Atmospheric Physics (Prof. Ulrike Lohmann)

Prof. Ulrike Lohmann's research in short:

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The Atmospheric Physics group focuses on the role of aerosols (also known as particulate matter) and clouds in the climate system. Clouds are one of the largest uncertainties for climate change predictions (IPCC, 2007). They scatter solar radiation causing a cooling (albedo effect of clouds) but absorb and re-emit terrestrial radiation causing a warming (greenhouse effect of clouds). While the cooling effect of clouds dominates for low-level clouds (stratus, stratocumulus), the warming effect dominates for high-level ice clouds (cirrus).

Additionally anthropogenic aerosols such as sulfate, nitrate, soot and organic compounds can modify cloud microphysical properties. An increase in aerosols causes an increase in the number of cloud droplets. This causes the cloud to appear brighter from space (indirect cloud albedo effect), which offsets some of the greenhouse gas warming. More and smaller droplets also retard rain formation, which has implications for the amount and distribution of precipitation. Similarly aerosols also influence ice and mixed-phase clouds. Here much less is known about the relevant freezing processes and which aerosols act as centers for ice crystals, so-called ice nuclei (IN). Therefore it is not even clear yet if an increase in aerosols will also cause mixed-phase and ice clouds to be brighter and to precipitate less or if the contrary happens.

In our group, we address various aspects of aerosols and clouds in the climate system by combining field measurements, laboratory experiments and modeling on various scales. In addition we also investigate the dynamics of glaciers (Prof. Heinz Blatter).