Coriolis Effect – Theory tips – RYA Day Skipper & Yachtmaster –

Weather is one of the more difficult areas of sailing theory to understand - and one of the reasons is due to the earth's rotation!n

What is the Coriolis Effect?

The earth rotates in an anti-clockwise direction on its axis. This rotation causes the winds to deflect to the right in the northern hemisphere and to the left in the southern hemisphere. This is what causes wind to rotate around low and high pressure systems in opposite directions if you are north or south of the equator!nn

This effect is named after Gustave-Gaspard de Coriolis who worked out why in 1835.nnn

How does the Coriolis Effect affect me?

If you stand in the centre of a spinning playground roundabout (spinning anticlockwise) and attempt to throw a ball it appears to curve to the right. Anyone who is not on the roundabout and watching will see the ball travelling in a straight line. Have a look at our video to see why.

What happens to the winds?

Winds in the northern hemisphere appear very much like a ball thrown on a children's roundabout - they are deflected to the right and are a major factor in explaining why winds blow anticlockwise around low pressure and clockwise around high pressure in the northern hemisphere and visa versa in the southern hemisphere. nnIf it wasn't for the Coriolis Effect the wind would flow directly from high pressure areas to low pressure areas.

The Coriolis Effect influences global wind patterns - and also gives the UK the prevailing south-westerlies, and the Canary Islands the north-easterlies.nn

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