The rays of the The rays of the sun strike the sun strike the

Earth directly at Earth directly at the equator. At the equator. At

the poles the the poles the curvature of the curvature of the

Earth spreads the Earth spreads the rays out.rays out.

Why is the equator Why is the equator warmer than the warmer than the

poles?poles?

The solar radiation heats the surface of the earth.

Heat is transferred to air molecules that come in contact with the ground.

If all the air is rising, Why doesn’t this person suffocate?

The solar radiation heats the surface of the earth.

Heat is transferred to air molecules that come in contact with the ground.

As the

Warmer Air Rises…

Cooler air is pulled in from other places What is this called?

Convection current – the transfer of heat

through movement in the atmosphere.

The WindThe Wind Winds are the result of uneven heating of Winds are the result of uneven heating of

the Earth’s surfacethe Earth’s surface– This uneven heating This uneven heating

causes differences causes differences in air pressure in air pressure to developto develop

– Molecules always Molecules always move from areas of move from areas of high pressure to high pressure to areas of low areas of low pressurepressure

GLOBAL PRESSURE & WIND

Antarctic circle 66.5°S

Arctic circle 66.5°N

North Pole 90°N

North Pole 90°N

Equator 0°

Tropic of Cancer 23.5°N

Tropic of Capricorn 23.5°N

ZONE of greatest heating produces LOW PRESSURE

ZONE of least heating produces HIGH PRESSURE

ZONE of least heating produces HIGH PRESSURE

HIGH

HIGH

LOW

How would you expect air to move across the planet?How would you expect air to move across the planet?

GLOBAL PRESSURE & WIND

EQUATORIAL LOW

POLAR HIGH

Global circulation depends on differential heating over the globe.

The system is driven by strong equatorial heating, causing LOW PRESSURE.

GLOBAL PRESSURE & WIND

EQUATORIAL LOW

TROPICAL HIGH

POLAR HIGH

Equatorial air descends over the tropics, where HIGH PRESSURE dominates; where it diverges at ground level. This tropical air blows towards the equator, completing the equatorial cell.

GLOBAL PRESSURE & WIND

EQUATORIAL LOW

TROPICAL HIGH

POLAR HIGH

Some of the sinking air at the Tropical High moves towards the mid-latitides where it meets cold, dense polar air blown out from the polar HIGH PRESSURE.

GLOBAL PRESSURE & WIND

EQUATORIAL LOW

POLAR FRONT (LOW PRESSURE)

TROPICAL HIGH

POLAR HIGH

These contrasting tropical and polar air masses meet at the POLAR FRONT LOW PRESSURE BELT, where the warmer air is forced upwards by the polar air.

Actual wind which blows, as diverted by Coriolis Force

Theoretical wind which would result

solely from pressure gradient

CORIOLIS FORCEHigh

Low

� Pressure gradient wind blows from high pressure towards low pressure.� The earth’s rotation diverts this wind direction sideways. This force is called the CORIOLIS FORCE.� The Coriolis force diverts wind the the right in the northern hemisphere; to the left in the south.

Merry Go Round Demonstration

Coriolis Explained

Trade Winds – pattern of air movement in the tropics

Goes to the equator

WesterliesWesterlies – pattern of air movement in the mid-latitudes

Goes to the poles

EasterliesEasterlies – pattern of air movement at the poles

Goes to the mid-latitudes

Why do the gas giants appear to have a striped surface?

Jet Stream – is a band of fast moving air in

the stratosphere.

Formed where Westerly winds meet

the Easterly winds

Jet Stream Video

Summarizing ConvectionSummarizing Convection What is convection?What is convection? Where does convection occur?Where does convection occur? In what states of matter does In what states of matter does

convection occur?convection occur? What other liquid could convection What other liquid could convection

occur in on Earth?occur in on Earth?

Ocean CurrentsOcean Currents Atmospheric Atmospheric

CurrentsCurrents– Depend on Depend on

temperaturetemperature Ocean Surface Ocean Surface

CurrentsCurrents– Depend on windDepend on wind

Ocean CurrentsOcean Currents

Ocean CurrentsOcean Currents

Ocean CurrentsOcean Currents

Wind-drive ocean surface currentsWind driven surface currents

• How fast? A few miles/hr (Gulf Stream off of Miami = 4.5 mph)

• How much? Total water in ocean surface circulation = about 100 Amazon Rivers (20 million m3/s).

Ocean Currents Ocean Currents IllustratedIllustrated

Green Peace Today Show Investigates