Ice Crystal Habit Effects on the Resilience of Arctic Mixed-Phase Stratus Clouds in a One-Dimensional Model

Abstract

Arctic single-layer mixed-phase clouds were studied using a one-dimensional model that incorporated the adaptive habit growth model for ice microphysics. The base case was from the Indirect and Semidirect Aerosol Campaign, and it was perturbed over a range of cloud-average temperatures, maximum (per model run) ice nuclei (IN) concentrations, and large-scale subsidence velocities. For each parameter combination, the model was iterated out to 48 hr, and the time, called the glaciation time, to complete disappearance of liquid recorded if this occurred within the 48 hr. Dependence of glaciation times on cloud-average temperatures from −30°C to −5°C, maximum IN concentrations from 0.10 to 30 L⁻¹, and strong–no subsidence, with both isometric and habit-dependent ice crystal growth, were investigated. For isometric crystal growth, the relationship between the critical maximum IN concentration (IN_crit), the maximum (per model run) IN concentration above which a mixed-phase cloud glaciated within a fixed model runtime, and cloud-average temperature was monotonic. IN_crit decreased with decreasing cloud-average temperature. Strengthening of subsidence led to a further decrease in IN_crit for every cloud-average temperature. For habit-dependent ice crystal growth, the relationship between IN_crit and cloud-average temperature was nonmonotonic. Ice crystals develop dendritic and columnar habits near −15°C and −7°C, respectively, and at these two temperatures, ice crystals grew and depleted supercooled liquid water faster than the case when ice crystals grew isometrically. This led to deep local minima in IN_crit around these two temperatures in the model runs. Habit-dependent ice crystal growth, coupled with changes in cloud-average temperature, IN_crit, and subsidence strength, led to significant changes in Arctic single-layer mixed-phase cloud lifetimes.