Ripples in still water
When there is no pebble tossed
Nor wind to blow
- Grateful Dead “Ripple”
I don’t know where to start on this one. For some time I’ve been seeing concentric circular patterns on car windshields and car bodies – bands of white spreading out from a central point like ripples in a pond from a tossed pebble. Typically, they spread outward 3-10 inches or so before meeting up with ripples originating from another spot.
When I try to zoom in on the individual crystals, I usually see only vague outlines with the occasional recognizable form. What could cause this pattern?
Here's a clue.
I’ve seen this whirlpool pattern on two mornings on the same plastic side-mirrors of the same car.
The hollow columnar crystals are oriented lengthwise along concentric circles, which strongly suggests that an underlying film froze with the same rotating crystal orientation. This is strange. To see why I think it strange, we need to specify crystal direction. Consider the ice-crystal optic axis, the length-wise direction of the columns (or the direction straight into a stellar-star crystal). If we draw the optic axis for each crystal as an arrow, then we would have something like the following picture.
When a film of water on a smooth surface like glass or a car roof freezes, the preferred crystal orientation is that with the arrow pointing straight up and out of the surface. So, I find the above pattern mysterious - why don't the arrows have any trend toward pointing upward? Why do all the arrows stay in the same plane? Another mystery is the fact that I’ve seen this same whirlpool pattern with about the same center spot on both side mirrors on more than one morning. Perhaps the whirlpool pattern arises somehow because the surface is curved. Or maybe films of water on plastic freeze differently than films on smooth metal or glass. For now, I’ll call this the mystery of whirlpool hollows.
It often seems like people refer to any kind of ice stuck on something as frost. If one looks in books or the Internet, one can usually find a specific term for the many different and interesting ice formations, but a term used by one group of people generally differs from that used by another. Wouldn’t it be nice for scientists and naturalists (at least) to have some generally universal, agreed-upon way to describe any surface-ice formation? Snow crystals have such a system, so why not surface-ice forms?
We could try to establish word-names for each formation, like “frost flower”, but different people are used to using different names for the same thing, and they are unlikely to give up the habit, particularly if they are unfamiliar with the language of the term’s origin. For example, there are several well-used terms for the ice columns in dirt that I discuss in “Ice on the Rocks” including “frost heave”, “needle ice”, "ice columns", and “pipkrake”. But “needles” also names a type of snow. Another example: The white, curly ice hairs that can extrude from plant stems and logs is sometimes called “frost”, “frost flowers”, “Ice flowers”, "needle ice", and “sap crystals”. But the two flower terms are also used for several other, very different things. Though a few terms seem to be used consistently in English, like “hoarfrost” and “icicle”, most aren’t. And probably none work across all languages. So, instead of using word-names, a set of symbols may work best.
Wilson Bentley gave a good start to such a universal code for surface ice way back in 1907. His article “Studies of frost and ice crystals” gave an ingenious method for classifying several types of surface ice . The article is a fantastic source of information about hoarfrost, window-pane frost, and ice that grows in bodies of water like lakes and rivers. Unfortunately, I know of no one except Bentley who ever used his system. This lack of use is probably due to issues unrelated to his system’s merits, so his system might need only a little revision and some promotion to get it into use. My purpose here is to suggest such a revision.
Bentley’s system used three letters to classify many kinds of ice-forms:
Position 1: capital letter giving the kind of frost or place of deposition.
Position 2: capital letter giving the characteristic form of the ice.
Position 3: capital letter giving how common the ice form is.
Position one could be "W" for window frost, "H" for hoarfrost, "I" for window-ice, "M" for massive ice (e.g., ice in puddles, lakes, and rivers), and "S" for hailstones. For short, we could call it the WHIMS system. As an example, the following ice formation is “IFA” in his system.
Although the “I” stands for window-ice, ice on smooth black metal, as in the above case, has similar growth patterns.
This morning it just barely dipped below freezing, the first time in several days. Off I went to the usual black cars. And once again the frost to me looked like things I’d seen before. I decided to take a few pictures anyway, and once again I was surprised at what I saw in the zoomed images. To my eye, the site in the image below looked like small droplets that froze and then grew hoar.
But the camera revealed a little more variety. The site looks like a miniature seashore with a bunch of white shells of various shapes. The clumping of crystals is a little puzzling, as the close-ups below show no obvious resemblance to a frozen droplet. In some clumps, the hexagonal sides of the crystals are clear, in others, the crystals appear to be tilted up on end, such that their hexagonal sides are not shown in profile. In one case on the left, the crystals are rounded in outline, and some are not clumps at all, just a single crystal. (As with all images in this blog, a click will enlarge them.)
With my camera battery running low, I moved on to the tubs and rice fields.
The Story of Snow has been awarded a 2009 Blue Ribbon from the Bulletin of the Center for Children's Books! You can see all the details here:
A light snow has been falling for the last few days. It's not been much. I look out my window at the lawn mowed last fall, and green tips of grass blades poke out of the snow. On the internet I see the lake effect snow bands playing out to the north, but they seldom wander down here.
But for a few hours tonight a light, fluffy snow fell. I managed to get a few photos, and this in one of them. As always, click on the image for a larger view.
On the morning of December 7 of 2008, I saw a small yet distinct white patch on the ground amongst the dirty brown crunchy soil-ice columns in a rice field. If I hadn’t been looking straight at it, I would have missed it. Crouching down and clearing away some of the surrounding dirt-ice columns, I found it to be a white ice column resting on a small pebble, unlike the surrounding brown columns that rested on the soil. You can see this pebble and ice at the upper left in the image below.
The white ice “cap” detached easily and cleanly from the pebble (See the above image, upper right). I could put the cap back on the pebble, and it would stay in place, fitting snugly.
Though I appreciate seeing the old and familiar, when I venture outside on frosty mornings, I usually see at least three unexpected things. Three unexpected things before breakfast. A few days ago, the frost at first appeared more hoary than curvy, but when I peered over the top of a black SUV, I saw ice curves in the shape of an eye. Just for fun, I put an image of it next to a mirror-reversed copy, to give the following composite.
Call it the eyes of frost. Like me, you've probably seen curvy growth before, even if it didn't take the form of an eye. But let's venture into the eye of frost and notice something new: straight-segmented web-like growth.
I've never seen that before, and I never expected it.
The Story of Snow is featured in today's USA Today's Book Roundup - in an article entitled Weather the Winter with a Picture Book. The book is described as "an artistic science lesson about the rise and fall of snow crystals." The article also features Carl's Snowy Afternoon by Alexandra Day, Life in the Boreal Forest by Brenda Z. Guiberson, illustrated by Gennady Spirin and Testing the Ice: A True Story About Jackie Robinson by Sharon Robinson, illustrated by Kadir Nelson.
You can read the on-line version here:
Last night I spoke at the Grand Rapids Camera Club and provided a demo of how to take snow crystal photo. The turnout was great with well over 100 people in the room, and it was a lot of fun.
The presentation is a bit of a stroll down memory lane and the evolution of the process I use to take snow crystal photos. Of course, it starts at the beginning, with the very first snow crystal shots I managed to make. Here they are - from the winter of 1998/99. It was my second or third try at it, only very small crystals were falling, and on a wing and prayer I snapped a few shots with a high magnification setup, manual flash, and ancient Spotmatic film camera. I was really happy with the results, but it was the end of the season and there were no more opportunities that winter.
It took me a few more years till I was able to duplicate these results, but these photos gave me the inspiration to keep on trying...