Student _______________________________________________
MET 102
Earth’s Heat Budget
Introduction:
Insolation that Earth receives undergoes a cyclic change during the year at most places on Earth’s
surface. This change in intensity and duration of insolation has an effect on Earth’s surface temperatures.
In this activity the insolation received each month is compared to the insolation radiated back to the
atmosphere by Earth’s surface. To conceptualize this relationship imagine an analogy in which incoming solar
energy is money received and deposited into a bank account. In this analogy, energy emitted by Earth is money
withdrawn from the bank account in order to meet expenses. The balance is the remaining energy after the
deposits and withdrawals and represents average surface Earth temperature for each month.
In order to simplify the model, actual energy values have not been used. Values have been assigned to
the monthly deposits and withdrawals that show the relationships of the actual values. Consequently, energy is
simply labeled as “energy units.”
Procedure:
On the Report Sheet you will find a statement of monthly deposits and withdrawals from November of one
year to November of the next year. Assume there was a previous balance of 210 energy units (arbitrarily
determined). In November 100 energy units were received (deposited) and 120 energy units were re-radiated
(withdrawn). This results in a loss of 20 energy units (-20 units withdrawn). Since the balance for the previous
month was 210 energy units this leaves a balance of 190 energy units.
1. Calculate the difference between the deposit and withdrawal of energy for December. Record the difference
in the appropriate column on the Report Sheet.
2. Next, determine the new balance for December and record the value in balance column for December.
3. In a similar manner, calculate the balances for each month for the remaining months and record the data in
the Report Sheet. Note, that because the values represent averages and this is a cyclic change, if your
calculations are correct the balance for November at the bottom of the table should be 190 energy units.
4. Construct a line graph for the following data on the graph grid shown below the Report Sheet. Use a
different color for each line and provide a key.
a. Energy Absorbed (Deposit)
b. Energy Re-radiated (Withdrawn)
c. Surface Temperature (Balance)
5. By comparing the lines for the deposit and withdrawal:
a. Shade the region between the lines that represents months during which an energy surplus exists.
b. Shade the region between the lines that represents months during which an energy deficit exits.
c. Draw arrows to the locations on the graph where a radiative balance exists.
Activity adapted from:
Explorations in Earth Science by Osmun, R, Vorwald, B, and S. Wegner, ©2009 United Publishing Co.
M ET 102: Professor Vorw ald
Earth’s Heat Budget
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M ET 102: Professor Vorw ald
Earth’s Heat Budget
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Discussion Questions:
6. In which month does Earth receive the most insolation?
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7. During which month does the maximum temperature occur?
___________________
8. Do the months of maximum insolation and temperature coincide?
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9. In which month does Earth receive the least insolation?
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10. In which month does minimum temperature occur?
___________________
11. Do the month’s of minimum insolation and temperature coincide?
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12. In the space below, list the months during which Earth experienced an energy surplus.
13. During the months that have a surplus of heat energy, temperatures
a. decrease
b. increase
c. are not affected
______
14. In the space below, list the months during which Earth experiences an energy deficit.
15. During the months that have a deficit of heat energy, temperatures
a. decrease
b. increase
c. are not affected
______
16. The time when maximum temperature occurs is closest to
a. Minimum surplus
b. Maximum deficit
c. Radiative Balance
______
17. The time when minimum temperature occurs is closest
a. Maximum surplus
b. Minimum deficit
c. Radiative Balance.
______
18. Based on the slope of the temperature line on the graph, as the amount of surplus increases,
the rate of temperature increase
a. decreases
b. increases
c. is not affected
______
Conclusion:
Why don’t the dates of maximum and minimum temperatures coincide with the dates of maximum and
minimum insolation?
M ET 102: Professor Vorw ald
Earth’s Heat Budget
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