I struggled a bit with finding the right way of controlling this, but with some patience you can set up a cloud of nicely rotating particles, and try to reverse the overall direction of the swirl by adding particles that rotate in the other direction.
Thanks! Full disclosure: by the time this was done, the actual question that prompted this was long forgotten. I got a "huh, that's nice." for my trouble (:
https://strangeloop.nl/max.html
I struggled a bit with finding the right way of controlling this, but with some patience you can set up a cloud of nicely rotating particles, and try to reverse the overall direction of the swirl by adding particles that rotate in the other direction.