Can ENSO-related tidal modulations be explained using a barotropic tidal model?
Event: 2014 Ocean Surface Topography Science Team Meeting
Session: Tides, internal tides and high-frequency processes
Presentation type: Type Poster
A barotropic tidal model is used to examine the changes in the major oceanic diurnal and semi-diurnal tidal constituents (M2, S2, K1, and O1) caused by ENSO-related modulations in sea surface height (SSH) and ocean current. These investigations employ the Oregon State Tidal Inversion Software (OTIS) to model the barotropic tides in the Western Tropical Pacific Ocean, a region where large ENSO-related modulations are observed in both SSH and tidal properties. Modulations are analyzed for the years 1997-2000, which saw the strongest El Nino (1997-1998) and La Nina (1999-2000) events of the satellite era. The response of barotropic tides to three dynamical perturbations is presented, where the AVISO/DUACS SSH and geostrophic current products are used to define the ENSO-related modulations. First, the response of tides to modulations in the mean sea level is examined. The effect is found to be negligible at the sites of open-ocean tide gauges, but potentially measurable effects occur in shallow water regions, for example, in the Solomon Islands and the Coral Sea. Second, the response of tides to modulations in a spatially-variable drag coefficient is examined, where the latter is inferred from altimetry as a proxy for thermocline depth and stratification strength. Third, the response of tides to modulations in relative vorticity, calculated from altimeter-derived geostrophic currents, is examined.