Geoscience Reference
In-Depth Information
Layered Structure
of the Atmosphere
most active zone of the atmosphere, with vigorously mov-
ing currents of air. Physical geographers and meteorologists
are most interested in this atmospheric layer because it con-
tains the vast majority of nonmarine living organisms and is
the zone where most weather occurs, such as rain, wind, and
snow. Much of this weather occurs because the troposphere
contains most of the atmospheric water vapor and particulates.
The troposphere is warmed by longwave radiation emit-
ted from Earth as part of the global energy balance discussed in
Chapter 4. Because the source of heat in the troposphere is Earth,
temperature decreases with increasing altitude (Figure 5.2) at the
environmental lapse rate
. As altitude (from the Earth) increases
in the troposphere, the average temperature drops 6.4°C per
The place to begin a discussion of global temperature patterns
is in the atmosphere, which is the medium through which solar
radiation flows. The atmosphere technically extends from a very
shallow depth within Earth (because soil contains air and water)
to a height of about 480 km (300 mi). Most of the atmosphere's
mass, however, lies below an altitude of 30 km (18.6 mi). Al-
though we usually think of the atmosphere as a uniform gaseous
medium that envelops Earth, it actually contains four distinct
layers: the troposphere, stratosphere, mesosphere, and thermo-
sphere. These layers are distinguished by temperature and also
by what elements they contain. Figure 5.1 illustrates these major
layers and the temperature trends within them.
Troposphere
The lowermost layer of the atmosphere, which
lies between the Earth's surface and an altitude of about 12 km
(~7.5 mi).
The Troposphere
The
troposphere
is the lowest layer of the atmosphere,
extending from the surface to an average altitude of about
12 km (~7.5 mi). The name of this layer is derived from the
Greek word
tropos
for “turning” or “mixing” because it is the
Environmental lapse rate
The decrease in temperature that
generally occurs with respect to altitude in the troposphere.
This rate is 6.4°C per kilometer or 3.5°F per 1000 ft (a positive
lapse rate).
Figure 5.1 Layers and temperature patterns in the
atmosphere.
(a) The four major layers in the atmo-
sphere. Note the features such as clouds and auro-
ras that occur within specific layers. (b) Temperature
changes with respect to altitude in each of the four
major layers of the atmosphere.
Auroras
Thermosphere
Extends to 480 km
(300 mi)
Auroras
Up to
1200°C
100
Mesosphere
Extends to 80 km
(50 mi)
Thermosphere
Meteors burn up
from friction in
mesosphere
Mesopause
Stratosphere
Extends to 50 km
(30 mi)
Ozone layer
Mesosphere
Airliners travel
in stratosphere
Stratopause
50
Troposphere
Average thickness:
12 km (7.5 mi)
16 km (10 mi) thick
at Equator
8 km (5 mi) thick
at poles
Most weather
occurs in
troposphere
Ozone layer
Stratosphere
Tropopause
Clouds
Troposphere
0
-100
-50
0
20
40
