Weather in a Tank

Studying the behavior of rotating fluids is critical to understanding how weather and climate work, but the physics of these systems can be hard to grasp. Part of the problem is that instructors usually teach these abstract concepts using only equations or computer simulations.

But two educators from the Department of Earth, Atmospheric, and Planetary Sciences have found a way to make the abstract concrete. For nearly a decade, Lodovica Illari, an EAPS senior lecturer, and John Marshall, a professor of atmospheric and oceanic sciences, have been developing an undergraduate weather and climate curriculum that’s now being adopted by dozens of schools.

Illari and Marshall designed the experiment-­based curriculum, known as “Weather in a Tank,” in 2001 after they began offering an introductory weather and climate class that would fulfill their students’ lab requirements. Since 2006, MIT and five other universities have been testing the curriculum in a project funded by the National Science Foundation. It brings weather systems to life using low-tech lab equipment: an acrylic tank atop a rotating turntable on a portable cart. Experiments conducted in the tank demonstrate how the motion of water and air influences Earth’s climate.

One experiment, which demonstrates how Earth’s rotation creates weather systems that affect the temperature difference between the warm tropics and the cool poles, involves placing a bucket of ice in the center of the rotating tank of water. The ice creates a range of temperatures inside the cylindrical tank, making the center cooler than the relatively warm periphery. As the turntable rotates, its motion causes eddies, or small currents, inside the tank. A few drops of food coloring can help students see them.

The eddies simulate atmospheric weather systems by carrying warm fluid from the “equator” (the edges of the tank) to the “poles” (the bucket of ice). Simultaneously, they carry cold fluid from the bucket toward the periphery. Although the fluid cools significantly by the time it reaches the poles, the eddies help make the poles a little warmer (and the equator a tad cooler) than they might otherwise be. Students can then change parameters, such as the rotation rate, and see the effect on the eddies’ circulation at different latitudes.

The EAPS Weather in a Tank curriculum isn’t designed to let students avoid difficult equations or computer simulations. Instead, Illari says, it’s meant to help them grasp the processes that the equations and simulations describe. “We think it’s a mistake to give students the phenomena without the tools to understand,” she says.