Chapter 2

Weather Factors

Section 3

Winds

What causes wind?

Wind: The horizontal movement of air from an area of high pressure to an area of lower pressure.

What causes winds?

All winds are caused by differences in air pressure

HIGH LOW

What causes these differences in pressure?

• Unequal heating of the atmosphere• Remember convection currents?• As air becomes less dense, its air

pressure decreases.

Measuring Wind

• Winds are described by their direction and speed

Measuring Wind

To measure wind direction: we use a wind vane

Measuring Wind

To measure wind speed: we use an anemometer

Wind- Chill Factor

Wind Chill Factor: Increased cooling caused by the wind

Local Winds

• Local winds: winds that blow over short distances

Local Winds

• Local winds are caused by unequal heating of Earth’s surface within a small area

Local Winds

• Example: cool breezes blowing in from the water to the beach.

Sea Breeze

• Sea Breeze: The flow of air from an ocean or lake to the land.

• Daytime!

Land Breeze

• Land Breeze: The flow of air from land to a body of water.

• Night time!

Sea and Land Breezes

Monsoons

•Monsoons: Sea and land breezes over a large region that change directions with seasons

Global Winds• Global Winds: Winds that

blow steadily from specific directions over long distances

Temperatures• Temperatures near the equator are

much warmer than the temperatures near the poles.

• Temperature differences between the equator and the poles produce giant convection currents in the atmosphere.

Global Convection Currents

This movement of air between the equator and the poles produces global winds.

Global Convection Currents

• Coriolis Effect: The way Earth’s

rotation makes winds curve.

The Coriolis Effect

In the Northern

HemisphereIn the Southern

Hemisphere

Global winds turn toward

the RIGHT

Global winds turn toward

the LEFT

The 3 major wind belts are the:

1. trade winds 2.prevailing westerlies3. the polar easterlies.

Global Wind Belts

The 2 calm areas are the:

1. Doldrums2. Horse Latitudes

Global Wind Belts

• A calm area where warm air rises

• Regions near the equator with little or no

wind

Doldrums

• A calm area of falling air

• Latitudes 30° north and south of the equator

Horse Latitudes

• Steady easterly winds which blow from the horse latitudes

toward the equator.

Trade Winds

•Winds in the mid latitudes which blow from the west to the east.

• Play an important part in the weather of the United States

Prevailing Westerlies

•Cold air near the poles which sinks and flows back toward lower latitudes.

Polar Easterlies

• Jet Streams: Bands of high-speed winds about 10

kilometers above Earth’s surface

Jet Streams