IDS 102
Measurement of the Atmosphere
This quarter you have learned about the concepts of heat, temperature, force, pressure,
vapor pressure, and relative humidity. It is time to apply those important concepts to the
Earth’s atmosphere.
One of the methods used to study the atmosphere is a Rawinsonde sounding. This is a
radio transmitter that is carried up into the atmosphere by a helium balloon as illustrated
in this NOAA photo:
from: http://www.ncdc.noaa.gov/ol/climate/climateresources.html
These devices record the height of the instrument (in meters above sea level), the air
temperature (in C°), the air pressure (in hectopascals, which is essentially the same as
millibars), the dew point (in C°), and a tracking station determines the wind direction (in
compass degrees – N is 0, E is 90, etc.) and speed of the wind by tracking the balloon (in
meters/sec). (The balloons deflate and equipment is returned to the Earth by a parachute.)
We are going to analyze some of this sounding data collected by the National Ocean and
Atmosphere Agency to better understand the Earth’s atmosphere. We have data from a
summer day (July 1) and a winter day (January 13). We have data from stations from the
Arctic Ocean in the north to the Florida Keys in the south and data from Charleston,
South Carolina on the east to Quileute, Washington (near Forks) on the west. These data
sets are found as Excel files on the IDS web site.
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For the next part you will need access to the Internet and Excel. Go to:
http://www.ivygreen.ctc.edu/ids/102/IDS102.htm
Go the modules page and select the Sounding link
As you open the files, you may get a message indicating that the file contains a
“macro.” This is a short program that we used to aid in graphing the data. Your
understanding of macros is not important and you will not be expected to create or
produce a macro in the future. Click on either the disable or the enable, for our
purposes, it does not matter!
To save some time, we have graphed the data for you. To access the graphs click on the
Chart 1 for a graph of height above sea level versus atmospheric pressure and Chart 2 for
a graph of height above sea level versus air temperature and dew point.
**Special Note about the graphs we will use in this section:
Up to this point in IDS 101 and 102 we have used the expression, “as a function of” to
indicate which axis to use in graphing data. If we have a graph of distance as a function of
time, the distance values would be on the y-axis and the time values would be on the x-axis.
We can say the position of the object depends on the time we view the situation.
In this module we would like to have the height variable along the y-axis for the obvious
reason that we want to visually see the variation of pressure at different heights. If we asked
you to graph height as a function of pressure, you would put the height variable along the yaxis, but the expression has no meaning because it is pressure that depends on height, not
the other way around.
So, we are introducing a new terminology—height versus pressure. The first variable listed
will be along the y-axis and the second along the x-axis, but there is no implication of
dependence of one variable to the other. For example we could graph orange production in
Florida versus inches of snow in New York, but there is not necessarily a cause and effect
relationship.
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The various stations are listed below. We want you to explore the data and the graphs and
answer the questions below:
List of Sounding Locations: (to see a complete list of all the stations NOAA runs, see:
http://www.arl.noaa.gov/ready/sonde.html
ABQ – Albuquerque, New Mexico
ANC- Anchorage, Alaska
BIS- Bismarck, North Dakota
BNA- Nashville, Tennessee
BOI- Boise, Idaho
BUF- Buffalo, New York
CHS- Charleston, South Carolina
CRP- Corpus Christi, Texas
DEN- Denver, Colorado
EYW- Florida Keys
MFR- Medford, Oregon
NKX- San Diego, California
OAK- Oakland, California
OAX- Omaha, Nebraska
OTX- Spokane, Washington
REV- Reno, Nevada
RIW- Riverton, Wyoming
SLC- Salt Lake City
SLE- Salem, Oregon
TFX- Helena, Montana
UIL- Quileute, Washington
WSE- Edmonton, Alberta, Canada
YEV- Arctic Sea Station, Northwest Territories, Canada
YYQ- southern shore of Hudson Bay, Canada
Answer the questions below as you examine the sounding data and graphs. Look at data
and graphs from several different stations (north vs. south, west vs. east) as you answer
the questions below: (be specific about the data sets you used to answer the questions)
¾ Describe the height vs. atmospheric pressure graphs. Is there a lot of
variability in the graphs? Why do these trendlines have this shape?
¾ What is the air pressure at the top of Mt. Everest (about 29,000 feet in
elevation) Notice that the weather data is in meters! Show your work.
¾ Most Everest climbers require supplemental oxygen as they climb the
mountain. In a recent movie, Earth astronauts appear to breathe on the surface
of Mars. If you were on Mars (atmosphere pressure about 6 mbar), could you
breathe without supplemental oxygen? Compare the pressure for the top of
Mt. Everest to the atmospheric pressure of Mars.
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¾ The average atmospheric pressure at sea level is about 1013 mbar or Hpa.
What is the atmospheric pressure at 1000 meters? What is the difference in
pressure between sea level and 1000 meters? (This would be similar to going
from Seattle to Stevens Pass in the Cascade Mountains). Is this different from
place to place?
¾ Is there a difference in the pressure of the atmosphere at northerly latitudes
versus southerly latitudes? If so, what is the difference? (recall that you have
to compare the readings at the same elevations!)
¾ Describe how the temperature changes with height.
¾ How does the dew point change with increasing height?
¾ Use the graphs of the Quileutte station to estimate the differences in
temperature from about sea level to 1000 meters (about the elevation of
Stevens Pass in the Cascades)?
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¾ What does it mean when the air temperature and the dew point curves were
very close or overlapped?
Several graphs of height vs. air temperature and dew point from the January data sets in
the northerly latitude stations appear similar to the one below:
¾ Describe the temperature of the air as the balloon ascended.
¾ In the graph above, we have drawn three regions (A, B, and C—they are difficult
to see—Region A is the region with the positive slope from the ground to about
600 meters, region B is from 600 to about 1300 meters and region C is the air
above 1300 meters. Given the temperature of the air in regions A, B, and C,
where would you expect to see the densest air? Why? Explain your answer.
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This is sometimes called a thermal inversion. Normally the air becomes colder as we
increase in height (elevation). However, when the ground is cold and the input of solar
energy is at a minimum, the air near the ground may be colder and denser. Many times
this cold air (region A) does not mix well with the warmer air (region B) above it.
Sometimes in the fall and winter we get air stagnation alerts in western Washington and it
is illegal to burn wood in standard fireplaces because pollutants emitted into the colder
layer do not mix well with the less dense, warmer air above.
If we plot just the first measurement from each sounding we can map the surface
pressure at each recording station. Below is a map of the surface pressures on July 1,
2000.
¾ Do you notice any pattern to the pressure values?
¾ Is there a problem with using the values of pressure at the surface of each station?
Discuss this in your group and talk to an instructor before proceeding.
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You may have found that the elevation of the weather station influences the atmospheric
pressure more than the variations in the weather. Therefore, to use the surface pressures
to create a weather map, one must correct the values to sea level. Below is a pressure map
for January 16, 2002, in which the surface pressures have been corrected as though all of
the stations are at sea level.
This correction is not difficult, but is beyond the scope of this class. Any data that we
give you will be corrected for the elevation of the station unless we say otherwise. Notice
the values for the Rocky Mountain region are significantly different than our previous
map.
What causes the wind?
Why does the wind blow from west to east most of the time?
We will show you some weather maps and talk about the movement of air in the
atmosphere in class.
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