Testing freezing mechanisms in ICE-L lee wave clouds

Heterogeneous ice nucleation is not well represented in cloud models. We use a 1-D microphysics model to test heterogeneous ice nucleation mechanisms from data obtained in multiple passes through lee wave clouds. Clouds were sampled during the Ice in Clouds Experiment (ICE) - Layer (L) campaign over Wyoming and data from 9 flights in the temperature range -38 to -10C will be presented.

Each pass through the cloud is used to initialise the thermodynamic profile for the 1-D microphysical model and the driving winds. Ice nucleation mechanisms tested are deposition nucleation, immersion/condensation freezing and an evaporation freezing mechanism. This is achieved through the activation of pre-determined concentrations of ice nuclei at different relative humidities or when the cloud droplets are evaporating. By comparing the observed ice concentrations and condensed water contents to the model output, derived from varying the input ice nuclei concentration, the best combinations of ice nuclei concentration and freezing mechanism can be determined.

We will compare the inferred ice nuclei concentrations with measured ice nuclei concentrations and aerosol concentrations to test the hypothesis that the concentrations of insoluble aerosol larger than 500 microns are a good predictor of ice nuclei concentrations.