Wednesday, December 19, 2001 - Perspective
Snow: The Science Behind It

- By: Tasha Betcherman

What motivated me to write this article was a quote I came across by Wilson A. Bentley from 1925

"Under the microscope, I found that snowflakes were miracles of beauty; and it seemed a shame that this beauty should not be seen and appreciated by others. Every crystal was a masterpiece of design and no one design was ever repeated., When a snowflake melted, that design was forever lost. Just that much beauty was gone, without leaving any record behind."
Wilson "Snowflake" Bentley 1925

The scientist responsible for pioneering the study of snow crystals was undoubtedly Wilson A. Bentley. He is the man behind the phrase we all remember from our childhood "no two snowflakes are alike". He made this discovery in Jericho, Vermont (1865-1931).

A self educated farmer, Bentley attracted world attention with his pioneering work in the area of photomicrography, most notably his extensive work with snow crystals (commonly known as snowflakes). By adapting a microscope to a bellows camera, and years of trial and error, he became the first person to photograph a single snow crystal in 1885.

He would go on to capture more than 5000 snowflakes during his lifetime, not finding any two alike. His snow crystal photomicrographs were acquired by colleges and universities throughout the world and he published many articles for magazines and journals including, Scientific American and National Geographic. He did most his work in a makeshift shed outdoors with very little equipment. His work is revered as the most complete and beautiful compilation of its kind.

http://snowflakebentley.com/

In 1931 his book "Snow Crystals", containing more than 2400 snow crystal images, was published by McGraw-Hill but has long been out of print. A soft cover copy, identical in all respects, can be obtained today from Dover Publications, Inc.. On December 23, 1931, Bentley died at the family farmhouse in Jericho. Because of his wonderful work with snow crystals, he became affectionately known as "Snowflake" Bentley.

I dedicate this bit of information to his memory as it seems he would want the world to know.

http://snowflakebentley.com/

If youíve ever been out on a moonlit ski or even a walk in winter youíve seen the glittering beauty of snow. Itís white, itís fluffy and it covers everything in its path. At some point you were probably taught the science of snow. All I really remember is that each snowflake is different and has six sides and can be cut out of paper. When you think about this in terms of the billions and billions of snowflakes that could fall in a single moment or that have ever fallen and none have been the exact same. None have been the exact same- this is really truly amazing. I also remember learning about how the Inuit language has over thirty different words for snow, single words that in our language would take several descriptive words to explain what we mean. As winter athletes we are unknowingly students of snow. Weíve figured out which skis or wax works best in a certain type of snow or condition. Some people have made successful careers out of studying snow, many universities around the world offer extensive programs dedicated to snow studies. The science behind snow is probably something you learned before but a little refresher course might have you seeing snow in a whole new way.

How is snow made?

Snow crystals are made in the clouds when water vapor freezes on a particle of dust, bacteria or other floating matter. When cloud temperatures are at the freezing point or below, and there is an ample supply of moisture in the air, ice crystals form around the core particle. As water vapor condenses and freezes, the complex pattern of a snowflake is born, one molecule at a time. A snowflake's hexagonal shape is created at the atomic level. It is here that water molecules bond together into stable crystal structures. Hence, the snowflake.

Depending on the atmospheric conditions within the cloud one of six basic patterns is created, although no two snowflakes are alike. These basic patterns are known as needles, columns, plates, columns capped with plates, dendrites, and stars. Each pattern is the result of unique conditions within the cloud. Scientists can trace the atmospheric conditions by looking at the types of snow on the ground. 
http://www.teachervision.com/lesson-plans/lesson-3827.html?for_printing=1

Snow Crystals

Star
Star crystals are formed at temperatures near -15 degrees C, and are among the most common type of snowflakes.

Dendrite
Dendrites are similar to stars. Essentially, they are three dimensional star crystals with branches growing on more than a single plane. Branches connect randomly to a central structure. These complex shapes form under extremely cold conditions (-20 to -25 degrees C) when high levels of atmospheric moisture are present.

Columns
Columns are produced when the air is dry. They are generally smaller, have a higher density than star crystals, and form over a wide range of temperatures (15 to -25 degrees C).

Plate
Plates are stars that are moisture starved. They form at temperatures of -10 to -20 degrees C when there isn't enough atmospheric water vapor available to form the delicate arms of a classic star.

Column capped with plates
Capped columns are composite flakes formed when the particle of snow passes through different temperature and moisture zones on its journey to the ground. The columns form first, usually at higher and dryer regions of a cloud, and combine with star flakes as they fall through lower and wetter cloud elevations.

Needles
Needles are formed at the upper end of the temperature spectrum, usually when ground temperatures are at or near the freezing point. To grow, these crystals need an air temperature in the -5 to -10 degrees C range. Needles tend to produce a dense, stiff snow pack which is associated with avalanches.

http://www.teachervision.com/lesson-plans/lesson-3827.html?for_printing=1

As you well know snow varies greatly, some types being better for skiing and other types better for making snowballs. This has to do with the shape of the snowflake and the amount of air between the crystals as they fall on top of one another. Air temperature and humidity play an important part in gliding capabilities of a ski. For instance, youíve probably experienced some difficulty trying to get your skis to glide in very cold conditions, this has to do with water forming under the ski as it moves over the snow, the colder the temperature the less this occurs, at -40C no glide occurs at all. Downhill skiers often like skiing in powder which is very lightly packed snow meaning there is more air between the snowflakes and the humidity ranges from dry to slightly moist. Snowballs form best when the snowflakes are densely packed and the snow has a high humidity. As you can imagine the variations and combinations of snow crystal type, temperature and humidity are beyond comprehension. This is probably why the Inuit language has many words describing snow.

So that winter-sports can be enjoyed early and with prime conditions, many ski centres use man-made snow to enhance the trails. Freezing water to make snow might seem easy, but it is a fascinating manufacturing process. Natural snowflakes usually crystallize around dust ,pollution and bacteria-any particles on which water molecules can condense. These "ice nucleators" are essential; pure distilled water can otherwise remain liquid even at -40 degrees Celsius, a phenomenon known as supercooling. Scientists knew it was necessary to add nucleators to make snow but the question was what.

The nucleator at the heart of many man-made snowflakes is a natural protein named Snomax. Steve Lindow, a professor of plant pathology at the University of California at Berkeley, first noted the properties of Snomax in 1975, when he was a graduate student at the University of Wisconsin investigating ways to protect plants from frost damage. Today about half the snowmaking venues uses this discovery, which, on average, increases snow production by 50 percent and yields lighter, drier flakes. At the 1994 Winter Olympics in Lillehammer, Norway, all the man-made snow on the competition routes was produced with Snomax. Natural snow is always the best and makes the most enjoyable ski conditions but major events such as the Olympics need the back up in case of low precipitation.   http://www.sciam.com/0197issue/0197working.html

The study of snow requires a very sharp and creative mind. The passion expressed by men such as Bentley and Thoreau who pioneered early scientific research was heartfelt as you can tell from their work. To them it was so beautiful they couldn't not photograph or research even with the early scientific tools they had available to them. It is truly remarkable to me how man seeks to understand even the smallest snowflake. Iíll leave you with a final quote from a great man of science speaking about snowflakes.

How full of creative genius is the air in which these are generated! I should hardly admire them more if real stars fell and lodged on my coat." --Henry David Thoreau, 1856 [1]


[1] H. D. Thoreau, The Journal of Henry David Thoreau (edited by Bradford Torrey and Francis Allen) (Houghton Mifflin, Boston, 1906; Peregrine Smith, Salt Lake City, 1984) Vol. 8, 87-88.

http://snowflakebentley.com/

http://www.teachervision.com/lesson-plans/lesson-3827.html?for_printing=1

http://www.muohio.edu/dragonfly/snow/snow.HTMLX

http://www.its.caltech.edu/~atomic/snowcrystals/

http://www.sciam.com/0197issue/0197working.html


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