Earth’s Energy Budget-Seasonal Cycles
Students move through a series of short activities to explore and evaluate global solar radiation data from NASA satellites. In this process, students make qualitative and quantitative observations about seasonal variations in net energy input to the Earth system.
- Use evidence to create an explanation.
- Observe the seasonal changes to explain the phenomenon of Earth’s tilt and incoming solar energy.
NASA Phenomenon Connection
The Sun’s radiation and its interactions with different parts of the Earth system (atmosphere, biosphere, geosphere, hydrosphere) is the foundation of the global climate system. These interactions are key components of global climate models, which are developed by scientists and mathematicians to predict future changes to the climate. Using GLOBE and My NASA Data educators and students can access NASA satellite data to examine a variety of Earth system interactions. In this lesson, Earth’s Energy Budget-Seasonal Cycles, students move through a series of short activities to explore and evaluate Net Radiative Flux data from NASA satellites. In this process, students make qualitative and quantitative observations about seasonal variations in net energy input to the Earth system during the year of 2015.
- How does energy flow in and among the spheres within the Earth System?
- What does it mean that the atmosphere is in a "dynamic balance?"
- How do changes in one part of the Earth system affect other parts of the system?
National Geography Standards:
1. How to use maps and other geographic representations, tools, and technologies to acquire, process, and report information from a spatial perspective.
7. The physical processes that shape the patterns of Earth's surface.
STEM Career Connections
- Atmospheric and Space Scientists - Investigate weather and climate-related phenomena to prepare weather reports and forecasts for the public
- Computer and Information Scientists - Conduct research in the field of computer and information science
- Remote Sensing Scientists and Technologists - Research a variety of topics using techniques that allow the study of an object or phenomena without making contact directly with the object such as analyzing geological and geographical data. They typically work with aerial or satellite pictures.
Student Pages: Monthly TOA All-Sky Net Radiative Flux for Jan & March 2015 - July 2015
The Story of Energy in the Earth System
The Sun is the source of energy for the Earth system. This energy reaches the Earth primarily in the form of visible light, although it also includes some infrared energy (heat), ultraviolet energy, and other wavelengths of the electromagnetic spectrum. Taking into account night and day and the seasons, on average about 340 Watts of energy enter every square meter of the Earth system. This is slightly less than the energy that six 60 Watt light bulbs would produce, again, for every square meter of the Earth.
As it reaches the Earth system, some of the sunlight is reflected back to space by clouds and the atmosphere (particularly dust particles or aerosols in the atmosphere). A little more sunlight is reflected to space from the Earth surface, particularly from bright regions such as snow- and ice-covered areas. In total, about 30% of sunlight is reflected directly back to space. This percentage is called albedo. About 70% of the sunlight is absorbed by the Earth system (atmosphere and surface) and heats it up.
The elements of the Earth system (surface, atmosphere, clouds) emit infrared radiation according to their temperature, following the Planck function (http://phet.colorado.edu/simulations/sims.php?sim = Blackbody_Spectrum). Cold objects emit less energy; warm objects emit more. This infrared radiation is emitted in all directions.
Part of the infrared radiation emitted by the atmosphere is directed upward toward space. In fact, an amount of energy equivalent to the amount of sunlight energy absorbed by the Earth system goes back into space through this infrared radiation. This balance exists because the Earth system is in equilibrium. Scientists refer to all of the parts of this equilibrium as Earth's "radiation budget.”
The atmosphere also emits infrared radiation back towards the surface, at a rate of 340 Watts per square meter. Some gases in the atmosphere enhance this downward infrared radiation. This is called the greenhouse effect and is due mainly to water vapor in the atmosphere. Carbon dioxide, methane, and other infrared-absorbing gases enhance this effect. Without an atmosphere and the gases that are part of the greenhouse effect, the Earth would have an average temperature of -18 °C, too cold for life as we know it.
At the surface, two additional heat transfer mechanisms operate to balance the system, in addition to the radiation transfer: 1) convection and conduction in the form of thermals (which create weather), and 2) a change of state of water through evapotranspiration (which also feeds weather).
Just like a family budget for finances, the energy budget of the Earth should be balanced.
In equation form: Energy In = Energy Out
This balance can be considered at several levels in the Earth system: At the top of the atmosphere, the energy coming in from the Sun is balanced by sunlight reflected back to space and the net infrared emission from the Earth.
The equation is: Sunlight In = Sunlight reflected from clouds/atmosphere + Sunlight reflected from surface + IR emission
At the Earth’s surface, absorbed sunlight is balanced by the net IR emission and the conduction/convection and evapotranspiration.
The equation is: Sunlight absorbed + IR back radiation (greenhouse effect) = IR emission + Thermals + Evapotranspiration
The most complicated balance is in the atmosphere, where absorbed sunlight and energy absorbed from the surface are balanced by the net infrared emission.
The equation is: Sunlight absorbed + IR absorbed + Thermals + Evapotranspiration = IR emitted to space + IR emitted to ground
These balance equations are for an equilibrium state of the Earth. Equilibrium would be expected for a planet that has spent a long time in a stable solar system, but sometimes changes occur that take the system out of balance. For example, the ice ages occurred because of long-term changes in Earth’s orbit around the Sun, which resulted in a change to the “Sunlight In” term. Over time, reflected sunlight and IR emission changed to balance the first equation. The result was a colder surface and major glacial advances.
Prerequisites Student Knowledge
Locating given geographical locations using latitude and longitude and a world map
Seasons and Earth’s tilt
- “Where earth's axis of rotation points, with respect to a point in space, changes during the year.”
- “The angle between the earth's axis and the plane of the earth's orbit around the sun changes throughout the year.”
- “The orientation of earth's axis of rotation with respect to the sun does not change during the year.”
- “The intensity of sunlight at a place does not change from day to day during the year.”
- “The amount of time the sun is above the horizon at a given place does not change from day to day.”
Credit: AAAS Science Links
Display Student Page Monthly TOA All-Sky Net Radiative Flux for January 2015. Do not share the date of the image with students.
Have students brainstorm, journal, and share three qualitative and three quantitative observations. Possible answers may include, but not be limited to the following: (NOTE: It is hard to differentiate in the grayscale image; you may wish to project the colored image for whole class to view if color printer is unavailable).
Qualitative: e.g., 1.) There appears to be a balance of incoming and outgoing radiation at the Equator and at the northern edge of Antarctica. 2.) Antarctica is mostly losing energy by radiation. 3.) Greenland is losing energy by less radiation that its surrounding environments at its same latitude.
Quantitative: e.g., 1.) Around 10°N, there is a balance whereby there is an apparent balance between absorbing and reflecting energy. 2) The Southern Hemisphere falls mostly in the range of 30 - 162.5 W/m² . 3)The Northern Hemisphere falls mostly in the range of -30 to -207.1 W/m²
3. Direct students to observe the color legend and its values. It is important to note that the ranges vary among all plots, meaning that the minimum and maximum values may be different and represented by different colors on the color bar.
a. What could the false colors represent? units of measurement?
b. What time of year do you think this image represents? Why?
Again, review the Monthly TOA All-Sky Net Flux but tell students that this is an image captured by NASA satellites showing Atmospheric Radiation in January 2015.a. Knowing this date, how does this support or reject your ideas from earlier? Answers will vary.
Explain that places in white represent areas where the amount of incoming and outgoing energy are in balance. (NOTE: It is hard to differentiate in the grayscale image; you may wish to project the colored image for the whole class to view if a color printer is unavailable).a. Places where more energy comes into the Earth System then goes out (positive net radiation) are red/dark gray. Places where more energy goes out then comes in (negative net radiation) are blue/white.
Distribute the Student Sheet. Allow students to work in teams or independently to answer the following questions:
What systems are absorbing energy? atmosphere, land surfaces and oceans
Where do you think more heat is being given off? What evidence do you have to support this?
Where do you think there is more heat absorbed? What evidence do you have to support this claim?
Now, distribute compare with the image from March 2015.a. What do you notice? The red color is beginning to spread north, meaning that more solar energy is being absorbed in the Northern Hemisphere. The white areas are becoming more varied in location meaning that there is a balance of absorption and release.
b. Where is energy being released than absorbed? the Southern Ocean and Antarctica.
Post the following questions for students to consider as they watch an animation:
a.) How does net radiation vary over the year at key months in the solar cycle?
b.) What are the key months where you see the most change?
Show Animation of Earth Net Radiative Flux and then review students’ answers.
a.) The maps and animation illustrate how net radiation varies over the year at key months in the solar cycle. In June, the tilt in Earth’s rotational axis has its strongest influence on the amount of sunlight reaching the ground in each hemisphere. One hemisphere is tipped its farthest away from the Sun, and other is tipped toward it. Net radiation is strongly positive across the Northern Hemisphere in June and strongly negative across the Southern Hemisphere. In December, the pattern reverses.
3. Play the following video
Using the additional images provided on the Student Pages, compare the monthly changes. Note: The only Student Page with an unlabelled date is January 2015.
Discuss whether the patterns students observe are consistent with your earlier observations.