A Simplified Analytical Procedure for the Determination of Organically Bound Halogens in Salt‐containing Water Samples

A method was developed for the determination of organic halogens in water samples with the aim of minimizing matrix effects and simplifying the sample preparation technique commonly used. The method is based on the adsorption of organic halogens in modified hydrophilic divinylbenzene polymer columns and their elution with methanol. The adsorbent used enables rapid adsorption and desorption due to comparatively high operating flow rates and minimized solvent amounts. Furthermore, no additional reconcentration steps are needed. The methanol extract obtained is combusted with a standard EOX (extractable organic halogen) analyzer and the concentration of organically bound halogens is determined by microcoulometric analysis. The matrix effects are considerably reduced compared to the standard procedure (EN 1485) commonly used. A detection limit of 13 μg/L was established.     

Regional effects of large-scale extreme wind events over orographically structured terrain

Summary ?Above orographically structured terrain considerable differences of the regional wind field may be identified during large-scale extreme wind events. So far, these regional differences could not be resolved by climate models. To determine the relationships between large-scale atmospheric conditions, the influence of orography, and the regional wind field, data measured in the upper Rhine valley within the framework of the REKLIP Regional Climate Project were analyzed and calculations were made using the KAMM mesoscale model. In the area of the upper Rhine valley, ratios of the wind velocity in the Rhine valley at 10 m above ground level, ν_val, and the large-scale flow velocity, ν_lar, are between ν_val/ν_lar ≈ 0.1 and ν_val/ν_lar ≈ 1. The ν_val/ν_lar ratio exhibits a strong dependence on thermal stratification, δ, and decreases from ν_val/ν_lar ≈ 1 at δ = 0 K m⁻¹ to ν_val/ν_lar ≈ 0.2 at δ = 0.0075 K m⁻¹. In areas, where the lateral mountainous border of the Rhine valley is interrupted, the ν_val/ν_lar ratio increases again with increasing stability or decreasing Froude number. This is obviously due to flow around the Black Forest under stable stratification. It is demonstrated by model calculations that a complex wind field develops in the Rhine valley at small Froude numbers (Fr < 1) irrespective of the direction of large-scale flow. The ν_val/ν_lar ratio is characterized by small values in the direct lee side (ν_val/ν_lar ≈ 0.2) and high values on the windward side of the lateral mountainous border of the Rhine valley (ν_val/ν_lar ≈ 0.8). Received October 22, 2001; revised June 18, 2002; accepted June 23, 2002     

Very high CO2 exchange fluxes at the peak of the rainy season in a West African grazed semi-arid savanna ecosystem

Africa is a sink of carbon, but there are large gaps in our knowledge regarding the CO₂ exchange fluxes for many African ecosystems. Here, we analyse multi-annual eddy covariance data of CO₂ exchange fluxes for a grazed Sahelian semi-arid savanna ecosystem in Senegal, West Africa. The aim of the study is to investigate the high CO₂ exchange fluxes measured at the peak of the rainy season at the Dahra field site: gross primary productivity and ecosystem respiration peaked at values up to ?48 μmol CO₂ m^?2 s^?1 and 20 μmol CO₂ m^?2 s^?1, respectively. Possible explanations for such high fluxes include a combination of moderately dense herbaceous C4 ground vegetation, high soil nutrient availability and a grazing pressure increasing the fluxes. Even though the peak net CO₂ uptake was high, the annual budget of ?229 ± 7 ± 49 g C m^?2 y^?1 (±random errors ± systematic errors) is comparable to that of other semi-arid savanna sites due the short length of the rainy season. An inter-comparison between the open-path and a closed-path infrared sensor indicated no systematic errors related to the instrumentation. An uncertainty analysis of long-term NEE budgets indicated that corrections for air density fluctuations were the largest error source (11.3% out of 24.3% uncertainty). Soil organic carbon data indicated a substantial increase in the soil organic carbon pool for the uppermost .20 m. These findings have large implications for the perception of the carbon sink/source of Sahelian ecosystems and its response to climate change.     

Sulfide intrusion in the tropical seagrasses Thalassia testudinum and Syringodium filiforme

Sulfur and oxygen dynamics in the seagrasses Thalassia testudinum and Syringodium filiforme and their sediments were studied in the US Virgin Islands (USVI) in order to explore sulfide intrusion into tropical seagrasses. Four study sites were selected based on the iron concentration in sediments and on proximity to anthropogenic nutrient sources. Meadow characteristics (shoot density, above- and below-ground biomass, nutrient content) were sampled along with sediment biogeochemistry. Sulfide intrusion was high in T. testudinum, as up to 96% of total sulfur in the plant was derived from sediment-derived sulfides. The sulfide intrusion was negatively correlated to the turnover of sulfides in the sediments regulated by both plant parameters and sediment sulfur pools. Sediment iron content played an indirect role by affecting sulfide turnover rates. Leaf production was negatively correlated with sulfide intrusion suggesting that active growth reduced sulfide intrusion. Sulfide intrusion was lower in S. filiforme (up to 44%) compared to T. testudinum consistent with a higher internal nighttime oxygen concentrations found for S. filiforme. When S. filiforme can take advantage of its ability to maintain high internal oxygen concentrations, as was the case on the USVI, it could increase its success in colonizing unvegetated disturbed sediments with potentially high sulfide concentrations.     

Fe2+-Ti4+ charge transfer in stoichiometric Fe2+,Ti4+-minerals

Optical absorption spectra are presented for taramellite, traskite and neptunite, all of which have both Fe²⁺ and Ti⁴⁺ as major elements. The spectra of each of these minerals are dominated by a single, intense absorption band in the 415 to 460 nm region with 7000 to 9000 cm^?1 halfwidth. These transitions, assigned to Fe²⁺-Ti⁴⁺ intervalence charge transfer, showed little difference in intensity at 80 and 300 K and have molar absorptivities which range from ～100 to ～1300 M^?1 cm^?1. The Fe²⁺-Ti⁴⁺ absorptions in these standards generally compare well to other mineral spectra in which Fe²⁺ — Ti⁴⁺ intervalence absorption has previously been proposed with the exception of the most cited example, blue corundum.     

On the accuracy of location of local shocks on the territory of Czechoslovakia and adjacent areas

Summary The calculation procedures for determining epicentre parameters of weak near shocks with foci in Poland are discussed and tested for explosions with known epicentres.

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Inverted-polarity electrical structures in thunderstorms in the Severe Thunderstorm Electrification and Precipitation Study (STEPS)

Balloon-borne electric field soundings and lightning mapping data have been analyzed for three of the storms that occurred in the Severe Thunderstorm Electrification and Precipitation Study field program in 2000 to determine if the storms had inverted-polarity electrical structures. The polarities of all or some of the vertically stacked charge regions in such storms are opposite to the polarities observed at comparable heights in normal storms. Analyses compared the charge structures inferred from electric field soundings in the storms with charges inferred from three-dimensional lightning mapping data. Charge structures were inferred from electric field profiles by combining the one-dimensional approximation of Gauss's law with additional information from three-dimensional patterns in the electric field vectors. The three different ways of inferring the charge structure in the storms were found to complement each other and to be consistent overall. Charge deposition by lightning possibly occurred and increased the charge complexity of one of the storms.Many of the cloud flashes in each case were inverted-polarity flashes. Two storms produced ground flash activity comprised predominantly of positive ground flashes. One storm, which was an isolated thunderstorm, produced inverted-polarity cloud flashes, but no flashes to ground. The positive and negative thunderstorm charge regions were found at altitudes where, respectively, negative and positive charge would be found in normal-polarity storms. Thus, we conclude that these storms had anomalous and inverted-polarity electrical structures. Collectively, these three cases (along with the limited cases in the refereed literature) provide additional evidence that thunderstorms can have inverted-polarity electrical structures.     

Time-Relative Positioning with a Single Civil GPS Receiver

Time-relative positioning is a recent method for processing GPS phase observations. The operational method undertaken in this paper consists of the following steps: first, recording phase observations at a station of known coordinates; second, moving the GPS receiver to an unknown station (which can be located up to a few hundred meters away, dependint on what type of transportation – e. g., walking, motorcycle – is available) while continuously observing carrier phases; and, third, recording phase observations at a second station of unknown coordinates with a single GPS receiver. To obtain the position of the unknown station relative to the first (known) station, the processing method uses combined observations taken at two different epochs and two different stations with the same receiver. For this reason, the errors that vary between two epochs must be taken into account in an appropriate way, especially errors in satellite clock corrections and ephemerides, and errors related to tropospheric and ionospheric delays. Ionospheric modeling using IONEX files (the ionospheric maps calculated by the International GPS Service) was also tested to correct L1 phase observations. This method has been used to calculate short vectors with an accuracy of a few centimeters (for a processing interval of 30 s) using a single civil GPS receiver. ? 2001 John Wiley & Sons, Inc.     

Die seismische Aktivität in Venezuela im Zusammenhang mit den wichtigsten tektonischen Bruchzonen

Zusammenfassung Einem kurzen Überblick über die geologischen und tektonischen Zusammenhänge in den wichtigsten venezolanischen Erdbebengebieten folgt eine standardisierte Betrachtung der Einzelbeben, deren Magnitude gleich oder größer als 5,5 war. Die aus makroseismischer Intensität und/oder Magnitude (Richter) berechnete, ausgelöste Erdbebenenergie, summiert über 440 Jahre bekannter Erdbebengeschichte Venezuelas, wurde graphisch dargestellt. Die Neigung der so erhaltenen Energietreppen ist ein Maß für die Seismizität, i.e. der Vertikalabstand der Parallelen zwischen Maxima und Minima ist ein Maß für die größtmögliche Magnitude eines Erdbebens aus der entsprechenden Herdregion, und aus den zeitlichen Abständen der Energietreppen lassen sich Schlüsse ziehen über Erdbebenhäufigkeit bzw. Erdbebenerwartung. Schließlich wurde für alle Beben das der ausgelösten seismischen Energie unter gegebenen Voraussetzungen entsprechendeErdbebenvolumen berechnet, an die Erdoberfläche projiziert und als Epizentralgebiete in einer Isoseistenkarte dargestellt, in welchen Wellenbewegungen und Krustendeformationen zu erwarten sind. Besonders Brucherscheinungen sollten dann sichtbar sein, wenn eine der Oberflächen des Volumens mit der Erdoberfläche zusammenfällt. Mittels einer für alle größeren venezolanischen Erdbeben aus makroseismischen Beobachtungen berechneten Intensitäts-Abklingkonstanten c wurde schließlich eine Isoseistenkarte für Venezuela entworfen, in welcher mögliche Überlagerungen aus allen seismischen Zonen des Landes berücksichtigt wurden. Diese Karte kann als Grundlage für die Planung erdbebensicherer Bauten und für geotektonische Zwecke benutzt werden.

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A brief synopsis of the geological and tectonical context of the most important Venezuelan earthquake regions is followed by a standardized treatment of the single earthquakes with magnitudes greater then 5,5. From intensity and/or magnitude (Richter), the earthquake energy released was calculated, added up for the 440 years of known earthquake history of Venezuela, and presented in graphs. The slope of such cumulative energy histogram is a measure of the seismicity, i.e. the distance between the two parallel lines, which connect the maxima and the minima, gives an idea of the possible maximum magnitude in each region; from the time intervals of the steps one may draw conclusions concerning earthquake frequency and earthquake expectation. Finally the earthquake volume for each single quake, which under given conditions corresponds to the energy released, was calculated, its surfaces were projected on the earth's surface and mapped as epicentral regions of an isoseismal map, in which wave motion and crustal deformations may be expected. Special fracture features should be visible where one of the surfaces of the volume intersects the earth's surface. By means of an intensity decay constant c, which was determined from macroseismic observations for each greater earthquake, the isoseismal map for Venezuela was drawn, in which possible intensity superpositions of all seismic regions were taken into consideration. This map may be used as a base for earthquake engineering and geotectonical purposes.

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Résumé Un bref aperçu sur les rapports géologiques et tectoniques dans les régions de tremblements de terre les plus importantes au Vénézuéla est suivi d'une étude standardisée des tremblements individuels, dont la magnitude était égale ou supérieure à 5,5. L'énergie sismique dégagée, calculée à partir de l'intensité macro-sismique et/ou de la magnitude (Richter), accumulée pendant 440 ans d'histoire connue des tremblements au Vénézuéla, est représentée à l'aide d'esquisses graphiques. L'inclinaison des «escaliers d'énergie» qui en résultent est la mesure de la sismicité, c'est-à-dire la distance verticale des lignes parallèles entre maxima et minima est la mesure de la magnitude la plus grande possible d'un tremblement de la région sismique en question, et on peut déduire des intervalles de temps entre les escaliers d'énergie des conclusions sur la fréquence et la prévision des tremblements. Enfin, pour tous les tremblements le volume de tremblement correspondant sous des conditions données à l'énergie sismique dégagée est calculé, projeté sur la surface de la terre et représenté sur une carte isoséiste comme régions épicentrales où l'on peut prévoir un mouvement d'ondes et des déformations de l'écorce. En particulier, des phénomènes de fraction doivent être visibles quand l'une des surfaces du volume coincide avec la surface de la terre. Finalement, à l'aide d'une constante d'intensité diminuée «c», calculée pour tous les tremblements de terre majeurs du Vénézuéla par des observations macrosismiques une carte isoséiste est dessinée pour le Vénézuéla, dans laquelle il est tenu compte des superpositions possibles de toutes les zones sismiques du pays. Cette carte peut servir de base pour le projet de bâtiments résistant aux séismes et à des buts géotectoniques.

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Numerical models of quiescent normal polarity prominences

We present 2-D numerical models of quiescent solar prominences with normal magnetic polarity. These models represent an extension to the classical Kippenhahn-Schlüter model in that the prominence is treated as having finite width and height and the external coronal field is matched smoothly to the internal prominence field so that there are no current sheets at the prominence sides. Using typical prominence and coronal values we find solutions to the generalised Grad-Shafranov equation which illustrate the necessary magnetic support. We also discuss some extensions to the basic model.