A. de Guilhem de Lataille, M. El Hafi, R. Fournier, J.L. Dufresne

5th International Conference on Technologies and Combustion for a Clean Environment, Lisbon, Portugal, July 1999. Ed. Gordon and Breach, 1999

Dufresne, J.L., Fournier, R. and Grandpeix, J.Y.

Journal of Quantitative Spectroscopy and Radiative Transfer, Vol.61, N.4, pp.433-441, 1999

K-distributions corresponding to Malkmus' narrow band model are inverse Gaussian distributions. Inverse Gaussian theory developments are therefore directly relevant to gas radiative transfer modeling. The present text illustrates some significant benefits that could be made from this observation : i) k-distribution formulations are simplified, ii) numerical integration procedures can be optimized for each new configuration type, iii) frequently encountered integrals can be solved analyticaly and numerical integrations can be avoided. This last point is illustrated with the compuation of infra-red cooling rates in panetary atmospheres.

( The Exchange Monte-Carlo Method for radiative budget computation in a gas filled two-dimensional enclosure )

Dufresne, J.L., Fournier, R. and Grandpeix, J.Y.

C.R. Acad. Sci., Série II b, vol.236, p.33-38, janvier 1998

A formulation is presented based on the reciprocity principle in which radiative budgets are expressed as sums of Net Exchange Rates between all volume and surface elements. On this basis, a Monte-Carlo Method has been developed that proved numerically very efficient compared to standard Analog Monte-Carlo Methods. It was used for computation of radiative budgets inside a two-dimensional cavity field with a participating gas. Strongly irregular grids and a wide range of optical thicknesses can be studied with this method.

CHERKAOUI Moha, DUFRESNE Jean-Louis, FOURNIER Richard , GRANDPEIX Jean-Yves , LAHELLEC Alain

ASME Journal of Heat Transfer, Vol. 120, pp. 275-278, Febr. 1998

The Net Exchange Formulation (NEF) was proposed in (Cherkaoui et al., 1996) as a method for accurate computation of infra red radiative exchanges within gas enclosures. The Exchange Monte Carlo Method (EMCM) was then described, and applications to one dimensional configurations with either black or reflective surfaces were given. However, equations used in the reflective case were omitted. These are derived in the present technical note.

CHERKAOUI Moha , DUFRESNE Jean-Louis , FOURNIER Richard , GRANDPEIX Jean-Yves , LAHELLEC Alain

ASME Journal of Heat Transfer , May 1996, Vol. 118, pp.401-407

The Monte Carlo method is used for simulation of radiative heat transfers in non-gray gases. The proposed procedure is based on a Net-Exchange Formulation (NEF). Such a formulation provides an efficient way of systematically fulfilling the reciprocity principle, which avoids some of the major problems usually associated with the Monte Carlo method~: numerical efficiency becomes independent of optical thickness, strongly non uniform grid sizes can be used with no increase in computation times and configurations with small temperature differences can be addressed with very good accuracy. The Exchange Monte Carlo Method (EMCM) is detailed for a one-dimensional slab with diffusely or specularly reflecting surfaces.

CHERKAOUI Moha , DUFRESNE Jean-Louis , FOURNIER Richard , GRANDPEIX Jean-Yves , LAHELLEC Alain

Internal Report 204 , Jun 1996

Y. Le Clainche, P.Braconnot, O. Marti, S. Joussaume, J-L Dufresne and M-A Filiberti.

submitted to Climate Dynamics.

C. Laurent, H Le Treut, Z.X.Li, J.L. Dufresne and L. Fairhead,

submitted to Climate Dynamics.

Carine Laurent, Hervé Le Treut, Zhao-Xin Li, Laurent Fairhead and Jean-Louis Dufresne

Notes du pôle de modélisation de l'IPSL, N.8, 1998

Multidecadal numerical experiments have been realized at different resolutions using the coupled ocean-atmosphere general circulation model developed at IPSL (Institut Pierre Simon Laplace) in Paris. The atmospheric LMD model and the oceanic OPA-LODYC model are coupled without any flux adjustment. The mean simulated climate is stable and differs from reality through a few well established systematic errors. The variability simulated by the model at these different resolutions is compared for various areas, and more specifically the North Atlantic. A statistical method, the Multi-channel Singular Spectrum Analysis (M-SSA), is used to detect sea surface temperature oscillations at different time scales. Oscillations over the North Atlantic display a well-known tripole feature, which seems to depend primarily on the ocean resolution. The period of the oscillation (from 8 to 12 years) seems more sensitive to the atmospheric resolution.

( Global coupled simulations of climate change due to increased atmospheric CO2 concentration )

Pierre Barthelet, Sandrine Bony, Pascale Braconnot, Alain Braun, Daniel Cariolle, Emmanuelle Cohen-Solal, Jean-Louis Dufresne, Pascale Delecluse, Michel Deque, Laurent Fairhead, Marie-Angele Filiberti, Michelle Forichon, Jean-Yves Grandpeix, Eric Guilyardi, Marie-Noelle Houssais, Maurice Imbard, Herve Le Treut, Claire Levy, Zhao Xin Li, Gurvan Madec, Pascal Marquet, Olivier Marti, Serge Planton, Laurent Terray, Olivier Thual, Sophie Valcke

Compte Rendu Académie des Sciences Paris, Série II a, vol.326, p.677-684, mai 1998

Two transient CO2 experiments using two coupled general circulation models developped by the french GASTON group have been realized using the same methodology . No flux corrections at the air-sea interface were used in these experiments. The main features of the present climate are reasonably well captured by both coupled models in the control simulations, although the biases are not the same. The transient CO2 simulations show a global warming, ranging between 1.6 C and 2.0 C at the time of CO2 doubling(+70 years). These values, and the main geographical characteristics of climate change are in agreement with previous studies published by other research groups, using either flux corrected or non-flux corrected models.

S. Bony, J.-L. Dufresne, L. Fairhead

EGS XXIII General Assembly, Nice, France, 20-24 April 1998

L. Fairhead, J.-L. Dufresne, H. Le Treut, L. Li

EGS XXIII General Assembly, Nice, France, 20-24 April 1998

M.-A. Filiberti and J.-L. Dufresne

EGS XXIII General Assembly, Nice, France, 20-24 April 1998

Vintzileos A., Dufresne J.L., Le Treut H., Fairhead L.

EGS XXIII General Assembly, Nice, France, 20-24 April 1998

Filiberti M.A., Dufresne J.L., Madec G.

Atelier de Modélisation de l'Atmosphère, Toulouse, France, 8-9 décembre 1998

J-L.Dufresne, L.Bopp, P. Ciais, L. Fairhead, P. Friedlingstein, H.Le Treut, P.Monfray

EGS XXV General Assembly, Nice, France, 25-29 April 2000

In simulations carried out to estimate anthropogenic climate change, the atmospheric CO2 increase is commonly prescribed using different emission scenarii, like, for example, those assembled by the IPCC. The rate of atmospheric CO2 increase depends on the rate of these prescribed antropogenic emissions (changes in land use and fossil CO2 emissions) and on the uptake by the ocean and the biosphere. Carbon uptake by oceans and continents is not independent of climate change. Recent studies have suggested that over the next decades, the CO2 uptakes may be reduced by climate change thus introducing a positive feedback in the carbon-climate system. In order to study this feedback within the fully coupled carbon-climate system, we have recently added comprehensive, spatially resolved, oceanic and biospheric carbon models to the IPSL coupled AOGCM. The model configuration will be described and results from two 240 year long simulations carried out with it will be presented. The first simulation is a control simulation with no anthropogenic CO2 emissions. The second simulation is a scenario simulation using historical anthropogenic emissions from 1860 to 1990 and, from 1990 to 2100, emissions following the SRES98-A2 IPCC scenario. At the time of abstract submission the pertirbed experiment has reached year 1985, and the simulated CO2 content is realistic.

P. Friedlingstein, L.Bopp, P. Ciais, J-L.Dufresne, L. Fairhead, H.Le Treut, P.Monfray

EGS XXV General Assembly, Nice, France, 25-29 April 2000

In simulations carried out to study anthropogenic climate change, the atmospheric CO2 increase used has always been prescribed by different scenarii, like, for example, those suggested by the IPCC. The rate of CO2 increase depends on the rate of anthropogenic emissions and on the uptake by the ocean and the biosphere. However, recent studies suggest that those CO2 uptakes may be reduced by the climate change thus introducing a positive feedback in the carbon-climate system.
We will present here two estimates of this positive carbon-climate feedback. Our first estimation uses the results of a classical climate simulation carried out with the IPSL AOGCM where the CO2 increase is fixed at 1%/year (CMIP). These results are used to carry out two simulations of the carbon cycle: in the first, the carbon cycle models do not respond to climate change whereas in the second, they do. We can thus estimate the feedback between the carbon cycle and climate.
A second estimate of this feedback uses results from a fully coupled carbon-climate simulation now in progress.

L.Bopp, P.Monfray, O.Aumont, J.C.Orr, G.Madec, L.Terray, J-L.Dufresne, H.Le Treut.

EGS XXIV General Assembly, The Hague, The Netherlands, 19-23 April 1999

To investigate the effect of future climate change on marine biology and the ocean carbon cycle, we imbedded a prognostic model of ocean biogeochemistry in an oceanic general circulation model (OGCM). The same OGCM coupled to an atmospheric general circulation model, was used without flux correction to simulate climate response to increased greenhouse gases (+1\% CO2 yr$^{-1}$ for 80 years). At 2xCO2 in 2060, both reduced nutrient supply and increased light efficiency resulted from increased stratification in the upper ocean. Both effects lead to significant large-scale changes in marine primary production (from -20\% in the tropics to +5\% in the Southern Ocean for the zonal mean). In regards to the increasing air-sea CO2 flux, we will differentiate increases due to rising atmospheric CO2 from reductions by climate change. Furthermore we will describe sensitivity studies made with two different prognostic biogeochemical schemes, and climate change forcing from two different coupled models.

Bopp L., Monfray P., Aumont O., Dufresne J.L., Le Treut H., Madec G. And Orr J.

Abstract for the 3d US-JGOFS SMP meeting, 1998

Filiberti, M.A., Dufresne, J.L., Grandpeix, J.Y.,

Note technique de l'IPSL, 1999

M.A. Filiberti, J.L.Dufresne, M.N. Houssais, M.Imbard, G. Madec

EGS XXII General Assembly, Viena, Austria, 21-25 April 1997

J.L.Dufresne, L. Fairhead,M.A. Filiberti, M.N. Houssais

EGS XXII General Assembly, Viena, Austria, 21-25 April 1997

In sea ice covered regions, the ocean surface is highly heterogeneous (open water, new ice, thick pack ice...). The sea ice GCM we developed takes this heterogeneity into account by allowing various sea ice classes, whereas atmospheric models used in coupled GCMs usually allow only homogeneus surfaces. We analyse how the sea ice distribution is modified by the following different sea ice / atmosphere interface models :
- the atmospheric model only considers one type of surface and fluxes over open water and over ice are similar
- the atmospheric model only considers one type of surface but the atmospheric heat flux is redistributed through an interface that approximates the spatial heterogeneity of the underlying surface
- the atmospheric model computes a separate flux over each of this type of surface
These results were obtained with the LODYC ocean/sea ice GCM coupled to a simple bulk atmosphere and with the full coupled IPSL GCM.

Dufresne J.L, Filiberti M.A., Grandpeix J.Y., Houssais M.N.

Atelier de Modélisation de l'Atmosphère, Toulouse, 2-3 décembre 1996

L'interface océan-glace de mer-atmosphère est extrêmement hétérogène. Le modèle de glace-océan du LODYC, utilisé par la communauté "GASTON", reproduit en partie cette hétérogénéité (mailles mixtes contenant de l'océan libre et différents types de glace) alors que les modèles d'atmosphère (Arpège, LMD 5) ne la reproduisent pas ou peu (mailles homogènes ou mailles mixtes océan libre - un seul type de glace). De plus, aux hautes latitudes, une maille atmosphérique recouvre un nombre élevé de mailles océaniques. Nous avons développé un modèle de raccordement qui répartit de façon différenciée les flux calculés par le modèle d'atmosphère sur les differents types de surface (oc\'ean libre ou vari\'et\'es de glace) en fonction de leur distribution statistique (fraction surfacique) et de leur caracteristiques individuelles (temp. de surface, albedo, etc...). Ce modèle de raccordement garantit la conservation des flux à l'interface. Nous présentons le modèle de raccordement et montrons la sensibilité de la fraction de glace à la méthode de répartition des flux. Nous abordons également le problème de la stabilité numérique du raccordement glace-atmosphère.

M.A. Filiberti, J.L. Dufresne, G. Madec, M.N. Houssais, M. Imbard

Atelier de Modélisation de l'Atmosphère, Toulouse, 2-3 décembre 1996, pp.63-68

Dufresne J.L, Grandpeix J.Y., Houssais M.N.

EGS XXI General Assembly, Den Hague, 6-10 May 1996

Two important issues of sea-ice model coupling with AGCM are considered. First the numerical oscillations induced by straight sea-ice/atmosphere coupling (in a fashion similar to the usual ocean/ atmosphere coupling) are investigated. A simple explanation is presented and exemplified : the oscillations are primarily due to the strong feedbacks between SST and surface flux beeing not properly taken into account. The second important issue is the quality of flux repartition between a homogeneous AGCM mesh and the amalgam of open water, thin ice, thick pack ice ... which make up a sea-ice model mesh. Practical solutions are given for both issues. A first implementation is tested in a thermodynamic sea-ice model coupled to a simple bulk formula atmosphere. The inclusion in the full coupled GCM of the IPSL is under way; first results are presented.

Dufresne J.L, Grandpeix J.Y.

Laboratoire de Météorologie Dynamique, Note Interne 205, juin 1996

L'interface océan-glace de mer-atmosphère est extrêmement hétérogène. Le modèle de glace-océan du LODYC, utilisé par la comunauté "GASTON", reproduit en partie cette hétérogénéité (mailles mixtes contenant de l'océan libre et différents types de glace) alors que les modèles d'atmosphère (Arpège, LMD 5) ne la reproduisent pas ou peu (mailles homogènes ou mailles mixtes océan libre - un seul type de glace). De plus, aux hautes latitudes, une maille atmosphérique recouvre un nombre élevé de mailles océaniques. Nous avons développé un modèle de raccordement qui répartit de façon différenciée les flux calculés par le modèle d'atmosphère sur les diff'erents types de surface (océan libre ou variétés de glace) en fonction de leur distribution statistique (fraction surfacique) et de leur caracteristiques individuelles (temp. de surface, albédo, etc...). Ce modèle de raccordement garantit la conservation des flux à l'interface. Dans cette note, nous abordons tout d'abord le problème de la stabilité numérique du raccordement glace-atmosphère, puis présentons le modèle de raccordement développé.

D. Cruette, A. Marillier, J.L. Dufresne, J.Y. Grandpeix, P. Nacass, H.Bellec

to be published in the J. Atmos. Oceanic. Technol.