Humidity Exercise: Teacher's Edition | Student Version

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
 

Overview:

Humidity remains a misunderstood concept by many. Yet it is an important component of the water cycle and is important to sustain life on our planet. Perhaps this misunderstanding arises from the multiple ways scientists express humidity (including dew point and relative humidity), and the dependence of relative humidity upon the temperature. This exercise focuses on how temperature and humidity change on a typical fair-weather day.

This exercise was designed to accompany the distance learning module for teachers entitled "Humidity and Moisture: An Introduction for Science Teachers", which provides content knowledge about humidity concepts. This exercise also was designed to help students reinforce graphing and interpretation skills using actual observed data. Graphs may be produced by hand or by computer, based upon the teacher's judgment. The graphs may also be prepared by students working in groups, as a class, or individually. The exercise may be completed using data teachers obtain on their own, or by using data packaged alongside the exercise.

Background Information:

  • Humidity is the concentration of water vapor in the air.
  • Meteorologists express humidity in different ways, including relative humidity and dewpoint.
  • Relative humidity is related to the ratio of condensation and evaporation rates, which are dependent upon temperature. Relative humidity of 100% means that equilibrium has been achieved between condensation and evaporation.
  • The dewpoint temperature is the temperature that air must be cooled for condensation to occur. This value is related to the absolute moisture content in the air.
  • If the dewpoint temperature or actual moisture content remains constant, a rise in temperature results in a decrease in relative humidity
  • Because temperature exhibits a daily, or diurnal, cycle, a similar cycle is observed in relative humidity under calm, fair-weather conditions.

Classroom Introduction:

  • Fill a non-insulated container such as a glass, beaker, or plastic cup, with ice.
  • When the outside of the container becomes moist with condensation, ask the students to observe and explain what happened, especialy considering where the moisture came from.
  • This demonstration works best on more humid days. (For high school, students, ask the students to consider how the amount of condensation could be measured or quantified.)
  • Ask the students if they have noticed lots of condensation on their glasses on some days and little condensation on other days.
  • Then relate this qualitatively to the humidity in the atmosphere.

Provide students with weather data, graph paper, or and/or computer along with the exercise sheets.
Student 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.

Student 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).

 
First Value
Last Value
Change
Temperature      
Relative Humidity      
Dew Point      

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

Additional Resources

 

 

Grades: 6-12

Topics: Daily Temperature and Humidity Cycles, Graphing

Time Required: ???

Standards Addressed By This Lesson

Materials:

Option 1: Teacher-Collected Data

  • Obtain weather observations from a given station for one day. Ideally, the day you pick should have light or calm winds, no precipitation and mostly sunny skies, in order to capture a "normal" daily cycle. The observations should include temperature, dewpoint, and relative humidity data. Choose a time period that begins and ends at midnight. Look for a day where the dewpoint temperature doesn't change too much in order to simplify this exercise. Sources for tabular weather data include your local National Weather Service office (http://www.nws.noaa.gov) and the Weather Undergound (http://www.wunderground.com)
  • Graph Paper and/or Graphing Software (e.g., spreadsheet), especially if data is more frequent than hourly time resolution.
  • Computer to obtain sunrise and sunset from U.S. Naval Observatory
    (http://www.usno.navy.mil).

Option 2: Sample Data with Answers

Notes to Teacher: The provided sample data were chosen based on geographical considerations. You may pick one station that is relatively close to your location, or you may divide students into groups and distribute the stations among the groups. With the groups, lead the students to discuss similarities and differences among their graphs. You can also extend the exercise by comparing the provided data with locally observed data.

If students are proficient with graphing, they may use computer capabilities to make the graphs.

Option 3: Assessment / Application Exercises