Topic Guide: Seasonal Variation
and the Earth’s Heat Budget
In
this activity you will form groups, conduct research into Seasonal Variation
and the Earth’s Heat Budget, and report back to your lab section in
the form of a presentation. At the end of this activity you will find suggestions
for the format of the presentation. You will use the data you investigate
as evidence for your statements. Please use these suggestions and the “How
to make a class presentation” (Resource 1) as guidelines for your presentation.
Overview:
The Earth receives the energy that drives the climate from the sun. Because the Earth’s axis is tilted in relation to the plane of the Earth’s orbit around the Sun, the amount of solar radiation received by the Northern and Southern Hemispheres varies with the seasons. This variation produces interesting patterns in climatic parameters, some of which we will investigate in this activity.
Incident solar energy is transformed by the Earth’s atmosphere, clouds, and surface. It can be reflected, absorbed, and re-radiated. The datasets in Worldwatcher allow you to investigate satellite data that can be used to help understand these processes.
Key processes and concepts to review before beginning:
- Do the “Getting Started” tutorial in Worldwatcher (described in the lab book), if you haven’t already.
- How the Earth’s tilt and orbit cause the seasons
- Earth’s energy balance diagram in text or lab workbook
Resources:
- WorldWatcher
- Your textbook
- Heat Budget diagram
After completing this investigation you should be able to:
- Understand how solar energy is distributed over the Earth’s surface.
- Understand the effect of the latitudinal imbalance in the Earth’s radiation.
- Understand how heat is transferred from low latitudes to higher latitudes
- Understand the effect of the concentration of landmasses in the Northern Hemisphere on seasonal variations
You
can go straight into exploring the data, but if you need more background information
about paleoclimate, please review the websites that provide background information
(found after the data section).
Incident Solar
Energy Data:
Open the incoming
solar energy dataset (click
on “Energy Balance Dataset” in the Welcome to Worldwatcher
window) on the WorldWatcher CD. First open one dataset for
reference to its color scale and other metadata and then to create a movie
from the datasets using the months January through September.
The incoming solar energy
datasets represent solar energy averaged over the day, so the effect of Earth’s
rotation will not show up.
What does the distribution of incoming solar energy look like for January? What is the latitude of maximum incident energy? Why do we see this pattern?
Step through February, March and April. What changes are
happening? Can you explain what is happening to cause this change?
Step through May, June and July. What’s happening
to the pattern of incoming solar energy for these months?
Make a general statement about what is happening to this data as we progress from January to July.
Draw a diagram of the Earth and the Sun to illustrate what is happening. Include a diagram for the months of January, April, July, and September.
Puzzle: Notice that at the extreme winter months (e.g. January),
the incident solar energy seems to decrease as you move to lower latitudes,
but then increase near the South pole. Why should this be?
Reflected Solar Energy Data
Look at the reflected solar energy data also found on the WorldWatcher CD. It is helpful to follow the same steps as you did when exploring the previous dataset. First open one dataset for reference to its color scale and other metadata and then to create a movie from the datasets using the months January through September. The reflected energy dataset is the energy reflected from the Earth/atmosphere combination directly back into space. Read the legend on the plot of the single dataset to verify that this is true. Don’t use the “clear sky” data yet.
Is there a pattern there? Does this pattern have anything to do with what you saw in the incoming solar energy?
Make a general statement about what is happening to this data as we progress from January to July.
You can use the incident solar radiation to calculate the albedo of the Earth/atmosphere combination. What is the maximum and minimum albedo? Why does it occur where it does?
Open the “clear
sky” data and compare the results to the previous data.
What can you say about the effect of clouds from this? Suggestion: subtract the corresponding average and clear sky datasets for each month to see the effect of the clouds.
Absorbed Solar Energy Data
Now look at the absorbed solar energy dataset from the WorldWatcher CD. Begin by using the “clear sky’ datasets.
Is there a region where the values for the absorbed solar
energy don’t change much as we progress from January to July?
What do we call that region?
Why does this pattern occur?
Describe some of the other patterns you noticed.
Is there a difference between ocean and continents for the absorbed solar energy values in the same region?
What might cause these differences? Suggestion: to explain
a difference using data, use both the incident and reflected solar radiation
data.
Surface Temperature Data
We already looked at surface temperature dataset in the WorldWatcher tutorial, but we will now look at it more closely since there are some interesting patterns that we have not yet explored. First open one dataset for reference to its color scale and other metadata and then to create a movie from the datasets using the months January through September.
Step through the data from January to September. What can you say about the surface temperatures at the poles?
At the equatorial region?
First, concentrate on the Northern Hemisphere, stepping through the months from January to July.
What do you notice about the latitudinal extent of the cold region as compared to the Southern Hemisphere?
Why might this occur? A hint: what are the cold temperatures
overlaying?
Now watch the Northern Hemisphere as we slowly progress from January to February to March to April.
Do the temperature changes progress or regress evenly?
If not, why?
Look at March and April. What are these remaining pockets of cold temperatures?
Why are they there?
Now look at the Southern Hemisphere, stepping through the animation data from January to February to March to April.
What is the general pattern that you see?
Is it an even progression/regression?
What is a possible reason for this pattern?
Step through the animation data from May to June to July looking at the South American continent. What do you see happening?
Why is this happening?
Net Energy Balance Data
The last WorldWatcher dataset we will look at in the Energy Balance. First open one dataset for reference to its color scale and other metadata and then to create a movie from the datasets using the months January through September.
Net Energy Balance is equal to (absorbed solar energy – energy radiated back into space). A positive value indicates that more energy is being absorbed than is being radiated back to space (indicating warming), while a negative value indicates that more energy is being radiated back to space than is being absorbed (indicating cooling). This must be zero, averaged over the entire Earth (see the lab text). But the Net Energy Balance dataset shows that this balance does not exist at a given latitude, so the excess heat at the equator must somehow get to the higher latitudes.
Can you think of mechanisms that allow the excess heat at the equator to get to the higher latitudes?
What pattern do you see as you step through the months
January to July?
Is there a region where the net energy balance remains
fairly high?
What are the general relationships you have derived from
the data?
Background information: Please take some time to learn more about the background information available for the topic of Seasonal Variation and the Earth’s Heat Budget. If you learn something new and interesting, please share it with the lab in your presentation.
http://www.oceansonline.com/heat.htm
http://www.sfos.uaf.edu/msl111/notes/heat.html
http://www.cgd.ucar.edu/cas/papers/jgr2001a/jgr_interann.html
http://education.gsfc.nasa.gov/experimental/all98invProject.Site/Pages/trl/inv2-1.abstract.html
Presentation
Framework
Your presentation should include a brief overview explaining the significance of Seasonal Variation and the Earth’s Heat Budget. You should then choose as many of the following topics as is necessary to explain the concept. Choose topics that you think might be relevant to understanding seasonal variation, heat transfer, and uneven heating of the hemispheres. Your presentation should include interesting findings from your investigations, backed up with data. You must use the physical data in your presentation.
You
may choose from the following list of topics, or investigate a topic of your
own. The topics in the list are examples of investigations that could be made
using the data available at the URL’s listed above.
Data driven topics: