Quasi-2D turbulence in shallow fluid layers

Flows in thin fluid layers, like in the Earth’s atmosphere or oceans, tend to behave as quasi-two-dimensional flows. Their dynamics is strikingly different from three-dimensional flows, and main features of the flow dynamics can be understood by considering two-dimensional (2D) fluid flows. Inviscid 2D flows are governed by conservation of vorticity due to absence of vortex stretching and tilting. Together with conservation of kinetic energy this results in the famous inverse energy cascade and the emergence and persistence of large-scale vortices. This also occurs in shallow fluid-layer flows even if they are neither purely inviscid nor perfectly two-dimensional. Basic phenomena for understanding the dynamics of 2D flows will be discussed and 2D flows on bounded domains, mainly dealing with the large-scale phenomenology of the flow, will be addressed: the self-organization of 2D turbulence in confined domains and the interaction of coherent structures with domain walls. This will be complemented with some observations from recent experiments on quasi-2D turbulence in shallow-fluid layers including the role and impact of bottom friction and out-of-plane motion on the flow evolution.