Virtual Ballooning to Explore the Atmosphere Activity

SUNRISE Balloon inflation prior to launch in October 2007Introduction

In this computer-based virtual lab, students will learn about the layers of Earth's atmosphere by launching virtual balloons to collect temperature and pressure data at various altitudes. Given a limited number of balloon flights, students must plan carefully to gather data that generates a good "picture" of the atmosphere’s structure.

Credits

This activity and the accompanying software were developed at the UCAR Center for Science Education by staff member Randy Russell.

Student Learning Objectives

  • Students can name the layers of the atmosphere
  • Students can describe key traits of each atmospheric layer
  • Students can describe the altitude range for each layer of the atmosphere
  • Students can describe how air pressure and temperature vary with altitude
  • Students can design an experiment and can explain why they made certain design choices

Instructions for the Teacher

Materials

Directions for Teacher

  1. Ask students what they already know about the atmosphere. Prompt them to share their knowledge about how temperature and pressure in Earth's atmosphere vary with altitude. This could include sharing stories 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.") Also, through discussion, informally assess student understanding of the layers of the atmosphere and how researchers study the atmosphere.
  2. 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 collect their data about the atmosphere, 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).
  3. Provide each student with a copy of the worksheet and review the items they need to find out through their research. These include: temperature and pressure at the top of Mount 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.
  4. You may wish to have students work in groups or teams for this activity. Students can do the activity individually; however, group work could lead to interesting planning discussions between students. If you have few computers, you could have a single group do the planning for just one balloon flight in a series of flights.
  5. Have the students start the Virtual Ballooning software and click the "Play Game" button to go straight to the ballooning simulation. Or, ask students to 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 (and then 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 proceed 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 information 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 the UCAR Center for Science Education 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 & Extensions

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
millibarsatmosphereskilopascals
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

Data Table for the "Standard Atmosphere"

Scientists sometimes use a concept called the "standard atmosphere" to represent the conditions (such as temperature and pressure) in the "typical" atmosphere. The standard atmosphere removes variations from day to night, across the seasons, at different latitudes, and as weather systems move across regions. The standard atmosphere is more-or-less Earth's average atmosphere, with variations across space and time removed. The table below provides temperature and pressure data versus altitude for the standard atmosphere to a height of 60 kilometers (about 37 miles or 196,850 feet). These are the values used "behind the scenes" in the virtual ballooning software simulation.

Altitude
(km)
Temperature
(° C)
Pressure
(millibars)
 Altitude
(km)
Temperature
(° C)
Pressure
(millibars)
8-37.0356.535 -36.75.746 
9-43.530840 -22.8 2.871
10-49.926545-8.91.491
11-56.422750-2.40.7978
12-56.519455-12.40.425
13-56.5165.860-26.20.219
14-56.5141.7   

 

Teaching Tips for this Activity

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 you wish to make the activity less challenging. Limits on the amount of sampling in a scientific investigation reflect constraints that 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 their first trials.

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.

Student Worksheet for Virtual Ballooning Activity

Introduction

You are the leader of a team of atmospheric scientists. Your mission is to explore Earth's atmosphere using instruments carried into the sky by a balloon. Your instruments will measure altitude, air pressure, and temperature.

The lightweight batteries in your instrument package are not very strong. They only have enough charge to power the balloon's radio transmitter a few times. On each balloon flight you will only be able to collect pressure and temperature data at four different altitudes. However, you will be able to launch four balloons; so you will be able to take as many as 16 temperature, pressure, and altitude readings.

Before each balloon flight, you will set: 1) the altitude at which the balloon's instruments will start collecting data, and 2) the distance (altitude) between readings. For example: you might choose to start collecting data at an altitude of 5 km, and take readings every 2 km. Since you get four readings per flight, these settings would cause the balloon's instruments to measure temperature and pressure at altitudes of 5 km, 7 km, 9 km, and 11 km above sea level.

You will need to plan carefully to collect the data you need to see how pressure and temperature change with altitude. You should also take a look at patterns you see in your first flight to help you decide where you need more data. That information can help you decide what settings to use in later flights.

It may seem odd to think of Earth's atmosphere as having layers, but scientists know that it does. The layer closest to the ground is called the troposphere. The layer above that is called the stratosphere. Above the stratosphere is the mesosphere, and above that is the thermosphere. At certain altitudes the pressure or temperature (or both!) change suddenly. Those altitudes are the boundaries or borders between layers. Part of your mission is to find the boundaries between layers. Keep an eye on your data, looking for sudden changes. Keep in mind that balloons can only fly just so high; your balloon may not be able to reach all of the layers listed above (and certainly cannot fly up to the exosphere, the layer above the thermosphere).

Are you ready to start launching balloons?

Step-by-step Instructions

  1. Start up the software. Go to the following web page: scied.ucar.edu/interactive/virtual-ballooning
  2. About halfway down on the left side is a popup menu for setting the "Start Recording Altitude". This is the height at which your balloon will begin to recorddata. Choose a value from the popup menu.
    Flight #Start Recording
    Altitude
    Altitude
    Interval
    1  
    2  
    3  
    4  
  3. Just below that is the "Altitude Recording Interval" popup menu. That sets the distance (altitude) between data points. Choose a value from the menu.
  4. When you are happy with your settings, click the "Launch Balloon" button near the top of the screen.
  5. The balloon will rise, collecting and graphing data along the way.
  6. Click the "Show Pressure" button (lower left) to switch to a graph of pressure (in millibars) versus height. Click the "Show Temperature" button to return to the temperature vs. altitude graph.
  7. Plan your second flight. Take a look at your graphs. Where do you need more data? Select new values for the "Start Recording Altitude" and "Altitude Recording Interval".
  8. When you're happy with your settings, click the "New Flight" button. A new balloon appears. When you're ready, click the "Launch Balloon" button to start your second flight.
  9. Repeat these steps for flights 3 and 4. Remember, you only get 4 flights!
  10. Answer the questions and fill in the tables below.

Questions

Air Pressure

The top of Mt. Everest is about 10 km above sea level. Air pressure at sea level is about 1,013 millibars.

What is the air pressure (in millibars) at the top of Everest?                         
What % of sea level air pressure is that? 
What % of sea level air pressure is that? 

 

At what altitude has the air pressure dropped to 50% (half)
of air pressure at sea level (1,013 millibars)?
__________________

Layers of the Atmosphere

Can you see any sudden changes in the way pressure and/or temperature change with altitude? Those altitudes could be the boundaries between layers of the atmosphere. The boundaries between layers have names:

  1. Tropopause (the boundary between the top of the troposphere and the bottom of the stratosphere)
  2. Stratopause (the boundary between the top of the stratosphere and the bottom of the mesosphere)
  3. Mesopause (the boundary between the top of the mesosphere and the bottom of the thermosphere)
  4. Thermopause (the boundary between the top of the thermosphere and the bottom of the exosphere)

Remember, your balloon may not reach all of the layers of Earth's atmosphere. Fill in as much of the table below as you can.

BoundaryAltitude (km)Temperature (° C)Pressure (millibars)
Tropopause (top of troposphere)   
Stratopause (top of stratosphere)   
Mesopause (top of mesosphere)   
Thermopause (top of thermosphere)   

Fill in the table below for each layer you detected:

Atmosphere LayerHow does pressure change
as altitude increases?
How does temperature change
as altitude increases?
Troposphere
(lowest layer, starting at sea level)
  
Stratosphere
(layer above the troposphere)
  
Mesosphere
(layer above the stratosphere)
  
Thermosphere
(layer above the mesosphere)