Layers of the Atmosphere


Layers of the Atmosphere
The 5 layers of the atmosphere are the troposphere, stratosphere, mesosphere, thermosphere, and exosphere.

There are five layers of the atmosphere and several secondary layers. The dividing points between these layers are altitude and temperature. Here is the list of the layers of the atmosphere, their altitudes, temperatures, and other properties.

  • The atmosphere is the layer of gases that surround Earth.
  • The five layers of the atmosphere, in order from the ground up, are the troposphere, stratosphere, mesosphere, thermosphere, and exosphere.
  • The atmosphere extends to roughly 100 km or 62 miles. This is the Kármán line, which marks the beginning of space. Note part of the thermosphere and all of the exosphere are beyond this mark.

The 5 Layers of the Atmosphere

The five main layers are the troposphere, stratosphere, mesosphere, thermosphere, and exosphere. Mainly, temperature determines the altitude of these layers. The atmosphere is fluid and changes according to season, day/night cycle, and other factors, so the lower and upper limits of each layer shift.

Troposphere

The troposphere is the layer of the atmosphere that contacts the Earth’s surface. Its average height is 12 km (7.5 mi; 39,000 ft), but it is thickest at the equator and also varies according to weather.

The troposphere contains most of the air and water vapor in the atmosphere. Hence, most clouds and weather occur here. Mostly, temperature decreases with increasing altitude. This is because heat comes from the surface.

The tropopause is the layer separating the troposphere from the stratosphere.

Stratosphere

The stratosphere is the layer bounded by the tropopause at its base (12 km; 7.5 mi; 39,000 ft)) up to the stratopause (55 km; 31 to 34 mi; 164,000 to 180,000 ft). Air pressure within the stratosphere is only about 1/1000 of the pressure at sea level.

Temperature rises with increasing altitude, mainly from the absorption of ultraviolet radiation by the ozone layer. The stratosphere contains few clouds. Most commercial aircraft stay within the troposphere, but some fly in the lower stratosphere.

Mesosphere

The mesosphere is the atmospheric layer between the stratosphere and thermosphere. It is bounded by the stratopause (55 km; 31 to 34 mi; 164,000 to 180,000 ft) and mesopause (80–85 km; 50–53 mi; 260,000–280,000 ft).

The mesosphere is the coldest part of the atmosphere, with an average temperature of −85 °C (−120 °F; 190 K). Noctilucent clouds form in this layer. The informally-defined beginning of space begins in the mesosphere because there is just enough air to cause friction for objects approaching Earth from space. Meteors become visible as they enter the mesosphere.

Thermosphere

The thermosphere is the region of the atmosphere between the mesopause (80–85 km; 50–53 mi; 260,000–280,000 ft) and thermopause or exobase (500–1000 km; 310–620 mi; 1,600,000–3,300,000 ft). Its height depends on solar activity. The ionosphere roughly coincides with the lower part of the thermosphere.

The layer gets its name because of its high temperature (~1500 °C or 2700 °F), which increases with altitude. Gas atoms and molecules are far apart from one another. The aurora mainly occurs in the thermosphere. Many satellites and the International Space Station (ISS) are in this layer.

Also, note that “space” begins within the thermosphere at an altitude of 100 km or 62 mi. While part of Earth’s atmosphere actually extends beyond this point, it is where objects start experiencing friction from air.

Exosphere

The exosphere is the outer layer of the Earth’s atmosphere. It extends from the thermopause or exobase (500–1000 km; 310–620 mi; 1,600,000–3,300,000 ft) to around 100,000 km (6,200 mi; 33,000,000 ft). At this point, the atmosphere merges into the solar wind. Atoms and molecules are hundreds of kilometers apart and can escape into space.

The aurora sometimes extends into the lower exosphere. Many artificial satellites orbit within this layer, too.

Where Does Space Begin?

Where Does Space Start?

Space actually starts within the atmosphere, where objects start to experience friction from air.

Atmospheric Layers Table

This table sums up the key features of the layers of the atmosphere:

LayerAltitudeTemperatureContains?Features
Troposphere0-12 km
0 to 7 miles
−56 °C to 15 °C
(−69 °F to 59 °F)
most clouds
most water vapor
weather
balloons, aircraft
80% of the total atmosphere
Stratosphere12-50 km
7-31 miles
−56 °C to -2.5 °C
(−69 °F to 37 °F)
ozone layer
few clouds
highest altitude jets fly
pressure 1/1000 that of sea level
Mesosphere50-80 km
31-50 miles
average: −85 °C (−120 °F)noctilucent clouds
transient luminous events (TLEs)
meteors burn up
thin atmosphere
water vapor turns into ice crystals
Thermosphere80-700 km
50-440 miles
up to 1500 °C (2700 °F)aurora
International Space Station (ISS)
satellites
low density gases, including singlet oxygen
Exosphere700-10,000 km
440-6,200 miles
~1200 °C
(2200 °F)
satellites
aurora (lower portion)
low density atoms and molecules
hydrogen, helium, nitrogen, oxygen, carbon dioxide

Other Atmospheric Layers

Temperature determines the five main layers, but the atmosphere contains other layers, too.

  • Ozone Layer: The ozone layer is within the lower stratosphere. In this region, ozone concentration ranges from 2 to 8 parts per million. The layer’s altitude is from 15–35 km (9.3–21.7 mi), although its thickness varies geographically and seasonally. It is thinnest near the poles.
  • Ionosphere: The ionosphere ranges in altitude from 50 to 1,000 km (31 to 621 mi). It includes the mesosphere, thermosphere, and part of the exosphere. This is the region where solar radiation ionizes atmospheric gases. The aurora borealis and aurora australis form in the ionosphere.
  • Homosphere and Heterosphere: Another way of defining the atmosphere is according to whether the gases are well-mixed and homogeneous (homosphere) or layered (heterosphere). The homosphere includes the troposphere, stratosphere, mesosphere, and lower thermosphere. Most of the thermosphere together with all of the exosphere make up the heterosphere. Here, gases layer by molecular weight. Oxygen and nitrogen are near the bottom of the layer, with hydrogen and helium at the top.

References

  • Barry, R.G.; Chorley, R.J. (1971). Atmosphere, Weather and Climate. London: Menthuen & Co Ltd. ISBN 9780416079401.
  • Lutgens, Frederick K.; Edward J. Tarbuck (1995). The Atmosphere (6th ed.). Prentice Hall. ISBN 0-13-350612-6.
  • States, Robert J.; Gardner, Chester S. (2000). “Thermal Structure of the Mesopause Region (80–105 km) at 40°N Latitude. Part I: Seasonal Variations”. Journal of the Atmospheric Sciences. 57 (1): 66–77. doi:10.1175/1520-0469(2000)057<0066:TSOTMR>2.0.CO;2