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2010 .

(8 publications)

C. Rio, F. Hourdin, F. Couvreux, and A. Jam. Resolved Versus Parametrized Boundary-Layer Plumes. Part II: Continuous Formulations of Mixing Rates for Mass-Flux Schemes. Boundary-Layer Meteorology, 135:469-483, June 2010. [ bib | DOI | ADS link ]

The conditional sampling of coherent structures in large-eddy simulations of the convective boundary layer (Couvreux et al. Boundary-layer Meteorol 134:441-458, 2010) is used to propose and evaluate formulations of fractional entrainment and detrainment rates for mass-flux schemes. The proposed formulations are physically-based and continuous from the surface to the top of clouds. Entrainment is related to the updraft vertical velocity divergence, while detrainment depends on the thermal vertical velocity, on buoyancy and on the moisture contrast between the mean plume and its environment. The proposed formulations are first directly evaluated in simulations of shallow clouds. They are then tested in single-column simulations with the thermal plume model, a mass-flux representation of boundary-layer thermals.

S. Lebonnois, F. Hourdin, V. Eymet, A. Crespin, R. Fournier, and F. Forget. Superrotation of Venus' atmosphere analyzed with a full general circulation model. Journal of Geophysical Research (Planets), 115:6006, June 2010. [ bib | DOI | ADS link ]

A general circulation model (GCM) has been developed for the Venus atmosphere, from the surface up to 100 km altitude, based on the GCM developed for Earth at our laboratory. Key features of this new GCM include topography, diurnal cycle, dependence of the specific heat on temperature, and a consistent radiative transfer module based on net exchange rate matrices. This allows a consistent computation of the temperature field, in contrast to previous GCMs of Venus atmosphere that used simplified temperature forcing. The circulation is analyzed after 350 Venus days (111 Earth years). Superrotation is obtained above roughly 40 km altitude. Below, the zonal wind remains very small compared to observed values, which is a major pending question. The meridional circulation consists of equator-to-pole cells, the dominant one being located within the cloud layers. The modeled temperature structure is globally consistent with observations, though discrepancies persist in the stability of the lowest layers and equator-pole temperature contrast within the clouds (10 K in the model compared to the observed 40 K). In agreement with observational data, a convective layer is found between the base of the clouds (around 47 km) and the middle of the clouds (55-60 km altitude). The transport of angular momentum is analyzed, and comparison between the reference simulation and a simulation without diurnal cycle illustrates the role played by thermal tides in the equatorial region. Without diurnal cycle, the Gierasch-Rossow-Williams mechanism controls angular momentum transport. The diurnal tides add a significant downward transport of momentum in the equatorial region, causing low latitude momentum accumulation.

S. Diatta, F. Hourdin, A. T. Gaye, and N. Viltard. Comparison of Rainfall Profiles in the West African Monsoon as Depicted by TRMM PR and the LMDZ Climate Model. Monthly Weather Review, 138:1767-1777, May 2010. [ bib | DOI | ADS link ]

J. E. Williams, R. Scheele, P. van Velthoven, I. Bouarar, K. Law, B. Josse, V.-H. Peuch, X. Yang, J. Pyle, V. Thouret, B. Barret, C. Liousse, F. Hourdin, S. Szopa, and A. Cozic. Global Chemistry Simulations in the AMMA Multimodel Intercomparison Project. Bulletin of the American Meteorological Society, 91:611-624, May 2010. [ bib | DOI | ADS link ]

C. Rio, F. Hourdin, and A. Chédin. Numerical simulation of tropospheric injection of biomass burning products by pyro-thermal plumes. Atmospheric Chemistry & Physics, 10:3463-3478, April 2010. [ bib | ADS link ]

The thermal plume model, a mass-flux scheme originally developed to represent the vertical transport by convective structures within the boundary layer, is adapted to the representation of plumes generated by fires, with the aim of estimating the height at which fire emissions are actually injected in the atmosphere. The parameterization, which takes into account the excess of near surface temperature induced by fires and the mixing between convective plumes and environmental air, is first evaluated on two well-documented fires. Simulations over Southern Africa performed with the general circulation model LMDZ over one month show that the CO2 can be injected far above the boundary layer height, leading to a daily excess of CO2 in the mid-troposphere of an order of 2 ppmv. These results agree with satellite retrievals of a diurnal cycle of CO2 in the free troposphere over regions affected by biomass burning in the Tropics.

F. Couvreux, F. Hourdin, and C. Rio. Resolved Versus Parametrized Boundary-Layer Plumes. Part I: A Parametrization-Oriented Conditional Sampling in Large-Eddy Simulations. Boundary-Layer Meteorology, 134:441-458, March 2010. [ bib | DOI | ADS link ]

A conditional sampling based on the combination of a passive tracer emitted at the surface and thermodynamic variables is proposed to characterise organized structures in large-eddy simulations of cloud-free and cloudy boundary layers. The sampling is evaluated against more traditional sampling of dry thermals or clouds. It enables the characterization of convective updrafts from the surface to the top of the boundary layer (or the top of cumulus clouds), describing in particular the transition from the sub-cloud to the cloud layer, and retrieves plume characteristics, entrainment and detrainment rates, variances and fluxes. This sampling is used to analyze the contribution of boundary-layer thermals to vertical fluxes and variances.

O. Marti, P. Braconnot, J.-L. Dufresne, J. Bellier, R. Benshila, S. Bony, P. Brockmann, P. Cadule, A. Caubel, F. Codron, N. de Noblet, S. Denvil, L. Fairhead, T. Fichefet, M.-A. Foujols, P. Friedlingstein, H. Goosse, J.-Y. Grandpeix, E. Guilyardi, F. Hourdin, A. Idelkadi, M. Kageyama, G. Krinner, C. Lévy, G. Madec, J. Mignot, I. Musat, D. Swingedouw, and C. Talandier. Key features of the IPSL ocean atmosphere model and its sensitivity to atmospheric resolution. Climate Dynamics, 34:1-26, January 2010. [ bib | DOI | ADS link ]

This paper presents the major characteristics of the Institut Pierre Simon Laplace (IPSL) coupled ocean-atmosphere general circulation model. The model components and the coupling methodology are described, as well as the main characteristics of the climatology and interannual variability. The model results of the standard version used for IPCC climate projections, and for intercomparison projects like the Paleoclimate Modeling Intercomparison Project (PMIP 2) are compared to those with a higher resolution in the atmosphere. A focus on the North Atlantic and on the tropics is used to address the impact of the atmosphere resolution on processes and feedbacks. In the North Atlantic, the resolution change leads to an improved representation of the storm-tracks and the North Atlantic oscillation. The better representation of the wind structure increases the northward salt transports, the deep-water formation and the Atlantic meridional overturning circulation. In the tropics, the ocean-atmosphere dynamical coupling, or Bjerknes feedback, improves with the resolution. The amplitude of ENSO (El Niño-Southern oscillation) consequently increases, as the damping processes are left unchanged.

F. Hourdin, I. Musat, F. Guichard, P. M. Ruti, F. Favot, M.-A. Filiberti*, M. Pham, J.-Y. Grandpeix, J. Polcher, P. Marquet, A. Boone, J.-P. Lafore, J.-L. Redelsperger, A. Dell'Aquila, T. L. Doval, A. K. Traore, and H. Gallée. AMMA-Model Intercomparison Project. Bulletin of the American Meteorological Society, 91:95, 2010. [ bib | DOI | ADS link ]

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