Lightning in the Peaks: Lapse Rates and Stability : GPH 112: Intro to Phys Geography Lab (2024 Sprin
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112
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Apr 3, 2024
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7
Uploaded by DoctorPartridge4095
3/31/24, 11
:
18 PM
Lightning in the Peaks: Lapse Rates and Stability : GPH 112: Intro to Phys Geography Lab (2024 Spring)
Page 1 of 7
https://canvas.asu.edu/courses/178831/quizzes/1343120
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module_item_id=12797103
Lightning in the Peaks: Lapse Rates and
Stability Due Feb 14 at 11:59pm
Points 5
Questions 1
Available after Jan 21 at 12am
Time Limit None
Instructions
As the heated air rises off the surface, it cools according to temperature lapse rates.
These lapse rates are simply the rate that temperature changes with height in the atmosphere. You
may have worked with these lapse rates in the previous labs this semester, but below you can find a
description of the lapse rates used in this lab.
Dry Adiabatic Lapse Rate
– imagine filling a giant balloon filled with air at the surface, and then you
drag the balloon up into the atmosphere. The balloon will expand because of lower air pressure, and
the molecules inside the balloon will be further apart. This results in cooling at a lapse rate of about
10 ˚C per 1000 meters when the air is “dry” (no clouds). Moist (wet) Adiabatic Lapse Rate
– imagine that your rising giant balloon cooled enough to reach
the dew point (the temperature when the water vapor in the atmosphere condenses and starts to form
cloud droplets). When condensation occurs, heat is released (latent heat of about 580 calories per
gram of water). This latent heat release slightly offsets the dry adiabatic cooling from expansion, and
so the temperature change is a bit less. Just how much less depends on how much water is
3/31/24, 11
:
18 PM
Lightning in the Peaks: Lapse Rates and Stability : GPH 112: Intro to Phys Geography Lab (2024 Spring)
Page 2 of 7
https://canvas.asu.edu/courses/178831/quizzes/1343120
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module_item_id=12797103
condensing. This first question looks specifically at the lifted condensation level (LCL). This is the height that the
air parcel is cooled dry adiabatically to dew point. This height in the atmosphere is the lowest possible
height with the present conditions that clouds could form. You calculate this height by taking your
starting temperature and lifting it up into the atmosphere. When the parcel rises, it will cool
adiabatically as it expands. First, at the dry adiabatic lapse rate if it is warmer than dew point, and
then change to the wet adiabatic lapse rate at the LCL, as condensation begins and clouds form.
EXAMPLE QUESTION
Fast travel to Flagstaff (35.1983 N , -111.6513 W) .
With a dew point of 9.5
C, what is the height of the
lifted condensation level and air temperature
3000m above the surface if the air there is lifted
adiabatically? In this example, the air parcel starts above dew
point, so you use the dry adiabatic lapse rate of
10
C per 1000m or 5
C per 500m. By cooling at
this rate, the air parcel reaches dew point (9.5oC)
at 3565 meters. This is the lifted condensation
level. Now, since the parcel has reached dew point,
the air parcel will cool at the wet adiabatic lapse
rate, as clouds (condensation) is occurring. When
this condensation occurs, some extra heat is
transferred into the air temperature from this phase
change from gas to a liquid. Above this height, the
parcel is forming clouds, and cooling at 3
C/500m.
ANSWER: The LCL occurs at 3565 meters and the
air temperature is 0.5
C 3000m above Flagstaff. That is the lowest point that clouds can possibly
form. Try to imagine the impact that different humidity would have on this example. In drier circumstances,
where would the LCL be? The second part of this question looks at atmospheric stability. Depending on the air temperature that
the air parcel finds itself rising into, the air parcel will either continue to rise, stagnate, or sink back
towards the surface. For this lab, we will primarily just be focusing on stable or unstable
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3/31/24, 11
:
18 PM
Lightning in the Peaks: Lapse Rates and Stability : GPH 112: Intro to Phys Geography Lab (2024 Spring)
Page 3 of 7
https://canvas.asu.edu/courses/178831/quizzes/1343120
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module_item_id=12797103
environments. If an air parcel is warmer than the surround environmental air temperature, it is described as
unstable. Think of this like a hot air balloon on a cool morning. Warm air is less dense and more
buoyant than cold air, so the air parcel (or hot air balloon) rises quickly up into the air. This allows the
air parcel to continue to cool until it reaches dew point and form clouds. If an air parcel is cooler than the surrounding environmental air temperature, it is described as stable.
The air is denser, and less buoyant than the surrounding air, and it will tend to sink back towards the
surface. This type of environment leads to sunny skies, as the air parcels cannot continue to rise and
reach dew point to form clouds. The clouds that form as a result of atmospheric stability are directly linked with the amount of
moisture found in the atmosphere. The air is more likely to be stable if the dew point is lower, leading
to less heat through condensation in the air parcel. This stable atmosphere is more likely in the pre-
monsoon months of May and June, while unstable and conditionally unstable conditions occur when
more moisture is present in the atmosphere. That is because both the dew point, as well as the
environmental lapse rate change as summer progresses.
You can see an example of the stability conditions below for a lapse rate parcel location calculated
from the example above. You’ll have your own environmental lapse rate and location to consider
when making your own calculations. But you will have to make the same selection. You will have to
pick whether A or B is the environmental condition that will be the most favorable for thunderstorm
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