Internal tides in the Solomon Sea in contrasted ENSO conditions

Abstract

Abstract. 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 Niño and the April–June 1999 La Niña. 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 Niño and La Niña 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 Niño period when the stratification is closer to the surface. The La Niña 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 meso- and 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.

Imprint of chaotic ocean variability on transports in the southwestern Pacific at interannual timescales

“…Two regions of significant correlation emerge: the tropical band, including the Solomon Sea, and the Tasman Front region. A few months after an El Niño, EKE decreases in the tropics, consistent with findings from Tchilibou et al (2020); 15 months after an El Niño, EKE conversely increases in the Tasman Front area when the Tasman Front is stronger and shifted northward.…”

“…The first is the El Niño-Southern Oscillation (ENSO), the dominant mode of interannual variability in the tropical band with remote oceanic and atmospheric teleconnections (see Sprintall et al, 2020 for a review). The second, farther south in the extratropics, is the Southern Annular Mode (SAM) (Thompson and Wallace, 2000). The latter is characterized by meridional shifts in westerly wind stress, potentially influencing the transports at midlatitudes.…”

Internal tides off the Amazon shelf during two contrasted seasons: Interactions with background circulation and SSH imprints

“…The seasonality of the stratification induces a seasonality of the internal tides. Seasons with a shallow pycnocline coincide with the generation of high vertical modes, while a deeper pycnocline leads mostly to mode 1 internal tide generation (Tchilibou et al, 2020;Barbot et al, 2021). Idealized and, less often, realistic studies have looked at internal tides and current interactions.…”

The Three‐Dimensional Internal Tide Radiation and Dissipation in the Mariana Arc‐Trench System

“… is the baroclinic energy flux. The on the right‐hand side denotes the inferred dissipated term calculated as the residual term of the energy (Tchilibou et al., 2020). It primarily results from physical dissipation processes, although it does contain errors.…”