References of "Ouberdous, Mohamed"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailEffects of CO2, continental distribution, topography and vegetation changes on the climate at the Middle Miocene: a model study
Henrot, Alexandra ULg; François, Louis ULg; Favre, Eric ULg et al

in Climate of the Past (2010), 6

The Middle Miocene was one of the last warm periods of the Neogene, culminating with the Middle Miocene Climatic Optimum (MMCO, approximatively 17–15 Ma). Several proxy-based reconstructions support ... [more ▼]

The Middle Miocene was one of the last warm periods of the Neogene, culminating with the Middle Miocene Climatic Optimum (MMCO, approximatively 17–15 Ma). Several proxy-based reconstructions support warmer and more humid climate during the MMCO. The mechanisms responsible for the warmer climate at the MMCO and particularly the role of the atmospheric carbon dioxide are still highly debated. Here we carried out a series of sensitivity experiments with the model of intermediate complexity Planet Simulator, investigating the contributions of the absence of ice on the continents, the opening of the Central American and Eastern Tethys Seaways, the lowering of the topography on land, the effect of various atmospheric CO2 concentrations and the vegetation feedback. Our results show that a higher than present-day CO2 concentration is necessary to generate a warmer climate at all latitudes at the Middle Miocene, in agreement with the terrestrial proxy reconstructions which suggest high atmospheric CO2 concentrations at the MMCO. Nevertheless, the changes in sea-surface conditions, the lowering of the topography on land and the vegetation feedback also produce significant local warming that may, locally, even be stronger than the CO2 induced temperature increases. The lowering of the topography leads to a more zonal atmospheric circulation and allows the westerly flow to continue over the lowered Plateaus at mid-latitudes. The reduced height of the Tibetan Plateau notably prevents the development of a monsoon-like circulation, whereas the reduction of elevations of the North American and European reliefs strongly increases precipitation from northwestern to eastern Europe. The changes in vegetation cover contribute to maintain and even to intensify the warm and humid conditions produced by the other factors, suggesting that the vegetation-climate interactions could help to improve the model-data comparison. [less ▲]

Detailed reference viewed: 40 (5 ULg)
Full Text
See detailDIVA: new features
Beckers, Jean-Marie ULg; Alvera Azcarate, Aïda ULg; Barth, Alexander ULg et al

Scientific conference (2009, October 23)

Detailed reference viewed: 17 (3 ULg)
Full Text
Peer Reviewed
See detailHigh-resolution Climatology of the North-East Atlantic using Data-Interpolating Variational Analysis
Troupin, Charles ULg; Machín, Francisco; Ouberdous, Mohamed ULg et al

Conference (2009, April 21)

Detailed reference viewed: 19 (3 ULg)
Full Text
Peer Reviewed
See detailEvolution of Western Mediterranean Sea Surface Temperature between 1985 and 2005
Troupin, Charles ULg; Lenartz, Fabian; Sirjacobs, Damien ULg et al

Conference (2009, April 20)

Detailed reference viewed: 18 (2 ULg)
Full Text
Peer Reviewed
See detailS,T-climatologies of the North Sea using the Variational Inverse Method
Scory, Serge; Ouberdous, Mohamed ULg; Troupin, Charles ULg et al

Poster (2009, April 19)

Detailed reference viewed: 18 (0 ULg)
Full Text
See detailWeekly satellite sea surface temperature around Corsica, a DINEOF analysis of AVHRR data (1998), foreseeing comparison with interpolated and modelled fields.
Sirjacobs, Damien ULg; Lenartz, Fabian ULg; Troupin, Charles ULg et al

Poster (2009, January)

Providing wide coverage and high spatio-temporal resolution, SST satellite archives are valuable sources of information for sound understanding of the ocean dynamics, including validation of ... [more ▼]

Providing wide coverage and high spatio-temporal resolution, SST satellite archives are valuable sources of information for sound understanding of the ocean dynamics, including validation of hydrodynamical modelling studies. Yet original SST fields have also many gaps (clouds, retrieval problems), but they are known to exhibit strong spatial and temporal correlations for regions of similar dynamics. This is exploited by the parameter free statistical technique DINEOF (Data Interpolation with Empirical Orthogonal Functions) [Alvera-Azcárate et al. (2005) Ocean Modell.; Beckers et al. (2006) Ocean Sciences] to produce full weekly analysis of the variability of the sea surface temperature (SST) around Corsica and in the Ligurian Sea at weekly temporal resolution during the year 1998. A detection of outliers implemented in DINEOF analysis is tested for pointing out unusual or invalid SST data. This study is realised foreseeing a comparison of DINEOF weekly averaged reconstructed fields with those obtained by interpolating methods on the same dataset (Data Interpolating Variationnal Analysis and Optimal Interpolation schemes), and with outputs of an implementation of the GHER 3D model in this area. [less ▲]

Detailed reference viewed: 71 (23 ULg)
See detailA web interface for griding arbitrarily distributed in situ data based on Data-Interpolating Variational Analysis (Diva)
Barth, Alexander ULg; Alvera Azcarate, Aïda ULg; Troupin, Charles ULg et al

Conference (2009)

Spatial interpolation of observations on a regular grid is a common task in many ceanographic disciplines (and geosciences in general). It is often used to create climatological maps for physical ... [more ▼]

Spatial interpolation of observations on a regular grid is a common task in many ceanographic disciplines (and geosciences in general). It is often used to create climatological maps for physical, biological or chemical parameters representing e.g. monthly or seasonally averaged fields. Since instantaneous observations can not be directly related to a field representing an average, simple spatial interpolation of observations is in general not acceptable. Diva (Data-Interpolating Variational Analysis) is an analysis tool which takes the error in the observations and the typical spatial scale of the underlying field into account. Barriers due to the coastline and the topography in general and also currents estimates (if available) are used to propagate the information of a given observation spatially. Diva is a command-line driven application written in Fortran and Shell Scripts. The observations and parameters are specified by the user using text files. The analyzed field and the expected error variance are returned as NetCDF files. This form of interaction with Diva is very similar to other high-performance codes and is a familiar approach for ocean modelers. However it represents a steep learning curve for oceanographers from other disciplines not familiar with command-line applications and programming. To make Diva easier to use, a web interface has been developed (http://gher-diva.phys.ulg.ac.be). Installation and compilation of Diva is therefore not required. The user can directly upload his/her data in ASCII format and enter several parameters for the analysis. The analyzed field, location of the observations, and the error mask are presented as different layers using the Web Map Service protocol. They are visualized in the browser using the Javascript library OpenLayers allowing the user to interact with layers (for example zooming and panning). Finally, the results can be downloaded as a NetCDF file, Matlab file (also readable in Octave, an open source program similar to Matlab) and Keyhole Markup Language (KML) file for visualisation in applications such as Google Earth. [less ▲]

Detailed reference viewed: 60 (7 ULg)
Full Text
See detailUsing Diva on large datasets: applications and tips
Troupin, Charles ULg; Ouberdous, Mohamed ULg; Lenartz, Fabian et al

Scientific conference (2008, October 16)

Detailed reference viewed: 17 (0 ULg)
Full Text
See detailClimatology and circulation of the Azores-Canary region by Data-Interpolation Variational Analysis
Troupin, Charles ULg; Machín, Francisco; Ouberdous, Mohamed ULg et al

Poster (2008, June 02)

Detailed reference viewed: 16 (0 ULg)
Full Text
See detailThree-dimensional analysis of oceanographic data with the software DIVA
Troupin, Charles ULg; Ouberdous, Mohamed ULg; Machín, Francisco et al

Poster (2008, April 13)

Detailed reference viewed: 32 (0 ULg)
Full Text
See detailDIVA-4.2.1: presentation of the new features
Troupin, Charles ULg; Machín, Francisco; Ouberdous, Mohamed ULg et al

Poster (2008, April 03)

Detailed reference viewed: 14 (0 ULg)
Full Text
See detailImplementation of hydrostatic constraint in the software DIVA: Theory and applications
Troupin, Charles ULg; Ouberdous, Mohamed ULg; Rixen, Michel et al

Poster (2008, March 31)

Detailed reference viewed: 11 (1 ULg)
Peer Reviewed
See detailApplication of a data-interpolating variational analysis (DIVA) tool to physical and biogeochemical measurements covering the Black Sea
Joassin; Beckers, Jean-Marie ULg; Boicenco, L. et al

in Climate change in the Black Sea, hypthesis, observations, trends scenarios and mitigation strategy for the ecosystem (2008)

The European project SESAME (Southern European Seas: Assessing and Modelling Ecosystem changes) is dedicated to the assessment of ecological changes in the Mediterranean and Black seas during these last ... [more ▼]

The European project SESAME (Southern European Seas: Assessing and Modelling Ecosystem changes) is dedicated to the assessment of ecological changes in the Mediterranean and Black seas during these last decades. This assessment will be done by combining statistical analysis of available data and the development of a 3D hydrodynamical-biogeochemical model. Data available since 1960 for the Black Sea from the databases MEDAR and NATO have been completed with data provided by SESAME partners. These data sets have been analyzed using DIVA, a geostatistical analysis tool developed by the GHER laboratory of the University of Liège. The DIVA analysis relies on a finite element resolution, taking into account coastlines, sub-basins, and advection by ocean currents. DIVA analysis generates spatially interpolated fields for biogeochemical and physical variables. Outputs consist in sets of analysis as well as error fields, and colorimetric scaled maps related to several depth layers. Biogeochemical variables considered consist in measures of chlorophyll, inorganic nutrients concentration, and phytoplankton abundances; physical variables consist in temperature and salinity. These treatments of the Black sea data sets offer an overview of the global pattern of the Black sea biogeochemical structure, and its evolution through the time periods concerned by the project. The interpolated fields generated by the DIVA tool will be used to validate the outputs of the 3D hydrodynamical-biogeochemical model developed for the north-western shelf of the Black sea in the framework of SESAME. [less ▲]

Detailed reference viewed: 19 (2 ULg)
Full Text
Peer Reviewed
See detailThree-dimensional analysis of oceanographic data with the software DIVA
Troupin, Charles ULg; Ouberdous, Mohamed ULg; Rixen, Michel et al

in Geophysical Research Abstracts (2008)

In oceanography, the process of gridding data is frequently used for various purposes, e.g. initialization of hydrodynamic models, or graphical representation of sparse data. DIVA (Data-Interpolating ... [more ▼]

In oceanography, the process of gridding data is frequently used for various purposes, e.g. initialization of hydrodynamic models, or graphical representation of sparse data. DIVA (Data-Interpolating Variational Analysis) is designed to perform such gridding tasks. It has the advantage of taking into account the intrinsic nature of oceanographic data, i.e. uncertainty in in situ measurements and anisotropy due to advection and irregular coastlines and topography. Three-dimensional reconstruction of temperature and salinity fields is achieved by stacking horizontal layers where independent analysis with DIVA are performed. Nevertheless, analysis in regions void of data may result in the presence of static instabilities between two or more consecutive layers. The method implemented in DIVA to remove such kinds of instabilities is the object of the present work. It consists of adding pseudo-data from one layer to the upper adjacent layer in order to create stable stratification in the vicinity of instabilities. Two approaches for assigning values to the pseudo data are tested: the first is called the mixing approach and aims at simulating a mixing process between two layers; the second is called the minimal perturbation, as it strives to minimise the perturbations inthe pseudo-data. A realistic application using temperature and salinity profiles in the North Atlantic is carried out and the results are compared with World Ocean Atlas climatologies. [less ▲]

Detailed reference viewed: 55 (5 ULg)
See detailThe combined impact of changing terrestrial organic carbon reservoirs and fractionation effects induced by changing carbonate ion concentrations on the glacial-interglacial marine C-13 record
Munhoven, Guy ULg; François, Louis ULg; Ouberdous, Mohamed ULg

Conference (2005, April 27)

On the basis of the marine and atmospheric glacial-interglacial C-13 isotopic records, it has been calculated that the land biospheric carbon stock must have increased by 270–720 GtC from the Last Glacial ... [more ▼]

On the basis of the marine and atmospheric glacial-interglacial C-13 isotopic records, it has been calculated that the land biospheric carbon stock must have increased by 270–720 GtC from the Last Glacial Maximum (LGM) to the present. Estimates derived from vegetation mapping based on palynological or sedimentological data generally indicate a larger increase of the biospheric stock in the range of 700–1350 GtC and above. Although there is some overlap between the two ranges, they substantially disagree. Further complications arise when carbonate-ion dependent fractionation effects in the marine C-13 record are considered. A detailed budget of the C-13 isotope in the land biosphere at the LGM, as well as in the other reservoirs of the global carbon cycle is therefore required. Here, we analyse the response of the atmosphere–ocean–surface sediment system under the influence of variable release and uptake fluxes of C by the terrestrial biosphere. Glacial-interglacial variations of the carbon stocks and isotopic budgets of the land biosphere were derived from simulation experiments carried out with the global biosphere model CARAIB (CARbon Assimilation In the Biosphere) under boundary conditions typical for the Last Glacial Maximum and for mid-Holocene times. CARAIB uses a mechanistic description of both C3 and C4 photosynthetic pathways. It thus provides information on the C-13 signature of carbon fluxes involved. Using the eleven-box model MBM of the ocean-atmosphere system, we then investigate the effect of these biospheric changes on the oceanic carbon cycle and the CO2 concentration in the atmosphere. MBM has a complete representation of the transfer processes of carbon and alkalinity from the land to the ocean, and between the ocean and the surface sediment, including parameterisations for processes in the shelf area. MBM also considers C-13 signatures of the carbon fluxes and stocks represented. On the basis of empirical relationships for the incorporation of C-13 isotopes in foraminiferal shells as a function of carbonate ion concentration, synthetic carbon isotopic records are generated from the calculated seawater C-13 isotopic evolution, helping to better constrain estimates of the land biosphere carbon stock changes derived from the marine C-13 record. These simulations also test various scenarios for the alkalinity input to the system from weathering, which, through their effect on carbonate ion concentration, may also impinge to a non negligible extent on C-13 variations recorded in deep-sea sediments. [less ▲]

Detailed reference viewed: 13 (0 ULg)