Density stratification influences on generation of different modes internal solitary waves

Abstract

An ideal tide-topography interaction model is utilized for studying the influence of density stratification (pycnocline depth d, thickness d, and the density difference Dqa across the pycnocline) on nonlinear disintegration of the first (mode-1) and second (mode-2) baroclinic mode internal tides into internal solitary waves (ISWs). The solution methods include weakly nonlinear analysis and fully nonlinear simulation. It is found that as d increases, even though the energy flux into mode-1 internal tides is always larger than that into mode-2 ones at generation, mode-2 ISWs emerge and mode-1 ISWs are suppressed. As d increases, the total energy conversion and the fluxes into both mode-1 and mode-2 tides all increase first and then decrease. During propagation, a thick pycnocline is actually not favorable for the emergence of mode-2 ISWs, and the simulated well-developed mode-2 ISWs for a pycnocline of intermediate thickness are due to the tide generation process. As δqa increases, the total conversion and the fluxes into both mode-1 and mode-2 tides all increase almost linearly. Even though the flux into mode-1 tides is always larger than that into mode-2 ones at generation, mode-1 tides cannot disintegrate but mode-2 ISWs develop very well. During propagation, δqa has no influence on the generation of ISWs. The present work systematically investigates the influence of density stratification on formation of ISWs by considering both internal tide generation and propagation processes.