Before we get going, think about these questions: How often do you watch the weather on TV? What kind of weather conditions have you seen reported? What kinds of weather conditions have you experienced in your lifetime? How has weather impacted your life?
Get your brain warmed up! Write about a specific weather memory.
Make a connection: Why would you need to pay attention to the weather? Can you think of a time that knowing the approaching weather would be important?
Predict: Before you read ahead, hypothesize what do you think creates or influences weather conditions. Write down any guesses you think of!
When you were thinking of what might influence or change the weather, did you ever think of air masses? Air masses are extremely important to consider when predicting what the weather may be like!
According to education.com, an air mass is a large body of air with consistent temperature and humidity. When air masses form, they are taking on the temperature and humidity characteristics of the region they are in. The density of an air mass depends on the temperature and humidity levels. Warm or humid air masses are less dense then cold or dry air masses.
Does it surprise you that humid air is less dense than dry air?
This is because a molecule of water has a smaller mass than a molecule of oxygen or nitrogen (a large percentage of dry air molecules are nitrogen).
But what happens when two different air masses meet? That’s our focus today! Think of oil and water as two separate air masses. If oil represented the warm air mass and water represented the cold air mass, what would you see happen? A boundary would form between the oil and water, and the oil (warm air) would float above the water (cold air).
Here’s a little more information about fronts:
“Vilhelm Bjerknes (1862-1951), a Norwegian physicist and meteorologist, coined the term front to describe the boundary between warm and cold air masses. The leading edge of a warm air mass advancing into a region occupied by a cold air mass is called a warm front. A cold front occurs when a cold air mass advances into a region occupied by a warm air mass. If the boundary between the cold and warm air masses doesn't move, it is called a stationary front. The boundary where a cold air mass meets a cool air mass under a warm air mass is called an occluded front. At a front, the weather is usually unsettled and stormy, and precipitation is common."
Here is a visual to help you understand the difference in air movement during cold fronts and warm fronts:
As the warm front approaches, there may be fog or increasing rainfall, and thunderstorms may form, as well. This is due to the (usually) higher humidity in the air of warm fronts compared to that of cold fronts. Because warm air is less dense than cold air, the warm air rises as it runs into the cold air, which is followed by condensation and cloud-forming.
Similar events happen when a cold front encounters a warm front, except they happen more quickly. Because cold air is denser than warm air, cold fronts are able to force warm air out more quickly. The cold air pushes the warm air upwards, which may be followed by precipitation or storms due to moisture in the air.
Don’t quite get it? Try out this air mass activity to help you better understand air masses before we move on!
Our task today, using food-colored cold and hot water as a visual, is to find out what happens when a warm front and a cold front collide.
Hypothesize: What do you think will happen when you combine warm water and cold water? Will they mix immediately? If not, how long do you think it will take to mix?
YOU WILL NEED:
- Writing utensil
- Blue crayon or marker
- Red crayon or marker
- 10-gallon aquarium or container
- Piece of cardboard
- A large spoon
- Five gallons of very cold water (you may refrigerate the water in advance or put it in the freezer to chill it)
- Blue and red food coloring
- Five gallons of very hot water (you may use the stove or microwave to heat the water, but ask an adult for help)
HERE’S WHAT TO DO!
1. Before we start the demonstration, use a writing utensil to draw seven pictures of the aquarium we will be using. Label the pictures 0 minutes, 1 minute, 3 minutes, 5 minutes, 7 minutes, 10 minutes, and 15 minutes. You will be using these rectangles to create visuals of what you see for the next 15 minutes.
2. Measure the tank’s width and height, and then use those measurements to cut a piece of cardboard of identical measurements. Use the ruler to draw a straight line where you will cut the cardboard in order to make sure your piece of cardboard is cut as exactly as possible.
3. Place the piece of cardboard in the middle of the aquarium so that it fits snugly and can stand on its own. From an aerial view, you would see something like this:
5. Next, grab your container of cold water and your container of hot water. Color your cold water with blue food coloring and your hot water with red food coloring. Add the desired amount of food coloring to the water and mix in with a large spoon.
6. Once the water is colored, the cardboard is in place, and you have your drawings ready, fill the left side of the tank with the cold, blue water.
7. Now, fill the right side of the tank with the hot, red water.
8. Remember, the blue water represents a cold air mass and the red water represents a warm air mass.
9. Using the drawing labeled 0 minutes and the red and blue markers, sketch what the tank looks like right now. Do this quickly--it does not have to be perfect.
10. Finally, carefully remove the cardboard from the tank and start your stopwatch.
11. Using your pre-labeled drawings, sketch what the tank looks like at 1, 3, 5, 7, 10, and 15 minutes.
12. Organize your pictures in chronological order and analyze the sequence. What happened initially when you removed the cardboard barrier? What happened as time went on? Did the “air masses” stay side by side, or did they shift? Describe the movement. Explain the behavior you observed.
Extension: Create captions that describe what is happening for each visual you created.
YOU SHOULD KNOW:
What is an air mass?
What is a cold front?
What is a warm front?
What happens when two air masses collide?