Costa Rica Rainforest Experiment
"Cut the Humidity with a Knife"

PASPORT Humidity/Temp/Dew Point Sensor (PS-2124)

To observe the temperature, dew point, and relative humidity over a 24-hour period.

In this activity, students will measure the temperature, dew point, and relative humidity at Selva Verde for 24 hours.  Students will then examine the data and discuss the reasons for any changes or abnormalities that occur.

Humidity is a measure of the water vapor in the air.  As water molecules evaporate, the humidity of the air increases.  Certain climate regions on earth, such as deserts and the Arctic, have very low humidity, while other regions, such as tropical rainforests, have moderate to high humidity.

In general, the amount of water vapor that a given volume of air can hold increases as the temperature increases.  A higher temperature allows more water to evaporate.  As the temperature goes down, the amount of water vapor in the air goes down because the vapor can condense into a liquid, dropping the humidity.

Relative humidity is a common way to describe the amount of water vapor in the air.  Relative humidity is a ratio that compares the mass of water vapor in the air to the mass of water vapor that the air can hold at its saturation point.  Relative humidity is always written as a percentage.

Back to top

Equipment

• PASPORT Humidity/Temp/Dew Point Sensor
• PASPORT Xplorer GLX

Back to top

Data Collection Procedure

1. Plug the PASPORT Humidity/Temp/Dew Point Sensor into the port on the GLX.

2. From Home screen, press I to access the Sensors screen

3. Press c to change the sample rate unit to minutes.  Change the sample rate to 5.  The Humidity/Temp/Dew Point Sensor is now configured to take data every 5 minutes.

Equipment Setup:

Record Data:

Back to top

Data Analysis

1. From the Home screen, press F to access the Graph display.

2. Examine your data.

3. Using the Smart tool (H , 1) to find the approximate sunrise, sunset, and any change in visible weather patterns (rainstorm, clouds, etc.).

4. Display Temperature vs. Time and examine the graph. Display Relative Humidity vs. Time and examine the graph. Note: You can change what is being displayed by pressing c to highlight the active fields. Press c again to change measurements.

Back to top

Conclusions and Extensions

1. Compare the graph of Temperature vs. Time with the graph of Relative Humidity vs. Time.  How does a change in temperature affect relative humidity?

2. Did changes in relative humidity coincide with any changes in local weather patterns?

3. Is relative humidity generally higher during the day or night?  Why?

4. What unique characteristics of the rainforest contribute to high levels of humidity?  How does the humidity profile of the rainforest compare to seasons conditions in your hometown?

Back to top

Back to Costa Rica Summary -- October 2002