[tel-00673370] Caractérisation et Climatologie des Nuages Mésosphériques Polaires d'après les mesures de l'instrument GOMOS/ENVISAT

Noctilucent clouds, also called polar mesospheric clouds (PMC) when observed from space, are the visible manifestation of water ice particles persistently present near the summer mesopause at high latitudes, which is the coldest place on Earth. Because of their extraordinary height of about 83 km, at the edge of space, they can become visible to the naked eye when the sun sinks below the horizon, providing a dazzling display of bluish light. Since these clouds are extremely sensitive to changes in their environment, their observation conveys unique information concerning the various chemical and dynamical processes taking place in the mesosphere. GOMOS is a stellar occultation instrument combining 4 spectrometers in the spectral range 250 to 950 nm (UV-vis- near IR) and 2 fast photometers (470-520nm and 650-700nm). On the day side, in addition to star light, GOMOS measures also the solar light scattered by the atmospheric molecules. In the summer polar days, PMC are clearly detected using the photometers signals. The sun-synchronous orbit of ENVISAT allows observing them in both hemispheres. The main properties of these clouds (occurrence frequency, altitude, radiance) have been retrieved from GOMOS data. A very high accuracy is possible thanks to the solar occultation technique. Moreover, the observation of these clouds with the spectrometers provides the spectral dependence of the light scattered by the PMC particles, from which it is possible to derive their radii. A comprehensive climatology of all these properties has been established throughout 8 years, from 2002 to 2010.



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