For background information on Earth’s Energy Budget and on Electromagnetic Radiation, please refer to the Radiation and Energy Transfer page in the Lesson Links section. A review of vocabulary is also recommended, using the terms listed in the Vocabulary section as a guide.
Solar radiation (light) strikes Earth’s surface throughout the daylight hours. Radiation (heat or infrared) also leaves the Earth during daylight and at night. Averaged over time and space, these downward and upward energy fluxes are equal. If they were not, our planet would gradually heat up or gradually cool down. In the past geologic time there have been vast fluctuations in global average temperature. Some of these specific events include the past ice ages, the more recent Little Ice Age, and the Younger Dryas period. In recent years our planet Earth has stayed at a comfortable global average surface temperature of about 15 degrees Celsius. But the surface of our planet is not simply a mirror for radiation. Some of the incoming radiation goes through a process of change before it is radiated back into space.
This lesson will demonstrate examples of how this EM radiation changes, and will provide students an opportunity to qualitatively analyze sample plots for changes in data.
Part I Teacher-directed class discussion using prepared Powerpoint presentation
1. Open Powerpoint presentation (See Links section)
2. Scroll to Image 1. Define sea surface temperature (see Vocabulary), then ask the class the following questions (or add your own questions for discussion)
a. At what approximate latitudes is the sea surface temperature highest in this graph? Explain your answer by referring to the color and temperature scale.
b. At what approximate latitudes is the sea surface temperature lowest in this graph? Explain your answer by referring to the color and temperature scale.
3. Scroll to Image 2, and repeat questions a and b from Step 2.
4. Discuss with the class what changes occurred in the time interval between the samples of data. (i.e. an increase in temp, a decrease in temp, etc.)
5. Scroll to images 3 and 4. Using questions similar to Step 2, discuss with the class what changes occurred in the time interval between these samples of data.
6. Scroll to images A and B. Discuss with the class the point that these plots represent the difference between the two samples of data. If we were to graph the result when the data from Image 2 is subtracted from the data in Image 1, we would produce one of these images. If we graph the result when the data from Image 4 is subtracted from the data in Image 3 we would get the other.
7. Scroll between the 6 open images. Help the class to determine which difference plot goes with images 1 and 2, and which goes with 3 and 4.
8. Introduce the concept of the Earth’s energy budget. Define upward and downward flux. Review the electromagnetic spectrum. See Links and Vocabulary sections.
9. Scroll to both the downward and upward LW energy graphs from Jan 1, 2004, and discuss the change between the samples of data, (i.e. more energy hitting the surface, or more energy leaving the surface).
10. Do the same for the downward and upward SW energy graphs.
11. Scroll to the difference plots and ask students to predict which one represents SW and which represents LW.
12. Once the students have correctly related the images, continue the discussion on the Earth’s energy budget.
13. Lead the students in a discussion of how a large amount of SW radiation hits the Earth, but much of the energy leaves the surface as LW radiation. (See Vocabulary)
Part IIA: Student Practice in generating plots (students need access to computers)
1. Go to MY NASA DATA Live Access Server (see Links).
2. Click on Oceans.
3. Then Click on Daily Sea Surface Temperature (GHRSST).
4. In the map in the upper left hand corner of your screen click on the double downward arrow above the map, select South Atlantic. A yellow rectangle should appear on the map, indicating the southern Atlantic Ocean .
5. For Select time, from the three drop-down menus, choose, Mar, 07, 2005.
6. Click ‘Update Plot’ from the menu at the top of the screen.
7. In a few seconds, an image should appear. Carefully look at the image to make sure that it shows the southern Atlantic Ocean, then save this file as SST_Mar_2005.
8. Repeat steps 3-7, but for the Select time, choose Sep,07, 2005.
9. Click the red Next.
10. An image should appear. Again, make sure that the plot shows the southern Atlantic Ocean, then save this file as SST_Sep_2005.
11. Open both of the saved files on the desktop at the same time, so that you can either click back and forth or can place them side-by-side on the screen.
12. Notice any change in sea surface temperature from March to September, and answer questions under Part IIA Questions.
Part IIB: Student Practice in Analyzing Difference Plots
-Use the difference plots from the PowerPoint file to answer the questions regarding difference plots.
Part IIA Questions
1. Look at the latitudes below the equator. Did the sea surface temperature change from March to September in these areas? Explain by referring to specific latitudes and to the color and temperature scale for each plot.
2. Repeat Question 1, except looking at latitudes above the equator.
Part IIB Questions
1. Compare the two plots of sea surface temperature, and review your answers to Part II A Questions. The Difference Plot shows the result of subtracting the data represented by one image from the other. Was March subtracted from September, or was September subtracted from March? Explain your choice.
2. If the order of the subtraction is reversed, what changes in the Difference Plot would be noticed? If time permits, verify your answer by generating the Difference Plot with the order reversed. Save this file.
1. Choose a large body of water in the Northern Hemisphere, then develop plots of Weekly Sea Surface Temperature for March, June, September, and December of a particular year of your choice.
a. Describe the changes that occur in the four graphs.
b. Discuss which seasons are represented by the four graphs.
c. Are the changes what you would expect? Explain your answer by referring to the seasons.
d. Summarize your findings by writing a summary statement about seasonal trends in sea surface temperature.
2. Repeat Extension 1 and write your answers for Parts a through d for a large body of water in the Southern Hemisphere during the same year. Be sure to write the summary statement.
3. Research the heat capacity of water.
a. Does water have a higher or lower heat capacity than land?
b. How might this relate to the temperature of a body of water on Earth as the seasons progress?
c. How might the heat capacity of water relate to the Earth’s Energy Budget? Explain your answer.
4a. For a location and year of your choice, use the LAS to generate color plots of Monthly Surface Clear-sky SW Downward Flux and Monthly Surface Clear-sky SW Upward Flux. Compare the two plots, and describe your findings.
4b.Generate the Difference Plot for the two variables used in part 4a. State the order of the subtraction that was used. Compare the Difference Plot to your findings in part 4a, and write a summary of your findings.
4c. If you were to predict a ‘trend’ in SW flux data, what would be your prediction? Is one location and year enough data to make a prediction? How would you verify your prediction?
5. Depending on the grade level this lesson is used at, material can be added, subtracted or substituted to meet the needs of your course.
6. Depending on time and direction of the lesson, the extensions section can be incorporated into the body of the lesson.
7. Through the use a science journal in the classroom, students are able to make long term connections between the lessons. The cross categorical connections can help to develop individual scientific reasoning that will help with future science classes.