Ice in clouds experiment-layer clouds. Part II: Testing characteristics of heterogeneous ice formation in Lee Wave clouds

Heterogeneous ice nucleation is a source of uncertainty in models that represent ice clouds. The primary goal of the Ice in Clouds Experiment--Layer Clouds (ICE-L) field campaign was to determine if a link can be demonstrated between ice concentrations and the physical and chemical characteristics of the ambient aerosol. This study combines a 1D kinematic framework with lee wave cloud observations to infer ice nuclei (IN) concentrations that were compared to IN observations from the same flights. About 30 cloud penetrations from six flights were modeled. The temperature range of the observations was -16° to -32°C. Of the three simplified ice nucleation representations tested (deposition, evaporation freezing, and condensation/immersion droplet freezing), condensation/immersion freezing reproduced the lee wave cloud observations best. IN concentrations derived from the modeling ranged from 0.1 to 13 L⁻¹ compared to 0.4 to 6 L⁻¹ from an IN counter. A better correlation was found between temperature and the ratio of IN concentration to the concentration of large aerosol (>500 nm) than between IN concentration and the large aerosol concentration or temperature alone.