Fracturation tertiaire et évolution des contraintes en Bavière orientale: le Jura franconien et la forêt bavaroise (R.F.A.)

Résumé L'analyse géométrique et cinématique de la fracturation dans le Jura franconien et la bordure occidentale du Massif bohémien met en évidence les mécanismes de la tectonique cassante d'âge teriaire, essentiellement ceux des grands accidents SE-NW (lignes de Pfahl et de Franconie) qui ont présenté successivement des jeux en coulissement dextre, en faille normale et en faille inverse. Cinq états de contrainte ont été caractérisés et comparés à ceux définis antérieurement dans le Jura souabe, en liaison avec la cinématique des plaques Europe et Afrique: compression N-S, distension E-W, compression NE-SW puis E-W, distension N-S.

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The analysis of both the geometric and the kinematic cenozoic faulting in the Franconian Jura and in western Bohemia enables to characterize the mechanisms of cenozoic tectonics. More especially dextral strike-slip, normal fault and reverse fault have successively occurred along large SE-NW fault line, as the Pfahl and the Franconian fault systems. Five main stress patterns have thus been identified and then compared with those previously described in Swabian Jura. They are related to the kinematic of Europe and Africa plates, i. e.: (1) N-S compression, (2) E-W distension, (3) SW-NE compression, (4) E-W compression, (5) N-S distension.

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Zusammenfassung Durch die geometrische und kinematische Analyse der Brüche wird die tertiäre Bruchtektonik (tectonique cassante) im Fränkischen Jura und am westlichen Rand des Böhmischen Massifs belegt. Es handelt sich im wesentlichen um die großen SE-NW orientierten Störungen der Linie von Pfahl und der Fränkischen Linie, die nacheinander als dextrale Blattverschiebungen, als Normalverwerfungen und als inverse Verwerfungen wirkten. Fünf Spannungszustände können charakterisiert und mit jenen, die bereits im Schwäbischen Jura definiert wurden, verglichen werden. Sie spiegeln die verschiedenen Stadien der kinematischen Entwicklung der europäischen und afrikanischen Platte wider: Kompression N-S, Zerrung E-W, Kompression NE-SW, sodann E-W, Zerrung N-S.

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A Framework and Software Tool to Support Collaborative Landscape Analysis: Fitting Square Pegs into Square Holes

For landscape models to be applied successfully in management situations, models must address appropriate questions, include relevant processes and interactions, be perceived as credible and involve people affected by decisions. We propose a framework for collaborative model building that can address these issues, and has its roots in adaptive management, computer‐supported collaborative work and landscape ecology. Models built through this framework integrate a variety of information sources, address relevant questions, and are customized for the particular landscape and policy environment under study. Participants are involved in the process from the start, and because their input is incorporated, they feel ownership of the resulting models, increasing the chance of model acceptance and application. There are two requirements for success: a tool that supports rapid model prototyping and modification, that makes a clear link between a conceptual and implemented model, and that has the ability to implement a wide range of model types; and a core team with skills in communication, research and analysis, and knowledge of ecology and forestry in addition to modelling. SELES (Spatially Explicit Landscape Event Simulator) is a tool for building and running models of landscape dynamics. It combines discrete event simulation with a spatial database and a relatively simple modelling language to allow rapid development of landscape simulations, and provides a high‐level means of specifying complex model behaviours ranging from management actions to natural disturbance and succession. We have applied our framework in several forest modelling projects in British Columbia, Canada. We have found that this framework increases the interest by local experts and decision‐makers to participate actively in the model building process. The workshop process and resulting models have efficiently provided insight into the dynamics of large landscapes over long time frames. The use of SELES has facilitated this process by providing a flexible, transparent environment in which models can be rapidly implemented and refined. As a result, model findings may be more readily incorporated into decision‐support systems designed to assist resource managers in making informed decisions.     

ENSO cycle in a coupled ocean-atmosphere model and its negative feedback mechanism

Summary A coupled ocean-atmosphere anomaly model has been developed for simulating ENSO cycle and its mechanism-study in this paper. After a long model run, the coupled model is successful in demonstrating ENSO-like irregular interannual variability and corresponding horizontal spatial structures. Based on the simulated results, the dynamics and the thermodynamics of the model ENSO cycle have been investigated, and in particular the negative feedback mechanisms that act to oppose instability of air-sea interaction, inducing termination of warm and cold events, have been examined. A detailed analysis of the oceanic wave dynamical properties and heat budget of the SST changes in a representative cycle suggest that the negative feedback mechanism to check the unstable growth of a warm event obviously differs from that of a cold event. The mechanism that induces decay and termination of a cold event is closely related to the negative, delayed feedback effect produced by the oceanic dynamical wave reflection at the western boundary. However, independent of the wave reflection effect, the negative feedback mechanism by which the coupled system returns from a warm event is associated with a slowly eastward-propagating coupling mode. Accompanied with the strong unstable development of the equatorial positive SST anomaly, the anomalous upwelling of cold water generated off the equator and the nonlinear anomalous meridional advection generated in the equator west of instability area jointly restrain the instability and finally plunge the system from a mature warm phase into a weak cold phase. A comparison between the results from the present model and the previous works is also discussed in this paper.With 16 Figures     

Frequency of quasi-geostrophic modes on hexagonal grids

Summary Finite-difference analysis of Rossby modes has been performed for two staggered hexagonal grids. The solutions are compared with those obtained in analytical case and for rectangular grids. The result for one of the selected hexagonal grids better fits to the analytical solution then the results for the other considered grids. The obtained results may contribute to better understanding of the appropriateness of hexagonal grids in atmospheric and oceanographic modeling and numerical computations.With 6 Figures     

The use of dual channel circular-polarization radar observations for remotely sensing storm electrification

Summary Observations of thunderstorms with a dual channel circularpolarization radar have provided dramatic indications of the buildup of the electric field inside the storms and of the sudden collapse of the field at the time of lightning. The indications are obtained by coherently correlating the simultaneous returns in the right- and left-hand circular polarization channels of the radar, and follow up on the pioneering observations of this type by Hendry and McCormick (1976). The correlation is estimated and displayed in real time and the results enable one to predict when a storm has the potential for producing a lightning discharge, and often to anticipate the occurrence of individual discharges. The observations detect the presence of electrically aligned particles, believed to be small ice crystals, which are aligned by the electrostatic field of the storm. The aligned particles cause the radar signal to become progressively depolarized as it propagates through an alignment region, giving rise to correlated right- and left-circular polarization echoes. The alignment direction can be determined from the phase of the correlation and is found to be predominantly vertical, indicating a similar electric field orientation. Weaker horizontal alignment is often observed immediately following lightning discharges, consistent with the idea that the aligned particles are ice platelets which fall with horizontal orientation due to aerodynamic forces. The observations have been found to reveal the onset of strong electrification in developing storms and to indicate when decaying storms no longer have the potential to produce lightning. By compensating for signal-to-noise effects, the variation of the depolarization with range can be determined. This provides detailed pictures of the alignment regions which could be used as tracers of ice crystal populations in storms. The pictures also show the spatial variation of the alignment directions, raising the possibility of remotely mapping the storm electric field structure. Finally, the depolarization rate results readily enable one to distinguish between liquid and solid precipitation in the storms.With 7 Figures     

On the appearance of a cold front with a narrow rainband in the vicinity of the Alps

Summary First intensive observations of a narrow cold frontal rainband in southern Germany are described. The observations by Doppler radar and surface observations are in good agreement with others made in Great Britain and at the west coast of the United States. There are no principal differences between the observations close to the sea and those during the passage of the front across the Alpine foreland. The observed coexistence of short and elongated precipitation cells is explained by the local modification of convergence and vorticity. When approaching the Alps the precipitation patterns increased in size due to the upslope winds, and the pre-frontal low-level jet is reorganized completely in a manner such that the cross-frontal circulation was enhanced while the pre-frontal low-level jet disappeared.With 20 Figures     

Modification of fronts by the Alps: Simulations and numerical experimentation

Summary An isentropic limited area model is used to simulate and investigate the frontal passages of 3 May and 8 October 1987. It is demonstrated that a southward outbreak of air with high potential vorticity on 3 May 1987 affected the propagation of the front to the north of the Alps and the related formation of an orographic jet. Moreover, the outbreak plays a crucial role in the genesis of a lee cyclone. On the other hand, no such outbreak occurred on 8 October 1987 and it is shown that the propagation of the front near the ground was hardly affected by the flow at upper levels.With 10 Figures