Geography Reference
In-Depth Information
100
Thermosphere
0.001
90
0.002
Mesopause
0.005
0.01
80
Mesosphere
0.02
0.05
70
0.1
0.2
60
0.5
50
1
Stratopause
2
Stratosphere
40
5
10
30
20
50
20
100
200
Tropopause
10
Troposphere
500
1000
0
180
200
220
240
260
280
Temperature (K)
Fig. 12.1
Midlatitude mean temperature profile. Based on the
U.S. Standard Atmosphere
(1976).
on dynamical processes in the lower part of the middle atmosphere and their links
to the troposphere.
12.1
STRUCTURE AND CIRCULATION OF THE MIDDLE
ATMOSPHERE
Zonal mean temperature cross sections for January and July in the lower and mid-
dle atmosphere are shown in the upper panels of Figs. 12.2 and 12.3, respectively.
Because very little solar radiation is absorbed in the troposphere, the thermal struc-
ture of the troposphere is maintained by an approximate balance among infrared
radiative cooling, vertical transport of sensible and latent heat away from the sur-
face by small-scale eddies, and large-scale heat transport by synoptic-scale eddies.
The net result is a mean temperature structure in which the surface temperature
has its maximum in the equatorial region and decreases toward both the winter
and the summer poles. There is also a rapid decrease in altitude, with a lapse rate
of about 6
◦
Ckm
−
1
.
