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

the last video showed that our

atmospheric circulation is split into

three cells in each hemisphere the

Hadley cell Farrell cell and polar cell


in this third video in the global

circulation series we will look at the

winds within these cells and how the

rotation of the earth influences these

winds to give us jet streams and

prevailing wind patterns as well as

being split into three cells the global

circulation pattern is at an angle due

to the Earth's rotation the spin of the

earth induces an apparent motion to the

right in the northern hemisphere and to

the left in the southern hemisphere

this is the Coriolis effect

the key to the Coriolis effect lies in

the fact that the Earth's surface

rotates faster at the equator than at

the poles this is because the earth is

wider at the equator so has further to

travel in one day the result of this

means that as air moves away from the

equator it doesn't move in a straight


relative to the Earth's surface instead

it appears to an observer on the ground

to move in a slightly curved direction

but there is no physical force causing

this deflection as the atmosphere

rotates with the earth it is just due to

the air flowing for a region that is

moving faster to a region that is moving

more slowly to explain this further

imagine an air parcel as a ball the ball

is thrown from the equator towards a

point near the North Pole even though it

moves in a straight line the ball will

appear to an observer on the ground to

curve away and land to the right of its

targets as the points near the North

Pole is moving more slowly and is not

caught up if the ball is now thrown from

the North Pole towards a point near the

equator it will again appear to a

surface observer to land to the rights

of its targets but this time is because

the Earth's surface at the equator is

moving faster and has moved ahead of the

ball this effect only happens on objects

that are in motion this deflection is a

major factor in explaining why winds

blow anti-clockwise around low pressure

and clockwise around high pressure in

the northern hemisphere and vice versa

in the southern hemisphere so when

flowing towards the North Pole air is

deflected towards the east and when

traveling southwards back towards the

equator it is deflected westwards

the same overall result occurs in the

southern hemisphere how does this lead

to eastwards flowing jet streams and

prevailing winds as air moves away from

the equator at the top of the Hadley

cells toward higher latitudes it starts

to be deflected by the Coriolis force

just as a skater spins faster by

bringing their arms and legs closer to

their bodies air moving away from the

equator speeds up as it gets closer to

the Earth's spin axis this process is

known as the conservation of angular

momentum the magnitude of the Coriolis

force increases towards the poles so by

the time the air reaches 30 to 40

degrees north or south it is moving in

an eastward direction this subtropical

jet stream occurs high in the atmosphere

between 12 to 15 kilometers it is

associated with some of the strongest

winds on earth reaching over 280 miles

per hour at times as this jet sits

between the descending branches of the

Hadley and Farrell cells there is little

Associated weather the polar front jet

forms in a different way

this jet sits between the rising

branches of the polar and Farrell cells

it marks the boundary between cold polar

air and warm tropical air known as the

polar front the polar front jet occurs

at a height of 11 to 13 kilometers and

is primarily the results of the

temperature contrast across the polar

front the stronger the temperature

contrast across the front

the stronger the Jets so it follows that

the polar front jet is stronger in the

winter than the summer

waves or ripples along the jet stream

can cause Atlantic depressions to deepen


as they are steered towards the UK winds

at the surface are also subject to

deflection from the Coriolis force the

surface flow of the Hadley cells form

the persistent trade winds as air flows

towards the equator it is deflected

towards the west in both hemispheres

forming the Northeast trade winds in the

Northern Hemisphere and the southeast

trade winds in the southern hemisphere

the persistence of these winds allowed

sailing ships to cross the Atlantic and

opened up trade routes between Europe

and America giving them their name the

surface wind and the feral cells would

flow from a southerly direction in the

northern hemisphere but the Coriolis

effect causes this wind to be deflected

to the right leading to the prevailing

westerly and southwesterly winds often

experienced over the UK this setup is

not unique to our planet

Jupiter also has circulation cells

similar to those on earth a day on

Jupiter lasts for about nine and a half

hours so it is rotating much more

quickly than the earth the great size

and fast rotation of this planet makes

the Coriolis effect very strong this

splits the Jovian atmosphere into many

circulation cells in each hemisphere

producing numerous alternating bands of

rising and falling air in giving Jupiter

a distinctly striped appearance