Snowflakes Grown in Labs Answer Questions About the Ones Falling from the Sky

If middle schoolers are cutting out paper snowflakes for holiday decorations and one student insists on cutting white triangles, that’s okay. The six-sided snowflake is most often depicted, but three-sided snowflakes are not uncommon. They’ve been observed in nature for hundreds of years. Noted snowflake photographer W.A. Bentley (celebrated in the Caldecott Medal Book Bentley’s Snowflakes) and other scientists recorded them.

Physicists Kenneth G. Libbrecht and H. M. Arnold have created triangular snowflakes, as well as hexagons, in their laboratory at the California Institute of Technology. They found that the majority of flakes grown in a vapor diffusion chamber were hexagons but more than they had estimated became triangles, leading them to look for the trigger that turns hexagons into triangular shapes.

According to the authors in their published report, ”We have been studying the detailed physics of snow crystals as a case study in crystal growth, with the hope that developing a comprehensive mechanistic model for this specific system will shed light on the more general problem of structure formation during solidification.”

A single small growth perturbation on the forming hexagon flake resulted in a distorted, or triangular, shape under certain aerodynamic conditions. The perturbation caused the falling flake to tilt up. The airflow around the crystal produced instability in the growth of the facets, creating the triangular shape. After the triangular shape is initially formed, the flake stays triangular during the rest of its fall.

Libbrecht and Arnold point out, “The growth of triangular snow crystals is another piece in the puzzle that describes the many interconnected mechanisms by which complex structures emerge spontaneously during solidification.”

For all those interested in snowflakes, Libbrecht created the web site, with photo galleries of real and synthetic flakes, frequently asked questions, tips on photographing crystals and preserving them, snow activities for all age groups, and more. Libbrecht used a specially designed snowflake photomicroscope to photograph flakes. In 2006, the U.S. Postal Service used his photos as a set of commemorative stamps.

More Snowflake Studies. At Purdue University, a Ph.D. candidate in chemistry, Travis Knepp, has been growing ice crystals in his lab, subjecting the crystals to temperatures ranging from 110 degrees Fahrenheit down to minus 50 degrees. A press release from the university reports that Knepp’s experiments are part of his study of ground-level ozone depletion in the Arctic.

Knepp explains, “Most people have probably heard of ozone depletion in the North and South Poles. This occurs in the stratosphere, about 15 miles up, What people don’t know is that we also see ozone levels decrease significantly at ground level.” The complex chemical reactions that take place on the snow crystal’s surface cause the release of chemicals that reduce ozone at ground level. “How fast these reactions occur is partially limited by the snow crystals’ surface area,” he said. His findings are published in the journal Atmospheric Chemistry and Physics.

The International Polar Year

On March 1, 2007, teachers and students around the world are invited to help launch the International Polar Year 2007-2008 (IPY), a scientific program focused on the Arctic and the Antarctic. From March 2007 to March 2009, thousands of scientists from over 60 nations will be involved in more than 200 projects examining physical, biological and social research topics. IPY is an unprecedented opportunity for teachers and students to follow cutting-edge science.

The official web site, International Polar Year, includes a blog where teachers can share activities and ideas. An online flyer titled Breaking the Ice describes activities that can be carried out in classrooms. Here are resources that will help your students understand the IPY’s study of the impact of changes in earth’s ice and snow on our planet and our lives.

What Organisms Live in Antarctica?NSDL Annotation
In these activities, students will discover the characteristics that enable Antarctica’s many life forms to live in this continent of extreme cold, wind, and extended periods of light and darkness. In a weeklong unit, students research how flora and fauna have adapted to thrive in Antarctica and use their knowledge to create imaginary polar organisms.

Polar Bear CentralNSDL Annotation
From the World Wildlife Fund (WWF) Canada, this web site is all about the giant arctic bears, their habitat, and behavior. Also, you’ll find out what threatens the polar bears’ survival and how WWF is working to protect them.

To the Ends of the Earth: Research in Polar SeasNSDL Annotation
In this lesson, students will discover the differences between Arctic and Antarctic terrains, the hardships polar explorers endured, and how modern technologies have expedited polar exploration.

Melting Polar: Antarctica NSDL Annotation
This two-minute sound segment from Pulse of the Planet discusses the effect of global warming at the South Pole. It is thought that the effect would be different from that at the North Pole because the South Pole icecap is located over land.

Impact of Climate Warming on Polar Ice Sheets Confirmed
This page discusses recent changes in polar ice. Excellent photos are included.

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