Aerosol-cloud Interactions in Orographic Wave Clouds (ICE-L)

Ice nucleation and cloud droplet freezing are two of the most poorly constrained cloud microphysical processes in the atmosphere. Orographic wave clouds at mid-tropospheric levels provide an ideal testbed to study these processes by combining aircraft measurements and numerical modeling. In the presented work we investigate wave clouds observed over the Rocky Mountains during the ICE-L campaign using the Unified Model. The thermodynamic and dynamic properties of the wave clouds are extremely well captured in the simulations, which allows us to focus on the representation of cloud and aerosol processes. Cloud microphysics are represented with the newly developed CASIM microphysical scheme, which accounts for aerosol processing and vertical transport. We evaluate the performance of different ice nucleation parameterizations in representing the measured microphysical evolution. In addition the vertical redistribution of aerosol particles due to sedimenting ice crystals is investigated. This comparison provides important insights in our current understanding of cloud droplet freezing and ice nucleation and the role of mid-tropospheric clouds to redistribute aerosol particles.