Nous accueillons “studia geophysica et geodaetica» dans notre vie scientifique

Sans résumé le président du Comité national tchécoslovaque de géodésie et géophysique     

Electromagnetic measurements in the vicinity of the KTB drill site. Part I: The MV results across a 2-D array

Summary We have analysed magnetovariational data of ten temporary field stations deployed as a 2-D array covering about 50 km square of a SFR/FRG border area adjacent to the KTB superdeep drill site. Single- and inter-station induction vectors were computed by frequency and time domain analyses. The distribution of induction vector characteristics was analysed, interpreted in terms of the electrical conductivity distribution across the array, and correlated with geological phenomena.     

Namibia's orange river boundary — origin and reemerged effects of an inattentive colonial boundary delimination

Conclusion From the above and beside the securing of water rights for the national mining industry, the irrigation clusters scattered as if pearls along the Orange River's N bank are of an obviously unrenouncable significance for the Namibian agricultural production. In any case, it is clearly of utmost importance for Windhoek to secure the possession of the N flood plain by a boundary accord to be reached as soon as possible. This should determine as a minimal solution the border line finally along the low water mark, or, certainly more advantageous for the country, following the rivers median line. Even more so because, in spite of the high costs this would entail due to the lack of infrastructure in the inaccessible Orange gorge, the future extending potential of the irrigation schemes on the N bank are be estimated at least on 7800 ha (Otzen 1989) which is six times the developed irrigation area at the present stage and more than the actual overall Namibian irrigated cultivation area.In order to strengthen the claim to all areas presently disputed between the Republics of Namibia and South Africa and backed by several in international law not binding UN General Assembly resolutions, the Windhoek Constitutional Assembly resolved Article 1 (4) of the new Namibian constitution: The national of Namibia shall consist of the whole of territory recognised by the international community through the organs of the United Nations as Namibia, including the enclave, harbour and port of Walvis Bay, as well as the off-shore islands of Namibia, and its southern boundary shall extend to the middle of the Orange River. Secret negotiations have been taking place since 21st March 1990 but as in the case of the much disputed possession of Walvis Bay, the Republic of South Africa cannot be forced to accept the low water line or the now constitutionally claimed median line as the revised Orange River boundary. South Africa remains internationally unsuable and the small Namibia is presently unable to put pressure on the leading regional power. On the contrary, such a substantial revision of the failures of the late German colonial administration seems only be attainable, if it all, after a phase of positive development in Windhoek, so to be recognised by Pretoria, which then could be result in a voluntary surrender of the South African claim to the N bank to seal then hopefully reached good neighbourly relations between the Republic of South Africa and the recently emerged Republic of Namibia.     

An upper‐ocean general circulation model for the north pacific: Preliminary experiments

Abstract

A model with two active layers, a mixed layer and a pycnocline layer, over a semipassive deep ocean is described. The model is used to simulate a climatological seasonal cycle in the upper North Pacific. The formulation is similar to that in Cherniawsky et al. (1990). The model resolution is 1° latitude by 1.5° longitude, extending from 62°N to the equator. It is driven with monthly wind stress (Hellerman and Rosenstein, 1983) and with Newtonian heat and freshwater fluxes, which were inferred from climatological (Levitus, 1982) sea‐surface monthly temperatures and annual mean salinities. The monthly temperature anomalies (without the annual mean) are multiplied by a prescribed gain factor and advanced in time, compensating for time delay in the response of the mixed layer. No‐slip and no‐flux constraints are applied on north, east, west and land boundaries, while the following open boundary conditions are used at the equator: (a) free‐slip on zonal velocities in the two layers; (b) a prescribed meridional transport, due to local curl of the wind stress, in the mixed layer; (c) an antisymmetric meridional velocity plus a small flux‐balancing term in the second layer; and (d) across‐equator symmetry for layer depths, temperatures and salinities. Sensitivity to two aspects of parametrization is investigated: (1) the change to horizontal diffusion/viscosity coefficients that depend on the velocity deformation field (as in Smagorinsky, 1963), and (2) the use of idealized piecewise‐linear profiles for second‐layer temperatures and salinities for calculating mixed layer entrainment fluxes.     

Seasonal variation of the <Emphasis Type="Italic">M</Emphasis><Subscript>2</Subscript> tide

The seasonal cycle of the main lunar tidal constituent M ₂ is studied globally by an analysis of a high-resolution ocean circulation and tide model (STORMTIDE) simulation, of 19 years of satellite altimeter data, and of multiyear tide-gauge records. The barotropic seasonal tidal variability is dominant in coastal and polar regions with relative changes of the tidal amplitude of 5–10 %. A comparison with the observations shows that the ocean circulation and tide model captures the seasonal pattern of the M ₂ tide reasonably well. There are two main processes leading to the seasonal variability in the barotropic tide: First, seasonal changes in stratification on the continental shelf affect the vertical profile of eddy viscosity and, in turn, the vertical current profile. Second, the frictional effect between sea-ice and the surface ocean layer leads to seasonally varying tidal transport. We estimate from the model simulation that the M ₂ tidal energy dissipation at the sea surface varies seasonally in the Arctic (ocean regions north of 60°N) between 2 and 34 GW, whereas in the Southern Ocean, it varies between 0.5 and 2 GW. The M ₂ internal tide is mainly affected by stratification, and the induced modified phase speed of the internal waves leads to amplitude differences in the surface tide signal of 0.005–0.0150 m. The seasonal signals of the M ₂ surface tide are large compared to the accuracy demands of satellite altimetry and gravity observations and emphasize the importance to consider seasonal tidal variability in the correction processes of satellite data.     

Iterative Spherical Downward Continuation Applied to Magnetic and Gravitational Data from Satellite

In the last few decades, satellites have acquired various potential data sets hundreds of kilometers above the Earth’s surface. Conventionally, these global magnetic and gravitational data sets are approximated by using spherical harmonics that allow straightforward work with both fields outside the Earth’s mass. In this article, we present an alternative approach for working with potential data in mass-free space given over a regular coordinate grid on a spherical surface. The algorithm is based on an iterative scheme and the Poisson integral equation for the sphere. With help from the Fourier transform, global potential (magnetic or gravitational) data can efficiently be continued from a mean orbital sphere down to a reference surface without using the spherical harmonics. This is illustrated both with simulated magnetic field data and with real data from the satellite gradiometry mission GOCE. In the case of simulated magnetic data and the downward continuation for 450 km, we have achieved a root mean square at the level of 0.05 nT, while it was <1 E (eotvos) for real GOCE data continued for 250 km. The crucial point is to apply the algorithm twice as a large part of noise can be removed from the input data.     

Paleotopographic controls on loess deposition in the Loess Plateau of China

The underlying pre‐existing paleotopography directly influences the loess deposition process and shapes the morphology of current loess landforms. An understanding of the controlling effects of the underlying paleotopography on loess deposition is critical to revealing the mechanism of loess‐landform formation. However, these controlling effects exhibit spatial variation as well as uncertainty, depending on a study's data sources, methodologies and particular research scope. In this study, the geological history of a study area in the Loess Plateau of China that is subject to severe soil erosion is investigated using detailed geological information and digital elevation models (DEMs), and an underlying paleotopographic model of the area is constructed. Based on the models of modern terrain and paleotopography, we introduce a watershed hierarchy method to investigate the spatial variation of the loess‐landform inheritance relationship and reveal the loess deposition process over different scales of drainage. The landform inheritance relationships were characterized using a terrain‐relief change index (TRCI) and a bedrock terrain controllability index (BTCI). The results show that the TRCI appears to have an inverse relationship with increasing research scope, indicating that, compared with the paleotopography of the region, modern terrain has lower topographic relief over the entire area, while it has higher topographic relief in the smaller, local areas. The BTCI strengthens with increasing drainage area, which demonstrates a strong controlling effect over the entire study area, but a weak effect in the smaller, local areas because of the effect of paleotopography on modern terrain. The results provide for an understanding of the spatial variation of loess deposition in relation to paleotopography and contribute to the development of a process‐based loess‐landform evolution model. Copyright © 2015 John Wiley & Sons, Ltd.