Laboratory experiments of ice formation in cloud simulation chamber

A new cloud simulation chamber was built in 2005 at Meteorological Research Institute (MRI), Japan Meteorological Agency. Both temperature of the chamber wall and pressure inside the chamber are automatically controlled so as to simulate an adiabatic expansion (ascent) under a wide range of atmospheric conditions (30 to -100 C, 1000 to 30 hPa, 0 to 30 m/s), which leads to cooling of an air parcel and formation of cloud droplets and ice crystals in it. The MRI chamber is equipped with several optical and electrical sensors measuring size distributions, shapes and sphericity of aerosol and cloud particles from 0.3 µm to 5 mm in size.

Ice nucleation is one of the most important processes in cloud physics, especially for upper-level clouds and mid-latitude precipitating clouds. But it is not sufficiently understood how ice crystals form in clouds. The MRI chamber was started up for studies of ice formation and has been utilized in an attempt to identify ice nucleation modes and to quantify ice crystal concentrations activated under various tropospheric cloud conditions.

This paper describes an overview of basic features and instrumentation of MRI chamber and preliminary results in a first set of experiments. Data analysis revealed that the concentrations of ice particles were approximtely 20 L-1 in -25 C and very high, exceeding 1000 L-1 below -35 C. These findings will be compared with in situ observations.