CO2 atmosphérique et simulation de ses variations d'origine naturelle et anthropique

in Revue de la Science et des Techniques (1996), 14

A new distribution of vegetation types and its inclusion in a global biosphere model

Poster (1995, August)

Auroral Lyman alpha and H2 bands from the giant planets. 2: Effect of the anisotropy of the precipitating particles on the interpretation of the 'color ratio'

in Journal of Geophysical Research (1995), 100

Previous spectral analyses have given evidence of collisionally excited Jovian and (at times) Saturnian H2 Werner bands being absorbed by hydrocarbons at the shortest wavelengths along the auroral ovals ... [more ▼]

Previous spectral analyses have given evidence of collisionally excited Jovian and (at times) Saturnian H2 Werner bands being absorbed by hydrocarbons at the shortest wavelengths along the auroral ovals, and of a longitudinal dependence of this absorption in the Jovian aurorae. This 'color ratio' has been used to estimate the energy of the primary particles. In such estimates, particles are generally assumed to penetrate vertically into the atmosphere. However, the precipitating particle angular distribution is unknown, and a model developed for a diffuse aurora by Prange and Elkhamsi (1991), for instance, predicts quite different possible distributions. We consider here the influence of the angular distribution used in the model, and show that distributions peaking far from vertical may increase the energy derived from a given color ratio by as much as a factor of 3. We discuss previous interpretations of the color ratio longitudinal modulation (variation of the auroral atmosphere structure, or of the incident particle energy) in view of the subsequent increase in energy input. We argue that an interpretation in terms of energy variations only is not consistent with the energy available in the magnetosphere if the aurorae are diffuse, and we discuss this finding in the context of recent Hubble Space Telescope (HST) images. [less ▲]

A numerical study of the influence of the dirunal cycle on the surface energy and water budgets

in Journal of Geophysical Research (1995), 100

Global models including atmospheric, oceanic, and biogeochemical processes are needed for the study of possible environmental changes, but they require efficient approximations of physical processes in ... [more ▼]

Global models including atmospheric, oceanic, and biogeochemical processes are needed for the study of possible environmental changes, but they require efficient approximations of physical processes in order to reduce the computing time. The need to resolve the dirunal cycle when treating such problems is questionable. The Interaction Soil Biosphere Atmosphere (ISBA) model describing soil-vegetation-atmosphere interactions is used to analyze the importance of the dirunal cycle on the surface energy and water budjets. Stand-alone simulations are first performed using the Hydrologic Atmospheric Pilot EXperiment-MOdélisation du BILan HYdrique (HAPEX-MOBILHY) and Amazonian Region Micrometeorological Experiment (ARME) data sets to assess the need of an explicit dirunal variation of the atmospheric forcing for different sites. As a reference, the run is forced by measured values of atmospheric variables and radiative fluxes. As a test, ISBA is run forced by the 24-hour means of these atmospheric and radiative forcings. The surface and deep water content, the total evaporation, and the net radiation flux are correctly evaluated without the diurnal cycle. In contrast, the interception reservoir is highly overestimated. The model is then coupled with a one-dimensional atmospheic model in which, as test, the solar flux at the top of the atmosphere is replaced by a daily constant mean insolation. The superficial soil moisture content and the total evapotranspiration flux are correctly estimated. The surface temperature and the sensible heat flux are not satisfactorily predicted. Thus it appears that neglecting the diurnal cycle is adequate when considering the hydrologic balance of the surface but not the surface temperature. [less ▲]

The importance of new chemical sources for the hot oxygen geocorona

in Geophysical Research Letters (1995), 22

Exothermic reactions involving metastable neutrals and ions were recently proposed as sources of hot oxygen atoms in addition to the classical O2(+) and NO(+) dissociative recombination. The Boltzmann ... [more ▼]

Exothermic reactions involving metastable neutrals and ions were recently proposed as sources of hot oxygen atoms in addition to the classical O2(+) and NO(+) dissociative recombination. The Boltzmann equations for thermal and nonthermal populations of O atoms are solved with Monte Carlo stochastic simulation method. It is shown that the calculated energy distribution functions of O atoms are significantly in nonequilibrium in the transition region between the thermosphere and the exosphere. It is found that the inclusion of additional sources leads to stronger disturbances of the energy distribution function and, as a consequence, increases the nonthermal fraction of hot O atoms. The variation of the vertical distribution of hot O between solar maximum and minimum conditions is also evaluated and shows good agreement with the available experimental evidence. [less ▲]

Ultraviolet observations of the Saturnian north aurora and polar haze distribution with the HST-FOC

in NASA STI/Recon Technical Report N (1995), 96

Near simultaneous observations of the Saturnian H2 north ultraviolet aurora and the polar haze were made at 153 nm and 210 nm respectively with the Faint Object Camera on board the Hubble Space Telescope ... [more ▼]

Near simultaneous observations of the Saturnian H2 north ultraviolet aurora and the polar haze were made at 153 nm and 210 nm respectively with the Faint Object Camera on board the Hubble Space Telescope. The auroral observations cover a complete rotation of the planet and, when co-added, reveal the presence of an auroral emission near 80 deg N with a peak brightness of about 150 kR of total H2 emission. The maximum optical depth of the polar haze layer is found to be located approximately 5 deg equatorward of the auroral emission zone. The haze particles are presumably formed by hydrocarbon aerosols initiated by H2+ auroral production. In this case, the observed haze optical depth requires an efficiency of aerosol formation of about 6 percent, indicating that auroral production of hydrocarbon aerosols is a viable source of high-latitude haze. [less ▲]

Carbon cycle modelling and remote sensing

in Space scientific research in Belgium (Earth Observations) (1995)

Evolution du Climat et Paléoclimat : effet de serre et CO2

in Espace et environnement (1995)

SIMULTANEOUS OBSERVATIONS OF THE SATURNIAN AURORA AND POLAR HAZE WITH THE HST/FOC

in Geophysical Research Letters (1995), 22(20), 2685-2688

Near simultaneous observations of the Saturnian H-2 north ultraviolet aurora and the polar haze were made at 153 nm and 210 nm respectively with the Faint Object Camera on board the post-COSTAR Hubble ... [more ▼]

Near simultaneous observations of the Saturnian H-2 north ultraviolet aurora and the polar haze were made at 153 nm and 210 nm respectively with the Faint Object Camera on board the post-COSTAR Hubble Space Telescope. The auroral observations cover a complete rotation of the planet and, when co-added, they reveal the presence of an auroral emission near 80 degrees N with a brightness of about 150 kR of total H-2 emission. The maximum vertical optical depth at 210 nm is found to be located similar to 5 degrees equatorward of the auroral emission zone. The haze particles are presumably formed by hydrocarbon aerosols initiated by H-2(+) auroral production. In this case, the 3 x 10(10) W of H-2 emission observed with the FOG, combined with the deduced haze optical depth requires an efficiency of aerosol formation of about 7%. This result indicates that auroral production of hydrocarbon aerosols is a viable source of high-latitude haze. [less ▲]

The morphology of the north Jovian ultraviolet aurora observed with the Hubble Space Telescope

in Planetary and Space Science (1994), 42

A series of six images covering a complete rotation of the north polar region of Jupiter were obtained in February 1993 with the Faint Object Camera on board the Hubble Space Telescope (HST). These images ... [more ▼]

A series of six images covering a complete rotation of the north polar region of Jupiter were obtained in February 1993 with the Faint Object Camera on board the Hubble Space Telescope (HST). These images provide the first global picture of the morphology of the Jovian ultraviolet aurora observed from Earth orbit. The camera passband was centered near 153 nm, a region dominated by the H2 Lyman bands and continuum. The successive exposures, taken approximately 90 min apart, are used to construct a polar view of the auroral zone. It is found that the auroral emissions do not exactly follow the footprint of a constant L-shell although the size of the oval and its location agree best with the footprints of the approximately equal to 30 R[SUB]J[/SUB] field line in the GSFC O6 model of the Jovian magnetic field. The displacement between the observed auroral zone and the theoretical oval may indicate a possible distortion of the Jovian magnetic field lines near the surface. A comparison with two images at the same wavelength obtained 8 months earlier shows that the main morphological features are persistent, in spite of changes in the detailed emission distribution. Small scale features with characteristic sizes of approximately 1000 km are observed along the auroral oval. The change of morphology observed as a function of the System 3 longitude appears as a persistent characteristic of the morphology of the north polar aurora. [less ▲]