Guest Post: Robert Edmonds on Multiple Vortices

The following is an unexpected and interesting guest post from fellow storm chaser and atmospheric modeler Robert Edmonds. Earlier this week I got a note from Robert, and, recalling some of his very cool vortex models that he had posted on Stormtrack, I invited him to submit a guest post. At my suggestion–because Stormhorn.com is written on a popular rather than a scientific level–Robert has taken a concept that I’m certain can be expanded upon to incredible complexity and offered some essential thoughts on it which I think just about anyone can understand.

A bit on Robert’s background. A weather modeler for Mars who works frequently with NASA, Robert possesses a BS in astrophysics and a minor in mathematics, and is currently pursuing a Ph.D. With nine years experience chasing storms, he operates his own business as a storm chasing tour guide.

Without further ado, I give you Robert Edmonds sharing his insights on

Multiple Vortices: Stable and Unstable Configurations

Bob Hartig recently wrote an article titled  “Multiple Vortices: How Deep Do They Go?” Being both a storm chaser and an atmospheric modeler for Mars, I thought I might share some interesting insights about multiple vortices. There is a lot of fascinating physics going on inside multi-vortex tornadoes.

First, however, it might be good to understand the difference between vorticity and circulation. Imagine a boat in the ocean. Let’s say that in this ocean is a giant whirlpool. The boat is circulating about this whirlpool; however, the nose of the boat keeps pointing in the same direction–let’s say, north. Clearly there is circulation because the boat is going around and around the whirlpool, but in the water immediately surrounding the boat there is no vorticity.

Now let’s move the boat closer and closer to the center of the whirlpool while keeping the boat’s nose still pointed north. There is still no vorticity in the water immediately surrounding the boat.

Only when we find the nose of the boat turning is there vorticity in the water immediately surrounding the boat. The boat is now experiencing not only circulation, but also vorticity.

At the following link you will find an applet with two windows: https://stormchaseguide.com/blog.html. The black dots represent locations of concentrated vorticity (places where the boat’s nose would turn). You can think of these dots as multiple vortices within a larger tornadic circulation. What I want to show you is that certain vortex configurations are stable.

First, uncheck the two boxes next to “Running.” This will freeze the motions of the vortices.  Next: In each window there are vortices in a circular configuration. Drag one black dot in each window at most half a mouse cursor length (click and hold). When you’re done, go ahead and click the boxes next to “Running.”

You should find that in the panel with six vortices, the shape or configuration of the dots remains generally the same. However, in the panel with seven vortices the configuration eventually breaks down. This is because circular, evenly spaced configurations with more than six vortices are unstable.

This little demonstration touches on many aspects of weather, not just multi-vortex tornadoes. The chaotic behavior in the panel with seven or more vortices demonstrates why no weather forecast will ever be perfect. The air around us can be thought of as composed of billions, even trillions, of little vortices, all interacting in seemingly random fashion. As you’ve just seen for yourself in the very simplified model, small changes in the atmosphere can produce drastic differences over time–true of both tornadoes and of the larger weather systems that spawn them.