Geography Reference
In-Depth Information
1
ATMOSPHERE, OCEANS, WEATHER
AND CLIMATE
COMPOSITION OF THE ATMOSPHERE
The layer of gases surrounding the Earth rises about 500 kilometres
above the surface, although there is no distinct boundary between
the Earth's atmosphere and space. However, three-quarters of the
gas in the atmosphere is within 11 kilometres of the Earth's surface
as the density of gas is very small at high altitudes. This is why it
becomes more difficult to breathe when you climb mountains and
why people need oxygen masks if they are in the open air at high
altitudes. The lower layer of the atmosphere is called the tropo-
sphere and extends to about 6 kilometres altitude over the poles
and about 15 kilometres over equatorial regions. This layer is the
one in which air mixes most rapidly and where we experience
weather.
The Earth's atmosphere acts as a filter protecting us from space
debris and harmful radiation. The Earth receives only two-
billionths of the Sun's total energy release but this energy is the
main driver for water, air and wind motions and most life on Earth.
It is therefore important to understand how the energy from the
Sun drives these processes. When the Sun's energy reaches the
Earth about 6 per cent of it is scattered and returned to space by
the atmosphere, 21 per cent is scattered and reflected by clouds and
18 per cent is absorbed by the atmosphere and clouds temporarily
before being sent back out to space. Of the 55 per cent that reaches
the Earth's surface 4 parts are reflected back to space by reflective
surfaces such as ice sheets, snow and dry, light, sandy soils, while
51 parts are absorbed by the surface. This means that of the total
Search WWH ::




Custom Search