Atmosphere

UNIT 2

What is an atmosphere?• An atmosphere is a layer of gases

which may surround a material body (planets etc.) of sufficient mass.

• The gases are attracted by the gravity of the body.

• If the gravity is high enough, and the temperature is low enough the gases can be retained for a longer duration.

So…Earth's atmosphere is the layer of gases surrounding our

planet…duh!• These gases are held in place by Earth‘s gravity. • The atmosphere has no abrupt cut-off or

boundary. It slowly becomes thinner and fades into outer-space.

• Three-quarters of the atmosphere's mass is within 11 km of the surface of the planet.

• The atmosphere protects life on Earth by absorbing ultraviolet solar radiation and reducing temperature extremes between night and day.

Composition of the AIR or Atmosphere (obj. 1)

That’s Right… Atmosphere is what we call Air.• Air, or our atmosphere, is a mixture of different gases and

particles, each with its own properties. The composition of air varies from time to time and place to place.

• Two gases, nitrogen and oxygen, make up 99% of the volume of clean dry air. The composition are: Nitrogen 78%, Oxygen 21%– trace amounts of other gases such as water vapor, argon,

carbon dioxide, hydrogen, neon, helium, and other gases.• Nitrogen and Oxygen are the most plentiful components of air,

but they have little impact on the weather. • Carbon dioxide is present in small amounts, but it is an important

component of air. Carbon dioxide is an active absorber of energy given off by the Earth. Therefore, it plays a significant role in heating the atmosphere.

layers of the Atmosphere (obj. 2)

• The atmosphere can be divided into four layers based on temperature: the troposphere, stratosphere, mesosphere, and thermosphere.

• TROPOSPHERE is the bottom layer– where temperature decreases with an increase in altitude. – Where all essentially important weather phenomena occur.– thickness is not the same everywhere, and varies with latitude and the season.

• STRATOSPHERE is the 2nd layer– the temperature remains constant to a height of 20 kilometers. – It then begins an increase in temperature that continues up to 50 kilometers– atmosphere ozone absorbs ultraviolet radiation from the sun. As a result, the

stratosphere is heated.

• MESOPHERE the third layer– temperatures again decrease with height until mesopause. – The mesopause is more than 80 km above and temp. approach -90 degree Celsius.

• THERMOSPHERE the fourth layer– extends outward from the mesopause, and has no well-defined upper limit.– this layer contains a tiny fraction of the atmosphere’s mass. – Temp. increases because oxygen and nitrogen absorb short-wave, high energy solar

radiation.

Three Mechanisms of Energy Transfer throughout the

Atmosphere (obj. 3)

• The three mechanisms of heat energy transfer are:– conduction– convection– radiation

CONDUCTION• CONDUCTION is the transfer of heat through matter

by molecular activity.

• The energy of molecules is transferred by collisions from one molecule to another. Heat flows from higher temperature to the lower temperature matter.

• The ability of substances to conduct heat varies greatly. Metals are good conductors.

• Because air is a poor conductor of heat, conduction is important only between Earth’s surface and the air directly in contact with the surface.

• Conduction is the least important mechanism of heat transfer in the atmosphere.

CONVECTION• Much of the heat transfer that occurs in the

atmosphere is carried on by CONVECTION. • Convection is the transfer of heat by the actual

movement of the warmed matter. It takes place in fluids, like the ocean and air, where the atoms and the molecules are free to move about.

• Convection also takes place in solids, such as the Earth’s mantle, that behave like a fluid over periods of time. Warm, less dense air rises and is replaced with sinking cooler more dense air. As long as air and/or water are heated unequally, it will continue to circulate. In much the same way, most of the heat acquired by radiation and conduction in the lowest layer of the atmosphere is transferred by convective flow.

Radiant Energy• Radiant energy is the energy of

electromagnetic waves. .

• Shorter visible wavelengths correspond to colors closer to the blue.

• Red light has the longest wavelength and smallest frequency of any visible light.

• The shorter the wavelength of light, the higher its energy.

Radiation• Radiant energy is electromagnetic waves that

directly transport ENERGY through space.

• Conduction and convection need material to travel through…RADIANT energy can travel through the vacuum of space.

• Sunlight or solar radiation is a form of energy

that is radiated through space to our planet without the aid of fluids or solids.

There are 4 principal layers in the Atmosphere

• The first layer is the troposphere that is where the weather is made,

• then comes stratosphere which is where planes fly. The ozone layer is inside the stratosphere,

• next is the mesosphere that is where rocks burn so that they do not hit the earth,

• the last layer is the thermosphere which is really thin, space ships fly in this layer,

• Thermosphere is divided into two layer: ionosphere and mesosphere.

• The atmosphere gradually thins out into space. The atmosphere is the thickest near the earth.

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