Internal tides in the Solomon Sea in contrasted ENSO conditions

Abstract

Abstract. The Solomon Sea is a place of intense Low Latitudes Western Boundary current transiting to the equator where mesoscale activity is superimposed on internal tides. In this marginal sea, the cumulated effects of these dynamical constraints result in water mass transformation as observed by in situ observations. The objective of this paper is to document the M2 internal tides in the Solomon Sea and their impacts based on two regional simulations with and without tides. Because the Solomon Sea is under the influence of ENSO, the characteristics of the internal tides are analyzed for two contrasted ENSO conditions: the 1997–1998 El Niño and the 1999 La Niña. The generation, propagation and dissipation of the internal tides are sensitive to changes in stratification and mesoscale activity between El Niño and La Niña. Mode 1 is the dominant mode to propagate baroclinic tidal energy within the Solomon Sea, but the El Niño conditions, with stratification closer to the surface, are favorable for the propagation of mode 2. The la Niña case with a high level of mesoscale activity favors the appearance of incoherent internal tides. These results illustrate the complexity in predicting internal tides in order to access meso and submesoscale signatures from altimetric missions, including the future SWOT mission. Diapycnal mixing induced by the internal tides is efficient in eroding the salinity maximum of the upper thermocline water, and in cooling the surface temperature interacting with the atmosphere. Such effects are particularly visible far from the strong currents, where particles may experience the tidal effects during a longer time. Nevertheless, the impacts are different when considering particular ENSO conditions. The interaction of internal tides with the surface mesoscale activity reduces surface cooling during El Niño 1998, but increases surface warming during La Niña 1999, with possible impacts on regional air sea interaction.

Background stratification impacts on internal tide generation and abyssal propagation in the western equatorial Atlantic and the Bay of Biscay

“…This rough calculation helps to understand why small changes in the wavelength can completely change the shape of the surface IT signature. Tchilibou et al (2020) reported a similar observation comparing two simulations from El Niño and La Niña situations in the Solomon Sea. In this region, the El Niño stratification is characterized by a shallow pycnocline and the La Niña stratification is characterized by a deep pycnocline.…”

“…For these reasons an international effort is taking place in order to propose new methods for detecting ITs in SWOT observations (e.g., Zhao et al, 2018) and increasing the knowledge of ITs' non-stationarity (e.g., Tchilibou et al, 2020). In order to better understand the non-stationarity of the ITs, its variability needs to be better defined and quantified.…”

Comment on os-2021-19

“…This rough calculation helps to understand that small changes in the wavelength can completely change the shape of the surface ITs signature. Tchilibou et al (2019) reported a similar observation comparing two simulations from El Niño and La Niña context in the Salomon Sea. In this region, the El Niño stratification is characterized by a shallow pycnocline and the La Niña stratification is characterized by a deep pycnocline.…”

“…Zhao et al, 2018) and increase the knowledge on ITs' non-stationarity (e.i. Tchilibou et al, 2019). The present study aims at contributing to the understanding of the ITs' non-stationarity.…”

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

“…In addition, the varying depth of the pycnocline impacts the generation and the wavelength of the internal tide on seasonal timescales (Ray and Zaron, 2011;Müller et al, 2014;Gerkema et al, 2004;Lahaye et al, 2019). Seasons with a shallow pycnocline coincide with the intensification of the generation of high vertical modes, while a deeper pycnocline season leads mostly to mode 1 internal tide generation (Tchilibou et al, 2020;Barbot et al, 2021). The mean barotropic and baroclinic current act to deviate, trap, and advect the internal tide flux (Kelly et al, 2010Duda et al, 2018).…”