PhD-thesis

A short summary of my PhD thesis

Deep convection induced by vegetation fires is one of the most intense forms of atmospheric convection. The extreme cloud dynamics with high updraft velocities (up to 20 m/s) already at the cloud base, high water vapor supersaturations (up to 1%), and high number concentrations of aerosol particles freshly emitted by the fire (up to 100,000 cc) represent a particular setting for aerosol-cloud-interactions. A crucial step in the microphysical evolution of a convective cloud is the activation of aerosol particles to form cloud droplets. The activation process affects the initial number and size of cloud droplets, and can thus influence the evolution of the convective cloud and the formation of precipitation. The main parameters determining the initial number and size of cloud droplets are the number, size and hygroscopicity of aerosol particles available at the cloud base as well as the updraft velocity. To investigate the influence of these parameters under the conditions of pyro-convection, numerical simulations have been performed using a cloud parcel model with a detailed spectral description of cloud microphysics, including different Köhler model approaches for hygroscopic growth. The results show pronouncedly different regimes of dependence of aerosol activation on updraft velocity and aerosol particle concentration for regular and pyro-convective conditions. Building on a realistic parameterization of CCN activation derived from the parcel model simulations, a three-dimensional plume model (ATHAM) was used to further investigate the full range of cloud microphysical processes in pyroconvective clouds.