Sunday October 28, 1951
ASK THE WEATHERMAN
(CBC Trans-Canada Network)
"THE AIR ABOVE US"
By
P. P. Saltzman,
Dominion Public Weather Service,
Toronto.
One of the sweetest memories of my childhood revolved around the glorious summer holidays in southern Saskatchewan when, lying on the cool grass in the early morning, nibbling a chocolate bar and gazing up into the sky, I imagined I could feel my sight penetrating higher and higher to the very top of the air above me and the deep blue of the sky seems to have no limit. Those days are long past now, but I can still recapture that mood by watching a high flying plane painting it vapor trails six miles up across the heavens. Today it is not the same, for now I know that there is a limit to our sky. The question of how high is up? Can now be answered. Up is somewhere about 1000 miles aloft. Somewhere up there the blue of the sky ends and the black of outer pace begins. Our sky has a ceiling. How disillusioned would that lad have felt lying on his back in the cool grass in the southern Saskatchewan summer probing the azure vault.
But on the other hand how much more satisfying to the adult mind it is to know that our scientists are amassing a growing fund of knowledge about the air above us. Many years ago two Englishmen jumped into an open-basket type of balloon and soared seven miles up without oxygen or heated clothing. One man became unconscious and the other one's hands were so frozen that he had to grip the cored with his teeth and pull with his head in order to open the valve and let the balloon come down. Such were the intrepid exploders of our atmosphere in the pioneering days. Nowadays unmanned rockets carrying sensitive instruments are now prying nature's secrets from her bit by bit. It is vitally important to know these secrets, important for aviation, for radio communication, for nuclear physics and for weather forecasting.
The earth's atmosphere is made up of four layers, like a huge layer cake. From the bottom up these are called the troposphere, stratosphere, ionosphere and exosphere. Air has weight. A column of it one foot each way and 1000 miles high weight about a ton, but three-quarters of this weight is compressed into the lowest layer alone. This layer, the troposphere, is about 7 miles thick and it is here and only here that nature's forces make the weather. All our weather, ---clouds, rain snow, thunder, drizzle and fog - occur in the first 7 miles above us. As we go up in this layer the temperature drops steadily to about 70 degrees below zero at the top. Wind speed steadily increases and blows in general from the west.
It is near the top of this layer that we meet the jet stream, that snakelike fast flowing river of air that sometimes reaches speeds of 300 mph.
Above the troposphere lies the second layer, the stratosphere, which is about 30 miles thick. A good deal has been heard of the stratosphere in connection with the advances of modern aviation but flying in the stratosphere is not nearly as common as most people may think. Actually, at present there is very little flying in the stratosphere, but undoubtedly the time is not far off when the stratosphere will be the long distance highway of the sky. Here there is no troublesome weather for the air is very dry. Here the winds are from the west in summer and swing around to blow form the east in winter. Here the air moves rapidly and is often bumpy. Temperature in this layer is often nearly steady at about 70 below zero. The stratosphere layer has a ceiling, like a coat of icing, made of ozone. We must be thankful for this blanket of ozone for it protects us from an overdose of the sun's ultraviolet rays, which if they were allowed to come through to us unhindered would burn us to a crisp. The ozone layer Is hot, perhaps 170 degrees above zero. A moment ago I mentioned that all our clouds are found in the lower layer, the troposphere. This is true for the wet clouds, the ones that give us weather, but in the stratosphere we find a strange type of dry could, called mother of pearl, which is as yet little understood but is believed to consist of dust.
The bottom two layers just mentioned account for the lower 40 miles of the air above us. What about the remaining 930 miles or so? The third layer is called the ionosphere and extends to the 400 mile level. Here we think temperature first falls off to well below zero and then starts to climb rapidly until near the top it reaches the unbelievably hot figure of 4000 degrees Fahrenheit above zero. This may surprise some who have all along thought that it's always colder upstairs. The ionosphere is so named because it is here we find the several layers of free electrons which reflect back our radio waves and so make possible long distance radio transmission. The wind speeds up steadily as we climb in the ionosphere to well over 300 mph and here too it blows one direction in summer, another in winter. Here too we first encounter the meteors, most of them as small as a pea. What hazard to aviation these will be, we don't fully know, but most of the meteors burn up rapidly as they rub through the air at high speeds. Incidentally. radar is now used to track meteors and a good deal is being learned about them in this way. Here too in the ionosphere we find the home of those heavenly draperies called the aurora which stretch from 40 to 400 miles above the earth's surface. Here too are found another type of dry cloud, the strange and beautiful noctilucent or luminous night clouds. The noctilucent and the mother of pearl clouds I mentioned earlier are very useful to us in that we can follow them as they circle the earth and learn something of the wind speed and direction upstairs. We have learned that the wind is very fast and the air is very bumpy and flying to say the least would be a wee bit rocky up there.
The last layer of our four-layer air cake is called the exosphere. This fringe layer is made of a very skimpy group of gas particles and little is know about it. All we can say about it is that somewhere at the top it thins off into outer space.
One thing not yet mentioned is air pressure. The total pressure of 1000 miles of the air above us is about the same as you'd find if you were diving 34 feet below the surface of a lake. Pressure is the only weather element that falls off steadily with height so that from a pressure of about 15 pounds per square inch on the surface of the earth, it declines to zero at the top of the exosphere.
So you see, that little boy lying on his back in the grass staring into the sky could not really be expected to know that there was a mighty world in the 1000 miles of air above him. But look at another way. In relation to the size of the earth, our air is like a very thin layer over it, yet in this shallow skin, we live and breath and find a whole world of cosmic rays, clouds, meteors, aurora borealis, ozone, free electons, other nuclear particles, all the gases we breathe, noctilucent and mother of pearl cloud, and what not. As for the ordinary man in the street the weather he beefs about - and enjoys - is made in the lowest 7 mile layer of it all.
Most of us, I imagine, have seen in the papers and magazines the famous picture* of our earth taken by an automatic camera in the tail of a high -flying rocket. You have seen the sweeping curvature of the horizon, a vast chunk of the earth's surface, and a goodly number of tiny distant clouds, mottling the face of our planet. Truly a birds aye view of the troposphere and someday and probably sooner, than we expect people may be able to SE9 this glorious sight looking out the window on their first ionosphere jet flight.
[* Note: The picture to which Percy refers can be seen here in Air and Space Magazine]