The spatial cross-correlation structure induced by wave refraction near Scripps Canyon.

Monday, 15 December 2014
Pieter Bart Smit, Tim T Janssen and Thomas H C Herbers, Theiss Research, La Jolla, CA, United States
The interaction between ocean waves and nearshore topography, such as submarine canyons that extend close to shore, can - through wave interference - introduce fast (intra-wave scale) spatial variability in the mean wave statistics (e.g., the significant wave height). These variations are associated with refraction-induced cross-correlations in the wave field and cannot be resolved with conventional statistical wave models. To capture these effects, the evolution of the complete second-order statistics is required, as shown by Smit & Janssen (2013, J Phys Oceanogr, 43, 1741-1758) who consider an integro-differential equation to transport the complete correlation matrix. Their model captures spatial cross-correlations, thus identifying standing wave patterns affecting wave-induced momentum fluxes (radiation stresses) and circulation, and thus providing an additional level of information that was not available before in statistical wave models. In this work we apply the new quasi-coherent model to study the influence of Scripps Canyon (near San Diego) on nearshore wave statistics for different offshore wave conditions. Thereto we compare model results to observations near Scripps Canyon collected during the ONR Nearshore Canyon Experiment (NCEX), in the fall of 2003 (Magne et al., J Geophys Res, 2007). The focus of this paper is on the inhomogeneous wave effects near the Canyon, which we analyze by considering the spatial cross-correlation functions as predicted by the model and observed by arrays of sensors. The cross-correlations demonstrate that during swell conditions, partially standing wave patterns emerge in the vicinity of the canyons, which has important implications for nearshore modeling of circulation and transport processes.