Turbulence in Flatland

The earth’s oceans and atmosphere are full of large vortex structures. Their existence is Mainly due to the twodimensional nature of the large-scale geophysical flows. Two-dimensional turbulent flows are characterised by an ‘inverse energy cascade’, as visible in the self-organisation of these flows: larger vortices and structures are observed to emerge from initially random flow fields. Such vortices are weakly dissipative and hence quite persistent. In this lecture I will give an overview of a number of fascinating aspects of this type of turbulent flows. Ample attention will be given to laboratory experiments on forced and decaying quasi-two-dimensional turbulence, interaction between vortices, and vortices in perturbed ambient flow fields. In addition to the dynamical features, some aspects of (chaotic) tracer transport in such flow systems will be highlighted.