Observation of Yanai Wave Excitation by Tropical Instability Waves in the Equatorial Pacific

Abstract Yanai waves are observed in the central equatorial Pacific at 436–864 m depth, below the Equatorial Undercurrent. Applying maximum likelihood estimation to shipboard ADCP measurements enables identification of Yanai wave signals from irregularly sampled observations. Ray tracing links the observed wave to a tropical instability wave (TIW) passage ∼20° west of the survey site and ∼49 days earlier, where meridional velocity and sea surface temperature exhibit consistent variability with the Yanai wave. The influence of meridional wind on Yanai wave generation is unlikely due to the winds' high frequency and small amplitude. The estimated downward energy flux of Yanai wave (1.4 mW ) represents 14%–23% of the barotropic energy conversion sustaining TIWs at the equator. These results provide observational evidence linking a TIW passage to the observed subsurface Yanai wave and suggest that Yanai waves provide an important pathway for TIW energy dissipation and vertical energy redistribution.