Zonal flow reversals in two-dimensional Rayleigh-Bénard convection

We analyse the nonlinear dynamics of large scale flow in Rayleigh-B\'enard convection a two-dimensional, rectangular geometry aspect ratio $\Gamma$. impose periodic and free-slip boundary conditions streamwise spanwise directions, respectively. As Rayleigh number Ra increases, zonal dominates moderate Prandtl fluid. At high Ra, turbulent regime, transitions are seen probability density function (PDF) largest mode. For $\Gamma = 2$, PDF first from Gaussian to trimodal behaviour, signifying emergence reversals where fluctuates between three distinct states: two states which travels opposite directions one state with no mean flow. Further increase leads transition unimodal demonstrates disappearance reversals. On other hand, for 1$ characterised by bimodal mode, only travelling directions.