Ferrel Cells and Polar Cells

Source: WeatherSTEM

During the 1990’s, Brian Farrell, a professor of atmospheric science at Harvard (not to be confused with William Ferrel for whom Ferrel cells are named), proposed that during past climates on Earth, the Hadley cells extended all the way to the poles, like in the figure above-left. But in today’s climate, and due to the Coriolis Effect, air in the Hadley cells sinks to the surface at around 30° latitude, and two more separate sets of convection cells circulate in opposite directions. This is called the three cell model and is composed of the Hadley, Ferrel and Polar cells, as seen in the figure above-right.