Alpine tectonics and diapiric structures in the Pre-Betic zone of southeast Spain

The Pre-Betic is the most northerly of the Alpine zones forming the Betic Cordilleras of southern Spain. It consists of strongly folded and faulted Mesozoic and Tertiary rocks, the oldest of which are ferruginous and gypsiferous Triassic mudstones, followed by a predominantly carbonate facies of Cretaceous, Palaeogene and Miocene age. Although this sequence is interrupted by a number of minor unconformities, the major structures were formed during the middle or late Miocene. The highly incompetent Triassic rocks are the most strongly deformed, and form diapiric intrusions discordant to regional structural trends in the younger rocks. The latter are essentially of two facies: massive competent limestones which are deformed by relatively simple folds of large wavelength, and highly incompetent marl-limestone interbeds with complex disharmonic folds and crush belts. Faults include low-angle and high-angle thrusts, gravity slides and wrench faults. The regional tectonic strike is ENE to NE, but the diapiric intrusions mostly follow WNW and N directions. These intrusions have pushed the younger rocks aside, the result being polyphase structures of several trends.Less intense post-Miocene tectonics are mostly associated with continued diapirism and have resulted in the folding and tilting of the late Miocene to Quaternary elastic sediments.     

Land use and climate change on the Yamal Peninsula of north-west Siberia: some ecological and socio-economic implications

Compared to climate, land use change is expected to comprise a more important component of global change in the coming decades. However, climate is anticipated to supass land use as a factor later in the next century, particularly in the Arctic. Discussed here are the implications of land use and climate change on the Yamal peninsula of north-west Siberia, homeland of the Yamal Nenets. Since the discovery of super-giant natural gas fields in the 1960s, extensive exploration has resulted in direct withdrawal of large areas for infrastructure development and associated disturbance regimes have led to cumulative impacts on thousands of additional hectares of land. The land withdrawals have pushed a relatively consistent or increasing number of reindeer onto progressively smaller parcels of pasture. This has led to excessive grazing and trampling of lichens, bryophytes and shrubs and, in many areas, erosion of sandy soils via deflation. The low Arctic tundra lies entirely within the continuous permafrost zone and ice-rich substrates are widespread. One implication of this is that both anthropogenic and zoogenic distubance regimes may easily initiate thermokarst and aeolian rosion, leading to significant further losses of pastures. Even without industrial distubance, a slight change of the climate would result in massive thermokarst erosion. This would have negative consequences equal to or greater than the mechanical distubances described above. The synergistic effects of land use coupled with climate, change therefore have profound implication for the ecosystems of Yamal, as well as the future of the Nenets culture, society and economy.     

RHESSI Microflares: II. Implications for Loop Structure and Evolution

We present simple analytic models which predict the peak X-ray emission measure and temperature attained in flares in which the chromospheric evaporation process takes place either in a single ‘monolithic’ loop or in a loop consisting of several filaments that are created successively as the energy release process proceeds in time. As possible mechanisms driving chromospheric evaporation we consider both classical heat conduction from the loop top and non-thermal electron beams. The model predictions are tested for a set of 18 well studied RHESSI microflares. The results suggest beam driven evaporation in filamented loops as being capable of accounting for the observed emission measures and temperatures though there are issues with the very high beam densities needed. On the other hand, estimates of the emission measures achieved by conductive evaporation which are derived by using the Rosner – Tucker – Vaiana (RTV) scaling law are much larger than the observed ones. Possible reasons for this discrepancy are discussed.     

Validation of an annual cycle simulation with a T42-L20 GCM

An annual cycle of an atmospheric general circulation model (AGCM) is presented. The winter and summer zonal averages of the atmospheric fields are compared with an observed climatology. The main features of the observed seasonal means are well reproduced by the model. One of the main discrepancies is that the simulated atmosphere is too cold, particularly in its upper part. Some other discrepancies might be explained by the interannual variability. The AGCM surface fluxes are directly compared to climatological estimates. On the other hand, the calculation of meridional heat transport by the ocean, inferred from the simulated energy budget, can be compared to transport induced from climatologies. The main result of this double comparison is that AGCM fluxes generally are within the range of climatological estimates. The main deficiency of the model is poor partitioning between solar and non-solar heat fluxes in the tropical belt. The meridional heat transport also reveals a significant energy-loss by the Northern Hemisphere ocean north of 45° N. The possible implications of model surface flux deficiencies on coupling with an oceanic model are discussed.This paper was presented at the International Conference on Modelling of Global Climate Change and Variability, held in Hamburg 11–15 September 1989 under the auspices of the Meteorological Institute of the University of Hamburg and the Max Planck Institute for Meteorology. Guest Editor for these papers is Dr. L. Dümenil     

Impact of Gas Adsorption Induced Coal Matrix Damage on the Evolution of Coal Permeability

It has been widely reported that coal permeability can change from reduction to enhancement due to gas adsorption even under the constant effective stress condition, which is apparently inconsistent with the classic theoretical solutions. This study addresses this inconsistency through explicit simulations of the dynamic interactions between coal matrix swelling/shrinking induced damage and fracture aperture alteration, and translations of these interactions to permeability evolution under the constant effective stress condition. We develop a coupled coal–gas interaction model that incorporates the material heterogeneity and damage evolution of coal, which allows us to couple the progressive development of damage zone with gas adsorption processes within the coal matrix. For the case of constant effective stress, coal permeability changes from reduction to enhancement while the damage zone within the coal matrix develops from the fracture wall to further inside the matrix. As the peak Langmuir strain is approached, the decrease of permeability halts and permeability increases with pressure. The transition of permeability reduction to permeability enhancement during gas adsorption, which may be closely related to the damage zone development in coal matrix, is controlled by coal heterogeneity, external boundary condition, and adsorption-induced swelling.     

Invariant manifolds, phase correlations of chaotic orbits and the spiral structure of galaxies

In the presence of a strong   m = 2  component in a rotating galaxy, the phase-space structure near corotation is shaped to a large extent by the invariant manifolds of the short-period family of unstable periodic orbits terminating at L ₁ or L ₂. The main effect of these manifolds is to create robust phase correlations among a number of chaotic orbits large enough to support a spiral density wave outside corotation. The phenomenon is described theoretically by soliton-like solutions of a Sine–Gordon equation. Numerical examples are given in an N -body simulation of a barred spiral galaxy. In these examples, we demonstrate how the projection of unstable manifolds in configuration space reproduces essentially the entire observed bar–spiral pattern.