Geoscience Reference
In-Depth Information
until condensation occurs. This rate is 10°C/1000 m
(5.5°F/1000 ft). When air warms adiabatically, it always
does so at the DAR because condensation is not oc-
curring. Once the level of condensation is reached, the
air temperature begins to decrease at the wet adiabatic
lapse rate (WAR), which is 5°C/1000 m (2.7°F/1000 ft).
This lesser rate of cooling occurs because latent heat
of condensation is released when water changes from
vapor to liquid.
6.
Air is uplifted such that cloud formation and precipitation
occur in any of four different ways. The extent of uplift and
condensation depends greatly on the stability of the main
body of air. Orographic lifting occurs when air flows over
a mountain range. Convection occurs when bubbles of
warm air develop in a body of relatively cool air that has a
high environmental lapse rate. Frontal uplift occurs when
two contrasting bodies of air collide. Convergence occurs
when air flows into the center of a low-pressure system.
C H E C K y O U R U N D E R S T A N D I N G
1.
Describe the physical properties of water and its three
phases.
a humid air mass or dry? Would the actual temperature
of the air mass likely be more or less than the dew point?
8.
Imagine that the temperature of an air parcel is 20°C
(68°F) and the specific humidity is 10 g/kg. What would
the relative humidity be? To what temperature would
the air have to cool to reach a point of saturation?
9.
Why are condensation nuclei important for precipita-
tion to occur?
2.
Compare and contrast the various ways that water
changes phase.
3.
Discuss the hydrologic cycle and the concept of a
reservoir
.
4.
What are the various kinds of atmospheric humidity?
5.
Which body of air would have the higher maximum
humidity: an air parcel that has a temperature of 25°C
(77°F) or one that has an air temperature of 15°C (59°F)?
10.
Compare and contrast the wet adiabatic lapse rate
(WAR) with the dry adiabatic lapse rate (DAR). When
do you use the DAR as opposed to the WAR?
6.
Of the two air masses described in the previous ques-
tion, which of the two will likely have the higher specific
humidity? Which one will probably have the higher rela-
tive humidity?
11.
Discuss the three fundamental cloud types—cirrus,
cumulus, and stratus—and the kinds of atmospheric
conditions in which they form.
12.
Why is the specific humidity of an air parcel less on the
leeward side of a mountain range than on the wind-
ward side?
7.
Imagine that the dew-point temperature of an air mass is
30°C (86°F). What would the specific humidity be? (Hint:
Look at the saturation curve in Figure 7.6.) Would this be
ANSWERS TO VISUAL CONCEPT CHECKS
V I S U A L C O N C E P T C H E C K 7 . 1
The pond is part of the hydrologic cycle because it is a place where water is temporarily stored. Water
can enter the pond either through precipitation or from within the ground itself. Once the water is
stored in the pond, it can either flow back into the ground or evaporate into the atmosphere.
V I S U A L C O N C E P T C H E C K 7 . 2
The answer is
d
, “all of the above.” For contrails to form, the air must be close to saturation. Conden-
sation nuclei must be present for water droplets to form, and the plane must be above the level of
condensation.
V I S U A L C O N C E P T C H E C K 7 . 3
The answer is
d
. Given that the cloud pattern is distinctly associated with the peninsula, strong con-
vection must be occurring over the land. For this to happen, the Florida landmass must be warmer
than the surrounding water.
