Clausen_Solar Radiation and Albedo Activity-1
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Dec 6, 2023
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Solar Radiation and Albedo
In this activity, you will have a closer look at solar radiation and what happens with that radiation as it
travels through the atmosphere.
First, let’s look at a satellite composite image looking at the land surface albedo. This image is from
MODIS, the Moderate Resolution Imaging Spectroradiometer. Data for this image were collected over a
16-day period.
What is the albedo; how is it defined?
o
It is defined as follows: “The proportion of the incident light or radiation that is reflected
by a surface, typically that of a planet or moon.”
Explain the map shown below. What areas have a high albedo and why? Similarly, what areas
have low albedo? Why?
o
The areas that have a higher albedo are that way because they are much more reflective
(due to occurrences like snow and sand). The places with a lower albedo have a less
reflective surface, due to environments like forests which absorb more light.
Which season is represented by this map?
o
Spring.
Why is there no data over Antarctica and over northern Greenland?
o
Because they typically stay the same throughout the year, with only minor changes.
Explain how this map was created and why observations over a two-week period were required
to produce this map.
o
The map was created using a sensor in a satellite. Two weeks were necessary to produce
this map because changes happen slowly, so getting the “average” for a location is the
best bet.
The graph below shows the globally averaged albedo over the period 2000-2014.
What factors and processes can cause variations in the albedo?
o
Annual changes in air temperature and precipitation levels
Name one factor that could lead to a higher-than-normal albedo and explain how this works.
o
Fresh snowfall has the largest reflection hence the highest albedo.
What effect do volcanoes have on the global albedo?
o
Big volcanic eruptions have increased albedo due to volcanic aerosols.
Over this period, no trend in albedo is observed. If global warming continues, would you expect
a more sustained trend? In what direction, and why?
o
We would see a spike down because most of the light would not be reflected, as we
would get less snow.
Now, let’s look at radiation in some more detail. In particular, have you ever wondered why the sky is
blue and sunsets are red? After completing the following answers, hopefully you will understand.
First, consider why a rainbow forms.
What two “ingredients” do you need for a rainbow to form?
o
Rain and sunshine.
Because rainbows are created by light via raindrops, the best time to catch a rainbow is when it’s sunny
and raining. If you’re trying to spot one, the key is to face the rain and have your back in the sun.
What happens when light travels through a water droplet? (If you need a clue, recall the cover
art of Pink Floyd’s “Dark Side of the Moon”)
o
The light reflected or refracted into the water.
What looked like white light becomes separated into different colors. What does this tell you?
o
Shorter wavelengths refract more than longer wavelengths.
This explains the rainbow but does not quite explain why on a cloud-free day, the sky is blue.
How does solar radiation pass through the atmosphere on a clear day?
o
Through air molecules, water vapor, and clouds.
What happens when the blue and violet waves are separated from the other waves?
o
The blue and violet waves are scattered and can become visible.
And what happens to the other waves?
o
The other wavelengths stick together, remaining white.
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What happens when the Sun starts to set on the horizon?
o