Why Is Alaska So Cool?
Model Extender
Activity 9: Model Extender
Guiding Question
Is sunlight intensity the only factor in determining how cool it is in Alaska?
Objectives
After completing this activity, a student will be able to




Identify the simplifying assumptions in several models.
Identify five specific factors in an extended model of the earth’s energy budget.
Analyze the importance of one factor in determining the temperature of a place.
Report the findings to others in a team. Read and comment on the analysis done
by others on the team.
Materials
daily log, Excel spreadsheet June_climate_compare
Studying Simplifying Assumptions
As you read through this activity, write down your answers to the numbered questions
with numbers. Check your answers to these questions with the answer key provided.
Think a moment about the question for this module, “Why is Alaska so cool?”
1. Do you feel that you have learned enough from the set of activities you have
completed so far to be able to answer this question?
The word “cool” implies heat or temperature.
2. Did we study the temperature of Alaska or any other place in this set of activities?
We have made many simplifying assumptions by investigating only a few of the
factors that might help us answer the question “Why is Alaska so cool?” A simplifying
assumption is an assumption that “ignores” some aspect of a real situation in order to
simplify for analysis.
The focus of our studies to this point has been solar intensity, not heat. How are
sunshine and temperature related? We can begin to think about this by studying the
following diagram.
Activity 9
Page 1
Model Extender
Why Is Alaska So Cool?
This diagram is actually a very simple visual model that shows that the sun shines in a
place, the sunlight becomes heat, and the heat affects the temperature of the place.
3. What factor that you studied corresponds to the “sun shines” circle in the diagram
above?
4. Predict how the length of time that the sun shines would affect the temperature of a
place.
Look at the model below to see how it was modified to include both the sunshine
duration and intensity.
If you look at our visual model above, you will see that something is missing. If heat
just flowed into a place, it would get hotter and hotter. We know that the temperature
of Alaska doesn’t just get hotter and hotter.
5. Draw “heat flowing out” in the above model.
6. Did you collect any data that would correspond to this addition?
Extending the Model
The diagram on the next page depicts a model of the heat that flows to the earth and the
heat that flows away from the earth. Fewer simplifying assumptions have been made in
making this model. Let’s examine the parts of this model.
7. In this model, what color arrows would represent “heat flows in?”
8. What part of the model relates to the amount of sunlight that reaches the upper
atmosphere of the earth?
9. What part of the model below would relate to the solar intensity that you measured?
10. What parts of this model include “heat flows out?”
Page 2
Activity 9
Why Is Alaska So Cool?
Model Extender
http://asd-www.larc.nasa.gov/erbe/components2.gif
Activity 9
Page 3
Model Extender
Why Is Alaska So Cool?
The extended model was created from data that scientists collected from the ground
and from satellites. These are average values and do not necessarily reflect the
conditions at any particular spot on the earth on any specific date. Scientists might be
interested in collecting this kind of data to solve a variety of problems, for example
predicting the weather, locating good sites for solar energy, and modeling the effects of
increased production of carbon dioxide.
Factor Comparisons
In teams of students, you will consider each of the yellow arrows in the diagram. The
arrows were labeled by a green number so that you can correlate these factors with data
you collected and with the data available on a NASA website. Be sure that you
understand what each of these factors means. You will be considering each of these
factors in the final activity of this module when you write your answer to the question
“Why is Alaska So Cool (when the daylight hours are so long)?”
Insolation is the technical term given to the sunshine coming in. Look at the green
number 1 in the diagram. The term climate scientists give to this is Top-of-atmosphere
insolation, or the amount of sunlight that reaches the top of the atmosphere (in
kWh/m2/day). Please note that this is different from the unit in which you measured
solar intensity, W/cm2.
11. Did you measure top-of atmosphere insolation?
12. Which do you think measured this value, ground-based instruments or satellitebased instruments?
13. What did you measure that would relate to the green number 2 in the diagram?
Cloud cover is represented by the two green number “3’s”in the data. Refer to the data
you collected about clouds. You made general observations without assigning any
numbers to it. Scientists like to assign numbers that they can then use in their
computational models. A whole day without clouds is called a clear sky. Technically,
clear sky refers to a cloud amount less than 10%. A factor you will use in your further
study of this model is daylight cloud amount. If the daylight cloud amount is 100%,
then the skies are totally overcast during all of the daylight hours. This percentage,
then, refers to the average cloudiness during all of the daylight hours.
The green number 4’s in the diagram relate to how much sunlight is reflected
and absorbed by the atmosphere on a clear day. The clear sky insolation
clearness index is defined as the fraction of insolation at the top of the
atmosphere which reaches the surface of the earth during clear sky days (when
the cloud amount is less than 10%). If, for example, the values for atmospheric
reflection (6%) and absorption (16%) are added together, you get 22%. In
Page 4
Activity 9
Why Is Alaska So Cool?
Model Extender
fractional form, this is 0.22. If the fraction of absorption and reflection are 0.22 on
a clear day, the clear sky insolation clearness index is 1 - 0.22 = 0.78.
14. If the clear sky insolation clearness index is .70 and 10 kWh/m2/day are
coming in to the top of the atmosphere, how many kWh/m2/day of that
sunshine will reach the green number 2 in the diagram?
In the diagram, the green number 5 represents the percent of sunlight reflected
from the earth’s surface. This is called surface albedo by scientists and is
reported in percent or decimal form.
15. What kinds of terrain would you predict to have a high surface albedo?
(HINT: when do you most need to wear sunglasses?)
16. What data that you collected is represented by the green number 6 in the
diagram?
Predict which of the values represented by the green numbers 1 through 5 would
be different for different solar angles and latitudes. Write your predictions in
your journal.
Team Analysis
Open the Excel spreadsheet called “addfacts.” This spreadsheet contains solar and
climate data for 19 sites in the U.S. and Palau, a U.S. protectorate. The data comes from
the Surface meteorology and Solar Energy Data Set (release 3) and is posted on a NASA
website. Examine the spreadsheet, called “data.”
17. What is the range of latitudes represented?
Look at the names for the other kinds of data that are listed. The climate data is
averaged for ten years for the month of June. If your location is not represented and you
wish to include it in the spreadsheet, go to http://eosweb.larc.nasa.gov/sse/. Click on
“Meteorology and Solar Energy” and then click on “Enter the latitude and longitude.”
Register or log in if you previously registered. Enter your latitude and longitude in the
required format. Be sure to include the negative sign for longitudes west of the prime
meridian. Click “submit.”
Choose one of the following factors to analyze: clear sky insolation clearness index,
daylight cloud amount, top-of-atmosphere insolation, and surface albedo. Your tool
for this part will be Excel. Using the provided data set of locations throughout the
nation, analyze the effect, if any, of your particular factor on temperature. If your factor
is top-of-the atmosphere insolation, for example, plot temperature as a function of this
Activity 9
Page 5
Model Extender
Why Is Alaska So Cool?
factor. The temperature would be plotted on the X axis and the factor on the Y axis.
Then, decide whether this factor varies with latitude.
Write a paragraph for each relationship (temp vs. factor and factor vs. latitude) in which
you report your findings for the students in your team to review. With each paragraph
include a graph or other evidence to support your findings. Read, reflect on, and
respond to your teammate’s reports.
Page 6
Activity 9