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Analyse des mesures de l'expérience satellitaire SAGE III : algorithme d'inversion et validation des résultats. Comparaison des produits des instruments de la mission spatiale ACE avec des mesures corrélatives à distance et in situ.

Abstract : One of the conclusions of the last IPCC report (2007) is that the comprehension of climate change is still incomplete. In particular, the role of the stratosphere is not well known ; that is why it is important to study its composition and the physical and chemical processes in the stratosphere. Solar occultation measurements (like SAGE III) and in situ measurements are particularly appropriate for these studies. In this thesis, we have studied the consistency of the existing measurements. My work consists of the inversion of SAGE III transmissions in order to obtain vertical profiles of ozone and nitrogen dioxide concentrations and of aerosol extinction coefficients in nine channels between 385 and 1545 nm. In the channels around 450 nm, a vertical smoothing of the tangent transmissions is required to compensate for the problem of spectral neutrality of the attenuator. In the 1545 nm channel, CO2 absorption is computed using MODTRAN 5. The uncertainties are evaluated using a Monte Carlo method. SAGE III products obtained by our algorithm are compared to official products (NASA), to products from another algorithm developped in St. Petersburg and to coincident measurements from the SAGE II and POAM III sensors. Globally, these comparisons show that the SAGE III products from my LOA algorithm are of good quality. However, a comparison performed with data from the balloon-borne instrument SPIRALE (in situ measurements) on the edge of the polar vortex shows a good agreement between ozone and a disagreement for NO2. This disagreement shows that in complex dynamical situations, the solar occultation method for reactive species (such as NO2) is not well suited. Furthermore, diurnal variations of NO2 complicate the comparisons between remote sensing measurements and in situ ones. A specific study concerning aerosol resulting from forest fires in the western Canada (August 2003) has been done using official SAGE III data. Intrusions of biomass burning aerosols in the lower stratosphere by pyroconvection could be the reason for the increase in aerosol extinction coefficients in the lower stratosphere observed in SAGE III events. We have deduced the microphysical properties of these aerosols from the SAGE III measurements and showed that the increase in the aerosol extinction coefficient was caused by an increase in the number of particles in the lower stratosphere. Nevertheless, the chemical composition of these aerosols could not be deduced from the SAGE III measurements because extinction measurements are not sensitive enough to the refraction index. Since the end of the SAGE II, SAGE III and POAM III missions, the ACE-SCISAT instruments along with the SOFIE instrument are the only solar occultation instruments providing informations on the stratosphere. Thus, we have studied the consistency between ACE data and SAGE II, SAGE III and SPIRALE data. This work is carried out within the framework of the international validation campaign. We have shown that aerosol extinction coefficients retrieved using IMAGER data are in disagreement with those retrieved using SAGE II and SAGE III and that the ozone and NO2 volume mixing ratio from FTS and MAESTRO are in a good agreement with SAGE III data. However, we find also discrepancies between NO2 retrieved by ACE and that retrieved by SPIRALE although the other species retrieved using FTS (CH4, N2O, HNO3, O3, HCl) and MAESTRO (O3) are in a good agreement with SPIRALE data.
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Submitted on : Sunday, June 22, 2008 - 9:59:38 PM
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Cédric Tétard. Analyse des mesures de l'expérience satellitaire SAGE III : algorithme d'inversion et validation des résultats. Comparaison des produits des instruments de la mission spatiale ACE avec des mesures corrélatives à distance et in situ.. Océan, Atmosphère. Université des Sciences et Technologie de Lille - Lille I, 2003. Français. ⟨tel-00289578⟩

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