TAO data support the existence of large high frequency variations in
cross-equatorial overturning circulation
Abstract
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. 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.