Hands-On, Minds-On Meteorology
Description | Programming | Operation



The Humidity program is designed to allow the students to see how temperature and humidity are related.

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The objective of the Humidity program is to allow students the opportunity to change temperature and moisture content of the atmosphere and to see how the relative humidity and Heat Index is affected.




The premise of this program is that a man is sitting in a room with an initial temperature of 68°F. The student can then change the thermostat and initial humidity levels for the room. They then can start either the Heater or the A/C (whichever is appropriate) and watch how the relative humidity changes as the temperature changes. The thermostat is simply on a timer to increment the room's temperature 1°F per second. Data is saved on the graphing tool's table after each of these increments. When the room temperature is equal to the thermostat, the timer stops, and the student can attempt another experiment. They can also rest the program, which returns the room temperature to 68°F. Heat index is also calculated. It is only displayed, however, only if the value exceeds 80°F.




Relative Humidity
Dew Point
Heat Index





Running the Program

  • Click the link for Humidity.
  • Adjust the room temperature to the desired value. (Range: 50-90°F)
  • Adjust the thermostat to set the desired temperature. (Range: 50-90°F)
  • Adjust the Water and Vapor Amount to set a desired initial humidity level.
  • When ready, click the 'Start ____' button, where '____' can be Heater or A/C, depending on the situation.
  • If the button says 'Can't Start', the Room temperature is the same as the thermostat, and either the program must be reset, or the thermostat and/or room temperature must be changed.
  • Click the 'Stop' button to stop a run in progress.
  • Click the 'Reset' button to change the room temperature back to 68°F

Extra Knowledge


  • The water level in the cup changes with the humidity. Although it is not accurate in a time scale, it provides another illustration of the changing relative humidity in the room. It decreases when the RH goes down, and 'refills' when the RH goes back up.
  • For every degree that the heat index is above 80°F, a bead of sweat is placed on our man. They can form on his arms or head and serve as an illustration of the changing heat index.
  • It is possible to set the room's humidity and temperature so that it fogs up, much like one would see after taking a hot shower. To simulate this, when the RH = 100%, a gray transparent film is placed over the screen to simulate the appearance of a cloud in the room.



Department of Atmospheric Sciences
University of Illinois at Urbana Champaign

Created by Dan Bramer: Last Modified 07/27/2004
send questions/comments to bramer@atmos.uiuc.edu