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1.
Sylvie Charbit Masa Kageyama Didier Roche Catherine Ritz Gilles Ramstein 《Global and Planetary Change》2005,48(4):1887
A coupling procedure between a climate model of intermediate complexity (CLIMBER-2.3) and a 3-dimensional thermo-mechanical ice-sheet model (GREMLINS) has been elaborated. The resulting coupled model describes the evolution of atmosphere, ocean, biosphere, cryosphere and their mutual interactions. It is used to perform several simulations of the Last Deglaciation period to identify the physical mechanisms at the origin of the deglaciation process. Our baseline experiment, forced by insolation and atmospheric CO2, produces almost complete deglaciation of past northern hemisphere continental ice sheets, although ice remains over the Cordilleran region at the end of the simulation and also in Alaska and Eastern Siberia. Results clearly demonstrate that, in this study, the melting of the North American ice sheet is critically dependent on the deglaciation of Fennoscandia through processes involving switches of the thermohaline circulation from a glacial mode to a modern one and associated warming of the northern hemisphere. A set of sensitivity experiments has been carried out to test the relative importance of both forcing factors and internal processes in the deglaciation mechanism. It appears that the deglaciation is primarily driven by insolation. However, the atmospheric CO2 modulates the timing of the melting of the Fennoscandian ice sheet, and results relative to Laurentide illustrate the existence of threshold CO2 values, that can be translated in terms of critical temperature, below which the deglaciation is impeded. Finally, we show that the beginning of the deglaciation process of the Laurentide ice sheet may be influenced by the time at which the shift of the thermohaline circulation from one mode to the other occurs. 相似文献
2.
The Last Glacial Maximum climate over Europe and western Siberia: a PMIP comparison between models and data 总被引:3,自引:1,他引:3
M. Kageyama O. Peyron S. Pinot P. Tarasov J. Guiot S. Joussaume G. Ramstein 《Climate Dynamics》2001,17(1):23-43
Under the framework of the Palaeoclimate Modelling Intercomparison Project (PMIP), 17 climate models, 16 of which are atmospheric
general circulation models, have been run to simulate the climate of the Last Glacial Maximum (21 000 years ago) using the
same set of boundary conditions. Parallel to these numerical experiments, new, consistent, data bases have been developed
on a continental scale. The present work compares the range of the model responses to the large perturbation corresponding
to the conditions of the Last Glacial Maximum with consistently derived climate reconstructions from pollen records over Europe
and western Siberia. It accounts for the differences in the model results due to the models themselves and directly compares
this “error bar” due to the models to the uncertainties in the climate reconstructions from the pollen records. Overall the
Last Glacial Maximum climate simulated by the models over western Europe is warmer, especially in winter, and wetter than
the one depicted by the reconstructions. This is the region where the reconstructed increase in temperature, precipitation
and moisture index from the Last Glacial Maximum to the present conditions is largest. The same disagreement, but of smaller
amplitude, is found over Central Europe and the eastern Mediterranean Basin, while models and data are in broad agreement
over western Siberia. The numerous modelling results allow a study of the link between the changes in atmospheric circulation
and those in temperature, and an interpretation of the discrepancies in precipitation in terms of those in temperature.
Received: 1 February 2000 / Accepted: 9 May 2000 相似文献
3.
Past and future polar amplification of climate change: climate model intercomparisons and ice-core constraints 总被引:1,自引:0,他引:1
V. Masson-Delmotte M. Kageyama P. Braconnot S. Charbit G. Krinner C. Ritz E. Guilyardi J. Jouzel A. Abe-Ouchi M. Crucifix R. M. Gladstone C. D. Hewitt A. Kitoh A. N. LeGrande O. Marti U. Merkel T. Motoi R. Ohgaito B. Otto-Bliesner W. R. Peltier I. Ross P. J. Valdes G. Vettoretti S. L. Weber F. Wolk Y. Yu 《Climate Dynamics》2006,27(4):437-440
4.
Virginie Guemas David Salas-Mélia Masa Kageyama Hervé Giordani Aurore Voldoire Emilia Sanchez-Gomez 《Climate Dynamics》2010,34(4):527-546
This study aims at understanding the summer ocean-atmosphere interactions in the North Atlantic European region on intraseasonal
timescales. The CNRMOM1d ocean model is forced with ERA40 (ECMWF Re-Analysis) surface fluxes with a 1-h frequency in solar
heat flux (6 h for the other forcing fields) over the 1959–2001 period. The model has 124 vertical levels with a vertical
resolution of 1 m near the surface and 500 m at the bottom. This ocean forced experiment is used to assess the impact of the
North Atlantic weather regimes on the surface ocean. Composites of sea surface temperature (SST) anomalies associated with
each weather regime are computed and the mechanisms explaining these anomalies are investigated. Then, the SST anomalies related
to each weather regime in the ocean-forced experiment are prescribed to the ARPEGE Atmosphere General Circulation Model. We
show that the interaction with the surface ocean induces a positive feedback on the persistence of the Blocking regime, a
negative feedback on the persistence of the NAO-regime and favours the transition from the Atlantic Ridge regime to the NAO-regime
and from the Atlantic Low regime toward the Blocking regime. 相似文献
5.
Shea Goyette Masa Takatsuka Stuart Clark R. Dietmar Müller Patrice Rey Dave R. Stegman 《Visual Geosciences》2008,13(1):25-36
Geoscientists are faced with a number of complexities that represent obstacles to the development of realistic simulation
of deep earth processes. Realistic 4D thermo-mechanical simulation using software packages like Underworld and Gale, when
combined appropriately with geoscientific expertise, can lead to novel insights into the deformation of geological structures
at a wide range of time and spatial scales. The challenge for end-user geoscientists lies in applying their knowledge within
the framework of the software’s input specification, including initial, internal, and boundary conditions and output visualization
parameters. We have built a Graphical User Interface (GUI) to remove many of the difficulties related to editing the Extensible
Markup Language (XML) encoded input files of Underworld/Gale geomodels and therefore, to greatly broaden the user base of
these software packages. By helping Underworld/Gale to meet a large audience, we provide a tool to the geoscience community
that helps to move from untested conceptual models to physically valid, properly scaled modelling. Furthermore, the UnderworldGUI
offers a mechanism for storing and retrieving experimental models in a centralised database, thus providing the geoscience
community with a means to share the outcomes of its experimental research. Further details of the UnderworldGUI are available
at the web site .
相似文献
Shea GoyetteEmail: |
6.
7.
Maisa Rojas Patricio Moreno Masa Kageyama Michel Crucifix Chris Hewitt Ayako Abe-Ouchi Rumi Ohgaito Esther C. Brady Pandora Hope 《Climate Dynamics》2009,32(4):525-548
The Southern Hemisphere westerly winds are an important component of the climate system at hemispheric and global scales.
Variations in their intensity and latitudinal position through an ice-age cycle have been proposed as important drivers of
global climate change due to their influence on deep-ocean circulation and changes in atmospheric CO2. The position, intensity, and associated climatology of the southern westerlies during the last glacial maximum (LGM), however,
is still poorly understood from empirical and modelling standpoints. Here we analyse the behaviour of the southern westerlies
during the LGM using four coupled ocean-atmosphere simulations carried out by the Palaeoclimate Modelling Intercomparison
Project Phase 2 (PMIP2). We analysed the atmospheric circulation by direct inspection of the winds and by using a cyclone
tracking software to indicate storm tracks. The models suggest that changes were most significant during winter and over the
Pacific ocean. For this season and region, three out four models indicate decreased wind intensities at the near surface as
well as in the upper troposphere. Although the LGM atmosphere is colder and the equator to pole surface temperature gradient
generally increases, the tropospheric temperature gradients actually decrease, explaining the weaker circulation. We evaluated
the atmospheric influence on the Southern Ocean by examining the effect of wind stress on the Ekman pumping. Again, three
of the models indicate decreased upwelling in a latitudinal band over the Southern Ocean. All models indicate a drier LGM
than at present with a clear decrease in precipitation south of 40°S over the oceans. We identify important differences in
precipitation anomalies over the land masses at regional scale, including a drier climate over New Zealand and wetter over
NW Patagonia. 相似文献
8.
9.
Mid-Holocene and Last Glacial Maximum climate simulations with the IPSL model—part I: comparing IPSL_CM5A to IPSL_CM4 总被引:1,自引:0,他引:1
Masa Kageyama Pascale Braconnot Laurent Bopp Arnaud Caubel Marie-Alice Foujols Eric Guilyardi Myriam Khodri James Lloyd Fabien Lombard Véronique Mariotti Olivier Marti Tilla Roy Marie-Noëlle Woillez 《Climate Dynamics》2013,40(9-10):2447-2468
The climates of the mid-Holocene (MH), 6,000 years ago, and of the Last Glacial Maximum (LGM), 21,000 years ago, have extensively been simulated, in particular in the framework of the Palaeoclimate Modelling Intercomparion Project. These periods are well documented by paleo-records, which can be used for evaluating model results for climates different from the present one. Here, we present new simulations of the MH and the LGM climates obtained with the IPSL_CM5A model and compare them to our previous results obtained with the IPSL_CM4 model. Compared to IPSL_CM4, IPSL_CM5A includes two new features: the interactive representation of the plant phenology and marine biogeochemistry. But one of the most important differences between these models is the latitudinal resolution and vertical domain of their atmospheric component, which have been improved in IPSL_CM5A and results in a better representation of the mid-latitude jet-streams. The Asian monsoon’s representation is also substantially improved. The global average mean annual temperature simulated for the pre-industrial (PI) period is colder in IPSL_CM5A than in IPSL_CM4 but their climate sensitivity to a CO2 doubling is similar. Here we show that these differences in the simulated PI climate have an impact on the simulated MH and LGM climatic anomalies. The larger cooling response to LGM boundary conditions in IPSL_CM5A appears to be mainly due to differences between the PMIP3 and PMIP2 boundary conditions, as shown by a short wave radiative forcing/feedback analysis based on a simplified perturbation method. It is found that the sensitivity computed from the LGM climate is lower than that computed from 2 × CO2 simulations, confirming previous studies based on different models. For the MH, the Asian monsoon, stronger in the IPSL_CM5A PI simulation, is also more sensitive to the insolation changes. The African monsoon is also further amplified in IPSL_CM5A due to the impact of the interactive phenology. Finally the changes in variability for both models and for MH and LGM are presented taking the example of the El-Niño Southern Oscillation (ENSO), which is very different in the PI simulations. ENSO variability is damped in both model versions at the MH, whereas inconsistent responses are found between the two versions for the LGM. Part 2 of this paper examines whether these differences between IPSL_CM4 and IPSL_CM5A can be distinguished when comparing those results to palaeo-climatic reconstructions and investigates new approaches for model-data comparisons made possible by the inclusion of new components in IPSL_CM5A. 相似文献
10.
A. Laîné M. Kageyama D. Salas-Mélia A. Voldoire G. Rivière G. Ramstein S. Planton S. Tyteca J. Y. Peterschmitt 《Climate Dynamics》2009,32(5):593-614
Mid-latitude eddies are an important component of the climatic system due to their role in transporting heat, moisture and
momentum from the tropics to the poles, and also for the precipitation associated with their fronts, especially in winter.
We study northern hemisphere storm-tracks at the Last Glacial Maximum (LGM) and their influence on precipitation using ocean-atmosphere
general circulation model (OAGCM) simulations from the second phase of the Paleoclimate Modelling Intercomparison Project
(PMIP2). The difference with PMIP1 results in terms of sea-surface temperature forcing, fundamental for storm-track dynamics,
is large, especially in the eastern North Atlantic where sea-ice extends less to the south in OAGCMs compared to atmospheric-only
GCMs. Our analyses of the physics of the eddies are based on the equations of eddy energetics. All models simulate a consistent
southeastward shift of the North Pacific storm-track in winter, related to a similar displacement of the jet stream, partly
forced by the eddies themselves. Precipitation anomalies are consistent with storm-track changes, with a southeastward displacement
of the North Pacific precipitation pattern. The common features of North Atlantic changes in the LGM simulations consist of
a thinning of the storm-track in its western part and an amplification of synoptic activity to the southeast, in the region
between the Azores Islands and the Iberian Peninsula, which reflects on precipitation. This southeastward extension is related
to a similar displacement of the jet, partly forced by the eddies. In the western North Atlantic, the synoptic activity anomalies
are at first order related to baroclinic generation term anomalies, but the mean-flow baroclinicity increase due to the presence
of the Laurentide ice-sheet is partly balanced by a loss of eddy efficiency to convert energy from the mean flow. Moisture
availability in this region is greatly reduced due to more advection of dry polar air by stationary waves, leading to less
synoptic-scale latent heat release and hence less precipitation also. In terms of seasonality, the stormy season is shifted
later in the year by a few days to a month depending on the season and the model considered. This shift does not directly
reflect on the first-order seasonal cycle of precipitation, which also depends on other mechanisms, especially in summer. 相似文献