Ice nucleation in orographic wave clouds: Measurements made during INTACC

This paper reports on measurements made during the INTACC (INTeraction of Aerosol and Cold Clouds) experiment. Observations are shown from six wave cloud flights in the temperature range −12°C to −40 °C. In nearly all cases ice nucleation does not occur until after droplets have formed. Parcel trajectories that experience temperatures below −35°C are dominated by homogeneous nucleation, while parcel trajectories that stay above −35°C are affected by heterogeneous nucleation. Ice particles appear to be nucleated after the parent droplets reach their largest size and coldest temperature at the wave peak. The most likely heterogeneous nucleation mechanisms are immersion and/or contact nucleation.