Numerical simulations of the Sensitivity of Mixed-Phase Arctic Stratus to Ice Forming nuclei

We have conducted large-eddy simulations (LES) of a mixed-phase stratuscumulus cloud in the Arctic boundary layer observed on 4 May 1998 during the FIRE/SHEBA field experiment.

Using the latest version of the Regional Atmospheric Modeling System (RAMS), we initialized the IFN profile with the observed data measured with Colorado State University continuous flow diffusion Ice Nucleus Counter, and then prognose the IFN changes from its initial value due to entrainment at the cloud top. The IFN sounding exhibited concentrations ranging from less then 5 per liter below cloud base to a peak of 85 per liter at the inversion. In a sensitivity run, the initial IFN concentration is set to 5 per liter throughout the depth of the boundary layer.

Preliminary results using the observed IFN sounding showed that the thin layer of liquid water present initially near the cloud top disappeared completely after 90 min of the simulation due to the entrainment of IFN which resulted in glaciation of the cloud. The IFN concentration is quickly quadrupled from the initial value in the cloud layer. In the sensitivity run, the layer of the liquid water is maintained constant for 130 min of the simulation, and only experienced slight reduction after that.

A series of sensitivity simulations are being performed to investigate the influence of the entrainment of IFN and cloud condensation nuclei on the cloud thermodynamic, dynamic, and radiative properties of the Arctic boundary layer and on surface energy budget of sea ice.