Predicting ice habit evolution by riming for cloud models

 

Authors

Anders Jensen — Pennsylvania State University
Jerry Y. Harrington — Pennsylvania State University
Hugh Clifton Morrison — University Corporation for Atmospheric Research

Category

Cloud Properties

Description

The growth of ice crystal in clouds is a challenging problem given the variety of crystals that can occur. Prior methods for growing ice crystals have depended on the use of mass-size relationships as a way to close the growth equations and evolve particle sizes. In many applications, this has led to the definition of multiple particle classes (small ice, snow, graupel, etc.) and transfer functions between them based on somewhat arbitrary boundaries. In this work we extend the more recent trend towards predicting particle properties to habit evolution through riming. Recently, a method to capture habit evolution in mixed-phase bulk cloud models has been developed (e.g., Sulia and Harrington 2011; Harrington, Sulia, and Morrison 2012). This method captures the evolution of ice aspect ratio avoiding the need for multiple ice and snow classes. Following prior work this model is extended to include the impacts of riming on mass, size, and aspect ratio evolution of the ice habits. We show that the method produces a more natural evolution from more pristine ice classes with very large, or small, aspect ratios towards graupel-like particles with aspect ratios near unity.