22.3Atmospheric Circulation

It all starts with unequal heating of Earth that cause differences in pressure – resulting in air movement

• Warm air is less dense, rises and creates LOW pressure

• Cold air is more dense, sinks towards Earth’s surface and creates HIGH pressure.

• Air flows from poles (H) to equator (L)

• Air near Earth’s surface flows from the poles to the equator because of the spin of the Earth.

• Earth’s diameter is greatest at the equator and smaller at the poles.

• The equator must travel faster to complete one rotation than the poles.

• The air moves more slowly than the ground beneath it does.

• This causes the air to flow from the poles toward the equator.

• High pressure regions form where cold air sinks towards Earth’s surface.

• Low pressure regions form where warm air rises away from Earth’s surface.

• Circulation of the atmosphere and of the oceans is affected by the rotation of Earth on its axis.

• Earth’s rotation causes its diameter to be greatest through the equator and smallest through the poles.

• Points bear the equator travel further in a day.

Coriolis Effect

• Moving objects follow a curved path due to Earth’s rotation.

• Deflected right in northern hemisphere (Clockwise)

• Deflected left in southern hemishphere (Counterclockwise)

• Detectable only on objects that move very fast or over long distances.

Global Winds – 3 looping patterns called wind belts

• Wind flows from poles to equator in convective cells.

• Each cell correlates to a wind belt that forms wind that flows one way. (prevailing wind)

• Wind is named for the direction it come from.

• Winds that blow from E to W from 30* latitude to the equator are the trade winds.

• In the N Hemisphere, trade winds flow from the northeast.

• Prevailing winds that blow W to E are the westerlies.

• Winds from 60-90* E-W are the easterlies.• Stormy regions where easterlies meet

westerlies are fronts.

• Doldrums – form at equator where the warm air moves upward and there is little wind.

• Horse Latitudes –form at 30 degrees N and S where the air decends and there is little wind

Jet Stream

Narrow band of strong wind that blows in the upper troposphere

• Air movement caused by local conditions & temperature are local winds.

• Breeze – gentle winds that extend over distances of less than 100km

Local Wind – not part of global wind belts

Land Breeze – cool wind moving from land to water at night

Sea Breeze – cool wind moving from water to land in afternoon H

H

L

L

Warm Land

Cool Water

Cool LandWarm Water

Valley Breeze – warm air from the valley moves upslope during day

• Mountain Breeze

Mountain Breeze – cool air descends from mountain peak at night