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Hoar frost may have different names depending on where it forms: Air hoar is a deposit of hoar frost on objects above the surface, such as tree branches, plant stems, and wires. Surface hoar refers to fern-like ice crystals directly deposited on snow, ice, or already frozen surfaces.
A heavy coating of hoar frost, called white frost, is very similar in appearance to soft rime, but the formation process is different; it happens when there is no fog, but very high levels of air relative humidity (above 90%) and temperatures below −8 °C (18 °F). Soft rime formations appear as narrow white icy needles and scales.
The three main types of ground frost are radiation frost (), advection frost (advection hoar frost) and evaporation frost.The latter is a rare type which occurs when surface moisture evaporates into drier air causing its temperature at the surface to fall at or under the freezing point of water. [1]
Hoar frost on the snow surface from crystallized water vapor emerging on a cold, clear night Cornice on an alp in France Snowdrift in Gloucestershire Sastrugi in Norway Alpine firn in Austria Penitentes under the night sky of the Atacama Desert Suncups in England Packing snow being rolled into a large snowball in Oxford, England.
Freezing[1] or frost occurs when the air temperature falls below the freezing point of water (0 °C, 32 °F, 273 K). This is usually measured at the height of 1.2 metres above the ground surface. There exist some scales defining several degrees of frost severity (from "slight" to "very severe") but they depend on location thus the usual ...
Deposition (phase transition) Water vapour from humid winter-air deposits directly into a solid, crystalline frost pattern on a window, without ever being liquid in the process. Deposition is the phase transition in which gas transforms into solid without passing through the liquid phase. Deposition is a thermodynamic process.
More generally, water vapor depositing onto surfaces due to high relative humidity and then freezing results in various forms of atmospheric icing, or frost. Inside buildings, this can be seen as ice on the surface of un-insulated windows. [92] Hoar frost is common in the environment, particularly in the low-lying areas such as valleys. [93]
In the foreground are hoar frost crystals, formed by refrozen water vapor emerging to the cold surface. Sastrugi formed during a blizzard just a few hours earlier. According to the International Association of Cryospheric Sciences, snow metamorphism is "the transformation that the snow undergoes in the period from deposition to either melting ...