Geoscience Reference
In-Depth Information
2.2 Discovery of the tropopause and stratosphere
Early scientific exploration of the upper atmosphere began with manned balloon flights in the mid-
nineteenth century. Notable among these was the ascent by Glaisher and Cox in 1862. Glaisher lost
consciousness due to lack of oxygen at about 8800m altitude and they barely survived the hypoxia.
In 1902 Teisserenc de Bort in France reported a totally unexpected finding; that temperatures ceased
decreasing at altitudes of around 12km. Indeed, at higher elevations temperatures were commonly
observed to begin increasing with altitude. This means structure is shown in Figure 2.13.
The terms troposphere (turbulent sphere) and stratosphere (stratified sphere) were proposed
by Teisserenc de Bort in 1908; the use of 'tropopause' to denote the inversion or isothermal layer
separating them was introduced in Great Britain during World War I. The distinctive features of the
stratosphere are its stability compared with the troposphere, its dryness, and its high concentration
of ozone.
They can absorb odd nitrogen and thereby cause
catalytic destruction of ozone.
Marked seasonal changes of temperature
affect the stratosphere. The cold 'polar night'
winter stratosphere in the Arctic often undergoes
dramatic
sudden warmings
associated with sub-
sidence due to circulation changes in late winter
or early spring, when temperatures at about 25km
may jump from -80 to -40
2 Stratosphere
The stratosphere extends upward from the
tropopause to about 50km and accounts for about
10 percent of the atmospheric mass. Although
the stratosphere contains much of the total
atmospheric ozone (it reaches a peak density at
approximately 22km), maximum temperatures
associated with the absorption of the sun's
ultraviolet radiation by ozone occur at the
stratopause
where they may exceed 0
C over a two-day
period. The autumn cooling is a more gradual
process. In the tropical stratosphere there is a
quasi-biennial (26-month) wind regime, with
easterlies in the layer 18 to 30km for 12 to 13
months, followed by westerlies for a similar
period. The reversal begins first at high levels and
takes approximately 12 months to descend from
30 to 18km (10 to 60mb).
How far events in the stratosphere are linked
with temperature and circulation changes in the
troposphere remains a topic of meteorological
research. Any such interactions are undoubtedly
complex
°
C (see
Figure
2.15
). The air density is much less here, so even
limited absorption produces a large temperature
rise. Temperatures increase fairly generally with
height in summer, with the coldest air at the
equatorial tropopause. In winter, the structure
is more complex, with very low temperatures,
averaging -80
°
C, at the equatorial tropopause,
which is highest at this season. Similar low
temperatures are found in the middle stratosphere
at high latitudes, whereas over 50-60
°
N there is
a marked warm region with nearly isothermal
conditions at about -45 to -50
°
C. In the
circumpolar low pressure vortex over both polar
regions, polar stratospheric clouds (PSCs) are
sometimes present at 20-30km altitude. These
have a nacreous
(
'mother-of-pearl') appearance.
°
3 Mesosphere
Above the stratopause, average temperatures
decrease to a minimum of about -133
°
C (140K)
