Search results
Results from the WOW.Com Content Network
Hoar frost, also hoarfrost, radiation frost, or pruina, refers to white ice crystals deposited on the ground or loosely attached to exposed objects, such as wires or leaves. [3] They form on cold, clear nights when conditions are such that heat radiates into outer space faster than it can be replaced from nearby warm objects or brought in by ...
From a scientific standpoint, hoarfrost, like regular frost, forms when moisture freezes as ice crystals on an object. It often appears as soft needles of frost that are easily brushed away.
This page was last edited on 12 October 2014, at 23:18 (UTC).; Text is available under the Creative Commons Attribution-ShareAlike 4.0 License; additional terms may apply.
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]
The book On the Universe (De Mundo) (composed before 250 BC or between 350 and 200 BC) stated: "Dew is moisture minute in composition falling from a clear sky; ice is water congealed in a condensed form from a clear sky; hoar-frost is congealed dew, and 'dew-frost' is dew which is half congealed". [7]
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 ...
This is how frost and hoar frost form on the ground or other surfaces. Another example is when frost forms on a leaf. For deposition to occur, thermal energy must be removed from a gas. When the air becomes cold enough, water vapour in the air surrounding the leaf loses enough thermal energy to change into a solid.
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.