The Influence of Kinetically-limited Growth of Ice Crystal on Homogeneous Freezing Rates in Cold Clouds

The rates at which supercooled aerosol/drops freeze by the homogeneous freezing mechanism has been well studied. The freezing rates depend, among other things, on the evolution of the temperature and the surrounding humidity, i.e. the net vapor supply. However, the net vapor supply depends critically on the vertical motions in cold clouds and how fast vapor is depleted through vapor growth. In cold clouds with relatively low vapor mixing ratios, surface kinetic resistance can strongly limit vapor growth. Recent studies suggest that ice vapor growth impedance potentially leads to high supersaturations, and this could impact nucleation rates. However, all prior models of ice growth predict neither crystal habit nor the deposition coefficients, which control the rate of vapor uptake at the particle's surface. We will present a new ice crystal growth model with a consistent consideration of surface kinetics effects, but that is suitable for cloud models. Instead of assuming the ice particles are all spherical, our model predicts the primary habit of the crystals by assuming spheroidal particles: prolate (column like) or oblate (plate like). The model is coupled to a surface model which predicts the deposition coefficients along the primary dimensions of the particles (a and c axes) in a self-consist way. We use this model to examine the feedbacks between kinetically-limited growth and nucleation in ice clouds. Parcel model simulations for several cases will be presented at the meeting.