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Lesson 11: Energy Budget
The Earth's Radiation Energy Balance
The amount of solar energy reaching Earth at any particular latitude is defined by how the Earth orbits the Sun. Therefore, it is a function of the time of year and the
tilt of the Earth with respect to the Sun. Use the applet below to explore how the incoming energy from the sun varies with time of year and latitude. Text instructions are below, or you can hear an audio description. Questions to consider:
Set the date to March 21, the vernal equinox, and the latitude to the near the South Pole
(-89) for both cases, and hit the calculate button. You will see a plot of the incoming solar energy
at the top of the atmosphere. Now select another latitude (e.g 60 degress
S, or -60) and calculate. Repeat this process for other latitude
up to the North Pole and answer the question: "How does the
distribution of solar energy change as a function of latitude?"
Now change the date to June 21, the summer solstice, and
compute the incoming solar radiation at the same latitudes. How
does changing the date from March 22 to June 21 impact the distribution of solar energy?
- Compute the incoming solar radiation for June 21 at 23N (+23), the summer solstice for the Northern Hemisphere,
and December 21 at 23S (-23), the summer solstice for the Southern Hemisphere. Why is the distribution of solar energy different?
Instructions
This applet plots the incoming solar energy at the top of the atmosphere (no absorption by the atmosphere).
You can do this calculation for two locations at once. Select a month, day and latitude from each
scroll down menu, and click on calculate. Northern latitudes are positive, Southern latitudes are negative. The red curve
represents the calculation for the conditions set by the left menu bars, the
black dots for the right hand case.
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