Even though there is a severe drought in the area where we live, thunderstorms are still a common spring occurrence.
I have shown my kid how rain was created before. Now she’s curious how thunderstorms form and what causes them.
So what is a thunderstorm?
A thunderstorms is a storm with lightnings and thunders.
What causes a thunderstorm?
It is caused by unstable and humid air. When unusually warm air near the land surface rises or unusually cold air in the upper atmosphere falls (and oftentimes both!), the air churns violently.
Like air, warm water rises and cold water falls when they are mixed together.
Here is an experiment to show how a “thunderstorm” forms using water.
- washable paint or food coloring (2 different colors. I used blue for cold and red for warm.)
- 2 cups
- a large glass or clear plastic tank/container such as this (rectangular shaped preferred)
- adult supervision
- To get cold water, you can first add the blue coloring into tap water and then chill it in the refrigerator. Or you can make ice cubes by putting it into the freezer.
- For the warm water, I used the microwave. After adding the red coloring into the warm water, you can either use a cup to hold it, or put it into a narrow-necked bottle.
- Fill the large tank with room temperature water.
- Slowly pour the cold water (or ice cubes) into one end of the tank.
- Then pour the warm water into the other end. If you use a bottle, simply place it into the water. Depending on the weight of the bottle and how much air is left in it, the bottle may sink or it may float. Both are fine.
- Observe how the blue quickly descends into the bottom of the tank while the red floats on top and the water churns.
It is because low density fluid rises above high density fluid.
Warm water rises because it has a lower density than the room temperature water in the tank.
The cold water sinks because room temperature water has a lower density than it.
As the water moves, they mix and the temperatures change.
Eventually, the cold water becomes warmer and it starts to rise.
The warm water cools and it starts to sink.
This process is called convection.
In the ocean (i.e. giant water tank), when water from areas with different temperatures comes together, convection makes the water churn to create deep sea current.
Similarly in the atmosphere, warm air rises and cold air falls to churn the air.
In order to form a thunderstorm, the air also needs to be humid to form clouds and rain.
This is why thunderstorms are common in the afternoon over land, when daytime heating of the land by the sun causes the air nearer to the land to become hot and more water vapor in the air.