Air MovementAir MovementSection 3Section 3

Forming WindForming Wind

Wind is the movement of air from Wind is the movement of air from an area of high pressure to an area an area of high pressure to an area of lower pressure.of lower pressure.

Local Wind SystemsLocal Wind Systems

Local wind systems Local wind systems – affect local – affect local weatherweather

Sea breezes – a Sea breezes – a convection current convection current blows wind from blows wind from the cooler sea the cooler sea toward warmer toward warmer land during the land during the dayday

Local Wind SystemsLocal Wind Systems

Land breezes – at night, air moves off Land breezes – at night, air moves off the land toward the water as the land the land toward the water as the land cools more rapidly than the watercools more rapidly than the water

Forming WindForming Wind

Different areas of Earth receive Different areas of Earth receive different amounts of the Sun’s different amounts of the Sun’s radiation.radiation.

Forming Wind - 1Forming Wind - 1

The equator receives the Sun’s rays The equator receives the Sun’s rays more directly than do the north and more directly than do the north and south poles.south poles.

Forming Wind - 2Forming Wind - 2

As a result, the air near the equator As a result, the air near the equator is less dense than the colder air is less dense than the colder air masses near the poles.masses near the poles.

Forming Wind - 3Forming Wind - 3

Dense air moves from the poles Dense air moves from the poles toward the less dense air near the toward the less dense air near the equator to cause wind.equator to cause wind.

Forming Wind - 4Forming Wind - 4

The rotation The rotation of Earth of Earth causes the causes the moving air to moving air to turn.turn.

Forming Wind - 5Forming Wind - 5

Thus, the Coriolis effect causes Thus, the Coriolis effect causes surface wind to blow in bands: the surface wind to blow in bands: the polar easterlies, westerlies, and polar easterlies, westerlies, and trade winds.trade winds.

Near the equator, very little wind Near the equator, very little wind and daily rain patterns the and daily rain patterns the doldrums doldrums

Global WindsGlobal Winds

Surface WindsSurface Winds Between the equator and 30 latitude (north Between the equator and 30 latitude (north

and south) are steady trade winds, blowing and south) are steady trade winds, blowing to the westto the west

Between 30 and 60 latitude (north and Between 30 and 60 latitude (north and south) the prevailing westerlies blow to the south) the prevailing westerlies blow to the east, in the opposite direction of trade east, in the opposite direction of trade winds.winds.

Polar easterlies blow from northeast to Polar easterlies blow from northeast to southwest near the north pole and from southwest near the north pole and from southeast to northwest near the south pole.southeast to northwest near the south pole.

Global Wind Affecting Global Wind Affecting TradeTrade

The Coriolis Effect on Trade