Objectives:

• improve graphing skills using real, observed weather data
• describe, compare, and interpret trends revealed in graphs
• identify the daily temperature cycle
• describe the effect of the temperature cycle on relative humidity

Materials:

• Weather Data (provided by teacher)
• Graph Paper and colored pencils, Graphing Software (e.g., spreadsheet), and/or WeatherScope software
• Computer to obtain sunrise and sunset data from the U.S. Naval Observatory (http://www.usno.navy.mil).

Procedure: 

1a. Graph the temperature and dewpoint values on the same graph.

• Graph the temperature in red and dewpoint in blue.

1b. On a second graph, plot the corresponding relative humidity values in green. Alternatively, you can use the same graph with relative humidity in percent on the right axis and temperature on the left axis.

• Make sure the relative humidity axis has 0% and 100% as the minimum and maximum values.
• If you use Oklahoma Mesonet data, you may simplify the plotting by using data from every 30 minutes rather than every 15 minutes.
• With your teacher's permission or guidance, you may use a spreadsheet program like Excel to make the graphs.

2. Determine the sunrise and sunset times for your station for the day of your observations. One easy way to get sunrise and sunset times is from the U.S. Naval Observatory (http://www.usno.navy.mil). Mark the sunrise and sunset times on your graph. You may wish to shade the daylight hours on your graph in light yellow. If you are using data from the Oklahoma Mesonet, you may use the solar radiation observations to estimate sunrise and sunset to the nearest 15 minutes.

Questions:

1. Write a paragraph to describe the temperature graph. In your paragraph, be sure to answer the following questions:

• Do the temperatures stay the same through the entire day or do they change?
• If they change, how?
• How does the temperature change in relation to the sunrise and sunset?
• How does temperature normally change during daylight and at night?

2. Write another paragraph to describe the dewpoint graph. Be sure to answer these questions:

• Does dewpoint change during the day or stay relatively the same?
• If it changes, when does the atmosphere contain more water vapor and when does it have less water vapor?

3. Write another paragraph to describe the relative humidity graph to answer these questions:

• How is it related to the changes in temperature and dewpoint?
  How does relative humidity normally change during daylight and at night?
  What times of the day is the relative humidity highest and when is it lowest?

4. Compare the beginning and ending values of temperature, dewpoint, and relative humidity. The "beginning" values are the values from midnight on the first day. The "ending" values are those values from midnight the second day (24 hours later).

5. Does the amount of moisture in the air change during the day? If so, which graph accurately describes the moisture changes?