Rime ice

Rime ice is a rough, opaque deposit formed when supercooled cloud droplets freeze on contact with exposed surfaces. Its shape and density depend on droplet size, wind, and freezing conditions.

Supercooling: The cooling of a liquid below its freezing point without its becoming solid. Cloud droplets remain liquid below freezing until they strike a surface that triggers ice formation.
Supercooled water: Liquid water cooled below 0 °C while remaining unfrozen. Rime forms specifically when these metastable droplets freeze upon contact.
Aircraft icing: The accumulation of ice on aircraft surfaces during flight through atmospheric moisture. Rime is one form of in-flight ice that can alter lift, drag, and control.
Hoarfrost: A deposit of ice crystals formed when water vapor deposits directly onto a cold surface. Hoarfrost grows from vapor, whereas rime forms from freezing cloud droplets.
Heterogeneous nucleation: The initiation of a new phase on a surface or particle that lowers the energy barrier to formation. An exposed object provides a surface where supercooled droplets can begin freezing.
Cloud droplet: A tiny liquid-water particle suspended in a cloud, typically too small to fall as precipitation. Cloud droplets supply the liquid water that freezes into rime.
Rime ice on aircraft: A rough, opaque aircraft ice accretion formed when supercooled droplets freeze rapidly on impact. This specific accretion can disrupt airflow and is classified separately from clear ice.
Glaze ice: A smooth, dense ice deposit formed when supercooled water freezes slowly on a surface. Glaze is typically clear and compact, unlike rime’s opaque, porous texture.
Latent heat of fusion: The energy released or absorbed when a substance changes between liquid and solid at constant temperature. Freezing droplets release heat, influencing how quickly incoming water freezes and accumulates.
Freezing: The phase transition in which a liquid becomes a solid. Rime is a surface deposit produced by freezing droplets rather than by vapor crystallizing directly.

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