Atmospheric Circulation on the Red Planet

mars atmosphere

climate on marscredit: NASA

By Angela Zalucha, Research Scientist

Much of my work is about the atmosphere of Mars, and I use a computer to simulate its behavior. The computer solves physics equations under conditions appropriate for Mars – like the strength of the Sun, gravity, the composition of the atmosphere, and the elevation of the surface. Each time the computer solves these equations, it predicts the state of the atmosphere at one tiny increment of time in the future. Then it solves the equations again for this new state. This process is repeated many times, until the model atmosphere evolves into something we can use to learn about the real atmosphere.

hadley figure

I am interested in a particular circulation pattern, called the Hadley circulation, which occurs near the equator (on Mars, Earth, and most other planets). The Sun heats the air around the equator, and this air rises because hot air is less dense than cold air. It starts flowing towards the poles, since nature does not like to have large temperature differences within the atmosphere. As it flows away from the equator, it starts cooling by radiating its energy into space. Eventually, it becomes cold again and sinks, because cold air is less dense than warm air. The latitude at which it sinks depends on the planet; on Mars and Earth it is around 30 degrees latitude. The cold air sinks to the surface, and then flows back towards the equator again to mediate the temperature differences in the atmosphere. The air has then completed a loop around the atmosphere.

It turns out that the elevation of the surface of Mars is kind of strange. On Earth, there are some mountains, but otherwise the surface is pretty flat, especially because of the vast amount of ocean. Mars does not have a liquid ocean. Also, the southern pole of Mars has a relatively high elevation, which slopes downwards towards the north pole, and this slope affects the circulation of the atmosphere. I am studying how the slope affects the Hadley circulation described above. So far we’ve learned that the slope has a tendency to move the boundary between the cells upslope (in this case, southward).