David Dritschel Mathematical Institute, University of St Andrews, Scotland A new twist to rotating stratified turbulence Wednesday 6th, April 14:05-14:55pm, Carslaw Building Room 373. The turbulent motion of the Earth's atmosphere and oceans is strongly influenced by the effects of rotation and stratification. These effects alter the nature of turbulence profoundly from that of a homogeneous fluid. In particular, motions are dominantly horizontal, with vertical motions some three to four orders of magnitude smaller than horizontal motions. Moreover, coherent structures --- vortices --- are highly anisotropic, with vertical scales one to two orders of magnitude smaller than horizontal scales. And, fluid particle motions are doubly constrained: they must remain on (nearly flat) density surfaces while preserving their scalar value of `potential vorticity'. This talk presents new results showing that these contraints exert a powerful influence on the fluid motion even when rotation and stratification are not dominant effects. In effect, the motion is controlled by an underlying, vastly simpler dynamics.