TAO Data Support the Existence of Large High Frequency Variations in 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 similar to +/- 100 Sv in the Pacific, these oscillations have been shown to correspond to zonally integrated equatorially trapped waves forced by winds within 10 degrees N/S of the equator. 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 modeled 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. Plain Language Summary The meridional overturning circulation (MOC) is a large scale oceanic circulation that occurs in each of the main ocean basins and plays an important role in regulating Earth's climate. Global ocean models have shown that large oscillations of the MOC with periods of 3-15 days occur near the equator. These oscillations have been shown to be consistent with basin-scale internal waves, trapped near the equator by the Earth's rotation. Observations from a mooring array in the equatorial Pacific Ocean have previously been shown to exhibit oscillations at similar frequencies that correspond to these internal waves. In this study, we compare the model with the observations in order to determine whether the oscillations found in the model are realistic. We find that there is remarkable agreement between the modeled and observed waves. This supports the existence of the large scale MOC oscillations, and gives confidence in the global ocean model for representing these processes.