States of maximum entropy production in a one-dimensional vertical model with convective adjustment

We investigate the hypothesis that the atmosphere is constrained to maximize its entropy production by using a one-dimensional (1-D) vertical model. We prescribe the lapse rate in the convective layer as that of the standard troposphere. The assumption that convection sustains a critical lapse rate was absent in previous studies, which focused on the vertical distribution of climatic variables, since such a convective adjustment reduces the degrees of freedom of the system and may prevent the application of the maximum entropy production (MEP) principle. This is not the case in the radiative-convective model (RCM) developed here, since we accept a discontinuity of temperatures at the surface similar to that adopted in many RCMs.
For current conditions, the MEP state gives a difference between the ground temperature and the air temperature at the surface ≈10 K. In comparison, conventional RCMs obtain a discontinuity ≈2K only. However, the surface boundary layer velocity in the MEP state appears reasonable (≈m s⁻¹). Moreover, although the convective flux at the surface in MEP states is almost uniform in optically thick atmospheres, it reaches a maximum value for an optical thickness similar to current conditions. This additional result may support the maximum convection hypothesis suggested by Paltridge (1978 ).     

Sediment flux distribution in the Southern Brazil Basin during the late Quaternary: the role of deep-sea currents

Detailed sedimentological and stratigraphic analyses were carried out on seven Kullenberg cores collected across the Brazilian continental margin during the French cruises Byblos and Apsara III, in order to highlight the factors controlling the sediment flux distribution in the Southern Brazil Basin during the late Quaternary. On the continental slope and upper continental rise above 3000 m depth, sediment fluxes are important and highly variable (4·2–14·2 g cm^?2 10^?3 yr). The sediments show a pelagic or turbiditic character, depending on the width of the shelf and proximity of canyons. The material is characterized by high kaolinite contents, and originates from the coastal rivers draining the South American continent north of Rio de Janeiro. On the middle continental rise between 3000 and 4000 m depth, sediment fluxes are the lowest observed in the area (0·9 g cm^?2 10^?3 yr), because terrigenous input is trapped at shallower depths on the São Paulo Plateau. Pelagic settling is the dominant process. In the deep domains, below 4000 m depth, contouritic accumulations are developed on the path of the northwards moving Antarctic bottom water (AABW) currents. The deposits consist of fine-grained silty-clayey muds with very low carbonate contents. The sediment fluxes (1·45 g cm^?2 10^?3 yr) are higher than on the middle continental rise, as a consequence of fine-grained terrigenous supply derived from higher latitudes (Argentine Basin and Southern Ocean), and transported in the basin through the Vema Channel by the AABW currents. This material is characterized by high smectite and chlorite contents. These data reveal large sediment flux variations which are linked to distinct depth-related domains. Such a distribution is the consequence of the presence of two available sources of terrigenous sediments: (1) the Brazilian continental areas with a downslope material transport and a sediment distribution controlled by the morphology of the margin, and (2) the Argentine Basin with an alongslope material transport by deep-sea currents which dominate the sedimentation in the abyssal domains.     

Geodynamic Information in Peridotite Petrology

Systematic differences are observed in the petrology and majorelement geochemistry of natural peridotite samples from thesea floor near oceanic ridges and subduction zones, the mantlesection of ophiolites, massif peridotites, and xenoliths ofcratonic mantle in kimberlite. Some of these differences reflectvariable temperature and pressure conditions of melt extraction,and these have been calibrated by a parameterization of experimentaldata on fertile mantle peridotite. Abyssal peridotites are examplesof cold residues produced at oceanic ridges. High-MgO peridotitesfrom the Ronda massif are examples of hot residues producedin a plume. Most peridotites from subduction zones and ophiolitesare too enriched in SiO₂ and too depleted in Al₂O₃ to be residues,and were produced by melt–rock reaction of a precursorprotolith. Peridotite xenoliths from the Japan, Cascades andChile–Patagonian back-arcs are possible examples of arcprecursors, and they have the characteristics of hot residues.Opx-rich cratonic mantle is similar to subduction zone peridotites,but there are important differences in FeO_T. Opx-poor xenolithsof cratonic mantle were hot residues of primary magmas with16–20% MgO, and they may have formed in either ancientplumes or hot ridges. Cratonic mantle was not produced as aresidue of Archean komatiites. KEY WORDS: peridotite; residues; fractional melting; abyssal; cratonic mantle; subduction zone; ophiolite; potential temperature; plumes; hot ridges     

Geochemical characteristics of mineral air particles emitted inside a clay atomisation plant which introduces waste recycling processes

The objective of this work is to assess the concentrations of three factions of air particles (settable particles, TSP and PM10) and the levels of several toxic elements in a clay atomisation industry through aerosol sampling at several points inside an industrial plant. Mechanical activities, which produce diffuse emissions, are the main process of discharge of particles in both indoor and outdoor workplace environments in the atomisation plant. The levels of As, Cd, Pb, Zn, Ba and Ni increase in the zones with higher concentrations of particles and lower ventilation. The concentrations of As and F are not influenced by the recycling processes. The levels of Cd and Pb do not show great enrichment in air particles collected inside the atomisation plant although the content of both elements is associated with ceramic muck recycling. Finally, the content of B in waste water is mainly transferred in gaseous phase to the atmosphere during the process of drying by atomisation.     

NOUVELLE METHODE DE RESTITUTION D'UN HORIZON REFRAGTEUR PAR SISMIQUE REFRACTION*

The purpose of this report is to show a method of determining the top of a refractor departing from the times and slopes of the direct and inverse dromocrones. The method does not need topographical correction and can be applied without knowledge of the distance between the geophone and the shot point. These results having been obtained, the commonly accepted point of view is upset: instead of looking for two points on the surface corresponding to one point of the refractor, we try to etablish, starting with only one point from the surface, the two corresponding points from the top of the refractor. This method can be applied to isolated points and does not demand interpretative hypotheses of any kind, excluding the velocity evaluation of the overburden and of the refractor. The necessary calculations can be easily executed by means of a digital computer to which the dromocrone times and the distances between the geophones must be given. These calculations can also be executed by a person having no knowledge of refraction seismology. This report also examines the validity of the approximations involved in the method proposed.     

La sédimentation argileuse depuis l'Eocène sur le plateau Vøring et à son voisinage, d'après le Leg 38 DSDP (Mer de Norvège)

The study of clays from sites 338 to 343 enables the main lines of the palaeogeographical evolution of the Vøring plateau, off Norway, to be determined. The following stages are proposed: (1) In early Eocene sediments, clays provide evidence of erosion of the Scandinavian shield; detrital primary minerals (illite, chlorite) derived from crystalline rocks are dominant. This erosion results from tectonic movements coeval with the opening of the Norwegian basin. The rejuvenation of marginal relief hinders pedogenesis, which is only indicated by the presence of minerals coming from the few soils which are developed. (2) From the Middle Eocene, primary minerals decrease while smectite becomes dominant. This trend increases through the late Eocene and at the beginning of the Middle Oligocene, where only smectite is present. During this period the basin margins are stabilized after the initial movements. In essentially pelagic marine sediments, the smectite seems to be derived from volcanic rocks. (3) During the Middle Oligocene and early to Middle Miocene, smectite is always dominant, but primary minerals reappear, with mixed-layers indicating a moderate continental alteration. This composition suggests a modification of the climate, mainly marked by an increase in humidity. (4) In Pliocene and Plio-Pleistocene sediments, primary minerals are dominant, while smectite decreases. The glacial climate is responsible for this mineralogy. Detrital minerals would come from the erosion of Scandinavian moraines and from rafting by icebergs.     

CARTOGRAPHIE DES “PSEUDO-RESISTIVITES APPARENTES’ PAR PROFILAGE TELLURIQUE-TELLURIQUE ASSOCIE A LA MAGNETO-TELLURIQUE *

The magneto-telluric and telluric-telluric profiling techniques are presented, and then a new method which combines these two techniques for mapping a parameter defined as the “apparent pseudo-resistivity”. The results obtained for the uranium structures in the Cluff Lake district (Saskatchewan Canada) indicate the use of these different techniques in the detection of zones of conduction for surface zones and for deeper zones, and demonstrate the advantages of these methods over the usual electrical methods in problems of structural research.     

Le soutien de crue mobile dans le Fleuve Sénégal, à partir du barrage de Manantali

Résumé

Parmi les objectifs assignés au barrage de Manantali sur le Bafing, le soutien de pointe de crue, indispensable pour le maintien des cultures traditionnelles de décrue dans la vallée du Sénégal, concurrence gravement les autres besoins lors des années déficitaires en eau: baisse de production électrique et diminution des réserves d'eau destinées à l'irrigation. On propose ici des règles permettant de réaliser un soutien de crue mobile relativement économique en eau, coïncidant avec une pointe de débit sur les affluents non contrôlés pour lesquels on envisage une prévision à l'horizon 10 jours. On montre par simulation numérique au pas de temps journalier que le soutien mobile, comparé au soutien à date fixe, permet de faire en période sèche un gain important de production électrique, tout en conservant une fréquence de crue “correcte”, supérieure à celle du régime naturel.     

Flood forecasting with a watershed model: a new method of parameter updating

Abstract

Flood forecasting is of prime importance when it comes to reducing the possible number of lives lost to storm-induced floods. Because rainfall-runoff models are far from being perfect, hydrologists need to continuously update outputs from the rainfall-runoff model they use, in order to adapt to the actual emergency situation. This paper introduces a new updating procedure that can be combined with conceptual rainfall-runoff models for flood forecasting purposes. Conceptual models are highly nonlinear and cannot easily accommodate theoretically optimal methods such as Kalman filtering. Most methods developed so far mainly update the states of the system, i.e. the contents of the reservoirs involved in the rainfall-runoff model. The new parameter updating method proves to be superior to a standard error correction method on four watersheds whose floods can cause damage to the greater Paris area. Moreover, further developments of the approach are possible, especially along the idea of combining parameter updating with assimilation of additional data such as soil moisture data from field measurements and/or from remote sensing.