Weather Wise

Wind consists of air flowing from an area of high pressure into one of low pressure. But there is more to it than just counting the isobars.

Have you been watching all those isobars hovering menacingly near the coast of Scotland this week? As Ian McCaskill and his colleagues have been trying to hard to teach us, closely packed isobars mean wind; but that's not all there is to it. Here's what the weathermen will try to get us to understand when they are convinced we have a firm grip on the isobars.

If we simply had an area of high pressure next to an area of low pressure, the air from the former would flow into the latter. The direction of flow would be directly from one to the other, perpendicular to the isobars. What makes it more complicated is the rotation of the earth, which is generally moving much faster than the winds themselves.

The Coriolis force deflects winds to the right - winds blowing towards the equator seem to curve west, those blowing away from the equator seem to curve east. This results in wind blowing more or less along the lines of the isobars rather than perpendicular to them. And if you what to know which way it is blowing you just have to apply "Buys Ballot's Law" which states that if you stand with your back to the wind in the northern hemisphere, low pressure lies to your left and high pressure to your right. But it's the other way round in Australia.

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