Freezing Radiation Fog
February 15, 2013
Summary Authors: Bill Curry; Jim Foster
The photo above shows a hawthorn tree (Crataegus mollis) and surrounding vegetation encased in a freezing ground fog that gripped Port Maitland, Nova Scotia, on the morning of January 11, 2013. Ground fog, which is also called valley fog or radiation fog, like all other types of fog, forms when the surface cools to a temperature at or below its dew point. This most often occurs during the early morning hours when heat loss is maximized. Once a layer of fog has become established, it’ll stay in place as long as the air remains saturated. With a freezing fog, the fog droplets are supercooled. So when a fog droplet comes in contact with an object below freezing, it’ll turn to ice, even objects such as blades of grass will be coated with an icy film.
Photo details: NIKON D3S camera; 70.0-200.0 mm lens; f/2.8; 200mm (35mm equivalent: 200mm) focal length; infinite focus; f/18.0 aperture; 0.0040 sec. (1/250 sec.) exposure time; ISO equiv. 200; Adobe Photoshop CS6 Macintosh. Adobe Camera Raw used to tweak the raw-format image, adjusting the contrast to bring out the color.