Weather Wise

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The Independent Online
The next time you look upwards into the sky, spare a thought for what is really going on up there above the clouds.

The lowest level of the atmosphere is called the troposphere. Varying from five miles high at the poles to more than 10 miles at the equator, it is the layer in which great air masses form and most of our weather goes on.

Its winds vary from sea breezes at the lowest levels to jet streams of 80 mph or more at heights of six or seven miles. Within the troposphere, the temperature declines at a rate of about 10C per mile.

When this temperature drop ceases, we reach the tropopause, and above that the stratosphere.

The stratosphere extends to about 30 miles above the Earth.

It is a stable region of little wind and its temperature rises slowly with height from about -70C at the tropopause to near zero. The warming is linked to the formation of ozone from the action of the sun's ultraviolet radiation on oxygen atoms - for the lower stratosphere is where we find the ozone layer. There is very little water vapour in the stratosphere, so it tends to be free of clouds.

Continuing upwards, we reach the stratopause, then the mesosphere, which extends from about 30 to 50 miles above the earth, through which temperatures decrease from 0C to about -100C, which is as cold as the atmosphere gets. Above 50 miles, the atmosphere heats up again in the thermosphere.

In theory the temperature may rise to 2000C, but in practice the air is so rarefied that there is very little there to get hot at all.

But if you do happen to pick up an oxygen molecule warmed by solar radiation a hundred miles up, use heavy duty oven gloves.