Submesoscale dynamics of dense overflows. Part II: Near-inertial wave trapping and reflection

Victoria Whitley , Jacob O. Wenegrat, Leif Thomas

Near-inertial waves (NIWs) are energetic at high latitudes, yet their interactions with the strongly baroclinic flows of the dense overflows that ventilate the deep ocean have received little attention. Combining linear ray tracing and spectral analysis with a three-dimensional large-eddy simulation of an idealized dense overflow, we examine how the background flow and potential vorticity (PV) structure of a deep boundary current govern the propagation, reflection, and breaking of NIWs. Despite the surface cooling, the descent of gravity currents along the bottom results in layered high-PV bands capping the dense overflow and a wedge of high PV at the shelf break (discussed in Part I of this series). Here we show these high PV features modify the minimum allowable wave frequency and determine where NIWs may travel. Ray tracing shows that waves guided along the sloping isopycnals reflect off high-PV features on the slope and descend into slantwise critical layers along the topography. Power spectra confirm enhanced near-inertial dissipation at these reflection and trapping sites. This study focuses only on the waves generated by this idealized overflow, but the mechanism implies that storm- and tide-forced NIWs of real overflows can enhance mixing and water-mass transformation along deep boundary currents wherever a comparable PV structure arises.