Hydromagnetic spin-up under conditions of the earth's core-mantle boundary

Summary The disturbances of the velocity and magnetic fields close to the Earth's core-mantle boundary, caused by sudden irregular changes in the Earth's rotation, are investigated. The problem leads to the investigation of the structure of the Ekman-Hartman hydromagnetic boundary layer, the magnetic diffusive region and the currentless region. Precise Laplacean inversions of the images of all disturbances in the Earth's core-mantle system are obtained for the limiting case of a zero magnetic Prandtl number, =0. The disturbance of the velocity in the direction of the axis of rotation (Ekman suction) in the currentless region has the nature of inertial oscillations with a frequency of 2. Additional disturbances (with respect to the case of =0) of the velocity in the azimuthal and radial directions, particularly for the EHL and MDR region, are determined for the case when 0< « 1. The disturbance in the velocity again has the character of inertial oscillations with the frequency 2, being exponentially damped in EHL asexp (–2²t) and in MDR asexp (–²t).     

Use of mathematical modeling to investigate inter-aquifer contamination by organic-rich water through an unplugged well (central Wielkopolska, Poland)

Hydrogeological research was performed to establish the origin of organic-rich water in a Quaternary aquifer (Wielkopolska Buried Valley aquifer, Poland). The spatial distribution of such water was determined by means of multilevel sampling with a packer. The nature, spatial distribution and chemistry of the organic-rich water suggest hydraulic connection between the Quaternary aquifer and the underlying Neogene aquifer. This connection may be enabled by an old abandoned, improperly plugged well, and must therefore be considered as an artificial hydraulic connection between hydrogeologically separated aquifers. For the verification of this hypothesis, a groundwater contaminant transport model was constructed. The results of contaminant transport modeling allow the contaminant transport parameters (transverse and longitudinal dispersivity) to be identified in the field. The numerical groundwater model was used for the prognosis of organic-rich water remediation, and for specification of water-resource management principles in the region where organic-rich water occurs. The results of this research enable the verification of assumptions regarding complex groundwater flow conditions in the boundary zone of a buried valley.     

Noble gases in Grant and Carbo and the influence of S‐ and P‐rich mineral inclusions on the 41K‐40K dating system

Abstract— Cosmogenic He, Ne, and Ar were measured in the iron meteorites Grant (IIIAB) and Carbo (IID) to re‐determine their preatmospheric geometries and exposure histories. We also investigated the influence of sulphur‐ and/or phosphorus‐rich inclusions on the production rates of cosmogenic Ne. Depth profiles measured in Grant indicate a preatmospheric center location 117 mm left from the reference line and 9 mm below bar B, which is clearly different (?10 cm) from earlier results (?165 mm left from the reference line on bar F). For Carbo the preatmospheric center location was found to be 120 mm right of the reference line and 15 mm above bar J, which is in agreement with literature data. The new measurements indicate a spherical preatmospheric shape for both meteorites and, based on literature ³⁶C1 data, the radii were estimated to be about 32 cm and 70 cm for Grant and Carbo, respectively. We demonstrate that minor elements like S and P have a significant influence on the production rates of cosmogenic Ne. In our samples, containing on average 0.5% S and/or P, about 20% of ²¹Ne was produced from these minor elements. Using measured ²¹Ne concentrations and endmember ²²Ne/²¹Ne ratios for Fe + Ni and S + P, respectively, we show that it is possible to correct for ²¹Ne produced from S and/or P. The thus corrected data are then used to calculate new ⁴¹K‐⁴⁰K exposure ages—using published K data—which results in 564 ± 78 Ma for Grant and 725 ± 100 Ma for Carbo. The correction always lowers the ²¹Ne concentrations and consequently decreases the ⁴¹K‐⁴⁰K exposure ages. The discrepancies between ³⁶Cl‐³⁶Ar and ⁴¹K‐⁴⁰K ages are accordingly reduced. The existence of a significant long‐term variation of the GCR, which is based on a former 30–50% difference between ⁴¹K‐⁴⁰K and ³⁶Cl‐³⁶Ar ages, may warrant re‐investigation.     

Effects of land use,slope gradient,and soil and water conservation structures on runoff and soil loss in semi-arid Northern Ethiopia

April lightning production in Richmond County, Georgia, from 1995 to 2003 is considered with regard to the associated risk to golfers and spectators at the Master's Golf Tournament and courses throughout the county. An examination of the April lightning climatology of Georgia, focusing on Richmond County, reveals a minimum in lightning activity during the time of the tournament (the first full week of April). A discriminant analysis of Richmond County lightning production utilizes several meteorological variables in order to discern between three categories of April lightning days: little or no lightning activity, minimal lightning activity, and high lightning activity. The analysis distinguishes relatively well between the categories with only 13.5% of the events misclassified. A composite regional analysis of the three lightning categories illustrates the environmental differences between these events. Although the little or no lightning and high lightning categories are somewhat similar environmentally, the intensity of features separates these events and allows for interpretation. The statistical and synoptic analyses together emphasize the importance of low-level instability and frontal proximity and intensity in enhancing lightning production in thunderstorms during April in and surrounding Richmond County. A multitude of meteorological conditions can lead to thunderstorm development. Localized studies of these environments, especially during times of major outdoor sporting events, are needed to help mitigate the risk associated with lightning.     

Soil Microbial and Enzyme Activities Response to Pollution Near an Aluminium Smelter

The aim of this research was to assess the impact caused by a long‐term pollution by fluoride and heavy metals in two soils (PS1 and PS2) near an aluminium smelter in Slovakia, on soil microbial biomass C (MBC), basal respiration, metabolic quotient (qCO₂) water‐soluble organic C (WSOC) and enzymes activities involved in the C, N and P biogeochemical cycles. An unpolluted soil was used as control (C0). Results obtained for soil fluoride content reflected a gradient of fluoride exposure in topsoils of contaminated sites. Decreases in microbial and enzymatic activities and in MBC to organic C ratio were found in PS2 site, which is closer to the smelter and exhibited the highest fluoride content. PS1‐soil showed an extreme alkaline pH caused by leaching of waste effluents from the smelter dumping site, higher contents of Zn, Cu, Pb and Cd, significantly larger MBC, qCO₂ and catalase and urease activities, and much larger basal respiration and dehydrogenase activity than PS2 and C0‐soil. Phosphatase, β‐glucosidase and BAA‐protease were negatively correlated with WSOC, basal respiration and dehydrogenase activity, and showed some degree of inhibition in polluted sites. These results may indicate different responses of microbial communities to ecosystem disturbances, caused by the drastic changes in soil's physicochemical properties as result of the long‐term emissions of fly ash with high levels of contaminants that are still affecting soil microbial and enzymatic activities.     

A Generalized Structure-Activity Relationship for the Decomposition of (Substituted) Alkoxy Radicals

A novel and readily applicable Structure-Activity Relationship (SAR) for predicting the barrier height E_b to decomposition by C-C scission of (substituted) alkoxy radicals is presented. Alkoxy radicals are pivotal intermediates in the atmospheric oxidation of (biogenic) volatile organic compounds, and their fate is therefore of crucial importance to the understanding of atmospheric VOC degradation mechanisms. The SAR is based on available theoretical energy barriers and validated against barriers derived from experimental data. The SAR is expressed solely in terms of the number(s) N_i of alkyl-, hydroxy- and/or oxo-substituents on the - and -carbons of the breaking bond: E_b(kcal/mol) =17.5 – 2.1 × N(alk) – 3.1 ×N(alk) – 8.0 × N_,(OH) – 8.0 × N(O=) – 12 × N(O=). For barriers below 7 kcal/mol, an additional, second-order term accounts for the curvature. The SAR reproduces the available experimental and theoretical data within 0.5 to 1 kcal/mol. The SAR generally allows conclusive predictions as to the fate of alkoxy radicals; several examples concerning oxy radicals from prominent atmospheric VOC are presented. Specific limitations of the SAR are also discussed. Using the predicted barrier height E_b, the high-pressure rate coefficient for alkoxy decomposition k _diss (298 K) can be obtained from k _diss (298 K) = L ×1.8 × 10¹³ exp(–E_b/RT) s^–1, with L the reaction path degeneracy.     

Soil loss rates due to piping erosion

Compared with surface soil erosion by water, subsurface erosion (piping) is generally less studied and harder to quantify. However, wherever piping occurs, it is often a significant or even the main sediment source. In this study, the significance of soil loss due to piping is demonstrated through an estimation of soil volume lost from pipes and pipe collapses (n = 560) in 137 parcels under pasture on loess‐derived soils in a temperate humid climate (Belgium). Assuming a period of 5 to 10 years for pipe collapse to occur, mean soil loss rates of 2.3 and 4.6 t ha^?1 yr^?1 are obtained, which are at least one order of magnitude higher than surface erosion rates (0.01–0.29 t ha^?1 yr^?1) by sheet and rill erosion under a similar land use. The results obtained for the study area in the Flemish Ardennes correspond well to other measurements in temperate environments; they are, however, considerably smaller than soil loss rates due to subsurface erosion in semi‐arid environments. Although local slope gradient and drainage area largely control the location of collapsed pipes in the study area, these topographic parameters do not explain differences in eroded volumes by piping. Hence, incorporation of subsurface erosion in erosion models is not straightforward. Copyright © 2011 John Wiley & Sons, Ltd.     

Geoelectrical and geological structure of the crust in Western Slovakia

Electrical resistivity of the Earth’s crust is sensitive to a wide range of petrological and physical parameters, and it particularly clearly indicates crustal zones that have been tectonically or thermodynamically disturbed. A complex geological structure of the Alpine nappe system, remnants of older Hercynian units and Neogene block tectonics in Western Slovakia has been a target of recent magnetotelluric investigations which made a new and more precise identification of the crustal structural elements of the Western Carpathians possible. A NW-SE magnetotelluric profile, 150 km long, with 30 broad-band and 3 long-period magnetotelluric sites, was deployed, crossing the major regional tectonic elements listed from the north: Brunia (as a part of the European platform), Outer Carpathian Flysch, Klippen Belt, blocks of Penninic or Oravicum crust, Tatricum and Veporicum. Magnetotelluric models were combined with previous seismic and gravimetric results and jointly interpreted in the final integrated geological model. The magnetotelluric models of geoelectrical structures exhibit strong correlation with the geological structures of the crust in this part of the Western Carpathians. The significant resemblance in geoelectrical and crustal geological structures are highlighted in shallow resistive structures of the covering formations represented by mainly Tertiary sediments and volcanics. Also in the deeper parts of the crust highly resistive and conductive structures are shown, which reflect the original building Hercynian crust, with superposition of granitoids or granitised complexes and lower metamorphosed complexes. Another important typical feature in the construction of the Western Carpathians is the existence of young Neogene steep fault zones exhibited by conductive zones within the whole crust. The most significant fault zones separate individual blocks of the Western Carpathians and the Western Carpathians itself from the European Platform.     

Key structural parameters affecting earthquake ground motion in 2D and 3D sedimentary structures

Alluvial valleys generate strong effects on earthquake ground motion (EGM). These effects are rarely accounted for even in site-specific studies because of (a) the cost of the required geophysical surveys to constrain the site model, (b) lack of data for empirical prediction, and (c) poor knowledge of the key controlling parameters. We performed 3D, 2D and 1D simulations for six typical sedimentary valleys of various width and depth, and for a variety of modifications of these 6 “nominal models” to investigate sensitivity of EGM characteristics to impedance contrast, attenuation, velocity gradient and geometry. We calculated amplification factors, and 2D/1D and 3D/2D aggravation factors for 10 EGM characteristics, using a representative set of recorded accelerograms to account for input motion variability. The largest values of the amplification and aggravation factors are found for the Arias intensity and cumulative absolute velocity, the lowest for the root-mean-square acceleration. The aggravation factors are largest for the vertical component. For each model, at least one EGM characteristic exhibits a significant 2D/1D aggravation factor, while all EGM characteristics exhibit significant 2D/1D aggravation factor on the vertical component. For all investigated sites, there is always an area in the valley for which 1D estimates are not sufficient. 2D estimates are insufficient at several sites. The key structural parameters are the shape ratio and overall geometry of the sediment-bedrock interface, impedance contrast at the sediment-bedrock interface, and attenuation in sediments. The amplification factors may largely exceed the values that are usually considered in GMPEs between soft soils and rock sites.     

Factors controlling the morphology and volume (V)–length (L) relations of permanent gullies in the northern Ethiopian Highlands

Small‐scale aerial photographs and high‐resolution satellite images, available for Ethiopia since the second half of the twentieth century as for most countries, allow only the length of gullies to be determined. Understanding the development of gully volumes therefore requires that empirical relations between gully volume (V) and length (L) are established in the field. So far, such V–L relations have been proposed for a limited number of gullies/environments and were especially developed for ephemeral gullies. In this study, V–L relations were established for permanent gullies in northern Ethiopia, having a total length of 152 km. In order to take the regional variability in environmental characteristics into account, factors that control gully cross‐sectional morphology were studied from 811 cross‐sections. This indicated that the lithology and the presence of check dams or low‐active channels were the most important controls of gully cross‐sectional shape and size. Cross‐sectional size could be fairly well predicted by their drainage area. The V–L relation for the complete dataset was V = 0 · 562 L ^1·381 (n = 33, r² = 0 · 94, with 34 · 9% of the network having check dams and/or being low‐active). Producing such relations for the different lithologies and percentages of the gully network having check dams and/or being low‐active allows historical gully development from historical remote sensing data to be assessed. In addition, gully volume was also related to its catchments area (A) and catchment slope gradient (S_c). This study demonstrates that V–L and V–A × S_c relations can be very suitable for planners to assess gully volume, but that the establishment of such relations is necessarily region‐specific. Copyright © 2013 John Wiley & Sons, Ltd.