Publications (7)3.19 Total impact
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Article: A new Venus General Circulation Model, in the context of the Venus-Express mission
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ABSTRACT: The Venus-Express mission will soon be on its way to explore in depth the atmosphere of Venus. Many questions concerning the mechanisms controling this atmosphere are still open, and certainly this new mission will contribute to bring answers, while raising other puzzles. In this context, we are developing at the Laboratoire de Meteorologie Dynamique a new General Circulation Model for the atmosphere of Venus, based on our experience with GCMs for Earth, Mars and Titan. This new 3-dimensional GCM covers altitudes from the surface up to 100 km, with a horizontal grid resolution of 48 longitudes by 32 latitudes. A new radiative transfer scheme has been developed specifically for this dense CO2 atmosphere, based on a temperature-dependent power net-exchange matrix, which is calculated using a Monte-Carlo simulation. Though this is our next step, the GCM does not yet include a self-consistent description of the clouds and of the atmospheric composition. We present the new radiative transfer scheme, and the preliminary simulations obtained with this new GCM, mainly discussing here the super-rotation obtained, and the mechanisms that generate this circulation.07/2005; 37:742. -
Article: A Monte Carlo method to develop radiative transfer parametrizations for terrestrial gcm
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ABSTRACT: New accuracy requirements are described that make it necessary to reconsider the problem of parameterizing infrared radiative transfer in atmospheric global circulation models. On this basis a net-exchange Monte Carlo methodology is presented for exploration of the detailed physics of radiative exchanges in emitting, absorbing and scattering atmospheres, and first application examples are presented for Earth clear sky and cloudy atmospheres.01/2003; -
Article: A boundary-based net-exchange Monte Carlo method for absorbing and scattering thick media
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ABSTRACT: A boundary-based net-exchange Monte Carlo method was introduced (JQSRT 74 (2001) 563) that allows to bypass the difficulties encountered by standard Monte Carlo algorithms in the limit of optically thick absorption (and/or for quasi-isothermal configurations). With the present paper, this method is extended to scattering media. Developments are fully 3D, but illustrations are presented for plane parallel configuration. Compared to standard Monte Carlo algorithms, convergence qualities have been improved over a wide range of absorption and scattering optical thicknesses. The proposed algorithm still encounters a convergence difficulty in the case of optically thick, highly scattering media.Journal of Quantitative Spectroscopy and Radiative Transfer 91(1):27-46. · 3.19 Impact Factor -
Article: Numerical investigation of the effect of soot aggregation on the radiative properties in the infrared region and radiative heat transfer
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ABSTRACT: The effect of aggregation on soot radiative properties in the infrared region of the spectrum is numerically investigated using Rayleigh–Debye–Gans theory for fractal aggregates (RDG-FA). In order to use the RDG-FA theory for a wide range of aggregate sizes and wavelengths, the predicted phase functions, scattering and absorption coefficients are compared with a more accurate theory, the integral equation formulation for scattering—IEFS. The importance of scattering when compared with absorption is investigated, as well as the effect of aggregation on the phase function shape and on the scattering cross section. It is concluded that in the case of small aggregates formed with small primary particles the scattering coefficient is negligible compared with the absorption coefficient, and scattering and aggregation of primary particles can be ignored. Thus, the Rayleigh approximation can be used leading to isotropic scattering. In the case of large aggregates constituted by large primary particles, aggregation becomes important and the scattering cross section is of the same order of magnitude of the absorption cross section. Moreover, the phase function becomes highly peaked in the forward direction. Therefore, the Rayleigh and the equivalent volume Mie sphere approximations are not valid, and the RDG-FA method emerges as a good compromise between accuracy and simplicity of application. However, radiative transfer calculations between two infinite, parallel, black walls show that scattering may always be neglected in the calculation of total radiative heat source and heat fluxes to the walls. The minor influence of scattering on the accuracy of the predictions is explained by the shift between the spectral region where scattering is important and the region where the spectral radiative heat source is large.Journal of Quantitative Spectroscopy and Radiative Transfer. -
Article: A net-exchange Monte Carlo approach to radiation in optically thick systems
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ABSTRACT: A Monte Carlo approach to radiative transfer in participating media is described and tested. It solves to a large extent the well known problem of Monte Carlo simulation of optically thick absorption configurations. The approach which is based on a net-exchange formulation and on adapted optical path sampling procedures is carefully designed to insure satisfactory convergence for all types of optical thicknesses. The need for such adapted algorithms is mainly related to the problem of gaseous line spectra representation in which extremely large ranges of optical thicknesses may be simultaneously encountered. The algorithm is tested against various band average computations for simple geometries using the Malkmus statistical narrow band model.Journal of Quantitative Spectroscopy and Radiative Transfer. -
Article: Super-rotation simulated with the new LMD Venus General Circulation Model
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ABSTRACT: Venus-Express is now in orbit around Venus, and soon will bring us new insights on Venus' atmosphere. In this context, we have developed at the Laboratoire de Météorologie Dynamique a new 3-dimensional General Circulation Model of Venus atmosphere, based on our experience of Earth, Mars and Titan models. The main feature of this new model is the infrared radiative transfer module, which computes the temperature structure self-consistently. This module is based on a temperature-dependent Power Net Exchange matrix, computed with a Monte-Carlo model developed at the Laboratoire d'Energétique de Toulouse. The current version of the model is based on a 48x32 grid, on 50 levels from surface to roughly 95 km altitude. The clouds layers, atmospheric composition and surface interactions are not yet included in our computations (clouds layers are fixed for radiative calculations), though all the tools are ready for these evolutions. We will present here preliminary simulations made with this Venus General Circulation Model. Starting from rest, a satisfying super-rotation is developing , with winds of the order of 150 m s-1 near the clouds top obtained after several tens of Venus days (of the order of 5000 Earth days). Though the temperature structure is not yet fully satisfying, we will discuss the circulation obtained, with emphasis on angular moment transport by the mean circulation and by eddies.-1:167. -
Article: Long-wave radiative analysis of cloudy scattering atmospheres using a net exchange formulation
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ABSTRACT: The Net Exchange Formulation (NEF) is an alternative to the usual radiative transfer equation. It was proposed in 1967 by Green [Q. J. R. Meteorol. Soc. 93 (1967) 371] for atmospheric sciences and by Hottel [H.C. Hottel, A.F. Sarofim. Radiative Transfer McGraw Hill, New York, 1967] for engineering sciences. Until now, the NEF has been used only in a very few cases for atmospheric studies. Recently we have developed a long-wave radiative code based on this formulation for a GCM of the Mars planet. Here, we will present results for the Earth atmosphere, obtained with a Monte Carlo Method based on the NEF. In this method, fluxes are not addressed any more. The basic variables are the net exchange rates (NER) between each pair of atmospheric layer (i, j), i.e. the radiative power emitted by i and absorbed by j minus the radiative power emitted by j and absorbed by i. The graphical representation of the NER matrix highlights the radiative exchanges that dominate the radiative budget of the atmosphere and allows one to have a very good insight of the radiative exchanges. Results will be presented for clear sky atmospheres with Mid-Latitude Summer and Sub-Arctic Winter temperature profiles, and for the same atmospheres with three different types of clouds. The effect of scattering on long-wave radiative exchanges will also be analysed.Atmospheric Research.
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2003
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Université Paul Sabatier - Toulouse 3
Toulouse, Midi-Pyrenees, France
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