The Impact of Boundary Layer and Free-Troposphere Aerosol Particles on Arctic Low-Level Clouds

The impacts of aerosol particles on the lifecycle of Arctic mixed-phase clouds is still an open question for debate. We are using both observations and modeling simulations to specifically understand the influence of aerosol particles on the dissipation of these clouds. We have identified cases at the North Slope Alaska DOE observatory in which aerosol may have played a role in the dissipation of mixed-phase clouds. We’ve used one of these cases to design a series of large-eddy simulations in which allow the aerosol field to deplete naturally, or to decrease in a controlled way to isolate the impacts of aerosol particles both below and above the cloud layer. We find that particles both below cloud base are most important, as expected. However, particles above the cloud top can help to extend the cloud lifetime, particularly if the cloud top extends above the boundary layer inversion base. In all cases we find that the cloud will eventually decay, however the microphysical processes that control the decay – drizzle production or the WBF process – depends on the aerosol concentration.