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キーワード:
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要旨:
Atmospheric aerosol particles fundamentally affect cloud formation and properties by acting as cloud condensation nuclei (CCN) at cloud base and beyond. The effects of aerosols on clouds in theory and processes on small scale are well understood. For real clouds and for a range of atmospheric pollution states, however, the understand- ing of microphysical processes across the entire cloud structure still bears major open questions. Aircraft studies have accurately measured the aerosol effects on clouds on local scales and for short time periods. Satellite investigations cover large scales for extended periods, but with limited accuracy on microphysical processes at different cloud levels, often covering the cloud tops only. A combination of both,provides a comprehensive picture of aerosol and cloud microphysics on large geographic scales across multiple years, which is crucial to understand the current state and future development of the climate system. In this thesis, in situ aerosol data and high-resolution satellite observations across multiple years were combined for the atmosphere over the remote Amazon rain for- est. Satellite retrieved profiles of the temperature and the effective radius of cloud droplets were used to resolve seasonal changes in fundamental cloud properties. A clear seasonality was found in aerosol and cloud parameters. The fraction of aerosol particles being activated into cloud droplets was high during the pristine wet season, but also during the polluted dry season. It was higher than expected from previous studies. The results show that the cloud formation in the Amazon is both, aerosol- and updraft-sensitive, not just for the low aerosol concentrations in the wet season, but also under the heavy biomass burning smoke influence in the dry season. Our findings shed light on the aerosol-driven changes in fundamental parameters of trop- ical convective clouds and suggest that the buffering effect of updraft-limited droplet activation at high aerosol concentrations is smaller than expected. The effects of aerosol particles on cloud properties are not limited to cloud base, but cover the entire vertical cloud structure. Seasonal patterns in the vertical cloud structure were investigated by resolving the distinct microphysical zones of conden- sational droplet growth, collision and coalescence, secondary droplet activation, the mixed phase of water and ice particles as well as the ice phase. The vertical profiles of the effective radius of cloud particles as a function of temperature differ strongly between the low aerosol conditions during the wet season and the biomass burning smoke dominated dry season. The vertical depth of the cloud microphysical zones is strongly seasonal as well. The seasonality is most pronounced for the condensational growth zone, which is much deeper in the dry season. In contrast, the secondary activation zone plays a more significant role in the wet season. These findings under- line that the widely variable aerosol population in the Amazon has profound effects on microphysical processes across the entire vertical profile of convective clouds.
