Differential rotation and reconnection as basic causes of some coronal reorientations

A process is suggested by which a coronal structure (with underlying filament) may form between a polar crown structure and a low-latitude bipolar region. During the ascending phase of the solar cycle the identifying underlying filament should lie poleward and westward of the active region, but during the descending phase it should appear as an eastward extension of the filament separating leader and follower photospheric fields within the active region.     

Dynamics of flare sprays

During solar cycle No. 20 new insight into the flare-spray phenomenon has been attained due to several innovations in solar optical-observing techniques (higher spatial resolution cinema-photography, tunable pass-band filters, multi-slit spectroscopy and extended angular field coronagraphs). From combined analysis of 13 well-observed sprays which occurred between 1969–1974 we conclude that (i) the spray material originates from a preexisting active region filament which undergoes increased absorption some tens of minutes prior to the abrupt chromospheric brightening at the flare-start, and (ii) the spray material is confined within a steadily expanding, loop-shaped (presumably magnetically controlled) envelope with part of the material draining back down along one or both legs of the loop.     

Refraction Scattering in the Anomalous Reflections from Icy Surfaces

The modes of scatter at radar targets are discussed and in particular the mode due to internal refraction in the target material whenever a gradual transition in the refractive index occurs. The importance of this arises mainly in planetary radar, as this could account for the unusual polarization effects observed on the icy satellites of the major planets and in certain parts of Mercury and Mars. Ices with their low radar surface reflectivity and low internal absorption would be the best naturally occurring materials to cause these effects. Indeed similar effects have been reported in radar observations over sections of the Greenland ice shelf. The nature of these effects can most easily be seen in the simple approximation of geometrical optics, and a more detailed discussion presented in the applicable electromagnetic theory confirms these results, even when the size of the inclusions is only on the order of a wavelength.     

Cathodoluminescence studies and U/Pb dating of zircons in pre-Mesozoic gneisses of the Tauern Window: Implications for the Penninic basement evolution

The pre-Mesozoic basement in the eastern and central part of the Tauern Window (Eastern Alps) consists mainly of anatectic plagioclase gneisses and amphibolites intruded and migmatized by Carboniferous granitoids. The gneisses are geochemically similar to calcalkaline dacites of modern primitive island arcs. Cathodoluminescence investigations and U/Pb-data on zircons indicate an uppermost Proterozoic or Cambrian extrusion age of the dacitic protoliths and a Carboniferous syngranitoid anatexis around 320 Ma. High-K calcalkaline meta-rhyolites in the north central Tauern Window form a separate part of the basement not affected by Carboniferous anatexis and plutonism. Their protoliths extruded in the Lower Carboniferous. In the Permian, high-K granitoids intruded the anatectic basement.Results are consistent with an island-arc system evolving from a Late Proterozoic and Early Paleozoic primitive stage to a Lower Carboniferous mature stage represented by K-rich rhyolite volcanism. An Upper Carboniferous collisional event caused anatexis, affecting mainly the K-rich calcalkaline rocks. The last calcalkaline magmas intruded in a Permian post-collisional setting.

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Zusammenfassung Das prä-mesozoische Grundgebirge des östlichen und zentralen Tauernfensters (Ostalpen) besteht größtenteils aus anatektischen Plagioklasgneisen und Amphiboliten, welche von karbonischen Granitoiden intrudiert und migmatisiert werden. Die Plagioklasgneise entsprechen geochemisch kalkalkalischen Daziten primitiver Inselbögen. Die anhand von Kathodolumineszenzaufnahmen ausgewerteten U/Pb-Daten der Zirkone weisen auf ein jüngst-proterozoisches oder kambrisches Extrusionsalter der dazitischen Protolithe und auf eine karbonische syn-granitoide Anatexis um 320 Ma. High-K kalkalkalische Metarhyolithe im nördlichen Teil des zentralen Tauernfensters bilden einen separaten Teil des Grundgebirges, der von karbonischer Anatexis und Plutonismus nicht berührt wurde. Ihre Protolithe extrudierten im unteren Karbon. Das anatektisch überprägte Grundgebirge aus Plagioklasgneisen und Amphiboliten wurde im Perm von high-K Granitoiden intrudiert.Die Ergebnisse sind konsistent mit der Entwicklung von einem jung-proterozoischen und alt-paläozoischen primitiven Inselbogen zu einem unter-karbonischen reifen Inselbogen mit K-reichen Rhyolith-Vulkanismus. Ein ober-karbonisches Kollisions-Ereignis führte zur Anatexis insbesondere der K-reichen kalkalkalischen Gesteine. Die letzten kalkalkalischen Magmen intrudierten postkollisional im Perm.

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Résumé Le socle pré-Mésozoïque du centre et de l'est de la Fenêtre des Tauern (Alpes orientales), est principalement composé de gneiss plagioclasiques anatectiques et d'amphibolites. Des granitoïdes carbonifères sont intrusifs dans ce socle et le migmatitisent. Les gneiss sont géochimiquement comparables à des dacites calco-alcalines d'arc insulaire immature. Des études sur zircons par cathodoluminescence et datation U-Pb indiquent, pour les dacites, un âge d'extrusion protérozoïque supérieur ou cambrien. L'anatexie contemporaine de la mise en place des granitoïdes est datée aux alentours de 320 Ma. Dans le nord de la partie centrale de la fenêtre, des méta-rhyolites calco-alcalines riches en potassium forment une zone distincte du socle et ne sont pas affectées par l'anatexie et le plutonisme carbonifère. Leur extrusion date du Carbonifère inférieur. Au Permien, des granitoïdes riches en potassium ont recoupé le socle anatectique.Les résultats sont en accord avec une évolution d'arc insulaire depuis un stade primitif d'âge protérozoïque supérieur ou paléozoïque inférieur jusqu'à un stade de maturité d'âge carbonifère inférieur représenté par les rhyolites riches en potassium. Au Carbonifère supérieur, un événement de collision a provoqué l'anatexie qui affecte principalement les roches calco-alcalines riches en potassium. Les derniers magmas calco-alcalins se sont intrudés dans le contexte post-collisionnel Permien.

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Climate simulations for 1880–2003 with GISS modelE

We carry out climate simulations for 1880–2003 with GISS modelE driven by ten measured or estimated climate forcings. An ensemble of climate model runs is carried out for each forcing acting individually and for all forcing mechanisms acting together. We compare side-by-side simulated climate change for each forcing, all forcings, observations, unforced variability among model ensemble members, and, if available, observed variability. Discrepancies between observations and simulations with all forcings are due to model deficiencies, inaccurate or incomplete forcings, and imperfect observations. Although there are notable discrepancies between model and observations, the fidelity is sufficient to encourage use of the model for simulations of future climate change. By using a fixed well-documented model and accurately defining the 1880–2003 forcings, we aim to provide a benchmark against which the effect of improvements in the model, climate forcings, and observations can be tested. Principal model deficiencies include unrealistically weak tropical El Nino-like variability and a poor distribution of sea ice, with too much sea ice in the Northern Hemisphere and too little in the Southern Hemisphere. Greatest uncertainties in the forcings are the temporal and spatial variations of anthropogenic aerosols and their indirect effects on clouds. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

3D seismic expression of fluid migration and mud remobilization on the Gjallar Ridge, offshore mid-Norway

This paper presents a three‐dimensional (3D) seismic analysis of sediment remobilization and fluid migration in a 2000‐km² area above the Gjallar Ridge located in the Vøring Basin, offshore Norway. Three distinct types of mounded structures have been identified as resulting from focused fluid/gas migration and associated mud remobilization and intrusion. Type A structures are gently mounded, and we infer that these structures formed because of in situ remobilization of Middle Eocene to Lower–Middle Oligocene fine‐grained sediments in response to fluid and minor sediment injection via deep‐seated normal faults. Type B structures comprise relatively steep‐sided mounds and are restricted to the pre‐Miocene interval. They are often located above narrow zones of discontinuous low‐amplitude reflections resembling gas chimneys. Some of the Type B structures are associated with stacked amplitude anomalies and possible mud volcanoes at the base Pleistocene indicating their long‐term significance as vertical fluid conduits. Type C structures comprise discrete mound features that seem to jack up the Top Palaeocene (Top Brygge) horizon. These are similar to hydrothermal mounds found elsewhere on the Norwegian Margin and associated with igneous sill intrusion during North Atlantic breakup. This study highlights the utility of 3D seismic data for mapping of fluid and sediment mobilization through time over large basinal areas.