Analysis of tidal currents in the North Sea from shipboard acoustic Doppler current profiler data

Håvard Vindenes,Kjell Arild Orvik,Henrik Søiland,Henning Wehde

doi:10.1016/j.csr.2018.04.001

Abstract

North Sea tidal currents are determined by applying harmonic analysis to ship-borne acoustic Doppler current profiler data recorded from 1999 to 2016, covering large areas of the northern North Sea. Direct current measurement data sets of this magnitude are rare in the otherwise well investigated North Sea, and thus it is a valuable asset in studying and expanding our understanding of its tidal currents and circulation in general. The harmonic analysis is applied to a least squares fit of the current observations at a set of knot points. Results from the harmonic analysis compare favorably to tidal parameters estimated from observations from moored instruments. The analysis shows that the tides are characterized by strong semi-diurnal component, with amplitudes of the principal Lunar constituent ranging from 1.6 cm/s in the Skagerrak to 67 cm/s in the Fair Isle Channel. Diurnal tides are found to be approximately one fifth the strength of the predominant semi-diurnal constituent. Output from a regional barotropic tide model compares well to tidal current determined from the harmonic analysis of the Acoustic Doppler Current Profiler data.

Highlights

The North Sea is one of the most investigated marine areas in the world, remarkable data gaps still exist for spatial distributions and long-term records of velocity measurements (Sündermann and Pohlmann, 2011)
In this study we utilize an extensive set of current measurements from ship mounted Acoustic Doppler Current Profilers (ADCPs) to estimate tidal currents for the northern North Sea
Current meter data are sparse, we have shown good agreement between ADCP and current meter M2 ellipses, demonstrating the accuracy of the harmonic analysis of the ADCP data, given that it is limited to areas where ADCP data are relatively densely concentrated

Summary

Introduction

The North Sea is one of the most investigated marine areas in the world, remarkable data gaps still exist for spatial distributions and long-term records of velocity measurements (Sündermann and Pohlmann, 2011). It has a relatively broad connection to the North Atlantic and the Norwegian Sea at the northern edge, as well as a narrower connection to the North Atlantic through the English Channel in the south. This results in an interplay of oceanic influences like tides and the North Atlantic Oscillation, and continental influences like freshwater discharge and input of pollutants (Sündermann and Pohlmann, 2011). The Norwegian Trench, has the topography of a large fjord with a sill depth of around 270 m and a maximum depth in the inner end, in the Skagerrak, of approximately 700 m

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