What is happening in the Twister in a Jar activity?
As you twist the jar, the water inside that is up against the glass is pulled along due to friction against the glass walls. The fluid toward the center of the jar takes longer to get moving, but eventually, all the fluid is spinning as you rotate the jar. When you stop rotating the jar, the fluid inside keeps spinning. A mini twister can be seen for just a few seconds when the outer fluid slows down and the inner fluid continues to spin rapidly.
How do tornadoes form?
Tornadoes are associated with large (supercell) thunderstorms. As part of the storm, warm and humid air rises. As it rises, it can start to rotate. How the column of air begins to rotate is not completely understood by scientists, but one way the rotation appears to happen is when winds at different altitudes blow at two different speeds. For example, a wind at 1000 feet above the surface might blow at 5mph and wind at 5000 feet might blow at 25 mph. Winds moving in different speeds and directions at different altitudes cause the rising air to start spinning.
If the rotating column of air gets caught in an updraft (air flowing upward), the updraft tightens the spin and the rotation speeds up (much like a skater spins faster when arms are pulled close to the body). A funnel cloud is created.
The rain and hail in the thunderstorm cause the funnel to touch down creating a tornado.
The action of warm air rising and cold air sinking (convection) plays a key role in the formation of severe thunderstorms. If the warm surface air is forced to rise, it will continue to rise, because it is less dense than the surrounding air. This is called an updraft.
What is a supercell thunderstorm?
Supercell thunderstorms occur when very strong updrafts are balanced by downdrafts, which can allow the storm to persist for many hours. In a supercell, moist, warm air may be forced to rise by an approaching cold front. The result is a strong, persistent updraft of warm moist air. Speeds in an updraft can be as fast as 90 miles per hour! The air cools as it rises. Water vapor condenses and forms cumulus clouds. When condensation occurs, heat (latent heat/energy ) is released and helps the thunderstorm grow.
In the United States, supercells often form where warm, moist air from the Gulf of Mexico meets cool, dry air from over the North American continent.
This activity has been adapted from Web Weather for Kids by Melissa Rummel at the UCAR Center for Science Education.