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gfdl on-line bibliography > 2008 citations
Internal waves, baroclinic energy fluxes and mixing at the European shelf edge
| Green, J. A. Mattias, J. H. Simpson, S. Legg, and M. R. Palmer, 2008: Internal waves, baroclinic energy fluxes and mixing at the European shelf edge. Continental Shelf Research, 28(7), 937-950. |
Abstract: The energy flux in internal waves generated at
the Celtic Sea shelf break was estimated by (i) applying perturbation theory
to a week-long dataset from a mooring at 200 m depth, and (ii) using a 2D
non-hydrostatic circulation model over the shelf break. The dataset
consisted of high resolution time-series of currents and vertical
stratification together with two 25-h sets of vertical profiles of the
dissipation of turbulent kinetic energy. The observations indicated an
average energy flux of 139 W m−1, travelling along the shelf
break towards the northwest. The average energy flux across the shelf break
at the mooring was only 8 W m−1. However, the waves propagating
onshelf transported up to 200 W m−1, but they were only present
51% of the time. A comparison between the divergence of the baroclinic
energy flux and observed dissipation within the seasonal thermocline at the
mooring showed that the dissipation was at least one order of magnitude
larger. Results from a 2D model along a transect perpendicular to the shelf
break showed a time-averaged onshelf energy flux of 153–425 W m−1,
depending on the magnitude of the barotropic forcing. A divergence zone of
the energy flux was found a few kilometre offshore of the location of the
observations in the model results, and fluxes on the order of several kW m−1
were present in the deep waters further offshelf from the divergence zone.
The modelled fluxes exhibited qualitative agreements with the phase and
hourly onshelf magnitudes of the observed energy fluxes. Both the
observations and the model results show an intermittent onshelf energy flux
of 100-200 W m−1, but these waves could only propagate
 20–30 km
onshore before dissipating. This conclusion was supported by a 25-h dataset
sampled some 180 km onto the shelf, where a weak wave energy flux was found
going towards the shelf break. We therefore conclude that shelf break
generated internal waves are unlikely to be the main source of energy for
mixing on the inner part of the shelf. |