Asked by: Roger Evans, Argyll
As the Earth spins, the speed of rotation experienced at the equator is much faster than at the North Pole. This difference causes the ‘Coriolis effect’ – a force which appears to deflect winds towards the right in the northern hemisphere.
In a low pressure weather system, air flows inward, but this deflection twists the air flow towards the right, creating an anticlockwise swirl of winds. In a high pressure system, air flows outward, and the deflection results in a clockwise rotation. The Coriolis effect deflects winds towards the left in the southern hemisphere, so weather systems here spin in the opposite direction.