Consider the iconic six-sided snowflake: lacy, fluffy and the subject of interpretation by millions of children aided only by folded paper and scissors. Although the ground is covered in them in many parts of the country throughout winter, perfect, six-sided symmetrical snow crystals are rare and the physics of how they grow is ill-understood.
Kenneth Libbrecht, the “snowflake professor” who has been studying the physics of snow formation for more than a decade, works in the field in northern Ontario. He waits for the temperature to fall and the snow to come, then goes out with a piece of foam core board and a paintbrush to collect good crystals, looking with his naked eye for the best specimens.
The fact that the shape snow takes depends on the temperature was first shown by Japanese scientist Ukichiro Nakaya in the 1930s. From about freezing to 25 degrees Fahrenheit, snow forms as flakes.
When it hits about 23 degrees the snow forms into needles and at about 22 degrees hollow columns.
When the temperature drops to around 10, flakes start forming again.
But when it gets to -8 or so, it’s once again columns. At -30, snow stops forming altogether.
Despite 75 years of research, no one knows why, “There really isn’t any comprehensive theory of what’s going on,” says Charles Knight, at the National Center for Atmospheric Research in Boulder, Colo. “This is very striking and very odd behavior, and I do not know of any convincing explanation of it.”
Since then, he has published seven books of snowflake photographs, including a field guide to snow and a children’s book The Secret Life of a Snowflake, which the National Science Teachers Association says will “captivate” young readers. His photos of those frozen crystals of water graced more than 3 billion U.S. postage stamps in 2006 and a Swedish stamp in 2010. He has also authored numerous papers on the molecular dynamics that dictate how ice crystals grow.
Libbrecht is one of a small number of researchers who study snowflakes. As with much science, there is no consensus. Knight says he finds some of Libbrecht’s theories “unconvincing” but says “an adequate understanding has not yet been found.”
Studying snowflakes involves travel. “It just doesn’t get cold enough in the continental U.S.” much of the time, Libbrecht says. His Swedish stamp snowflakes were photographed in Kiruna, Sweden’s northernmost city.
“I tell my wife, ‘I’ve got to go to work; snowflakes aren’t going to grow themselves, not around here at least,’ ” he says of his Pasadena, Calif., university.
When he’s making his photographs, he waits for the temperature to fall and then for the snow to come. Then he goes out with a piece of blue foam core board and lets the snow fall on it, looking for good crystals.
“People think that every crystal is perfect, but far from it,” he says. “Most of them look like sand, but mixed in with that are these beautiful structures.”
When he’s got a nice one, he picks it up with a paintbrush and puts it on a glass slide and into his microscope to photograph.
Though the snow itself may be in different forms, it doesn’t feel all that different when you’re out in it — with the possible exception of snow called stellar dendrites, which form at about 5 degrees. “They’re flat plates with barbs, so when the snow falls, it packs very lightly. Columns or sand-like crystals will pack more densely,” so they’re not as fluffy, he says.
Fluff as in powder, the ultimate skiing snow.
Get a couple of billion of these stellar dendrites “on a good 45-degree slope and you’ve got something,” says Libbrecht, admitting that though he knows how to ski, he doesn’t do it much. “I am more interested in looking at the crystals than skiing on them.”
Link to the USA Today full story:
http://www.usatoday.com/tech/science/story/2011-12-18/snowflakes-form/52049686/1?csp=obnetwork