Image of air masses across the UK

Coriolis effect

What is the Coriolis effect?

The Earth's rotation means that we experience an apparent force known as the Coriolis force. This deflects the direction of the wind to the right in the northern hemisphere and to the left in the southern hemisphere. This is why the wind-flow around low and high-pressure systems circulates in opposing directions in each hemisphere.

The Coriolis effect was described by the 19th-century French physicist and mathematician Gustave-Gaspard de Coriolis in 1835. He formulated theories of fluid dynamics through studying waterwheels, and realized the same theories could be applied to the motion of fluids on the surface of the Earth.

The Coriolis effect in action

One of the most common examples of the Coriolis effect in action is seen through the deflection of winds on Earth.

Another example of the Coriolis effect can be demonstrated by looking at a typical playground roundabout. If you are standing in the centre of a spinning roundabout (spinning anticlockwise) and attempt to throw a ball, it will appear to curve to the right, when in fact it is travelling in a straight line to anyone watching who is not on the roundabout. This is similar to what happens in the northern hemisphere of the Earth, where winds are deflected to the right.

This deflection is 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. Without the Coriolis effect air would simply flow directly from areas of high pressure to areas of low pressure.

The Coriolis effect influences the global wind patterns and gives the UK is prevailing south-westerlies. Here, winds blowing from the subtropical highs towards the low pressure in the north get deflected to the right.