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Virtual Ballooning to Explore Earth's Atmosphere

Summary:
Students will use software to launch virtual weather balloons and collect data about Earth's atmosphere. Materials:

Worksheets:

Source:
Windows to the Universe original activity by Randy Russell.
Grade level:
6 - 12
Time:
1 hour
Student Learning Outcomes:
  • Students will be able to describe how temperature and air pressure vary with altitude in Earth's atmosphere.
  • Students will design a research plan and make decisions in the process of conducting a simple experiment or "research project".
  • Students will learn about layers of Earth's atmosphere, electromagnetic radiation, the ozone layer, and the Greenhouse Effect.
Lesson format:
Computer and paper-and-pencil based activity.

National Standards Addressed:

DIRECTIONS:

  1. Ask students what they already know about the atmosphere. Prompt them especially to share their knowledge about layers of Earth's atmosphere and how they think temperature and pressure vary with altitude. This could include having them draw from personal experience ("Last summer my family went on a vacation to the mountains... I was surprised to see snow in June... we kept getting out of breath while hiking.")
  2. Decide whether and how you want to divide up students into groups or teams for this activity. Students can do the activity individually; however, group work could lead to interesting planning discussions between students. Especially if you have few computers, you could have a single group do the planning for just one balloon flight in a series of flights.
  3. Set the stage for the scenario of this activity - "You are researchers studying the atmosphere... you have a limited number of balloon flights with which to collect data...". Let the students know that they have just four flights in which to accomplish this, and that each flight can only gather four data points (or however many flights and data records per flight you decide is appropriate for your students, if you decide to use something other than the default values).
  4. Give students copies of the worksheet. Point out the items they need to find out as a result of their "research program". These include: temperature and pressure at the top of Mt. Everest, altitude at which air pressure is half of sea level value, sudden changes in temperature or pressure that indicate boundaries between atmosphere layers, and trends in temperature and/or pressure vs. altitude within each atmospheric layer.
  5. Have the students start the Virtual Ballooning software. Tell them to click the "Play Game" button to go straight to the ballooning simulation; or have them first click the "Settings" button to adjust the number of flights and number of records per flight if you decided to use values other than the defaults (then have them click the "Play Game" button).
  6. Decide how much (or little) advice you want to give students in planning their initial balloon flight. It is probably wise for them to gather data across a wide range of altitudes at first, and then to fill in the "more interesting" parts of that "rough sketch" graph where properties are changing quickly with later flights. The default values of 10 km for the starting altitude and 10 km for the altitude interval are pretty good for this. Once the students have planned their first flight, have them click the "Launch Balloon" button. Remind them to fill in data about each flight on the student worksheet.
  7. After the first flight, remind students to look at both temperature and pressure data (use the buttons below the graph to switch back and forth)... and to recall the questions on the student worksheet they are expected to answer.
  8. Once again, decide how much (or little) advice you want to give students in planning their second balloon flight. In general, they should 1) try to fill in altitude ranges where there are gaps in their data and 2) try to get more data in altitude ranges where unpredictable change is happening as opposed to ranges in which the data seems to have a predictable trend (a straight line, etc.). They should also avoid repeated sampling of the same altitudes (if they already have data at 10 km, they should fill in values at 9 or 11 km on later flights, for instance).
  9. Have students click the "New Flight" button to prepare for their second flight. Then have them set new "Start Recording Altitude" and "Altitude Recording Interval" values using the popup menus. Remind them to record data about this flight. Tell them to click the "Launch Balloon" button when they are ready.
  10. Remind students that they now have only two flights remaining. Encourage them to revisit the questions on the worksheet and choose options for their remaining flights that allow them to gather the data they need to answer those questions.
  11. Proceed in a similar fashion to complete the 3rd and 4th flights.
  12. Have students report on their results to the class. Ask each group after the first to remark on any details they discovered that had not been reported by prior groups, or any of their findings which conflict with those of another group.
  13. Getting all of the necessary data in just four flights with four records per flight may be very challenging for your students, depending on their age and level of comprehension. We recommend announcing at this point that the "researchers" have received a new grant to continue their study of the atmosphere, and thus have sufficient funding for another series of four flights. You may want to make a judgment call, after you watch students report their results, as to whether a second set of flights is needed. Class time may also factor into this decision. If you decide to award your students a new set of flights, have them click the "New Game"; button to start again and then precede in the same fashion as before.
  14. After students finish their "research campaign", you may want them to see a full set of results to help them fill in knowledge about altitude ranges that they may not have sampled fully. Have students click the "Settings" button, then set the "Data Sample per Flight" to 60. Then click the "Play Game" button, click the "New Game" button, set the "Start Recording Altitude" to sea level and the "Altitude Recording Interval" to 1 km. Launch the balloon and watch it fill in a detailed graph. Make sure students look at both the temperature and pressure graphs.
  15. Follow up with discussions of experimental design, more info about layers of the atmosphere, explanations about ozone in the stratosphere or the Greenhouse Effect, a review of the electromagnetic spectrum, etc. See the "Background Information" section below to delve into these topics in more detail. We also have numerous pages on our web site covering these topics as well; you may want your students to read those and look at the accompanying pictures, diagrams, and graphs to extend their understanding of these topics.

BACKGROUND INFORMATION:

Layers of the Atmosphere

Scientists divide the atmosphere up into 4 or 5 distinct layers, as follows:

  • Troposphere - from ground level up to somewhere between 8 and 16 km (5 and 10 miles, or 26,000 to 53,000 feet), depending on latitude and season. Most of the mass (~80%) of the atmosphere is here and essentially all weather occurs in the troposphere. Temperature decreases with increasing altitude. The tropopause is the name given to the boundary between the top of the troposphere and the bottom of the stratosphere above.
  • Stratosphere - extends from the tropopause to about 50 km (31 km) up. Temperature rises with altitude. Contains the ozone layer, which shields Earth's surface from most solar ultraviolet radiation. Top boundary is called the stratopause.
  • Mesosphere - extends from the stratopause to about 85 km (53 miles). Many meteors burn up here. Temperature decreases with altitude. The coldest temperatures in Earth's atmosphere, about -85° C (-120° F), are found near the top of this layer. Top boundary is called the mesopause. Part of the ionosphere, a series of sub-layers containing higher levels of ionized and thus electrically charged atoms and molecules, is in the mesosphere.
  • Thermosphere - from the mesopause to between 500 and 1,000 km (311 to 621 miles) up. Air is very, very thin here. Variations in solar heating due to the Sun's 11-year sunspot cycle and to short-term space weather storms cause the air in this layer to expand and contract; thus the large variation in altitude of the top of this layer (the thermopause). Most of the ionosphere is within the thermosphere. Temperatures increase with altitude, but also vary dramatically over time in response to solar activity. The aurora (Southern and Northern Lights) periodically light up the thermosphere. Top boundary is called the thermopause. Many spacecraft actually orbit within the thermosphere.
  • Exosphere - from the thermopause on upward. Not universally recognized as a layer of the atmosphere. The exosphere is essentially the sparse scattering of atmospheric gasses as they gradually thin to the near-vacuum of space.

Concepts Embedded in this Activity

There are several interrelated concepts relevant to Earth's atmosphere and the process of scientific investigation embedded within this activity. You may wish to emphasize certain aspects that best match your curriculum. Topics this activity touches upon include:

  • layers of Earth's atmosphere (and especially temperature variations within those layers)
  • air pressure & density throughout the atmosphere (including the concept of lapse rate for more advanced students)
  • ozone, the Ozone Layer, and the Ozone Hole - including the creation of ozone, where it is found, and its role in heating the stratosphere and protecting us from excessive UV radiation
  • greenhouse gases and the Greenhouse Effect - and their role in warming Earth and the troposphere from the ground upward
  • electromagnetic radiation and the electromagnetic spectrum - especially visible light, ultraviolet radiation, and infrared "light"
  • electromagnetic radiation and the atmosphere - at which wavelengths is the atmosphere transparent or opaque, which gases absorb which frequencies of UV (ozone) or IR (water vapor, carbon dioxide, methane, etc.), how absorption of EM radiation can cause heating of certain regions of the atmosphere
  • effects of human activities on the atmosphere - global warming due to increases in anthropogenic greenhouse gases in the troposphere, increased UV exposure due to ozone depletion in the stratosphere

The Greenhouse Effect and greenhouse gases: Solar energy of various wavelengths across the electromagnetic spectrum arrives at Earth at the "top" of our planet's atmosphere. Most of that solar energy is in the form of visible light. There is also quite a bit of ultraviolet (UV) and infrared (IR) radiation, and lesser amounts of X-rays and radio waves. Our atmosphere is mostly transparent at visible wavelengths. Although some sunlight is scattered by air molecules or reflected by clouds, most of it passes straight through the atmosphere and impinges upon the land or sea beneath. The atmosphere is not as transparent at UV and IR wavelengths; most of the UV is absorbed by ozone in the stratosphere, while much of the incoming IR is absorbed by various greenhouse gases (water vapor, carbon dioxide, methane, and others). Sunlight that strikes the Earth's surface (including oceans) warms the land or water. The warm ground or ocean emits infrared radiation, which carries energy back upward into the atmosphere. However, greenhouse gases quickly absorb much of that outbound IR energy, heating the lower atmosphere.

The troposphere (lowest layer of the atmosphere, which extends down to ground level) is warmest at low altitudes and cools as one goes higher. The troposphere is mainly heated by IR energy rising from the surface; therefore, the troposphere is warmest near ground level where the heating source is nearby, and cooler at higher altitudes as one gets further and further from the warm ground.

The Ozone Layer, UV radiation, and the stratosphere: Normal oxygen molecules (O2) have two oxygen atoms. Ozone (O3), a special type of oxygen molecule, has three atoms instead of two. UV photons from the Sun hit normal oxygen molecules in the stratosphere. The high-energy photons break the molecular bonds holding the oxygen atoms together, splitting the O2 molecule apart into two separate oxygen atoms (the process is called photodissociation). Some of those individual atoms combine with other oxygen molecules to form ozone (O3) molecules. Over time, ozone accumulates in the stratosphere, forming the ozone layer - a region in the stratosphere with elevated concentrations of ozone.

Ozone is almost opaque at UV wavelengths. The ozone layer absorbs most of the incoming solar UV radiation. Ozone molecules shed the energy they absorbed from UV photons as heat, warming the stratosphere. The intensity of UV radiation is greatest at the top of the stratosphere, where energy from the incoming sunlight hasn't yet been "diluted" by atmospheric absorption. The temperature trend in the stratosphere is, therefore, exactly opposite of that in the troposphere below - the warmest area is at the highest altitudes and temperatures grow cooler as one goes lower and moves away from the main source of heating.

Let's consider an analogy to help us understand the temperature trends in the troposphere and stratosphere. Imagine two giant hot plates as heat sources. One is on the ground, facing upwards. It represents the heating of the atmosphere by IR radiation emitted by the warm ground (which was warmed by incoming sunlight). The second hot plate is at the top of the stratosphere, facing downward. It represents the heat given off by ozone molecules after they had absorbed energy from incoming UV radiation. So where are the warmest and coolest areas in the lower atmosphere? The air nearest the lower "hot plate" (Earth's surface) figures to be warm, with temperature decreasing as one moves upward away from the heat source. Likewise, air near the upper "hot plate" should be warm, with temperature dropping off as one moves downward away from the heat source. It also makes sense that the coolest temperatures in the lower atmosphere should be roughly midway between the two "hot plates". The tropopause, the boundary between the troposphere and the stratosphere, corresponds to this relatively cool spot between the two heating sources. If you look at a graph of temperature versus altitude in the lower atmosphere you can see how this "pair of hot plates" analogy plays out in the real atmosphere.

Mesosphere: Above the stratopause (the boundary between the top of the stratosphere and the bottom of the mesosphere) temperatures once again decrease with altitude, as was the case in the troposphere. The air is so thin above the stratosphere that relatively few photons of incoming solar radiation (whether visible light, IR, or UV) collide with air molecules. Temperatures in the mesosphere are therefore quite cold, dropping to -85° C (-120° F) near the top of the layer. The "hot plate" (from the previous analogy) near the top of the stratosphere provides some warmth to the mesosphere above, but temperatures quickly cool as one moves higher and away from that heat source as one climbs through the mesosphere.

How high do balloons fly? We've taken a bit of "artistic license" in this activity by allowing balloons to climb into the mesosphere 60 km above Earth's surface. Typical weather balloons have an operational ceiling somewhere around 30 km. Special-purpose high-altitude research balloons sometimes reach as high as 35 km or even 45 km. The altitude record for a balloon carrying people is just shy of 35 km. The altitude record for unmanned balloons is 51.8 km.

The minimum altitude for spacecraft is about 100 km; below that level atmospheric drag is strong enough to quickly pluck a satellite from orbit. Regions of the atmosphere between 40 and 100 km are therefore difficult to study; too high for balloons, too low for satellites. Researchers use sub-orbital sounding rocket flights to probe the mesosphere directly, but such flights last just minutes and thus supply relatively limited data. Because of these difficulties, study of the mesosphere is difficult and less is known about that region than about other layers of the atmosphere. Some scientists jokingly refer to the mesosphere as the "ignorosphere".

Air pressure: Air pressure variation with altitude is much simpler than temperature variation. Standard pressure at sea level is defined as 1 atmosphere ( = 1013 millibars = 14.7 lb/in2 = 101.3 kilopascals). Pressure drops steadily with altitude; at roughly 5,500 meters it is down to 1/2 of the sea level value. Rise up another 5,500 meters and the pressure drops by half again, so that pressure at 11 km altitude is roughly a quarter of the sea level value. In fact, the decrease of air pressure with altitude approximately follows an exponential decay curve. Atmospheric scientists use a concept called "scale height" (H) to express the rate of this decay. In Earth's troposphere, the scale height is about 8.4 km. The equation that expresses this trend is:

 

P = P0 e – z / H  
  • P = the air pressure at a given altitude
  • P0 = air pressure at sea level
  • z = altitude in kilometers
  • H = scale height in km

If you have advanced students or like to mix some math into your science lessons, you might want to have your students try to determine the scale height from the data they gather from their balloon flights. This could be a trial-and-error iterative approach, where the students first guess at the scale height, plug it into the equation above and see how well it matches their data, and then iteratively adjust their hypothesized scale height until it fits their data pretty well. You could also have the students graph their pressure vs. altitude data on semi-log paper; the data should generate a more-or-less straight line, with the slope representing the scale height.

Please note that the equation above is an approximation, though a pretty good one. The actual behavior of the atmosphere is a bit more complex than portrayed by this simple equation. As mentioned above, the scale height in the troposphere is about 8.4 km in the troposphere. If we extend our area of interest higher into the atmosphere, it turns out that the average scale height from sea level to 70 km is about 7.6 km; so scale height does vary with altitude. Any value between 7.5 and 8.5 km that your students determine for scale height would be a pretty good result. Here are some values for pressure at various altitudes, to help you get a feel for this:

Pressure
Altitude
(meters)
Altitude
(ft)
Notes
millibars atmospheres kilopascals
1,013
1
101.3
0
0
Sea level
~835
~0.82
~83.5
1,610
5,281
Denver's altitude ("mile high")
507
0.5
50.7
5,486
18,000
Half of sea level pressure
~316
~0.31
~31.6
8,840
29,002
Top of Mt. Everest
101
0.1
10.1
16,132
52,926
10% of sea level pressure

Scientific Investigation

We recommend allowing students four balloon flights to collect data; and permitting them to collect data at four altitudes on each flight. Increasing either or both of these allotments would make this activity easier, so that is something you might wish to do if the activity is too challenging for your students as is. These limits reflect the constraints scientists are often under, usually as a result of limited funding for research flights (or perhaps limited battery power for transmitting data in the case of data points per flight). We recommend that you keep this activity pretty challenging, so students have to think a bit and plan their flights to get the data they need. We also recommend giving them a surprise - "funding" for a second set of flights - after they've completed their initial four flights. This will allow them to fine-tune the results obtained in the first go-round.

You can have students conduct this activity by themselves or in teams. You could have small groups (3-4 students) each conduct a series of balloon flights. Students would consult with one another before each flight to choose settings for that flight. Alternately, you could have individual students (or even groups) each choose settings for one flight out of the four flights in a given "research campaign". Students should examine data from previous flight(s) to see where the remaining gaps in their data are, adjusting forthcoming flight settings to fill in those holes.

You may want to have each team report on their results. One team might do a better job filling in data about temperature in the stratosphere, while another group may have collected better data about pressure in the troposphere. Each group would learn from the reports of others. This approach also models the way in which real science is often conducted, with groups sharing limited data sets to build up a more complete picture.

Data Table for the "Standard Atmosphere"

Altitude
(km)
Temperature
(kelvins)
Pressure
(millibars)
0
288.2
1013
1
281.7
898.8
2
275.2
795
3
268.7
701.2
4
262.7
616.6
5
255.7
540.5
6
249.2
472.2
7
242.7
411.1
8
236.2
356.5
9
229.7
308
10
223.3
265
11
216.8
227
12
216.7
194
13
216.7
165.8
14
216.7
141.7
15
216.7
121.1
16
216.7
103.5
17
216.7
88.5
18
216.7
75.65
19
216.7
64.67
20
216.7
55.29
25
221.6
25.49
30
226.5
11.97
35
236.5
5.746
40
250.4
2.871
45
264.2
1.491
50
270.7
0.7978
55
260.8
0.425
60
247
0.219
  Temperatures in °C can be found by subtracting 273.15 from the temperature in kelvins

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Last modified December 1, 2009 by Randy Russell.

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