Kleintektonik im Gebiet der Glarner überschiebung

Ohne Zusammenfassung     

Meridional transport of particles and standard vector deviation of upper winds

Summary The meridional dispersion of particles depends from the mean meridional circulation (Hadley-type) and the turbulent mass exchange. The velocity of the latter process can be estimated with the standard deviation of the meridional wind component, which is represented in two diagrams.

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Zusammenfassung Die meridionale Ausbreitung von Partikeln hängt von der mittleren Meridionalzirkulation in der Vertikalebene (Hadley-Zirkulation) und dem turbulenten Massenaustausch ab. Die Geschwindigkeit des turbulenten Austauschs kann mit Hilfe der Streung der meridionalen Windkomponente abgeschätzt werden. Diese Größe wird in zwei Diagrammen dargestellt.

     

Multiscale Gravitational Field Recovery from GPS-Satellite-to-Satellite Tracking

The purpose of GPS-satellite-to-satellite tracking (GPS-SST) is to determine the gravitational potential at the earth's surface from measured ranges (geometrical distances) between a low-flying satellite and the high-flying satellites of the Global Positioning System (GPS). In this paper, GPS-satellite-to-satellite tracking is reformulated as the problem of determining the gravitational potential of the earth from given gradients at satellite altitude. The uniqueness and stability of the solution are investigated. The essential tool is to split the gradient field into a normal part (i.e. the first-order radial derivative) and a tangential part (i.e. the surface gradient). Uniqueness is proved for polar, circular orbits corresponding to both types of data (first radial derivative and/or surface gradient). In both cases gravity recovery based on satellite-to-satellite tracking turns out to be an exponentially ill-posed problem. Regularization in terms of spherical wavelets is proposed as an appropriate solution method, based on the knowledge of the singular system. Finally, the extension of this method is generalized to a nonspherical earth and a non-spherical orbital surface, based on combined terrestrial and satellite data.     

Mega-monsoon variability during the late Triassic: Re-assessing the role of orbital forcing in the deposition of playa sediments in the Germanic Basin

The formation of the supercontinent Pangaea during the Permo–Triassic gave rise to an extreme monsoonal climate (often termed ‘mega-monsoon’) that has been documented by numerous palaeo-records. However, considerable debate exists about the role of orbital forcing in causing humid intervals in an otherwise arid climate. To shed new light on the forcing of monsoonal variability in subtropical Pangaea, this study focuses on sediment facies and colour variability of playa and alluvial fan deposits in an outcrop from the late Carnian (ca 225 Ma) in the southern Germanic Basin, south-western Germany. The sediments were deposited against a background of increasingly arid conditions following the humid Carnian Pluvial Event (ca 234 to 232 Ma). The ca 2·4 Myr long sedimentary succession studied shows a tripartite long-term evolution, starting with a distal mud-flat facies deposited under arid conditions. This phase was followed by a highly variable playa-lake environment that documents more humid conditions and finally a regression of the playa-lake due to a return of arid conditions. The red–green (a*) and lightness (L*) records show that this long-term variability was overprinted by alternating wet/dry cycles driven by orbital precession and ca 405 kyr eccentricity, without significant influence of obliquity. The absence of obliquity in this record indicates that high-latitude forcing played only a minor role in the southern Germanic Basin during the late Carnian. This is different from the subsequent Norian when high-latitude signals became more pronounced, potentially related to the northward drift of the Germanic Basin. The recurring pattern of pluvial events during the late Triassic demonstrates that orbital forcing, in particular eccentricity, stimulated the occurrence and intensity of wet phases. It also highlights the possibility that the Carnian Pluvial Event, although most likely triggered by enhanced volcanic activity, may also have been modified by an orbital stimulus.     

Late Pleistocene outburst floods from Issyk Kul,Kyrgyzstan?

Elevated shorelines and lake sediments surrounding Issyk Kul, the world's second largest mountain lake, record fluctuating lake levels during Quaternary times. Together with bathymetric and geochemical data, these markers document alternating phases of lake closure and external drainage. The uppermost level of lake sediments requires a former damming of the lake's western outlet through the Boam gorge. We test previous hypothesised ice or landslide dam failures by exploring possible links between late Quaternary lake levels and outbursts. We review and recompile the chronology of reported changes in lake site, and offer new ages of abandoned shorelines using ¹⁴C in bivalve and gastropod shells, and plant detritus, as well as sand lenses in delta and river sediments using Infrared Stimulated Luminescence. Our dates are consistent with elevated lake levels between ~45 ka and 22 ka. Cosmogenic ¹⁰Be and ²⁶Al exposure ages of fan terraces containing erratic boulders (>3 m) downstream of the gorge constrain the timing of floods to 20.5–18.5 ka, postdating a highstand of Issyk Kul. A flow‐competence analysis gives a peak discharge of >10⁴ m³ s^–1 for entraining and transporting these boulders. Palaeoflood modelling, however, shows that naturally dammed lakes unconnected to Issyk Kul could have produced such high discharges upon sudden emptying. Hence, although our data are consistent with hypotheses of catastrophic outburst floods, average lake‐level changes of up to 90 mm yr^–1 in the past 150 years were highly variable without any outbursts, so that linking lake‐level drops to catastrophic dam breaks remains ambiguous using sedimentary archives alone. This constraint may readily apply to other Quaternary lakes of that size elsewhere. Nonetheless, our reconstructed Pleistocene floods are among the largest reported worldwide, and motivate further research into the palaeoflood hydrology of Central Asia. Copyright © 2017 John Wiley & Sons, Ltd.     

GIOVE-A initial signal analysis

In late December 2005 the GIOVE-A test satellite was launched by the European Space Agency (ESA) to secure the frequencies for the Galileo system and to provide a platform for testing the new navigation signals. We performed an initial assessment of these signals using the 30 m deep space antenna of the DLR ground station in Weilheim (Germany). The antenna gain raised the signals above the noise level, thus allowing a detailed analysis even without knowledge of the ranging codes. The present paper covers the analysis of the L1/E1 signals, which includes a discussion of the spectrum, the time domain signal and a decoding of the spreading codes for the Open Service.     

A parcel formulation of Hamiltonian layer models

Starting from the three-dimensional hydrostatic primitive equations, we derive Hamiltonian N-layer models with isentropic tropospheric and isentropic or isothermal stratospheric layers. Our construction employs a new parcel Hamiltonian formulation which describes the fluid as a continuum of Hamiltonian ordinary differential equations bound together by integral transport laws. In particular, we show that this parcel Hamiltonian structure is compatible with the stacking of layers under isentropic or isothermal constraints. The appeal of the parcel formulation is the simplification of various calculations, in particular the derivation of the continuum Poisson bracket and the proof of the Jacobi identity. A comparison and connection is made between the Hamiltonian dynamics of fluid parcels and the Hamiltonian system of partial differential equations. The parcel formulation can be seen as a precursor and tool for the study of Hamiltonian numerical schemes.     

Two-dimensional modelling of some CFC replacement compounds

The Cambridge 2-D Eulerian model has been used to study the potential atmospheric distributions and lifetimes of a number of CFC replacement compounds and their degradation products. The study has focused on HFC 134a and HCFCs 123, 141b and 142b and the major products formed by their atmospheric degradation. The loss of these compounds and their products by hydroxyl radical attack, photolysis and in-cloud hydrolysis have been investigated. The study has shown that HCFCs 141b and 142b have sufficiently long lifetimes to enter the stratosphere in significant quantities, where degradation leads to an increase in the total stratospheric chlorine concentration. The study has also highlighted areas where further experimental work would be valuable, in particular characterisation of the product channels for the degradation reactions and determination of the removal rates of the products in the aqueous phase.