ABSTRACT:
The physics of natural systems is often highly influenced by spatial dimensionality from the nature of phase transitions to the properties of materials. These effects may arise from symmetries or conservation laws. Fluid turbulence is central to transport and mixing in many contexts from atmospheres and oceans to internal combustion vehicles. Turbulence in three spatial dimensions reflects the net transfer of kinetic energy from large scales to small scales where it is dissipated as heat. In contrast, conservation laws in two dimensions lead to a very different scenario, namely that energy flows to larger scales whereas the flow to smaller scales is dominated by a process of vortex gradient stretching. I will discuss the characteristics of 2D turbulence and its applicability (or not) to atmospheres and oceans where lateral extent is large compared to vertical height. Because 2D turbulence technically only occurs in a computer, quasi-2D experiments that are well described by 2D turbulence phenomenology suggest its relevance to real physical systems. In particular, I will describe experiments in flowing soap films and in electrically forced thin salt layers that show remarkable correspondence to the theory and numerical simulation of 2D turbulence.