- The Washington Times - Thursday, January 2, 2003

frosty the Snowman consists of millions of snowflakes, and the odds are good that every flake in his body is unique. With about 100,000 quadrillion water molecules in one snowflake, the chances that any two pieces of snow are completely alike is incredibly rare, says David Starr, head of the Mesoscale Atmospheric Processes Branch at the National Aeronautics and Space Administration's Goddard Space Flight Center in Greenbelt.

If they did exist, it's even more unlikely that scientists could locate them, says Mr. Starr, who holds a doctorate in atmospheric science.

"Are two grains of sand the same at the beach?" he says. "With all the individual pieces assembled into the crystal puzzle of one snowflake, it would seem that the odds are very long in finding two exactly identical flakes. Though, who's to say that two snowflakes aren't alike given how many snowflakes fall in an average snowstorm?"

At first glance, snowflakes seem like relatively simple substances, but nothing is further from the truth.

Since temperatures become colder as ascending into the Earth's atmosphere, snowflake formation begins in its highest areas, where ice crystals originate, says Ivan Cheung, assistant professor in geography at George Washington University in Northwest. Mr. Cheung holds a doctorate in geography and is a climatologist who studies conditions in the atmosphere.

Ice crystals are formed in the clouds when water vapor or water molecules freeze onto a particle called an aerosol, which could be anything from bacteria to dirt, Mr. Cheung says.

Most aerosols are smaller than 10 millionths of an inch, and more than 10,000 of them exist per cubic inch in polluted air. However, few are used as nuclei for ice crystals. Also, at below freezing temperatures, sometimes, liquid water molecules spontaneously freeze without a nuclei.

After ice crystals are formed, water vapor or water molecules are naturally attracted to them. As the water vapor or water molecules attach themselves to the ice crystals, the structures grow, forming a snowflake. The various pieces always form in hexagonal shapes because of the way hydrogen and oxygen bond in the water molecules. Mr. Cheung says the tiny objects display a fascinating symmetry.

"The typical snowflake is very geometrical," he says. "I personally like to see things that have systematic shapes."

As the ice crystals become heavier while gaining size from water vapor or water molecules, they start to fall through the atmosphere to the Earth, collecting mass along the way, Mr. Cheung says.

The largest snowflakes are usually the ones that have fallen the farthest distance before reaching the ground because they have had the most time to increase their size. An average flake has a diameter of about 3 millimeters and a thickness of about .50 millimeters, weighing about 2 milligrams.

"Even on days when it's not raining and snowing, there are ice crystals in the air," Mr. Cheung says. "They exist in the summer, but they melt or evaporate before they get low enough for us to see them."

Although scientists have never found two snowflakes exactly alike, they can be classified into six basic designs, says Neal Dipasquale, a meteorologist with the National Weather Service in Sterling, Va. For instance, needles, columns, plates, columns capped with plates, dendrites and stars develop according to atmospheric and temperature conditions within a cloud.

"Snowflakes have similar patterns, but inside the patterns they are different," he says. "They're like fingerprints."

Star snowflakes, which are one of the most common designs, originate in about 5 degrees Fahrenheit. Sometimes, multiple star snowflakes join to create a giant snowflake. The largest snowflake on record was reported as 8 inches by 12 inches, which fell in Bratsk, Siberia, in 1971. However, Mr. Dipasquale says gigantic snowflakes are rare. They tend to break easily from wind or collision with other snowflakes.

Dendrite snowflakes, which are similar to star snowflakes in that they have a star-shaped body, have branches growing on more than one plane. They are three-dimensional flakes with arms connected randomly to their central structure. They usually form in about -13 degrees Fahrenheit to -4 degrees Fahrenheit, when high levels of moisture are present in the atmosphere.

On the contrary, Mr. Dipasquale says, column snow-flakes are produced when the air is dryer. They have a higher density than star snowflakes and originate from about -13 degrees Fahrenheit to 5 degrees Fahrenheit. Also, plate snowflakes, which form from -4 degrees Fahrenheit to 14 degrees Fahrenheit, develop when there isn't enough water vapor in the atmosphere to create the intricate arms of a star snowflake.

Occasionally, a column snowflake capped with plates forms when the particle of snow passes through different temperature and moisture zones. Usually, the columns are created first in higher and dryer regions of a cloud and combine with star snowflakes as they fall through other atmospheric elevations.

At the warmer end of the temperature spectrum, needle snowflakes develop, usually from 14 degrees Fahrenheit to 23 degrees Fahrenheit. Needles often produce dense snow, which could cause an avalanche.

The intricate nature of snowflakes was first discovered in 1885 by Wilson "Snowflake" Bentley of Jericho, Vt., says Louise Miglionico, a member of the board of the Jericho Historical Society in Jericho, Vt. He worked in photomicrography by taking pictures of small items by adapting a microscope to a camera.

The proposition that two snowflakes have never been the same started with Mr. Bentley, Mrs. Miglionico says. He photographed more than 5,000 snowflakes during his lifetime, without finding any two alike.

Since Mr. Bentley believed every snowflake was a masterpiece of design, Mrs. Miglionico says he recorded as many as possible for public enjoyment. His book "Snow Crystals," which was published in 1931, contains pictures of more than 2,400 snowflakes. A softcover edition of the book is available through Dover Publications Inc. in Mineola, N.Y. There is a Web site, www.snowflakebentley.com.

Colleges and universities throughout the world also acquired Mr. Bentley's photomicrographs, and he published articles for various publications, including Scientific American and National Geographic.

"He was just fascinated by the artistry and beauty of a snowflake," Mrs. Miglionico says. "People are still fascinated by it today."


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