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Among the many cloud types important to climate, supercooled water clouds over polar regions have been identified as a relevant challenge for climate models, owing in part to a paucity of observations adequate to study the dominant processes. Detailed remote sensing observations of persistent drizzle at cloud temperatures below –25°C over McMurdo Station, Antarctica, motivated a recent modeling study using large-eddy simulation and a climate model run in single-column model mode. The case study includes development of a stratiform water cloud in a relatively stable pre-cloud environment substantially above the surface layer, its transition to a continuously turbulent decoupled layer via rapid cloud-top cooling, and sustained drizzle and ice formation and precipitation. Representing this sequence of coupled dynamical and microphysical processes under highly supercooled conditions provides a strong test for climate model physics. We place this case study and this sequence of processes into the context of the most common types of supercooled water-bearing clouds found over polar regions, with an emphasis on the basic coupling of dynamical and microphysical processes.
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