Along-coast Variability of Internal Wave Energy on the Inner Shelf

Internal waves transport substantial energy to shallow waters of the coastal ocean. These waves can have long coherence scales along the coast ~O(5-50 km) and include bores and high-frequency waves, the latter evolving with rich spatiotemporal variability. Remote sensing measurements, for example from satellite and X-band radar systems, have revealed spatial heterogeneity of coastal internal waves, but the importance of this heterogeneity has been difficult to assess with in situ observations since the scales are challenging to resolve. We present data from the Inner Shelf Dynamics Experiment, which included >100 moorings over a 400 km² region of the central California inner shelf. Using moorings that ranged from 100 m to 9 m water depth and spanned ~40 km of coastline (roughly centered at Pt. Sal), we calculate the semidiurnal kinetic energy density and kinetic energy flux at 45 moorings. We illustrate that an individual internal bore that is continuously observed along the coast can have large along-coast variability in energy density and energy flux. This leads to spatial heterogeneity in the time-average internal wave energy fluxes. We also analyze how low- and high-frequency processes are interconnected through their influences on the waveguide. For example, low-frequency changes in the shelf stratification, such as that caused by wind relaxations, strongly modulate the evolution of internal waves during shoaling. Additionally, the internal waves themselves can significantly modify the stratification and change the upstream conditions encountered by subsequent internal wave packets. We demonstrate that the internal wave properties are strongly influenced by these modulations of the waveguide.