Shoaling Internal Gravity Waves

Abstract We introduce a new statistical framework that operates directly in space and time to detect shoaling internal waves as seabed temperature structures observed by a fiber optic distributed temperature sensing array deployed in the coastal waters offshore of California. The nonlinear internal wave exhibited a mean shoaling velocity of approximately 0.09\pm 0.04 m \mathrms^-1, with the most commonly observed speed near 0.08 m \mathrms^-1, a mean period of 14\pm 7 minutes, and arrived at the fiber at an average angle of incidence of 23^∘\pm 8^∘ relative to shore-normal. This angle is similar to the orientation of the nearby Scripps branch of the La Jolla Canyon, suggesting that the canyon is a generation site. Nonlinear wave events preferentially occurred during specific phases of the background internal tide, clustered around the ebb phase. To investigate the impact of the oblique angle of approach on the dynamics of shoaling, the observations were used as inspiration for a idealized simulation of a shoaling internal wave approaching a slope at an angle. In the simulation, an initial solitary-like depression wave evolved into elevation boluses propagating obliquely to the isobaths, remaining closely attached to the seafloor as they transported cold water upslope. The shoaling bolus both developed an organized along-crest trailing wake and entrained upslope waters in ways that were quantitatively consistent with the observations. The oblique incidence generated vertically sheared along-crest flow, which may contribute to the coherent structures forming in the trailing wake.