Analysis of the Variations of the Whitecap Fraction as Measured in a Coastal Zone

The whitecap coverage generated by breaking waves plays a major role in the transfer of heat, momentum, water vapour and particles at the air-sea interface. The sea surface covered by whitecaps strongly depends on both the wind and the wave-field characteristics. In particular, in coastal zones, the variations of the whitecap fraction, commonly noted W, differ from open ocean conditions, due to fetch effects, wave-current interactions, bottom influence and irregular coastlines affecting both the wind properties and the wave development. We present an analysis of the whitecap-fraction variations using experimental data acquired during FETCH (Flux, Etat de mer, et Télédétection en Condition de fetcH variable), an experimental campaign that took place in the Gulf of Lion off the French Mediterranean coast in 1998. The data include various conditions of wave development associated with fetch and unsteady effects. The whitecap fraction W was measured using an original image processing technique applied to sea surface photography. Specific relationships between the whitecap fraction and both atmospheric and oceanic parameters are investigated, which confirm the suitability of the friction velocity for modelling W. However, W has also been parameterised using wave-parameter dependent relationships, which is of interest for very short fetches.     

Recent lake level variations in Lake Haubi, central Tanzania, interpreted from pollen and sediment studies

Variations in pollen assemblages and in physical and chemical composition of a dated sediment record from the small Lake Haubi in north central Tanzania, reveal lake level fluctuations since the late 19th century. Lake Haubi changed from a seasonally inundated swamp to a lake in the beginning of the 20th century. With the exception of 1942-44, when it dried out completely, it remained water filled until 1994 when it again turned into a swamp. The lake level fluctuations in Lake Haubi are largely in phase with fluctuations of the larger East African lakes levels during the 20th century, and are therefore interpreted as being mainly controlled by regional climatic fluctuations. However, the initial formation of Lake Haubi at the turn of the century was likely due to local catchment specific causes, e.g. changes in land use, as the rapid increase in the water level at this time does not correspond to other lake level records from the region.     

The effects of reflection coefficient of the harbour sidewall on the performance of floating breakwaters

This paper studies the interaction of linear water waves with a moored floating breakwater with a leeward boundary composed from a vertical wall. This describes a real modelling for the case of ports in contrary to the problems of unbounded domains. It involves the application of a partial reflection boundary condition for this sidewall. In fact, the partial reflection problem in practical application is of great importance in the design of a harbour or breakwater and mainly for short waves. The reflection coefficient of the harbour boundary (sidewall) plays an important role in modifying the performance of the floating breakwater. Moreover, it reduces the resonant peaks appearing inside the ports due to the energy accumulation in an enclosed domain. The effects of the variation of structural parameters of the breakwater on the transmitted wave height are discussed in details for various values of partial reflection.     

东秦岭石窑沟斑岩钼矿床地质特征及辉钼矿Re-Os年龄

在东秦岭钼成矿带最近探明的石窑沟大型钼矿床位于近东西向马超营断裂带与北东向石窑沟-焦园断裂带的交汇部位,获得钼金属储量10余万吨,平均品位0.068%。钼矿化呈细脉-网脉状分布于花岗斑岩体及其围岩熊耳群火山岩中,与矿化有关的围岩蚀变有钾长石化、硅化、绢云母化、黄铁矿化等,具有斑岩型钼矿床的一些基本特点。在矿床中选取5件不同矿化类型的辉钼矿样品,采用ICP-MS法进行Re-Os同位素定年,获得模式年龄131.3±2.4～134.3±2.6Ma,等时线年龄135.2±1.8Ma(MSWD=0.18),形成于早白垩世,与豫西熊耳山地区雷门沟、鱼池岭等钼矿床形成时代相近。据辉钼矿Re含量(8.242×10-6～30.24×10-6)推测,矿床成矿物质主要来自于下地壳。矿床为东秦岭-大别山地区中生代第三期钼成矿作用产物,形成于早白垩世中国东部岩石圈伸展环境。     

Seasonal variations in lipid composition of the hydrothermal vent mussel Bathymodiolus azoricus from the Menez Gwen vent field

Specimens of the hydrothermal mussel Bathymodiolus azoricus collected in Menez Gwen hydrothermal vent field (NE Atlantic) during 2002–2003 were examined for feeding patterns variations through three seasons. The fatty acid profile and lipid classes of the mussels were studied, together with the MODIS/AQUA-derived near-surface chlorophyll a to test the hypothesis that surface productivity might be related to the feeding patterns of this species. The lipid levels showed pronounced seasonal fluctuations with the highest values occurring in January and August. Seasonal variations in lipid classes and fatty acid composition of neutral and polar lipids in the mussels are presented. Differences in the fatty acid profile of lipid classes in different seasons suggest that the higher energy requirements in summer and winter were supplied by bacterial biomarkers ω7 MUFA (monounsaturated fatty acids), whereas ω6 PUFA (polyunsaturated fatty acids) and NMI (non-methylene-interrupted) fatty acids predominated during the spring. The MODIS/AQUA data show marked seasonal variability and an anomalous peak during January of 2003, although this cannot be directly linked to lipid composition variation.     

Mass loss mechanisms in evolved stars

Summary Mass loss is a very important phenomenon for stellar evolution. In the late stages of stars it becomes fairly high (up to 10^–4 M/yr) though with a much decreased expansion velocity (about 30 kms^–1). It can also be variable, sporadic. Now, though the first observational evidence for mass loss from cool stars is usually attributed to Adams and McCormak in 1935 and though a lot of observational and theoretical papers have been devoted to it since this discovery, we only know mechanisms which are probably efficient under the dominant physical conditions, but neither one mechanism nor a combination of mechanisms is able to produce the observed effects. Those most invoked (thermal gas pressure, radiation pressure, acoustic waves, shock waves, Alfvén waves, ) will be described and criticized, with emphasis on the radiation pressure on dust grains at work at least in the outer part of cool atmospheres. The geometry and the content of expanding atmospheres are also discussed together with the mechanisms that may be important at small scales. Both theory and observations are taken into accout.     

Self-generated aperiodic behaviour in a simple climate model

Climatic variability arising from the coupling between ocean temperature and sea-ice extent is studied in a spatially distributed system. A spatial degree of freedom is crudely introduced by the coupling, through energy transfer, of two box models each of which describes a different space region. The evolution equations are cast into a normal form and some qualitative features of this general class of models are predicted. It is shown, both analytically and numerically, that internally generated complexity in the form of aperiodic behaviour can be a natural consequence of spatially distributed systems.