Tchilibou M., Gourdeau Lionel, Lyard F., Morrow R., Larrouy A. K., Allain D., Djath B. (2020). Internal tides in the Solomon Sea in contrasted ENSO conditions. Ocean Science, 16 (3), p. 615-635. ISSN 1812-0784.
Titre du document
Internal tides in the Solomon Sea in contrasted ENSO conditions
Tchilibou M., Gourdeau Lionel, Lyard F., Morrow R., Larrouy A. K., Allain D., Djath B.
Source
Ocean Science, 2020,
16 (3), p. 615-635 ISSN 1812-0784
Intense equatorward western boundary currents transit the Solomon Sea, where active mesoscale structures exist with energetic internal tides. In this marginal sea, the mixing induced by these features can play a role in the observed water mass transformation. The objective of this paper is to document the M2 internal tides in the Solomon Sea and their impacts on the circulation and water masses, based on two regional simulations with and without tides. Since the Solomon Sea is under the influence of ENSO, the characteristics of the internal tides are also analyzed for two contrasted conditions: the January-March 1998 El Nino and the April-June 1999 La Nina. The generation, propagation, and dissipation of the internal tides are sensitive to changes in stratification and mesoscale activity, and these differ between these contrasted El Nino and La Nina case studies. Mode 1 is the dominant vertical mode to propagate baroclinic tidal energy within the Solomon Sea, but mode 2 becomes more energetic during the El Nino period when the stratification is closer to the surface. The La Nina period with a higher level of mesoscale activity exhibits more incoherent internal tides. These results illustrate the complexity of predicting internal tides in marginal seas in order to clearly observe mesoand submesoscale signatures from altimetric missions, including the future Surface Water Ocean Topography (SWOT) mission. Diapycnal mixing induced by tides contributes to a stronger erosion of the salinity maximum of the upper thermocline water and to cooling of the surface temperature interacting with the atmosphere. Such effects are particularly visible in quieter regions, where particles may experience the tidal effects over a longer time. However, when averaged over the Solomon Sea, the tidal effect on water mass transformation is an order of magnitude less than that observed at the entrance and exits of the Solomon Sea. These localized sites appear crucial for diapycnal mixing, since most of the baroclinic tidal energy is generated and dissipated locally here, and the different currents entering/exiting the Solomon Sea merge and mix. Finally, the extreme ENSO condition case studies suggest the strong role of local circulation changes, as well as stratification changes, in modifying the internal tides.
