Lagrangian studies of ice nucleation and growth 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 results building on a recently proposed theoretical model linking ice microphysical properties to the ice nucleation process (Yang et al. 2013). That model predicts that the ice mass is proportional to the ice number to the 2.5 power. We have performed Lagrangian tracking of ice particles in idealized and modeled clouds from a detailed large eddy simulation. The Lagrangian particle histories allow us to gain additional insight into the origin of the predicted power law between ice number and ice mass. For example, they validate the essential picture of enhanced ice growth in updraft regions. The approach also allows us to explore how the power law changes as the source of ice nuclei is altered. It reproduces the 2.5 power law for spatially uniform, steady ice nucleation, but the power law disappears when ice nuclei are introduced, for example, exclusively from the cloud top. Morrison, H, G de Boer, G Feingold, J Harrington, MD Shupe, and K Sulia. 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 139: 2209-2221. Yang, F, M Ovchinnikov, and RA Shaw. 2013. “Minimalist model of ice microphysics in mixed-phase stratiform clouds.” Geophysical Research Letters 40: 3756-3760.