In this lesson students will learn how isolines are used in the creation of weather maps to show areas of similar temperature (isotherms) and areas with similar barometric pressure (isobars).
For this lesson you will need:
Begin class by reviewing the following with students:
1) The air masses that effect weather in North America.
2) The characteristics of high and low pressure systems.
3) The characteristics of cold and warm fronts.
Before proceeding please refer to my lesson on air masses and fronts for the content listed above. It is a good idea to have taught this lesson first.
Project an image of a weather map that shows current temperature across the United States. You can find these using a quick Google image search for "weather maps". Here is an example:
Ask your students to describe the patterns they see in the image. What data is shown? What is the unit of measurement? What time of the year was this captured? What do the colors represent? What are the boundaries between the colors? Is there a key we can create?
If you have the ability to project this image on a white board, ask a student to come and draw lines across the map at the boundaries of the colors. What do they notice?
These lines (isolines) represent areas with similar temperatures. Ask your students what would cause these areas to form? How are air masses involved? How would this map look at different times of the year?
Here are a few more images. Note the key at the top of the first one:
Next, show them a different weather map, one that shows isobars. Again, a quick Google image search will produce these. Here is an example:
In addition to isobars this map includes the centers of high and low pressure areas, the position of warm, cold and stationary fronts, and precipitation.
Again, ask your students what they notice in the image. Have them pay attention to the lines and ask what they might represent. Guide their thinking by asking them to notice the spacing between the lines near the centers of high and low pressure. Higher pressure = lines are further apart; lower pressure = lines are closer together.
These are called isobars, lines of equal air pressure. Show them the following map that includes values for each line:
You can tell your students that these are values for air pressure at sea level. Ask them how the values would change if the measurements were taken at higher and yet higher altitudes. This should be a review question for them if you have previously taught a lesson on the relationship between air pressure and altitude like the lesson found here.
Show them one last image, shown below, projected onto the board that includes only the air pressure values and not the lines.
Ask a volunteer to come to board and ask them to connect the lines of similar pressure staring with the highest then the lowest values first so that you encircle the high and low pressure areas. Then continue out from the centers. Below is an example of a completed map. Nite, you can also have them identify the centers of high and low pressure.
Now it's time for your students to practice.
Hand out the maps and instructions and have your students with a partner (optional) to complete the exercise. You will want to have a few extra maps on hand in case students need to start over.
One idea to help your class get started is to project the map on the board and walk them through drawing in the isotherm and isobar lines.
As structured, and visual, as this activity is presented, I have found that often students need additional instruction, so be prepared to go back over the previous exercises.
Once the class is completed with the activity, ask them how air masses affect the presence of isotherms and isobars. To respond to this question, they will need a basic understanding of the characteristics of air masses.
I make sure to spend time at the end of this lesson to insure that my students are understanding how to interpret and make sense of this data, in particular, the relationship between air pressure, temperature, fronts and precipitation as we will use these connections when making weather forecasts in a future lesson in this unit.
In the video below, two of my students demonstrate their understanding of the interaction of these Earth systems at the conclusion of the lesson.