Main Content Garage Photos About


What is the coriolis and why should I care about it?

The coriolis effect is why everything that is moving in the Northern hemisphere turns right and everything that is moving in the Southern hemisphere turns left-the reason why lows and highs, ocean currents and tides circulate the way they do

We all know that the Earth rotates from west to east and takes about 24 hrs to go around. If you stood on the equator you would be moving faster than if you were standing on the North and South pole and so in 24 hrs you would make more distance .So in effect a point on the equator travelling at about 1,600 km/h) travels more than a point on the 60 degrees Northpole travelling at about 800km/h.

To understand the coriolis effect, think of a cloud in Dublin.Before you do anything you must realise that its travelling west to east at a certain speed, say for example "Dublin speed". If you now suddenly push it southwards towards Spain the cloud will be travelling at Dublin speed but the ground beneath it is travelling at a faster speed. Therefore the clouds will lag behind relative to earth surface. Instead of travelling directly north to south it will veer to the right.

If on the other hand the cloud starts in Spain and you push it towards Dublin, the opposite will happen. The cloud having carried with it its Spanish west east velocity, will find itself travelling eastwards faster than the Earth beneath it, and so it will swerve to the right.If you force the cloud in an east west direction, say from Dublin travelling from west to east with the earth at Dublin speed .This time as it moves eastward towards say Moscow its rotational speed has increased slightly, This increase in speed means an increase in the centrifugal force, which tends to throw the cloud outwards, the easiest thing the cloud can do is to increase its radius of curvature is to move to a position where the earth is fatter and so the cloud ends up swerving south towards the equator.

Alternatively if you move the cloud westwards from Moscow to Dublin, you decrease its rotational force and so decrease its centrifugal force. As a result it wants to travel around a smaller radius of curvature nearer the North pole. It veers off towards the north.
In summary by a combination of two different mechanisms , air in the northern hemisphere will swerve right and in the southern hemisphere the opposite occurs with air moving to the left. 

How does all this help us understand weather patterns and why highs and lows move they way they do. The natural tendency for any of these clouds or air parcels is to move from high to low pressure i.e. down the pressure gradient. Imagine a centre of low pressure in the Northern hemisphere surrounded by air at a relatively higher pressure.Immediately there will be a stream of air parcels trying to rush into the low from outside i.e. trying to fill up the low and equalise the pressure. But the coriolis force deflects them to the right and they end up revolving around the low pressure in an anticlockwise direction. The same principle applies to a high pressure cell surrounded but lower pressure. The air will try to flow out and and equalise the pressure, however they will be deflected to the right and end up going around in a clockwise direction. In the southern hemisphere the opposite happens and so lows go clockwise and highs go anticlockwise.

It should now be obvious that the coriolis force is central now only to meteorology but oceanography as well and can be used to explain why ocean currents bring cold polar water to west facing coasts and why tides behave in such strange ways.

Copyright Celtic Sea 2010  Footerspacer  Footerwebmaster