How Important is the Growth of Ice from Frozen Solution Droplets for Cirrus Clouds?

All cloud and climate models assume ice crystals are pure even though cloud and haze drops are solutions. Prior experiments show that, during the freezing of solution drops, phase separation into pure ice and a freeze-concentrated solution takes place, affecting the ice nucleation process. This may also affect the subsequent growth as the resulting ice crystal. We present measurements of ice crystal growth from frozen 20% weight-percent sodium chloride (NaCl) solution drops in the button electrode levitation (BEL) diffusion chamber at temperatures below -40°C. Measured scattering diffraction patterns show that concentrated solution droplets remain unfrozen with classical diffraction fringes until the droplets freeze. Upon freezing, the scattering patterns become complex with 0.1 seconds which is in contrast with frozen pure water, which retains a liquid-like scattering pattern. After freezing, solution particles initially grow as spherical-like crystals, and then transition to faster growth indicative of a morphological transformation (such as the development of branching arms). The measurements indicate that ice formed from solution droplets grows differently and has higher growth rate than ice formed from pure water. We use these results to develop a power-law based parameterization, and show the impacts on parcel model simulations of cirrus.