The direction of the equatorial jet. (a) Nondimensionalized equatorial zonal jet speed (u_eq/(2ΩR)) as a function of the ratio of the Rhines wavenumber n_Rh to the domain wavenumber n_domain. Since our model domain does not extend exactly to the equator, we take the velocity at the lowest simulated latitude to represent the equatorial jet speed. Panels (b) and (c) show the zonal-mean zonal velocity profiles, normalized by the equatorial jet speed magnitude (u/∣u_eq∣), with a deep (b) or shallow (c) β profile. Parameters for Jupiter (“J”), Saturn (“S”), Uranus (“U”), and Neptune (“N”) are marked with crosses. In (b) and (c) the gray shading indicates regions outside the TC, and the gray hatched region marks the area excluded from our simulation domain. The β profiles applied for the deep and shallow cases are shown as blue lines in Figures 2(b) and (d), respectively. In (b) and (c) only μ = 10⁻⁷ simulations are shown. The line colors correspond to marker colors in (a) representing different energy injection rates.