Spread F bubbles: Nonlinear Rayleigh‐Taylor mode in two dimensions

Analytic results on the nonlinear evolution of the Rayleigh‐Taylor instability into equatorial spread F bubbles are presented. The nonlinear saturation amplitude and k spectrum of the inertia‐dominated Rayleigh‐Taylor instability is computed in two dimensions (east‐west and vertical). Analogous to the collisional case, the dominant nonlinearity is found to be two dimensional. The linearly most unstable modes which are primarily horizontal ( k x < k y ) saturate by nonlinear generation of vertical spatial harmonics which may be damped by either recombination or diffusion. The resulting 1/ k x amplitude spectrum is consistent with observations and suggests that bubbles will be vertically elongated in the inertial as well as collisional regimes.