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:
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 NationalOcean 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.
For the next part you will need access to the Internet and Excel. Go to:
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.
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:
ABQ – Albuquerque, New MexicoANC- Anchorage, Alaska
BIS- Bismarck, North DakotaBNA- Nashville, Tennessee
BOI- Boise, IdahoBUF- Buffalo, New York
CHS- Charleston, South CarolinaCRP- Corpus Christi, Texas
DEN- Denver, ColoradoEYW- Florida Keys
MFR- Medford, OregonNKX- San Diego, California
OAK- Oakland, CaliforniaOAX- Omaha, Nebraska
OTX- Spokane, WashingtonREV- Reno, Nevada
RIW- Riverton, WyomingSLC-SaltLake City
SLE- Salem, OregonTFX- Helena, Montana
UIL- Quileute, WashingtonWSE- Edmonton, Alberta, Canada
YEV-ArcticSeaStation, 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)
Describe the height vs. atmospheric pressure graphs. Is there a lot of variability in the graphs? Why do these trendlines have this shape?
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.
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.
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 StevensPass in the Cascade Mountains). Is this different from place to place?
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!)
Describe how the temperature changes with height.
How does the dew point change with increasing height?
Use the graphs of the Quileutte station to estimate the differences in temperature from about sea level to 1000 meters (about the elevation of StevensPass in the Cascades)?
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:
Describe the temperature of the air as the balloon ascended.
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.
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.
Do you notice any pattern to the pressure values?
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.
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 RockyMountain 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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