# Geography Lab- The Reason for the Seasons

Description

The Reasons For Seasons: Seasonal Change on Land and WaterDirections1. Read through the background and the two parts of the lab2. Complete Parts A and B4.Turn only the answers to the questions in A and B. 16 questions total

Lab 2
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This has been adapted from an activity developed through the GLOBE project at SRI International
The Reasons For Seasons: Seasonal Change on Land and Water
Directions
1. Read through the background and the two parts of the lab
2. Complete Parts A and B
4.Turn only the answers to the questions in A and B as pasted text under “The Reasons for the Seasons Assignment”. 16 questions total.
Background
Why do we have seasons?
The short answer for this is the tilt of the earth.
The tilt causes an uneven distribution of sunlight energy (insolation) by latitude and time of year. Insolation, or INcoming SOLar radiATION
is the focus of this lab. Insolation refers to the energy that is coming to Earth in the form of sunlight. This energy (or light) is measured in
units of watts per meter squared or W/m2.
One way to think about insolation is to consider that the average amount of energy coming to Earth in July is roughly 300 W/m2. Imagine
this as hanging three 100-watt light bulbs over every square meter of the earth. It is this energy that provides the basis for all life on Earth.
The amount that arrives each day dwarfs the amount of energy that people produce with power plants.
We are going to be examining a couple of things in this lab. First, we will be using a graph to look at the amount of sunlight that is received
by the earth. Next, we will visualize the insolation as a map. As you look at these visualizations of insolation consider the following:
Why does the energy vary by latitude?
The explanation for this has to do with how sunlight spreads over the spherical (and tilted) earth. Recall our
discussion in lecture about the subsolar point and how it shifts with the seasons.
Why is the energy evenly distributed across the lines of laitude?
The answer is that the earth turning on its axis forms these lines, or this is averaged out over the day.
The relationship between insolation and surface temperature is the next thing that we will focus on. One thing that may be immediately
clear to you is that while two locations such as San Francisco, CA and Wichita, KS have the same insolation (and are at about the same
latitude), their temperatures are very different on a given day.
Why do two locations that receive the same insolation have different surface temperatures?
The answer lies in the heat capacity of the surface materials. While insolation is the primary cause for surface
temperature, the heat capacity of the surface materials have an effect as well. Recall from lecture that land and
water have different heat capacities. In other words, water can absorb much more heat energy before it heats up,
while land heats and cools very quickly as it absorbs incoming solar radiation (insolation). Recall the example we
discussed in lecture where the concrete around a pool will often be very hot, while the water remains cool, yet both
have been subject to the same amount of insolation and both have absorbed the same amount of insolation. The
reason the water is cool is that it is much more resistant to change. So over a very large area, the amount of land
and water can have a large affect on regional temperatures. Most of the land on Earth is located in the Northern
Hemisphere. Therefore, seasonal change in the Northern Hemisphere is more extreme than in the Southern
Hemisphere.
Part A: Graphing Insolation
Graphing insolation
In this section we are going to use graphs to better understand how sunlight varies by latitude and by season.
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Lab 2
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Insolation by Latitude, shows the amount of insolation received at four different latitudes during each month of the year. Observe what
months the insolation values are high at each latitude, and which months they are low. How do they compare to each other overall?
Questions: Use the graph above to answer the following questions.
Insolation by Latitude
1. (1 points) Compare the amount of insolation that the equator receives in June with the amount that it receives in December
(include the numbers from the graph).
2. (1 points) Compare the amount of insolation that 30 degrees North receives in June with the amount that it receives in
December (include the numbers from the graph).
3. (1 points) Compare the amount of insolation that 90 degrees North receives in June with the amount that it receives in
December (include the numbers from the graph).
4. (1 points) Based on the graphic below, compare the amount of time in one day that a person on the equator would be within
the circle of illumination, with the amount of time that they would be outside of the circle of illumination in June and
December. Would the person spend more, less, or the same amount of time in the circle of illumination in June as compared
with December? Note: You are not expected to calculate exact numbers, just discuss overall patterns.
5. (1 points) Based on the graphic below, compare the amount of time in one day that a person at 30 degrees North would be
within the circle of illumination, with the amount of time that they would be outside of the circle of illumination in June and
December. Would the person spend more, less, or the same amount of time in the circle of illumination in June as compared
with December? Note: You are not expected to calculate exact numbers, just discuss overall patterns.
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Part B: Understanding insolation and surface temperature
Understanding insolation and surface temperature
In this section you will examine the relationship between insolation, seasons and surface temperature. We will look at three maps: January
and July insolation, January and July surface temperature, and the seasonal change in surface temperature. I am first going to walk you
through each visualization, then we will explore their relationships. The worksheets are based on the visualizations below. While you do not
have to turn in the worksheets, I encourage you to color them as that often helps you to understand what they are showing.
Maps
Map 1 shows the incoming solar energy in January and July. Color in the legend and the visualizations.
Map 2 shows visualizations of earth surface temperature for January and July. Color in the legend and the visualizations.
Map 3 shows the seasonal temperature change, or July minus January in worksheet #2. Color in the legend and the
visualization.
Insolation and surface temperature
Click on each visualization below to view a larger version
Insolation (map 1)
Surface Temperature (map 2)
Seasonal temperature difference
Change in Surface Temperature from January to July (map 3)
The following visualization was achieved by subtracting January from July. Click on it to see a larger version.
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Understanding seasonal temperature difference
The map 3 visualization has a lot of information in it. Let’s look at it a litte more closely. Think about each visualization as being
made up of little cells. Each cell is assigned a color. The color corresponds with a value, in this case, temperature. The red areas
represent a positive value, meaning that the temperature is warmer in July than in January. The blue areas represent a negative
value, meaning that the temperature is cooler in July than in January. This type of visualization is useful to understand how
areas change over time. What does a very dark red color mean? What does a color very close to white mean? Compare this
figure to the ‘Normal Annual Range in Temperature’ figure on page 33 of Goodes World Atlas.
Here is another way to understand what this visualization is showing. It was created by overlaying the January and July surface
temperature visualizations (worksheet 2) and subtracting them. So, for given the following cell values:
Location
January Temperature
July Temperature
Difference
Color
San Francisco
15
30
+15
red
Tierra del Fuego
10
-5
-15
blue
The negative value for Tierra del Fuego would indicate that January is warmer than July, while a positive value for San
Francisco indicates that July is warmer than January. Basically, you are looking at the net difference, but the value (positive or
negative) tells you which month is warmer.
Answer these questions using Maps 1, 2 & 3
All answers must be in complete sentences
Insolation (Map 1)
6. (1 pts) The hemisphere getting the most energy is the one experiencing summer. Which hemisphere is experiencing summer
in January? Which hemisphere is experiencing summer in July?
7. (1 pts) Why are the incoming solar energy visualizations for January and July nearly opposite of each other?
8. (1 pts) Notice that the two hemispheres do not get equal amounts of energy. During which month does the hemisphere
experiencing summer get the most energy? Is it the Southern Hemisphere in January or the Northern Hemisphere in July?
9. (1 pts) Why do you think that the summer hemisphere you selected in question 8 is getting more energy?
Surface Temperature (Map 2)
10. (2 pts) Why are the temperature patterns (map 2) so much more complex that the incoming solar energy patterns (map 1)?
11. (1 pts) Look at the visualization of earth surface temperature for January and July (map 2). Overall, which month is
warmer? (Hint: look at the extremes — where are the coldest areas? Where are the hottest areas?)
Seasonal temperature difference (Map 3)
Notice that the month with the highest temperature in #11 is the month getting less energy in #8. Why is that? In this section
you will explore this question by looking at differences in temperature. In the final section you will put it all together.
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12. (2 pts) The visualization in map 3 of seasonal difference is calculated by subtracting the January temperature from the July
temperature. Given the January and July temperatures for the following cities, calculate the seasonal difference (July January). What is the temperature difference and, based on the color bar in map #3, what color would each be?
City
Monterey, CA
Bismarck, ND
Honolulu, HI
Christchurch, NZ
Sydney, Aust.
July temp (C)
20
21
22
January temp (C)
18
-12
24
8
10
20
25
Difference (C)
Color
13. (1 pts) Why is the red mainly in the north and the blue mainly in the south (e.g. what do the colors red and blue mean in this
visualization)?
14. (1 pts) Contrast the changes on land with the changes on water. Which changes more, Land or Water?
15. (1 pts) Using the land mass distribution graph in map 3, which hemisphere has the most land, the Northern or the Southern?
Putting it all together
16. (3 pts) Look at the surface temperature by hemisphere graph in map 3. Why does the Northern hemisphere have a hotter
summer and a colder winter than the Southern Hemisphere? Write at least two paragraphs justifying your answer citing
evidence from the worksheets and graphics.
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