Low and high frequency Madden–Julian oscillations in austral summer: interannual variations     

Takeshi Izumo  Sébastien Masson  Jérome Vialard  Clément de Boyer Montegut  Swadhin K. Behera  Gurvan Madec  Keiko Takahashi  Toshio Yamagata 《Climate Dynamics》2010,35(4):669-683

The Madden–Julian oscillation (MJO) is the main component of intraseasonal variability of the tropical convection, with clear climatic impacts at an almost-global scale. Based on satellite observations, it is shown that there are two types of austral-summer MJO events (broadly defined as 30–120 days convective variability with eastward propagation of about 5 m/s). Equatorial MJO events have a period of 30–50 days and tend to be symmetric about the equator, whereas MJO events centered near 8°S tend to have a longer period of 55–100 days. The lower-frequency variability is associated with a strong upper-ocean response, having a clear signature in both sea surface temperature and its diurnal cycle. These two MJO types have different interannual variations, and are modulated by the Indian Ocean Dipole (IOD). Following a negative IOD event, the lower-frequency southern MJO variability increases, while the higher-frequency equatorial MJO strongly diminishes. We propose two possible explanations for this change in properties of the MJO. One possibility is that changes in the background atmospheric circulation after an IOD favour the development of the low-frequency MJO. The other possibility is that the shallower thermocline ridge and mixed layer depth, by enhancing SST intraseasonal variability and thus ocean–atmosphere coupling in the southwest Indian Ocean (the breeding ground of southern MJO onset), favour the lower-frequency southern MJO variability.  相似文献   

Extreme geomagnetic storms,recent Gleissberg cycles and space era-superintense storms     

W.D. Gonzalez  E. Echer  A.L. Clúa de Gonzalez  B.T. Tsurutani  G.S. Lakhina 《Journal of Atmospheric and Solar》2011,73(11-12):1447-1453

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Floods control the influence of environmental gradients on the diversity of zooplankton communities in a neotropical floodplain     

Nadson Ressyé Simões  Juliana Déo Dias  Clarice Maria Leal  Louizi de Souza Magalhães Braghin  Fábio Amodêo Lansac-Tôha  Cláudia Costa Bonecker 《Aquatic Sciences - Research Across Boundaries》2013,75(4):607-617

Floodplains show a high biodiversity due to their spatial heterogeneity and temporal variability, which are governed by environmental dynamics resulting from the flood pulse. We evaluated the importance of this driving force, the flood pulse, in the structuring of environmental gradients that influence species diversity in a neotropical floodplain. Gamma (γ) and alpha (α) zooplankton diversities were higher in the year with a typical flood pulse (2010), indicating that flood dynamics contributed to high diversity component values. We found significant relationships between α- and β-diversity and local environmental gradients, indicating that in years with a flood pulse, environmental filters might be the dominant mechanisms that structure the zooplankton community. Additive partitioning of γ-diversity showed that even in 2000 with atypical flood conditions, zooplankton diversities showed non-random patterns of spatial distribution and temporal variation in the floodplain. Our results indicate that the driving force of a floodplain can determine the spatial distribution of α- and β-diversity of aquatic communities owing to its primary effect on environmental filters. Therefore, if human activities that influence this driving force, such as water regulation, affect those environmental filters, floodplain biodiversity may decline.  相似文献   

The role of laboratory experiments in the characterisation of silicon–based cosmic material     

L. Colangeli  Th. Henning  J.R. Brucato  D. Clément  D. Fabian  O. Guillois  F. Huisken  C. Jäger  E.K. Jessberger  A. Jones  G. Ledoux  G. Manicó  V. Mennella  F.J. Molster  H. Mutschke  V. Pirronello  C. Reynaud  J. Roser  G. Vidali  L.B.F.M. Waters 《Astronomy and Astrophysics Review》2003,11(2-3):97-152

Abstract. Silicate grains in space have attracted recently a wide interest of astrophysicists due to the increasing amount and quality of observational data, especially thanks to the results obtained by the Infrared Space Observatory. The observations have shown that the presence of silicates is ubiquitous in space and that their properties vary with environmental characteristics. Silicates, together with carbon, are the principal components of solid matter in space. Since their formation, silicate grains cross many environments characterised by different physical and chemical conditions which can induce changes to their nature. Moreover, the transformations experienced in the interplay of silicate grains and the medium where they are dipped, are part of a series of processes which are the subject of possible changes in the nature of the space environment itself. Then, chemical and physical changes of silicate grains during their life play a key role in the chemical evolution of the entire Galaxy. The knowledge of silicate properties related to the conditions where they are found in space is strictly related to the study in the laboratory of the possible formation and transformation mechanisms they experience. The application of production and processing methods, capable to reproduce actual space conditions, together with the use of analytical techniques to investigate the nature of the material samples, form a subject of a complex laboratory experimental approach directed to the understanding of cosmic matter. The goal of the present paper is to review the experimental methods applied in various laboratories to the simulation and characterisation of cosmic silicate analogues. The paper describes also laboratory studies of the chemical reactions undergone and induced by silicate grains. The comparison of available laboratory results with observational data shows the essential constraints imposed by astronomical observations and, at the same time, indicates the most puzzling problems that deserve particular attention for the future. The outstanding open problems are reported and discussed. The final purpose of this paper is to provide an overview of the present stage of knowledge about silicates in space and to provide to the reader some indication of the future developments in the field. Received 25 April 2002 / Published online 14 November 2002 Send offprint requests to: L. Colangeli e–mail: colangeli@na.astro.it  相似文献   

Estimating return periods for daily precipitation extreme events over the Brazilian Amazon     

Eliane Barbosa Santos  Paulo Sérgio Lucio  Cláudio Moisés Santos e Silva 《Theoretical and Applied Climatology》2016,126(3-4):585-595

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On several numerical strategies to solve Richards’ equation in heterogeneous media with finite volumes     

Bassetto  Sabrina  Cancès  Clément  Enchéry  Guillaume  Tran  Quang-Huy 《Computational Geosciences》2022,26(5):1297-1322

Computational Geosciences - We propose several numerical approaches building on upstream mobility two-point flux approximation finite volumes to solve Richards’ equation in domains made of...  相似文献   

Kampf um die Fläche     

H. Cl. 《International Journal of Earth Sciences》1940,31(5-6):321-327

Ohne Zusammenfassung  相似文献   

Declutching control of a wave energy converter     

Aurélien Babarit  Michel Guglielmi  Alain H. Clément 《Ocean Engineering》2009,36(12-13):1015-1024

When hydraulic power take off (PTO) is used to convert the mechanical energy of a wave energy converter (WEC) into a more useful form of energy, the PTO force needs to be controlled. Continuous controlled variation of the PTO force can be approximated by a set of discrete values. This can be implemented using either variable displacement pumps or several hydraulic cylinders or several high pressure accumulators with different pressure levels. This pseudo-continuous control could lead to a complex PTO with a lot of components. A simpler way for controlling this hydraulic PTO is declutching control, which consists in switching on and off alternatively the wave energy converter's PTO. This can be achieved practically using a simple by-pass valve. In this paper, the control law of the valve is determined by using the optimal command theory. It is shown that, theoretically when considering a wave activated body type of WEC, declutching control can lead to energy absorption performance at least equivalent to that of pseudo-continuous control. The method is then applied to the case of the SEAREV wave energy converter, and it is shown than declutching control can even lead to a higher energy absorption, both in regular and irregular waves.  相似文献   

Western boundary upwelling dynamics off Oman     

Clément Vic  Xavier Capet  Guillaume Roullet  Xavier Carton 《Ocean Dynamics》2017,67(5):585-595

Despite its climatic and ecosystemic significance, the coastal upwelling that takes place off Oman is not well understood. A primitive-equation, regional model forced by climatological wind stress is used to investigate its dynamics and to compare it with the better-known Eastern Boundary Upwellings (EBUs). The solution compares favorably with existing observations, simulating well the seasonal cycles of thermal structure, surface circulation (mean and turbulent), and sea-surface temperature (SST). There is a 1.5-month lag between the maximum of the upwelling-favorable wind-stress-curl forcing and the oceanic response (minima in sea-surface height and SST), which we attribute to onshore-propagating Rossby waves. A southwestward-flowing undercurrent (opposite to the direction of the near-surface flow) is also simulated with a core depth of 1000 m, much deeper than found in EBUs (150–200 m). An EKE budget reveals that, in contrast to EBUs, the upwelling jet is more prone to barotropic than baroclinic instability and the contribution of locally-generated instabilities to EKE is higher by an order of magnitude. Advection and redistribution of EKE by standing mesoscale features also play a significant role in EKE budget.  相似文献   

Depositional controls on a hypertidal barrier-spit system architecture and evolution,Pointe du Banc spit,north-western France     

Mikkel Fruergaard  Bernadette Tessier  Clément Poirier  Dominique Mouazé  Pierre Weill  Suzanne Noël 《Sedimentology》2020,67(1):502-533

Physical stratigraphy, architecture and evolution of barrier systems in hypertidal environments (tidal range above 6 m) are understudied, and depositional controls are poorly understood compared with wave-dominated barrier systems and barrier spits in microtidal, mesotidal and macrotidal settings. Based on vibracores, ground-penetrating radar, radiocarbon and optically stimulated luminescence age data, the formation and evolution of the hypertidal barrier system of Pointe du Banc, north-western France has been reconstructed. The study shows that the barrier spit has a complex composite sedimentary architecture consisting of wave-dominated and tide-dominated sedimentary bodies. A morpho-sedimentary model is presented that demonstrates how barrier-spit progradation resulting from littoral drift was the main manner of spit elongation, whereas sediment convergence caused by landward migration of swash bars and seaward migration of tidal dunes caused the spit terminus to grow in height and width. These results suggest that long-term accretion rates varied considerably in response to changes in sediment supply. Variations in storminess together with the large-scale topography of the coast controlled the sediment supply and thus the evolution of the barrier system during latest Holocene. Despite architectural complexity, hypertidal barrier systems preserve records of past climate changes.  相似文献