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

Description

Arctic mixed-phase clouds are ubiquitous for much of the year, and the persistence of supercooled liquid in these clouds is not well understood. Most prior studies of mixed-phase clouds suggest that ice concentration plays the strongest role in controlling the structure, phase partitioning, and lifetime of these clouds. However, these prior studies assumed spherical particles or simple shapes that led to an over-estimate of mixed-phase cloud lifetime. These methods lack the ability to accurately evolve particle shape by adjusting particle growth parameters approximated off of in situ data. We show that this method is inconsistent with the vapor growth equations. To improve ice prediction, we present a new parameterization to proficiently predict single-particle or bulk-averaged aspect ratio evolution with a historical tracking parameter. The method is implemented into a two-dimensional Kinematic model and into the Weather Research and Forecasting model. Initial studies show that predicting ice habits have strong effects on cloud and water phase partitioning. Cloud dynamics modify these results as vertical motions can support the simultaneous growth of both liquid and ice. Dynamics extend cloud lifetime when ice concentrations are low, and ice crystals grow at temperatures that promote isometric growth (around -10°C). Temperatures where growth is highly non-spherical (-15°C and -6°C) require higher vertical motions and lower ice concentrations to maintain the liquid phase. Our results suggest a strong temperature dependency as well as varying degrees of microphysical and macrophysical dependencies to supercooled liquid maintenance in Arctic clouds.