Thursday, 7 July 2011

Structure of the atmosphere

As ocean circulations and atmospheric circulations are a couple system, I need to have a basic understanding of the atmosphere and so what better place to start that the structure of the atmosphere!

The atmosphere is split up into 4 main zones, each of which has distinct characteristics......

TROPOSPHERE:- this zone lies closest to the Earth and is the zone where the majority of the weather processes take place. It exhibits the highest temperatures as solar radiation warms the Earth's surface which, in turn, warms the air directly above it (via convection, conduction a d radiation).  However, this effect decreases rapdily with distance away from the surface and air temperature drops by 6.4 degrees Celcius with every 1000m gained in height. Wind speeds also increase with increasing altitude as frictional drag with the surface plays a diminishing role. This is the mst unstable layer and contains most water vapour and particulate matter. The end of the troposphere is marked by the TROPOPAUSE which is an isothermal layer where the temperature remains constant, despite the increase in altitude. The tropopause marks the upper limit of the zone of weather and climate.

STRATOSPHERE:- this zone is characterised by a steady increase in temperature (this is known as a temperature inversion) as a result of solar radiation by the ozone layer. The ozone layer absorbs much of the incoming UV radiation that would be harmful to humans otherwise. the atmosphere is noticeably thinner in this zone as pressure decreases with height and there is a lack of vapour and dust. Wind speeds increase with height tomwards the STRATOPAUSE - another isothermal layer.

MESOSPHERE:- temperature declines rapidly to c.-90 degrees Celcius in this zone as there is not water vapour or particulate matter to absorb radiation. it is characterised by very strong winds (often approaching 3000km/hr) and culminates in another isothermal layer known as the MESOPAUSE.

THERMOSPHERE:- this is so named because of the increase in temperature resulting from the absorption of UV radiation by the atomic oxygen found at this altitude.

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