let it snow

Foolsjenluc_8My last evening in Seattle, I was hanging out at a local Starbucks in Renton, a suburb just south of the city. So engrossed was I in my work, that I failed to notice it had begun to snow. In less than an hour, a good three inches had accumulated, and it didn’t show any sign of stopping. Lacking snow tires on my rental car, I realized I’d never get back up the long steep hill leading to my folks’ place (where I was staying), so I parked the car in a nearby corporate lot, and bummed a ride with a local guy named Joe who’d had the foresight to pack some chains in the back of his pickup. (Thanks again, Joe Whoever-You-Are; you spared me a mile walk in the snow.) It made the next morning a little stressful, given my noon flight back to DC. I had to dig out the car and gingerly navigate the by-then very icy side roads to the freeway — which, mercifully, was dry as a bone. In fact, you’d never know people were stranded in the suburbs if you were driving on I-405, which might explain why Avis was so incredibly unsympathetic when I returned the car with only half a tank of gas, citing the inclement weather as an excuse.

Chalk it up to one of those weather flukes; it’s been an unseasonably cold winter in Seattle, and the city does occasionally get a heavy snowstorm. But it snowed in Los Angeles this week! Los Angeles, people! As in, southern California, land of the orange groves, and my soon-to-be-hometown. (This year’s crop went straight to orange concentrate, I’d wager.) Now that’s an historic event! It reminded me of a scene in To Kill a Mockingbird, where  the little girl-narrator, Scout, sees pretty white snow flakes falling and assumes the world is ending. She’s never seen snow before, since it’s a very rare occurrence in rural Georgia Alabama. The world didn’t end then, and it’s not ending now, but it’s just one more bit of evidence that weather is a very wacky thing.

Unless, like Scout, we’ve never experienced a genuine snowfall, we probably take snow a bit for granted. It’s just another form of precipitation, after all, and we have a pretty solid grasp of that particular cycle. Just for the record, snow is not frozen raindrops; that would be sleet. Under certain conditions, water vapor can condense directly into tiny ice crystals, skipping the raindrop phase altogether, and usually forming the shape of a hexagonal prism (two hexagonal "basal" faces and six rectangular "prism" faces). But that crystal also attracts more cooled water drops in the air. Branchings sprout out from the single crystals’ corners to form snowflakes of increasingly complex shapes. And yes, for all intents and purposes, no two snowflakes are shaped exactly alike, at least according to Caltech physicist Kenneth Libbrecht, who runs this Website devoted entirely to snow crystals. But there are 35 different types of snow crystals, all of which he has carefully documented.

Libbrecht must have been thrilled to see snow in Los Angeles, since he usually has to create his own ice crystals in the lab, or go to more frigid climes, like Michigan or Alaska or Ontario, to make his high-resolution microscope images of snowflakes. (You can see movies of lab-based snow crystals forming here.) Even then it’s a tricky business. He has to use a small paintbrush to transfer the delicate structures to a glass slide, taking the picture with a digital camera mounted on a high-resolution microscope. All of this is done outside to keep the crystals from melting too quickly. The final images are quite striking — so much so that last October, they were featured on a new 39-cent commemorative postage stamp, courtesy of the US Postal Service.


Not surprisingly, the shapes of snowflakes and snow crystals have long fascinated scientists, like Johannes Kepler, who took some time away from his star-gazing in 1611 to publish a short paper entitled "On the Six-Cornered Snowflake." He was intrigued by the fact that snow crystals always seem to exhibit a six-fold symmetry. Some 20 years later, Rene Descartes waxed poetical after observing much rarer 12-sided snowflakes, "so perfectly formed in hexagons and of which the six sides were so straight, and the six angles so equal, that it is impossible for men to make anything so exact." He pondered how such a perfectly symmetrical shape might have been created, and eventually arrived at a reasonably accurate description of the water cycle, adding that "they were obliged to arrange themselves in such a way that each was surrounded by six others in the same plane, following the ordinary order of nature." (The lack of a detailed explanation can be excused: it took the development of x-ray crystallography for scientists to really be able to study the shape and structure of snow crystals/flakes in any great detail.)

Libbrecht has an historical predecessor in Robert Hooke. Hooke’s Micrographia, published in 1665, contained a few sketches of snowflakes he observed under his microscope — sketched rapidly, one assumes, since the flakes no doubt melted soon after being placed under the lens, even working outdoors. If only he’d had access to Libbrecht’s equipment, he wouldn’t have had to do everything by hand — and he would have appreciated the far more intricate details observable under orders-of-magnitude increases in resolution.

But nobody performed a truly systematic study of snow crystals until the 1950s, when a Japanese nuclear physicist named Ukichiro Nakaya identified and cataloged all the major types of snow crystals. (Nakaya had the bad luck to be appointed to a professorship in Hokkaido, with no available facilities for his nuclear research, so he applied his considerable skills to what was readily available: snow crystals. Now that’s taking lemons and making lemonade.) He also proved Descartes wrong in the Frenchman’s assertion that no man could make anything so perfect. Nakaya was the first person to grow artificial snow crystals in the laboratory. In 1954 he published a book on his findings: Snow Crystals: Natural and Artificial. Here’s what Libbrecht’s Website has to say about it: "Nakaya’s book offers a superb look at a scientific investigation which begins with almost nothing, and proceeds through systematic observation toward an accurate description of a fascinating natural phenomenon."

Thanks to Nakaya’s pioneering work, we now know that certain atmospheric conditions, like temperature and humidity, can influence a snowflake’s shape. For instance, those shapes tend to be simpler in low humidity. The higher the humidity, the more complex the shape, and if the humidity is especially high, they can even form into long needles or large thin plates. Scientists aren’t entirely sure why, but they suspect it has to do with the complex underlying physics of how water vapor molecules are slowly incorporated into the growing ice crystal — what Descartes termed the "ordinary order of Nature." There’s still a lot of mystery in that ordinariness.

That’s why NASA has launched the Global Snowflake Network, a massive project that aims to involve the general public to  "collect and classify" falling snowflakes. The data will be compiled into a massive database, along with satellite images, that will help climatologists and others who study climate-related phenomena gain a better understanding of wintry meteorology as they track various snowstorms around the globe. Participating students, teachers, and other interested parties will have the chance to take part in real science, and learn more about how climate, temperature and other atmospheric features combine to produce weather phenomena.

So next time snow falls in your area this winter, take a few moments from building snowmen and lobbing snowy missiles at the annoying kid down the street, and look more closely at each individual flake. You might even consider signing up with the GSN, thereby recording your observations for scientific posterity.

17 thoughts on “let it snow”

  1. Jennifer, you will enjoy sunny southern CA. In the Winter you are never far from snowy mountains, like Mount Wilson. Nakaya’s work shows how much of a contribution a physicist can make working outside the field. Unlike NYC, you are far from tsunami zones.

  2. “She’s never seen snow before, since it’s a very rare occurrence in rural Georgia.”
    You mean rural Alabama?
    I was in LA last weekend, but alas didn’t see any snow (except on the mountains). Too bad, because I love snow. It was so rare to see it where I grew up…in rural Mississippi.

  3. A couple of years ago I got into my car one morning, and noticed how beautiful the snow flakes were that were falling on my car windows. I went back inside, put the macro lens on my camera and got this shot:
    It’s a big image as I wanted to preserve all the detail I could.
    What I find very interesting, is that the actual flake forms in the normal hexagonal way. the streaky, spiderwebbish growth appears to be the form that ice crystals were forming on the surface of the glass. Given that evidence, I think you can clearly identify how big the central flake was when it landed on the glass, with the tips of the flake then growing in the spiderweb fashion out from the ends to produce a kind of hybrid ice structure.
    Beautiful in any case.

  4. I have never understood what people mean when they say no two snowflakes are the same. Surely all crystalline structures have flaws and thus the occurrence of any two identical structures (even with something like table salt) is unlikely… maybe I am missing something?

  5. I’ve always loved the names of the types of snowflakes. Bullet rosettes, Graupel, arrowhead twins – the limited number, the ability to see these things as well as place them in our immediate reality makes their names much more appealing than the dry and arcane names we give things like molecules or nebula clouds.

  6. We too have had an unusually cold winter here in Grants Pass, OR. With snow that is sticking around quite a while and really cold temperatures. I found the comment “But it snowed in Los Angeles this week! Los Angeles, people! As in, southern California, land of the orange groves, and my soon-to-be-hometown.” Interesting as this is where I grew up and had a thriving business until recently when circumstances forced me to move here.
    As an amateur meteorologist, in my research I find these weather extremes interesting (the extreme cold that grips the Northern Hemisphere while the Southern Hemisphere bakes), I personally believe we are not necessarily warming, but headed to extremes of cold winters and hot summers.

  7. Three inches in less than an hour, that’s really unfair. We haven’t had any snow here in south east England for over a year.

  8. Extremes of weather? Here in SE Michigan, the trend has been towards mild weather. Little snow in winter, and fewer heat waves in summer. Last summer, i ran my A/C just one day. And that was mostly to prove it still works.
    All right. I like it hot. But we’re just now getting a good cold wave, and a light dusting of snow.
    … I’m dreaming of a brown Christmas…
    … Just like the one we had last year…
    (this comes out better than you’d expect – I have some voice training)

  9. On an entirely different note, I just _have_ to bring up a particularly choice subject – Rupert Sheldrake.
    In his book “The Presence of the Past – Morphic Fields and the Habits of Nature”, Sheldrake asks the following question: how does a snowflake know how to be symmetric? That is, as a hexagonally symmetric snowflake develops it develops identical features at (six or more)widely separated points. How does this happen? How does the process know to develop identical features and branchings at just the right places to maintain symmetry?
    It’s a fun question, and I have my own explanation, but I thought I’d throw it out for discussion.
    Sheldrake, for those who aren’t aware of him, explains this by positing “morphic fields” which contain the essence of shape (and all sorts of other information)and which provide a pre-existing template for the arms of the snowflake to use. Repeated use of a morphic field strengthens the field, causing that morphology to be used more frequently. And that’s why snowflakes look the way they do.

  10. theresa (ramseth) strutynski

    Hey Jennifer, I remember walking up that hill to your parents house with you! It was about 1977, can’t remember if there was snow. Mom showed me an article about you, and I decided to send you a line just for fun. Be glad to hear from you sometime. Give me a call when you are back in town. Best of Luck,
    Theresa R

  11. Morphogenetic fields have been speculated for over 100 years. They could be responsible for the form of an organism. Sheldrake later refined this theory to account for a wider range of phenomenon – like collective consciousness, etc.

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