Category: "News"

New Capillary Crystal-Growth Device

December 11th, 2014

After several years of planning and several more years of construction, our new crystal-growth device is operational. We are now tuning the electronics, vacuum system, data collection method, and other aspects, but we can indeed produce ice crystals on a glass capillary under controlled conditions.

The thing works!

The first two capillaries we tried basically exploded, due to my having loaded them with way too much water, but the third produced a nice frozen droplet. The frozen droplet, or "droxtal" did not grow on account of all the water that had spewed down from the previous attempts, but we cleaned up the debris, and started anew. That case, pictured above, produced a nice spatial dendrite. I could control the growth condition quite well, and kept growing, sublimating, and regrowing the same crystal for a few days. We now need to refine our capillary-making method and make them about 10x thinner (as I used to do in my previous experiments).

The overall setup is pictured below, Brian at the controls.

The white thing on the right is the cooler. It pumps cold methanol into the big aluminum box sitting on the table. That box is actually three boxes: an innermost crystal box (consisting of several chambers), a bath box that holds the cold methanol cooling fluid, and a vacuum box around that to help insulate the system.

All the controls enter from the top, so we have lots of things sticking up on top: fluid in-out ports, vacuum control of the growth chamber, reference chamber access, access to two vapor-supply chambers plus vacuum control of the chambers, a valve system to connect vapor to growth chambers, and a bunch of wires... The inside of the innermost crystal box is gold-plated to deter corrosion and help us keep contaminants to a minimum.

We hope to have more crystal images soon.


The new ice-crystal-growth apparatus

July 1st, 2014

After a few years in the making, our new device for growing single ice crystals in a well-controlled laboratory environment is nearly ready. We are just adding a few small accessory pieces to allow us to start testing. I was to describe the apparatus at the cloud-physics conference this month in Boston, and made a poster to present, but decided to opt out. But, having spent a few days making the poster, I present it below.

As with all images here, click on image to see large-scale view.

And below is the same, but in blog format.

Full story »

Trip of the Ice Man

November 9th, 2012

The "Ice Man" -- that's how a newspaper header referred to me after I gave a recent conference lecture:

A link to the article is here:

It was a very enjoyable visit to the 7th annual Northern Plains Winter Storms Conference on the campus of St. Cloud State University in St. Cloud, Minn. We had various talks including one about forecasting a storm, the statistics of the snow-to-liquid equivalent ratio (e.g., in some areas about 13" of snow will melt to 1" of water, but regions and storms vary considerably, some being over 70 to 1),and one talk about how a late-season snowstorm might end a locust plague (unlikely, according to the speaker).

My talk described how a simple principle allows us to understand how a wide variety of snow crystal forms originate.

Here's the narrated talk. To view, click the image, then enlarge to full screen:

Part 1 (10 min):
-> Why study snow crystal shapes?
-> Some history about snow science.
-> The habit map.
-> Questions that will be answered in the rest of the talk.

Part 2 (13.5 min):
-> Basics of snow crystal science.
-> Why dendrites grow so thin.
-> Why needles and columns sometimes form.

Part 3 (6 min):
-> How the crystals get their branches.
-> Why they are six-fold symmetric.

Part 4 (14.5 min):
-> How the crystals get sidebranches.
-> Common errors we make when drawing snow.
-> Why they have so much variety.
-> Mysteries about snow.
-> What are the "messages in water".

It is a scientific talk, so it involves some diagrams and technical terms. But this one is pretty easy. Perhaps the only technical terms are "vapor deposition" and "supersaturation". Vapor deposition happens when water molecules in the air (i.e. water vapor) crystallize onto something, like a snow crystal or hoarfrost. The vapor must be "super" saturated for this to happen. Greater supersaturation means greater vapor density and thus faster growth. The above link goes to the first segment, and from there you can click on the subsequent segments.

On the flight home, I saw a subsun on the clouds below. A subsun is a reflection of the sun from tiny, flat, hovering plate-like (tabular) ice crystals. They are essentially hovering like microscopic flying saucers.

In the photo above, you can see the sun's reflection off the wing on top. The smaller reflection on the clouds below is the subsun. I used to think the subsun was rare, but apparently I simply wasn't looking. This subsun was there in various forms for at least 2/3rds of the flight. I've seen them on most previous flights. More on subsuns in the next post.

- Jon

Here's the abstract to the talk:
snow crystal seminar abstract.pdf

And here are the four parts of the talk in pdf form (from the PowerPoint slides):
snow order and mystery - 1of 4.pdf
snow order and mystery - 2 of 4.pdf
snow order and mystery - 3 of 4.pdf
snow order and mystery - 4 of 4.pdf