Global modelling of ice nucleating particles and their effects on cirrus clouds

Abstract

Atmospheric ice nucleating aerosol particles (INPs) can influence the climate system by modifying cloud properties and consequently the Earth's radiation budget. However, these aerosol-cloud interactions and their effects on the global scale, especially regarding cirrus clouds, are still only poorly understood, and subject to large uncertainties. In this thesis INP-induced modifications of cirrus clouds are analysed by employing the atmospheric chemistry general circulation model EMAC, including the aerosol microphysics submodel MADE3. To facilitate the analysis of INP-effects, model improvements and developments with respect to the representation of ice nucleating particles are applied. Besides mineral dust and soot aerosols, additional types of INPs are implemented, i.e. crystalline ammonium sulfate and glassy organic particles. A global climatology of the different INP-types is presented and global effects on cirrus coud properties and the radiative balance are quantified. Sensitivities with respect to the freezing efficiency of INPs, to the vertical velocities during cloud formation, and the effects of anthropogenic INPs are analysed.