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.
  • Some younger students will say the moisture somehow comes from the melted ice.
  • 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:

1. Make separate bar graphs of temperature and relative humidity. You may use the blank charts that are provided and color each bar to the correct level. On the first graph, color the temperature in red. For the second graph, color the relative humidity values in green. If students are proficient with constructing graphs, they 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. Shade the daylight hours on your graph in light yellow.

 

Student Questions:

1. Write a short paragraph to describe the temperature graph. In your paragraph, make sure you answer these questions:

  • Did the temperature warm or cool before sunrise?
  • Did the temperature warm or cool in the morning (between sunrise and 12 PM)?
  • Did the temperature warm or cool in the afternoon (between 12 PM and 6 PM)?
  • What was the high (warmest) temperature?
  • When did the warmest temperature occur?
  • What was the low (coolest) temperature?
  • When did the coolest temperature occur?

2. Write another paragraph to describe the relative humidity graph by answering these questions:

  • Did the relative humidity increase or decrease before sunrise?
  • Did the relative humidity increase or decrease in the morning (between sunrise and 12 PM)?
  • Did the relative humidity increase or decrease in the afternoon (between 12 PM and 6 PM)?
  • What was the highest relative humidity value?
  • When did the highest relative humidity occur?
  • What was the lowest relative humidity value?
  • When did the lowest relative humidity occur?
  • Compare the relative humidity graph to the temperature graph. Are they both high at the same time, or is one graph high when the other is low?

3. Compare the first and last values of temperature, and relative humidity. The "first" values are the values from midnight on the first day. The "last" values are those values from midnight the second day (24 hours later). Were the last values the same, higher, or lower than the first values?

 
First Value
Last Value
Change
Temperature      
Relative Humidity      

Additional Resources

 

 

Grades: 2-3

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 and relative humidity data. Choose a time period that begins and ends at midnight. Although you will not provide dewpoint data to the students, look for a day where the dewpoint temperature doesn't change too much (provides a better relationship between temperature and relative humidity). 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.