Cloud Chamber Experiments Assessing the Principle of Arctic Cirrus Cloud Thinning

Cirrus clouds are an important component in the Arctic climate because of their net warming contribution to the radiation budget, which is especially dominant in the Arctic winter. The Arctic is one of the areas affected most severely by the global climate change, with a rise of the mean temperature and a continuous melting of the ice being observed since years. Therefore decreasing cirrus cloud coverage in the Arctic winter could potentially lead to an effective cooling at the surface.

Seeding with ice-nucleating particles (INPs) may suppress the homogeneous freezing of sulfuric acid solution droplets, consequently leading to a reduced number of ice crystals with bigger sizes (Mitchell and Finnegan, 2009). The residence time and optical properties of cirrus clouds strongly depend on the size and number of the ice crystals.

To untangle the effects of different parameters on cirrus cloud properties we performed cloud chamber expansion experiments, simulating the formation of Arctic cirrus clouds at temperatures between 200 and 230 K. Among the experiments we varied the aerosol number concentration, the aerosol types, the cooling rate and the temperature. Three different seeding aerosols were tested, namely quartz, fumed silica and calcium carbonate.

Our study describes the sensitivity of homogeneous ice formation as a function of ambient conditions. One of the main findings is that the total ice number concentration, which strongly depends on the number and type of seeding INPs, can be minimized.