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Daily Weather Information

Lower Layers of the Atmosphere• You study, eat, sleep,

and play in the troposphere, which is the lowest of Earth’s atmospheric layers.

1Earth’s Atmosphere

• Earth’s weather occurs in the troposphere.

Energy from the Sun

• The Sun provides most of Earth's energy.

• When Earth receives energy from the Sun, three different things can happen to that energy.

2Energy Transfer in the Atmosphere

Energy from the Sun• Some energy is

reflected back into space.

• Some is absorbed by the atmosphere.

• Some is absorbed by land and water on Earth's surface.

2Energy Transfer in the Atmosphere

Heat

• Heat is energy that flows from an object with a higher temperature to an object with a lower temperature.

• Energy from the Sun reaches Earth's surface and heats it.

2Energy Transfer in the Atmosphere

• Heat is eventually redistributed by air and water currents.

Heat is transferred through the atmosphere in three ways—radiation, conduction, and

convection.

Energy Transfer in the Atmosphere

2

Radiation• Radiation is energy that is transferred in

the form of rays or waves.

• Heat from the Sun reaches Earth in the form of radiation.

2Energy Transfer in the Atmosphere

• Heat is transferred from the Sun to the surface of Earth, which warms the surface of Earth.

Conduction• Conduction is the

transfer of energy that occurs when molecules bump into one another. This occurs when two objects are touching.

2Energy Transfer in the Atmosphere

• Heat from the surface of Earth is transferred to the air directly above the surface by conduction, causing the air directly above the surface to become warmer.

Convection• Convection is

the transfer of heat by the flow of material.

• Convection currents circulate heat throughout Earth’s atmosphere.

2Energy Transfer in the Atmosphere

Convection

• When air is warmed, the molecules in it move apart and the air becomes less dense.

• Air pressure decreases because fewer molecules are in the same space.

2Energy Transfer in the Atmosphere

• Warm air has low air pressure.

Convection

• The air becomes denser and air pressure increases.

• Cold air has high air pressure.

2Energy Transfer in the Atmosphere

• In cold air, the molecules move closer together.

Heat is transferred through the atmosphere in 3 ways: radiation, conduction, and convection.

Energy Transfer in the Atmosphere

2

Forming Wind3Air Movement

Because Earth is curved, areas of Earth receive different amounts of radiation from the Sun.

Forming Wind3Air Movement

• The air at the equator is warmer, less dense, and has lower pressure.

• The air at the poles is colder, denser, and has higher pressure.

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

• Differences in air pressure is what causes wind to blow.

Forming Wind3Air Movement

The Sun’s uneven heating of Earth’s surface forms giant convection currents of wind.

• The rotation of Earth causes moving air and water to turn to the right north ofthe equator and to the left south of the equator.

The Coriolis Effect

• This is called the Coriolis effect.

3Air Movement

Global Winds

• Global winds are wind patterns caused by the giant convection currents combined with the Coriolis Effect.

3Air Movement

Global Winds• Early sailors discovered that the wind

patterns on Earth helped them navigate the oceans.

3Air Movement

• Near the equator, sailors sometimes found little or no wind to move their ships, and it rained nearly every afternoon.

• The area near the equator where very little wind occurs and daily rain falls is called the doldrums.

Global Winds - Surface Winds

• Air moving along Earth’s surface between the equator and 30º latitude (north and south) creates steady trade winds that blow to the west.

3Air Movement

• These are called trade winds because early sailors used their dependability to establish trade routes.

Global Winds - Surface Winds

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

3Air Movement

• Prevailing westerlies are responsible for much of the movement of weather across North America.

Global Winds - Surface Winds

• Polar easterlies are found near the poles.

3Air Movement

• Near the north pole, easterlies blow from northeast to southwest.

• Near the south pole, polar easterlies blow from the southeast to the northwest.

Global Winds - Surface Winds

Air Movement

3

Air Movement

Global Winds - Surface Winds3

Global Winds - Jet Stream• Narrow belts

of strong winds, called jet streams, blow near the top of the troposphere.

3Air Movement

• The jet streams move storm systems across North America from west to east.

Local Winds

• Global wind systems determine the major weather patterns for the entire planet.

3Air Movement

• Smaller wind systems affect local weather.

• If you live near a large body of water, you’re familiar with two such wind systems—sea breezes and land breezes.

A sea breeze is a convection current that blows wind from the cooler sea (high pressure) toward the warmer land (low pressure) during the day.

Local Winds - Sea and Land Breezes3Air Movement

Local Winds - Sea and Land Breezes3Air Movement

At night, the reverse occurs. Air moves off the land toward the water as the land cools more quickly than the water. This is called a land breeze.