Credit: UCAR/NCAR

This time-lapse video shows 12 time steps in a hands-on activity that illustrates how models of Earth's atmosphere and climate work.

The What is a "model"? activity was created by the Little Shop of Physics at Colorado State University.

In the activity, students move red markers - which represent sunlight, heat, and longwave infrared radiation - between three game boards representing Earth's surface and the lower and upper parts of Earth's atmosphere. The "rules" of the model tell students how many of the red markers to move, and where, each turn. As the model runs, it illustrates how heat flows throughout the Earth system. The model illustrates how the greenhouse effect warms Earth's surface and how Earth's atmosphere is cooler at higher altitudes.

The model gradually "spins up" from the arbitrary initial state, eventually settling into a repeating pattern of temperatures in each of the regions represented in this model - Earth's surface, the lower atmosphere, and the upper atmosphere. This repeating pattern of temperatures throughout the day/night cycles is called a dynamic equilibrium state.

This looping video clip shows the dynamic equilibrium state after the model has been "spun up" from the arbitrary initial state. During the daytime, when the Sun is shining, Earth's surface heats up to to 22 degrees (as indicated by 22 red markers on the Earth's Surface board on the left). Each night, Earth's surface cools down to 17 degrees. Temperatures in the atmosphere fluctuate less than the surface temperature. The lower atmosphere cycles between 18 and 19 degrees, while the upper atmosphere is cooler and cycles between 8 and 9 degrees.

The graph below shows the changes in temperature of Earth's surface, the lower atmosphere, and the upper atmosphere over the course of this model run. The green, shaded part on the right side of the graph shows the dynamic equilibrium state portrayed in the time-lapse video above. A seperate video shows the spinup phase of this model run, which is depicted in the portion of the graph to the left of the green shading.

If the Sun is left "on" all the time, the model eventually reaches an unchanging state with fixed temperatures in each of the three regions. That state is referred to as a "static equilibrium". Since this model run includes the varying input of sunlight caused by the day/night cycle, it did not settle into fixed temperatures in a static equilibrium state. Instead, it settled into a dynamic equilibrium state with a repeating pattern of rising and falling temperatures through each day/night cycle.