The seasonal circulation and volume transport on the northwest European continental shelf: a fine-resolution model study

In this paper the circulation of the northwest European continental shelf is investigated using the first year-long density-evolving simulation at shelf wide scales and sub-Rossby Radius resolution (similar to 1.8 km). A series of numerical experiments are conducted to distinguish between the wind-, density-, and oceanic-driven components of the flow. These demonstrate that, while all components have a role throughout the year, the density- driven component is particularly important during the summer and autumn months. The time evolution of the density field makes a significant contribution to the seasonal variation of volume transport on shelf wide scales and is persistent in direction; whereas the wind- driven volume transport acts on much shorter timescales and is more variable in direction. The importance of the oceanic forcing is demonstrated, representing tidal residuals and large-scale oceanic sea level (pressure) variation; this forcing drives a substantial component of the circulation throughout the year. Twenty six satellite tracked drifters deployed in the summer of 2001 are used for a direct validation of the model currents. The model current speeds are found to be accurate to similar to 46% when averaged over similar to 40 d, but tend to be too slow. The summer volume fluxes are compared with estimates in the literature showing good agreement, although there is a suggestion that the North Sea inflows are overestimated. Comparisons with the coarser resolution model used for boundary conditions demonstrate the importance of fine-resolution to the details of the frontal currents with consequences for modeling exchange processes and biological activity in these regions