Recall from your readings that the atmospheric structure consists of 5 distinct layers. The TROPOSPHERE is the layer closest to the earth. This is the layer where all weather occurs. Upper air soundings, via balloons are accomplished at 00 hrs. Z (UTC) and 1200 hrs. Z (UTC). These balloons use a RADIOSONDE to send information concerning the current structure of the atmosphere. This information is graphed on a SKEW-T Chart ( Image courtesy of the University of Wyoming).

This Skew-t image chart above (original image @ http://www.nssl.noaa.gov/projects/swamp/skewt/skewtgif/910704.00.TUS.gif is located at the U.S. National Severe Storms Laboratory (NSSL). It represents the state of the atmosphere in the southwestern area of the United States on July 4th 1991 at 0000 UTC. Can you tell where this information is recorded?

The chart (and all others like this) consist of the following information:

1. Pressure in millibars, mb (left side of chart)

2. Altitude in meters (left size of chart/not available on the above chart)

3. Temperature in degrees Celsius (bottom of chart)

4. Water vapor content in grams per kilogram (bottom of chart/not available on the above chart)

5. Wind direction, indicated by an arrow like shaft (right side of chart/North pointing to the top of the page. This image indicates that the wind at 900 mb is from the North-West).

6. Wind speed is indicated by long/short bar attached to wind direction shaft (right side of chart/ flag (triangle shape) indicates 50 knots/hr; long bar 10 knots/hr, and the short bar 5 knots/hr This image indicates that the wind at 900 mb is from the North-West at 10 knots per hour).

7. Two graph lines; These lines are the radiosonde information sent back to the receiver. The line on the right (higher temperatures) record air temperature. The line on the left (lower temperatures) is the DEWPOINT.

Remember that the higher the balloon ascends in altitude, the cooler the temperature becomes. On average, air temperature declines by one degree Celsius for every 1000 meters it ascends.

Looking at the example provided, the temperature indeed decreases in altitude.

1. At what altitude ( air pressure in millibars) does the temperature begin to increase?

2. What is the significance of this point? (Hint: refer to the structure of the atmosphere)

Use the SOUNDING ( Image courtesy of the University of Wyoming) page and click on three different stations around the country (place mouse pointer on top of 3 letter station identifier and click). The sounding image will down load to your screen (print each one of these graphs).

3. Are the soundings the same for each station?

4. At what altitude does the temperature begin to increase for each of the soundings?

5. Do steady increases in temperature occur at the same altitude for each of the 3 cities? Why or why not?

6. As you study the charts from these 3 cities, what do they tell you about the first two layers of the atmosphere?

7. What are the names of these first two layers?

8. Obtain the soundings from the same station over a 48 hour time period. Are the soundings the same? If not, how are they different? What does this tell you about the state of the earth's atmosphere?