Download Air Pressure Workbook

PHYSICAL GEOGRAPHY GPH111
LAB G - ATMOSPHERE AND CLIMATE LAB I
TEMPERATURE AND PRESSURE
Introduction
This lab will provide the student with the opportunity to become familiar with the concepts
introduced in Chapter 5. Students will review the elements pressure and its effect on global
circulation and weather patterns.
Materials needed: textbook, atlas, pencil, calculator, colored pencils, and World Map (last page)
Part II. Atmospheric Pressure and Wind
The atmosphere (air) does weigh something and this weight exerts force or pressure on all
surfaces. At Sea Level air presses down at an average of 14.7 lbs. per square inch. At Phoenix
(1,092 ft. above Sea Level) the atmospheric pressure, or weight of the air, is less than 14.7 lbs.
per square inch because there is 1,092 fewer feet of atmosphere above the city. Around the
globe, air is either rising (warm air) or sinking (cool air), in response to temperature variations.
If air is sinking, the weight of the atmosphere above is increased and the atmospheric pressure is
said to be high (high pressure). Conversely, if the surrounding air is rising, the weight of the
atmosphere above is decreased and the atmospheric pressure is low (low pressure). If air is
rising in some places and sinking in others, the sinking air must flow back to places where the air
is rising in order to balance global atmospheric pressure. Thus, air always flows from areas of
high pressure (sinking air) to areas of low pressure (rising air). This horizontal movement of air
is known as advection, or wind. Atmospheric pressure, also known as barometric pressure, is
measured with a barometer. Different types of barometers are used and they measure pressure in
different units. Some
barometers measure
pressure in lbs. per
square inch or in inches
of mercury, as differing
weights of air will push
mercury up a glass tube
to differing heights.
Other barometers
measure the pressure of
the atmosphere in SI
units called millibars
(mb). The average
atmospheric pressure
at Sea Level on earth is
14.7 lbs. per square
inch, 29.92 inches of
mercury or 1013.25
millibars (mb).
Image source: Christopherson, R.W., 1994: Geosystems: An Introduction to Physical Geography
G-1
PHYSICAL GEOGRAPHY GPH111
A. Using the graph paper below, plot the data from Table G-1. These data are pressures in
relationship to altitude for a “Standard Atmosphere”. Connect your points with a line. The
curve you will draw shows how pressure changes as altitude increases.
Table G-1
Standard Barometric Pressures at specified
heights above sea level
Height (km)
Pressure (mb)
0
1013.25
1
899
3
701
5
540
7
411
10
264
20
55
30
12
40
3
50
1
1. Using your own words, describe what you see in terms of the relationship between height
and pressure. Be sure to comment on the rate of change with altitude.
_____________________
___________________________________________________________________________
___________________________________________________________________________
2. Using the following locations and what you learned above, answer the following.
a. Which location would have the lowest standard barometric pressure? ________________
b. Which location would have the highest standard barometric pressure? _______________
Lewis Hills, Newfoundland (2,672 ft)
Mt. Hood, Oregon (2.13 miles)
Humphrey’s Peak, Arizona (12,633 ft)
Cheyenne, Wyoming (6,100 ft)
Mt. McKinley, Alaska (20,320 ft)
Mt. Mitchell, North Carolina (2,040 meters)
G-2
PHYSICAL GEOGRAPHY GPH111
B. Air flows from areas of high pressure to areas of low pressure. The direction of this flow is
influenced by three variables: Pressure Gradient, Coriolis Effect and Friction.
Remember that pressure gradient is the force that causes air to move from areas of high
pressure to areas of low pressure. Once the air is moving, Coriolis will then act upon it
causing it to be deflected from its path of motion.
Pressure gradient is related to wind speed. In
regions where the pressure gradient is weak
(small change in pressure over distance = wide
spacing between isobars), the winds are weak;
where the pressure gradient is steep (large
change in pressure over distance = closely
spaced isobars), the winds are strong.
This relationship is depicted in Figure G-4.
Figure G-4
Using the diagrams below, indicate with an arrow, the direction of movement of a parcel of air
in the Northern Hemisphere under the following conditions (variables): Fig G-5: influenced by
Pressure Gradient only and Fig G-6: influenced by Pressure Gradient and Coriolis Effect.
Figure G-5: Pressure Gradient only
Figure G-6: Pressure Gradient
and Coriolis Effect
C. Using Figure G-5, examine the pressure gradient between 1004 mb and 998 mb and the
pressure gradient between 998 mb and 990 mb. Describe the difference between these two
regions. Hint: Review the relationship between isobar spacing, pressure gradient and wind
speed.
G-3
PHYSICAL GEOGRAPHY GPH111
D. How does air flow if pressure gradient is the only force? (across the isobars at a right angle,
parallel to the isobars, across the isobars at a 45° angle). Circle the correct answer.
Diagram wind direction associated with the following pressure cells influenced by pressure
gradient only. (NO Coriolis Effect and NO Friction).
Northern Hemisphere
Southern Hemisphere
E. How does air flow if pressure gradient and coriolis are the only forces? (across the isobars at
a right angle, parallel to the isobars, across the isobars at a 45° angle). Circle your answer.
Diagram wind direction associated with the following pressure cells influenced by pressure
gradient and Coriolis effect (NO Friction).
Northern Hemisphere
Southern Hemisphere
F. How does air flow if pressure gradient, coriolis, and friction are the forces? (across the
isobars at a right angle, parallel to the isobars, across the isobars at a 45° angle).
Diagram wind direction associated with the following pressure cells influenced by pressure
gradient, coriolis effect and friction.
Northern Hemisphere
Southern Hemisphere
G-4
PHYSICAL GEOGRAPHY GPH111
G. Why is friction so important in determining wind direction? _______________________
________________________________________________________________________
H. Which low pressure cell has the steeper (stronger) gradient? (left or right picture) _________
I. Which low pressure cell would have the stronger/faster winds? Why? ________________
__________________________________________________________________________
Part III. Global Pressure and Wind Systems
The following questions refer to the World Map (attached - see last page). Use this map to
construct a generalized global circulation model for an Equinox. Then answer the associated
questions.
A. Draw in the Intertropical Convergence Zone (ITCZ).
1. Is this a high pressure or low pressure zone?
2. Why?
3. Is the air rising or sinking?
B. Draw in the Subtropical High (STH) pressure zones and their five main cells of high
pressure.
1. Why is the air sinking here?
2. Use the Goode’s World Atlas 21st edition pp 18-19 (top images) and compare the size and
location of the STH cells in the Northern Hemisphere with those in the Southern Hemisphere
in January and July.
3. Which hemisphere experiences less change?
4. Why?
G-5
PHYSICAL GEOGRAPHY GPH111
C. Draw in the Trade Winds. From which global pressure system do the Trade Winds in the
Northern Hemisphere originate?
D. Draw in the Westerlies.
1. Describe the general flow pattern of the Westerlies.
2. Is there a difference between surface air patterns and those in the upper atmosphere?
E. Mark the location of the Subpolar Lows. Why is air rising here?
F. Draw in the Polar Easterlies. What is the relative temperature of these winds?
G. Mark the location of the Polar Highs. Why is there high pressure here?
Is the air sinking or rising here? __________________
H. Draw arrows on the world map denoting the general direction of the major ocean currents.
Draw warm currents in red and cold currents in blue.
I. Using the 3-cell model (with no seasonal shifting) for the general circulation of the
atmosphere, give the prevailing wind direction for the following locations. Use the atlas to
determine the latitude and longitude for each location, then answer the question.
1.
2.
3.
4.
5.
Skjálfandafljót River, Iceland (______°N, _____°W) = ______________________
Yozgat, Turkey (______°N, _____°E) = __________________________________
Kimba, Australia (______°S, ______°E) = ________________________________
Goundam, Mali (_____°N, ______°W) = _________________________________
Molepolole, Botswana (_____°S, ______°E) = _____________________________
G-6
PHYSICAL GEOGRAPHY GPH111
J. Name five countries dominated by the Westerlies.
K. Name five countries dominated by the Trade Winds.
L. Name three countries that are influenced by the ITCZ in June but not in December.
M. Why do the global pressure zones and wind systems shift north and south during the year?
N. Phoenix, Arizona is located at approximately 33° N. What global pressure zone or wind
system dominates the region May through September? What type of weather does the region
experience? What happens to this pressure zone or wind system October through April?
What changes in weather would be experienced?
O. Using the circulation diagram for the month of June (below), diagram the corresponding
situation for the month of December and an Equinox date. Show the shift of the ITCZ
and the new locations of the subtropical high pressure zones.
JUNE
STH
ITCZ
STH
⇑ ⇑
60ºN___________⇓__30ºN_____⇒___⇐_____0º_____⇓_________30ºS_____________60ºS
NE Trades
SE Trades
EQUINOX
60ºN______________30ºN________________0º________________30ºS______________60ºS
DECEMBER
60ºN______________30ºN________________0º________________30ºS______________60ºS
G-7