hoar frost A deposit of patterned (‘feathers’, ‘needles’, ‘spines’, etc.) ice crystals on surfaces chilled by radiation cooling. The feature is seen particularly well on vegetation. The ice is derived from the sublimation of water vapour on surfaces, as well as from frozen dew.

hoar frost Deposit of patterned (‘feathers’, ‘needles’, ‘spines’, etc.) ice crystals on surfaces chilled by radiation cooling. The feature is seen particularly well on vegetation. The ice is derived from the sublimation of water vapour on surfaces, as well as from frozen dew.