Kien Dominh

Recent sea level change in the Mediterranean Sea revealed by Topex/Poseidon satellite altimetry

Using altimetry data of the Topex/Poseidon satellite available since early 1993, we show that the eastern Mediterranean sea level has been continuously rising during 1993–1999, at a rate up to 20 mm/yr southeast of Crete. Sea level rise is also observed in the Algerian-Provencal basin as well as in the Tyrrhenian and Adriatic seas. The north Ionian sea, on the other hand, shows an opposite trend, i.e., a sea level drop during the past seven years. Sea surface temperature trends are strongly correlated to sea level trends, indicating that at least part of the observed sea level change has a thermal origin. The recent Mediterranean sea level rise observed by Topex/Poseidon may be related to the warming trends reported from hydrographic cruises in the intermediate and deep waters of the eastern basin since the early 1990s, and of the western basin since the 1960s.

Geosat‐derived geoid anomalies at medium wavelength

Geosat profiles of the Exact Repeat Mission have been averaged over a 1-year period and high-pass-filtered using inverse method techniques. The geoid surface constructed with both ascending and descending profiles shows at medium wavelengths band-shaped anomalies preferentially elongated in the east-west direction. These anomalies have an average amplitude of ∼30 cm and dominant wavelengths to 750km and 1100 km. We have performed numerous tests to show that the lineations are not artefacts created by the filtering process. Moreover, two-dimensional (2-D) filtering with the inverse method applied on a regional basis over the Pacific gives essentially similar results, indicating that the filtered geoid is not affected by directional bias. Seafloor topography in the Pacific filtered by 2-D inverse method also shows east-west trending depth anomalies positively correlated to medium-wavelength geoid lineations. Along the East Pacific Rise, there is a clear correlation between geoid lineations and regional variations in axial depth. Cross-spectral analysis carried out on geoid and topography data over the Pacific area gives coherence maxima at 750-km and 1100-km wavelengths and admittance values of 2–3 m/km. Observed admittance matches the magnitude and shape of admittance predicted by lithospheric cooling models, suggesting that the lineations are related to regional variations in the plate cooling process. Convection models produce much higher admittances than observed unless a low-viscosity layer is assumed so that dynamical support cannot be completely discarded. In most instances, however, the position and direction of the lineations seem to be controlled by major fractures zones which is in favor of a lithospheric origin. In the south central Pacific where the lineations appear parallel to absolute plate motion, there may be a combination of both lithospheric and sublithospheric processes.

Numerical experiment applicable to the latest stage of planet growth

Abstract A three-dimensional numerical model was developed with the goal of studying limited dynamical problems relevant to the latest stage of planet growth in the accretion theory. A small number of large protoplanets (∼ Moon size) of different masses, moving around the Sun, are considered. The dynamical evolution and growth of the population is studied under mutual gravitational perturbations, accretion, and collisional fragmentation processes. Gravitational encounters are treated exactly by numerical integration of the N-body problem. Outcomes of collisional fragmentation are modeled according to the results of R. Greenberg et al. (1978, Icarus , 35 , 1–26). In the present work, we consider 25 protoplanets with uniform mass distribution in the range 2 × 10 25 −4 × 10 26 g on heliocentric orbits in the Earth zone. These bodies are initially confined to a small volume of space to permit gravitational perturbations by close approaches and collisions within a finite length of integration time. The dynamical evolution of the swarm is followed for four different sets of initial ranges in semimajor axis, eccentricity, and inclination: Δa =0.01, 0.02, 0.04, 0.08 AU; Δe = 0.005, 0.01, 0.02, 0.04; Δi =0°3, 0°6, 1°2, 2°4. Among other results, it is found that average eccentricities and inclinations evolve toward a steady state such that i ⋍ 1 2 , e ; it is also found that, whatever the initial conditions, the population evolves toward a quasi-equilibrium relative velocity distribution corresponding to a Safronov parameter value θ⋍10 . Moreover, the growth process of the growing planet presents very similar behavior in the four cases considered, except for the time scale of evolution, which increases with the initial range of orbital elements. Earlier works of this kind have been presented by L.P. Cox and J.S. Lewis (1980, Icarus , 44 , 706–721) and by G.N. Wetherill (1980b, In Geol. Soc. Canad. Spec. Publ. , p. 20), although a number of differences exist between the three approaches.