Abstract
Time variability of Eulerian residual currents in the German Bight (North Sea) is studied drawing on existing multi-decadal 2D barotropic simulations (1.6 km resolution) for the period Jan. 1958–Aug. 2015. Residual currents are calculated as 25 h means of velocity fields stored every hour. Principal component analysis (PCA) reveals that daily variations of these residual currents can be reasonably well represented in terms of only 2–3 degrees of freedom, partly linked to wind directions. The daily data refine monthly data already used in the past. Unlike existing classifications based on subjective assessment, numerical principal components (PCs) provide measures of strength and can directly be incorporated into more comprehensive statistical data analyses. Daily resolution in particular fits the time schedule of data sampled at the German Bight long-term monitoring station at Helgoland Roads. An example demonstrates the use of PCs and corresponding empirical orthogonal functions (EOFs) for the interpretation of short-term variations of these local observations. On the other hand, monthly averaging of the daily PCs enables to link up with previous studies on longer timescales.
Highlights
The North Sea is a shallow shelf sea in northwest Europe
EOF2 represents a southward transport of coastal waters and its subsequent discharge into the open North Sea
EOF3 represents transport towards the south-eastern coast of the German Bight and an eddy-like structure centred at the island of Helgoland
Summary
The North Sea is a shallow shelf sea in northwest Europe. To the north the North Sea adjoins the north-eastern Atlantic (cf connections via the Fair Island Current and Norwegian Trench), and in the south it connects to the Atlantic through the English Channel. The German Bight is the shallow south-eastern part of the North Sea, where strong mixing processes caused by tidal currents and wind forcing counteract thermohaline stratification. Variations of the general circulation pattern in the German Bight and the whole North Sea are mainly controlled by variable atmospheric conditions Frequent westerly winds induce a mean cyclonic circulation. This pattern of transport is often disturbed and even reverses for longer periods in summer
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
