When freezing fog blows through a wire fence, every strand can grow a white crust of ice that points straight into the wind. The result looks like a fence knitted from frost. This kind of ice is called rime, and it can coat fences, roofs, towers and trees in shapes that make ordinary objects look unrecognisable.
What is rime ice?
Rime forms when supercooled water droplets, tiny drops in fog or cloud that remain liquid below 0 °C, freeze the instant they touch a solid surface. It differs from hoar frost, which grows directly from water vapour with no liquid droplets involved.
Because the droplets are carried by the wind, rime builds up on the windward side of branches, wires, buildings and other objects. A thin wire catches droplets along its whole length, so a fence becomes a grid of white projections all aligned in the same direction. That is why a wire fence after a night of freezing fog can look as if ice has been blown through it.
Soft rime and hard rime
- Soft rime forms in calm air or a light breeze. It is white and feathery, made of fragile needle-like growths that shake off easily.
- Hard rime forms in at least a moderate wind. The droplets freeze quickly and separately, trapping air between them, so the ice is denser, harder to remove and has a comb-like look with streaks aligned to the wind.
Rime is most common on mountaintops and ridges in winter, where low cloud brings freezing fog. Weather instruments at exposed sites such as Mount Washington in New Hampshire can need rime cleared off to keep them working, and towers and masts on high ground can end up wrapped in thick, wind-shaped ice.
Glaze ice and ice storms
Clear ice on trees and plants usually comes from a different process. Glaze forms in an ice storm, when a layer of air above freezing sits over sub-freezing air near the ground. Snow melts as it falls through the warm layer, then the raindrops cool below 0 °C without freezing and turn to ice the moment they land, leaving a smooth, glassy coating.
Glaze is denser and sticks more strongly than rime, and it is heavy. The US National Weather Service defines an ice storm as one that leaves at least 0.25 inch (6.4 mm) of ice on exposed surfaces. That much ice can add about 500 pounds (230 kg) to a single span of power line, enough to snap lines, poles and even steel pylons, and to bring down branches and whole trees. Deciduous trees, bare in winter, suffer less breakage in ice storms than they would with leaves.
How to photograph rime and ice
Rime is at its best after a still, foggy night followed by a clear morning. Shoot with the light coming from the side so the feathery edges stand out, and look for repeating structures such as fences, wires and railings that give the ice a pattern to follow. Clear glaze sparkles most when the sun is behind it.
For more frozen forms, see Jan Bainar’s frost-covered Beskydy forest and more snow-and-ice patterns that look like art.
Related reading
- 24 Ice and Snow Formations: From Frozen Bubbles to Lake Michigan Lighthouses
- 10 Ice and Snow Art Projects: Sculptures, Snow Drawings and a Playable Record
- Curling Snow on a Cabin Roof: A Small-Scale Winter Transformation
- A Frozen Channel Between Trees: Reading the Forest-Ice Photographs
The third picture, with the sideways icicles, isn't from an updraft. As the snow slowly slides off the roof the weight of it bends the overhanging part down, and the attached icicles point to the side, and even upward.
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