LINET—An international lightning detection network in Europe

During the past years a VLF/LF lightning detection network (LINET) was developed at the University of Munich, which provides continuous data for both research and operational purposes. In particular, the network introduces five new features: a) total lightning capability: both cloud-to-ground strokes (CG) and cloud lightning (IC) are measured; b) low-amplitude reporting: weak lightning events from discharge channel with currents well below 5 kA are detected within the central part of the network, whereby IC events dominate; c) new 3D-discrimination: a time-of-arrival method is utilized to separate CG from IC with good reliability, provided that the sensor baseline does not exceed ~ 250 km; d) IC emission height: for each cloud event a height is determined which is thought to reflect the central region of the involved channel; and e) optimised location accuracy: due to precision and combined action of all influential network components, complemented by site-error corrections, the position accuracy of strokes reaches an average value as small as ~ 150 m, whereby false locations (‘outliers’) rarely occur. During international co-operations LINET has been deployed in four continents: Europe (initially Germany), South America (area of Bauru, Brazil), Australia (around Darwin), and Central Africa (Benin). Since the features quoted above could be verified in the tests, a 65-sensor network was established in Europe and started on May 1, 2006, in co-operation with the service company nowcast. LINET covers a wide area approximately from longitude − 10° to 25° to latitude 35° to 66°; it is available for scientific projects and officially utilized by the German Weather Service for operational purposes. Meanwhile, the network was extended by deployment of additional sites so that it comprises about 90 sensors in 17 countries.     

Helium-rich hot subdwarfs and single low-mass white dwarfs: formation mechanisms and further implications

Variations in the mass loss from single stars have been used to explain the existence of hot subdwarf stars and the existence of single low-mass white dwarfs (LMWDs). Hence remaining uncertainty in mass loss from single red-giant stars is important to the understanding of these problems. However, natural formation channels for hot subdwarfs and single LMWDs have also been proposed which do not rely on unexplained mass loss from single red-giant stars. We outline these, and discuss how the different mechanisms could be distinguished. For example, a formation channel for single LMWDs which involves the break-up of a binary system by a type Ia supernova should produce a population of single LMWDs with a distinct kinematic signature. If that population is found to exist, it could be used to study one of the popular single-degenerate formation channels for type Ia supernovae in a previously impossible way. In addition, we examine the formation of helium-rich sdO stars—which are shown to emerge from one of the previously existing binary formation channels for hot subdwarfs. Both the SN Ia formation mechanism for single LMWDs and the formation channel for He-sdOs are a natural consequence of existing models. Hence if these formation channels do not work at all, then the result is a significant one.     

Deglacial land emergence and lateral upper-mantle heterogeneity in the Svalbard Archipelago—II. Extended results for high-resolution load models

In Paper I (Breuer & Wolf 1995), a preliminary interpretation of the postglacial land emergence observed at a restricted set of six locations in the Svalbard Archipelago was given. The study was based on a simple model of the Barents Sea ice sheet and suggested increases in lithosphere thickness and asthenosphere viscosity with increasing distance from the continental margin.
In the present paper, the newly developed high-resolution load model. BARENTS-2, and land-uplift observations from an extended set of 25 locations are used to study further the possibility of resolving lateral heterogeneity in the upper mantle below the northern Barents Sea. A comparison of the calculated and observed uplift values shows that the lithosphere thickness is not well resolved by the observations, although values above 110 km are most common for this parameter. In contrast to this, there are indications of a lateral variation of asthenosphere viscosity. Whereas values in the range 10¹⁸-10²⁰Pas are inferred for locations close to the continental margin, 10²⁰-10²¹ Pa s are suggested further away from the margin.
A study of the sensitivity of the values found for lithosphere thickness and asthenosphere viscosity to modifications of load model BARENTS-2 shows that such modifications can be largely accommodated by appropriate changes in lithosphere thickness, whereas the suggested lateral variation of asthenosphere viscosity is essentially unaffected. An estimate of the influence of the Fennoscandian. ice sheet leads to the conclusion that its neglect results in an underestimation of the thickness of the Barents Sea ice sheet by about 10 per cent.     

Note on estimates of the glacial-isostatic decay spectrum for Fennoscandia

For more than 30 years, Sauramo's (1958) shoreline diagram of the Fennoscandian uplift has been used in geophysical studies for estimates of the glacial-isostatic decay spectrum in order to infer from it the viscosity stratification in the Earth's mantle below Fennoscandia. The intent of the present note is to point out that more recent geological studies suggest that Sauramo's shoreline diagram is an incorrect representation of the Fennoscandian uplift. Geophysical interpretations based on the diagram may therefore require revision.     

Zum Anteil des Faraday-Sohncke-Effekts am Zustandekommen der Gewitterelektrizität

Zusammenfassung Eine Übersicht über die bisher vorgeschlagenen Quellen für die Gewitterelektrizität zeigt, daß diese den Erfordernissen der Wirklichkeit kaum genügen. Daher wird der Versuch gemacht, das Zustandekommen des unteren positiven Raumladungsgebiets im Gewitter auf die Aufladung zurückzuführen, die Hagelkörner während ihres Wachstums aus Wolkentröpfchen im Aufwind durch den Faraday-Sohnckeschen Tropfenzerreißeffekt erfahren. Quantitative Ausrechnung der Ladung eines Hagels und der gesamten Ladungsproduktion einer aktiven Gewitterzelle sowie Abschätzung aller wesentlichen Einflüsse im wirklichen Cumulonimbus führen zu Gesamtleistungen des Effekts, mittels deren gerade eben der Blitzmechanismus eines bescheidenen Gewitters erklärt werden kann. Der Vorgang ist aber in der gewählten Form einstweilen viel zu schwach, um auch für die außerordentlich großen Verlustströme durch Niederschlag und Ionenabwanderung aufkommen zu können.

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Summary A survey of the sources of thunderstorm electricity taken into consideration up to now shows that they are scarcely sufficient when confronted with the requirements of reality. An attempt has been made, therefore, to account for the origin of the lower positive space-charge region in thunderstorms by the fact that hailstones accept an electric charge by the Faraday-Sohncke-effect when growing from cloud droplets in upwind. Quantitative calculation of the charge of a hailstone and of the total production of electricity in an active thunderstorm cell and estimation of all essential influences in a real cumulonimbus lead to a total energy of the effect by which just the lightning mechanism of a modest thunderstorm can be covered. For the present, the process as considered above is much to weak to be made responsible also for the extraordinarily great losses of electricity by precipitation and migration of ions.

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Résumé Les sources de l'électricité orageuse considérées jusqu'ici sont insuffisantes en regard des faits observés. On tente ici de ramener la charge spatiale positive de la partie inférieure du nuage orageux à la charge dont sont le siège les grêlons au cours de leur croissance dans le vent ascendant par suite de l'effet Faraday-Sohncke. le calcul de la charge d'une grêle en formation et de la charge totale d'une cellule orageuse active, ainsi que l'estimation de tous les effets produits au sein du cumulonimbus, conduisent à une valeur correspondant aux décharges d'un modeste orage. Le processus invoqué est toutefois beaucoup trop faible pour tenir compte des pertes considérables dues aux précipitations et au transport d'ions.

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Mit 4 Textabbildungen     

Why cone models can represent the elastic half-space

In lieu of the rigorous elastodynamical approach, many problems in foundation dynamics may be solved quite accurately via simple cone models of the soil. Although these cone models are amenable to very simple analysis, they have not yet been widely accepted in engineering practice. The reservations against their use are possibly due to the fact that cones are based on non-rigorous strength-of-materials assumptions, they neglect large portions of the half-space, and cannot represent Rayleigh surface waves. These potential objections are investigated step by step and proven to be unfounded. It turns out that cone models indeed incorporate and provide valuable insight into all the salient features of rigorous solutions; the aspects omitted by cones are revealed to be of minor physical importance.