates X-rays in late-B stars. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hydrothermal alteration and associated mineralization in the Freda-Rebecca gold deposit – Bindura District, Zimbabwe

The Freda-Rebecca Mine is currently the largest gold producer in Zimbabwe. The ore deposit is hosted by two main shear systems crosscutting the Rebecca diorite and Bindura granodiorite (2.65 Ga) as well as Shamvaian metasediments, which are affected by contact metamorphism. Following the intrusion of the Bindura granodiorite, intensive hydrothermal alteration developed preferentially in the dioritic part of the igneous complex (Rebecca diorite). The hydrothermal alteration started with an extensive K-dominated hydrothermal metasomatism in the whole Rebecca diorite. It was followed by less penetrative hydrothermal alteration developed preferentially near shear zones and veinlets. Hydrothermal metasomatism caused microcline and biotite formation, prevailing in the Rebecca diorite. Two main stages of post-metasomatic hydrothermal alteration and mineralization were distinguished, based on spatial relationships between different minerals and some geochemical aspects. In the first stage, an actinolite-tourmaline-arsenopyrite mineralization formed, which is characterized by Ni-Co arsenopyrite associated with actinolite, tourmaline and quartz. The second, lower temperature stage gave a polyphase gold-rich mineralization that developed in four phases which are distinguished by different parageneses including: Phase 1. Actinolite, chlorite, clinozoisite/epidote, quartz, calcite, arsenopyrite, pyrite, pyrrhotite, chalcopyrite. Phase 2. Chlorite, epidote, calcite, gold, native Bi, Bi-Pb sulfides, galena, chalcopyrite, fahlore, pyrite, Fe-gersdorffite. Phase 3. Epidote, calcite, (Ni, Co, Fe) As S phases, Co-Fe-gersdorffite. Phase 4. Chlorite, calcite, quartz. The gold mineralization is exclusively associated with phase 2 and developed in three sulfide parageneses: – Gold + Bi-Pb sulfides + bismuth + chalcopyrite + galena, associated with chlorite (Au 1). – Gold + galena + pyrite, associated with calcite and chlorite (Au 2). – Gold + pyrite + Fe-gersdorffite, associated with epidote, chlorite and calcite (Au 3). The hydrothermal alteration and mineralization formed after the consolidation of the Rebecca diorite and Bindura granodiorite, most probably in the postmagmatic cooling stage. The mineralization was emplaced either synchronously or subsequently to the shear zones which crosscut the consolidated pluton. Not all shear zones are mineralized and different shear zones show different amounts of mineralization and hydrothermal alteration. Thus, it is suggested that during the cooling stage of the pluton and subsequent to the formation of the K-metasomatic zone (microcline + biotite), hydrothermal fluids preferentially followed just forming or pre-existing shear zones. It cannot be excluded that this process developed in a plutonic porphyry copper-like environment, in which the classically hydrothermal zonation did not form due to synchronous tectonic disturbance, which preferentially drives the hydrothermal flow along shear zones. Mineral parageneses and data from chlorite geothermometry indicate that the different stages and phases of hydrothermal alteration reflect cooling stages of the hydrothermal system, from >300 °C in the first stage to about 150 °C in the last phases. Received: 4 January 1999 / Accepted: 13 August 1999     

Remote sensing of terrestrial impact craters: The TanDEM‐X digital elevation model

With the TanDEM‐X digital elevation model (DEM), the terrestrial solid surface is globally mapped with unprecedented accuracy. TanDEM‐X is a German X‐band radar mission whose two identical satellites have been operated in single‐pass interferometer configuration over several years. The acquired data are processed to yield a global DEM with 12 m independent posting and relative vertical accuracies of better than 2 m and 4 m in moderate and mountainous terrain, respectively. This DEM provides new opportunities for space‐borne remote‐sensing studies of the entire sample of terrestrial impact craters. In addition, it represents an interesting repository to aid in the search for new impact crater candidates. We have used the TanDEM‐X DEM to investigate the current set of confirmed impact structures. For a subsample of the craters, including small, midsized, and large structures, we compared the results with those from other DEMs. This quantitative analysis demonstrates the excellent quality of the TanDEM‐X elevation data. Our findings help to estimate what can be gained by using the TanDEM‐X DEM in impact crater studies. They may also be beneficial in identifying the regions and morphologies where the search for currently unknown impact structures might be most promising.     

Seeking commonalities of community resilience to natural hazards: A cluster analysis approach

ABSTRACT

The aim of the study on which the article is based was to identify groups of communities with similar resilience profiles, using Norwegian municipalities as a case. The authors used a set of socioeconomic and environmental indicators as measures of municipalities’ resilience and performed a cluster analysis to divide the municipalities into groups with similar multivariate resilience signatures. The results revealed six groups of municipalities that, apart from their unique combinations of indicator scores, featured certain spatial patterns, such as an “urban cluster” with urbanized municipalities and a “suburban cluster” with municipalities concentrated around major cities. The authors conclude that municipalities in each of the groups shared aspects that made them either more or less resilient to natural hazards, which could make them potential targets for shared interventions. Additionally, the authors conclude that clustering can be used to identify municipalities with similar resilience features and that could benefit from networking and sharing operational planning as a way to improve their respective communities' resilience to natural hazards.