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It’s Snow Wonder

The views expressed are those of the author and are not necessarily those of Scientific American.


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Ok, I admit it. I love snow. There I said it.

As a kid growing up in Central New York, we always had plenty of snow thanks to the lake effect off of the Great Lakes. I would sled and ski, cross country and downhill constantly. Each year once Halloween passed, I found myself with elbows pressed on the window sills, head in my hands, just waiting for the first snowfall to totally transform the earth white.

Even if you despise snow, you have to admit the first snowfall and accumulation of the season is quite beautiful. Everything is clean, white and pure. The eyes are instantly aware of something new and your senses may delight in a change to the normal daily environment to which they have grown accustomed.

So what causes our region to undergo this wardrobe change into white? The answer lies partly in the intricate design of each snowflake and science oh mystical science.

A snow crystal forms in a cloud when water vapor condenses and crystallizes around a single particle of dust. In order for the water vapor to crystallize, the atmospheric temperature has to be at or below freezing point. It is interesting to note that the temperature here on the earth’s surface that we pay attention to isn’t very important when it comes to the formation of snow occurring up in the clouds. In other words, it can snow even when we see our thermometers above 32 degrees Fahrenheit  (0 degrees Celsius).

As the air gets colder, molecules of water in a cloud can join together to construct an ice lattice in the shape of a hexagon. Some of the prettiest snow crystals are the ones that have this little hexagon shaped ice prism as their foundation. Once the hexagon shaped base is established, beautiful arms or dendrites can grow outwards from each of its six corners. This is what most people usually picture in their mind when they think of a snowflake.

However, the term “snowflake” is actually incorrect. Scientifically speaking, the word snowflake refers to a cluster of snow crystals stuck together. Snowflakes are what we usually encounter in an everyday flurry. The awe-inspiring six-sided individual snow crystals are spotted falling softly from the sky only on those special winter days where there is little to no wind and the weather conditions are just right. Most of us probably recall seeing a perfect snow crystal fall onto our gloved hand at one point or another in our lives and it really is amazing to see.

Kenneth Libbrecht is a physicist and researcher at Caltech who spends more than just the winter months admiring snow crystals. He has provided us with actual images of the stunning snow crystal you see throughout this article. Ken studies the physics of crystal formation and “lets it snow” in his lab all year round as he works to uncover and capture the beauty and wonder of snow crystals with his camera lens.  “I enjoy photographing snowflakes, it’s like a treasure hunt,” he says.

Many different shapes and types of snow crystals exist, not just the aforementioned six cornered variety. The type and shape of each snow crystal is determined by the atmospheric temperature and supersaturation of water vapor in the air, also known as the humidity. The most complex designs occur when humidity in the air is the highest.

Even on the same day, there is a unique design seemingly carved into the arms of each snow crystal. This is in part due to each snow crystal following a slightly different path as it falls through the sky and it endures different temperature and environmental changes along the way as its arms developed. This gives it individualized beauty and lends some truth to the legend of how “no two snowflakes are alike.”

Morphology diagram used with permission from Kenneth Libbrecht

On the ground, as snow crystals and snowflakes fall and accumulate, they do so in a very light and airy arrangement. In fact, 80% of fresh snow accumulation on the ground is composed of air. When we look at freshly fallen snow, we see it as white. This is because sunlight traveling to and through the airy snow is made up of all of the colors in the visible spectrum of light. This light is scattered and reflected through the many snow crystals and flakes. The hexagonal bases of snow crystals act like thousands of prisms lying on the ground, refracting and reflecting all of the colors of the visible light. In most cases, no wavelengths or colors of light are absorbed by the snow and nearly all of the light is reflected back towards our eyes which interpret all of these reflected wavelengths together as the color white.

Having said that, there is more to the picture than just what we see on the surface. If you pierce a small, deep hole in the snow you may notice the snow way down inside appearing bright blue. Also, different layers of snow and bubbly ice like that of frozen waterfalls and glaciers sometimes have been observed to emit a subtle blue or even greenish hue. Red algae is also said to alter the perceived color of snow. These and other topics relating to the physics of snow continue to captivate researchers and science lovers alike as they have for over 100 years.

Studying and understanding crystal formation can have other benefits for the advancement of science and technology such as making “better artificial snow, better ice for Olympic skating, bigger diamonds, faster computers…” but that is not the reason why Ken and others really study it. He says he believes “that basic science can and should be pursued for its own sake.”

So this winter, maybe instead of focusing on the negative aspects of snow such as shoveling and slush, we should once again stop and look at the wonder of snow through the eyes of the child, or better yet, through those of the scientist inside all of us. After all, it is freshly fallen physics.

Acknowledgements: With very special thanks to Ken Libbrecht for allowing me to interview him via email. I learned so much and he really helped make this article possible. If you want to savor the magic of snowflakes a little longer, check out his amazing books on Snow Crystals and Snowflakes! His website is also well written and very fun to read! Thank you Ken for sharing your knowledge and passion with all of us. Also, thank you to Erica Angiolillo for allowing the use of her exquisite wintery pics!

Photo credits: (Snow Day), (Tranquility), (Cold Veins), (A Taste of Winter), and (Author) by Erica Angiolillo/Gotcha! by Erica photography (Snow Crystal pictures 1, 2 and 3) and (Morphology Diagram) by Kenneth Libbrecht.

References:

Bohren, Craig. Colors of snow, frozen waterfalls and icebergs. J. Opt. Soc. Am 1983 Dec; 73 (12): 1646-51. doi:10.1364/JOSA.73.001646

Doesken, Nolan and Judson, Arthur. The Snow Booklet. Colorado Climate Center, Colorado State Univ. Fort Collins, CO. ISBN #0-9651056-2-8 (2nd Edition)

Libbrecht, Kenneth. Personal Interview via electronic mail. Dec 2011.

Libbrecht, Kenneth. The physics of snow crystals. Rep. Prog. Physics 2005; 68: 855-895. doi:10.1088/0034-4885/68/4/R03

Cheryl Murphy About the Author: Cheryl G. Murphy is an optometrist and freelance science writer living and working in New York State. She began writing about vision science on her blog,Science Hidden in Plain Sight, in 2008. Links to her previous contributions to Scientific American’s guest blog can be found here. Follow her on Facebook or Twitter. Follow on Twitter @murphyod.

The views expressed are those of the author and are not necessarily those of Scientific American.






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