Statistics of Internal Tide Bores and Internal Solitary Waves Observed on the Inner Continental Shelf off Point Sal, California

Abstract

Moored observations of temperature and current were collected on the inner continental shelf off Point Sal, California, between 9 June and 8 August 2015. The measurements consist of 10 moorings in total: 4 moorings each on the 50- and 30-m isobaths covering a 10-km along-shelf distance and an across-shelf section of moorings on the 50-, 40-, 30-, and 20-m isobaths covering a 5-km distance. Energetic, highly variable, and strongly dissipating transient wave events termed internal tide bores and internal solitary waves (ISWs) dominate the records. Simple models of the bore and ISW space–time behavior are implemented as a temperature match filter to detect events and estimate wave packet parameters as a function of time and mooring position. Wave-derived quantities include 1) group speed and direction; 2) time of arrival, time duration, vertical displacement amplitude, and waves per day; and 3) energy density, energy flux, and propagation loss. In total, over 1000 bore events and over 9000 ISW events were detected providing well-sampled statistical distributions. Statistics of the waves are rather insensitive to position along shelf but change markedly in the across-shelf direction. Two compelling results are 1) that the probability density functions for bore and ISW energy flux are nearly exponential, suggesting the importance of interference and 2) that wave propagation loss is proportional to energy flux, thus giving an exponential decay of energy flux toward shore with an e-folding scale of 2–2.4 km and average dissipation rates for bores and ISWs of 144 and 1.5 W m−1, respectively.

Coastal Semidiurnal Internal Tidal Incoherence in the Santa Maria Basin, California: Observations and Model Simulations

“…Previously, internal tidal bore statistics off Pt. Sal were shown to be consistent with the interference from multiple waves (Colosi et al, ). Wave interference may lead to incoherence if energy from multiple sources interacts with background currents and mesoscale eddy activity (e.g., Ponte & Klein, ; Zaron & Egbert, ).…”

“…Colorbar is the water depth h in meters; (b) L3 grid (resolution 200 m); and (c) L4 grid (resolution 66 m). Red squares are mooring locations at 50‐ and 30‐m water depth (also see Colosi et al, ). In (a) dashed black lines are depth contours 30, 50, 100, 200, 500, 1,000, 1,500, 2,000, 2,500, and 3,000 m. Parent grids L0 and L1 are shown elsewhere (Suanda et al, ).…”

“…In coastal regions, small‐scale bathymetric variations, stratification variability from wind‐driven processes, buoyancy input from riverine runoff, and shoaling remotely generated internal tides can modify local internal tide generation and propagation (e.g., Martini et al, ; Nash et al, ; Nash, Kelly, et al, ). These factors result in highly variable continental shelf internal tides on both seasonal (e.g., Xu et al, ) and shorter time scales (Colosi et al, ; Colosi et al, ).…”

“…Discussion of the findings and conclusions are in sections 5 and 6, respectively. Colosi et al, 2018). In (a) dashed black lines are depth contours 30, 50, 100, 200, 500, 1,000, 1,500, 2,000, 2,500, and 3,000 m. Parent grids L0 and L1 are shown elsewhere .…”

Fully nonlinear simple internal waves over subcritical slopes in continuously stratified fluids: Theoretical development

“…This could be one of the causes for the relatively rapid modulation of the bore or ISW activity. 64 Since the proposed theory uses a perturbation approach to include diabatic topographic effects, the applicable slope range needs to be checked using some reference solutions. In this study, this was done using the analytic linear solution to Wunsch's subcritical wedge problem (Fig.…”