Minimalist model of ice microphysics in mixed-phase stratiform clouds

Description

The persistent presence of ice in long-lived, supercooled stratiform clouds is the result of a delicate balance between environmental conditions, ice nucleus abundance, and microphysical properties (Morrison et al. 2012, Westbrook and Illingworth 2013). The role of ice nucleation, including the origin of the ice nuclei themselves as well as the modes in which they are active, is of special interest because properties of these long-lived clouds are extremely sensitive to the amount of ice (Ovchinnikov et al. 2011). In this work we present a minimalist model that links ice microphysical properties to the ice nucleation process and to macroscale cloud properties. The model assumes steady-state conditions and low ice concentrations in the presence of supercooled liquid water. We explore model behavior in the context of clouds observed during the Indirect and Semi‐Direct Aerosol Campaign (ISDAC) held during spring 2008 in the vicinity of Barrow, Alaska (McFarquhar et al. 2011). Implications for model assumptions and for ice nucleation are discussed.

McFarquhar, GM, et al. 2011. “Indirect and Semi-Direct Aerosol Campaign: The impact of aerosols on clouds.” Bulletin of the American Meteorological Society 92: 183–201.

Morrison, H, G de Boer, and G Feingold. 2012. “Resilience of persistent Arctic mixed-phase clouds.” Nature Geosciences 5: 11–17.

Ovchinnikov, M, A Korolev, and J Fan. 2011. “Effects of ice number concentration on dynamics of a shallow mixed-phase stratiform cloud.” Journal of Geophysical Research 116: doi:10.1029/2011JD015888.

Westbrook, CD, and AJ Illingworth. 2013. “The formation of ice in a long-lived supercooled layer cloud.” Quarterly Journal of the Royal Meteorological Society: doi:10.1002/qj.2096.