TAO data support the existence of large amplitude wind-driven high frequency variations in the cross-equatorial overturning circulation

Large amplitude oscillations in the meridional overturning circulation (MOC) have been found near the equator in all major ocean basins in the NEMO ocean general circulation model. With periods of 3-15 days and amplitudes of ~±100 Sv in the Pacific, these oscillations have been shown to correspond to zonally integrated equatorially trapped waves forced by winds within 10° N/S of the equator, and can be well reproduced by idealized wind-driven simulations linearized about a state of rest. Observations of dynamic height from the Tropical Atmosphere Ocean (TAO) mooring array in the equatorial Pacific also exhibit spectral peaks consistent with the dispersion relation for equatorially trapped waves. Here, we revisit the TAO observations to confirm that the amplitude of the oscillations is consistent with the simulations, supporting the modelled large amplitude MOC oscillations. We also show that the zonal structure of the frequency spectrum in both observations and simulations is predicted by changes in the baroclinic wave speed with variation in stratification across the ocean basin.