Ice of Hearts

December 28th, 2009

Back when I lived in Boulder CO, I worked with Charles Knight on developing a new way to grow ice crystals for experimental study. I knew that the problem with most methods was twofold: there were too many crystals too close together to be able to learn how each one behaved on its own, and the surface that held the crystal would influence the crystal’s growth. Charlie hit on a great way to eliminate the first problem: put some water in a small pipette (like a narrow, tapering straw) and freeze the water from the wide end. At the tip, which stuck out into a small observation chamber, ice would grow out as a single crystal. Unfortunately, the smallest pipette tip was about a millimeter in diameter, which is too large. I then tried using Dupont hollowfill fibers, which are about 20 times thinner – about as thick as fine human hair. But this was still too thick. So I started using glass capillaries, which I could heat with a small torch to draw down to sizes 100-1000 times thinner than the pipette – about as thin as small cloud droplets before they freeze into ice. We had our method. From the start we would see things that hadn’t been reported before. Some of these things we (or I) published, but most of the things still remain unpublished. One of them is the heart-shaped crystals. The photo below shows the tip of the capillary, which is about 10 times thinner than human hair, along with a thin heart-shaped crystal.

 

 

After the heart grew a little more, it developed into a hexagonal shape. But probably the most bizarre thing I saw occurred when I decided, just for kicks, to try to evaporate ice from the inside of a crystal by connecting the wide end of the capillary up to a vacuum pump.

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Hoar in a Hole

December 26th, 2009
A hole in the ground is a good place to look for large hoar crystals. Next to some rice paddies, just uphill from the tubs, lies a few small holes in the cement roadway. From eye level, the white tinge of hoar frost just inside the lip is easily overlooked. Indeed, the hole pictured below is slightly less than 3 cm across at the widest and I sometimes have to look twice before I notice the ice.

Like snow, hoar can grow as a thin plate, a thin dendrite, a long column, a sharp needle, or some intermediate form, except hoar generally grows out in only one direction, not the six directions of the snow crystal. The ground surface here can dip slightly below freezing, but a short distance below the surface lies warmer, often moister, ground. At such temperatures (i.e., within a few degrees of freezing), both snow and hoar grow into platelike, or tabular, forms. Even when nearby blades of grass or foliage have columnar hoar crystals, the hole usually has tabular, showing that a small change of temperature changes the crystal considerably. (The dendrite, the most extreme tabular crystal form, grows at temperatures even lower than the columns.) (a) shows a few long, narrow crystals with jagged edges like a sawblade. And like a sawblade, these crystals are thin, as some of the side-views in (b) show.

-JN 

Oddly Glazed Bathtub

December 26th, 2009

I often see curious ice patterns on the surface of frozen water. On Christmas morning, I saw this strange pattern on one of the farmer's outdoor bathtubs. The foreground region looks a little like terraced rice fields on both sides of a mountain pass, but each terrace seems to have a structure like veins on a leaf. Indeed, the pattern within the 'mountain' on the right looks very much like a leaf. I have no idea how these patterns formed. The image is about 3 cm across.

-JN 

Reflections off Falling Crystals

December 26th, 2009

On my morning icespotting trip the other day (12/23), I caught a glimpse of an unusual sight - a sun pillar. I thought I saw one once last winter, but this one was unmistakable. It seemed more striking even than the one in Robert Greenler's book "Rainbows, Haloes, and Glories", a classic book on atmospheric displays. A line of light above the sun forms when sunlight reflects off the bottoms of falling crystals that fall a certain way - nearly horizontal. A pillar can form from either columnar crystals, oriented like a log floating on water, or tabular crystals, oriented like a frisbee in flight. For the reflection to reach our eyes, only the crystals that appear above the sun can reflect sunlight to our eye. So we see the reflections coming from the region directly above the sun, as in the picture. The same effect can occur below the sun, when the sunlight reflects of the tops of the crystals. I took this picture on the sunset setting of my camera, which boosts the reds, but the view to my eye was, if anything, more stunning.

-JN 

It Came Out of the Sky

December 26th, 2009

Our first snowfall this season came overnight with a howling westerly, but left just a light dusting. Only certain surfaces with a wide view of the sky were cool enough to preserve the snow. The only place in our yard was the roof of our car, which I've found in the past to cool about 8 degrees Celcius below that of the air at head-height. But looking out our window this morning (the 19th), I saw something else that came down - a spider. It might have come from the telephone wire about 30 feet above the car, or, with all the wind, might have blown in from a more distant place. We see these colorful spiders on their webs all over our yard and have come to view a few of them as familiar friends. The one near our front door last year seemed to freeze up and die when the first cold weather came, but later, after being warmed by the sun, popped back into action. I set this fallen spider out in a warm and dry spot, but alas, it did not recover.

- JN 

Colors of Ice

December 18th, 2009

The farmer's bathtub finally froze over. The surface had an interesting freezing pattern, but I've photographed similar ones many times before. So I picked up a rock, broke the surface, put a chunk between two crossed polaroid sheets and shot a picture.

The colors arise from the birefringent nature of ice, which means that light can pass through crossed polarizers if ice lies in between. But only some colors can make it through both polarizers.

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First Frost

December 15th, 2009

Here in this neighborhood of Japan, we finally had our first good frost day. By frost, I mean any ice that forms from vapor that condenses (wet or dry) onto a surface. We rarely get snow, typically just one or two short-lived, wet snowfalls over winter, but we often get frost.  Frost might be common here because the temperature just dips a little below freezing (0 degrees Celcius), winter skies are often clear, and the humidity is high. For example, in my yard, about seven feet above ground (where I have a safe place for my temperature/humidity meter), the relative humidity last night stayed between 80 and 87% and the air temperature got down to 1.6 Celcius. But the temperature on surfaces exposed to the sky got colder. For example, on some metal plates I put in our carport, the temperature reached -6.0 Celcius. Roofs of cars parked in a more exposed area probably got even colder. The pictures below show frost from two black car roofs.

These pictures show a mixture of two types of frost: windowpane, or film, frost, which is often clear and curvy, and hoar frost, which is white and straight. Film frost grows along the surface; hoar grows out of the surface. For the snow crystal fan who lives in a place with little snow, hoar frost is the next best thing. I say this because hoar grows just like snow - sometimes like a branch of a thin star and sometimes like a column. Film frost is ice that grows in a thin film of liquid water that condensed like dew on the surface. For reasons that remain mysterious, film frost usually curves. After the liquid in the film crystallizes, hoar crystals sprout off the ice, growing upward, away from the surface. In the top image, hoar has just started, but enough has grown to make the curved ice white, in good contrast with the black surface below. In the bottom image, if you look closely, you can see the stubble of hoar whiskers growing as tiny ice columns off the surface (at this magnification, it is hard to determine if the hoar consists of columns or thin-star branches).

The thing that is totally bizzare about film frost is that the ice not only curves, but each curve consists of a crystal structure that twists. Hoar and snow do not twist. To picture what I mean by twist, imagine holding a huge snow star and twisting each branch in such a way that the crystal resembles a six-blade propeller. Real snow doesn't twist, but film frost does. Because the hoar grows off the twisting ice, the hoar columns tilt differently in different regions. You can see this if you look closely at the bottom image.