Reynolds stresses contributing to zonal flow in hydrodynamic models (a,b, model M7) and MHD models (c, d, model M7b1) at the equator as a function of time and pressure in the atmosphere. One can see that the velocity fluctuations are anticorrelated and steady in time in the hydrodynamic models, but this correlation is intermittently disrupted with opposite correlations in the MHD cases. This results in variability of the equatorial zonal wind.