Name: ________________________________________
Date: _________________
Lab: Adiabatic Temperature and Clouds
Introduction: You have probably heard people say “hot air rises”, after all isn’t that why hot air balloons rise? Well,
if this were the case shouldn’t we be sun bathing instead of skiing on the mountaintops? What happened to all that hot
air? There must be more to this story. In this laboratory you will be investigating how pressure affects the temperature
of air and how this relates to the formation of clouds in the troposphere. You will form a cloud in a bottle, find the
dew point and relative humidity of air use a chart to estimate how high that air would have to rise to form a cloud.
Part 1: In order to explore how clouds form in the atmosphere we have to examine the relationship between changes
in air pressure and temperature. As air rises in the atmosphere, the air pressure decreases. This is because there is less
air (atmosphere) above it pushing down. With less atmosphere (air molecules), the air expands. You will be adding
air to a two liter soda-pop bottle and examine what happens to the mass and temperature of the air inside the bottle.
Data Table 1
Problem: What happens to air temperature when pressure increases?
Pumps
Hypothesis: ____________________________________
______________________________________________
Mass
(g)
Temperature
ÞF
0
Materials: Digital Scale, empty 2 liter bottle, fizz keeper pressure
pump, thermometer, smoke from incense
30
Procedure Part 1: Relationships
1. Attach a pressure pump to a two-liter bottle.
2. Measure the Mass the container and record the temperature.
3. Pump 30 times. Record mass and temperature each 30 pumps.
4. Complete Data Table then release the pressure and record
data.
5. Define a scale for mass and temperature and graph your data
using two different symbols, and connect your data points. Be
sure to make a key.
6. Connect your data points for mass and temperature (two
lines).
90
60
120
150
180
210
Release
The Affects of Pressure changes on both Mass and Temperature
Mass
0
30
60
Number of Pumps, Increasing Pressure
Temperature
90
120
150
180
210
Part 1 Questions:
1. What happened to the mass and temperature of the air when the top was open?
_________________________________________________________________________________
_________________________________________________________________________________
2. When the 2L bottle was being pumped, the air was
expanding or compressing. (circle one) What
did the temperature do in response to the bottle being pumped? _______________________
3. When the bottle was opened, the pressure increased or decreased.
(circle one) What did
the temperature do in response to the bottle being opened? _______________________
4. Using ESRT p14, what happens to the pressure as you increase altitude in the troposphere? _______
5. Using ESRT p14, what happens to the temperature as you increase altitude in the troposphere?
______________
6. As air rises in the atmosphere, does the air expand or compress? ____________________
7. When air rises in the atmosphere, the air expands and then ___________________. (warms or cools)
Part 1 Conclusion: What is the relationship between pressure and temperature? Was your hypothesis
supported? Provide evidence from the lab to support or not support your hypothessis
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Procedure Part 2: Creating a Cloud
1. Pressurize your two-liter bottle by pumping it at least 100 times.
2. Release the pressure. Do you see a cloud? __________________
3. Bring your bottle to the incense burner and collect 2 seconds of smoke (or smoke from a
match).
4. Re-pressurize your bottle to the same amount.
5. Release the pressure. Do you see a cloud? __________________
6. Define: Condensation Nuclei:
_______________________________________________________________________________
____________________________________________________________________________________
7. What are some examples of condensation nuclei in the atmosphere? _____________________________
8. Why didn’t a cloud form both times? ______________________________________________________
Part 2 Questions:
1. Are clouds water vapor? Why or why not? Explain:
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Part 3:
Introduction:
As air rises, there is less atmosphere above it so there is less pressure on it and the air molecules can spread
out or expand. As they spread out, they take their heat with them. The expansion of air causes the
temperature to drop, though no heat is actually taken from the air. Temperature changes that occur due to
expansion or contraction and without gain or loss of heat are called adiabatic temperature changes.
Normally as air rises in the lower atmosphere the temperature drops at a rate of 10oC for each kilometer it
rises. This is known as the Dry Adiabatic Lapse Rate.
When the air spreads out (as it rises) it opens up space which more water molecules can fill, allowing more
water molecules to evaporate into the air than would have at a lower altitude. This lowers the dewpoint by a
rate of about 2 oC for each kilometer of rise. This is known as the dewpoint lapse rate.
You’ve already learned that when air is cooled below the dewpoint, condensation exceeds evaporations and
the amount of liquid water increases as dew or cloud/fog droplets form and grow. As air rises, the
temperature drops 10 oC for each kilometer, and the dewpoint drops 2 oC for each kilometer. If this goes on
long enough, the falling temperatures will eventually catch up to the falling dewpoint. When this happens,
condensation will exceed evaporation and tiny droplets of liquid water will form in the air. We call a mass
of tiny water droplets in the air a ___________ (or ________ if at ground level.
Procedure
In this part of the lab, you will use the diagram on the back page to find the cloud base altitude:
1. Find the dry bulb the dewpoint temperatures on the x-axis of the “Generalized Graph for Determining
Cloud Base Altitude”.
2. Find the dewpoint temperature on the x-axis of the “Generalized Graph for Determining Cloud Base
Altitude”.
3. Follow the solid diagonal lines up from the dry bulb temperature, and the dashed diagonal lines up
from the dewpoint temperature. Record the altitude (on the Y-axis) where the dewpoint line crosses
the dry bulb line – that is, the elevation at which the dewpoint and the temperature are the same, and
net condensation begins.
Use the chart on page 12 of the ESRT and the “Generalized Graph for Determining Cloud Base Altitude” to
fill in the table below.
Dry Temp
20
Wet Temp
19
20
17
20
13
16
13
6
0
Dewpoint (oC)
Rel Hum (%)
Cloud Base Alt (km)
Then answer the following questions.
1. Why does the height of the cumulus cloud base change from day to day?
2. What would happen to the height of the cloud base if the dew point temperature were lower?
3. How would it be possible to have a day without any clouds?
4. What relationship would you expect to find between the air temperature and dew point temperature at
ground level if the area is covered by fog?
5. What happens to the air temperature of a descending mass of air?
6. What happens to the dew point temperature of a descending mass of air?
7. Explain why a descending mass of air would tend to be drier?
CONCLUSION
What are the 5 steps in the formation of a cloud? Begin with air, does it rise or fall. Does it compress or
expand, does it cool or warm, does it cool or warm to the dew point, and does evaporation or condensation
occur.
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