Geomagnetic Storm Effects at <Emphasis Type="Italic">F</Emphasis>1 Layer Altitudes in Various Periods of Solar Activity (Irkutsk Station)

The influence of geomagnetic disturbances on electron density Ne at F1 layer altitudes in different conditions of solar activity during the autumnal and vernal seasons of 2003–2015, according to the data from the Irkutsk digital ionospheric station (52° N, 104° Е) is examined. Variations of Ne at heights of 150–190 km during the periods of twenty medium-scale and strong geomagnetic storms have been analyzed. At these specified heights, a vernal–autumn asymmetry of geomagnetic storm effects is discovered in all periods of solar activity of 2003–2015: a considerable Ne decrease at a height of 190 km and a weaker effect at lower levels during the autumnal storms. During vernal storms, no significant Ne decrease as compared with quiet conditions was registered over the entire analyzed interval of 150?190 km.     

Continuous zircon growth during long-lived granulite facies metamorphism: a microtextural,U–Pb,Lu–Hf and trace element study of Caledonian rocks from the Arctic

Microtextural, U–Pb, trace element and Lu–Hf analyses of zircons from gneisses dredged from the Chukchi Borderland indicate a long-lived, Cambrian–Ordovician, granulite facies metamorphism. These results reveal a complete prograde, peak and cooling history of zircon growth during anatexis. Early increasing temperatures caused modification and Pb-loss of Precambrian zircons by recrystallization and dissolution/re-precipitation of existing grains. Small variations in initial ¹⁷⁶Hf/¹⁷⁷Hf results (0.282325–0.282042) and flat HREE patterns of these zircons indicate that they grew by dissolution/re-precipitation in the presence of garnet. Zircons subsequently crystallized from a partial melt during peak to post-peak metamorphism from 530 to 485 Ma. A broad range of initial ¹⁷⁶Hf/¹⁷⁷Hf ratios (0.282693–0.282050) and mineral inclusions within zircons suggest that this phase of growth incorporated Zr and Hf obtained from the breakdown of Zr-enriched phases. Microtextural evidence along with trace element and isotopic data suggests that final growth of metamorphic rims on zircon occurred during slow cooling and crystallization of residual partial melts during the early Ordovician (485–470 Ma). Younger, late Ordovician–Silurian (420–450 Ma) euhedral, oscillatory-zoned, trace element-enriched zircons crystallized within leucocratic veins that intrude the gneisses. Their age corresponds to granitoids dated from this same dredge. The intrusives and veins provide evidence that the Chukchi Borderland rifted from a position near Pearya and northwest Svalbard, which represent the northern continuation of the Caledonian orogen. Evidence for earlier Cambrian metamorphism has not been reported from this region. The age of granulite facies metamorphism reported here represents the earliest phase of deformation in the Arctic Caledonides.     

Über die Mischungsarbeit von stabil geschichteten Wassermassen

Zusammenfassung Es wird gezeigt, daß — entgegen der bisherigen Ansicht — die Mischungsarbeit von verschieden temperierten Wassermassen nicht unbegrenzt mit der Größe des Temperaturunterschiedes der Wassermassen anwächst, sondern daß sie für einen bestimmten Temperaturunterschied (bzw. bestimmten Temperaturgradienten) ein Maximum erreicht, für größere Temperaturunterschiede aber wieder auf wesentlich kleinere Beträge abnimmt.

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Summary It is shown that — in contradiction to the hitherto existing view — the energy resulting from the mixture of water-masses with different temperatures does not increase infinitely with the value of the temperature-difference of the water-masses, but that it reaches a maximum for a determined temperature-difference (respectively a determined temperature lapse rate), whereas it decreases to much smaller amounts for greater temperature-differences.

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Résumé On montre que, contrairement aux vues admises jusqu'ici, l'énergie résultant du mélange de masses d'eau à températures différentes ne croît pas sans limite avec l'écart de température, mais qu'elle atteint un maximum pour un écart déterminé (ou pour un gradient de température déterminé) et décroît de nouveau notablement pour des écarts plus grands.

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Mit 1 Textabbildung.     

Model for the formation of arsenic contamination in groundwater. 1. Datong Basin,China

Mineral equilibria were analyzed in the system As-bearing rock-meteoric water. It was shown that carbonate rocks are the most probable source of As and Sr in the waters of the Datong Basin (People's Republic of China). The reason for groundwater enrichment in As is the shift of the equilibrium FeCO₃ (siderite) + H₂O = FeOOH(goethite) + CO₂(g) + H₂(g) to the left (toward siderite formation) owing to organic matter oxidation by atmospheric oxygen and an increase in the equilibrium partial pressure of CO₂, while the Eh of the system remains below ?0.30 ± 0.06 V.     

Textural-structural,mineralogical, isotopic,and age characteristics of Jurassic terrigenous rocks of the northwestern Caucasus (the Belaya River section)

Results of the comprehensive study of structural, lithological, mineralogical, and isotopic characteristics of Lower Jurassic rocks exposed in the Belaya River valley (Adygeya) in meganticlinorium of the Greater Caucasus are presented. Deformation microstructures were studied. Lithological and textural-structural changes in sequences related to intense secondary transformations should affect the state of isotopic systems of rocks. To reveal basic trends in the evolution of isotopic systems, investigation using the K-Ar method was carried out. Clay fraction (less than 1 μm) separated from rocks and bulk samples were analyzed. Cleavage development, approximate value of rock contraction, and isotopic characteristics are compared with the available data on alteration of clay mineral assemblages. Relationship between the degree of rock deformation at the microlevel and calculated K-Ar ages has been established. K-Ar systems of clayey rocks indicate the age of cleavage formation and correspond to the Bajocian-Bathonian contraction period.     

Quaternary sediments in the axial zone of the Brazil Basin

Lithological and micropaleontological studies of sediments were carried out along the meridional profile across the Brazil Basin. Based on nannoplankton and diatom assemblages, the sediments represented by oxidized miopelagic clays, differently reduced hemipelagic clays, and clayey-siliceous (Ethmodiscus) and calcareous (coccolith-foraminiferal) oozes are attributed to the Pleistocene-Holocene. Specific features of sedimentary material indicate its redeposition by Antarctic bottom waters, mudflows, slumps, and rockslides. It is shown that sedimentation in the Brazil Basin corresponds to the incomplete pelagic (miopelagic) type of oceanic lithogenesis transitional to the near-continental one.     

Some foundation stability problems of the railway bridge over the Mala Rijeka

SummarySome Foundation Stability Problems of the Railway Bridge over the Mala Rijeka The authors presented an outlay of problems occurring in estimating the stability of rocky slopes loaded by large vertical forces. General attitudes, kept by the authors during the stability analysis for an actual case — foundation of piers No. 3 and 4 of the railway bridge across the Mala Rijeka, are also presented. The results of calculation as well as the advantages of the approach applied are outlined in the paper. Finally, general conclusions are drawn regarding the method to be kept in solving the stability of slopes loaded by large artificial loading.With 7 Figures     

Combination Scattering by Anisotropic Langmuir Turbulence with Application to Solar Radar Experiments

We develop a theory for radar signal scattering by anisotropic Langmuir turbulence in the solar corona due to a t+l ⇄ t process. Langmuir turbulence is assumed to be generated within a cone by a narrow type III burst electron beam. Using wave-kinetic theory we obtain expressions for the frequency shift, scattering cross-section of the turbulence, coefficient of absorption (due to scattering) and optical depth. On the basis of those expressions we give some estimates for an echo spectrum. We show that the minimum radar echo frequency shift is determined by the minimal phase velocity of the Langmuir waves, the maximum shift is determined by the electron beam velocity, but in any case it can not exceed −wt/2 (decay) and wt (coalescence), where wt is the frequency of a radar signal. The angular characteristics of the scattered signal differ dramatically for the cases of coalescence and decay. The signal is scattered into a narrow cone high above the specular reflection point (wp ≪ wt), but in the vicinity of wp ∼ wt/2 the red-shifted echo is scattered isotropically, while the blue-shifted echo is scattered into a even narrower cone. We show that absorption (due to scattering) increases with increasing radar frequency. The dependence of the absorption on the local plasma frequency is strongly determined by the Langmuir turbulence spectrum. Our theory shows that the role of the nonlinear scattering process t+l ⇄ t is essential and that such process can be used for radar studies of the spectral energy density of anisotropic Langmuir turbulence.     

Zonal circulation indices, 500 hPa April ridge position along 75° E and Indian summer monsoon rainfall: Statistical relationships

Summary This paper presents an examination of the statistical relationship between summer monsoon rainfall over all India, and two sub-regions (north west India and peninsular India) and the indices of mid-latitude (35° to 70° N) zonal circulation at 500 hPa level, over different sectors of the hemisphere, based on 19 years (1971–1989) data. The results indicate that summer monsoon rainfall (June–September) over India shows; (i) a significant and direct relationship with the strength of the zonal circulation index during concurrent July over the sector 90° E to 160° E. (ii) a significant inverse relationship with the strength of the zonal index during the previous April over the sector 160° E to 45° W and a similar relationship with the whole northern hemisphere and (iii) a significant and direct relationship with the frequency of the zonal index during the previous January over the sector 45° W to 90° E.Significant relationships are also observed between the zonal circulation indices of the above mentioned months and sectors with the 500 hPa ridge location in April at 75° E over India.With 4 Figures