ESC 1000L Broward College Barometric Pressure Lab Report

Barometric PressureLab #6
Objective
• Students should be able to understand barometric pressure units and
isobars, and identify barometric pressures using a weather map.
• Students should be able to draw a reasonable barograph.
Lab materials
• Lab # 6 (Pages 67-74 in lab book) – A digital copy of this lab activity is
also available in your D2L class shell.
• 2 Instructional videos in your D2l lab shell
• 1 Month of actual weather maps of the United States for the month
of March 1993 – PDF file in D2L class shell
Lab instructions
• Before starting• Read all of Exercise 6 – Barometric pressure in your lab manual
• Watch the two instructional videos in your D2L
• Download the digital (Word document) file to record your data and
submit to your Professor
• Lab submission is to be made through D2L- Upload and submit Lab 6
to assignment 6 in D2L by 11pm on Thursday March 26th
Deliverables
Activities to be graded-
• Exercise 1 (page 71) : question 1- fill in the blank atmospheric pressure values
• Exercise 1 (page 71) : question 2 – isobar map
• Exercise 1 (page 72) : question 3 – isobar map of the United States
• Exercise 2 (page 73-74) : Use the blank graph on Page 74 to draw barograph based on
March 1993 weather maps provided.
• Exercise 3 (page 73): Since we are not in the classroom, find the barometric pressure in
your area using the web site link on page 73. Is this pressure high,
low or standard?
How to submit lab for grading
• Upload the completed word document file to D2L assignment #6
• Remember to press submit.
EARTH SCIENCE
Barometric Pressure
OBJECTIVE : To be able to read barometers, understand barometric pressure units and
isobars, find barometric pressures using a weather maps to draw a reasonable barograph.
MAIN CONCEPT: In 1643 the Italian scientist Evangelista Torricelli (1608-1647)
invented the most important of weather instruments, the barometer. This instrument allowed
direct measurement, for the first time, the weight of the air pressing down from above. This
value has become known as the barometric pressure. Pressure is defined as force per unit area.
Torricelli filled a glass tube, which was closed at one end with liquid mercury (symbol Hg). The
open end of the tube was then placed in a vessel partially filled with mercury. The mercury in the
tube falls until the weight of the mercury is balanced by the atmospheric force exerted on the
mercury in the open vessel (fig 1). This column of mercury measured about 30 inches high.
If colder, heavier, denser air should move into the area, the air would exert a stronger downward
push on the mercury in the vessel and thus force the mercury in the tube to rise. We say the
barometer is rising. On the other hand warmer, lighter, less dense air will allow the mercury in
the tube to drop a little. We then say the barometer is falling. It is common to use the height of
the mercury column to express the current barometric pressure. 29.92 inches (760 millimeters)
of Hg is considered to be the average pressure at sea level. Thus 29.92 inches of Hg is the value
of one (1) atmosphere.
Although the weather forecast seen on evening television channels usually state the barometric
pressure in inches of Hg, meteorologists prefer using actual pressure units. The most commonly
used unit in the United States is the millibar. 1013 millibars is equal 29.92 inches of Hg which
equals one (1) atmosphere.
Although the mercury barometer invented by Torricelli is still the standard pressure measuring
instrument used today, a smaller more portable and less expensive instrument was developed.
The aneroid (from Greek without liquid) barometer consists of a metal chamber from which
most of the air has been removed (fig 2). A spring prevents the chamber from collapsing. The
chamber is now very sensitive to pressure changes. As the pressure outside changes the chamber
itself either expands or contracts accordingly. Usually a clock face dial is used to reflect these
changes.
Figure 1. MERCURY BAROMETER
Figure 2. ANEROID BAROMETER
One nice advantage of the aneroid barometer is its capability, with the use of a pen, to record a
written record of the changing pressure. Such a record is called a barogram (Figure 3) while the
recording instrument is called a barograph. A barograph is simply a recording aneroid
barometer (Figure 4).
Miami International Airport-May 2013
Figure 3. Barogram
Figure 4. Barograph
ISOBARS, PRESSURE GRADIENT and WIND
At any given time the air pressure is never the same over the entire earth but varies from place to
place and from time to time. Consequently, in order to interpret weather conditions, a knowledge
of the distribution of atmospheric pressure is necessary. This is best shown on weather maps
through the use of isobars. Isobars are lines on a weather map which connects points of equal
pressure (Figure 5). The amount of change in pressure over distance is known as the pressure
gradient. Closely spaced isobars indicate a steep pressure gradient and strong winds. Isobars
spaced far apart indicate a weak pressure gradient and light winds. Note in figure 4 the closely
spaced isobars over eastern US and hence strong winds there and the widely spaced ones over
western US and thus light winds.
DATE _____________
Figure 5. Weather map with isobars.
Barometric Pressure
NAME__________________________
DATE _____________ Lab Section ________
Exercise 1: Be able to draw isobars on a map with known points of atmospheric pressure.
Procedure: If you were to drive from a location of high atmospheric pressure (let’s say
1020mb) to a location of lower atmospheric pressure (perhaps 1012mb) you would experience a
pressure drop of first 1019mb then 1018, 1017, 1016, etc. until finally 1012. Using this line of
thinking make a reasonable guess of the pressure values for the points not given below.
Question 1.
1013
1005
______
1017
1004
1018
1006
______
1012
1008
______
1014
1016
Question 2.
Using the knowledge you now obtained, draw the 1012 isobar in the figure below. The 1016
isobar is already drawn as a guide line. Remember, isobars connect points of equal pressure.
NOTE: isobars cannot cross each other.
1009
1011
1008
1011
1010
1017
1013
1011
1018
1011
1015
1015
1016
Question 3.
Using the technique you already learned draw the 1010 and 1020 isobars on the US map below.
Label each isobar. When complete proceed to Exercise 2.
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Exercise 2: Construct a barogram from isobars from the weather maps provided.
Materials: Set of weather maps from MIAMI HERALD for the month of march, 1993
(provided by instructor); red pencil; blue pencil
Procedure: Using the weather maps provided and the technique you just learned, “read” the
barometric pressures for both Miami and New York City for the month of march, 1993.
Using a red pencil for Miami and a blue pencil for New York City plot the pressures for each day
in March with a point in the appropriate place on the blank barogram. Complete the graph by
connecting the dots using the same colored pencils. Note that the isobars are labeled in millibars.
Further note that adjacent isobars are spaced 4 millibars apart. Since isobars may not pass
directly through these cities some interpretation between isobars is necessary.
Exercise 3: Read the current barometric pressure from the mercury barometer in your area to
the nearest 1/10inch of Hg. Record your findings.
Barometric Pressure = ___________ inches of Hg
Is this pressure considered high; standard; low? ___________
NOTE: Standard is considered 29.92 in Hg
FYI – For current weather condition throughout the State of Florida search:
http://www.usairnet.com/weather/maps/current/florida/weather/
NAME ____________________________
Date ____________________
Millibar
BAROGRAM: New York City (blue/black); Miami (red) – March, 1993
Days of the Month
Lab Section _____________________