Numerical Investigation of Bidirectional Mode-1 and -2 Internal Solitary Wave Generation from North and South of Batti Malv Island, Nicobar Islands, India

Abstract

Strong bidirectional Internal Solitary Waves (ISWs) generate from a shallow channel between Car Nicobar and Chowra Islands of Nicobar Islands, India and propagate towards the Andaman Sea (eastward) and Bay of Bengal (westward). Batti Malv Island separates this shallow channel into two ridges, North of Batti Malv (NBM) and South of Batti Malv (SBM). Firstly, this study identifies the prominent mode-1 and mode-2 ISWs emerging from NBM and SBM using Synthetic Aperture Radar images and then explores their generation mechanism(s) using a nonlinear, unstructured and non-hydrostatic model, SUNTANS. During spring tide, flow over NBM is supercritical with respect to mode-1 internal wave. Model simulations reveal that mode-1 ISWs are generated at NBM by “Lee wave mechanism” and propagate both in the east and west directions depending on the tidal phases. However, the flow over SBM is subcritical with respect to mode-1 internal wave. The bidirectional propagating mode-1 ISWs evolve from a long wave disturbance induced by “upstream influence”. But, during spring tide, with an increased tidal flow over SBM, it is observed that the westward propagating ISWs are formed by a dispersed hydraulic jump observed over the ridge. Moreover, the bidirectional mode-2 waves from SBM are generated by “Lee wave mechanism”. An energy budget comparison reveals that the region surrounding NBM is efficient in radiating low-mode baroclinic energy (0.98 GW), while SBM is highly efficient in converting barotropic to baroclinic energy (4.1 GW).