(color online) (a) A sketch of the side–mid separation for Ra = 10⁹. The bifurcation point is indicated by the cyan dot and the dash line represents the bifurcation height. (b) A bidirectional histogram of region-averaged TDR in two dimensions (red bars) and quasi-two dimensions (blue bars). The portions of bars that are above and below the zero axis represent ⟨ε_θ⟩_Vside,t and ⟨ε_θ⟩_Vmid,t, respectively.