Dynamics of sea-surface temperature anomalies in the Southern Ocean diagnosed from a 2D mixed-layer model     

Frédéric Vivier  Daniele Iudicone  Fabiano Busdraghi  Young-Hyang Park 《Climate Dynamics》2010,34(2-3):153-184

We analyze the processes responsible for the generation and evolution of sea-surface temperature anomalies observed in the Southern Ocean during a decade based on a 2D diagnostic mixed-layer model in which geostrophic advection is prescribed from altimetry. Anomalous air–sea heat flux is the dominant term of the heat budget over most of the domain, while anomalous Ekman heat fluxes account for 20–40% of the variance in the latitude band 40°?60°S. In the ACC pathway, lateral fluxes of heat associated with anomalous geostrophic currents are a major contributor, dominating downstream of several topographic features, reflecting the influence of eddies and frontal migrations. A significant fraction of the variability of large-scale SST anomalies is correlated with either ENSO or the SAM, each mode contributing roughly equally. The relation between the heat budget terms and these climate modes is investigated, showing in particular that anomalous Ekman and air–sea heat fluxes have a co-operating effect (with regional exceptions), hence the large SST response associated with each mode. It is further shown that ENSO- or SAM-locked anomalous geostrophic currents generate substantial heat fluxes in all three basins with magnitude comparable with that of atmospheric forcings for ENSO, and smaller for the SAM except for limited areas. ENSO-locked forcings generate SST anomalies along the ACC pathway, and advection by mean flows is found to be a non-negligible contribution to the heat budget, exhibiting a wavenumber two zonal structure, characteristic of the Antarctic Circumpolar Wave. By contrast SAM-related forcings are predominantly zonally uniform along the ACC, hence smaller zonal SST gradients and a lesser role of mean advection, except in the SouthWest Atlantic. While modeled SST anomalies are significantly correlated with observations over most of the Southern Ocean, the analysis of the data-model discrepancies suggests that vertical ocean physics may play a significant role in the nonseasonal heat budget, especially in some key regions for mode water formation.  相似文献   

Impacts of precipitation events and land-use changes on West African river discharges during the years 1951–2000     

Tristan d’Orgeval  J. Polcher 《Climate Dynamics》2008,31(2-3):249-262

The aim of this article is to determine the main sources of the variability of large West African river discharges during the years 1951–2000. The analysis is based on river discharge simulations of ORCHIDEE Land-Surface Model forced by NCC (NCEP Corrected by CRU) over this period. In a first part, an analysis of the partitionning of precipitation in the different basins is given. It is first shown that total runoff is more variable and better correlated to precipitation than evapotranspiration over every basin on annual means. Then the more complex link between evapotranspiration and precipitation is investigated through correlation and regression analyses. Over the “dry” (soudano-sahelian) catchments, evapotranspiration is the most variable and mainly correlated to the annual precipitation. Over the “humid” (equatorial) catchment, it is mainly correlated to the season length and does not depend on other characteristics of the precipitation. Over the “intermediate” (guinean) catchments, annual precipitation and season length both play a role, along with the average intensity of rainfall events, and other characteristics such as the number of long breaks in the rainy season. A second part focuses on the way ORCHIDEE reproduces the variability of river discharges for the years 1951–2000. It is shown that relative anomalies are correctly simulated by ORCHIDEE forced by NCC over every catchment without taking into account any land-use change. Moreover, no significant difference is found in the accuracy with which ORCHIDEE simulates the humid (1953–1970) and the dry (1973–1990) periods over two selected catchments. This implies that the impact of land-use changes was much less important than the impact of precipitation changes over the years 1951–2000 in large West African catchments.  相似文献   

Crash-testing the cauldron code for joint lensing and dynamics analysis of early-type galaxies     

Matteo Barnabè  Carlo Nipoti  Léon V. E. Koopmans  Simona Vegetti  Luca Ciotti 《Monthly notices of the Royal Astronomical Society》2009,393(4):1114-1126

We apply the joint lensing and dynamics code for the analysis of early-type galaxies, 'Combined Algorithm for Unified Lensing and Dynamics ReconstructiON ( cauldron )', to a rotating N -body stellar system with dark matter halo which significantly violates the two major assumptions of the method, i.e. axial symmetry supported by a two-integral distribution function. The goal is to study how cauldron performs in an extreme case, and to determine which galaxy properties can still be robustly recovered. Three data sets, corresponding to orthogonal lines of sight, are generated from the N -body system and analysed with the identical procedure followed in the study of real lens galaxies, adopting an axisymmetric power-law total density distribution. We find that several global properties of the N -body system are recovered with remarkable accuracy, despite the fact that the adopted power-law model is too simple to account for the lack of symmetry of the true density distribution. In particular, the logarithmic slope of the total density distribution is robustly recovered to within less than 10 per cent (with the exception of the ill-constrained very inner regions), the inferred angle-averaged radial profile of the total mass closely follows the true distribution, and the dark matter fraction of the system (inside the effective radius) is correctly determined within ∼10 per cent of the total mass. Unless the line-of-sight direction is almost parallel to the total angular momentum vector of the system, reliably recovered quantities also include the angular momentum, the   V /σ  ratio and the anisotropy parameter δ. We conclude that the cauldron code can be safely and effectively applied to real early-type lens galaxies, also providing reliable information for the systems that depart significantly from the method's assumptions.  相似文献   

Binary gas sorption/desorption experiments on a bituminous coal: Simultaneous measurements on sorption kinetics,volumetric strain and acoustic emission     

Zofia Majewska  Grażyna Ceglarska-Stefańska  Stanisław Majewski  Jerzy Ziętek 《International Journal of Coal Geology》2009,77(1-2):90-102

There is still no clear understanding of the specific interactions between coal and gas molecules. In this context sorption–desorption studies of methane and carbon dioxide, both in a single gas environment and gas mixtures, are of fundamental interest. This paper presents the results of unique simultaneous measurements of sorption kinetics, volumetric strain and acoustic emission (AE) on three tetragonal coal samples subjected to sorption of carbon dioxide and methane mixtures. The coal was a high volatile bituminous C coal taken from the Budryk mine in the Upper Silesia Basin, Poland. Three different gas mixtures were used in the sorption tests, with dominant CO₂, with dominant CH₄ and a 50/50 mixture.The experimental set-up was designed specially for this study. It consisted of three individual units working together: (i) a unit for gas sorption experiments using a volumetric method, (ii) an AE apparatus for detecting, recording and analysing AE, and (iii) a strain meter for measuring strains induced in the coal sample by gas sorption/desorption. All measurements were computer aided.The experiments indicated that the coal tested showed preferential sorption of CH₄ at 2.6 MPa pressure and exhibited comparable affinities for CH₄ and CO₂ at higher pressures (4.0 MPa). The results of chromatographic analysis of the gas released on desorption suggested that the desorption of methane from the coal was favoured. The relationship between the volumetric strain and the amount of sorbed gas was found to be non-linear. These results were contrary to common opinions on the coal behaviour. Furthermore, it appeared that the swelling/shrinkage of coal was clearly influenced by the network of fractures. Besides, the AE and strain characteristics suggested common sources of sorption induced AE and strain.The present results may have implications for the sequestration of carbon dioxide in coal seams and enhanced coalbed methane recovery (ECBM).  相似文献   

Modelling of sediment supply from torrent catchments in the Western Alps using the sediment contributing area (SCA) approach     

Moritz Altmann  Florian Haas  Tobias Heckmann  Frédéric Liébault  Michael Becht 《地球表面变化过程与地形》2021,46(5):889-906

The production of coarse sediment in mountain landscapes depends mainly on the type and activity of geomorphic processes and topographic and natural conditions (e.g. vegetation cover) of these catchments. The supply of sediment from these slopes to mountain streams and its subsequent transport lead to sediment connectivity, which describes the integrated coupled state of these systems. Studies from the Northern Calcareous Alps show that the size of the sediment contributing area (SCA), a subset of the drainage area that effectively delivers sediment to the channel network, can be used as a predictor of sediment delivery to mountain streams. The SCA concept is delineated on a digital elevation model (DEM) using a set of rules related to the steepness and length of slopes directly adjacent to the channel network, the gradient of the latter and the vegetation cover. The present study investigates the applicability of this concept to the Western Alps to identify geomorphologically active areas and to estimate mean annual sediment yield (SY) in mainly debris-flow-prone catchments. We use a statistical approach that shows a parameter optimisation and a linear regression of SY on SCA extent. We use a dataset of ~25 years of assessed coarse sediment accumulation in 35 sediment retention basins. In the investigated catchments, sediment transport is governed by several factors, mainly by the extent of vegetation-free areas with a minimum slope of 23° that is coupled to the channel network with a very low gradient of the latter. With our improved framework, we can show that the SCA approach can be applied to catchments that are widely distributed, in a large spatial scale (hectare area) and very heterogeneous in their properties. In general, the investigated catchments show high connectivity, resulting in significant correlations between long-term average yield and the size of the SCA.  相似文献   

Spin rate distribution of small asteroids     

P. Pravec  A.W. Harris  B.D. Warner  K. Hornoch  D. Higgins  A. Galád  Š. Gajdoš  J. Világi  Yu.N. Krugly  V. Chiorny  W.R. Cooney Jr.  D. Terrell  R.D. Stephens  V. Reddy  F. Colas  R. Durkee  R.A. Koff 《Icarus》2008,197(2):497-504

The spin rate distribution of main belt/Mars crossing (MB/MC) asteroids with diameters 3-15 km is uniform in the range from f=1 to 9.5 d⁻¹, and there is an excess of slow rotators with f<1 d⁻¹. The observed distribution appears to be controlled by the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect. The magnitude of the excess of slow rotators is related to the residence time of slowed down asteroids in the excess and the rate of spin rate change outside the excess. We estimated a median YORP spin rate change of ≈0.022 d⁻¹/Myr for asteroids in our sample (i.e., a median time in which the spin rate changes by 1 d⁻¹ is ≈45 Myr), thus the residence time of slowed down asteroids in the excess is ≈110 Myr. The spin rate distribution of near-Earth asteroids (NEAs) with sizes in the range 0.2-3 km (∼5 times smaller in median diameter than the MB/MC asteroids sample) shows a similar excess of slow rotators, but there is also a concentration of NEAs at fast spin rates with f=9-10 d⁻¹. The concentration at fast spin rates is correlated with a narrower distribution of spin rates of primaries of binary systems among NEAs; the difference may be due to the apparently more evolved population of binaries among MB/MC asteroids.  相似文献   

Comprehensive study of the drying behavior of Boom clay: Experimental investigation and numerical modeling          下载免费PDF全文

Julien Hubert  Erwan Plougonven  Noémie Prime  Angélique Léonard  Frédéric Collin 《国际地质力学数值与分析法杂志》2018,42(2):211-230

This paper presents a thermo‐hydro‐mechanical framework to model the drying behavior of Boom clay. First, the experimental campaign conducted Noémie Prime is briefly presented because it is used to validate the model. The data acquisition and processing is emphasized because of the use of X‐ray microtomography to be able to more accurately compare experimental and numerical strain fields. The different submodels are introduced. Numerical simulations are performed to illustrate the capability of the proposed model to reproduce the observed behavior. Finally, a comprehensive sensitivity study on several key model parameters associated with the water retention curve, and the permeability of the medium, is performed to get a better understanding of the physics behind the coupled model.  相似文献   

Solid–fluid transition modelling in geomaterials and application to a mudflow interacting with an obstacle     

Noémie Prime  Frédéric Dufour  Félix Darve 《国际地质力学数值与分析法杂志》2014,38(13):1341-1361

Given the contrasting behaviour observed for geomaterials, for example, during landslides of the flow type, this contribution proposes an original constitutive model, which associates both an elasto‐plastic relation and a Bingham viscous law linked by a mechanical transition criterion. This last is defined as the second‐order work sign for each material point, which is a general criterion for divergence instabilities. Finite element method with Lagrangian integration points is chosen as a framework for implementing the new model because of its well‐known ability to deal with both solid and fluid behaviours in large deformation processes. A first boundary model considering a sample of initially stable soil, a slope and an obstacle is performed. The results show the power of the constitutive model because the consistent evolution of initiation, propagation and arrest of the mudflow is described. A parametric study is led on various plastic and viscous parameters to determine their influence on the flow development and arrest. Finally, forces against the obstacle are compared with good agreement with those of other authors for the same geometry and a pure viscous behaviour. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

The integrated use of GPS/GLONASS observations in network code differential positioning     

Przestrzelski  Paweł  Bakuła  Mieczysław  Galas  Roman 《GPS Solutions》2017,21(2):627-638

GPS Solutions - We present the methodology and results of GPS/GLONASS integration in network code differential positioning for regional coverage across Poland using single frequency. Previous...  相似文献   

Performance of CMORPH,TMPA, and PERSIANN rainfall datasets over plain,mountainous, and glacial regions of Pakistan     

Yawar?HussainEmail author  Frédéric?Satgé  Muhammad?Babar?Hussain  Hernan?Martinez-Carvajal  Marie-Paule?Bonnet  Martin?Cárdenas-Soto  Henrique?Llacer?Roig  Gulraiz?Akhter 《Theoretical and Applied Climatology》2018,131(3-4):1119-1132

The present study aims at the assessment of six satellite rainfall estimates (SREs) in Pakistan. For each assessed products, both real-time (RT) and post adjusted (Adj) versions are considered to highlight their potential benefits in the rainfall estimation at annual, monthly, and daily temporal scales. Three geomorphological climatic zones, i.e., plain, mountainous, and glacial are taken under considerations for the determination of relative potentials of these SREs over Pakistan at global and regional scales. All SREs, in general, have well captured the annual north-south rainfall decreasing patterns and rainfall amounts over the typical arid regions of the country. Regarding the zonal approach, the performance of all SREs has remained good over mountainous region comparative to arid regions. This poor performance in accurate rainfall estimation of all the six SREs over arid regions has made their use questionable in these regions. Over glacier region, all SREs have highly overestimated the rainfall. One possible cause of this overestimation may be due to the low surface temperature and radiation absorption over snow and ice cover, resulting in their misidentification with rainy clouds as daily false alarm ratio has increased from mountainous to glacial regions. Among RT products, CMORPH-RT is the most biased product. The Bias was almost removed on CMORPH-Adj thanks to the gauge adjustment. On a general way, all Adj versions outperformed their respective RT versions at all considered temporal scales and have confirmed the positive effects of gauge adjustment. CMORPH-Adj and TMPA-Adj have shown the best agreement with in situ data in terms of Bias, RMSE, and CC over the entire study area.  相似文献