Unit 4Unit 4WeatherWeather

Lesson 1Lesson 1How Does Uneven Heating How Does Uneven Heating of Earth Affect Weather?of Earth Affect Weather?

The AtmosphereThe Atmosphere-The atmosphere is a The atmosphere is a thin blanket of air that thin blanket of air that surrounds Earth. surrounds Earth. -It is very thin compared It is very thin compared to the size of Earth.to the size of Earth.-The atmosphere is The atmosphere is made up of many layers: made up of many layers: troposphere, troposphere, stratosphere, and ozone.stratosphere, and ozone.

TroposphereTroposphere The troposphere is the The troposphere is the

layer that is closest to layer that is closest to Earth’s surface. Earth’s surface.

It contains 90% of the It contains 90% of the atmosphere’s gases.atmosphere’s gases.

Most of the Earth’s Most of the Earth’s weather happens in weather happens in the troposphere.the troposphere.

How Do You Know Air is There?How Do You Know Air is There? You know the air is there You know the air is there

because you can feel it because you can feel it every time the wind blows. every time the wind blows.

You can feel air blow You can feel air blow against you because it has against you because it has mass.mass.

Everything on Earth that Everything on Earth that has mass is pulled toward has mass is pulled toward Earth’s center by gravity.Earth’s center by gravity.

This pull causes air to This pull causes air to have weight.have weight.

Air PressureAir Pressure Air particles closer to Air particles closer to

Earth’s surface have Earth’s surface have more weight than the more weight than the air higher in the air higher in the atmosphere.atmosphere.

This means that air This means that air pressure, or the weight pressure, or the weight of air in the of air in the atmosphere in one unit atmosphere in one unit area, is greatest at sea area, is greatest at sea level. level.

Air Pressure (cont.)Air Pressure (cont.) The higher you go into the The higher you go into the

atmosphere, the less air there is atmosphere, the less air there is above you.above you.

Air pushes downward as well as Air pushes downward as well as in all directions. This is because in all directions. This is because gas molecules are constantly gas molecules are constantly moving in all directions.moving in all directions.

Temperature also affects air Temperature also affects air pressure. Cold air is denser pressure. Cold air is denser than warm air. Because of this, than warm air. Because of this, it sinks toward Earth’s surface. it sinks toward Earth’s surface. This forces warmer, less dense This forces warmer, less dense air to rise. As warm air rises, it air to rise. As warm air rises, it cools. The cooler air is now cools. The cooler air is now denser, so it sinks back to the denser, so it sinks back to the surface.surface.

Air DensityAir Density

Another factor that causes air pressure Another factor that causes air pressure to be greater at sea level is air density.to be greater at sea level is air density.

Gravity pulls most of the air in the Gravity pulls most of the air in the atmosphere down to the surface.atmosphere down to the surface.

Because of this, the air closer to Because of this, the air closer to Earth’s surface is much denser than Earth’s surface is much denser than the air father away from the surface.the air father away from the surface.

Convection CurrentsConvection Currents

Air that is warm is less Air that is warm is less dense, so it is pushed dense, so it is pushed upward by the cooler, upward by the cooler, denser air.denser air.

This upward and This upward and downward movement downward movement of air is called of air is called convection currents in convection currents in the atmospherethe atmosphere

Sea & Land BreezesSea & Land Breezes During the day, the land During the day, the land

heats up faster than the heats up faster than the sea. Cooler sea air moves sea. Cooler sea air moves toward the land. This is toward the land. This is called a sea breeze.called a sea breeze.

At night, the land loses At night, the land loses heat faster than the sea heat faster than the sea does. Cooler air over the does. Cooler air over the land moves toward the land moves toward the sea. This is called a land sea. This is called a land breeze.breeze.

Local WindLocal Wind Winds can be local, affecting small areas, or Winds can be local, affecting small areas, or

global, affecting larger parts of the Earth.global, affecting larger parts of the Earth. Sometimes, places in the same general Sometimes, places in the same general

area have slightly different temperatures. area have slightly different temperatures. This produces local wind, or wind that This produces local wind, or wind that results from a local difference in results from a local difference in temperature. temperature.

Local winds often occur along lakeshores or Local winds often occur along lakeshores or seashores.seashores.

Global WindsGlobal Winds A prevailing wind is a global wind that almost always blows from the A prevailing wind is a global wind that almost always blows from the

same direction. same direction. Prevailing winds result from uneven heating of large parts of Earth’s Prevailing winds result from uneven heating of large parts of Earth’s

surface.surface. An area’s latitude (distance from the equator), Earth’s rotation, and An area’s latitude (distance from the equator), Earth’s rotation, and

uneven heating of Earth’s surface all affect prevailing winds. uneven heating of Earth’s surface all affect prevailing winds.

Trade Winds & Trade Winds & Prevailing WesterliesPrevailing Westerlies

Winds moving north curve Winds moving north curve to the east. Winds moving to the east. Winds moving south curve to the west.south curve to the west.

Around the equator, this Around the equator, this curving causes the curving causes the prevailing winds – called prevailing winds – called trade windstrade winds – to blow from – to blow from the east.the east.

In the United States, this In the United States, this curving causes the curving causes the prevailing winds – the prevailing winds – the prevailing westerliesprevailing westerlies – to – to blow from the west.blow from the west.

Bill Nye VideosBill Nye VideosAtmosphere Part 1Atmosphere Part 1http://www.gamequarhttp://www.gamequarium.org/cgi-bin/search/linfo.cgi?id=8436ium.org/cgi-bin/search/linfo.cgi?id=8436

Atmosphere Part 2Atmosphere Part 2http://www.gamequarium.org/cgi-bin/search/linfo.cgi?http://www.gamequarium.org/cgi-bin/search/linfo.cgi?

id=8437id=8437

Atmosphere Part 3Atmosphere Part 3http://www.gamequarium.org/cgi-bin/search/linfo.cgi?http://www.gamequarium.org/cgi-bin/search/linfo.cgi?

id=8438id=8438