Snow Falling on Tehachapi
Snow Falling on Tehachapi
By: Jon Hammond
Description: What determines the size of snowflakes?
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Posted by editor Tue Nov 30, 1999 00:00:00 PST
Viewed 1004 times
0 responses 0 comments It wasn’t exactly a White Christmas, but we did have some intermittent snow and sleet and with low temperatures this has felt like an acceptably cold Tehachapi holiday season. I hope some good snowstorms will visit us this winter — I love the white pillowy sculpting and smoothing effect of snow on the Tehachapi landscape.
And, of course, the slow-release quality of snow means that the moisture contained within has more time to absorb than would an equivalent amount of rain.
But as much as I like the aftermath of a snowstorm, I especially enjoy watching it snow. . .
I also like to photograph snow actually falling but it isn’t always easy to do. For one thing, much of our snow falls at night, which tends to reduce photo opportunities. And while you can go out taking photos for hours or days after a snowstorm, the snowfall itself is of much shorter duration and may only last for a couple of hours.
Much of the charm of watching it snow is provided by the snowflakes themselves. There are many different sizes and shapes of snowflakes and these are determined by the air temperature and the amount of available water vapor when the snow crystal formed.
The relationship between air temperature and snowflake size and shape was first proposed by the eminent citizen-scientist Wilson A. Bentley, a Vermont farmer who loved snow crystals and spent his life photographing them through microscopes to reveal their amazing shapes.
In 1880, when he was 15, Bentley’s mother gave him a microscope which he used to examine snowflakes on a glass slide. Bentley was so delighted by what he saw that he spent one year sketching the snow crystals and another three years trying to photograph them.
On Jan. 15, 1885,when he finally succeeded in capturing the first photomicrographs of an ice crystal that anyone had ever seen, he was ecstatic.
“The day that I developed the first negative made by this method, and found it good, I almost felt like falling on my knees beside that apparatus and worshipping it,” he later wrote. “It was the greatest moment of my life.”
Over the next 50 years Bentley took thousands of images of snowflakes and his 1931 book Snow Crystals, written with W. J. Humphreys, contains over 2,000 black-and-white images of snow crystals that he collected and photographed.
Bentley believed that snow crystals form differently depending on the air temperatures they encounter as they fall toward Earth and science has confirmed his suspicions.
The large, branching six-sided snow crystals that everyone thinks of as the classic snowflake shape are called dendrites and are only one of several different types of snowflakes.
The word “dendrite” comes from the Greek word dendron which means “like a tree.” Snow crystals (and mineral crystals as well) are referred to as dendrites when they branch out like trees. Dendritic snowflakes are the most complex form of snow crystals that fall from the sky.
More common are snowflakes that are simple hexagons or even those that have no recognizable shape at all. The hexagon pattern, identical to that used by bees in building their honeycomb, reflects the hexagonal arrangement that water molecule form when they freeze.
Dendrites tend to appear when the air temperature where they are forming is about 5 degrees Fahrenheit (or at least between 3 and 10 degrees F). Temperatures that are either higher or lower produce simpler structures.
The very largest snowflakes of all are produced when falling dendrites encounter warmer air near the ground and start melting slightly as they fall. The water on their surface binds little clumps of dendrites together to form huge fluffy snowflakes that resemble the white down inside a feather pillow.
Pay attention and you’ll see for yourself: the biggest snowflakes fall in Tehachapi when the weather is barely cold enough for snow — between 29 and 35 degrees Fahrenheit.
This week I’ve included photos of dendritic snowfalls in Tehachapi, when the air was confettied with snowflakes like a tickertape parade. It can make for hazardous driving (or flying, worse yet) but the effect is magical, like being inside a Christmas snow globe.
In an 1898 description of how snowflakes change as they encounter different temperatures, Vermont farmer and photographer Bentley wrote that “Much may be learned of the history of each crystal and the changes through which it has passed in its journey through cloudland. Was ever life history written in more dainty hieroglyphics?”
Have a good week.
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