Lab 3 - Munson
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Kent State University *
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Feb 20, 2024
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Lab 3: Atmospheric Pressure and Winds
Instructions
Watch the lectures on atmospheric pressure, winds and Coriolis Effect, and
atmospheric circulation, and watch the video on atmospheric pressure. After you have
reviewed the lectures, notes, and the video, use this document to work through your lab.
Once you have finished answering all questions in this lab, submit your answers online
in the link titled “Lab 3 – Atmospheric Pressure and Winds”. After the due date when
your lab is graded, you will be able to review your lab and answers. When you first
submit your lab, your score may appear low. Keep in mind that your lab instructor will
need to grade your lab, especially the written responses. The computer can
automatically grade and score multiple choice, matching, and true/false questions. Any
written or essay responses will need to be graded by your instructor. Once your lab
instructor grades those questions, your lab grade will be updated to the correct grade.
Goals
o
Understand the concept of atmospheric pressure and how it plays a role in
weather.
o
Interpret graphs to measure how atmospheric pressure changes with height
above the Earth’s surface.
o
Identify high and low pressure centers on a weather map.
o
Understand and analyze the relationship of pressure to winds.
o
Interpret wind direction and speed using a weather map.
Key Terms / Concepts
Barometric Pressure Millibar
Standard Sea-level Pressure Isobar
Coriolis Effect Cyclone
Anticyclone Pressure Gradient Force
Once you have completed questions 1 through 40 below, fill in your answers in the
assessment link online in module 4 folder titled “Lab 3 – Atmospheric Pressure and
Winds”.
Instructions
The purpose of this lab is to introduce you to the concept of atmospheric pressure and
to become familiar with the relationship of pressure to winds. This lab will focus on
constructing and interpreting graphs to measure how atmospheric pressure changes
with height above the Earth’s surface. Each question below is worth .5 each. Some
questions require you to use proper units. You will not be given proper credit if you
choose to not use proper units for the questions below.
Atmospheric Pressure and Altitude
The Earth’s atmosphere is a compressible fluid comprised mainly of gases that are
pulled to the surface by gravity. The weight of the atmosphere produces a force on the
Earth’s surface called
pressure
, and the standard unit to measure atmospheric
pressure is the
millibar
(mb). The average atmospheric pressure is 1013.2 mb, which is
equivalent to 14.7lb/sq. inch. This is referred to as
standard sea-level pressure
and it
varies for a particular time or place on Earth. Also, pressure determines wind speed and
direction and affects whether or not we are going to have precipitation.
The density of gas molecules in the atmosphere is greatest at the Earth’s surface (sea
level) and thins as you travel higher in the atmosphere (Figure 1). At 5.6 kilometers (km)
(equivalent to 3.47 miles) above the Earth’s surface, approximately one-half of the total
mass of the atmosphere will be below you. At that height, fifty percent of the
atmosphere will be above you. If you move another 5.6 km to 11.2 km (equivalent to 6.9
miles) above the earth’s surface, approximately one-fourth of the atmosphere will be
above you, and three-quarters will be below you. The atmospheric mass decreases at a
rate of 50 percent every 5.6 km you increase in height. In general, as you increase in
elevation, there is less atmospheric mass and a decrease in atmospheric pressure.
Figure 1
Imagine yourself standing at several elevations (refer to
column 1
) when you fill in your
answers in Table 1 below. Determine the atmospheric mass above and below for each
elevation above sea-level in Table 4.1. The first two lines (responses in purple) have
been completed for you. So, when you look at the percent atmospheric mass above in
column 2
at being 100, this means as you stand at 0.0 km (surface of the Earth), 100
percent of the atmospheric mass is above you and 0% is below you (refer to
column 2
).
To get values in
column 3
, you will use the equation (100 – mass above). The
atmospheric pressure on the surface is 1013.2 mb (
column 4
).
When you are standing at 5.6 km in elevation, you already know that half the
atmospheric mass is above you and half is below you. So, to get the
column 2
(percent
atmospheric mass above), you divide by half, so 100 divided by 2 equals 50. You will
divide by two all the way up in
column 2
. So, when you stand at 5.6 km above the
earth’s surface, 50 % of the atmosphere is above you. How much is below you now? If
50% is above you, 50% is below (this totals to 100%). The formula for the
third column
is 100 – mass above (100 - 50 = 50). So, at 5.6 km, 50% of the atmospheric mass is
below you. What about atmospheric pressure? You would divide each value up by two
in
column 4
. So, 1013.2 mb divided by 2 equals 506.6 mb.
Fill in the table below. You will notice that the blank cells have numbers encased in
parentheses. The numbers will correspond to the lab assessment (and questions below)
when you are ready to submit your answers online. Use proper units in (% or mb) for
the questions below. Your responses should go to one decimal point, if needed. (refer to
column 4 answers below). You can round your answers if, for example, you have an
answer of 15.65, you can round to 15.7. If you have 15.43, you can submit your answer
as 15.4. Note: You will have decimal points for columns 2 and 3 and 4 as you work
through the table.
Column 1 Column 2 Column 3 Column 4
Height
(km)
Percent
Atmospheric Mass
Above
Percent
Atmospheric Mass
Below
Atmospheric
Pressure (mb)
33.6
1.6
98.4
15.8
28.0
3.1
96.9
31.7
22.4
6.3
93.8
63.3
16.8
12.5
87.5
126.7
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11.2
25
75
253.3
5.6
50%
50%
506.6 mb
0.0
100%
0%
1013.3 mb
Table 1. Atmospheric Mass and Pressure
Use your answers here to fill in the assessment online.
(1) What is the atmospheric mass above you at 11.2 km? ______________ (.5 point)
(2) What is the atmospheric mass below you at 11.2 km? ______________ (.5 point)
(3) What is the atmospheric pressure at 11.2 km? ______________ (.5 point) (4)
What is the atmospheric mass above you at 16.8 km? ______________ (.5 point) (5)
What is the atmospheric mass below you at 16.8 km? ______________ (.5 point) (6)
What is the atmospheric pressure at 16.8 km? ______________ (.5 point) (7) What is
the atmospheric mass above you at 22.4 km? ______________ (.5 point) (8) What is
the atmospheric mass below you at 22.4 km? ______________ (.5 point) (9) What is
the atmospheric pressure at 22.4 km? ______________ (.5 point) (10) What is the
atmospheric mass above you at 28.0 km? ______________ (.5 point) (11) What is
the atmospheric mass below you at 28.0 km? ______________ (.5 point) (12) What is
the atmospheric pressure at 28.0 km? ______________ (.5 point) (13) What is the
atmospheric mass above you at 33.6 km? ______________ (.5 point) (14) What is
the atmospheric mass below you at 33.6 km? ______________ (.5 point) (15) What is
the atmospheric pressure at 33.6 km? ______________ (.5 point)
16. Write a brief paragraph to describe the trend in atmospheric mass and pressure as
you increase in altitude from the Earth’s surface. (.5 point)
As you increase in altitude from the Earth’s surface, the atmospheric pressure and
mass decreases.
Pressure and Winds
Differences in pressure from one place to another (at the same elevation) result in a
pressure gradient
. Put another way, the pressure gradient is the rate of change of
atmospheric pressure between two points at the same elevation, and are the driving
force of winds on Earth. A strong pressure gradient occurs when there is a large
difference in pressure over a short distance. The winds will be strong. A weak pressure
gradient results in weaker winds. The lines on a map that connect points of equal
barometric pressure are called isobars. Remember, the isobar lines never cross one
another. The strength of the pressure gradient is illustrated by the spacing of the isobars
on a weather map. A steeper pressure gradient will be illustrated by closer spacing of
isobars on a map and the winds will be strong. The farther apart the isobar lines are
from one another results in a weak pressure gradient, and the winds will be weak.
Winds have a tendency to flow down the pressure gradient away from high pressure to
low pressure.
On the diagram below you will see isobars (indicated as lines) and atmospheric
pressure units in millibars (mb). Alongside and within the diagram you will see alphabet
letters in red. Answer the questions below the diagram.
Multiple Choice:
The letter choices on the diagram will only be used one time in the
questions below.
17. On the diagram above, which area given by letter, indicates the area of highest
pressure? A) Letter A (.5 point)
B) Letter E
18. On the diagram above, which area given by letter, indicates the area of lowest
pressure?
A) Letter A
(.5 point)
B) Letter E
19. On the diagram above, which area given by letter, indicates the area of strongest
winds?
A) Letter B
(.5 point)
B) Letter C
C) Letter D
20. On the diagram above, which area given by letter, indicates the area of a weak or
shallow pressure gradient? (.5 point)
A) Letter B
B) Letter C
C) Letter D
21. On the diagram above, which area given by letter, indicates the area of a strong
pressure gradient? (.5 point)
A) Letter B
B) Letter C
C) Letter D
Coriolis Effect
As stated in the previous section, the pressure gradient is the driving force of winds.
The winds are directed perpendicular to isobars away from high pressure to low
pressure. The wind always blow from high to low. However, the winds do not move
perpendicular to isobars due to the Coriolis effect. Once air has been set in motion by
the pressure gradient force (PGF), it undergoes an apparent deflection from its path, as
seen by an observer on Earth. The Coriolis effect defined is an apparent deflection of
moving bodies, such as winds, caused by the Earth’s rotation. The winds in the
Northern Hemisphere tend to be deflected to the right, and deflected to the left in the
Southern Hemisphere. The air movement at the surface of the Earth is at an angle
across isobars toward low pressure (more on this below).
On a weather map, isobars are closed circles that illustrate areas of high and low
pressure. A low pressure cell (cyclone) illustrates where air is rising (ascending). High
pressure cells, or an anticyclone illustrates where air is sinking (descending). As winds
move toward the center of low pressure (cyclone) in the northern hemisphere, they
circulate counter-clockwise. Winds circulate clockwise in the northern hemisphere
around high pressure cells (anticyclone). Conversely, in the southern hemisphere, the
coriolis effect deflects moving bodies such as winds to the left, so circulation around
high pressure (anticyclone) is counter-clockwise and clockwise around low pressure
(cyclone).
An air parcel will move from high pressure (anticyclonic) to low pressure (cyclonic)
because of the PGF, and is deflected by the Coriolis force (effect) which is to the right in
the northern hemisphere (to the left on the southern hemisphere). As the wind gains
speed, the deflection increases until the Coriolis force equals the pressure gradient
force. At this point, the wind will be blowing parallel to the isobars. So, when this
happens, the wind is referred to as a geostrophic wind, an upper level wind in which
friction is not an issue (Figure 2) below.
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Figure 2
Image Source: http://www.goes-r.gov/users/comet/tropical/textbook_2nd_edition/media/graphics/forces_winds.jpg
The surface of the Earth exerts a frictional drag on the air blowing just above it. At or
near the Earth’s surface, where the wind encounters obstacles like trees, buildings, and
mountains, for example, this frictional drag slows the wind down, keeping it from
blowing as fast as the wind aloft. Actually, the difference in terrain conditions directly
affects how much friction is exerted. A calm ocean surface is pretty smooth, so the wind
blowing over it does not move up, down, and around any features. By contrast, hills,
mountains, and forests act to slow the wind down. The coriolis effect and pressure
gradient are no longer in balance so the wind (indicated by real wind in Figure 3) will
flow across isobars at an angle to an area of low pressure.
Figure 3
Image Source: http://www.goes-r.gov/users/comet/tropical/textbook_2nd_edition/media/graphics/forces_winds.jpg
Image Source: https://wxgeeknation.wordpress.com/2011/06/06/hot-today-back-to-you/
Figure 4
Using Figure 4 above, identify each letter to the questions below. You will only use one
illustration with its corresponding alphabet letter only once in the following questions.
22. Using Figure 4, which illustration with its corresponding letter illustrates anticyclonic
flow on the Earth’s surface in the northern hemisphere? (.5 point)
A) Letter A
B) Letter B
C) Letter C
D) Letter D
23. Using Figure 4, which illustration with its corresponding letter illustrates cyclonic flow
on the Earth’s surface in the southern hemisphere? (.5 point)
A) Letter A
B) Letter B
C) Letter C
D) Letter D
24. Using Figure 4, which illustration with its corresponding letter illustrates anticyclonic
flow on the Earth’s surface in the southern hemisphere? (.5 point) A) Letter A
B) Letter B
C) Letter C
D) Letter D
25. Using Figure 4, which illustration with its corresponding letter illustrates cyclonic flow
on the Earth’s surface in the northern hemisphere? (.5 point)
A) Letter A
B) Letter B
C) Letter C
D) Letter D
Atmospheric Pressure, Winds, and Circulation Patterns.
Using the model below (Figure 5), identify the following pressure, wind, and circulation
patterns. You will only use each letter on the illustration below one time. Each question
can have one letter correct or two letters correct. When you answer on the assessment,
use capital letters for your written response and put a space in between the letters if
there are 2 letters correct on the question (Example: M N)
26. Using Figure 4.5, identify by letter or letters the Subtropical high pressure belt(s).
(.5 point) D H
27. Using Figure 4.5, identify by letter or letters the Equatorial low pressure belt(s).
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(.5 point) F
28. Using Figure 4.5, identify by letter or letters the Subpolar low pressure belt(s).
(.5 point) B J
29. Using Figure 4.5, identify by letter or letters the Westerly winds.
(.5 point) C K
30. Using Figure 4.5, identify by letter or letters the Polar Easterly winds.
(.5 point) A I
31. Using Figure 4.5, identify by letter or letters the Northeast trade
winds. (.5 point) E
32. Using Figure 4.5, identify by letter or letters the Southeast trade
winds. (.5 point) G
Map Interpretation
The map below is an example of barometric pressures (mb). The lines on the map are
isobars indicating lines of equal barometric pressure in millibars (mb) for the eastern half
of the United States and parts of Canada and Mexico. Each line (isobar) represents a
specific barometric pressure at a particular time/day. For example in the map below, the
barometric pressure in San Antonio, Texas is approximately 1032 mb and Oklahoma
City, Oklahoma has a barometric pressure reading of 1036 mb. The pressure is
increasing as you drive north from San Antonio to Oklahoma City.
Image Source: http://mathsheet.ifcpnice.com/isobars-and-air-pressure-worksheet-answers/
33. What is the approximate lowest barometric pressure (isobar reading) on this
map? (.5 point) 1004
34. In regards to question 33, is this lowest pressure reading located in the United
States, Canada, or Mexico? (.5 point) canada
35. What is the highest barometric pressure (isobar reading) on this map? (.5 point)
1036
36. In regards to question 35, is the highest pressure reading located in the United
States, Canada, or Mexico? (.5 point)
US
37. What is the barometric pressure in or near Kent, Ohio? Use nearest isobar
reading. (.5 point) 1032
38. In regards to question 37, is the barometric pressure at Kent, OH higher or lower
than Washington DC? (.5 point) higher
39. Which area is experiencing the steepest pressure gradient, Point A, B, or C ?
(.5 point) A
40. Is point A or point C experiencing the weakest pressure gradient? (.5 point) C
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