![]() ![]() If parts of clouds have small droplets or crystals of similar size, their cumulative effect is seen as colors. Iridescence should similarly be distinguished from the refraction in larger raindrops that makes a rainbow. Larger ice crystals produce halos, which are a refraction phenomena rather than iridescence. ![]() Iridescent clouds are a diffraction phenomenon cause by small water droplets or small ice crystals individually scattering light. ![]() Other aids are dark glasses, or observing the sky reflected in a convex mirror or in a pool of water. Iridescence is generally produced near the sun, with the sun’s glare masking it, so it is more easily seen by hiding the sun behind a tree or building. The colors are usually pastel, but can be very vivid. It is a fairly uncommon phenomenon, most often observed in altocumulus, cirrocumulus and lenticular clouds, and very rarely in Cirrus clouds. Photograph by Esther Havens (Light the World)Ĭloud iridescence is the occurrence of colors in a cloud similar to those seen in oil films on puddles, and is similar to irisation. Because of their rarity and unusual appearance, fallstreak holes are often mistaken for or attributed to unidentified flying objects. Such clouds are not unique to any one geographic area and have been photographed from the United States to Russia. It is believed that a disruption in the stability of the cloud layer, such as that caused by a passing jet, may induce the domino process of evaporation which creates the hole. This leaves a large, often circular, hole in the cloud. When a portion of the water does start to freeze it will set off a domino effect, due to the Bergeron process, causing the water vapor around it to freeze and fall to the earth as well. Such holes are formed when the water temperature in the clouds is below freezing but the water has not frozen yet due to the lack of ice nucleation particles. Ī fallstreak hole, also known as a hole punch cloud, punch hole cloud, canal cloud or cloud hole, is a large circular gap that can appear in cirrocumulus or altocumulus clouds. It is theorized that this increase is connected to climate change. Since they are a relatively recent classification, the occurrence of noctilucent clouds appears to be increasing in frequency, brightness and extent. Noctilucent clouds can form only under very restrictive conditions their occurrence can be used as a sensitive guide to changes in the upper atmosphere. Noctilucent clouds are not fully understood and are a recently discovered meteorological phenomenon there is no record of their observation before 1885. They are normally too faint to be seen, and are visible only when illuminated by sunlight from below the horizon while the lower layers of the atmosphere are in the Earth’s shadow. They are the highest clouds in the Earth’s atmosphere, located in the mesosphere at altitudes of around 76 to 85 kilometres (47 to 53 mi). They are most commonly observed in the summer months at latitudes between 50° and 70° north and south of the equator. The name means roughly night shining in Latin. Night clouds or noctilucent clouds are tenuous cloud-like phenomena that are the “ragged-edge” of a much brighter and pervasive polar cloud layer called polar mesospheric clouds in the upper atmosphere, visible in a deep twilight. ![]()
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