Evaluating the surface circulation in the Ebro delta (northeastern Spain) with quality-controlled high-frequency radar measurements

摘要

The Ebro River delta is a relevant marine protected area in the westernMediterranean. In order to promote the conservation of its ecosystem andsupport operational decision making in this sensitive area, a three-sitestandard-range (13.5 MHz) CODAR SeaSonde high-frequency (HF) radar wasdeployed in December 2013. The main goal of this work is to explore basicfeatures of the sea surface circulation in the Ebro deltaic region as derivedfrom reliable HF radar surface current measurements. For this aim, a combinedquality control methodology was applied: firstly, 1-year long (2014)real-time web monitoring of nonvelocity-based diagnostic parameters wasconducted to infer both radar site status and HF radar system performance.The signal-to-noise ratio at the monopole exhibited a consistent monthlyevolution, although some abrupt decreases (below 10 dB), occasionallydetected in June for one of the radar sites, impacted negatively on thespatiotemporal coverage of total current vectors. It seemed to be sporadicepisodes since radar site overall performance was found to be robust during2014. Secondly, a validation of HF radar data with independent in situobservations from a moored current meter was attempted for May–October 2014.The accuracy assessment of radial and total vectors revealed a consistentlyhigh agreement. The directional accuracy of the HF radar was rated at betterthan 8°. The correlation coefficient and root mean square error(RMSE) values emerged in the ranges [0.58–0.83] and[4.02–18.31] cm s?1, respectively. The analysis of the monthlyaveraged current maps for 2014 showed that the HF radar properly representedbasic oceanographic features previously reported, namely, the predominantsouthwestward flow, the coastal clockwise eddy confined south of the Ebrodelta mouth, or the Ebro River impulsive-type freshwater discharge. The EOFanalysis related the flow response to local wind forcing and confirmed thatthe surface current field evolved in space and time according to threesignificantly dominant modes of variability.