What is global circulation? | Part Three | The Coriolis effect & winds

This video, part three of the global circulation series, will explore how the Earth's rotation influences atmospheric winds, leading to jet streams and prevailing wind patterns. The Earth's rotation causes an apparent motion to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, known as the Coriolis effect.

The Coriolis effect occurs because the Earth's surface rotates faster at the equator than at the poles. As air moves away from the equator, it appears to curve relative to the Earth's surface, even though there's no physical force causing this deflection. This is due to air flowing from a faster-moving region to a slower-moving region, causing it to appear to land to the right of its target in the Northern Hemisphere.

This deflection is crucial in understanding why winds blow anti-clockwise around low pressure and clockwise around high pressure in the Northern Hemisphere, and vice versa in the Southern Hemisphere. Air moving towards the North Pole is deflected eastwards, while air moving southwards towards the equator is deflected westwards.

As air moves away from the equator at the top of the Hadley cells, the Coriolis force deflects it. Due to the conservation of angular momentum, this air speeds up as it approaches the Earth's spin axis, forming the subtropical jet stream at 30-40 degrees north or south. The polar front jet, forming between the polar and Ferrel cells, results from the temperature contrast between cold polar air and warm tropical air, explaining why it's stronger in winter.

Surface winds are also affected by the Coriolis force. The Hadley cells' surface flow creates the persistent trade winds; air flowing towards the equator is deflected westwards, forming the Northeast and Southeast trade winds. In the Ferrel cells, the Coriolis effect deflects southerly winds in the Northern Hemisphere to the right, leading to the prevailing westerly and southwesterly winds experienced in areas like the UK.

Jupiter, with its rapid rotation (a day lasts about 9.5 hours), exhibits a very strong Coriolis effect. This leads to numerous circulation cells in each hemisphere, producing alternating bands of rising and falling air, which gives Jupiter its distinct striped appearance.