Sensitivity of Arctic mixed-phase clouds to changes in ice nuclei

Description

Arctic mixed-phase stratocumulus clouds have been observed to be in a coupled or decoupled state with the surface beneath them. In either of these states, the cloud's characteristically long lifetime and its ability to maintain its liquid-to-ice ratio, (known as its phase) has been a source of study and research. Among other parameters, a water vapor source and an ice nuclei source are needed to maintain the structure of these clouds. If the cloud is decoupled from the surface, then the source of water vapor and ice nuclei could be entrained into the cloud from above. Similarly, if the mixed-phase cloud is coupled to the surface, then the water vapor and nuclei source can be from below the cloud. Ice nuclei in the Arctic can be advected into the region from sources in lower latitudes. The composition and concentration of the ice nuclei that are brought to the Arctic from foreign air masses is not constant in the time. It is suspected that the longevity, phase, and other properties of the mixed-phase cloud could be sensitive to changes in ice nuclei in the coupled and decoupled states. Using a large-eddy simulation with a two-moment bulk microphysics mode, we investigate how the cloud phase is modulated by changing aerosol concentrations. Preliminary work simulating the cloud in an uncoupled state shows a strong sensitivity to a prescribed ice concentration and ice nucleation assumptions. Additional experiments will reveal the cloud’s sensitivity to changes in ice nuclei in a coupled state.