PURPOSE:  To identify and explain areas of high and low heat loss in the winter environment.

MATERIALS (per group): 2 min-max thermometers, masking tape, 2 stakes marked with flagging tape, 2 cardboard shoe or jewelry boxes, string, meter stick, hammer (optional).

INTRODUCTION: "It is always darkest before the dawn," or so states an old adage.  It is also usually coldest just before sunrise. The minimum temperature in a 24 hour period can differ by several degrees from place to place, even within a small backyard. This temperature difference may seem insignificant, but to a rabbit or bird seeking shelter for the night it can be a life or death difference.

Radiation is probably the most important form of heat transfer between the ground and the atmosphere.  All objects -- including the atmosphere itself -- radiate heat energy, but those of higher temperature radiate more.  Cooler objects nearby heat up when they receive this radiation. Objects which lose more heat than they gain, cool off.

When the sun is shining, bare ground receives much radiation and heats up.  At night, the ground radiates much more heat than the air, and quickly becomes cooler than the atmosphere.  Vegetation and snow cover modify this radiation balance by changing the surface reflection (albedo) and providing insulation. Clouds are warmer than space so the ground will lose less heat on cloudy nights. The topography of an area also plays a role: low areas tend to collect dense cool air.

You can see that there are many reasons why the minimum temperature in an area will vary from one location to the next.  In this activity you will decide which environmental factors are most important in a given situation.  Your mission is to locate the area of highest and lowest minimum overnight temperature.

PREDICTION: Use what you know about radiation heat transfer, vegetation and snow conditions, and topography to make a prediction.

1. Where are the warmest and coolest places in the winter environment for small animal to spend the night? Consider wide and narrow depressions or hills in the ground, burrows under the snow, high and low roosting areas in trees, shrubs, and buildings, and so on.

PROCEDURE:

A.  Use masking tape to label one thermometer "high minimum" and the other "low minimum". Put your names on both labels.

B. Cross calibrate the thermometers to ensure that they all read the same temperature at the start of the experiment. If your thermometers read a few degrees high or low relative to the standard, record this information on your data sheet.

C. Reset the minimum scales of your thermometers.  Reading and resetting thermometers will be demonstrated by your teacher.

D. Tape both thermometers to bird or rabbit sized cardboard boxes. These are the "animals" that will spend the night in the warmest and coolest places in the environment.

D. Go to the assigned area and study it carefully to decide which locations will have the highest and lowest overnight minimum temperature. Play fair! Consider only those locations in the existing environment that are accessible to a bird or rabbit.

E. Place each thermometer flat or bulb up in the locations you have chosen.  The bulb should be at least 5 cm above any snow that is existing or that might fall during the night. 

F. Put a stake near each thermometer. Describe the location of your thermometers on the data sheet since snow may cover your tracks.  Also note the reasons for selecting the site.

G.  Go back to the sites you selected the next day. The thermometers must be read in place.  This is especially important if the site you have chosen is warmer than the surrounding air.  Remember that the minimum scale of the thermometer is an inverse scale. Record your data on the data sheet.

H.  Add or subtract the appropriate number of degrees to express your data in standard form. Share your adjusted data with others in your class. If possible, determine the cloud cover for the night of the experiment.  The Weather Bureau may be able to help.

GOING FURTHER: Attach min-max thermometers to the rope on the school flagpole at various heights (0.5 m, 2 m, 5 m and 10 m) and leave them overnight. Predict which of the thermometers will record the highest and lowest minimum temperatures and explain your choices. Compare your results with your predictions.

CONCLUSIONS:

2. Of all sites examined, which had the highest minimum temperature?  Why do you think this was so?

3. Of all the sites examined, which had the lowest minimum temperature?  Why do you think this was so?

4. How did your results compare with your predictions?

DISCUSSION:

5.  Examine the data for areas in which the 3 highest minimum temperatures were recorded.  Summarize the characteristics of an area with high minimum temperature based on this data.

6.  Examine the data for areas in which the 3 lowest minimum temperatures were recorded.  Summarize the characteristics of an area with low minimum temperature based on this data.

7. Using what you have learned about minimum temperature, should a rabbit huddle in a narrow depression or a wide depression in an open field?

8. Should a squirrel sleep in the hollow of a tree trunk high in the branches or in a hollow at the base of the tree?

9. In cold areas, orchards are often planted on slopes and hillsides to avoid frost.  Explain the advantage of this.

10. Explain why less heat is lost in a dense forest than in an open field.

11. Describe the circulation pattern which exists over a sidewalk-grass micro-environment at night.

12. Consider an open field with a flagpole in the center.  If thermometers were hoisted to heights of 0.5 m, 2 m, 5 m, and 10 m which of the thermometers would usually record the highest minimum temperature?  The lowest minimum temperature?  Explain your answers.  Describe a situation where the lowest minimum might be at one of the other heights.

13. What effect would wind have on the minimum temperature pattern recorded by the thermometers on the flagpole in question 12?

YOUR DATA:

High Minimum Thermometer Degrees from Standard (+/-): __________

Low Minimum Thermometer Degrees from Standard (+/-): __________