Bernd Karcher is working with Graham Feingold and David Fahey at the National Oceanic and Atmospheric Administration and others to investigate dynamical and microphysical controls of ice formation in clouds. A lack of proper representation of cloud ice in global models compromises the fidelity with which weather and climate can be simulated. Karcher will strive to improve the understanding of ice formation processes in tropospheric clouds, resorting to theoretical and numerical methods and making use of results from high resolution atmospheric models. He will be studying fundamental issues regarding links between small-scale variability in relative humidity and ice nucleation, while at the same time recognizing that ice crystals may nucleate on a plethora of atmospheric aerosol particles with vastly different ice-forming properties. Due to their relevance for the Earth's radiative and the stratospheric moisture budget, emphasis is placed on cirrus clouds originating from convective detrainment or forming in-situ.