Scientist wants to make snowflake formation crystal-clear

— -- 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.

That growth pattern, involving ever-sharper edges of water crystals, is described in a recent paper in the journal Materials Science by Caltech physics professor Kenneth Libbrecht, who has spent much of his career feeding the public's endless fascination with the beauty and mystery of snowflakes.

It's such basic science that it's only for those with tenure, quips Libbrecht. "There are no grants, you can't get funded for it." But the mystery of how snow forms is still unsolved, and that calls to him and a small group of researchers in the field for that very reason.

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."

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Libbrecht has been studying the physics of snow formation for more than a decade. In the late 1990s, he ran across an article describing the physics of capped snow crystals, hollow columns that are capped at the ends.

"I grew up in North Dakota, and I said, 'How come I never knew this?' That's when I decided I wanted to write a popular science book about it, because people who grow up in cold places should know about snow formation," he says. "Once you go out and look, it's pretty easy to find, but you've got to know what you're looking for."

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.