Monday, December 06, 2010
I'd never heard of Diamond Dust until fellow Etsy Teambritannia crafter DottyBlueBird reported seeing "millions of glittery sparkles" in the air today. It was beautiful, and she thought it might be moisture or ice crystals in the air glittering in the sun. Another Teambritannia crafter, Stupidcats, has also seen this phenomenon, which is apparently known as Diamond Dust. The following information is was gleaned from various online sources, including the British Antarctic Survey, WeatherFreaks and Wikipedia.
When the air is bitterly cold, you might notice a beautiful and ephemeral fine twinkling and sparkling in the air. This fine, shimmering mist of ice crystals is called diamond dust, and it usually only occurs in very cold regions during the winter. Since it has been as low as -25 °C/-13 °F in the British Isles over the past few days, the UK certainly qualifies as a very cold region right now! While I was writing this I checked the thermometer, and discovered that it is currently -6 °C/21 °F here in Cambridge, UK. The sky is clear so, if it wasn't already dark, I might be able to see some diamond dust!
Diamond dust is a ground level cloud composed of tiny ice crystals, and generally forms under otherwise clear or nearly clear skies. It is most commonly observed in Antarctica and the Arctic, but it can occur anywhere with a temperature well below freezing. It is similar to fog but differs from it in two main ways. Firstly, fog generally refers to a cloud composed of liquid water. Secondly, fog is dense enough cloud to significantly reduce visibility. Diamond dust, on the other hand, is usually very thin and does not always reduce visibility, so it is often first noticed by the brief flashes caused when the tiny crystals, tumbling through the air, reflect sunlight to your eye.
This glittering effect gives the phenomenon its name, since it looks like many tiny diamonds are flashing in the air. Diamond dust occurs when there is a winter temperature inversion, when the coldest air is near the ground and a warmer, moister layer of air lies above it. The diamond dust forms when the warmer air blends with the colder, and the moisture it contains condenses out in the colder air, freezing into tiny crystals of ice. These fine crystals drift and sparkle, and eventually settle out, making them a type of precipitation as well as mist.
It cannot form at temperatures above the freezing point of water, 0 °C/32 °F, but at lower temperatures down to about −39 °C/−38 °F, an increase in relative humidity can cause fog or diamond dust. In temperate latitudes, even in cold regions like the Upper Midwest or Siberia, diamond dust is usually too thin to obscure vision or to accumulate more than a fraction of an inch on the ground. It is mostly significant at these latitudes because it makes haloes around the sun, moon, or outdoor lamps. These result because the diamond dust crystals form directly as simple hexagonal ice crystals rather tgan as freezing drops, and because they generally form slowly. This combination results in crystals with well defined shapes, usually either hexagonal plates or columns, which can refract light in specific directions like a prism.
By contrast, it is most frequent in the frozen interior of Antarctica, where it is common all year round. It makes up the majority of the precipitation that falls there, and has been observed on average 316 days a year at Plateau Station. The Antarctic ice cap is maintained by Diamond Dust, and without it the south polar region would be even more parched than it already is. For most people, however, Diamond Dust is only an intriguing curiosity - a beautiful twinkling of light and motion in the deep winter air, caused by tiny flecks of drifting ice too small to be seen except when they reflect the sun.
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