Secondary ice production - A cellular automaton approach

Clouds play a key role in the hydrological cycle and the Earth’s radiation budget. Their macroscopic properties are strongly influenced by the size, number, and phase of suspended particles. Understanding the evolution of these microphysical properties is therefore essential for weather prediction and for quantifying the impact of clouds on the Earth’s climate. In mixed-phase clouds, one process that can strongly modify the ice particle population is secondary ice production (SIP), which encompasses all mechanisms that increase the number of ice particles from pre-existing ice. While numerous SIP pathways have been proposed, no consensus has been reached about their relative importance and quantitative contributions, since observational studies often yield contradictory results.

In this work, a two-dimensional model of SIP is introduced which utilizes a combination of a cellular automaton approach pioneered by Clifford A. Reiter (Reiter, 2004) and a finite elements stress solver as well as concepts from graphs theory. The model represents the temporal evolution of the growth and
sublimation of an ensemble of ice crystals, their shape, and the formation of new crystals through SIP. Secondary ice production in the model is governed by two simplified mechanisms: shear-force induced breakup and fragmentation during sublimation.

A qualitative analysis of the model results shows that this reduced approach, which does not explicitly represent all known SIP pathways, is nevertheless able to reproduce key features of secondary ice production.

References
Reiter, Clifford A. "A local cellular model for snow crystal growth." Chaos, Solitons & Fractals 23.4 (2005): 1111-1119.