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Comparison of remotely measured and modelled currents in coastal areas of Norway and Spain
H. H. ESSEN, Ø. BREIVIK, H. GÜNTHER, K.-W. GURGEL, J. JOHANNESSEN, H. KLEIN, T. SCHLICK, and M. STAWARZ
The Global Atmosphere and Ocean System (ISSN 1023-6732), Volume 9, Number 1-2, pp. 38...64, 2003..
Abstract - - Data from two six-week current measurement campaigns at the coasts of Norway and Spain are presented. Spatial coverage of surface currents was obtained by an HF (high frequency) radar. Subsurface currents were measured by bottom-mounted and ship-borne ADCPs (acoustic doppler current profiler). The HF data were assimilated by a fine gridded model with the aim of predicting currents for about 6 h. The objective of this paper is twofold, to investigate the performance of the instruments and the model, and to show the high temporal and spatial variability of currents in the coastal zones under investigation.
Several strong storms occured during the experiments with significant waveheights exceeding 11 m (Norway) and 8 m (Spain), respectively. High waves affected both the WERA (reduced ranges) and the ADCP (unreliable near-surface current velocities). The assimilation algorithm of the model worked well. The comparisons of measured and modelled maps of the surface-current velocity, time series and horizontal gradients reveal good agreement.
The analysis of current data shows similar features for both experimental areas. The dominant M2-tidal currents are weak (amplitudes of about 0.15 m/s). The spatial distribution of the vector correlation between surface current and wind is homogeneous, although single current maps contain strong horizontal variabilities. The portion of current variance linearly forced by wind is about 30 %.
Keywords - - coastal zone, ocean currents, HF radar, ADCP, fine-gridded model