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Temperature Structure
The vertical distribution of global average temperature, as seen in
Figure 7, shows that the surface of the earth
has a temperature of about 288 Kelvin (15°C) or about
59°F. The temperature decreases with height from the surface to
about 10 kilometers, equivalent to an altitude of about 6 miles. This level is
called the tropopause which marks the upper boundary of the troposphere.
Above this level, in what is known as the stratosphere, the temperature remains
constant with height at a value of about -55°C to a height of about
20 km, above which it increases to a maximum at the stratopause, an altitude
of about 50 km. This plot is a very idealized picture of the atmospheric temperature profile. Over the polar
regions the tropopause will be only perhaps 8 km and over the tropics it may
reach 17 km. It also is interesting to note that the coldest tropopause
temperature is over the tropics where it might typically reach -80°C.
This temperature structure is very critical for how moisture and trace gases move in the atmosphere. Air in the troposphere is quite well mixed. Moisture, pollutants, or trace gases that are put into the atmosphere at the surface are usually mixed quite thoroughly throughout the troposphere within a matter of 2 or 3 days. And precipitation processes usually wash soluble particles out of the troposphere in 1 to 3 weeks. If foreign material gets into the stratosphere, however, it may persist there for 1 to 3 years. So, for instance, the soot from the Kuwaiti oil fires during the Gulf War was confined to the troposphere and was washed out before it traveled very far from the fire region, whereas dust from the eruption of Mount Pinatubo in the Philippines in 1991 spewed large amounts of dust into the stratosphere that reduced sunlight levels over the globe for about 3 years. The fact that the stratosphere is a very stable region that doesn't foster mixing will be important later when we discuss ozone.
