Clark College meteorology
Mountain Cloud Activity
Use the Iowa State University simulation at the link below to help you
work through this activity.
http://www.pals.iastate.edu/simulations/Mtnsim/index.html
Objective: Learn what happens to air temperature, vapor pressure,
and dew point as an air parcel is force up and over a mountain range.
Here’s a quick youtube
video introducing the Mountain Cloud Environment.
Here are some easy questions to get you started. These are directly from the
Mountain Cloud Simulation Website.
1) Start with a vapor pressure of 10mb. Enter a temperature (between0 C and
40 C) that will cause a cloud to form. T=____________
2) Start with a vapor pressure of 10mb. Enter a temperature (between 0 C
and 40 C) that will not cause a cloud to form. T=___________
3) Given an initial air temperature of 28 C, enter an initial dew point
temperature (between 0 C and 40 C) which will cause a cloud to form below
500m. T=___________
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Clark College meteorology
4) Given an initial air temperature of 28 C, enter an initial dew point
temperature (between 0 C and 40 C) which will cause a cloud to form above
1000m. Td=_________
5) Given an initial air temperature of 28 C, enter an initial dew point
temperature (between -10 C and 40 C) which will cause no cloud to form.
Td=_________
6) Given an initial air temperature of 20 C, enter an initial water vapor
pressure (between 0 mb and 24 mb) which will cause instantaneous cloud
formation. Vapor Pressure (mb)=_________
7) Given an initial air temperature of 20 C, enter an initial water vapor
pressure (between 0 mb and 24 mb) which will cause cloud formation above
1000m. Vapor Pressure (mb)=_________
8) Given an initial air temperature of 20 C, enter an initial water vapor
pressure (between 0 mb and 24 mb) which will cause no cloud formation.
Vapor Pressure (mb)=_________
Part 2. Set the initial temperature to 25 C and then adjust the vapor pressure
of the air so that a cloud will form at 1 km - 1.1 km (i.e., the altitude of
cloud base is between 1 km and 1.1 km).
To get the best answer on this adjust the wind speed to be fairly slow so you
can see how each number changes in the table below the graphs on the
simulation page. Notice the six parameters given in this display for any time
during the simulation.
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For your simulation: (Make sure to include the correct units with all numbers)
The initial temperature (C) at the base of the windward side of the mountain
is 25 C (this is the prescribed value)
1. What is the initial water vapor pressure (in mb) at the base of the
windward side of the mountain that was needed to create a cloud base
at between 1.0 to 1.1 km? ______________________
2. What is the initial dew point temperature(C) at the base of the
windward side of the mountain? ______________________
3. What is the slope in temperature (lapse rate in C/km) as the air parcel
rises up the windward side of the mountain but before a cloud forms?
________________
4. At what altitude does the cloud form? _______________
5. What is the slope in temperature (lapse rate in C/km) as the air parcel
rises up the windward side of the mountain but after a cloud forms?
________________ (Rerun the simulation if you didn’t catch it the
first time.)
6. Which slope value above (from Ques 3 or 5) represents the dry
adiabatic lapse rate? ______________________
7. Which slope value above (from Ques 3 or 5) represents the moist
adiabatic lapse rate? ______________________
8. What is the slope in temperature (lapse rate in C/km) as the air parcel
descends the leeward side of the mountain ? ________________
(Rerun the simulation if you didn’t catch it the first time.)
9. What was the water vapor pressure (in mb) at the base of the leeward
side of the mountain? ______________________
10.What is the Dew Point (C) at the base of the leeward side of the
mountain? ______________________
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Clark College meteorology
11.What is the air temperature (C) at the base of the leeward side of the
mountain? ______________________
12.Is the air warmer or cooler after it completes its trip over the
mountain? _________________________
13.What is the source of this energy giving the observed temperature
change?
14.Does the air have more or less moisture in it after it completes its trip
over the mountain? ______________________
15. Water cannot come from nowhere or magically disappear. Where
does this moisture go or come from?
http://www.atmosedu.com/meteor/images/WAStatePrecip.gif (Ctrl-click for larger image)
The above map shows the annual precipitation for Washington State. The are two
major rain shadows shown on this map. One, the rainshadow formed by the
cascades, is Eastern Washington. Where is the other rainshadow and forms it?
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Clark College meteorology
Part 3. Objective: Learn how to determine where a cloud will
form.
A wind is blowing from left to right over the mountain. For each
initial temperature in the table below adjust the vapor pressure
(dew point temperature) of the air so that a cloud will form at 1 km
(i.e., the altitude of cloud base is about1 km). Complete the table
below.
Initial values for a cloud to form at 1.0 km. Also calculate the
difference between the air temperature and the dew point required
to give a cloud with 1.0 km cloud base. (include in column 3).
Air Temperature ( C)
Dew Point ( C)
Air Temp-Dew Pt
Vapor Pressure
(mb)
30
25
20
15
10
What dew point temperature will give a cloud base of 1.0 km when the air temperature is
28 C? _____________________________
What air temperature will give a cloud base of 1.0 km when the dew point temperature is
4 C? ______________________
Given a particular air temperature, explain how to estimate the dew point temperature
that gives a cloud base of 1.0 km.
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