Prof. Christian von Savigny  (Institute of Physics, University of Greifswald) will deliver a talk in IAP colloquium on 21st April at 10:00 AM on the topic "Volcanic impact on atmosphere and climate: results from the DFG research unit VolImpact (FOR 2820)".

He will talk about how, Volcanic eruptions represent one of the most important drivers of climate change on time scales from a few years up to a decade. Studying the effects of volcanic eruptions allows improving the understanding of the climate system’s response to perturbations. Within the DFG funded Research Unit (Forschungsgruppe) VolImpact (FOR 2820), we investigate in five projects different aspects of volcanic eruptions on atmosphere and climate, i.e. (1) the initial development of volcanic plumes on time scales from hours to a few days, (2) the evolution of volcanic aerosol layers in the stratosphere, (3) the interactions of volcanic aerosols and tropospheric clouds, (4) dynamic and thermal effects of volcanic eruptions on the middle atmosphere as well as (5) volcanic effects on the hydrological cycle. 
This talk will first provide a brief review of volcanic effects on the earth system, followed by selected science results from the first phase of Volimpact. An important finding is related to the evolution of the particle size of stratospheric sulfate aerosols after volcanic eruptions. In contrast to previous expectations, the mean size of stratospheric sulfate aerosols decreases after many eruptions, which has important implications for the chemical and radiative effects of the eruptions. The talk will also address potential thermal effects of volcanic eruptions on the mesosphere and mesopause region. Initial simulations with the Upper Atmosphere version of ICON with idealized volcanic forcing will be presented, showing a significant warming of the mesopause region mediated via gravity-wave driven vertical coupling. We also investigated unusual optical phenomena that sometimes occur after volcanic eruptions, such as the rare occurrence of blue or green suns. All potential mechanisms leading to blue/green suns proposed in previous studies were investigated. The most likely cause remains anomalous aerosol scattering by a suitably shaped aerosol size distribution. Finally, previous attempts to estimate aerosol optical density from colors in historic paintings will be critically reviewed.