The seminar is free to attend but registration is required – please email the organizers to receive an invitation

Two-dimensional (2d) and quasi-2d flows occur at macro- and mesoscale in a variety of physical
systems. Examples include stratified layers in Earth’s atmosphere and the ocean, soap films and
more recently also in dense bacterial suspensions, where the collective motion of microswimmers
induces patterns of mesoscale vortices. A characteristic feature of turbulence in 2d and thin fluid
layers is the occurrence of an inverse energy cascade. In case of weak Rayleigh damping the
inverse energy cascade results in the formation of large-scale coherent structures, so-called
condensates, which can take the form of jets or large-scale vortices. With a view towards
atmospheric physics, we study the formation of the condensate in a rotating thin fluid layer with
free-slip boundary conditions as function of the amplitude of the forcing, and we compare with
results obtained in strictly 2d domains. Direct numerical simulations show that the condensate in
the thin rotating layer appears in a first-order non-equilibrium phase transition, with rare transitions
occurring towards and away from the condensate state. In contrast, condensate formation 2d can
proceed by means of either a first or a second-order non-equilibrium phase transition, depending
on the type of driving.