Meteorologische Faktoren bei der Ausbreitung ultrakurzer Funkwellen

Zusammenfassung Aus der formalen Aehnlichkeit des Brechungsquotienten (refraction index) für Licht und Ultrakurzwellen (short radio waves) lassen sich gemeinsame Gesichtspunkte für die Ausbreitung des Lichtes und der UK-Wellen (short waves propagation) entwickeln. Anomale Refraktion der Radiowellen insbesondere aussergewöhnliche Reichweite (superrefraction) lassen sich auf diese Weise leicht deuten. Es bestehen hierbei enge Beziehungen zum Aufbau der jeweiligen Grundschicht, wobei erdgebundene Führungen (ground based ducts) auf interne Grenzschichten dicht über der Erdoberfläche, abgehobene Führungen (elevated ducts) auf anomale Refraktion in der Peplopause einer Grundschicht vom Typ A, B oder C zurückzuführen sind. Grundschichten mit einer höher gelegenen Peplopause (Typ D oder E) kommen für eine Führung (duct) nicht mehr in Frage.

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Summary Formal similarity of refraction indices for light and for ultrashort radio waves permits developing common viewpoints of light and of short wave propagation. Thus, anomalous refraction of radio waves, especially superrefraction, is easily explained. With the existing close relations to the structure of the appropriate ground layer, ground based ducts will be traced back to internal limiting layers immediately above the earth's surface, and elevated ducts to anomalous refraction within the peplopause of a Type A, B and/or C ground layer. Ground layers with more elevated peplopause (Types D and/or E) are out of the question for ducts.

     

Die Corioliskraft im Anfängerunterricht

Zusammenfassung Es wird eine quantitative Ableitung der Coriolisbeschleunigung auf einer rotierenden Kugel gegeben. Die Rechnungen setzen etwa die Kenntnisse eines Abiturienten voraus und sind so geführt, daß die Coriolisbeschleunigung rein in Erscheinung tritt. Erdabplattung und horizontale Führungskräfte, die mit dem Wesen der Corioliskraft nichts zu tun haben, kommen in der Ableitung nicht vor.

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An introductory mathematical treatment of the Coriolis force

Summary A quantitative derivation of the Coriolis acceleration on a rotating sphere is given which is considered adequate for students who have passed the final examination of a German High School. Computations are presented in a way that demonstrates the Coriolis acceleration without distracting side issues. The earth's oblateness and the horizontal guiding forces not essentially relating to the Coriolis force are not taken into account in this derivation.

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Une introduction dans l'étude de la force de Coriolis

Résumé On donne une dérivation quantitative de l'accélération de Coriolis sur un globe rotatoire. Les calculations nécessaires sont adaptées au savoir d'un bachelier et sont présentées d'une manière que l'accélération de Coriolis est démontrée sans digressions. L'aplatissement de la terre aux pôles et les forces guidantes horizontales qui n'ont pas de rapport essentiel à la nature de l'accélération de Coriolis sont laissés de côté dans cette déduction.

     

Characterization of a major refractory component of marine dissolved organic matter

Refractory carboxyl-rich alicyclic molecules (CRAM) are characterized in marine dissolved organic matter (DOM) using nuclear magnetic resonance spectroscopy and ultrahigh resolution mass spectrometry. CRAM are distributed throughout the water column and are the most abundant components of deep ocean DOM ever characterized. CRAM are comprised of a complex mixture of carboxylated and fused alicyclic structures with a carboxyl-C:aliphatic-C ratio of 1:2 to 1:7. CRAM are expected to constitute a strong ligand for metal binding, and multiple coordination across cations could promote aggregation and marine gel formation thereby affecting CRAM reactivity and the bioavailability of nutrients and trace metals. It appears CRAM are ultimately derived from biomolecules with structural similarities to sterols and hopanoids. The occurrence of CRAM in freshwater and terrestrial environments seems likely, considering the global distribution of biomolecules and the similarities of biogeochemical processes among environments.     

Eastern Altantic fracture zones as potential disposal sites for radioactive waste

Disposal of radioactive waste in the sea floor of fracture zones associated with the flanks of the Mid-Atlantic Ridge may be a satisfactory alternative to land disposal. Effective physiographic, sedimentary, chemical, and oceanographic barriers exist in these aseismic deep canyons, especially in the eastern Atlantic. In addition, the major producers of radioactive wastes are likely to be near the Atlantic Ocean. If such a disposal strategy is adopted, intensive study of the sedimentologic and oceanographic properties of oceanic fracture zones will be necessary.     

PERSPECTIVE ON CLIMATE CHANGE IN NORTH AMERICA DURING THE TWENTIETH CENTURY

The climate record from many parts of North America provides ample evidence of climate change. For specific elements such as temperature or precipitation, a substantial portion of these changes can be shown to be statistically significant; that is, they either reflect an unusual combination of events in a stationary process or they reflect a nonstationary process. The practical significance of a climate change, however, even when it can be shown to be statistically significant, cannot be assumed. Conversely, it is entirely possible to have a practically significant climate change without statistical significance, although this is less likely to occur.

The preponderance of evidence over recent years suggests that any notion regarding static climate regimes must be dismissed in favor of a dynamic system. The differential heating of our planet which results in a restless atmosphere can also yield a restless climate. Whether this dynamic climate system is merely a manifestation of natural variations or at least partly caused by changes in external influences, we cannot yet be certain. The fact that the climate has changed in North America during the 20th century, and in all likelihood will probably continue to do so in the future, should be considered in any decision-making process related to climate. [Key words: climatic change.]     

The Holocene Lake Plain of North Rudolph,East Africa

During most of the early and middle Holocene, Lake Rudolf was 75m deeper than today, flooding the Kibish Lake Plain as much as 60–100km north and northwest of the modern shore, with periodic overflow across the White Nile watershed. The landforms and sediment sequences of this lake plain are mapped or profiled, described, and integrated into a regional geomorphologic framework, controlled by a suite of ¹⁴C dates. High lake stands are dated 10,000–7,000, 6500–4000 and about 3250 years ago (uncalibrated), with levels fluctuating around that of the present 7000–6500 and since 2500 years. Environmental changes of such magnitude reflect long-term changes of East African climate, so that the Rudolf Basin provides a well-documented index of regional climatic trends for the last 10 millenia. Since shortly after 10,000 years, prehistoric fishing and hunting settlements dotted the rivers and shorelines, favored by optimal aquatic resources but inhibited by a higher incidence of malaria. Aquatic subsistence patterns survived severe but temporary lake shrinkage 7000 years ago; during the last 5 millennia they have gradually given way to pastoral cultures. The Kibish Lake Plain serves to illustrate that geographic landscape analysis can rarely afford to be ahistorical.     

Prediction Errors Associated with Sparse Grid Estimates of Flows over Hills

Numerical simulations of geophysical flows have to be done on very sparse grids. Nevertheless, flows over moderately sloped hills can be predicted quite accurately as long as the near ground vertical resolution is reasonably dense. Recirculation flows behind steeper hills are associated with slow convergence towards grid independent integrations, but even then moderately stratified flows of this type can be predicted usefully accurately. For better horizontal grids than about half the hill-height Δx ₁/H ≈ 0.5 or so, separation and recirculating domains are predicted with an error factor comparable to 0.3. The characteristic wavelength of lee waves is predicted more accurately while the lee wave amplitude and the maximum turbulence intensity in recirculating domains are underestimated by factors comparable to 0.3. Strongly stratified flows may be associated with hydraulic transitions and even this is predicted on quite coarse grids, up to say Δx ₁/H ≈ 0.5. However, the details of such flows turn out to be predicted with considerable errors also on high-resolution grids. Inaccurate modelling of stratified turbulence is a main contributor to this error.     

A Bayesian approach to inverse modelling of stratigraphy, part 1: method

The inference of ancient environmental conditions from their preserved response in the sedimentary record still remains an outstanding issue in stratigraphy. Since the 1970s, conceptual stratigraphic models (e.g. sequence stratigraphy) based on the underlying assumption that accommodation space is the critical control on stratigraphic architecture have been widely used. Although these methods considered more recently other possible parameters such as sediment supply and transport efficiency, they still lack in taking into account the full range of possible parameters, processes, and their complex interactions that control stratigraphic architecture. In this contribution, we present a new quantitative method for the inference of key environmental parameters (specifically sediment supply and relative sea level) that control stratigraphy. The approach combines a fully non‐linear inversion scheme with a ‘process–response’ forward model of stratigraphy. We formulate the inverse problem using a Bayesian framework in order to sample the full range of possible solutions and explicitly build in prior geological knowledge. Our methodology combines Reversible Jump Markov chain Monte Carlo and Simulated Tempering algorithms which are able to deal with variable‐dimensional inverse problems and multi‐modal posterior probability distributions, respectively. The inverse scheme has been linked to a forward stratigraphic model, BARSIM (developed by Joep Storms, University of Delft), which simulates shallow‐marine wave/storm‐dominated systems over geological timescales. This link requires the construction of a likelihood function to quantify the agreement between simulated and observed data of different types (e.g. sediment age and thickness, grain size distributions). The technique has been tested and validated with synthetic data, in which all the parameters are specified to produce a ‘perfect’ simulation, although we add noise to these synthetic data for subsequent testing of the inverse modelling approach. These tests addressed convergence and computational‐overhead issues, and highlight the robustness of the inverse scheme, which is able to assess the full range of uncertainties on the inferred environmental parameters and facies distributions.     

Seismische Anisotropie des oberen Erdmantels und Intraplatten-Tektonik

Specially planned explosion seismic measurements in the oceans provided conclusive evidence that the velocity of P_n-waves depends on the azimuths of the direction of propagation through the upper mantle. The orientation of this azimuthal anisotropy suggests a close connection with the generation of the oceanic lithosphere: in the Pacific the maximum and minimum velocities are measured in a perpendicular and parallel direction to the axis of the oceanic ridges respectively. The observed anisotropy is so strong that a number of models for the generation of anisotropy can be discarded. The most likely cause is a preferred orientation of minerals. The generation of the anisotropy can be simulated in the laboratory under P-T-conditions of the upper mantle. The influence of the rate of deformation can be studied as well. A recent analysis of explosion seismic data in Southern Germany suggests that the continental upper mantle possesses also a velocity anisotropy dependent on azimuth.