Credit: J. B. Marston
(Top) Direct numerical simulation (DNS) of a stochastically driven two-dimensional fluid on a rotating sphere. The component of the fluid velocity in the zonal (longitudinal) direction is shown, highlighting the emergence of a strong equatorial jet from the synergy of the Coriolis force acting in concert with the nonlinear fluid motion. (Bottom left) Time-averaged zonal velocity, showing the recovery of azimuthal symmetry in the statistic. (Bottom right) The mean zonal velocity obtained directly from the fixed-point of a second-order cumulant expansion, demonstrating that the flow is only weakly nonlinear.