The electromagnetic radiations of the Sun, with in particular
its infrared and visible elements, are indispensable to
life: they heat up the Earth's atmosphere
give light… The electromagnetic radiations can however
be harmful for mankind. The radiations are filtered by
the atmosphere (picture 1)
and the absorption causes local heating, which contributes
to the atmospheric structure.
The profile of the temperature determines different layers(pictures
2 et 3):
 Troposphere |
 The mount Everest |
 Stratosphere |
 Stratospheric
Balloon |
 Mesosphere |
 Space Shuttle |
 Thermosphere |
 Space Station |
 Exosphere |
 Rocket |
The troposphere is the part of the atmosphere between
the Earth’s surface and the tropopause,
situated at an altitude of about 8 to 15 km. In the troposphere
the temperature decreases according to the altitude. Studying
the troposphere is very important, because we breath the
air from this layer. The troposphere encloses for about
85% of the total mass of the atmosphere. Tropospheric
processes regulate meteorology and climate. (picture
4) The stratosphere is the part of the atmosphere
above the troposphere. The stratosphere stretches out
from the tropopause to an altitude of about 50 km. Because
of absorption of one large part of the ultraviolet radiations
coming from the Sun by the ozone layer, the temperature
in the stratosphere rises according to the height. With
this absorption, the ozone layer protects life on Earth.
(picture 5)
The mesosphere is the part of the atmosphere on top
of the stratosphere, between 50 and 90 km above the
surface. Just like the troposphere it is characterised
by a decreasing temperature according to the altitude.
At the upper limits of the mesosphere, the lowest temperatures
are measured; the temperatures can go down locally to
-173°C.
Thermosphere and exosphere are the parts of the Earth’s
upper atmosphere where artificial satellites and spacecrafts
(picture 6) are revolving.
A good knowledge of this environment appears indispensable
for the determination of aerodynamic characteristics
of spacecrafts, their lifetime and the selection of
the most suitable orbits for particular research and
applications. |
