The self-similar stratified inner-shelf response to transient rip-current-induced mixing

Abstract

The stratified inner-shelf response to surf-zone-generated transient rip currents (TRC) is examined using idealized simulations with uniform initial thermal stratification, with initial temperature T0 and vertical coordinate z, or initial squared buoyancy frequency, varying from unstratified to highly stratified. The TRC-induced depth-integrated cross-shore eddy kinetic energy flux is independent of and decays to near zero within (surf-zone width m). Cross-shore inhomogeneous TRC mixing causes shoreward broadening isotherms, driving a near-field inner-shelf overturning circulation and a far-field geostrophic along-shore velocity that strengthen with. TRC mixing mostly (90Â %) increases background potential energy (BPE) and also available (APE, 10Â %) potential energy, driving inner-shelf mean circulation. The specific BPE zero-crossing depth collapses the near-field-layer cross-shore velocity, using an intrusive gravity current scaling. The approximately steady exchange flow exports low-stratification fluid at a depth, re-supplying the TRC region with stratified fluid from above/below, similar to localized mixing laboratory experiments. Offshore of, a self-similar far-field intrusion with characteristic isotherm slope (Rossby deformation radius) is in approximate geostrophic balance with the non-dimensional along-shore velocity. Inner-shelf near-field and far-field horizontal length scales vary as and, respectively. The length scale is related to the work performed by TRC mixing using an idealized well-mixed wedge geometry. Idealized analytical scalings are qualitatively consistent with modelled BPE and APE distributions. Thus, the self-similar stratified inner-shelf response to TRC-driven mixing depends on key dimensional parameters and.