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71.
The amount of useful scientific data that a space-borne telescope produces is often limited by the available telemetry of
the platform. General purpose image compression schemes are usually used to compress the image either lossy or losslessly.
These schemes do not take into account the fact that pixel values of typical solar images are only known to within a certain
uncertainty range. We present a preprocessing method to enhance the performance (compression ratio) of any subsequent image
compression scheme. The method uses estimates of the photon shot and thermal noises to compute a recoding look-up table that
maps the initial data into uncertainty intervals. The recoding method is lossy in a mathematical sense but lossless in a physical
sense, since the image alterations are guaranteed to be smaller than the Poisson noise. The performance of any further compression
algorithm is enhanced while achieving a known guaranteed maximum absolute error for each pixel in the case of lossless compression.
This revised version was published online in October 2005 with corrections to one of the authors' names. 相似文献
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74.
Aurore Voldoire Bas Eickhout Michiel Schaeffer Jean-François Royer Fabrice Chauvin 《Climate Dynamics》2007,29(2-3):177-193
To include land-use dynamics in a general circulation model (GCM), the physical system has to be linked to a system that represents
socio-economy. This issue is addressed by coupling an integrated assessment model, IMAGE2.2, to an ocean–atmosphere GCM, CNRM-CM3.
In the new system, IMAGE2.2 provides CNRM-CM3 with all the external forcings that are scenario dependent: greenhouse gas (GHGs)
concentrations, sulfate aerosols charge and land cover. Conversely, the GCM gives IMAGE changes in mean temperature and precipitation.
With this new system, we have run an adapted scenario of the IPCC SRES scenario family. We have chosen a single scenario with
maximum land-use changes (SRES A2), to illustrate some important feedback issues. Even in this two-way coupled model set-up,
land use in this scenario is mainly driven by demographic and agricultural practices, which overpowers a potential influence
of climate feedbacks on land-use patterns. This suggests that for scenarios in which socio-economically driven land-use change
is very large, land-use changes can be incorporated in GCM simulations as a one-way driving force, without taking into account
climate feedbacks. The dynamics of natural vegetation is more closely linked to climate but the time-scale of changes is of
the order of a century. Thus, the coupling between natural vegetation and climate could generate important feedbacks but these
effects are relevant mainly for multi-centennial simulations. 相似文献
75.
Mathieu Joly Aurore Voldoire Hervé Douville Pascal Terray Jean-François Royer 《Climate Dynamics》2007,29(1):1-20
A set of 12 state-of-the-art coupled ocean-atmosphere general circulation models (OAGCMs) is explored to assess their ability to simulate the main teleconnections between the West African monsoon (WAM) and the tropical sea surface temperatures (SSTs) at the interannual to multi-decadal time scales. Such teleconnections are indeed responsible for the main modes of precipitation variability observed over West Africa and represent an interesting benchmark for the models that have contributed to the fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC4). The evaluation is based on a maximum covariance analysis (MCA) applied on tropical SSTs and WAM rainfall. To distinguish between interannual and multi-decadal variability, all datasets are partitioned into low-frequency (LF) and high-frequency (HF) components prior to analysis. First applied to HF observations, the MCA reveals two major teleconnections. The first mode highlights the strong influence of the El Niño Southern Oscillation (ENSO). The second mode reveals a relationship between the SST in the Gulf of Guinea and the northward migration of the monsoon rainbelt over the West African continent. When applied to HF outputs of the twentieth century IPCC4 simulations, the MCA provides heterogeneous results. Most simulations show a single dominant Pacific teleconnection, which is, however, of the wrong sign for half of the models. Only one model shows a significant second mode, emphasizing the OAGCMs’ difficulty in simulating the response of the African rainbelt to Atlantic SST anomalies that are not synchronous with Pacific anomalies. The LF modulation of these HF teleconnections is then explored through running correlations between expansion coefficients (ECs) for SSTs and precipitation. The observed time series indicate that both Pacific and Atlantic teleconnections get stronger during the twentieth century. The IPCC4 simulations of the twentieth and twenty-first centuries do not show any significant change in the pattern of the teleconnections, but the dominant ENSO teleconnection also exhibits a significant strengthening, thereby suggesting that the observed trend could be partly a response to the anthropogenic forcing. Finally, the MCA is also applied to the LF data. The first observed mode reveals a well-known inter-hemispheric SST pattern that is strongly related to the multi-decadal variability of the WAM rainfall dominated by the severe drying trend from the 1950s to the 1980s. Whereas recent studies suggest that this drying could be partly caused by anthropogenic forcings, only 5 among the 12 IPCC4 models capture some features of this LF coupled mode. This result suggests the need for a more detailed validation of the WAM variability, including a dynamical interpretation of the SST–rainfall relationships. 相似文献
76.
Pierre-Yves Bourlier Patrick Lachassagne Jean-François Desprats Emmanuel Gille 《Comptes Rendus Geoscience》2005,337(7):663-673
In volcanic areas, the quality of the geological data at the various scales is of paramount importance for the estimation of aquifer potentialities and thus for groundwater exploitation. Geological and hydrogeological investigation (synthesis of existing data, field geological observations, reconstruction of the infra-volcanic morphology, stream gauging, field hydrogeology, etc.) have been performed on the 450-km2 Aubrac basaltic plateau (Massif Central, France). These results allow us to specify the hydrological structure and functioning of this volcanic plateau that were quite unknown before. It is mainly constituted by the piling up of lava flows resting on a plutonic and metamorphic substratum. This volcanic unit constitutes an aquifer of regional importance whose groundwater resources are currently underexploited. These results allow us to delineate zones and strategies for priority hydrogeological prospecting. To cite this article: P.-Y. Bourlier et al., C. R. Geoscience 337 (2005). 相似文献
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78.
Annie Souriau Matthieu Sylvander Valérie Maupin Jean-François Fels Alexis Rigo 《Comptes Rendus Geoscience》2002,334(3):155-161
This study presents a detailed analysis of the seismic records of a strong explosion that occurred on 21 September 2001 at a chemical complex located south of Toulouse, France, and provoked important damages. The explosion, which is equivalent to a 3.4 magnitude earthquake, has been recorded at most of the stations of the National Seismological Network, as well as at a station under test at the ‘Observatoire Midi-Pyrénées’, 4.2 km away from the epicentre. The main seismic phases are interpreted using the known crustal structures, and a modelling with synthetic seismograms is performed. To cite this article: A. Souriau et al., C. R. Geoscience 334 (2002) 155–161. 相似文献
79.
Jinfeng Chang Philippe Ciais Nicolas Viovy Jean-François Soussana Katja Klumpp Benjamin Sultan 《Carbon balance and management》2017,12(1):11
Background
Europe has warmed more than the global average (land and ocean) since pre-industrial times, and is also projected to continue to warm faster than the global average in the twenty-first century. According to the climate models ensemble projections for various climate scenarios, annual mean temperature of Europe for 2071–2100 is predicted to be 1–5.5 °C higher than that for 1971–2000. Climate change and elevated CO2 concentration are anticipated to affect grassland management and livestock production in Europe. However, there has been little work done to quantify the European-wide response of grassland to future climate change. Here we applied ORCHIDEE-GM v2.2, a grid-based model for managed grassland, over European grassland to estimate the impacts of future global change.Results
Increases in grassland productivity are simulated in response to future global change, which are mainly attributed to the simulated fertilization effect of rising CO2. The results show significant phenology shifts, in particular an earlier winter-spring onset of grass growth over Europe. A longer growing season is projected over southern and southeastern Europe. In other regions, summer drought causes an earlier end to the growing season, overall reducing growing season length. Future global change allows an increase of management intensity with higher than current potential annual grass forage yield, grazing capacity and livestock density, and a shift in seasonal grazing capacity. We found a continual grassland soil carbon sink in Mediterranean, Alpine, North eastern, South eastern and Eastern regions under specific warming level (SWL) of 1.5 and 2 °C relative to pre-industrial climate. However, this carbon sink is found to saturate, and gradually turn to a carbon source at warming level reaching 3.5 °C.Conclusions
This study provides a European-wide assessment of the future changes in productivity and phenology of grassland, and their consequences for the management intensity and the carbon balance. The simulated productivity increase in response to future global change enables an intensification of grassland management over Europe. However, the simulated increase in the interannual variability of grassland productivity over some regions may reduce the farmers’ ability to take advantage of the increased long-term mean productivity in the face of more frequent, and more severe drops of productivity in the future.80.
Sébastien Zaragosi Jean-François Bourillet Frédérique Eynaud Samuel Toucanne Benjamin Denhard Aurélie Van Toer Valentine Lanfumey 《Geo-Marine Letters》2006,26(6):317-329
The compilation of results obtained on three giant piston cores from the Whittard, Shamrock and Guilcher turbidite levees reveals a high-resolution stratigraphic record for the Bay of Biscay. Due to the abundance of reworked sediments in these sedimentary environments, a specific methodological approach, based on an X-ray-assisted subsampling phase associated with sedimentological, geochemical and micropalaeontological analyses, was implemented. With an accurate chronological framework, this multi-proxy investigation provides observations on the ‘Fleuve Manche’ palaeoriver and the British-Irish Ice Sheet (BIS) histories over the last 20,000 years. The results obtained highlight the direct influence of the decay of the BIS on the Bay of Biscay deep-sea clastic sedimentation during the last European deglacial phase. During this period, the annual BIS cycle of meltwater seems enough to generate seasonal turbidity currents associated with exceptional sedimentation rates in all the Celtic and Armorican turbidite systems. With very high sedimentation rates, the turbidite levees represent the main deep-sea clastic depositional area. Long coring combined with a very careful subsampling method can provide continuous high-resolution palaeoenvironmental signals. 相似文献