Cloud-Aerosol-Dynamic Interactions Measured in a New Expansion Chamber

Microphysical properties of cloud particles, such as concentration, size, composition, phase, and shape produce complex feedback processes, and thus large uncertainties in cloud behavior. Measuring these properties under controlled thermodynamic conditions (e.g., temperature, pressure, and relative humidity) is necessary for understanding and modeling cloud particle interactions in the atmosphere. We introduce a new cloud chamber facility to study the growth of cloud particles under controlled thermodynamic conditions. The facility comprises of two vacuum-sealed chambers, each with an approximate volume of 0.14 m³. A cloud is nucleated in one chamber via rapid expansion, producing a temperature decrease: this causes moist air and aerosol to produce droplets, ice crystals, or a mixture thereof, given the thermodynamic conditions. During the experiment, we take measurements of key conditions and statistics, such as temperature, pressure, relative humidity, aerosol concentration, and particle size and speed distributions. Preliminary results are presented from a range of initial conditions and their impact on the subsequent droplet or ice nucleation and growth.