New paperback edition out, Sept. 2017

October 25th, 2017

After eight years, several translated editions, a teacher's guide, and a Scholastic edition, The Story of Snow had a paperback edition, also from Chronicle books. The size is the same, and the content is the same except for one thing. This version lists some of the glowing reviews and accolades on the inside cover (click on image to read):

New paperback edition out, Sept. 2017



- JN

Concentric Film Frost

October 25th, 2017

October 16, 2017, the first frost of the 2017-18 winter as far as I know. Frost in Eastern Washington anyway, those of us on the west side of the Cascade Mts have not gotten any yet. Marc Fairbanks, an avid nature observer from the mountains near Cle Elum, sent me the following shot (click on the image to fully appreciate the pattern).

Concentric Film Frost


This is primarily film-frost, that is, is based on ice that formed when liquid film froze. But as I discussed in a previous post, some important growth processes here also occur through the vapor phase:

http://www.storyofsnow.com/blog1.php/crystal-to-crystal-communication-through-vapor-and-heat

I had even earlier noted some "ripple" patterns on a windshield and mused about their formation:

http://www.storyofsnow.com/blog1.php/ripples


As I'll discuss next, there are some other illuminating observations here.

Full story »

A complete picture book of all (known) snow types

February 24th, 2017

Prof. Katsuhiro Kikuchi, a highly regarded ice and snow researcher from Hokkaido, Japan, kindly mailed me a copy of his wonderful new book (coauthored with Dr. Masahiro Kajikawa). Never before has there been anything nearly as complete as this book in describing and showing all known types of falling snow. It is called "Picture Book of Natural Snow Crystals” and published by the Hokkaido Shinbun News Paper Co., Sapporo. 

A complete picture book of all (known) snow types

The only issue for most of the readers here is the fact that it is written in Japanese. This issue though does not mean one cannot learn a lot from the pictures. Here are a few sample pages: 

First, the broad-branch planar crystals P4d, P4e, and P4f: 

A complete picture book of all (known) snow types

Next, some basic combination forms (columnar and planar), specifically CP1a and CP1b: 

A complete picture book of all (known) snow types

A few of the above have been named after the Japanese-type drum "tsuzumi" due to their resemblance to this drum. Next, a type named for its resemblance to a flying seagull, the CP9a and CP9b: 

A complete picture book of all (known) snow types

Finally, a sample of the many explanatory diagrams: 

A complete picture book of all (known) snow types

The above diagrams explain how some crystals transform from a frozen sphere ("droxtal"), which all snow-crystals begin as (excluding broken fragments), to the larger forms we see on the pages. About these crystal images, Prof. Kikuchi collected them from a range of locations he visited including his nearby area of Hokkaido and Honshu, and further north and south, to the Arctic, Greenland, and the South Pole. So, though it may be possible, don't expect to see all these forms in your neighborhood. 

Overall, it is an amazing book, and I wish we had something like it in English. 

 

- JN

 

 

Columns!

January 18th, 2017

The poor columns get left out of nearly all snow-crystal discussions, but they are an interesting type. So, to help them out a bit, here's my first column appreciation post. 

Let's start with perhaps the most extreme column of all, the Shimizu prism*: 

Columns!

I say 'extreme' because they are so long and thin--sometimes over 1-mm long yet just 0.01-0.02 mm in diameter. These types have so far been found to fall only on the Antarctic Plateau. But in theory, they should be able to form elsewhere. It is like a "whisker" crystal, which Teisaku Kobayashi grew below -50 C on a surface in the lab.  The image above shows many other crystals as well, including another solid column crossing the Shimizu prism.

Next, the bullet rosette: 

Columns!

The bullet rosette is most often found below -25 C in high cirrus clouds. It is an example of a polycrystal; in this case, a frozen droplet that froze into several distinct crystals (one for each "bullet"). 

Next, one of my favorites, the scroll column (though the picture doesn't quite do it justice): 

Columns!

In this form, the sides of the crystal seem to fold inward, like a scroll. 

Finally (for now, anyway), the ubiquitous hollow column: 

Columns!

 The funny banding you see (horizontal lines inside the 'hollow') is a mystery. 

There are many other columnar forms, many of which are in the following diagram (as with all images here, click on it to see it enlarged)**: 

Columns!

 One neat thing about the columnar forms is that you can see roughly exact replicas of them in hoarfrost. The Shimizu prism may be hard to find, but the others are common if you look closely. 

 

-JN 

 

* Images are from the Magono & Lee collection, used in their paper: Meteorological classification of natural snow crystals. J. Fac. Sci., Hokkaido Univ., Ser. VII 4, 321335.

 

**Drawings are based on those in Kikuchi, Kameda, Higuchi, and Yamashita: A global classification of snow crystals, ice crystals, and solid precipitation based on observations from middle latitudes to polar regions. Atmos. Res. 132-133 (2013) 460-472. 

 

 

How clouds form snow

January 14th, 2017

To understand snow formation, one must know a little about clouds. 

Q: What is in a cloud?

A: Air, dust, vapor, droplets, and often, ice. 

Q: How much air? How much liquid water? How much ice?

A: The answers will probably surprise you. See my short 20-min presentation below. I gave this recently to the Bellingham, WA Snow School. (23 slides, but due to file-upload-size restrictions, I had to put them into three parts below, 10 slides, 6 slides, 7 slides.)

Snow, rain, and weather affect everybody, yet how many of us learned in school even the most basic facts about precipitation in school?

Q: Who first realized how ice grew in a cloud?

How clouds form snow

As described in my presentation, he realized this by observing frost on the ground. 

Q: Who first realized how Alfred's theory was intimately connected with rainfall? 

How clouds form snow

Tor discovered this by observing fog in a mountain forest, and like Alfred, applied some of his physics knowledge. 

In my presentation, I discussed Alfred Wegener, the roles of the different cloud components, and briefly how the ice, once formed, takes on its strange shapes: 

 

First 10 slides (with blue text added to account for the things I said during the talk):

http://www.storyofsnow.com/media/blogs/a/Jan2017/snowschool_annotated1t10.pdf?mtime=1484585328

 

Next 6 slides:

http://www.storyofsnow.com/media/blogs/a/Jan2017/snowschool_annotated11t16.pdf?mtime=1484585328

 

Last 7 slides:

http://www.storyofsnow.com/media/blogs/a/Jan2017/snowschool_annotated17t23.pdf?mtime=1484585309

 

 

Later, I will show specifically how the ice gets arranged into all these strange shapes. 

- JN

More frost patterns on black cars

January 7th, 2017

Black cars remain my favorite place to observe frost patterns. Here are a few I saw on one car today. 

More frost patterns on black cars

The straight lines of frost are more common when it is drier. And it has been quite dry here due to the very low temperatures. 

More frost patterns on black cars

 These pictures show an interesting mixture of straight lines and curved boundaries. 

More frost patterns on black cars

 And finally, the windshield had a pattern that resembled a hilly landscape. 

More frost patterns on black cars

But the pattern is actually quite flat. The frost is playing mind games on us, presenting an optical illusion of 3D topography. 

As with all cases of frost on surfaces, the ice initially got started when a thin layer of liquid (melt) froze in various spots. The ice that grew, first grew in the melt layer, then grew on top, essentially "sucking"** the vapor out of the surrounding air, thus drying out surrounding regions. This is why we see bare surfaces near the larger frost crystals. Those frost crystals grew from the vapor, just like snow, but are anchored to the surface because that's where the film froze. So, two types of crystallization are important: freezing of the melt (melt --> ice) then vapor deposition (vapor --> ice). 

 

- JN 

** The actual process is diffusion (the way perfume molecules reach our noses), but this term is a little more vivid.  

 

Snow Science: an annotated list to topics

December 17th, 2016

For those interested in the science of snow, I give an annotated list of relevant blog links.  

Snow Science: an annotated list to topics

 

I) Seminar about snow science (sequence of four videos): 

http://www.storyofsnow.com/blog1.php/trip-of-the-ice-man

II) All the different types of falling ice in one diagram: 

http://www.storyofsnow.com/blog1.php/one-hundred-twenty-one-forms-of-falling-ice-the-new-snow-classification-system

An older, simpler diagram:

http://www.storyofsnow.com/blog1.php/how-to-classify-snow-crystals

 III)  Why snow has six sides (the real answer, not the sloppy, standard answer):
http://www.storyofsnow.com/blog1.php/how-the-crystal-got-its-six

IV) How snow forms and how it is analogous to people:
http://www.storyofsnow.com/blog1.php/i-am-a-giant-snow-crystal-imperfect-thing-of-habit-bouncing-along-life-s-gusts

V) How to determine what the cloud conditions were like by looking at a snow crystal:

http://www.storyofsnow.com/blog1.php/new-habit-diagram-for-branched-tabular-crystals

VI) How snow crystal shapes are like frost crystal shapes (many blog entries about this, but here are just two):

http://www.storyofsnow.com/blog1.php/a-change-in-habit
http://www.storyofsnow.com/blog1.php/the-cup-and-the-butterfly

VII) Why is  snow sometimes white and sometimes black? Also, why is snowpack so bright? 
http://www.storyofsnow.com/blog1.php/white-snow-black-snow-pink-snow-blue-snow

VIII) Some finer details of those star-shaped crystals and what they tell us: 

Two-level;
http://www.storyofsnow.com/blog1.php/two-level-nature-of-branched

Droplet origin:
http://www.storyofsnow.com/blog1.php/how-some-snow-crystals-hide
http://www.storyofsnow.com/blog1.php/how-some-snow-crystal-centers

A signature of sublimation:
http://www.storyofsnow.com/blog1.php/how
http://www.storyofsnow.com/blog1.php/akira-s-corner-pockets 

IX) If you look up at a cloud, how do you know it has ice crystals in it? 
http://www.storyofsnow.com/blog1.php/it-s-not-a-rainbow-it-s-better
http://www.storyofsnow.com/blog1.php/halo-in-the-sky-uh-i-don-t-see-no-halo

 

Over the coming year, I'll be adding to this and reposting it. 

-- JN

 

Two-level nature of branched crystals

December 11th, 2016

The common branched crystal looks like a paper cut-out, but actually has a complex 3-D nature. One aspect of this nature, which I have alluded to in prior posts, is the two-level structure: What appears to be happening on one plane, is actually occurring on two. For example, consider the following dendrite of Mark's:

Two-level nature of branched crystals

The six branches of this crystal are not on the same level: the three on the right are on the top level, whereas the three on the left are on the bottom. If I could break the connection between the levels and pull them apart, they would look similar to this: 

Two-level nature of branched crystals

Actually, the connection can be broken. The fellow who first did this was Ukichiro Nakaya back in the 1930s. 

Two-level nature of branched crystals

Instead of using photoshop (as I did above), Nakaya (or rather Nakaya's assistant) used a razor blade in a very cold room. His assistant must have been both highly skilled as well as very patient, because each level is separated by less than half the width of a typical human scalp hair. 

The levels themselves are even thinner. For a fern-like dendrite, which may be 2 mm across, the thickness of one level may be 300 to 500 times thinner. A recent study ** by Wataru Shimada and Kazuki Ohtake of Toyama Univ. in Japan used a laser-imaging device to map out the contours on such a branch. The result shows an intricate 3-D structure: 

Two-level nature of branched crystals

(Thanks to Prof. Shimada for sending me this image. I have slightly simplified it.) The image shows the central part of the branch as a ridge, with numerous valleys running down both sides. The thickness of the region in red is only 5 micro-meters (5 millionth of a meter or about 0.2 thousandths of an inch).

None of this is the flat facet that we imagine a snow crystal to be. There is one flat facet however -- it is on the bottom side. 

-- JN

**The study is here, though not freely accessible: http://pubs.acs.org/doi/abs/10.1021/acs.cgd.6b01263

 

How some snow crystals hide their droplet origin

December 5th, 2016

Look closely at the center of a snow crystal. In many, or most, you will often not find a droplet center as we described in the previous post. Indeed, for the columnar crystals, you may never see a droplet center. As an example, look at the center of the dendrite crystal below (one of Mark's):

How some snow crystals hide their droplet origin

Why? Do these not also start on droplets?
Or are the droplets just too small?

This crystal, like all snow crystals did start on a frozen droplet, but the vapor deposited all around the frozen droplet (also called a 'droxtal'). The resulting growth can vary quite a bit, but roughly proceeds in a way first described in detail by the physicist Sir Charles Frank:

How some snow crystals hide their droplet origin

The crystal will still develop its two levels, top and bottom, just like we saw in the previous post, but in this process, it takes a little longer for the two levels to develop. The first stages involve the frozen droplet gaining flat faces (see steps (i) to (ii) below). Initially, as in (ii), there are more than 8 faces, but the fastest-growing faces soon vanish (they essentially grow themselves out of existence), leaving only the slower basal and prism faces in (iii):

How some snow crystals hide their droplet origin

The slower-growing faces win the game and are allowed to reveal themselves. With snow, we learn that sometimes slow wins.

In the above sequence, follow the red arrows for the time sequence. (From "(a)", I am borrowing some sketches I made for a publication in 2008. These differ slightly from those originally proposed by Frank.) The crystal sizes here are very small, about 1/10 to 1/2 the width of typical scalp hair (i.e., about 7 to 40 micro-meters). The axes on "(a)" show the crystallographic axes for ice, remnants of my paper.

You can see though that by stage (iii), the form of the original droplet has vanished. But let's continue, along the path to a recognizable branched crystal, roughly as described by Frank.

How some snow crystals hide their droplet origin

The crystal face grows outward by the spreading of layers. In the sketch above, the edge of these layers, called "steps", are shown by fine lines in the front view at right. The steps start near a corner, say at "A" or "C" in the sketch, and spread inward, closing in on the center. But soon a problem emerges: the steps are coming too fast and the center region cannot keep up. So a small pit emerges in the center of the face as you see at (b). On a symmetric hexagonal form like that above, this pit forms roughly at the same time on all six "prism" faces. (Pits may also form on the top and bottom faces, but for a crystal shape like that above, will not become very deep.) Here "SCR" stands for step-clumping region.

Typically, the rim of this pit expands as the crystal grows (c).

How some snow crystals hide their droplet origin

And grows. Eventually, the rim breaks through a crystal edge. Usually, it is the edge between two prism faces as shown below.

How some snow crystals hide their droplet origin

Notice that at stage (d), the crystal now has two levels, a top side and a bottom side. From this stage on, the two levels will compete with each other, with one eventually getting much larger than the other. This same process was shown in the previous post. But let's continue on and see how this develops.

How some snow crystals hide their droplet origin

Either one, or both levels may sprout branches. In the case (e) above, both have sprouted (note the notches that divide the just-sprouted branches). So far, both levels are developing at the same rate. But that cannot continue: the situation is unstable because if one level gets just a little bit ahead, it will stay ahead and increase its size difference with time. In fact, the smaller level will hardly grow at all - it is stuck in a region largely devoid of vapor excess.

How some snow crystals hide their droplet origin

Typically, it is the bottom level that gets ahead, as shown in (f) above because the crystal is falling down through the onrushing vapor-laden air. (The interior lines labeled in (f) above will be discussed another day.) Looking directly down on this crystal, it would look roughly like the following.

How some snow crystals hide their droplet origin

Consider that every crystal is a little bit different, but the basic features in (f) exist in the original picture at the top. I reproduce it below with a close-up of the center.

How some snow crystals hide their droplet origin

Some of these finer details will be discussed in a later post.
Finally, as to why this process sometimes occurs but sometimes the process of the previous post occurs instead remains a mystery. There are a few factors that will favor this process though: smaller initial droplets, and conditions of slower growth.

-- JN

How some snow-crystal centers retain their droplet origin

November 22nd, 2016

If you zoom in on the center of some snow crystals, you may see a small circle, or near circle. In some cases, the crystal will have other circles of similar size as well, but the one to focus on is the one at the exact center of the crystal. Here marks the spot where the crystal was born.

Look at the center of this one (one of Mark's crystals):

How some snow-crystal centers retain their droplet origin

The question is, what is that circle in the center?

The answer is: It is the original droplet upon which the crystal first formed.

Now that is the answer that I had heard a long time back. The originator, I think, was the incredible Wilson Bentley, the farmer-scientist of Jericho, Vermont during the early 1900s.

How some snow-crystal centers retain their droplet origin

The problem was that it was never clear how the crystal could build upon the frozen droplet without erasing its boundary. We see this all the time in the lab - the droplet freezes, and then the vapor molecules add onto the crystal, turning it into a hexagonal prism, and then growing into whatever shape the conditions and crystal structure determine. There are absolutely no markings, borders, or interfaces that show what the original frozen droplet looked like. It is like pouring water into a cup that is half full: after you pour a little, you cannot tell that the cup once had less water. So, I never understood how Bentley's answer actually worked. Indeed, I think that until Akira Yamashita came along and pointed out how the boundaries of the original droplet could remain, nobody knew. His argument, which he proposed just a few years ago, involved the same curious process that we found in the corner pockets (see the previous post).

The process is sketched out in A-D below:

How some snow-crystal centers retain their droplet origin

The frozen droplet under "a)" spreads an ice layer mainly along the top and bottom, making the cap and boot in 'b)". The molecules spreading across the flat surfaces migrate over the edges to the adjacent rim region, and plug into growth sites there. So the cap and boot spread out beyond the rest of the frozen droplet, as in "c)". The sides of the frozen droplet are essentially in a "vapor shadow" and receive almost no vapor: they hardly grow at all, and remain essentially frozen at their original size.

This process of the top and bottom (cap and boot) levels growing outward continues, making the crystal look like the empire fighter ships in Star Wars.

So, "c)" shows the two levels of every snow crystal. But the top and bottom levels are too close to each other. If one gets ahead of the other, it leaves the smaller one in a vapor shadow, just like the sides of the original frozen droplet. These other Japanese physicists found out how one side gets favored: It is all in the fall orientation. Remember that snow crystals are falling through the air, even as the air pushes them higher. Small, flat objects tend to hang in the air broad-wise, like a frisbee or flying saucer. The lower side (boot) gets a little more vapor, being upwind, and robs the top side (cap) of its fair share. So the lower level gets much bigger. Later, this frisbee flips back over, but it is too late for the stunted level: it remains forever stunted as the other level takes off, growing the six main branches, side-branches, and whatever features develop on its long journey to the ground.

But these stunted regions remain, including the sides of the original droplet. Not all snow crystals have this center. In many, the droplet gets erased as we observe in the lab. More on that in my next post. If you read this far, you now know something about snow that essentially nobody else does.

Finally, about those other circles on the crystal, the ones that look similar to the one in the center. These too are frozen droplets, droplets that had a startling run-in with the crystal and froze on contact. When they do this, we call them "rime".

-JN

(Crystal image is copyrighted to Mark Cassino, who let me repost here. The Bentley excerpt is from a poster I made years ago. Please do not reproduce without permission, thanks.)