A non-hydrostatic algorithm for free-surface ocean modelling

An original implementation of a non-hydrostatic, free-surface algorithm based on a pressure correction method is proposed for ocean modelling. The free surface is implemented through an explicit scheme combined with a mode-spitting method but the depth-averaged velocity and the position of the free surface are updated at each non-hydrostatic iteration. The vertical momentum equation is also integrated up to the surface enabling a natural and accurate treatment of the surface layer. The consistent specification of the numerical schemes provides balanced transfers of potential and kinetic energy. This algorithm is well-suited for implementation as a non-hydrostatic kernel on originally hydrostatic free-surface ocean models such as Symphonie (http://poc.obs-mip.fr/pages/research_topics/modelling/symphonie/symphonie.htm) for which it has originally been developed.Energy balances associated with the propagation of short surface waves and solitary waves are presented for two dedicated well-documented configurations over closed domains. The buoyancy flux, the work rate of the pressure force together with the power of the advective terms are evaluated and discussed for the generation and the propagation of these two types of waves. The dissipation rate is in particular shown to be several orders of magnitude smaller than the work rates of the hydrostatic and non-hydrostatic pressure forces confirming the necessity for the exchanges of energy to be numerically balanced. The algorithm is subsequently applied to the complex generation of non-linear solitary internal waves by surface tides over Georges Bank, in the Gulf of Maine. The generation and the propagation of the observed non-linear and non-hydrostatic features in this region are correctly reproduced.     

A fast computation of the diurnal secondary ion production in the ionosphere of Titan

We propose an analytic model that allows rapid computation of the secondary ion production due to electron impact from the primary photo-production in the ionosphere of Titan. The model parameters are given for each of the 5 major ion productions (N⁺₂, CH⁺₄, N⁺, CH⁺₃, N⁺⁺₂) as well as for the electron production.     

PAMPRE: A dusty plasma experiment for Titan's tholins production and study

Organic aerosols play a significant role in the properties and evolution of Titan's atmosphere. But our knowledge of them and their physico-chemical mechanisms of formation and evolution are currently limited to a few data obtained by Titan observations from the Earth or from space probes. For this reason, laboratory experiments are developed to simulate the atmospheric chemistry and produce analogues of these aerosols in order to understand better their properties and how they are formed. The plasma discharges are the most efficient devices for the production of such analogues. However, the existing plasmas simulations introduce experimental biases compared with the conditions of aerosols production in Titan's atmosphere: chemistry is induced by electrons instead of photons; the solid analogues are produced and deposited on solid surfaces; direct analysis of the particles inside the reactive chamber is not easy. In order to avoid some of these experimental problems, we have developed another method of production of Titan's aerosols analogues. It is based on a capacitively coupled radio-frequency (RF) cold plasma system at low pressure in a N₂-CH₄ gaseous mixture. In this plasma, solid particles produced from the gas phase are in levitation, thus preventing any wall effect on their production, and allowing the study of the formation and growth of the particles directly in the plasma. Moreover, the electron energy distribution of this plasma can be compared with the solar spectrum. This article describes the RF plasma experiment and presents the first results obtained with an initial N₂-CH₄ (90:10) gaseous mixture which produced our first studied analogues of Titan's aerosols.     

A compound Ca‐, Al‐rich inclusion from CV3 chondrite Northwest Africa 3118: Implications for understanding processes during CAI formation

A calcium‐aluminum‐rich inclusion 3N from the Northwest Africa (NWA) 3118 CV3 carbonaceous chondrite is a unique cm‐sized compound object, primarily a forsterite‐bearing type B (FoB) CAI, that encloses at least 26 smaller CAIs of different types, including compact type A (CTA), B, C, and an ultra‐refractory inclusion. Relative to typical type A and B CAIs found elsewhere, the bulk compositions of the types A and B CAIs within 3N more closely match the bulk compositions predicted by equilibrium condensation of a gas of solar composition. Being trapped within the FoB melt may have protected them from melt evaporation that affected most “stand‐alone” CAIs. 3N originated either as an aggregate of many smaller (mostly types A, B, C) CAIs plus accreted Fo‐bearing material (like an amoeboid olivine aggregate) which experienced partial melting of the whole, or else as a FoB melt droplet that collided with and trapped many smaller solid CAIs. In the former case, 3N recorded the earliest accretion of pebble‐sized bodies known. In the latter case, the presence of a large number of individual refractory inclusions within 3N suggests a very high local density of refractory solids in the immediate region of the host CAI during the brief time while it was melted. Collisions would have occurred on time scales of hours at most, assuming a melt solidification interval for the host CAI of 300–400 °C (maximum) and a cooling rate of ~10 °C/h.     

Robe’s circular restricted three-body problem with a Roche ellipsoid-triaxial versus oblate system

This paper investigates Robe’s circular restricted three-body problem for two cases: with a Roche ellipsoid-triaxial system and with a Roche ellipsoid-oblate system. Without ignoring any component in both problems, a full treatment is given of the buoyancy force. The relevant equations of motion are established, and the special case where the density of the fluid and that of the infinitesimal mass are equal (D=0) is discussed. The location of the libration point and its stability when the infinitesimal mass is denser than the medium (D>0) are studied and it is found that the point (0,0,0) is the only libration point and this point is stable.     

The Piànico tephra: an early Middle Pleistocene record of intraplate volcanism in the Mediterranean

ABSTRACT Distal tephra are a valuable record of the volcano-tectonic evolution of an area under study. Here, we document the case of the Early Middle Pleistocene rhyolitic tephra of Piànico, discovered in the Southern Italian Alps. The geochemical characteristics of Piànico are unique among the distal tephra outcropping in Italy and indicate an intraplate volcanism at the source. The alkali composition and trace elements show a striking resemblance with the rhyolitic complex of the Euganean Hills, located 170 km from Piànico. However, these rhyolites are much older (Oligocene). Alternatively, the source of this intraplate volcanic episode could be located in the southern Tyrrhenian Sea.     

Calibration of a Ge crystal with nuclear recoils for the development of a dark matter detector

The ionization deposited in a Ge crystal by the scattering of ≈ 1 MeV neutrons on Ge nuclei is measured and its lowenergy behavior is investigated down to recoil energies of 3 keV. This calibration study is fundamental for the discrimination of Weakly Interacting Massive Particles (WIMPs) from the radioactive background. Experimental results are compared with theoretical predictions.     

Anticipate response of climate change on coastal risks at regional scale in Aquitaine and Languedoc Roussillon (France)

LIFE Environment/RESPONSE project (2003–2006) aimed to evaluate and map, at regional scale, the impact of climate change on coastal risks (erosion and marine flooding), by anticipating the response to regional climatic change scenarios of coastal systems. These are described by their geomorphology, coastal processes, known hazardous events and existing defences. Application on Aquitaine and Languedoc Roussillon regions (France) assesses the likely increase of the coastal risks. In both regions, the weight of geomorphology and settlement development is underlined. The results point out the need for better knowledge on physical resilience capacity of the coast, assets values and vulnerability, and the urge of an integrated management approach of coastal risk, at least at the scale of sedimentary cell.     

Protracted,coeval crust and mantle melting during Variscan late-orogenic evolution: U–Pb dating in the eastern French Massif Central

International Journal of Earth Sciences - The late stages of the Variscan orogeny are characterized by middle to lower crustal melting and intrusion of voluminous granitoids throughout the belt,...