The Generation and Fate of internal tides on the North West European Shelf

The lifecycle of long internal tides are investigated on the North West European Shelf using a kilometric scale 3D NEMO simulation (AMM60). The lifecycle starts with the generation of long internal waves by the conversion from planetary scale baroptropic tides and ends in dissipation by mixing processes.

For many years observational studies showed intermittent mixing in seasonally stratified shelf seas to be patchy. Here, with recent advances in numerical modelling capability, the spatial and temporal extent of the internal wave field is shown, using Available Potential Energy (APE) as a diagnostic.

170 GW of tidal energy is dissipated on the shelf but less than 1% is converted and lost via the baroclinic pathways. Nevertheless, the dissipation of internal tides contributes to mixing across the pycnocline, which is known to mediate the biogeochemistry of shelf sea system. However, climate scale simulations are, at the present time, unable to resolve these processes. Here, it is found that a Froude number, for the internal waves, is a useful spatial and temporal predictor of the APE field. This Froude number can be diagnosed from courser resolution (e.g. climate) models, and presents a pathway towards parameterisation of shelf internal waves.