S. H. Suanda,
J. A. Colosi,
A. J. Miller
and C. A. Edwards, 2019:
Coastal semidiurnal internal tidal incoherence in the
Santa Maria Basin, California: Observations and model simulations.
Journal of Geophysical Research-Oceans, 124, 5158-5179.
A series of five realistic, nested, hydrostatic numerical ocean model simulations are used to
study semidiurnal internal tide generation and propagation from the continental slope, through the shelf
break and to the midshelf adjacent to Point Sal, CA. The statistics of modeled temperature and horizontal
velocity fluctuations are compared to midshelf observations (30- to 50-m water depth). Time- and
frequency-domain methods are used to decompose internal tides into components that are coherent and
incoherent with the barotropic tide, and the incoherence fraction is 0.5–0.7 at the midshelf locations in
both the realistic model and observations. In contrast, the incoherence fraction is at the most 0.45 for a
simulation with idealized stratification, and neither atmospheric forcing nor mesoscale currents.
Negligible conversion from barotropic to baroclinic energy occurs at the local shelf break. Instead, the
dominant internal tide energy sources are regions of small-scale near-critical to supercritical bathymetry
on the Santa Lucia escarpment (1,000–3,000 m), 70–80 km from the continental shelf. Near the generation
region, semidiurnal baroclinic energy is primarily coherent and rapidly decays adjacent to the shelf break.
In the realistically forced model, incoherent energy is less than 10% in the generation region, with a steady
increase in incoherence fraction from the continental slope to the midshelf. Backward ray tracing from the
midshelf to the Santa Lucia escarpment identifies multiple energy pathways potentially leading to spatial
interference. As internal tides shoal on the predominantly subcritical slope/shelf system, temporally
variable stratification and Doppler shifting from mesoscale and submesoscale features appear equally
important in leading to the loss of coherence.