1. Begin the lesson by asking students to discuss what they know about jet streams. During and after the discussion, have students record some of what they knew about jet streams before the discussion, what they learned about jet streams during the discussion, and what they still don't know. You may wish to ask them some of the following questions to guide the discussion:

1. How would you describe a jet stream?
2. What do you think causes a jet stream?
3. How many jet streams do you think there are, and where are they located across the globe?
4. What effect do you think jet streams have on weather patterns, and why?
5. How do jet streams affect your everyday life?
6. Why do you think these winds are called "jet" streams?

2. Next, have students work in pairs as they explore the Giving Rise to the Jet Stream Flash Interactive . Ask them to take notes on what they learn in the activity. Tell them that after they are finished with the activity, they should not only be able to answer the questions you asked in the earlier discussion, but these as well:

1. What causes jet stream winds to travel fast and in the same direction as Earth rotates?
2. What is the main cause of the subtropical jet stream?
3. What is the main cause of the polar-front jet stream?
4. What causes jet streams to change position from day to day and season to season?

Resume the full-class discussion by replaying the interactive activity using a projector, and call on students to describe what they observe in each frame. Provide opportunities for students to ask questions if they don't understand.

3. In the previous activity, students learned that the uneven heating of Earth's surface is critical to the formation of jet streams. The The Jet Stream and Horizontal Temperature Gradients Flash Interactive models the factors that contribute to jet stream formation in greater detail. Through interactive graphs, the model depicts the relationships between latitude and temperature, wind speed, and altitude.

1. Graph 1 shows temperature differences (gradients) in degrees Celsius by latitude.
2. Graph 2 shows maximum wind speed in meters per second by latitude.
3. Graph 3 shows the altitude of the maximum wind speed for a given latitude in Graph 2.

Hand out copies of the Wind Speed Data Tables PDF Document and have students work in pairs as they use the interactive model to determine how various temperature differences (differences of 10°C, 20° C, and 30°C) between two air masses influence maximum wind speeds at different latitudes (15°, 45°, and 75°).

Tell students that they can experiment with the model by changing the temperature difference and latitude as they choose. However, they should begin by using the information provided in the model.

Have students use Graph 2 to complete the wind speed information in each table below. To convert meters per second to miles per hour, multiply by 2.24.

Then have students use Graph 3 to determine the altitude of the maximum winds. Repeat for each table's temperature difference.

4. Have students discuss with their partner any patterns they see regarding temperature differences, the speed of the wind, and the altitude of maximum winds. Which season do they think corresponds to each temperature difference — that is, at what time of year do small, medium, and large temperature differences generally occur? Then have them label each table with the appropriate season.

5. Next, have students work with their partner to answer the following questions. Have one of the students in each pair record their answers, and have both students be prepared to discuss them with the class.

1. What is a temperature gradient? Describe why it exists.
2. As you change the temperature gradient, what happens to the maximum wind speed?
3. What does the model predict would happen to global winds if the temperature were uniform across the globe?
4. Does the model predict stronger winds during summer or winter?
5. At what height does the polar-front jet stream generally occur in the atmosphere?
6. Which factor (altitude, latitude, temperature differences) has the most influence on the speed of the jet stream?

6. Based on what they explored in the previous section — especially seasonal variations in the jet stream's position — ask students to discuss what effect they think the jet stream has on daily weather and on the paths of storms.

7. Have students watch The Great Flood of 1993 QuickTime Video . Make sure they pay particular attention to the jet stream section (minutes 1:32 to 2:23). After watching the video, discuss these questions:

1. How did the jet stream's position in the summer of 1993 affect weather patterns over the mid-western United States?
2. How would you describe atmospheric conditions (in terms of temperature and humidity) on either side of the jet stream?
3. Why does this pattern result in powerful storms along the path of the jet stream?

8. Have pairs of students look at A Five-Day View of the Jet Stream GIF Image from January 2001. Have them discuss with their partner what they observe about the jet stream's path and surrounding weather pattern. Ask them to contrast this with what they remember about the path of the jet stream during the summer of 1993.

Hand out a copy of the Jet Stream Map PDF Image to each pair of students.Have students locate the polar-front jet stream. Have them use one colored pencil to trace contour lines for winds that are 70 knots and higher, and the other colored pencil to trace contour lines for winds of 90 knots and higher. (The map already has contour lines for 10, 50, and 90 knots.) Tell students that a wind barb looks like this:

Hand out copies of the Weather Map Symbols PDF Image . Students can use this detailed key to interpret the map.

9. Have pairs of students compare the Jet Stream Map to the A Five-Day View of the Jet Stream GIF Image from January 2001 and answer the following questions:

1. Does the location of the jet stream on the two maps differ?
2. Does the path of the jet stream on the two maps differ? Is it straighter on one and more undulating on the other? Meteorologists call straight patterns zonal flows, and undulating patterns meridional flows. These patterns have a huge impact on daily weather.
3. Which pattern (zonal or meridional) do you think might be associated with large storms?

10. Next, have pairs of students explore the Surface Map PDF Image (taken at the same time as the Jet Stream Map) to see how the location of the polar-front jet stream influences weather at Earth's surface. Have students compare the temperatures at locations north and south of the jet stream. For example, have them look at Boise, Idaho (the southernmost station in Idaho), and compare it to Grand Junction, Colorado (the westernmost station in Colorado).

To interpret the station information on the Surface Map, use the Surface Station Model table in the Weather Map Symbols PDF Image .

11. As students explore and compare the weather maps with their partners, have them record the answers to these questions in their notebooks and be prepared to discuss them with the rest of the class.

1. Which location is warmer: Boise or Grand Junction?
2. In general, are locations north of the polar-front jet stream warmer or colder than locations south of the polar-front jet stream?
3. For the October 1997 weather scenario, is the polar- front jet stream in a zonal or meridional flow pattern? Use the Surface Map to help answer this question by looking at how uniform temperatures appear to be across the eastern two- thirds of the country.

12. Have students discuss as a class their answers to the previous questions as well as general observations they made about the path of the jet stream and weather patterns at Earth's surface.

13. As students have observed in this lesson, the polar-front jet stream travels at altitudes of 10 to 15 kilometers above Earth's surface. Have students discuss as a class why they think the polar-front jet stream occurs high in the atmosphere rather than at Earth's surface.

14. Explain that upper-level wind speeds, like those in jet streams, are directly proportional to temperature differences between air masses, which in turn are proportional to differences in air pressure. Therefore, one would expect that the high-speed winds of jet streams would occur where temperature differences and pressure differences are greatest. The following activity will help them clarify this phenomenon. Hand out a copy of Pressure-Temperature-Altitude Data for Green Bay and Nashville PDF Document to each pair of students. Ask students to read the explanation and directions at the top of the table and work in pairs to analyze the differences between the two cities in the heights of each pressure level.

An easy method to determine the altitude where pressure and temperature differences are greatest would be to take atmospheric pressure measurements at different heights at various locations. Meteorologists make such measurements, but instead of taking pressure measurements at various heights, they take height measurements at various pressure levels.

This table contains real data from Green Bay, Wisconsin, and Nashville, Tennessee, on 23 September 2005. At each location, temperature and the height of different pressure levels were measured. Green Bay is in cold air on the north side of a cold front, and Nashville is in warm air on the south side of a cold front. (The way the front divides warm and cold air is analogous to how the polar-front jet stream separates air masses of different temperatures.)

15. While analyzing the data in Table 1, students should record in their notebooks their answers to the following questions:

1. At what pressure does the greatest height difference occur?
2. What is the height above each location at this pressure reading?
3. How does this compare with the altitude of maximum winds calculated earlier in the lesson when exploring the [Jet Stream and Horizontal Temperature Gradients interactive]?

16. Have each student pair use graph paper to plot pressure values as a function of height for Green Bay and Nashville. Use the horizontal axis to indicate pressure in increments of 100 millibars, and use the vertical axis to indicate height in 1000- meter increments. Use different-colored pencils to plot data for each location. For clarity, be sure to label each pressure value during plotting.

17. Have each pair calculate the differences between locations in the pressure at each height, recording answers in Table 2.

18. When students have finished graphing and calculating pressure differences at various heights, discuss the following questions as a class:

1. At what altitude does the largest pressure difference occur?
2. How does this explain why wind speeds are faster at high altitudes than at Earth's surface? Relate your answer to pressure differences.
3. Does pressure decrease with altitude more rapidly in cold air or warm air?
4. Does this explain why pressure differences generally increase with altitude?