Breaking of internal solitary waves generated by an estuarine gravity current

Abstract

AbstractMooring and ship‐based data collected in a stratified estuary showed the generation of internal solitary waves by a bottom gravity current. Down‐estuary winds drove a counterclockwise lateral circulation over channel‐shoal bathymetry. When the lateral flows became supercritical, the pycnocline was sharply raised at the edge of the deep channel, leading to flow convergences and formation of a bottom gravity current. As the lateral circulation weakened during wind relaxation, the gravity current propagated onto the shoal and excited internal disturbances around its head. These disturbances evolved into a train of large‐amplitude internal solitary waves that subsequently propagated ahead of the gravity current. The waves moving out of the gravity current broke, generating overturning and turbulence with energy dissipation rate reaching ~1 × 10−4 m2 s−3, 3 orders of magnitude larger than the background value. Our observations suggest that breaking internal waves may be an important source of turbulent mixing in stratified estuaries.