Atmosphere Test Review

Atmosphere Composition

• Composition of Earth’s Atmosphere:– 78% Nitrogen– 21% Oxygen– 1% Other

Air Pressure and Altitude

• Gas molecules in the atmosphere are pulled to the Earth’s surface by gravity, making the troposphere the most dense layer of the atmosphere.

• For each layer of the atmosphere:– As altitude increases, density decreases– As altitude increases, air pressure decreases

Layers of the Atmosphere

• Troposphere– Lowest layer of the

atmosphere– Most dense layer of

atmosphere– Where weather

happens– Temperature

decreases as altitude increases

Layers of the Atmosphere

• Stratosphere: – Layer above the

troposphere– Temperature increases as

altitude increases. This occurs because the ozone layer, found at the top of the stratosphere, absorbs ultraviolet radiation from the sun, which warms the air.

Layers of the Atmosphere

• Mesosphere:– The layer between the

stratosphere and the thermosphere.

– Temperature decreases as altitude increases.

– The Mesosphere is the coldest layer of the atmosphere.

Layers of the Atmosphere

• Thermosphere:– The uppermost layer

of the atmosphere.– Temperature

increases as altitude increases. Atoms of nitrogen and oxygen absorb high-energy solar radiation and release thermal energy.

Radiation

• Radiation is the transfer of thermal energy (heat) by electromagnetic waves. – The sun heats the

Earth by radiation (visible and ultraviolet light)

Conduction

• Conduction occurs when thermal energy (heat) is transferred through a material. – Conduction occurs

when the surface of the Earth transfers heat to the atmosphere directly above it.

Convection

• Convection is the transfer of energy by the circulation of gases or liquids. – Convection occurs in

the atmosphere when warm, less dense air rises and cool, more dense air sinks.

Sun’s Heat

• 25% of the Sun’s radiation that reaches Earth is reflected back into space by the atmosphere

• 5% of the Sun’s radiation that reaches Earth is reflected by the Earth’s surface

• 20% of the Sun’s radiation that reaches Earth is absorbed by the Earth’s atmosphere

• 50% of the Sun’s radiation that reaches Earth is absorbed by the Earth’s surface

Greenhouse Effect

• The greenhouse effect occurs when gases in the Earth’s atmosphere absorb heat energy and radiate it back to Earth.– Examples of greenhouse gases are: carbon

dioxide and water vapor– Humans emit carbon dioxide into the air by

burning fossil fuels. This occurs in factories, transportation, the production of electricity, and when heating homes and businesses.

Global Warming

• When the Earth’s atmosphere is polluted with too many greenhouse gases such as carbon dioxide, the atmosphere begins to absorb more heat than is natural and radiate it to Earth. This can lead to a rise in average global temperatures.

Air Pressure

• Temperature has an effect on air pressure– When air molecules are heated they speed up and

spread out, making the air less dense. There are fewer air molecules pushing on a surface, creating a lower pressure.

– When air molecules are cooled, they slow down and move closer together, making the air more dense. There are more air molecules pushing on a surface, creating a larger pressure.

• Warm air=less dense=lower pressure• Cool air=more dense=higher pressure

Wind

• Wind occurs when there is a difference in air pressure.

• Air molecules will move from a high pressure area to a low pressure area.

Convection Cells

• Warm air rises at the equator and travels toward the poles. At about 30o N and S latitude, the air has cooled and become dense enough to sink to Earth’s surface. The air then travels back toward the equator, warming as it moves. This creates a circular pattern of air called a convection cell.

• Convection cells form about every 30o in latitude.

Pressure Belts

• Pressure belts are bands of high and low pressure that occur at every 30o of latutide, where convection cells meet.

Coriolis Effect

• Global winds travel on a curved path because of the rotation of the Earth. This is called the Coriolis Effect.– Winds traveling northward curve to the east– Winds traveling southward curve to the west

Winds

Global Winds

• Trade winds: Winds that occur on either side of the equator to 30o N and S latitude.

• Westerlies: Winds that occur from 30o to 60o N and S latitude. Westerlies travel from west to east.

• Polar Easterlies. Winds that occur from 60o N and S latitude to the poles. Winds travel from east to west.

Local Winds

• Local winds only occur near specific geographic features. – Example: Sea and Land Breezes: During

daytime, the surface of the Earth heats more quickly than water. Warm (less dense) air over the surface of the Earth rises, and cooler (more dense) air comes from the lake/ocean to the land to replace it. During nighttime, the surface of the Earth cools faster than the water. Warm air over the water rises, and cooler air from the land comes in to replace it.