On the influence of ice habit on the lifetime of Arctic mixed-phase clouds

Description

Mixed-phase clouds are common over the Arctic sea ice for much of the year. The persistence of supercooled liquid in these clouds is not well understood, but it is climatologically important because of the strong impact it has on the surface radiative budget. Most prior studies of mixed-phase cloud lifetime have assumed spherical particles or, at times, simple shapes. We show that these simplified methods lead to an over-estimate of mixed-phase cloud lifetime. Predicting ice habits have the strongest effects on cloud lifetime at -6C and -15C, where needle and dendritic crystals grow. Furthermore, we show that predicting ice habits is most critical at low ice concentrations (less than about 100 L-1), whereas at high ice concentrations, simple models of ice growth are sufficient. Cloud dynamics modify these results, since vertical motions can support the simultaneous growth of both liquid and ice. We show that dynamics can extend cloud lifetime when ice concentrations are low, and ice crystals grow in at temperatures that promote isometric growth (around -10C). Growth at habit-prone temperatures such as -15C and -6C requires higher vertical motions and lower ice concentrations to maintain the liquid. Our results suggest a strong temperature-dependence to supercooled liquid maintenance in Arctic clouds.