Archive for October, 2010

Wind October 27

So it’s been blowing for two days, and no end in sight. This is a good time to go to the Jet Stream Animation page, which is always in the margin of the blog, but in case you didn’t notice, here’s the link. What’s fun here is that the page tells you how to choose an animation. The default is a two-day animation, ending today (the day of your search) but you can get seven days, so you could put the 21st as a start day, or, in fact, choose any seven days. and get a longer view.

The jet stream is an upper wind that races along year round, sometimes, flowing mostly above Canada, and other times dipping quite a distance south. Of course it drags the air below it, so it can have a very strong effect on our lower winds if it is anywhere nearby.

The darkened area on the map is where the wind is at least 60 mph in the jet stream.  With each step inwards, marked by a dotted line, the speed is 10 mph faster. Sometimes the center is 160, sometimes even higher. The ground speed is much lower of course, but I was told that even the ground wind reached 80 mph in gusts yesterday, and there were some roof parts flapping in various places around town, as well as mailboxes toppled.

From the looks of the stream, there’s plenty more wind coming, but perhaps not quite so strong. The center is actually flowing somewhat south of us as well, so it could be worse.

I wish I could import the image, but anyway, it’s interesting to watch.

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Besides green chlorophyll, yellow carotene, and red-to-purple anthocyanins, there are tannins, which contribute a brown color to leaves. Because brown is also the color of a leaf that is dead, this is not a very impressive show, but tannins are not the same as death. They come in reddish colors, and in paler yellow-brown shades, none of them very showy, but all contributing, in a quiet way, to the characteristic deep copper colors of oak trees in the fall. There is a time between the living green and the dead brown when this copper shine through and gives the oak a special sheen. When I was little, I just didn’t like these colors, whether because they are not, in fact, the right colors for me to wear or for some other reason. Now I enjoy them, but they are a more subtle display than the flaming maple or the golden aspen.

Actually, tannins are found in many, perhaps all, trees, but they are particularly prevalent in oak trees. In fact, oaks very often have little swellings called galls, which are particularly full of tannin. The galls are a response to parasites, and though I guess some parasites do fine in all that bitterness, many others are kept out. Be that as it may, oak galls have so much tannin that they were long used for the most expensive brown inks! In fact, you can still obtain oak-gall ink, if you really want it.

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The second color of autumn is red, and it comes from a group of pigments called anthocyanins, whose synthesis in the cell is favored by cool weather. Because these chemicals are formed by a reaction between concentrated sugars and certain proteins in the cell fluid, they are also favored by dry weather, which concentrates the sugars. That’s why the red colors, the anthocyanin colors, don’t develop strongly in a wet fall; the sugars have a hard time concentrating.

The anthocyanins have another interesting character: they are Ph sensitive – that is, sensitive to acids and bases. In an acid environment, they are red; in a basic environment, they are more blue or blue-violet. This is the same reaction you see when blueberries are served on yogurt and turn a darker and less appetizing blue, whereas if you add a little lemon juice, they turn a lovely raspberry color.

When autumn leaves have a flaming orange color, you have the yellow of carotenes mixed with a lovely red anthocyanin. When the color is a light but distinct violet, you have only anthocyanins.


So where is the green of summer?

Green comes from chlorophyll, a chemical famous for its role in forming sugars from water and carbon dioxide. It is the entire food system for the plant and for everyone else as well, since we all eat plants, or eat creatures that eat plants, or at least eat creatures that eat creatures that eat plants… Chlorophyll is the essential foundation of the food system.

It is not a very stable chemical, however, and must be constantly re-synthesized by plants. A few minutes reflection will remind you of some time when you noticed a patch of grass or a plant that was covered up for some reason and quickly turned yellow. Well, the yellow is carotene, which was always there, but the plant lost its green color because the leaves require both sunshine and warmth to synthesize chlorophyll. When the chlorophyll degrades, you see the carotene. A yellow plant is not necessarily dying, however; a day in the sun quickly replenishes the chlorophyll and the light yellow becomes just a background pigment, brightening the usual green.

In the fall, even while sunshine remains strong, chlorophyll diminishes. Its synthesis requires warmth, so cool weather slows its production at the same time that it favors the production of anthocyanins. The result is that leaves can have every variation of red, deep red, green, and mixed red and green which is sort of murky. Plus, of course, yellow which can make a red or a green look much brighter.

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Carotene in the trees

Every fall, in the northern states especially, there is a blaze of color before the trees drop their leaves for the winter.  With so many colors on display, one might ask how many pigments are involved.

Basically, four, one of which is carotene, the same as you have in carrots and sweet potatoes. A little carotene is yellow. More can become very deep yellow, almost orange, but not quite. The green color is, of course, from chlorophyll, (C55H70MgN4O6), a very large molecule, as you can see, and one that is present all summer long, making sugars for the plant. Varying amounts are left in the fall, leading to different levels of yellow and yellow-green.

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