Geoscience Reference
In-Depth Information
Temperature (°F)
40°
50°
60°
70°
80°
3000
2°C (35.6°F)
2500
Wet adiabatic
lapse rate
5°C/1000 m
(2.7°F/1000 ft)
8000
2000
8°C (46.4°F)
18°C (64.4°F)
6000
14°C (57.2°F)
20.5°C (68.9°F)
1500
4000
Level of condensation
1000
20°C (68°F)
23°C (73.4°F)
Environmental
lapse rate
12°C/1000 m
(6.6°F/1000 ft)
Dry adiabatic
lapse rate
10°C/1000 m
(5.5°F/1000 ft)
2000
26°C (78.8°F)
28°C (82.4°F)
500
32°C (89.6°F)
33°C (91.4°F)
0
0
5°
10°
15°
20°
25°
30°
Main air
body
Uplifting air
body
(a) Unstable air
Temperature (°C)
Temperature (°F)
40°
50°
60°
70°
80°
3000
2500
19.5°C (67.1°F)
8000
Environmental
lapse rate
5°C/1000 m
(3.3°F/1000 ft)
2000
22°C (71.6°F)
6000
1500
24.5°C (76.1°F)
4000
Dry adiabatic
lapse rate
10°C/1000 m
(5.5°F/1000 ft)
27°C (80.6°F)
No further
uplift possible
1000
2000
500
29.5°C (85.1°F)
28°C (82.4°F)
32°C (89.6°F)
33°C (91.4°F)
0
0
5°
10°
15°
20°
25°
30°
Main air
body
Uplifting air
body
(b) Stable air
Temperature (°C)
Figure 7.26 Graphical representations of unstable and stable bodies of air.
(a) In this hypothetical body of unstable air,
strong convection occurs when the environmental lapse rate is high and a bubble of relatively warm air forms at the surface.
The graphical representation of temperature on the left shows changes with respect to altitude in the bubble and surround-
ing air mass; these changes can also be seen in numerical form to the right within the convecting air bubble and main air
body. (b) In this hypothetical body of stable air, the environmental lapse rate is relatively low and the convecting air cannot lift
because it cools more quickly than the surrounding air.
and convection continues. This is why the air temperature of
the convective bubble is 18°C (64.4°F) at 2000 m, whereas it is
only 8°C (46.4°F) in the surrounding air.
Now, let's look at what happens in a stable body of air by
examining Figure 7.26b. Imagine in this scenario that the en-
vironmental lapse rate of the main body of air is 5°C/1000 m
(3.3°F/1000 ft) and that the temperature at ground level is 32°C
(89.6°F), which is the same as in the previous example. In this
case, the temperature of the main body of air would be 27°C
(80.6°F) at 1000 m and 22°C (71.6°F) at 2000 m.
Consider what happens over the warm parking lot de-
scribed in the example of unstable air. Let's imagine that the
air immediately above this parking lot warms to the same tem-
perature it did previously, that is, 33°C (91.4°F). Given that this
bubble of air is warmer than the surrounding air at the surface,
it begins to convect. As it does, it cools at the dry adiabatic lapse
rate of 10°C/1000 m (5.5°F/1000 ft) because the air pressure
decreases as the air lifts. In this example, however, this rate of
cooling is
greater
than that observed in the surrounding body of
air. Thus, at 500 m the temperature of the convecting air bubble
