Frosty Winter Sunrise Over the Gwda River by Krzysztof Tollas
Photo location: Pila, Poland
Camera: Nikon D750 NIKKOR AF 70-300mm
Krzysztof captured a frosty and picturesque sunrise over the Gwda River in Poland.
Hoar frost is the most common type of frost and occurs on clear winter nights when the surface temperature falls below 0ºC, and there is enough moisture in the air for a frost to form. Hoar frost is composed of tiny ice particles formed by the same process as dew, but when the surface temperature is below freezing.
The 'feathery' variety of hoar frost initially forms when the surface temperature falls below freezing before dew begins to form. Ice crystals start to form as water vapour suspended in the air freezes on contact with the surface – this process is known as deposition. The 'white' frost, composed of more globular ice, forms when dew forms first on a surface and the temperature falls below 0ºC.
There are a few other types of frost, including ground frost, when the ground temperature falls to or below freezing, but the air temperature may remain above freezing. For an air frost to occur, the air temperature must drop to, or below, freezing at the height of at least one metre above the ground.
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