CAMEL
Module #7 - The Earth’s Radiation Budget (LAB)
Module Title
Summary
Short Description
The Earth’s Radiation Budget: Balancing Your Heat
Book
In this lab, students learn how the Earth’s radiation
budget works and the ways certain events or forces
impact that budget. Some radiation from the sun is
reflected back into space (shortwave) and some of it is
absorbed. The absorbed energy warms the Earth’s
surface (longer wavelength). This process of absorption,
reflection, and reemission establishes the global energy
balance, which is fundamental to Earth’s climate system.
Students enhance their understanding of the Earth’s
radiation budget and how it influences the Earth’s
climate through the application of NASA data.
Additionally, there’s a hands-on activity to test assess
students’ knowledge of the lab’s concepts.
Image
Source: http://calipsooutreach.hamptonu.edu/aerosols-graphics/radiation_budget.jpg
Learning Goals
Context for Use
Students will learn the following:
 To utilize real data to create spatial and temporal
maps
 To plot data that demonstrates the different types of
radiation
 To consider the ways the Earth’s radiation budget
affects climate.
The format suggested for this lesson is a lab. Since it
requires no laboratory equipment, the class size and
classroom type can range from a small seminar to a
medium sized lecture hall. The only mitigating factor
related to class size is the necessity for each student (or
perhaps pairs if the instructor elects to make the lab
report a paired activity) to have a computer terminal or
laptops. The class does not need to have a SmartBoard
or LCD projector, since the lab work will be conducted
at individual computers, but access to multimedia
Description and Teaching
Materials
equipment is preferred. The hands-on portion of the lab
requires adequate space and equipment. See
“Description and Teaching Materials” below for link to
the source lab.
Description and Teaching Materials:
The structure and primary components of this lab lesson
is sourced from Columbia University’s Earth
Environmental Systems Climate (EESC) course (Spring
2011). The instructor/TA will need to be familiar with
the introductory content of the lab. There are a number
of terms that need to be understood before the computer
lab begins (see the first section below for a review of key
concepts/terms).
I. Background Information
A. How the data were collected
The Earth Radiation Budget Experiment (ERBE) was
designed to collect information about sunlight reaching
the Earth, sunlight reflected by the Earth, and heat
released by the Earth into space. Since October 1984,
ERBE has employed three satellites to collect this
information: ERBS, NOAA-9, and NOAA-10. Each
satellite was equipped with special instruments
(scanners) that measured radiation. Radiation was
measured in three wavelength bands:
 Total: radiation in the 0.2 to 50 micron (mm;
1x10-6 meters) wavelength band.
 Longwave: radiation in the 5 to 50 mm
wavelength band.
 Shortwave: radiation in the 0.2 to 5 mm
wavelength band.
Technical information about the scanners and other
information about the experiment can be found at the
following NASA web sites.
1. The Earth Radiation Budget Experiment.
2. The NASA Educational Resources website - the
Trading Card page (click on Earth's radiation
budget ).
3. JPL Quick-Look at ERBS site.
4. A NASA Fact Sheet on ERBE.
B. The structure of the ERBE dataset, and how to
access it
The ERBE data available from the IRI/LDEO Climate
Data Library, contains information from all three ERB
satellites and their combinations (for the periods when
the satellite provided overlapping observations). The data
are organized by satellite and variable.
Open the ERBE dataset. (Note that you just opened a
new browser window. Please move that browser aside
so you can continue to access it later).
As indicated above, the ERBE data include shortwave
(solar) radiation reflected by the Earth's surface and
longwave radiation emitted by the Earth. These data are
processed by month for the duration of the satellite flight,
and are provided on a grid of latitude and longitude lines.
On this grid, longitude varies from 1.25°E to 1.25°W by
intervals of 2.5° and latitude varies from 88.75°N to
88.75°S by intervals of 2.5°, making a grid with144
longitude points and 72 latitude points. You can read the
information on the time and space grids when you click
on a satellite name in the viewer. For example, in the
ERBE dataset page you opened earlier, click on the link
Climatology. This is a time averaged set using data from
the NOAA 9 and NOAA 10 satellites. Each calendar
month was averaged for four full years of available data
(February 1985 to January 1989).
The Climatology dataset is divided again into three data
types (as are all other ERBE datasets as well):



clear-sky: Satellite measured radiation averaged
only from satellite views that were free of clouds.
cloud-forcing: The difference between clear-sky
and cloudy-sky radiation, showing how radiation
at the top of the atmosphere differs in the
presence or absence of clouds.
total: Satellite measured radiation averaged over
an entire month regardless of cloud coverage.
For each of these data types, the "data tree" branches off
further, as you can see by clicking on their links. For
example, on the NASA ERBE Climatology page, click
on clear-sky. Now you can see the different variables
measured by the satellites, and provided by NASA in the
ERBE dataset:




albedo: The ratio between the shortwave
radiation reflected from Earth and what is coming
in from space (this is a unit-less number
expressed in percent).
longwave radiation: The longwave radiative flux
emitted from Earth (in W/m2).
shortwave radiation: The shortwave radiative
flux reflected from Earth (in W/m2).
net radiation: The difference between the
shortwave radiative flux absorbed by the Earth
climate system and the longwave radiation
emitted into space (in W/m2).
Also on this page (titled NASA ERBE Climatology
clear-sky), under the section Grids, you can find the
Latitude and Longitude grid information described
above. Note that the Time grid for this dataset is the
period of overlap between the two satellites, NOAA 9
and NOAA 10.
More information about the ERBE dataset can be
accessed by clicking on the "NASA ERBE
documentation" link in the blue IRI box in the upper left
corner of the browser window.
Click on albedo. Notice that the page no longer contains
dataset links. You are now ready to access the actual
albedo data month by month and to view them using the
different buttons on the page.
The same set of variables is given in the total dataset but
the variable list under cloud-forcing is somewhat
different. In the next section, we will work with the latter
data sets to study the effects of clouds on the Earth
radiation budget.
Click on the New Views link to access the NASA ERBE
Climatology clear-sky albedo data.
A. Clear-Sky Albedo
The instructions below assume you arrived at the
radiation budget data web site following the instructions
above.
Go to the open viewer window displaying the NASA
ERBE Climatology clear-sky albedo data. Clear sky
albedo is the light reflected back only from cloudless
areas of the Earth's surface (this is calculated by ERBE
scientists by identifying cloud-free regions during each
satellite's observations and averaging their data
separately). If the maps you are examining of clear-sky
albedo have white patches, these patches are areas so
often covered by clouds that there are not enough cloudfree observations to create a reliable average.
All ERBE data are taken from January to December for
annual variations to be apparent in the measured
variable. Use the pop-up menus to look at the data as
colored contoured values, outline the continents by
"drawing coasts," and then set the range of the albedo
from 0 to 90. Click the "Redraw" button.
Task 1: Create albedo maps for January, March, July and
September.
 Spatial patterns: Which regions have > 30% albedo,
and which regions have < 30% albedo?
 Patterns through time: In a few sentences, describe
how the albedo varies seasonally by comparing data
for the four key calendar months.
B. Short Wavelength Solar Radiation Reflected from
the Earth
Reflected short wavelength radiation (SW) is a direct
measurement of short wavelength radiative flux reflected
from the Earth’s surface. Unlike albedo, this is an
absolute measurement and not a ratio. Thus, the albedo
can be where the actual reflected radiation is low.
Task 2: Create 4 maps for reflected SW radiation.
Briefly compare January albedo and January SW maps.
Focus on Antarctica and northern Europe, Asia and
North America. Is high albedo always accompanied by
high outgoing SW? If not, where?
C. Total Incoming Radiation
There isn’t an ERBE data set of total incoming radiation
received at the top of the atmosphere. However, if the
total amount of short wave radiation that is reflected and
the albedo is known the amount of incoming solar
radiation can be calculated. How is this done?
Remember that:
Albedo = (reflected solar radiation) / (incoming solar
radiation)
This implies that:
(incoming solar radiation) = (reflected solar radiation) /
albedo
Review results of from the browser interface and the
maps illustrating results. Note that the lines of equal
radiation are all straight and paralle to lines of latitude.
Task 3: Examine the plots of incoming solar radiation in
March, June, September, and December to see the
changes through time. In two sentences, describe how the
incoming solar radiation varies with A) Latitude, and (B)
Seasons.
D. Clear-Sky Long Wavelength Radiation
This last data set is for the radiation that the Earth emits
in response to being warmed by the Sun. Since the Earth
is much colder than the sun, its radiation to space peaks
in the infrared (long wavelength) band of the
electromagnetic spectrum. Because some components of
Earth’s atmosphere trap longwave radiation (the
greenhouse effect), emission to space occurs not at
Earth’s surface, but at a higher level in the atmosphere
that varies depending on the concentration of greenhouse
gases (mainly water vapor) at that location.
Geographic variations in this data set are a result of
differences in the effective temperature (the temperature
at which the planet is emitting radiation to space) at
various locations. Effective temperature depends both on
the temperature at the surface, and on the concentrations
and vertical profiles of greenhouse gases.
Task 4: Study the longwave maps provided for January,
March, July and September (see accompanying pdf file).


In no more than 3 sentences, describe the regions on
the globe that emit the least and most longwave
radiation (you can be general here – wide latitude
bands, “desert,” “Northern Africa,” etc.).
Look at your January map, at 40˚N latitude.
Compare emitted longwave radiation for oceans and

continents (North America is the best example in this
case). Also broadly compare Northern and Southern
hemispheres – which emits more longwave?
In two sentences, describe the outstanding changes
you see in the 4 maps that occur as you move through
the year.
Discussion
1. Why does reflectivity vary across latitudes, and
within continents such as Africa and North America?
2. Some regions (like Greenland) have high albedo, but
low outgoing shortwave radiation. Why?
3. Why does incoming radiation vary with latitude and
time of year?
II. Hands-on Experiments
Experiment A: Measuring Incoming Solar Radiation
as a Function of Latitude
In this experiment, students will try to demonstrate the
effect of Earth's spherical shape on the change of solar
radiation with latitude. In most places on the Earth,
sunlight does not strike perpendicularly to the surface,
but at some oblique angle, even at local noon. In general,
the warmest part of each day occurs when the sun is most
directly overhead (i.e. closest to a 90 degree angle). Now
students will demonstrate this effect in a simple
laboratory setting.
The experiment equipment consists of a circular globe
section, a solar cell mounted on this globe section, and a
current meter connected to the solar cell. Set the digital
current meter to mA (milliamps). The solar cell generates
electrical energy proportional to the amount of light it
receives. The class will be able to tell how much shortwave (visible) energy reaches the solar cell by looking at
the strength of the electrical current. Start by turning the
globe so that the solar cell is exactly perpendicular to the
line between the light source and the globe section. This
is analogous to standing on the Equator at noon during
equinox (or to standing at 23.5°N during the summer
solstice). Write down the current shown on the current
meter. Now rotate the globe section so that the solar cell
moves to various "latitudes." This will be analogous to
standing anywhere but directly under the sun. For
instance, if you move the solar cell to 41 degrees north
latitude, that is analogous to measuring the angle of the
sun while standing in Manhattan at noon on the equinox.
RESULTS
 Write down the currents for various latitudes. It
doesn't matter which "latitudes" you use, as long as
you include the equator and you find a range of
values (about 10 – 15 data points are good). Report
these in a table.
 Enter your values in Excel and make a plot of current
(analogous to solar intensity) vs. latitude. Make sure
you label your plot well (that is, give your graph a
title and label the axes).
DISCUSSION
1. What kind of a trigonometric function should this
curve trace? Does it? If not can you explain the
source of errors?
Experiment B: Albedo
This experiment should give students an appreciation for
where on Earth albedo might be high or low.
Students mount a photometer about 20 cm above the
table pointing down. The light source is a desk lamp,
which also is pointing down 20 cm above the table.
Make sure that the reflected light from the light source
can reach the photometer. To find the intensity of light
being reflected, we place a piece of aluminum on the
table below the photometer and measure the current
output of the photometer (use the unpainted back of the
granite colored metal panel to do this).
Students assume that the aluminum perfectly reflects all
the light shone upon it and thus the photometer picks up
all the light emitted by the source. This is therefore a
case of perfect reflectivity, or an albedo of 1 (100%).
Write down the corresponding current output by the
photometer. Now replace the plain aluminum panel with
the white painted panel. Write down the current. The
ratio between the current now and that recorded by the
bare aluminum is the albedo of the white panel. Any
light lost is either absorbed by the white panel or
scattered such that it does not reach the photometer. The
albedo is the percentage of energy that is not absorbed or
scattered.
Measure the albedo for white panel and the remaining
five colored mental panels (black, tan, green, blue, and
granite).
RESULTS
 Make a bar graph of albedo vs. color using Excel.
 In one or two sentences, compare the albedos of the
black and white panels.
DISCUSSION (In 1/3 of a page or less – be concise)
1. What regions or materials on Earth might be
represented by the six painted panels?
2. Do you think there are any significant regions on
earth that are not represented by these six colors?
3. Are your answers to 4 and 5 supported by the
albedo values from the ERBE data that you
examined? Do they make sense?
Below are the links for source material and resources:
 EESC course page:
https://courseworks.columbia.edu/cms/
Handouts and Directions:
 Lab instructions
 Data
 Lab materials and instructions
Background Information for instructors/TAs:
Instructors/TAs should familiarize themselves with the
introductory information provided with the EESC lab.
Equipment/Supplies:
Data Lab
 Computer lab or moveable laptops with Internet
access and Excel.
 LCD projector
 Handouts - lab instructions
 “Writing a Lab Report” (may have already been
disseminated)
Hands-on Experiments
 Instructions
 Circular globe section,
 Solar cell
Teaching Tips and Notes
Assessment
 Current meter
 Photometer
 Desk lamp,
 Metal panel
See background information for instructors/TAs.
Students summarize their findings in a lab report.
References and Resources
All resources cited in the description of the course.