[en] The generation of large-scale electric fields and currents due to the dynamo process has been reviewed, especially for the low latitudinal ionosphere of the Earth. Tidal motions in the atmosphere are described in brief. The kinematic dynamo giving rise for the three-dimensional Sq-current system and the electric field distribution disregarding the recoupling effect of the plasma on the neutral wind velocity field has been described. Taking additionally into account the dragging of neutrals by ions (hydromagnetic dynamo theory) results in good agreement of the theoretical distribution of the zonal electric field with the experimental data. (author)

[en] The crystallographic texture of magnetite occuring in two skarn ore associations of the Erzgebirge anticlinal zone was investigated by neutron texture analysis: 1. Lower Paleozoic skarn ore association: samples from the Medenec formation (Upper Proterozoic, probably); localites: Voclav-mine near Medenec/CSSR and Niederschmiedeberg/G.D.R.; 2. Variscan skarn ore association: samples from the Jachymov group (Cambrian, probably); locality: ore deposit Ehrenfriedersdorf/G.D.R., Oelsnitz/Vogtland, G.D.R. The magnetite pole figures of the investigated types differ significantly. The results of samples from the Lower Paleozoic skarn ore association demonstrate a reference to the tectonical coordinate system with a texture on the base of contour lines (multiples of the irregularity). On the other hand the magnetite skarns of the Variscan skarn ore association have no crystallographic texture. Both of the ore types originated et about T = 550-600 ⁰C, p: LSA approximately 8 kbars, VSA - 1 kbar. The orientation of crystallites should be caused by high oriented pressure. These results correspond with experimental results described in the literature. (author)

[en] Short note

[en] The reconnection of plasma and magnetic flux, disconnected from the Earth's magnetosphere on its dayside, to the Earth through the geomagnetotail is investigated. A new approach is proposed explaining the physical mechanism responsible for more stationary reconnection in the extremely collisionless plasma of the far magnetotail. Specially the average behaviour of a parameter along the Earth's magnetotail is analyzed, determining the threshold of a collisionless tearing mode instability due to chaotization of the thermal electron motion

[en] Data taken by the Atmosphere Explorer C satellite (AE-C) during a geomagnetic storm are used to investigate the changes of thermospheric composition and ionospheric plasma density. The storm time variations of the density of molecular nitrogen, atomic oxygen and oxygen ions are observed in middle latitudes (58⁰ and 47⁰ N) and low latitudes (21⁰ and 10⁰ N). A comparison between observation data and the MSIS-86 neutral thermospheric model is made, and a direct correlation between the changes in the ratio of O/N₂ and in the density of 0⁺ is found. Some mechanisms causing these changes are discussed. (author)

[en] Starting from the migration equation for radon in a double-layered non-radioactive covering sheet, the radon concentration was estimated. This allows a better geological interpretation of practical measurements for engineering and mining purposes. (author)

[en] We explore the scenario that the large random velocity (∼ 5 km/s) among the asteroids is the result of dynamical interaction between the original population of the parent asteroids in near-circular orbits with some large planetesimals or Jupiter zone bodies (JZB) scattered from the accretion zone of Jupiter. The statistical property of such a gravitational scattering process is evaluated using a Monte Carlo method. It is found that a few tens of JZB with individual masses reaching 3 x 10²⁷ g would be needed to provide the necessary orbital velocity dispersion. (author)

[en] In the design and analysis of structures with a high potential of risk like nuclear power plant buildings, special considerations are necessary concerning the description of site conditions and expected earthquake motions. For Central Europe only a small number of earthquake records is available and difficulties arise in defining representative response spectra. Based on spectra from seismic events in the area of Schwaebische Alb FRG characteristics of frequency content and spectral amplitudes are discussed. Current concepts and design spectra for the analysis of nuclear power plant structures, following codes or guidelines in France, Japan and the U.S.A., are compared. The presented results underline that for the specific conditions of Central Europe spectra can be adapted using procedures described in the paper. Conclusions are made involving discussed differences in the amplitudes of the design spectra. (author)

[en] The question whether a series of samples from an igneous rock can be attributed to an isochron for radiogeochronological dating or for determining the initial isotope ratio of the daughter element of the radioactive decay can be valued by investigating the correlation between the concentrations ¹c and ²c of mother (¹c) and daughter element (²c). The slope of the regression line in a lg ¹c to lg ²c diagram is given by ¹D - 1/²D - 1 or ¹D - 1/²D - 1 · ²D/¹D, where ¹D and ²D are the solid-liquid distribution coefficients of parent and daughter element, if the concentration patterns are ruled by fractional crystallization or by partial melting, respectively. The agreement between experimentally found slopes and those calculated from distribution coefficients thus gives additional evidence whether or not the isochron reflects a magma solidification or magma generation age, respectively. The method is discussed for the Rb-Sr-, Sm-Nd-, La-Ce-, La-Ba- and K-Ca-geochronometers, using distribution coefficients calculated on the basis of a global model of the generation of the most abundant continental igneous rocks. The application on Rb-Sr-isochrons of a series of various granites of the Erzgebirge and the Saxonian Granulite Massif in the Southern Part of the GDR reveals new evidence of postmagmatic autosomatosis having altered the chemical composition of the Younger granites of the Western Ore Mountains (Erzgebirge). (author)

[en] Purpose of this paper is to study Alfven resonance heating, analogous to the process of supplementary heating of a Tokamak plasma, under magnetospheric conditions. Steady state resonance coupling is considered between a monochromatic MHD surface wave excited at magnetopause due to Kelvin-Helmholtz instability (and/or other mechanisms) and a shear Alfven wave associated with local magnetic field line oscillations (long-period magnetospheric pulsations, Pc3 to Pc5). In contrast to previous papers the damping of an Alfven wave in the ionosphere is taken into account. Furthermore a more general model of this process is used, i.e. we do not limit ourselves to the linear profile approximation of plasma density, but consider an arbitrary smooth profile. (author)