This winter is turning out to be disappointing. We've had day after day of warm temperature, often barely dropping below freezing even in the evenings. What little snow we have gotten has been sloppy an d mixed with rain.
Last weekend we finally had a hard snow and a true blast of cold weather. While the detached garage in which I take these snow crystal photos had cooled down a bit, it still took till the next morning to finally drop below freezing inside the structure - even though it was well below freezing outside.
And so on Saturday morning I set up the camera and managed to get one, just one, snow crystal photo. The snow stopped just as I set up the rig and prepared to start photographing. Here's the one photo I did get - click for larger version.
And here we are - another warm day and rain on the way. Maybe more crystals will come soon...
Back when I was doing post-doctoral work in Boulder, Colorado, Charlie Knight, the head of my lab, introduced me to strange ice phenomena. The most memorable one happened after the weather had been sub-zero for a few days and then we got some snow. When this happened, we stopped work and drove out to some shallow ponds to look at the patterns on the surface. Sometimes odd, concentric circles formed.
To see the size of the rings, check out the overview.
The guy in the background is Charlie. He is sawing through the ice to get a sample. Behind him are two visitors who came out with us that day. The ice was about 2" thick, if I remember right, and would make some cracking noises sometimes as we walked on it.
I don't know if he figured out the cause of the pattern. I never made any progress in understanding it. Anyway, what seems to happen is that water gets pushed out through a small hole in the ice, and the water apparently spreads out in a circular region. But why does the lightness of the ice change in nearly equally spaced, discrete steps? And why is it whitest in the center?
I figured that if water flooded over the ice in discrete steps (day-night temperature fluctuations, as we think happens with the pancake ice?), then the region in the center would be the darkest, not the whitest. For example look at this counterexample.
This shows the hole where water comes out, but the water floods outward in a ragged fashion, not like a concentric circle. This type of flow has been studied a lot in the laboratory and has the technical name "viscous fingering". Anyway, notice that the region near the center is darker, not whiter.
Any ideas about the concentric circles?
In looking at the Cloud Appreciation Society's website recently, I started wondering; if they can have so much fun finding clouds that resemble various objects, why can't we do that for frost patterns?
Awhile back, I posted frost that looked like an eye ("Eyes and Dry Moats" Jan. 22, 2010). Here are a few other forms:
A lawn rake (or hand) and a spider web.
Two bats and some ferns?
I noticed a few interesting things about the ferns in the above image. Look at the close-up below:
If you were to follow a line of crystals out one of the curves, and then take a ruler to the edges of the crystals, you will find that crystals at one end are slightly turned from crystals at the other. It's a slight effect, more easily seen in longer, curvy patterns, but it shows that when a finger of ice grew in the underlying water film, the crystal lattice actually twisted with strain as the finger curved. This was found out by experiments in the 1960s, so I was aware of this effect. But the other curious thing is that the line of crystals has two basic shapes: long but stubby ones and nearly hexagon-shaped crystals. They all have the same crystal orientation, but they look different. I hadn't noticed that effect before.
In my last post, I pointed out that you can determine the crystal orientation in a film of ice by looking at hoar-frost that sprouts from its surface. Here's another way, but it only works if the ice is on glass. For example, here's ice on my windshield, as seen through crossed polaroids:
To get colors, the ice must be sufficiently thick. You can play around by spraying a mist of water onto your windshield (or some other sufficiently cold pane of glass), letting it freeze, looking through the polaroid sheets, and then spraying some more if you don't see colors you like. One polaroid sheet must be in front of the ice, the other behind the ice. And you need to cross the sheets. You can tell when the sheets are crossed because a bare pane of glass will be black between crossed polaroids.
Two things determine the color: the thickness of the ice and the crystal orientation. So, the boundary between different colors marks the boundary between different crystals. Black regions usually mark regions where the crystal is "basal" orientation; that is, you are viewing the ice crystal lattice from the same angle that you are viewing the nice dendrite crystals that Mark posts here. And where the color changes gradually, you are seeing where the ice thickness is changing gradually.
Of course, don't try this while driving!
I thought this hoar frost pattern looked like rough seas. I see choppy, cusp-like waves down there.
Not having any pictures of rough seas, I hopped in our bathtub and kicked my legs around to make waves. Perhaps you can see a little resemblance.
However, the processes that caused the cusp-like, choppy wave pattern in the frost are completely different from those in the bathtub. Look more closely at the hoar-frost pattern:
It just goes to show you that hoar frost is never as simple as you’d think. Though from a distance it might look like white whiskers, up close it shows unexpected patterns. These patterns reveal something about how the crystals strained, twisted, and competed with each other.
Though it is true that the hoar crystals we see are built of deposited vapor molecules (invisible water molecules once floating in the air that happened to strike and freeze onto a cold surface), the story of hoar has an earlier beginning. In the beginning, the surface already had a thin film of liquid water. See the top panel in the sketch below.
How the crystal got its “six”
For the first few years in which I would excitedly go out on frosty mornings to photograph ice formations, I never paid any attention to frost on car bodies. Sometimes I would notice something on our car window, but that was basically it – I was essentially blind to ice in places where I didn’t expect to see anything interesting. Then one day, while returning from an area that often had fascinating puddles and ground ice, I walked next to a black car with the most stunning display of frost that I had ever seen. The car was completely covered roof, hood, and trunk with a thick, large, curvy white pattern of ice made distinct by the background of black underneath.
I spent the next hour or so taking pictures, returning home once to get another camera when my roll of film ran out. Though I understood roughly the processes involved, the initial freezing of a thin layer of water, making curvy ice patterns, followed by vapor depositing onto the frozen parts as hoar, making the ice white, there were other puzzling things that kept me entertained. However, the most puzzling thing of all was the fact that people would walk right by without even slowing down. Here was a strange and rare sight: strange because of the hastily dressed man (myself) leaning over a parked car with a tripod snapping pictures, and a rare yet striking display of curving frost in full view, and yet they paid me nor my prize no mind. It was as if I was the only person who could see the pattern.
The reverse thing happened to me just a few days ago. We had wet weather one day followed by a cold, clear night – perfect conditions for good hoary film frost. And indeed, many cars in our parking lot had beautiful curvy film-frost. I walked around, looking specifically for black cars, which show the most contrast to the white hoar, and photographed some on one car, but somehow overlooked the most amazing one of all: a speckled-seaweed-like pattern that I've seen only once before (see the Dec. 1 posting).
Even though the above was on a black car in a region I checked, I still missed it. But luckily, my neighbor caught it and emailed a few photos. In the image, some of the trails seem to cross over each other, but closer inspection instead suggests a coincidental merging of two trails on one side with a forking off on the other side.
Someone recently sent me a beautiful image of an ice structure in the shape of a vase. The vase in that case had somehow sprouted out of a frozen birdbath. The thing reminded me of an ice vase I once found on an old plugged-up bathtub in a farmer’s field in Japan. See the photo below.
On approaching the tub, I first thought the ice bump on top was some chunk that had fallen off the roof and refrozen. But on closer view, I found that the thing had sprouted out of the surface. How did I know? Well, as I leaned over it, my body pressed against the tub wall, and I noticed something move. Turned out it was water on top, filling up the vase to the brim! See the sequence below.
Clearly, I’m not pushing that flimsy twig through solid ice.
Of all the curious things I’ve seen here, never before nor since did I see something like this water-filled ice vase. However, the vase forms in much the same way as the somewhat-more-common “ice-cube spikes” that sprout from ice cube trays. But how do such spikes and vases form?
We had a blizzard last night. (By 'we' I mean the mid section of the continental United States. ) Here in Michigan it started in the early evening, quickly accelerated, and lingered on till around noon today. At least a foot of snow fell overnight and in the morning. I reckon more like 16 inches.
Blizzards and other major snow events usually are not conducive to taking snow crystal photos. At least that has been my experience. The snow crystals are usually broken, battered or clumped together. A blizzard is particularly rough on the crystals, since by definition a blizzard has damaging high winds.
I ventured out a few times last night to watch the snow flying in the night, in the howling storm. As expected, any perfect crystals had been destroyed.
But this morning I managed to find a few intact crystals that fell from the sky, and took their photos with a crimson light.
Here are three snaps from this morning. As you see - they are worn and weathered, irregular (though whole) and they show arches and curves in their structure, which I find to be unusual:
(As always, click on the images for a larger view.)