Winds

Chapter 2, Section 3p. 52-60

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!

Land Breeze/ Sea Breeze

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

TemperaturesTemperatures near the

equator are much warmer than the temperatures near the poles.

IntermissionChapter 2, Section 3

p. 57-60

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.

Give students this analogy: Assume a plane takes off from some northern location in the U.S. (pick one from your area) and flies several hours due south (pick another location). When the plane arrives, the destination city has moved east due to the Earth’s rotation. To really reach the destination due south, the plane actually has to fly a curved path to where the city will be when the plane lands. This is what happens with the air “turning to the right.”

The Coriolis Effect

In the Northern Hemisphere

In 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

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

Global Wind Belts

Jet Streams: Bands of high-speed winds about

10 kilometers above Earth’s surface

Jet Streams