Frost Crystals on Hawthorn

January 16, 2011


: Jeanette Stafford
Summary Author: Jeanette Stafford

The British Isles along with much of Northern Europe experienced a very cold winter last year (2009/2010), but the current winter has thus far been even colder. December was especially bitter with a number of locations failing to register above freezing temperatures for several consecutive days. High pressure brought calm conditions and then freezing fogs, which in turn created amazing frosts. Twelve hours of continuous freezing fog in Bearsden, Scotland on December 20 produced the needle-shaped crystals seen above that grew from every imperfection on each twig, leaf and berry of this hawthorn (Crataegus monogyna). The crystals reached a length of between 0.5 in to 1.0 in (1 cm to 2 cm). Temperatures were around 23 F (-5 C) the entire time. After another bout of subfreezing fog on the 21st (36 hours total), the needles, with the addition of rime, were then transformed into thick, feathery clumps (click here for photo). Even when the Sun finally reappeared, these tufted crystals persisted all the next day.

Photo Details: Camera Maker: PENTAX; Camera Model: PENTAX K-x; Focal Length: 100mm (35mm equivalent: 150mm); Aperture: f/5.0; Exposure Time: 0.0025 s (1/400); ISO equiv: 200.