Locally Modified Winds Regulate Circulation in a Semi-Enclosed Shelf Sea

Wind driven circulation in the North Sea is revisited with a specific focus on locally modified winds and their impacts. We show for the first time that local extrema of the wind stress curl (WSC), generated by orography and ocean-atmosphere interactions, help regulate circulation in the northern North Sea. While calculated transports are strongly coupled with wind stress, which itself is driven by large-scale forcing, transports through the Norwegian Trench have higher correlations with the WSC field due to local extrema. Such WSC extrema regulate the eddy activity around the Norwegian Trench. We conclude that orography and ocean-atmosphere interaction are two important mechanisms contributing to the generation of the WSC extrema around the Norwegian coast. Ocean-atmosphere interaction is considered a potential mechanism developing the WSC extrema. Our results show that local winds are more important than previously documented, with important implications for regional circulation likely to result from future changes to local surface gradients, such as may arise from changing meteorological or hydro-climatic forcing. These are additional impacts on North Sea circulation that may not be accounted for from changes in wind stress alone. Plain Language Summary North Sea circulation is investigated with a specific focus on the local winds and their impacts. We show for the first time that the local extrema of the wind field, generated by the coastline and oceanic contributions, help regulate circulation in the northern North Sea. Wind is driven by large-scale forcing mechanisms, and is closely related with volume transports. Volume transports through the Norwegian Trench are better related to the wind field, due to local extrema of wind. Local extrema of wind, and their direction, stimulates rotation in the region, controlling the eddy activity around the Norwegian Trench. We conclude that interaction of winds with the land and an ocean-atmosphere feedback mechanism contribute to the generation of the local extrema of wind along the Norwegian coastline. Our results show that local winds are more important than previously known and have important implications for regional circulation. Therefore, future changes to local density differences from changing meteorological conditions may have further impacts on North Sea circulation, which may not be accountable from changes in wind stress alone.