Tilting shear flows occur in the lee of islands and headlands and estuarine outflows in the coastal ocean, where lateral density gradients lead to gravitational tilting of barotropic shear and intense vertical mixing. Using high-resolution simulations and novel laboratory experiments, we have been studying the three-dimensional instabilities that drive intense surface vortices, which were observed by David Farmer and co-workers in the tidal separation flow around Stuart Island in the Haro Straight. Our original work on these flows (White & Helfrich 2013) was was funded by NSF. With funding by a recent grant from the Office of Naval Research we will explore the importance of these flows in the complex reef and island topography around Palau in the western Pacific.
a) Sketch of tilting, horizontal shear layer near Stuart Island from Farmer et al. (2002). b) Photograph of the surface expression of intense vortices near Stuart Island (Farmer et al. Dyn. Atm. Oceans 2002). c) Infra-red image of a tilting shear layer in the Snohomish River (from A. Jessup).