kuura

Kuura is a Finnish word that refers to a type of hoarfrost. It is a delicate ice formation that appears on surfaces, particularly on trees and other vegetation, when the air temperature is below freezing and the humidity is high. Kuura typically forms when water vapor in the air deposits directly onto a cold surface as ice crystals, bypassing the liquid phase. This process is known as desublimation.

The appearance of kuura can vary depending on the atmospheric conditions. It can manifest as feathery, crystalline structures, or as a more uniform coating of ice. The formation of kuura is often associated with clear, calm nights when the ground cools down significantly. It is a common sight in Finland, especially during the winter months, and contributes to the winter landscape's aesthetic appeal.

While similar to other frost formations like rime ice, kuura is generally understood to be a finer and more delicate structure. The term is distinct from "huurre," which typically refers to a thicker layer of rime ice formed by supercooled water droplets. Kuura is a natural phenomenon that plays a role in the local microclimate and can affect plant life by insulating it or, in some cases, causing damage due to its weight.