Nonlinear Release of Subinertial Diurnal Internal Tides Forms Spiral Internal Solitary Waves

Abstract

Earth's rotation imposes a dynamical barrier on the free propagation of internal tides at high latitudes, raising questions about the fate of tidal energy poleward of the critical latitude. Satellite observations reveal spiral internal solitary waves (ISWs) along the continental slope of the South Orkney Plateau. Although these waves might be attributed to direct steepening of low‐frequency internal tides, theoretical estimates of their propagation speed are nearly twice those inferred from observations. Using high‐resolution simulations, we resolve this inconsistency by identifying a topographically steered energy cascade: subinertial diurnal internal tides, initially trapped by the slope, undergo nonlinear evolution that generates superinertial harmonics. This frequency upshift allows tidal energy to surpass rotational constraints, radiate offshore, and ultimately evolve into the spiral ISWs. These results identify a distinct energy cascade pathway for internal wave dynamics in polar oceans and demonstrate how tidal energy can be redistributed despite rotational limitations.