RK mode in a high-Ro_T tidally locked simulation (Ro_T = 10, T_rad = 250). (a) Time series of equatorial RK mode power, as measured as the power contained in the [0.2, 0.25] frequency band of the k = 1 equatorial zonal wind (green line), along with time series of the equatorial zonal-mean zonal wind (orange line). Both time series are smoothed with a Gaussian filter with standard deviation 4π (1 rotation period). (b) Upper-layer geopotential and winds filtered for k = 1 and ﹩\omega ={\omega }_{{\rm{\max }}}﹩, where ﹩{\omega }_{{\rm{\max }}}﹩ is the frequency that has maximal EMFC contribution over 30^∘S–30^∘N for t ≤ 2000 (see text).