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There is a larger wedge of cold air that refreezes the partially melted snowflakes into ice pellets (aka sleet). For freezing rain to occur, the warm air layer is thicker.
In areas with a lot of small particles in the air, from human pollution or natural sources like dust, the water droplets are likely to be able to freeze at a temperature around −10 °C (14 °F), but in very clean areas, where there are no particles to help the droplets freeze, they can remain liquid to −39 °C (−38 °F), at which point ...
Atmospheric icing occurs in the atmosphere when water droplets suspended in air freeze on objects they come in contact with. It is not the same as freezing rain, which is caused directly by precipitation. Atmospheric icing occurs on aircraft, towers, wind turbines, boats, oil rigs, and trees. Unmanned aircraft are particularly sensitive to ...
Contact nucleation can occur if an ice nucleus collides with a supercooled droplet, but the more important mechanism of freezing is when an ice nucleus becomes immersed in a supercooled water droplet and then triggers freezing. In the absence of an ice nucleating particle, pure water droplets can persist in a supercooled state to temperatures ...
The droplets freeze more or less individually, leaving air gaps. Clear ice forms by slow freezing of supercooled water. Clear ice is typically transparent and homogeneous. Its amorphous and dense structure makes it adhesive. Soft and hard rime are less dense than clear ice and less adhesive, thus generally cause less damage.
Freezing air down to −3 °C (27 °F) promotes planar crystals (thin and flat). In colder air down to −8 °C (18 °F), the crystals form as hollow columns, prisms or needles. In air as cold as −22 °C (−8 °F), shapes become plate-like again, often with branched or dendritic features.
Alternatively, the liquid droplets can continue to fall without freezing, passing through the cold air just above the surface. This thin layer of air then cools the rain to a temperature below freezing (0 °C or 32 °F). However, the drops themselves do not freeze, a phenomenon called supercooling (or forming "supercooled drops"). When the ...
Accretion is defined as the gradual collection of something over time. [1] In meteorology or atmospheric science it is the process of accumulation of frozen water as precipitation over time as it descends through the atmosphere, in particular when an ice crystal or snowflake hits a supercooled liquid droplet, which then freeze together, increasing the size of the water particle.