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The North Atlantic winds and the elongation of the Gulf Stream into the Norwegian Sea

A new study published in Journal of Geophysical Research by Nansen- and Bjerknes Center researchers show that the North Atlantic winds are important for the variability of the inflow to the Norwegian Sea.

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The inflow of warm and saline Atlantic water into the Norwegian Sea is of significant importance to the regional ocean climate, and especially to the life in the ocean and the fisheries. It is therefore important to explore the potential predictability of the system.

The strength of the winds is decisive  

Changes in the wind forcing tend to regulate the depth of the upper ocean mixed layer. Disturbances in the density layers forced by variations in the wind forcing tend to follow the depth contours in the ocean. For the period 1995-2001 the wind forcing in the northeastern North Atlantic was relatively weak, and the depth of the mixed layer was shallower than the sill depths of the Greenland-Scotland Ridge. Slowly moving disturbances caused by changes in the wind forcing south of the ridge were transmitted into the Norwegian Sea where they were recorded as anomalous volume transports in the Norwegian Atlantic Current, with a lag of 15 months.

In contrast, for the pentad prior to this period the wind forcing was much more intense, and generated mixing well below sill depths of the Greenland-Scotland Ridge for all winters. Disturbances forced by variations in the wind forcing then tended to follow depth contours that did not enter the Norwegian Sea, and the 15 months lagged relation between the wind forcing and the volume transports vanished.

This study was initiated to find the observed relation between the winds in the North Atlantic and volume transports in the Svinøy section, and to check if this relation was valid also prior to the period of current measurements.

A likely mechanism for this relation is revealed, but the fact that this seems to hold only for periods of low wind forcing, makes prediction for longer periods with variable forcing difficult.

Reference: Sandø, A. B., and T. Furevik, The relation between the wind stress curl in the North Atlantic and the Atlantic in flow to the Nordic Seas, J. Geoph. Res., 2008.