Dust particles are an important driver of ice nucleation in clouds leading to precipitation. Dust particles consist mostly of mineral particles but in contrast to desert dust, soil dust consist also of a small fraction of organic matter. Conen et al. (2011) show that “particles from the clay and silt size fraction of four different soils naturally associated with 0.7 to 11.8 % organic carbon (w/w) can have up to four orders of magnitude more ice nucleation sites per unit mass active in the immersion freezing mode at −12°C than montmorillonite, the nucleation properties of which are often used to represent those of mineral dusts in modelling studies”. Currently global climate models do not consider a difference between soil dust and desert dust.

We want to make a first attempt to quantify the importance of soil dust as ice nuclei on a global scale in present and possible future conditions. Therefore we use a modified version of the global climate-aerosol model ECHAM6-HAM2. In that version we are able to differentiate between emissions from agricultural sites (soil dust) and natural source regions (desert dust) (Stanelle et al., 2014). Further new parameterizations to describe the ice nucleation capability of desert and soil dusts are currently being implemented. The parameterizations are empirical schemes based on laboratory measurements, which include the ice nucleation ability of the different dust types. The student will investigate how the different parameterization schemes in combination with the dust type influence the freezing process and thus the properties of clouds and their climate impact.

This topic is ideal for a student interested in global climate modeling and cloud microphysics.