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2008 .

(6 publications)

G. Gastineau, H. Le Treut, and L. Li. Hadley circulation changes under global warming conditions indicated by coupled climate models. Tellus Series A, 60:863-884, October 2008. [ bib | DOI | ADS link ]

We use the mean meridional tropical circulation of the Atmospheric Ocean Coupled General Circulation Models (AOGCM) to diagnose and quantify the modifications of the mean meridional circulation of the atmosphere under global warming conditions. The AOGCMs generally show a weakening of the Hadley circulation for the winter cell in both hemispheres, accompanied by a poleward extension of the Hadley circulation area. The conditions explaining these modifications are analysed using detailed outputs from IPSL-CM4. The AOGCM IPSL-CM4 shows changes, under CO2 doubling, that are in accordance with the other models, for austral winter. On the other hand, for boreal winter, the winter cell shows little change in intensity and in extension. The poleward shift of the Southern Hemisphere winter Hadley cell corresponds to changes in the transient eddies, whereas the increase of the dry static stability is mainly responsible for the mean weakening of the cell. For boreal winter, a strong shrinking of the ascending branch area, and an increase of the latent heating, is found to cancel the weakening of the circulation due to dry static stability increase.

R. James, M. Bonazzola, B. Legras, K. Surbled, and S. Fueglistaler. Water vapor transport and dehydration above convective outflow during Asian monsoon. Geophysical Research Letters, 35:20810, October 2008. [ bib | DOI | ADS link ]

We investigate the respective roles of large-scale transport and convection in determining the water vapor maximum at 100 hPa in the Asian monsoon region. The study uses backward trajectories with ECMWF ERA-Interim heating rates. It includes simple microphysics with supersaturation and takes into account convective sources based on CLAUS data with a simple parameterization of overshoots. A good agreement between reconstructed water vapor and observations is obtained over Asia. It is found that parcels belonging to the water vapor maximum have been first lifted by convection over the Bay of Bengal and the Sea of China and then transported through the tropical tropopause layer (TTL) via the monsoon anticyclonic circulation towards North-West India, where they are eventually dehydrated, avoiding the coldest temperatures of the TTL. Convective moistening accounts for about 0.3 ppmv in the Asian monsoon region and overshoots do not have a significant impact on the water vapor budget.

H. Le Treut, G. Gastineau, and L. Li. Uncertainties attached to global or local climate changes. Comptes Rendus Geoscience, 340:584-590, September 2008. [ bib | DOI | ADS link ]

The successive reports of the Intergovernmental Panel on Climate Change (IPCC) illustrate an apparent contradiction. On the one hand, the large scale climatic change in response to the increase of greenhouse gases is structured following patterns which have remained surprisingly stable throughout the development of climate models. Already in the 1980s model simulations of climate change were characterized by a larger warming in polar areas and over the continents, and a tendency for precipitations to accentuate existing contrasts, with a drier climate in semiarid regions and more precipitations at mid-latitudes or near the Equator. On the other hand, models have made little progress in predicting more unanimously and more reliably the global amplitude of climate changes and their geographical distributions. This lack of progress is certainly linked with the role of the atmospheric dynamics in shaping up certain aspects of climate response, either small scales which affect atmospheric stratification, or synoptic scales, whose inherent complexity and nonlinear interactions also limit the possibility of more accurate regional predictions.

J.-A. Wartho, Z.-X. Li, S. A. Occhipinti, and S. Reddy. 40Ar/39Ar UV laser dating, EBSD and EMP analysis of 1040-940 Ma metamorphic/deformation/cooling events recorded in Sibao Orogen white micas, South China. Geochimica et Cosmochimica Acta Supplement, 72:1006, July 2008. [ bib | ADS link ]

P. Yiou, K. Goubanova, Z. X. Li, and M. Nogaj. Weather regime dependence of extreme value statistics for summer temperature and precipitation. Nonlinear Processes in Geophysics, 15:365-378, May 2008. [ bib | ADS link ]

Extreme Value Theory (EVT) is a useful tool to describe the statistical properties of extreme events. Its underlying assumptions include some form of temporal stationarity in the data. Previous studies have been able to treat long-term trends in datasets, to obtain the time dependence of EVT parameters in a parametric form. Since there is also a dependence of surface temperature and precipitation to weather patterns obtained from pressure data, we determine the EVT parameters of those meteorological variables over France conditional to the occurrence of North Atlantic weather patterns in the summer. We use a clustering algorithm on geopotential height data over the North Atlantic to obtain those patterns. This approach refines the straightforward application of EVT on climate data by allowing us to assess the role of atmospheric variability on temperature and precipitation extreme parameters. This study also investigates the statistical robustness of this relation. Our results show how weather regimes can modulate the different behavior of mean climate variables and their extremes. Such a modulation can be very different for the mean and extreme precipitation.

A. Hollingsworth, R. J. Engelen, C. Textor, A. Benedetti, O. Boucher, F. Chevallier, A. Dethof, H. Elbern, H. Eskes, J. Flemming, C. Granier, J. W. Kaiser, J.-J. Morcrette, P. Rayner, V.-H. Peuch, L. Rouil, M. G. Schultz, and A. J. Simmons. Toward a Monitoring and Forecasting System For Atmospheric Composition: The GEMS Project. Bulletin of the American Meteorological Society, 89:1147, 2008. [ bib | DOI | ADS link ]

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