Earth's Atmosphere

The Earth is surrounded by a blanket of air, which we call the atmosphere. The atmosphere has no precise upper limit, but for all practical purposes the absolute top can be regarded as being at about 200 km. However, from a scientific point of view the atmosphere reaches up to 600-700 km. Thus we are only able to see - and feel - what occurs fairly close to the ground. The atmospheric air has over large parts a fairly stable composition of roughly 70% nitrogene, 21% oxygene and a variety of trace gases.

Life on Earth is supported by the atmosphere. The atmosphere absorbs the energy from the Sun, recycles water and other chemicals, and works with the electrical and magnetic forces to provide a moderate climate. The atmosphere also protects us from high-energy radiation and the frigid vacuum of space.

The structure of the atmosphere

The envelope of gas surrounding the Earth changes from the ground up. Four distinct horizontal layers have been identified based on thermal and convective characteristics (temperature changes), chemical composition, movement, and density. From the surface of the Earth upwards the layers are:

(a) The troposphere, in which convection is often prominent and in which most significant weather occurs, where temperature generally declines with height. It is extending to the tropopause at a somewhat variable height, generally about 11 km over middle and higher latitudes and 18 km near the Equator. This layer is known as the lower atmosphere.

(b) The stratosphere, in which there is much less vertical motion, and which extends from the tropopause to about 50 km at the stratopaus e. The lowest region of this layer is usually isothermal, but the temperature then increases with height.

(c) The mesosphere, in which there is once again more convection, extending from the stratopause to a height of about 86-100 km at the mesopause. In this region, the temperatures again fall as low as -93°C as you increase in altitude. The chemicals are in an excited state, as they absorb energy from the Sun. The regions of the stratosphere and the mesosphere, along with the stratopause and mesopause, are called the middle atmosphere.

(d) The thermosphere, extending from the mesopause to the effective limit of the atmosphere, at about 200-600 km. Temperatures in this region can go as high as 1,727°C. Chemical reactions occur much faster here than on the surface of the Earth. This layer is known as the upper atmosphere.

(e) The region above 700 km, at which height atoms may begin to escape into space is known as the exosphere.

On the basis of chemical composition the atmosphere consists of only two layers, the homosphere (largely identical with the troposphere, stratosphere and mesosphere) in which the composition is essentially constant, an the overlying heterosphere.

Specific ionization and photochemical processes occur in the ionosphere(encompassing part of the upper mesosphere and thermosphere) and the chemosphere and ozonosphere (both part of the upper stratosphere).

Add to social bookmarking:  | more |
A is for Air
Accessory clouds
Air masses and their sources
Air-mass Thunderstorm
Alpine Glow
Atmosphere - Diagram
Aurorae - Northern Lights
Average rainfall over England and Wales
Azores High
Banner Cloud - the peak's flag
Beaufort Scale
British Weather Terms
Brocken Spectre
Bubble High
Burning Time
CAPE - Convective Available Potential Energy
Cap cloud
Cc floccus
Cc lacunosus
Cc stratiformis
Cc undulatus
Central England Temperature
Centres of action
Ci fibratus
Ci radiatus
Ci spissatus
Ci uncinus
Ci vertebratus
Clocks go Back from BST to GMT
Cloud classification
Cloud seeding
Cloud species
Cloud streets
Cloud types (genera)
Cloud variety
Clouds - sentry of the sky
Cold low
Comma Cloud
Comma Cloud
Coriolis effect
Crepuscular rays
Cut-off low
Dew Point
Discovery of the Jet Stream
Doppler radar
Drifting snow - blowing snow
Earth's Atmosphere
Easterly wave - the Hurricane's cradle
El Nino
Föhn (foehn) wind
Föhn wall
Flash Flood
Fog and Mist
Forecasting weather
Frost hollow
Fujita Scale Statistics
Fujita Tornado Scale
Funnel cloud
Genoa Low
Geostationary Satellites
Geostrophic Wind
Glaze and Black Ice
Grass Minimum Temperature
Hailstorms in Britain
Highs and Lows and Winds
History of Hurricane Names
Hoar Frost
Isobars on surface maps
Jack Frost
Jet stream cirrus from space
Katabatic winds
Key to our weather symbols
Lake-effect snow
Latent Heat
Levanter cloud
Millibar and hectopascal
NOAA satellites
North Atlantic Drift (Gulf Stream)
Polar Orbiting Satellites
Polar low - the arctic hurricane
Precipitation Map
Rain gauge
Roll cloud
Rotor cloud
Saffir-Simpson scales
Sc duplicatus
Sc perlucidus
Sc undulatus
Shelf Cloud
Sometimes a bit fishy
Southern Oscillation
St. Swithun's Day
Standard Reference Period
Stevenson Screen
Sun pillar
Supercooled clouds
Surface wind
Thunderstorm Probability
Tornado Alley
Troposphere - Diagram
UV Index
Ultraviolet radiation
Virga or Fallstreak
What Makes Northern Lights Happen?
What does it mean?
Why Skies are Blue
Why Thunder Rumbles
World Meteorological Organisation (WMO)