Solar Radiation Lab by xuyuzhu


									Solar Radiation and Atmospheric Circulation
The solar radiation reaching the top of the earth’s atmosphere is remarkably consistent.
However, because the earth is not flat and is tilted on its axis, this radiation is distributed
unevenly across the surface of earth. Since solar radiation warms the surface of the earth, the
warming is also uneven. It is this “differential heating” that sets up the initial stages of global
atmospheric circulation.

Lab Group Discussion
1. Where are the areas with the highest and lowest temperatures located?
2. Why are the temperatures different at the poles and the equator?
3. What happens when air is heated? If you were a parcel of air being heated at the equator,
   where would you travel? Why do you say that?

In this exercise, we will not be measuring the sun’s radiation. Rather, we will model the sun’s
radiation using lamps and measure the resulting temperature on the surface of the globe.

Each group requires the following:
 1 old globe                                             desk lamps or heating lamps
 3 flexible aquarium thermometers                        ruler
   (thermometer strips for reptiles work                  graph paper
   best)                                                  colored pencils
 double-faced tape or poster putty

Set Up
 Using double-faced tape or poster putty, secure the thermometers to the globe. Place them at
    60N, the equator, and 60S.
 Place the desk lamp approximately 18 inches away from the globe. Position it so that the
    light is directly hitting the equator. (You want to reduce shading on the “sunlit” side of the
    globe, so you may need to adjust this distance. You may also need to adjust the distance if
    the temperature is outside the range measured by the thermometers.)

 Read and record the starting temperature.
 Turn on the lamps.
 Record the temperature every 5 minutes for 20 minutes.
 Graph the results.

Lab Group Discussion
1. Was there a difference in the temperature between 60N and 60S? Why or why not? What
   would happen if the globe were not tilted (e.g., if the equator were level with the table top?)
2. What do your results show about the temperature distribution on the earth?
3. What do these results suggest about the distribution of solar radiation?
4. How do you think the distribution of solar radiation affect global air circulation?
If there is time, you should perform the experiment twice. In the first experiment, tilt the globe so
that the equator on the globe is level with the table top using a lab jack. Then, perform the
experiment. In the second experiment, set the globe on the table so that it is tilted at 23.5 (the
base of the globe should be flat on the table). Perform the experiment again. The differences in
the results demonstrate the impact of the earth’s orbit on the amount of solar radiation received at
different latitudes on the earth. This is one of the primary causes of the seasons.

This experiment demonstrates that the amount of solar radiation received at a given area depends
on the latitude of the area. Solar radiation is generally constant at the top of the atmosphere.
However, since the sun’s rays must travel through more atmosphere to reach the earth’s surface,
less radiation actually reaches the earth’s surface at higher latitudes. Therefore, the equator tends
to be warmer than polar regions. Because air at the equator is warm, it rises. Because air at the
poles is cooler, it sinks. These two facts contribute to the global circulation of air. Tropical air
rises, moves towards the poles, and then sinks. This provides us with a general view of global
atmospheric circulation.

In reality, the circulation is more complex, and we will discuss the reasons for that next.

This exercise was based on:
 “Weather with a Latitude” by Jollyn Nolan (
 “Solar Radiation, Albedo, and Light Transmission in Seawater” by Christian Solem
 “Lesson 4: Global wind patterns and convection” by Digital Library for Earth Science Education

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