Éditeur(s) : Springer
Résumé : We present the global general circulation model IPSL-CM5 developed to study the long-term response of the climate system to natural and anthropogenic forcings as part of the 5th Phase of the Coupled Model Intercomparison Project (CMIP5). This model includes an interactive carbon cycle, a representation of tropospheric and stratospheric chemistry, and a comprehensive representation of aerosols. As it represents the principal dynamical, physical, and bio-geochemical processes relevant to the climate system, it may be referred to as an Earth System Model. However, the IPSL-CM5 model may be used in a multitude of configurations associated with different boundary conditions and with a range of complexities in terms of processes and interactions. This paper presents an overview of the different model components and explains how they were coupled and used to simulate historical climate changes over the past 150 years and different scenarios of future climate change. A single version of the IPSL-CM5 model (IPSL-CM5A-LR) was used to provide climate projections associated with different socio-economic scenarios, including the different Representative Concentration Pathways considered by CMIP5 and several scenarios from the Special Report on Emission Scenarios considered by CMIP3. Results suggest that the magnitude of global warming projections primarily depends on the socio-economic scenario considered, that there is potential for an aggressive mitigation policy to limit global warming to about two degrees, and that the behavior of some components of the climate system such as the Arctic sea ice and the Atlantic Meridional Overturning Circulation may change drastically by the end of the twenty-first century in the case of a no climate policy scenario. Although the magnitude of regional temperature and precipitation changes depends fairly linearly on the magnitude of the projected global warming (and thus on the scenario considered), the geographical pattern of these changes is strikingly similar for the different scenarios. The representation of atmospheric physical processes in the model is shown to strongly influence the simulated climate variability and both the magnitude and pattern of the projected climate changes.
Climate Dynamics (0930-7575) (Springer), 2013-05 , Vol. 40 , N. 9-10 , P. 2123-2165

Droits : The Author(s) 2013. This article is published with open access at Springerlink.com
http://archimer.ifremer.fr/doc/00138/24966/23079.pdf
DOI:10.1007/s00382-012-1636-1
http://archimer.ifremer.fr/doc/00138/24966/

Éditeur(s) : HAL CCSD Nature Publishing Group
Résumé : International audience
Collisional mountain belts grow as a consequence of continental plate convergence and eventuallydisappear under the combined effects of gravitational collapse and erosion. Using a decade ofGPS data, we show that the western Alps are currently characterized by zero horizontal velocityboundary conditions, offering the opportunity to investigate orogen evolution at the time ofcessation of plate convergence. We find no significant horizontal motion within the belt, but GPS andlevelling measurements independently show a regional pattern of uplift reaching ~2.5 mm/yr in thenorthwestern Alps. Unless a low viscosity crustal root under the northwestern Alps locally enhancesthe vertical response to surface unloading, the summed effects of isostatic responses to erosion andglaciation explain at most 60% of the observed uplift rates. Rock-uplift rates corrected from transientglacial isostatic adjustment contributions likely exceed erosion rates in the northwestern Alps. In theabsence of active convergence, the observed surface uplift must result from deep-seated processes.
ISSN: 2045-2322

hal-01357450
https://hal.archives-ouvertes.fr/hal-01357450
https://hal.archives-ouvertes.fr/hal-01357450/document
https://hal.archives-ouvertes.fr/hal-01357450/file/noquet2016.pdf
DOI : 10.1038/srep28404

Éditeur(s) : HAL CCSD Elsevier
Résumé : This paper is the first presentation of a project called GHYRAF (Gravity and Hydrology in Africa) devoted to the detailed comparison between models and multidisciplinary observations (ground and satellite gravity, geodesy, hydrology, meteorology) of the variations of water storage in Africa from the Sahara and part to the monsoon equatorial part. We describe the various actions planned in this project. We first detail the actions planned in gravimetry which consist in two main surface gravity experiments: on the one hand the periodic repetition of absolute gravity measurements along a north-south monsoonal gradient of rainfall in West Africa, going from Tamanrasset (20 mm/year) in southern Algeria to Djougou (1200 mm/year) in central Benin; on the other hand the continuous measurements at Djougou (Benin) with a superconducting gravimeter to monitor with a higher sampling rate the gravity changes related to an extreme hydrological cycle. Another section describes the actions planned in GPS which will maintain and develop the present-day existing network in West Africa. The third type of actions deals with hydrology and we review the three sites that will be investigated in this joint hydrogeophysics project namely Wankama (near Niamey) and Bagara (near Diffa) in the Niger Sahelian zone and Nalohou (near Djougou) in the Benin monsoon zone. We also address the question of the ground truth of satellite-derived missions: in this context the GHYRAF project will lead to test the hydrology models by comparison both with in situ and satellite data such as GRACE, as well as to an important increase of our knowledge of the seasonal water cycle in Africa. We finally present preliminary results in GPS based on the analysis of the vertical motion of the Djougou site. The resulting absolute gravity changes related to the 2008 monsoon are finally given.
ISSN: 0264-3707

hal-00475660
https://hal.archives-ouvertes.fr/hal-00475660
DOI : 10.1016/j.jog.2009.09.014

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
A network of 26 GPS sites was implemented in Iran and Northern Oman to measure displacements in this part of the Arabia–Eurasia collision zone. We present the GPS velocity field obtained from three surveys performed in 1999 September, 2001 October and 2005 September and the deduced strain tensor. This study refines previous studies inferred from only the two first surveys. Improvements are significant in NE Iran. The present-day shortening rate across the mountain belts of NE Iran is estimated to 5 ± 1 mm yr−1 at about N11°, 2 ± 1 mm yr−1 of NS shortening across the eastern Kopet Dag and 3 ± 1 mm yr−1 of NS shortening across Binalud and Kuh-e-Sorkh. Our GPS measurements emphasize the varying character of the Kopet Dag deformation between its southeastern part with prevailing thrusting at low rates and its northwestern part with dominant strike-slip activity at increasing rates. The principal axes of the horizontal strain tensor appears very homogeneous from the Zagros to the Alborz and the Kopet-Dag (N20°) and in eastern Iran (Makran and Lut block: N30°). Only NW Iran suffers a variable strain pattern which seems to wrap the Caspian basin. The strain tensor map underlines the existence of large homogeneous tectonic provinces in terms of style and amplitude of the deformation.
ISSN: 0956-540X

insu-00346744
https://hal-insu.archives-ouvertes.fr/insu-00346744
DOI : 10.1111/j.1365-246X.2007.03477.x

Éditeur(s) : HAL CCSD Météo et Climat
Résumé : International audience
Le premier volet du projet Cyprim vise à mieux identifier les précurseurs des cyclogenèses et des précipitations intenses en région méditerranéenne. Cet article en présente les principaux résultats. Il est question des ingrédients météorologiques à l'origine de ces systèmes, de la grande à la mésoéchelle, des causes des fortes intensités, localisations et parfois stationnarité des récipitations associées. Le coeur de l'article présente des méthodes d'identification des anomalies de tourbillon potentiel liées à l'occurrence d'événements précipitants intenses et dresse une climatologie de ces anomalies. Les perspectives d'exploitation de cette information pour améliorer la qualité des prévisions sont évoquées. ENGLISH VERSION: The first part of the CYPRIM project (Cyclogenesis and intense precipitations in the Mediterranean region) aims at a better identification of the precursor structures of cyclogenesis and heavy precipitation in the Mediterranean region. This article presents the main results. It mentions the meteorological ingredients from which these systems originate from the large to themesoscale, the reasons for large intensities, the localization and sometimes stationarity of the associated precipitations. The heart of the article shows methods for identifiying potential vorticity anomalies involved in the occurrence of heavy precipitation events and sets up a climatology of these anomalies.The perspectives of the usefulness of this information for improving forecast quality are discussed.
ISSN: 0026-1181

insu-00448250
https://hal-insu.archives-ouvertes.fr/insu-00448250
DOI : 10.4267/2042/28828

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
The impact of stratospheric ozone on the tropospheric general circulation of theSouthern Hemisphere (SH) is examined with a set of chemistry‐climate models participatingin the Stratospheric Processes and their Role in Climate (SPARC)/Chemistry‐ClimateModel Validation project phase 2 (CCMVal‐2). Model integrations of both the past andfuture climates reveal the crucial role of stratospheric ozone in driving SH circulationchange: stronger ozone depletion in late spring generally leads to greater polewarddisplacement and intensification of the tropospheric midlatitude jet, and greater expansion ofthe SH Hadley cell in the summer. These circulation changes are systematic as polewarddisplacement of the jet is typically accompanied by intensification of the jet and expansion ofthe Hadley cell. Overall results are compared with coupled models participating in theIntergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4), andpossible mechanisms are discussed. While the tropospheric circulation response appearsquasi‐linearly related to stratospheric ozone changes, the quantitative response to a givenforcing varies considerably from one model to another. This scatter partly results fromdifferences in model climatology. It is shown that poleward intensification of the westerly jetis generally stronger in models whose climatological jet is biased toward lower latitudes.This result is discussed in the context of quasi‐geostrophic zonal mean dynamics.
ISSN: 2169-897X

hal-00337060
https://hal.archives-ouvertes.fr/hal-00337060
https://hal.archives-ouvertes.fr/hal-00337060/document
https://hal.archives-ouvertes.fr/hal-00337060/file/Bock_et_al-2008-Journalsur Geophysical_Research__Solid_Earth_%281978-2012%29.pdf
DOI : 10.1029/2008JD010327

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The island of Taiwan is located on the convergent boundary between the Philippine Sea plate and the Chinese continental margin. It offers very active mountain building and collapsing processes well illustrated by the rugged topography, rapid uplift and denudation, young tectonic landforms, active faulting and numerous earthquakes. In this paper, using simple models, we have estimated vertical movements and associated absolute gravity variations which can be expected along a profile crossing the southern part of the island and probably suffering the highest rates of rising. The two different tectonic styles proposed for the island, thin-skinned and thick-skinned, were taken into account. Horizontal and vertical movements were modeled by an elastic deformation code. Gravity variations due to these deformations are then modeled at a second step. They are dominated by plate and free-air effects, i.e. elevation of the topography, with several mu Gal yr(-1). By comparison, gravity changes generated by mass transfers are weak: maximum 0.1 mu Gal yr(-1) with the thin-skinned tectonic and 0.3 mu Gal yr(-1) with the thick-skinned tectonic. Though elastic rheology has limitations, this modeling offers interesting results on what gravity signal can be expected from the AGTO project (Absolute Gravity in the Taiwanese Orogen), which proposes to study the dynamic of these mountain ranges using absolute gravimetry (AG) and also including relative gravimetry (RG) and GPS measurements.
ISSN: 0264-3707

hal-00456035
https://hal.archives-ouvertes.fr/hal-00456035
DOI : 10.1016/j.jog.2009.09.004

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : Geophysical Journal International, v. 173, n. 2, p. 473-482, 2008. http://dx.doi.org/10.1111/j.1365-246X.2008.03718.x
International audience
The western Provence in southern France is an intraplate low deforming region, cut by large sinistral strike-slip faults as the Nîmes Fault. The deformation rate of this fault was estimated at 0.1 mm yr−1 from geological and morphological observations. Nevertheless, some large earthquakes occurred in this area in historical times inducing well-documented partial destructions on the roman monument 'Pont-du-Gard'. In order to investigate if this area is seismically active, we installed a temporary seismological network of 14 stations between the cities of Nîmes and Avignon for a 1-yr period (2002 July–2003 June). We recorded and located a total amount of 80 earthquakes of magnitude Ml smaller than 2.8, and of 153 quarry blasts. The seismic event locations are interpreted in terms of regional tectonics as well as of geometry at depth of the Nîmes Fault and of possible seismic activity of the Roquemaure Fault. At the beginning of 2002 September, a catastrophic storm occurred in the same area with cumulated precipitations at 600 mm in 28 hr, causing casualties and major inundations and damages. We identified a clear and sudden increase of the seismic activity as an immediate consequence of this exceptional meteorological phenomenon. We interpret this rainfall triggering of earthquakes as the response of the crust to an abrupt vertical loading. The geological context of this zone is characterized by the presence of sedimentary basins and of an important karstic network in a calcareous environment allowing the retention of a third of the total rainwater volume during few weeks after the catastrophic storm. Month by month inversion of the seismic wave velocities for only the first 1-km thick layer of the crust allows investigating the influence of the stored water. A clear decrease of both P- and S-velocities, and an increase of the Vp/Vs ratio are evidenced. The variations obtained are at 2, 6 and 4.5 per cent for P-, S-velocities and Vp/Vs ratio, respectively. These variations are discussed in confront of previous studies and can be directly related to the known water volume.
ISSN: 0956-540X

hal-00407884
https://hal.archives-ouvertes.fr/hal-00407884
https://hal.archives-ouvertes.fr/hal-00407884v2/document
https://hal.archives-ouvertes.fr/hal-00407884/file/rigoGJI2008.pdf
DOI : 10.1111/j.1365-246X.2008.03718.x

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
Ocean loading effects cause 3-D displacements large enough to affect space geodesy measurements either at the subdiurnal periods or at longer time scales by the means of spurious signals. GPS measurements, in turn, could provide local improvements of the models in coastal areas if their ability to precisely monitor such rapid displacements is assessed. In this paper, we use 105 days of continuous GPS measurements collected in 2004 in the French Brittany and Cotentin region to investigate: (1) the precision achieved by the GPS analysis on measuring 3-D subdiurnal displacements and amplitude and phase of the tidal constituents, (2) the quality of the most recent ocean tide model FES2004 in such a complex coastal context. Indeed, in this area, tide amplitudes are among the largest in the world (up to 16 cm of loading displacements on the vertical component) and are believed to show strong shallow-water tides. From a state of the art GPS analysis using the scientific GAMIT software over 2-h sessions, we test two independent strategies for the realization of the reference frame. The position time series are then compared with the displacements predicted by the FES2004 model applied on an elastic Earth model. The two sets of results are consistent with each other at the same level of agreement than with the predicted displacements, namely 3–5 mm on the horizontal components, 10 mm on the vertical. This assesses the capability of this technique for measuring 3-D ocean tide loading deformation. We validate the FES2004 model in the Brittany area, even though it slightly (2–7 mm) underestimates the three components amplitudes. With a harmonic analysis of the observed position time series, we obtain nevertheless an agreement at a submillimetre level for the M2, N2, O1, Q1 tidal constituents and at a millimetre level for the K1 and S2 tidal constituents. Moreover, we can extract a significant M4 load signal at the 95 per cent confidence level from the GPS time series at the stations located in the Mont St Michel area. The detection of other shallow-water constituents would be helpful to understand the amplitude deficit between the FES2004 predicted and GPS observed displacements.
ISSN: 0956-540X

insu-00335909
https://hal-insu.archives-ouvertes.fr/insu-00335909
https://hal-insu.archives-ouvertes.fr/insu-00335909/document
https://hal-insu.archives-ouvertes.fr/insu-00335909/file/Vergnolle_GJI_08_revised.pdf
DOI : 10.1111/j.1365-246X.2008.03734.x

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
ISSN: 0035-9009

hal-00372548
https://hal.archives-ouvertes.fr/hal-00372548
DOI : 10.1002/qj.386