Hoar frost
Hoar frost is a solid precipitate that is formed from supercooled water droplets from light fog or directly from the water vapor contained in the air through resublimation . This requires a very high relative humidity of over 90% and an air temperature of below −8 ° C. The resulting heat is transferred to the surrounding air by convection , so wind increases the formation of hoarfrost. However, the wind must not be too strong either, otherwise it would destroy the sensitive structures.
Especially against the direction of the wind, needle-shaped ice crystals in the form of six-pointed dendrites are created , which can reach a considerable size and bizarre shapes and usually only grow slowly. Hoar frost grows against the wind, as the air arriving on the windward side has a higher degree of humidity than on the leeward side .
Rime arises comparatively rarely and is often confused with frost or rough ice , for which it represents a kind of intermediate stage. Ice flowers are a special form of hoarfrost .
Damage to trees caused by hoar frost is referred to as fragrance break in forestry .
photos
Hoar frost in Marienheide
Hoar frost on a soap bubble
literature
- Tönjes de Vries, Antje Paschmann: Resublimation - the fascinating formation of hoarfrost. In: CHEMKON. 11 (4) 2004, ISSN 0944-5846 , pp. 185-190.
- Dew, frost and hoar frost. In: Hannelore Dittmar-Ilgen: How the salt gets into the sea water and why there are no more ice flowers: even more physics for the curious. Hirzel-Verlag, Stuttgart 2005, ISBN 3-7776-1315-0 , p. 72.
Web links
- deutscher-wetterdienst.de: signs of ripening , 23 January 2016
- wetter24.de: How does frost come about ? , January 23, 2016
supporting documents
- ↑ Joseph Krauß: Basic features of maritime meteorology and oceanography, reprint of the original from 1917 . Salzwasser Verlag, Paderborn 2011, ISBN 978-3-86444-130-1 ( limited preview in the Google book search).