This research gives a new twist to a 100-year old problem in the theory of vortex motion.
A E H Love (1863-1940)
In 1894, Love showed that two identical vortex pairs can engage in a perpetual leapfrogging motion, but it now turns out that this motion can be unstable, in a very curious way.
"Walkabout" instability of vortex leapfrogging
The research is described in European Journal of Physics Vol. 21, pp 269-273 (2000), and the animation software leapfrog.zip has been specially written to accompany that paper.
(To run the software on a modern PC, I suggest using qb64 and consulting the notes here.)
Not quite the Indian Rope Trick
Nonlinear inverted pendulum dynamics
'Valve'-effect at a critical layer
'Stability' as a catalyst for instability
Magnetic instabilities of rotating fluids
Westward drift of the Earth's magnetic field
Magnetic buoyancy in the Sun
'Local' analysis of astrophysical instabilities