The fog with below freezing temperatures led to some pretty accumulation of white ice on trees and other objects last night and this morning. This icing is called "rime" and is white because of air trapped inside. This is different from "glaze" which is what happens in freezing rain/drizzle situations.Â
Picture of freezing fog in Meade County this morning from Jeffrey Houchin
By definition, rime is a deposit of interlocking ice crystals formed by direct sublimation on objects, usually those of small diameter freely exposed to the air, such as tree branches.
Picture of rime ice in Campbellsburg, IN, from Fatima Scott
The deposition of rime is different than the process in which frost is formed. In the case of rime, the object and the air are both below freezing and liquid drops (e.g. fog) must be present. For frost, the object itself must be below freezing but the air can be above freezing. Also, water vapor (not droplets) are the source of moisture, so frost forms on clear cold nights.
