Abstract

Objective

The goal of this project is to use weather balloon sounding data to investigate how air temperature and pressure vary with altitude.

Introduction

Twice a day all over the U.S., the National Weather Service launches weather balloons with instrumentation packages called radiosondes to collect data on the current conditions of the upper atmosphere. As they ascend with the weather balloon, the radiosondes measure profiles of pressure, temperature, and relative humidity. The radiosondes contain radio transmitters that send the collected data back to Earth. The data are used for weather forecasting, and are available online.

You can use this data for a science fair project on atmospheric conditions. We will show you how to read temperature and pressure data from a standard upper air sounding plot—the same graphs that are used by meteorologists for weather forecasting. This project shows you how to find out how the temperature changes with altitude in the lowest layer of the Earth's atmosphere, the troposphere.

Figure 1 shows an example of an upper air sounding plot. This is a standard graph used by meteorologists to analyze data from a balloon sounding. There is a lot of additional information in the graph, but basically it is a plot of temperature (x-axis) vs. height (y-axis). The white data line on the left shows the dewpoint vs. pressure, and the white data line on the right shows the temperature vs. pressure. The pressure (in millibars, mb) is shown on the y-axis in blue lettering, and the height (in m) is shown in white lettering. A sounding plot is also called a "Skew T" plot, because the temperature axis is plotted at an angle (i.e., skew) of 45°. The temperature lines of the Skew T are in blue (at 45°).

Figure 1. Example of an upper air sounding plot from the Unisys Weather webpage. Data shown are from International Falls, MN, March 23, 2007. Brrrrr!

Atmospheric pressure decreases with height above the Earth's surface. The higher you go, the less atmosphere remains above you, so the pressure decreases. "Meteorology uses pressure as the vertical coordinate and not height. This works out better for thermodynamic computations that are done on a regular basis. Pressure decreases in the atmosphere exponentially as height increases reaching 0 pressure in space. The standard unit of pressure is millibars (mb or hectopascals-hPa) of which sea level is around 1015 mb. Here is a table of pressure levels and approximate heights (Unisys Corp., 2001):"

Pressure	Approximate Height		Approximate Temperature
(mb)	(m)	(ft)	(°C)	(°F)
1015 (sea level)	0	0	15	59
1000	100	300	15	59
850	1500	5000	5	41
700	3000	10000	−5	23
500	5000	18000	−20	−4
300	9000	30000	−45	−49
200	12000	40000	−55	−67
100	16000	53000	−56	−69

Figure 2 shows how to read the temperature at a chosen pressure level (height). On the y-axis, find the pressure level (in mb) where you want to know the temperature. Follow the horizontal pressure line over until it intersects with the temperature plot (right-hand data plot, in white). Then follow the 45° temperature line down and to the left to the temperature axis. In the example below, the temperature at 700 mb was about −11°C.

Figure 2. Reading the temperature of the atmosphere at 700 mb (3022 m) from the sounding plot. Follow the horizontal pressure line to where it intersects with the temperature plot (right hand data line, in white). Then follow the 45° temperature line down and to the left to the temperature axis. In this example, the temperature at 700 mb was about −11°C.

There is a lot more information in the sounding plot, but it isn't important for this project. If you want to learn more about sounding plots, see the references in the Bibliography section (Unisys Corp., 1998, 2001; Millersville University LEAD Undergraduates, date unknown).

In this project you will use balloon sounding data to investigate how atmospheric temperature and pressure change with altitude.

Terms, Concepts, and Questions to Start Background Research

To do this project, you should do research that enables you to understand the following terms and concepts:

• Troposphere
• Pressure
• Temperature

Questions

• What is the source of heat for the troposphere?

Bibliography

• For more information about the layers of the Earth's atmosphere, see:
  • UCAR, 2000. "Windows to the Universe: Layers of the Earth's Atmosphere," University Corporation for Atmospheric Research [accessed March 27, 2007] http://www.windows.ucar.edu/tour/link=/earth/Atmosphere/layers.html.
  • University of Tennessee, date unknown. "The Solar System: The Earth's Atmosphere," Astronomy 161, Department of Physics and Astronomy, University of Tennessee, Knoxville [accessed March 27, 2007] http://csep10.phys.utk.edu/astr161/lect/earth/atmosphere.html.
• For current sounding data, see:
  Unisys Corp., 2005. "Unisys Weather: Upper Air: Upper Air Sounding Plots," Unisys Weather [accessed March 27, 2007] http://weather.unisys.com/upper_air/skew/.
• For more information on the data contained in upper air sounding plots, see the following references:
  • Unisys Corp., 1998. "Unisys Weather: Upper Air: Upper Air Sounding Details," Unisys Weather [accessed March 27, 2007] http://weather.unisys.com/upper_air/skew/details.html.
  • Unisys Corp., 2001. "Unisys Weather: Information: Vertical Coordinate—Pressure," Unisys Weather [accessed March 27, 2007] http://weather.unisys.com/info/press.html.
  • Advanced. There is a lot more information in a sounding plot than just temperature. If you'd like to learn more, check out this page:
    Millersville University LEAD Undergraduates, date unknown. "Lead-to-Learn: Understanding a Sounding/Skew-T," Millersville University [accessed March 27, 2007] http://www.atmos.millersville.edu/~lead/SkewT_Home.html.
• This fact sheet from the National Weather Service describes the instrumentation used for upper air soundings:
  NWS, date unknown. "NWS Radiosonde Observations - Factsheet," U.S. National Weather Service, National Oceanic and Atmospheric Administration [accessed March 28, 2007] http://www.ua.nws.noaa.gov/factsheet.htm.

Materials and Equipment

To do this experiment you will need the following materials and equipment:

• Computer with Internet access
• Graph paper or graphing software

Experimental Procedure

1. Do your background research so that you are knowledgeable about the terms, concepts, and questions, above.
2. For current weather balloon data from across the U.S., go to the Unisys Weather Upper Air Sounding Plots webpage (Unisys Corp., 2005).
3. Click on the map (see illustration below) to get sounding data from a particular station. Clicking on a station will load a webpage with the current sounding data from that station. You'll see a sounding plot like those in the Introduction.

   Upper air sounding station map (Unisys Corp., 2005)

4. Above the sounding plot are controls for changing the plot that you are viewing from the currently selected station (see illustration below).

   Upper air sounding plot controls (Unisys Corp., 2005)

   Explanation of the controls:
   1. The type of plot can be switched between "Norm" (black background for computer monitor display) or "Inv" (white background for printing on paper).
   2. The "Text" button switches to a view of the current sounding data in tabular format.
   3. The time controls allow you to switch between the last four sounding plots (current, −12 h, −24 h, and −36 h) for the selected station.
   4. Note: although you can view graphs of data from four different time points, the text data option is for current sounding data only.
5. Follow the instructions in the Introduction for reading the sounding plot. Make a table like the one below, showing pressure (in mb), altitude (in m), and temperature (in °C) for each of the pressure levels shown in the sounding plot.

   pressure (mb)	altitude (m)	temperature (°C)

6. Repeat this for at least 5 different sounding stations.
7. Make a graph of your results that shows how temperature varies with atmospheric pressure for each station.
8. Make a graph of your results that shows how pressure varies with altitude for each station.

Variations

• Balloon soundings are taken at 12-hour intervals. (Notice that the time given in the plots is coordinated universal time (UCT), not local time.) Depending on the station location and time of year, you may be able to compare soundings taken during daylight hours to those taken after sundown. Compare several sequential pairs of soundings (daylight/after sundown) for several locations. Do you see any consistent relationships in the two temperature plots? What do they tell you about the sun's contribution to heating different levels of the atmosphere?
• For an experiment that relates atmospheric temperature and characteristics of snow, see the Science Buddies project How Does Atmospheric Temperature Affect the Water Content of Snow?

• For more science project ideas in this area of science, see Weather & Atmosphere Project Ideas.

Credits

Andrew Olson, Ph.D., Science Buddies

Sources

This project is based on:

• Millersville University LEAD Undergraduates, n.d. "Lead-to-Learn: Exploring Temperature and Pressure Changes with Altitude" Millersville University [accessed March 27, 2007] http://www.atmos.millersville.edu/~lead/LEAD_%20Learning_%20Module_Altitude.doc.

Last edit date: 2007-05-25 12:00:00