Abstract:

Internal solitary waves (ISWs) are commonly observed in the coastal ocean, where they are known to contribute to transport and turbulent mixing. While ISWs are often assumed to result from cross-isobathbarotropictidal flows, we present novel observations suggesting that ISWs can result from along-isobathbarotropictidal flows over channel-shoal bathymetry. Mooring and ship-based velocity, temperature and salinity data were collected along a cross-channel section in a coastal stratified estuary featuring channel-shoal bathymetry. These data show that the along-isobath tidal flows initially drive a cross-isobath Ekman transport, forming lateral circulation. When the lateral current flowed into the stratified water over the deep channel and became supercritical, a mode-2 internal lee wave was generated at the edge of the deep channel. This lee wave propagated onto the shallow shoaland evolved into a group of ISWs of elevation due to nonlinear steepening. These observations highlight importance of the three-dimensional nature of flows on conversion of tidal flows to internal waves in the rotating ocean.