Sunday, March 25, 2007

Great Lumps of Air

I keep promising weather theory, but I get distracted. It's also hard to start in the middle as I have to assume something. So I'll start at the beginning and weave more weather into the continuing story, continuing to be distracted on and off. My life is alrady a soap opera, so now I'll run multiple story lines. In any one week everyone should be able to find something of interest. And that will distract you from the fact that I haven't confessed what I'm doing yet. Today you have my take on some of the basic components of weather.

The Earth, as those of you who breathe regularly will have noticed, is surrounded by air. All the air contains the same gases: nitrogen, oxygen, argon, water vapour and a number of lesser components like carbon dioxide, helium, and even krypton (no, it's not green). The proportions of the non-water gases are almost completely uniform from place to place, so in dry air, that's 78% nitrogen, 21% oxygen and 1% argon (the other gases are present in a few parts per million, sharing that one percent with the argon). Air temperature varies from place to place, both horizontally and vertically. Plus the air is not distributed perfectly uniformly about the earth. There are bigger piles of it some places than others.

Some of you won't believe me about the bigger piles thing, thinking that making a bigger pile of air would be like making a bigger pile of water, and that differences in pressure thus created would fill in the gaps and and even out the piles. Of course that does happen, and that plus the behaviour of the water vapour makes weather.

I didn't mention water vapour yet, because its variation would have made it awkward to include in the general composition of air, and it's important enough to merit its own paragraph. Water vapour is the gas form of the wet stuff we normally call water. It is a colourless, invisible gas. (The steam you see coming out of the kettle is not actually water vapour, it is liquid water droplets. If you want to 'see' water vapour, crouch down to eye level with the spout of the boiling kettle. Be careful not to burn your nose, and you will be able to observe a space in the first centimetre above the spout in which there is no appearance of steam. That's air with a high concentration of water vapour, rising from the kettle. As the liquid water boils, it turns to hot vapour and rises. As it leaves the spout of your kettle it mixes with the much cooler air of your kitchen and condenses, turning back into liquid water. Because the liquid water is in the form of very small droplets, the warm rising air can support its weight and it continues to rise as steam. Until it condenses on the underside of your cupboards and makes them all soggy so they won't hold plates anymore. But I digress.) So there is water vapour in the air all around you, but you can't see it any more than you can see the nitrogen. The proportion of water vapour may be up to about 4% of the total air, but can be 1% or less. So where you sit right now the actual proportion of gases in the air might be something like 76% nitrogen, 20% oxygen, 3% water vapour and 1% argon and other.

So we have these great piles of air. Each pile, called an air mass, starts at the surface and wherever it ends, somewhere between around 30,000' and 60,000' up, is called the tropopause. There's more air above the tropopause, but that's called the stratosphere and stratospheric weather is a different subject. Air masses are formed by air lying around in one place for a while. Air masses are big, so by "one place" I mean "Antarctica," "subtropical Africa," "the Pacific Ocean" or "the far north of Canada." The air takes on the relative characteristics of the place it hangs out. Well not all of them. We don't get pointy air or high-crime air or fundamentalist Christian air. We just get moist air versus dry air and cold air versus warm air. It's all relative, so an air mass that forms over the Canadian prairies/American midwest in winter is cold compared to the air mass that formed over the southern states, but warm compared to the one that formed over the bleak arctic tundra and frozen seas. Yes, frozen seas. But it's a dry cold.

Of course everything has special names so that you don't think this weather stuff is easy. Moist air masses, like the kind that form over non-frozen seas, lakes, and jungles is called maritime, and dry air, like the kind formed over deserts or frozen landscapes is called continental. If you've ever had a "continental breakfast" at a Holiday Inn you can remember this by the dry, cellophane wrapped pastry. Or you can just remember it, because continents that don't have the Great Lakes and Michigan/Manitoba in the middle of them tend to be drier in the middle and wetter at the (maritime) coasts. That second way would really be a better way to remember it, because it is actually true, but isn't as funny as Holiday Inn breakfasts.

The cold and warm air masses mostly just go by "cold" and "warm" but they do have fancy-schmancy names, too. From north to south in Canada we are influenced by two different Arctic air masses, Polar, and Tropical air masses. South of the tropical air lurks an Equatorial air mass, but I must confess to being largely unfamiliar with its whims.


Anonymous said...

"We don't get pointy air or high-crime air or fundamentalist Christian air."

I suppose it's safe to say air is above all that.


i think this is a neat and concise distillation Sure wish you'd been there to teach my initial ground school.

Aviatrix said...

*pulls Concise Oxford* off bookshelf*

A meter is a person or thing that measures, and the verb for the corresponding action.

A metre is a form of poetic rhythm or a unit of length in the metric system.

The Concise Oxford offers that Americans spell the later the same as the former, but seeing as Americans don't even use metres, I see no reason to pander to them.

Aviatrix said...

Oh, and in reference to the language translations in your software, please please, if you have any influence in the matter, convince your company that Canada exists. We have our very own spelling, different from the rest of the world, and we're always forced to choose between using the American spellchecker and having words like colour and labour and metre flagged as incorrest, or using the British spellchecker and having words like organzation and aluminum flagged.

Aviatrix said...

Ha ha, Daily Aviator. You got me.

Anonymous said...


Don't get me started about the spelling of element no. 13.

The International Union of Pure and Applied Chemists (, the ruling body on the names of elements and compounds, has ruled in 1997 or 1998 that the correct spelling is "aluminium", and not "aluminum". However, the Americans show no sign of changing their view on this, just as in the metric system...

Just my pet peeve about good old element no. 13, without which much in aviation would not have been achieved.

Aviatrix said...

Hmm, an official IUPAC ruling, eh? This table shows that IUPAC used the um ending from 1903 to at least 1961, so it's not like the name doesn't have a venerable history.

If it were merely a matter of spelling like sulphur/sulfur (BTW the latter is official but IUPAC tolerates British and Canadians who go on using the former), that would be one thing, but it's literally a different word. The one I grew up with has four syllables; yours has five.

But I concede that the ium is now preferred by the body that matters. Therefore, for all blog entries which I submit to IUPAC publications, I will be sure to use the ium ending. And I'll be sure to use the full IUPAC nomenclature for propylene glycol, too.