APPENDIX C
ATMOSPHERIC STABILITY AND CLOUDS
PRACTICAL EXERCISE
TITLE: ATMOSPHERIC STABILTY AND CLOUDS
TERMINAL LEARNING OBJECTIVE: At the completion of this PE, the student will:
ACTION: Plan a flight mission IFR and VFR in accordance with weather conditions.
CONDITION: In a classroom environment.
STANDARD: IAW FM 1-230.
EVALUATION: At the end of this PE the instructor will conduct an after action review (AAR) concerning
the PE.
RESOURCE REQUIREMENTS: Students need a pen or pencil and this PE.
SPECIAL INSTRUCTION: None.
PROCEDURES:
1. This is a written exercise covering the instruction you received on atmospheric stability and clouds.
2. Record your answers on the actual PE handout.
3. All work must be done on your own. If you raise your hand, the instructor will provide assistance.
4. Upon completion of this PE, compare your answers with the solution provided. You will then be able
to identify any weak areas to overcome prior to the examination.
5. If unable to complete this PE during the allotted class time, complete it prior to the next class.
6. Clear up any misunderstandings with the instructor.
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QUESTIONS
1. A change of state from a gas to a liquid is called ________________.
2. When ice changes state from solid to liquid, heat is absorbed from the surrounding air. This change
of state is called _______________.
3. When ice changes state from a solid directly to a gas, it is called
__________________________________________________.
4. Weather hazards are related to water in one of its three states which are ___________________,
_____________________, and _________________.
5. When water droplets are cooled below freezing, they are referred to as ___________________ water
droplets.
6. Evaporation is a change of state from a ___________________ to a ________________________.
7. Condensation ______________________ (absorbs/releases) latent heat ______________ (into/from)
the surrounding air.
8. Sublimation takes place at temperature? ___________________
9. Through what process is snow formed? ________________
10. What is dew point temperature? _____________________________________________________
_______________________________
11. Dew point temperature is important to the aviator because it tells the temperature at which
_____________ should start forming.
12. If condensation takes place close to the ground, ____________________ will form.
13. What do we mean by the term “the spread?” ___________________________________________
________________________________________________________________________________
________________________________________________________________________________
14. Generally, condensation will not take place when the spread exceeds ________C.
15. The larger the difference between temperature and dew point, the __________________ the relative
humidity.
16. How do you express relative humidity when reporting it? _________________________________
________________________________________________________________________________
17. An example of solid moisture in the atmosphere would be
a.
b.
c.
d.
ice pellets (sleet).
snow.
hail.
all of the above.
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18. The amount of water vapor a given volume of air can contain depends upon the
a.
b.
c.
d.
humidity of the air.
amount of air pressure.
temperature of the air.
dew point temperature.
19. The temperature at which air will become saturated is known as
a.
b.
c.
d.
dew point.
relative humidity.
specific humidity.
free air temperature.
20. Dew is a form of
a.
b.
c.
d.
condensation.
precipitation.
coalescence.
sublimation.
21. The dry adiabatic cooling rate per 1,000 feet is
a.
b.
c.
d.
1.5C.
3C.
1.5F.
3F.
22. The moist adiabatic cooling rate is approximately
a.
b.
c.
d.
3C per 1,000 feet.
unsaturated air cooling at 1.5C per 1,000 feet.
1.5C per 1,000 feet.
the standard lapse rate.
23. Air being lifted over a mountain range will cool on the windward side and heat up as it moves
downslope on the leeward side. This temperature change is a result of
a.
b.
c.
d.
thermal currents.
cold and warm air advection.
cold mountaintops.
adiabatic process.
24. The level of free convection is
a.
b.
c.
d.
the level at which the temperature outside the lifted parcel is the same as inside the lifted parcel.
the level where the temperature and dew point are the same and condensation takes place.
the level where latent heat is released.
the level where air is forced up the side of a mountain and condensation takes place.
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25. If the OLR for a given observation was 2.5C per 1,000 feet, you could expect the air to be
a.
b.
c.
d.
stable.
unstable.
wet.
conditionally unstable.
26. You observe, from upper air reports, that the OLR in the first 8,000 feet of the atmosphere is 3.5C.
You could therefore expect
a.
b.
c.
d.
absolutely stable air.
conditionally unstable air.
stable air up to 8,000 feet and conditionally unstable air above that level.
absolutely unstable air up to 8,000 feet.
27. If the OLR for a given observation was 1C per 1,000 feet, you could expect the air to be
a. absolutely stable.
b. absolutely unstable.
c. conditionally unstable.
The weather station took a winds-aloft analysis and after plotting the information received, it was
determined that the OLR was 2C per 1,000 feet. The surface temperature was 20C and the dew point
was 14C. Under these conditions, a parcel of air is being lifted up a mountainside. Because of the
lifting, it will cool adiabatically.
Enter the correct temperature in each block of the illustration. Then, using this information and the above
description, answer the following four questions.
28. At what altitude would condensation take
place?
a.
b.
c.
d.
1,000 feet
2,000 feet
3,000 feet
could not take place
29. What would the level of free convection
be in a parcel of the lifted air?
a. 4,000 feet
b. 5,000 feet
c. 6,000 feet
d. would not reach the level of free
convection
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30. Compared to the standard temperature for 4,000 feet, the OLR shows the actual temperature to be
a.
b.
c.
d.
below standard.
standard.
standard for 2,000 feet.
above standard.
31. According to the OLR, you would expect to find the freezing level at _________ feet.
a.
b.
c.
d.
7,000
8,000
9,000
10,000
32. If lifting action occurs, air with high moisture content tends to be
a. more stable than dry air.
b. more unstable than dry air.
c. conditionally stable.
33. Clouds form in various ways, but most clouds form because of
a.
b.
c.
d.
radiational cooling.
adiabatic cooling.
cooling by conduction.
adiabatic heating.
34. You would expect more clouds to form in
a.
b.
c.
d.
air rising up a mountainside.
the valleys beyond the mountains.
air descending from the mountaintop.
air undergoing adiabatic warming.
35. Clouds associated with the nocturnal cooling process would be
a.
b.
c.
d.
cirrus.
cumulus.
low stratus and fog.
altocumulus.
36. The two general (basic) types of clouds are
a.
b.
c.
d.
stratus and stratocumulus.
cumulus and cumulonimbus.
stratus and cumulus.
altocumulus and cirrostratus.
37. In addition to moisture, ______________ must be present in the atmosphere to act as a nucleus for
forming cloud droplets.
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38. When the word nimbus is added to names of clouds, it means that
a.
b.
c.
d.
some form of precipitation is associated with the cloud.
the cloud system had its base above 6,500 feet.
the cloud was caused by local convective currents.
the cloud has vertical development and ice crystals at the top.
39. Fill in the altitudes typical for the bases of low, middle, and high clouds.
Low clouds: less than ___________ feet.
Middle clouds: from __________ feet to __________ feet.
High clouds: over ___________ feet.
40. Match the cloud abbreviations with the correct name.
______ Nimbostratus
a. Cu
______ Stratus
b. Sc
______ Cirrus
c. As
______ Cumulus
d. Ns
______ Altostratus
e. Ac
______ Cirrocumulus
f. Cb
______ Cirrostratus
g. Cc
______ Stratocumulus
h. St
______ Cumulonimbus
i. Ci
______ Altocumulus
j. Cs
41. Which of the following series of cloud abbreviations has only those clouds of a lumpy or billowing
appearance?
a.
b.
c.
d.
Sc, Ac, Ns, St
Sc, Ac, Cu, Cc
Cb, As, Cs, Ci
Ns, As, Cs, Ci
42. Turbulent (rough) flying weather is common with
a.
b.
c.
d.
nimbostratus clouds.
stratiform clouds.
cumuliform clouds.
all low clouds.
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APPENDIX C
ATMOSPHERIC STABILITY AND CLOUDS
PRACTICAL EXERCISE SOLUTIONS
1. condensation
24. a.
2. melting
25. d.
3. sublimation
26. d.
4. solid, liquid, gas
27. a.
5. supercooled
28. b.
6. liquid, gas
29. c.
7. releases, into
30. d.
8. below 0C
31. d.
9. sublimation
32. b.
10. the temperature to which air must be cooled
to become saturated
33. b.
34. a.
11. fog or clouds
35. c.
12. fog
36. c.
13. the difference between the temperature and
dew point temperature
37. Condensation nuclei / impurities
14. 2C
38. a.
15. lower
39. 6,500; 6,500 to 18,000; 18,000 and above
16. as a percent
40. d, h, i, a, c, g, j, b, f, e
17. d.
41. b.
18. c.
42. c.
19. a.
20. a.
21. b.
22. c.
23. d.
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