The clear, almost pollution-free skies of Antarctica’s interior combined with extremely low humidities make it an ideal location for viewing spectacular optical displays – Optical Weather Phenomena. Wide open vistas unobstructed by trees, buildings or other clutter give panoramas of the sky that stretch for dizzying distances. The frigid temperatures mean that little or no water vapor is held in the air, instead it freezes and falls out as ice crystals, builds up on surfaces as frost, or is suspended in the air. Depending on the particular atmospheric conditions, these ice crystals can reflect sunlight in a variety of ways resulting in many fantastic and fascinating atmospheric phenomena.
Solar Haloes occur around the sun when light is refracted through ice crystals. They are usually encountered in the winter when lower temperatures make such occurrences more likely.
Sun dogs are luminous spots on both sides of the sun that occasionally occur with a halo.
Air of different temperatures refracts light in different ways. Mirages are commonly seen on the horizon in the winter or at the end of winter when the sea-ice has just broken up. They are a result of temperature differences in the bottom few yards just above the ice or sea surface. This is the same phenomena responsible for “heat haze” as seen above a road on a very hot day.
The fata morgana is a complex mirage in which distant flat objects appear to have tall cliffs, columns, and pedestals.
A superior mirage occurs when an image of an object appears above the actual object, due to the downward refraction of light in cold, dense air.
Ice blink refers to a white glare seen on the underside of low clouds indicating the presence of ice which may be beyond the range of vision.
Water sky refers to the dark appearance of the underside of a cloud layer when it is over a surface of open water.
A corona is a ring of deflected light that surrounds the sun or moon, sometimes forming a colorful disk with the sun or moon at its center.
A fog bow is similar to a rainbow, but without any colors due to the very small size of the water droplets.
A Solar Pillar occurs when the sun is reflected so strongly that the reflection is almost as bright as the sun itself. The pillar appears to move when the observer moves, but always remains directly below the sun. Like a rainbow, this sight is dependent on where the light is coming from and where the observer is standing.
Ice fog occurs when seawater exposed to much colder air above pack ice condenses into fog. It is often seen at “tide-cracks”– openings that form around offshore rocks and small islands when the tide rises and falls with continuous sea-ice present. As the ice is not flexible it cracks and as it does, exposes an amount of open water to the air.
Antarctic sea water temperatures vary between about 34ºF and 28ºF over the course of a year, so the exposed sea water is often more than 70ºF warmer than the surrounding air. Sunshine makes the fog more visible and different temperature layers in the air cause it form in bands above the clearer air close to the ice surface.
A Föhn bank is formed by a warm contour-hugging wind (a Föhn wind) that is blowing across the land. As the warmer wind blows across the much cooler land, it causes snow and ice to sublime (change from solid directly to gas). The overall effect as seen from a distance is that the land is covered by a very large blanket of condensed vapor. The gross contours can be seen through the cloud layer, but all of the finer detail is obscured.
Noctilucent clouds are clouds that form in the cold, summer mesopause at latitudes of 60 to 70 degrees north and south and are believed to be made of ice crystals. They are seen at extremely high altitudes (about 50 miles) and are thus, illuminated by the sun long after it has set over the horizon. The terms ‘nocti’ and ‘lucent’ are derived from the Latin where they roughly translate to ‘night’ and ‘luminous’. They appear pearly white in color and often appear very delicate in texture.