Atmospheric Humidity Question Sheet
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School
Cosumnes River College *
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Course
391
Subject
Aerospace Engineering
Date
Dec 6, 2023
Type
Pages
6
Uploaded by MasterPower12125
Part C. Lifting Mechanisms
6
Figure by Scott Crosier is licensed under
CC BY-NC-SA 4.0
9
|
Lab 6: Atmospheric Humidity
There are four major
lifting mechanisms
in which air is forced upwards:
➢
Convergent Lifting
: Air flowing from different directions ‘crashes’ into one another,
causing the air to be forced upward
➢
Convectional Lifting
: Over a warm surface, the heated air is forced upwards
➢
Orographic Lifting
: Air forced up and over a mountain
➢
Frontal Lifting
: As two different air masses intersect, the warm, humid air is forced
upward
19. Label the following lifting mechanism diagrams based on their descriptions.
a. __________Convergent lifting
______________________________________________:
Figure 6.7: Lifting Mechanism Sample 1.
7
b. ____________orographic lifting
____________________________________________:
Figure 6.8: Lifting Mechanism Sample 2.
8
c. ________________frontaaal lifting
________________________________________:
7
Figure by Scott Crosier is licensed under
CC BY-NC-SA 4.0
8
Figures by Scott Crosier is licensed under
CC BY-NC-SA 4.0
10
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Lab 6: Atmospheric Humidity
Figure 6.9: Lifting Mechanism Sample 3.
8
d. ________________convectionall lifting
________________________________________:
Figure 6.10: Lifting Mechanism Sample 4.
8
Part D. Adiabatic Rates
Assume an unsaturated air mass located at sea level (0 meters) in the Sacramento Valley has an
initial air temperature of 17°C and a specific humidity of 4g H
2
O/kg air. The prevailing westerlies
are forcing the air mass towards the western slope of the Sierras.
20. Calculate the relative humidity and the dew point temperature of the air mass. Show
your work.
Given, initial air temperature T = 17 C.
specific humidity of 4g H
2
O/kg air.
The saturation water content at 17 C can be found from the saturation specific humidity
table.
Es = 13 g H
2
O/kg air.
The relative humidity is given by,
RH = (4/13) x 100
RH = 30.76 %
, the dew point temperature is given by,
Td = T - (100-RH)/5
putting the required values, we see
Td = 17 - (100-30.8)/5
Td = 3.16 C
LCL = (Air Temperature - Dew Point Temperature)
|DAR| (in ‘000s of m)
21. At what elevation will clouds start to form? Calculate the LCL for this air mass using the
following formula. Show your work.
LCL = ___1767.5m____ meters
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11
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Lab 6: Atmospheric Humidity
22. Calculate the expected temperature of the air mass at the ridge of the Sierras (4,000
meters). Don’t forget to calculate the DAR of the air before it reaches the LCL and the
MAR as it continues to rise to the peak. Show your work.
T
air
(LCL)=t
air
(surface)-
dry
(z2-z1)
T
air
(LCL)= 7-10(1.7675)
T
air
(LCL)=-10.675 C
T
air
(z2)=T
air
(z1)-
moist
(z2-z1)
T
air
(z2)= -10.675-6.5 x (4- 1.7675)
T
air
(z2)=-25.18
The following formula might be of assistance:
Change in Temp = Rate (DAR or MAR) x Change in Elevation
Temp at the LCL =__-10.675____°C
Temp at 4,000 m =___-25.18___°C
As the air descends down the leeward side of the Sierra Nevada mountain range, the air mass is
heated by compression.
23. If temperature rises, what happens to the relative humidity?
As the temperature rises due to heating due to adiabatic compression, the water holding
capacity of the air will increase. This will eventually lead to decrease in the relative humidity.
24. Based on your answer above, will the sinking air warm at the DAR or MAR? Why?
Explain your response in one to two sentences.
The sinking air will warm at a dry adiabatic rate once it crosses the dew point
temperature. This is because the cooling due to adiabatic expansion is opposite to the
heating due to the adiabatic compression. So, the rate of heating should be equal to the
rate of cooling.
25. What is the temperature of the air mass once it reaches Reno at 1,500 meters? Show
your work.
Temp at Reno=___7___°C
26. Based on your calculations above, use the profile below (Figure 6.12) and fill in any
missing information about the labeled locations.
27. Draw arrows indicating the movement of air over the range and label the regions where
the air will warm or cool based on the DAR or the MAR.
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Lab 6: Atmospheric Humidity
Figure 6.12: Temperature and Relative Humidity over the Sierra Nevada Mountain Range.
9
9
Figure by Scott Crosier is licensed under
CC BY-NC-SA 4.0
13
|
Lab 6: Atmospheric Humidity
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