Long lived second mode internal solitary waves in the Andaman Sea

J M Magalhaes,M C Buijsman,J C B da Silva

doi:10.1038/s41598-020-66335-9

J M Magalhaes, M C Buijsman + Show 1 more

Open Access

https://doi.org/10.1038/s41598-020-66335-9

Copy DOI

Journal: Scientific Reports	Publication Date: Jun 24, 2020
Citations: 22	License type: open-access

Affiliation: University of Porto, Stennis Space Center

Abstract

Internal waves are density oscillations propagating along the ocean’s inner stratification, which are now acknowledged as a key constituent of the ocean’s dynamics. They usually result from barotropic tides, which flow over bottom topography, causing density oscillations to propagate along the pycnocline with a tidal frequency (i.e. internal tides). These large-scale waves propagate away from their forcing bathymetry and frequently disintegrate into nonlinear short-scale (higher-frequency) internal wave packets. Typically, short-scale internal wave observations in the ocean are associated with vertical structures (in the water column) of the lowest fundamental mode. Higher vertical modes have recently been documented as well, but these are commonly short-lived (up to a few hours). However, unprecedented satellite images showing long-lived short-scale mode-2 internal waves have now been documented in the Andaman Sea, and we report here the companion results of a non-hydrostatic and fully nonlinear numerical model. The simulations reproduce the waves’ main characteristics as observed in satellite imagery, and the results suggest a resonant coupling with a larger-scale mode-4 internal tide as an explanation for their long-lived character.

Highlights

A higher resolution domain was set along the main ridge and the waves’ propagation path as observed in the SAR (roughly between 91.5 and 95 °E, see Fig. 5)
The model setup follows from that used in Buijsman et al.[33] for the Luzon Strait and in da Silva et al.[6] in for Mascarene Ridge, whereas in this case reduced grid spacing and time steps were used to model the short-scale mode-2 solitary-like waves in the Andaman Sea
The horizontal grid size ensures that numerical dispersion is smaller than physical dispersion, allowing for proper non-hydrostatic effects[34,35]

Summary

Introduction

A higher resolution domain was set along the main ridge and the waves’ propagation path as observed in the SAR (roughly between 91.5 and 95 °E, see Fig. 5). The increased resolution is needed to resolve the IW features anticipated in the SAR, which range from the shorter mode-2 solitary-like waves to the larger internal tides – a time step of 2 seconds ensured a proper Courant–Friedrichs–Lewy condition and stable model runs.

Results

Conclusion