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Les aérosols et le transport dans la haute troposphère et la stratosphère tropicale à partir des mesures du lidar spatial CALIPSO

Jean-Paul Vernier 1
LATMOS - Laboratoire Atmosphères, Milieux, Observations Spatiales
Abstract : This work deals with a study of stratospheric aerosols and transport processes responsible for their time evolution from the first two years observations of the CALIOP lidar carried on the French-US CALIPSO satellite launched in May 2006. After adaptation of the retrieval algorithms to the faint Mie scattering signal and calibration correction required by the presence of aerosols at altitude levels of standard calibration, it is shown that zonal mean scattering ratios of 2% precision could be obtained. After applying those corrections as well as a cloud mask based on the depolarization of the lidar signal, the time evolution of the aerosols between 15-40 km altitude from July 2006 to September 2008, leads to the following conclusions: i) a significant contribution, often ignored, of volcanic eruptions of medium 3-4 explosivity index resulting in plumes injected at around 19-20 km altitude, then slowly lifted by the Brewer-Dobson circulation until 25 km within one year; and ii) the decoupling between, the mid- and lower stratosphere separated by a region of small or zero vertical velocity at around 20 km. In agreement with generally accepted ideas, the tropical midstratosphere displays a slow upwelling at an average of 300 m/month within the "tropical pipe", and meridional exchange intensity modulated by the quasi-biennial oscillation. In contrast and in contradiction with the currently accepted scheme of slow ascent by radiative heating of air above the top altitude of convective outflow around 14 km, the region below 20 km is found to be the location of frequent injections of clean air, likely washed-out from the troposphere, and particularly intense at equatorial latitudes during austral summer. Since the TTL, the Tropical Tropopause Layer, is defined as the region of the stratosphere under influence of the troposphere, those observations suggest a top of this layer at around 20 km. A consequence of the mixing with injected clean air is the fast cleansing of volcanic aerosols occasionally present in the TTL. Finally, another unexpected feature reported by the lidar is the presence of additional seasonal aerosols between 15-18 km, above West Africa and South Asia during their respective monsoon season, which could be small mineral dust lifted by convection from neighbouring desert areas.
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  • HAL Id : tel-00669120, version 1


Jean-Paul Vernier. Les aérosols et le transport dans la haute troposphère et la stratosphère tropicale à partir des mesures du lidar spatial CALIPSO. Physique Atmosphérique et Océanique []. Université de Versailles-Saint Quentin en Yvelines, 2010. Français. ⟨NNT : 2010VERS0006⟩. ⟨tel-00669120⟩



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