Abstract
AbstractTemperature and current measurements from two moorings onshore of the Celtic Sea shelf break, a well‐known hot spot for tidal energy conversion, show the impact of passing summer storms on the baroclinic wavefield. Wind‐driven vertical mixing changed stratification to permit an increased on‐shelf energy transport, and baroclinic energy in the semidiurnal band appeared at the moorings 1–4 days after the storm mixed the upper 50 m of the water column. The timing of the maximum in the baroclinic energy flux is consistent with the propagation of the semidiurnal internal tide from generation sites at the shelf break to the moorings 40 km away. Also, the ∼3 day duration of the peak in M2 baroclinic energy flux at the moorings corresponds to the restratification time scale following the first storm.
Highlights
Where the barotropic tide flows over steep topography, internal waves are generated at tidal frequencies
A wave travels ∼10 to 15 km per day, so an M2 internal wave generated at the point on the shelf break nearest ST5 during the stratification minimum on year-day 168 would appear at ST5 around day 172
Baroclinic energy at the semidiurnal tidal frequency appears at moorings on the Celtic Sea continental shelf 1–4 days after a strong wind event thoroughly mixed the upper 50 m of the water column
Summary
Where the barotropic tide flows over steep topography, internal waves are generated at tidal frequencies. This study uses the same data set to examine a second, previously unrecognized mechanism by which the wind can affect tidal energy fluxes on short time scales, namely, how stratification changes due to wind-mixing can affect the propagation of the internal tide on the shelf. Shorter time scale variations in stratification, in particular those associated with wind-mixing, are likely to impact the generation and propagation of IT from the shelf break; these effects are the focus of this study. We expect to see a shift in generation sites as newly critical topographic slopes “switch on,” and a shift in propagation of the IT as supercritical bathymetry becomes subcritical, allowing the shoreward propagation of IT energy that would previously have been reflected. Using observations from a mooring array deployed across the Celtic Sea shelf break in June 2012, we describe the impact of two wind-mixing events on internal wave energetics
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