Gravitational potential energy of the Sun

Summary The gravitational potential energy of the Sun and its corresponding internal energy have been estimated on the basis of the standard model of the Sun's internal structure. It is demonstrated that the principal moment of inertia of the Sun, computed from the model, does not fit the hydrostatic equilibrium limit.     

Comparative influence of land and sea surfaces on the Sahelian drought: a numerical study

The aim of this work is to compare the relative impact of land and sea surface anomalies on Sahel rainfall and to describe the associated anomalies in the atmospheric general circulation. This sensitivity study was done with the Météo-France climate model: ARPEGE. The sensitivity to land surface conditions consists of changes in the management of water and heat exchanges by vegetation cover and bare soil. The sensitivity to ocean surfaces consists in forcing the lower boundary of the model with worldwide composite sea surface temperature (SST) anomalies obtained from the difference between 4 dry Sahel years and 4 wet Sahel years observed since 1970. For each case, the spatiotemporal variability of the simulated rainfall anomaly and changes in the modelled tropical easterly jet (TEJ) and African easterly jet (AEJ) are discussed. The global changes in land surface evaporation have caused a rainfall deficit over the Sahel and over the Guinea Coast. No significant changes in the simulated TEJ and an enhancement of the AEJ are found; at the surface, the energy budget and the hydrological cycle are substantially modified. On the other hand, SST anomalies induce a negative rainfall anomaly over the Sahel and a positive rainfall anomaly to the south of this area. The rainfall deficit due to those anomalies is consistent with previous diagnostic and sensitivity studies. The TEJ is weaker and the AEJ is stronger than in the reference. The composite impact of SST and land surfaces anomalies is also analyzed: the simulated rainfall anomaly is similar to the observed mean African drought patterns. This work suggests that large-scale variations of surface conditions may have a substantial influence on Sahel rainfall and shows the importance of land surface parameterization in climate change modelling. In addition, it points out the interest in accurately considering the land and sea surfaces conditions in sensitivity studies on Sahel rainfall.     

Geochemical Processes Controlling the Formation of As-Rich Waters Within a Tailings Impoundment (Carnoulès, France)

The distribution of arsenic (As(III), As(V)) and iron (Fe(II), Fe(III)) species was monitored during 1 year in a borehole drilled in the Carnoulès tailings impoundment which contains As-rich pyrite. The concentrations of total As and Fe in subsurface waters exhibited strong variations over one year, which were controlled by dissolved oxygen concentrations. At high oxygen levels, extremely high As (up to 162 mM) and Fe (up to 364 mM) concentrations were reached in the borehole, with the oxidised species predominant. As and Fe concentrations decreased 10-fold under oxygen-deficient conditions, as a result of pH increase and subsequent precipitation of As(V) and Fe(III). From drill core sections, it appeared that at low dissolved oxygen levels, As(III) was primarily released into water by the oxidation of As-rich pyrite in the unsaturated zone. Subsequent As and Fe precipitation was promoted during transport to the saturated zone; this reaction resulted in As enrichments in the sediment below the water table compared to the original content in pyrite, together with the formation of As-rich (up to 35 wt% As) ferruginous material in the unsaturated zone. High amounts of As(V) were released from these secondary phases during leaching experiments with oxygenated acid sulfate-rich waters; this process is believed to contribute to As(V) enrichment in the subsurface waters of the Carnoulès tailings during periods of high dissolved oxygen level.     

The role of the crust in the magmatic evolution of the island of Lipari (Aeolian Islands,Italy)

Volcanic rocks on the island of Lipari show the entire range of Sr, Nd, Pb isotopic compositions displayed by other islands in the Aeolian archipelago. The rapid isotopic evolution of subaerial volcanic rocks on Lipari towards crustal values together with the appropriate isotopic composition of the neighbouring Calabrian crust (Serre) indicate that many geochemical characteristics observed in the lavas can be attributed to contamination and mixing with crustal materials and melts. Interpretation of the data is complicated by the fact that underplating onto the crust-mantle boundary and the specific lithologies present in the crustal section differ underneath each individual sector of the island. In the central and northern parts of the island, metapelitic rocks were incorporated to provide the more radiogenic Sr isotopic compositions of some lavas. The products from M. Guardia in the southern part of Lipari, where activity is restricted to the last 30–40 ka, bear geochemical similarities to the island of Vulcano, where it is proposed that considerable remobilization of the crust took place in the presence of mafic mantle-derived melts. On Lipari the petrogenetic processes of magma mixing and assimilation dominate over fractional crystallization, and the observed increase of K₂O over Na₂O can be correlated with contributions from metapelitic crustal lithologies. It is suggested that the variability in isotopic composition and the budget of alkalis (Na₂O versus K₂O) in the lavas can be explained by invoking a heat source from an intruding asthenospheric MORB-type mantle into a cooler lithospheric crust/mantle during the opening of the Tyrrhenian basin.     

Crustal seismic profiles in the Alboran Sea — Preliminary results

In September 1974, deep seismic sounding experiments were performed in the Alboran Sea. The crustal seismic profiles were carried out with shotpoints at sea along approximately the 36°N parallel and along 3°W and 5°W meridians with stations on land in Morocco and Spain following these three directions. The first interpretation of the data indicates a thinned continental crust with a Moho depth of 16 km on top of a slightly anomalous upper mantle (7.5<V _p<7.9 km/s) beneath the center of the Alboran Sea. Towards Spain the transition to the continental margin is characterized by a very rapid thickening of the crust. Towards Morocco a rather abrupt thickening is observed only for the Rif region, while in the eastern part (north-south profile along 3°W) the dip of the Moho is very slight.     

Gravity potential of the normal body in the outer and inner space

Summary The level rotational ellipsoid, best fitting the actual Earth, rotating with the same angular velocity around a common axis of rotation, is assumed to be a mathematical model of the real Earth. The gravity potential of this body and its derivatives in the outer space are derived by means of the generalized Pizzetti method[1]. For some analyses of the structure of the Earth we need to know the gravity anomaly and thus the gravity potential and its derivatives inside the mathematical model. These values are not defined in the classical conception. In this paper, the normal potential and its derivatives in the inner space are derived up to a certain depth, which is still of significance for gravimetric research.Dedicated to RNDr Jan Pícha, CSc., on his 60th Birthday     

On the solution of the boundary problem of the potential theory by means of the vertical derivative of the gravity anomaly

Summary The boundary problem of the potential theory is treated for the case in which the values of the vertical derivative of the gravity anomaly are known. There boundary conditions are derived and alternatives are also treated.Dedicated to RNDr. Jan Pícha, CSc., on his 60th Birthday