CoAuthors

Ted Durland (Oregon State University, USA)

Oceanic equatorial waves play a fundamental role in ocean adjustment in the tropics, and can rapidly transmit forcing over planetary scales. Satellite altimetry data contain a wealth of underexploited information on equatorial inertial gravity waves, down to periods of a few days. The long and relatively continuous altimetry record allows us to achieve a high-resolution view of the zonal-wavenumber frequency spectrum of variability in the equatorial Pacific, providing a depiction of the spectrum of SSH variability spanning periods of days to years and Rossby waves to inertia gravity waves. Consistent with previous results, there is clear evidence for equatorial wave vertical and meridional modes resembling linear theory, but the altimetry data reveal some new observational insights. In the Pacific, we find clear evidence for two baroclinic modes and at least seven meridional modes. There has been some doubt as to whether high meridional modes could actually be established, but we find clear evidence for meridional modes up to mode 5 in the inertia-gravity wave spectrum. In the 5th meridional mode, SSH oscillates coherently over a latitudinal range of about 2000 km (10°S to 10°N), but with six sign changes in between. We briefly contrast these results with similar observations in the Atlantic and Indian Oceans—the evidence for discrete vertical-meridional equatorial wave modes is not as strong in these basins, which is consistent with other analyses going back to the 1980s.