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Cosmic Dust in the Terrestrial Atmosphere (CODITA)
Date du début: 1 avr. 2012, Date de fin: 31 mars 2017 PROJET  TERMINÉ 

"This project addresses a fundamental problem – the size of the cosmic dust input to the earth’s atmosphere. Zodiacal cloud observations and spaceborne dust detection indicate a daily input of 100 – 300 tonnes, in agreement with the accumulation rates of cosmic elements (e.g. Ir, Pt) in polar ice cores and deep-sea sediments. In contrast, measurements in the middle atmosphere – by radar, lidar, high-flying aircraft and satellite remote sensing – indicate that the input is only 5 - 50 tonnes. The aim of CODITA is to resolve this huge discrepancy.There are two reasons why this matters. First, if the upper range of estimates is correct, then vertical transport in the middle atmosphere must be considerably faster than generally believed; whereas if the lower range is correct, then our understanding of dust evolution in the solar system, and transport from the middle atmosphere to the surface, will need substantial revision. Second, cosmic dust particles enter the atmosphere at high speeds and in most cases completely ablate. The resulting metals injected into the atmosphere are involved in a diverse range of phenomena, including: formation of layers of metal atoms and ions; nucleation of noctilucent clouds; impacts on stratospheric aerosols and O3 chemistry (which need to be evaluated against the background of a cooling stratosphere and geo-engineering plans to increase sulphate aerosol); and fertilization of the ocean with bio-available Fe, which has potential climate feedbacks.CODITA will use laboratory studies to target poorly understood aspects of this problem, such as the nature of the ablation process itself, the formation of meteoric smoke particles, and their role in ice nucleation and the freezing of polar stratospheric clouds. The results will be incorporated into a chemistry-climate model of the whole atmosphere, so that it will be possible, for the first time, to model the effects of cosmic dust self-consistently from the thermosphere to the surface."