The global distribution of gravity wave energy in the lower stratosphere derived from GPS data and gravity wave modelling: Attempt and challenges

Five years of global temperatures retrieved from radio occultations measured by Champ (Challenging Minisatellite Payload) and SAC-C (Satelite de Aplicaciones Cientificas-C) are analyzed for gravity waves (GWs). In order to separate GWs from other atmospheric variations, a high-pass filter was applied on the vertical profile. Resulting temperature fluctuations correspond to vertical wavelengths between 400 m (instrumental resolution) and 10 km (limit of the high-pass filter). The temperature fluctuations can be converted into GW potential energy, but for comparison with parameterization schemes GW momentum flux is required. We therefore used representative values for the vertical and horizontal wavelength to infer GW momentum flux from the GPS measurements. The vertical wavelength value is determined by high-pass filtering, the horizontal wavelength is adopted from a latitude-dependent climatology. The obtained momentum flux distributions agree well, both in global distribution and in absolute values, with simulations using the Warner and McIntyre parameterization (WM) scheme. However, discrepancies are found in the annual cycle. Online simulations, implementing the WM scheme in the mechanistic COMMA-LIM (Cologne Model of the Middle Atmosphere—Leipzig Institute for Meteorology) general circulation model (GCM), do not converge, demonstrating that a good representation of GWs in a GCM requires both a realistic launch distribution and an adequate representation of GW breaking and momentum transfer.     

Discontinuous Galerkin method for two-component liquid–gas porous media flows

We consider two-component (typically, water and hydrogen) compressible liquid–gas porous media flows including mass exchange between phases possibly leading to gas-phase (dis)appearance, as motivated by hydrogen production in underground repositories of radioactive waste. Following recent work by Bourgeat, Jurak, and Smaï, we formulate the governing equations in terms of liquid pressure and dissolved hydrogen density as main unknowns, leading mathematically to a nonlinear elliptic–parabolic system of partial differential equations, in which the equations degenerate when the gas phase disappears. We develop a discontinuous Galerkin method for space discretization, combined with a backward Euler scheme for time discretization and an incomplete Newton method for linearization. Numerical examples deal with gas-phase (dis)appearance, ill-prepared initial conditions, and heterogeneous problem with different rock types.     

Effective utilization of seismic reflection technique with moderate cost in uranium exploration

In participation with numerous industrial partners, the Seismic Laboratory of the University of Saskatchewan has conducted a variety of active seismic reflection experiments; both on the west and east sides of the Athabasca Basin. Results of the investigations at Shea Creek, McArthur River and Keefe Lake illustrate that the seismic investigations deliver effective, highly relevant primary structural images of the subsurface, with resolution that no other geophysical technique can match. Correlation of similar seismic signatures, on several distant but inter-related seismic sections, allowed spatial extension of promising exploration target zones previously unrecognized. Within the three-dimensional seismic volume, comparable reflectivity patterns defined the complex areal distribution of mineralization-related fault systems. Beyond these novel contributions, extended analysis of seismic signal attributes (amplitude and frequency), optical televiewer, and full-wave sonic data offer detailed lithological characterization, including alteration zones, clay content, as well as porosity and fracture density information. Although these structural and geologically relevant anomalies are primary indicators of mineralization, presenting novel exploration advantages, the seismic method is still not a standard component of the Athabasca Basin exploration approach, due to the negative perception that ‘it is very expensive’. Comparing the costs of all geophysical techniques to the cost of a single logged drill hole illustrates that the results of a properly designed seismic data acquisition program not only leads to more effective planning of a drilling program, but also would lead to a much quicker recognition of the major mineralized zone(s), and a reduction in the number of required exploration boreholes. This integrated approach to exploration would then translate into a significant reduction of the total exploration expenditures. Unquestionably, the drilling of boreholes provides the most explicit, reliable information to a certain depth, but only within a very small area. Directly connecting the borehole information to seismic results extends the local reliable data; permitting reduction of the number of boreholes to create accurate two-dimensional or three-dimensional subsurface images and reduction of the expenditures of the total exploration program.     

Study on the Chemical Character of Water Soluble Organic Compounds in Fine Atmospheric Aerosol at the Jungfraujoch

In this study the chemical nature of the bulk of water soluble organic compounds in fine atmospheric aerosol collected during summer 1998 at the Jungfraujoch, Switzerland (3580 m asl) is characterised. The mass concentration of water soluble organic substances was similar to those of major inorganic ions, and the water soluble organic matter was found to be composed of two main fractions: (i) highly polyconjugated, acidic compounds with a varying degree of hydrophobicity and (ii) slightly polyconjugated, neutral and very hydrophilic compounds. The contribution of both fractions to the total water soluble organic carbon was about 50%. Separation into individual components was impossible either by HPLC or capillary electrophoresis which indicates the presence of a high number of chemically similar but not identical species. Results obtained by ultrafiltration and HPLC-MS have shown that the molecular weights are of the order of several hundreds. Most of the protonation constants for the acidic compounds determined by capillary electrophoresis were in the range 10⁴–10⁷.     

Processes in soils and paleosoils

We determined the quantitative mineralogical compositions of various grain size fractions of soil samples that were collected from 10-cm depth intervals. Our results show that the grain size distribution curve of a given mineral is related to the mineral's origin and can be used as a source of information when soil-forming processes are studied.     

Die quantitative Erfassung von Methan im Seewasser

A preparation method for the quantitative analysis of methane in lake water samples has been developed. The method is based on the equilibrium reactions of gases in a closed two-phase (headspace-water) system, in which the headspace gas is analyzed gaschromatographically. The method shows a standard deviation of ±5%, including sampling and sample preparation and can also be used for the quantitative determination of other dissolved gases.      

Finite element evaluation of diffusion and dispersion tensors in periodic porous media with advection

This paper presents three-dimensional finite element simulations to evaluate diffusion and dispersion tensors in periodic porous media in the presence of an advective velocity field. These tensors are evaluated in the framework of the double-scale expansion technique. Two problems, a Newtonian flow and a vector-valued advection–diffusion equation, have to be sequentially solved at the pore scale. Finite element techniques to approximate these problems are proposed and analyzed. Numerical results in three-dimensional networks of spheres are presented to quantitatively assess the impact of the pore morphology and of the advection velocity on the diffusion and dispersion tensors.