Ice fog
(Section 3.2.1.1.2)Definition: Ice fog: A suspension of numerous minute ice particles in the air, reducing the visibility at the Earth’s surface.
Ice fog forms when water vapour, mainly resulting from human activities, is introduced into the atmosphere. This vapour condenses, forming droplets that freeze rapidly into ice particles that have no well-defined crystalline form. It is observed at high latitudes, usually in clear, calm weather when the temperature is below −30 °C.
Horizontal visibility is usually very restricted in ice fog, often to less than 50 m. This is due to the small diameter of the ice particles, typically 2−30 μm with the smaller particles forming when the temperature is between −40 °C and −50 °C.
Ice fog does not produce halo phenomena, although such phenomena may be present if the fog also contains diamond dust.