Impact of Boundary-Layer Processes on Near-Surface Turbulence Within the West African Monsoon   总被引：1，自引：1，他引：0  

Fabienne Lohou  Frédérique Saïd  Marie Lothon  Pierre Durand  Dominique Serça 《Boundary-Layer Meteorology》2010,136(1):1-23

High frequency measurements of near-surface meteorological data acquired in north Benin during the 2006 West African monsoon seasonal cycle, in the context of the African Monsoon Multidisciplinary Analysis (AMMA) experiment, offer insight into the characteristics of surface turbulence in relation to planetary boundary-layer (PBL) processes. A wide range of conditions is encountered at the lower and upper limits of the PBL: (i) from water-stressed to well-fed vegetation, and (ii) from small to large humidity and temperature jumps at the PBL top inversion, due to the Saharan air layer overlying the monsoonal flow. As a result, buoyant convection at the surface and entrainment at the PBL top play very different roles according to the considered scalar. We show that, when the boundary-layer height reaches the shear level between the monsoonal and Harmattan flows, the temperature source and humidity sink at the boundary-layer top are sufficient to allow the entrainment to affect the entire boundary layer down to the surface. This situation occurs mainly during the drying and moistening periods of the monsoon cycle and affects the humidity statistics in particular. In this case, the humidity turbulent characteristics at the surface are no longer driven solely by buoyant convection, but also by entrainment at the boundary-layer top. Consequently, the Monin–Obukhov similarity theory appears to fail for the parameterisation of humidity-related moments.  相似文献   

The Würmian Late-glacial in Iowland Switzerland     

B. Ammann  A. F. Lotter  U. Eicher  M.-J. Gaillard  B. Wohlfarth  W. Haeberli  G. Lister  M. Maisch  F. Niessen  Ch. Schlüchter 《第四纪科学杂志》1994,9(2):119-125

A synthesis is provided of Late-glacial (14-9 ka BP) environmental changes in lowland Switzerland (the ‘Swiss Plateau’). The chronology of deglaciation and subsequent developments in vegetation cover in the area are summarised. The sequence of climatic variations experienced in the region during the Late-glacial is then described and a curve representing the main palaeotemperature variations is presented.  相似文献   

The plant-macrofossil record of past lake-level changes   总被引：1，自引：0，他引：1  

Gina E. Hannon  Marie-José Gaillard 《Journal of Paleolimnology》1997,18(1):15-28

Plant-macrofossil analysis is one of the most useful biostratigraphical methods for the reconstruction of former lake-level changes. The distribution of submerged, floating-leaved and emergent lake-shore vegetation is mainly dependant on water depth, but water chemistry and nutrient status must also be taken into account when interpreting water-level changes. Lake-level studies should be based on the investigation of several littoral cores along a transect perpendicular to the lake-shore. Multiple cores are essential for separating genuine lake-level changes from other processes influencing the plant-macrofossil record. Physical analyses of sediment stratigraphy provide important additional information to the plant-fossil record, because natural infilling processes and erosion from the catchment must be distinguished from climatic events causing a change in the water level. Here we review several important concepts, including suitability of lakes for lake-level study, the degree of detail required in the analysis, and macrofossil records of lake-level changes, and illustrate those concepts by examples from southern Sweden and Minnesota. We discuss how to reconcile alternative hypotheses for the stratigraphic changes seen in the macrofossil assemblages.  相似文献   

Taraxerol and Rhizophora pollen as proxies for tracking past mangrove ecosystems     

Gerard J.M Versteegh  Enno Schefuß  Fabienne Marret  J.H.Fred Jansen 《Geochimica et cosmochimica acta》2004,68(3):411-422

Angola Basin and Cape Basin (southeast Atlantic) surface sediments and sediment cores show that maxima in the abundance of taraxerol (relative to other land-derived lipids) covary with maxima in the relative abundance of pollen from the mangrove tree genus Rhizophora and that in the surface sediments offshore maxima in the relative abundance of taraxerol occur at latitudes with abundant coastal mangrove forests. Together with the observation that Rhizophora mangle and Rhizophora racemosa leaves are extraordinarily rich in taraxerol, this strongly indicates that taraxerol can be used as a lipid biomarker for mangrove input to the SE Atlantic. The proxy-environment relations for taraxerol and Rhizophora pollen down-core show that increased taraxerol and Rhizophora pollen abundances occur during transgressions and periods with a humid climate. These environmental changes modify the coastal erosion and sedimentation patterns, enhancing the extent of the mangrove ecosystem and/or the transport of mangrove organic matter offshore. Analyses of mid-Pleistocene sediments show that interruption of the pattern of taraxerol maxima during precession minima occurs almost only during periods of low obliquity. This demonstrates the complex environmental response of the interaction between precession-related humidity cycles and obliquity-related sea-level changes on mangrove input.  相似文献   

The REVEALS model,a new tool to estimate past regional plant abundance from pollen data in large lakes: validation in southern Sweden     

Sofie Hellman  Marie‐José Gaillard  Anna Broström  Shinya Sugita 《第四纪科学杂志》2008,23(1):21-42

The REVEALS model was developed to reconstruct quantitatively regional vegetation abundance (in a 10⁴–10⁵ km² area) from pollen assemblages in large lakes (≥100–500 ha). This model corrects for biases in pollen percentages caused by inter‐taxonomic differences in pollen productivity and dispersal. This paper presents the first case study to validate REVEALS, using empirical data from southern Sweden. Percentage cover of modern regional vegetation in Skåne and Småland, two contrasting vegetation regions, was predicted with REVEALS for 26 key taxa, using pollen assemblages from surface sediments in 10 large lakes, and compared to the actual vegetation within 10⁴ km² compiled from satellite data, forestry inventories, crop statistics, aerial photographs, and vegetation inventories. REVEALS works well in predicting the percentage cover of large vegetation units such as total trees (wooded land), total herbs (open land), total conifers and total broad‐leaved trees, and it provides reasonable estimates for individual taxa, including Pinus, Picea, Betula, Corylus, Alnus, Tilia, Salix spp., Juniperus, Poaceae, Cyperaceae, Cerealia and Secale. The results show great potential for REVEALS applications, including (1) quantitative reconstructions of past regional land cover important for palaeoclimatology and nature conservation, and (2) local‐scale reconstruction of vegetation (<1 km² up to ～ 5 km² area) relevant for palaeoecology and archaeology. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

New aspects of magma storage and transfer     

Bruno Scaillet  Laurent Arbaret  Fabrice Gaillard 《Comptes Rendus Geoscience》2019,351(8):523-524

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Validation of age and growth of the Picasso triggerfish (Balistidae: Rhinecanthus aculeatus) from Okinawa Island, Japan, using sectioned vertebrae and dorsal spines     

Fabienne Künzli  Katsunori Tachihara 《Journal of Oceanography》2012,68(6):817-829

To understand age and growth of the Picasso triggerfish, Rhinecanthus aculeatus, monthly sampling was conducted from February 2010 to October 2011 on the subtropical Okinawa Island, Japan, using trammel net and speargun. Fish were measured by weight (W) and standard length (SL) and age was determined by examining thin-sections of the first dorsal spine and the second abdominal vertebra. A total of 352 fish were caught ranging from 20.9?mm to 209.5?mm (SL). Marginal increment analysis indicated that translucent rings were deposited annually during the colder season from October to January. The relationship of observed SL and age was described by the original form of the von Bertalanffy growth equation. Male and female growth models were significantly different. Overall growth was rapid during the first 2.5?years for both sexes, thereafter growth curves diverged. Males consequently reached larger sizes and greater ages. Maximum age for males and females was 13.5 and 9.5?years, respectively. Regression models of somatic growth (SL) as a function of vertebral and spine radii were significantly correlated (r?=?0.98 and r?=?0.96, respectively). According to the weight?Clength relationship, growth in R. aculeatus was negative allometric. Small recruits (SL?<?40?mm) appeared in high numbers in shallow coastal areas starting from August. This is the first record of age and growth for R. aculeatus. Our data suggest that the Picasso triggerfish is a moderately long-lived balistid and that the observed sex-specific growth pattern is driven by the fish??s polygynous mating system and different reproduction strategies of males and females.  相似文献   

Yam Cultivation on the East Coast of New Caledonia: adaptation of agriculture to social and economic changes     

Catherine Gaillard  Harley I. Manner 《The Australian geographer》2010,41(4):485-505

Agriculture represents less than 2 per cent of the GDP of New Caledonia where the economy (and wage-earning activities) is dominated by the service sector and the nickel industry. However, family farming remains strong, especially for the Indigenous Melanesian tribes of the east coast of New Caledonia. Yams (Dioscorea spp.) are still one of the pillars of traditional Kanak society despite the social and economic changes that followed colonisation by France. This study of Kanak yam cultivation on the north-eastern coast of New Caledonia underscores the fact that yam cultivation systems have greatly changed since the 1950s, when they were last described. In addition to customary gift exchanges and subsistence consumption, yams are increasingly being grown for market sales. Five cropping systems, three yam production systems, and three Kanak social activity systems are described and their linkages to each other are explained. There are three levels of Kanak market participation: none, transitional, and fully engaged, and the extent of market participation and associated technical choices defines farmers’ levels of cultural activity and the nature and characteristics of yam cultivation.  相似文献   

Minor changes in surface-water fertility across the oceanic anoxic event 1d (latest Albian,SE France) evidenced by calcareous nannofossils     

Fabienne?GiraudEmail author  Davide?Olivero  Fran?ois?Baudin  Stéphane?Reboulet  Bernard?Pittet  Olivier?Proux 《International Journal of Earth Sciences》2003,92(2):267-284

The latest Albian sediments deposited in the Vocontian basin in south-eastern France record the oceanic anoxic event (OAE) 1d, locally named the Breistroffer interval. They are represented by argillaceous marls and marls, containing organic matter (total organic carbon varying from 0.8 to 1%). Changes in calcareous nannofossil abundance and assemblage composition as well as macrofauna abundance, ichnofossil assemblage, and bioturbation intensity were analysed in order to evaluate the main palaeoenvironmental factors controlling the deposition of the OAE 1d sediments in this area. The pelagic carbonate production is limited and the carbonate fraction is predominantly of nektonic/benthic, and of allochthonous origin from carbonate platforms. The enrichment in organic carbon within the Breistroffer interval is weak and not associated with high surface-water productivity. The organic matter is mainly terrigenous. Its record is due to (1) a good preservation under dysoxic conditions within the sediments, and (2) a weak input of allochthonous carbonates. Eustatic fluctuations strongly influenced the variations of nannofossil and macrofauna abundances. Distinctive patterns in nannofossil assemblages and macrofauna abundances within the Breistroffer interval are also recognized, reflecting changes from mesotrophic to more oligotrophic conditions which are probably controlled by climate.  相似文献   

Luni-solar effects of geosynchronous orbits at the critical inclination     

Fabienne Delhaise  Alessandro Morbidelli 《Celestial Mechanics and Dynamical Astronomy》1993,57(1-2):155-173

The luni-solar effects of a geosynchronous artificial satellite orbiting near the critical inclination is investigated. To tackle this four-degrees-of-freedom problem, a preliminary exploration separately analyzing each harmonic formed by a combination of the satellite longitude of the node and the Moon longitude of the node is opportune. This study demonstrates that the dynamics induced by these harmonics does not show resonance phenomena. In a second approach, the number of degrees of freedom is halved by averaging the total Hamiltonian over the two non-resonant angular variables. A semi-numerical method can now be applied as was done when considering solely the inhomogeneity of the geopotential (see Delhaise et Henrard, 1992). Approximate surfaces of section are constructed in the plane of the inclination and argument of perigee. The main effects of the Sun and Moon attractions compared to the terrestrial attraction alone are a strong increase in the amplitude of libration in inclination (from 0.6° to 3.2°) and a decrease of the corresponding libration period (from the order of 200 years to the order of 20 years).Research Assistant for the Belgian National Fund for Scientific Research  相似文献