Variability in the air-sea interaction patterns and timescales within the south-eastern Bay of Biscay, as observed by HF radar data

Two high-frequency (HF) radar stations were installed on the coast of the south-eastern Bay of Biscay in 2009, providing high spatial and temporal resolution and large spatial coverage of currents in the area for the first time. This has made it possible to quantitatively assess the air-sea interaction patterns and timescales for the period 2009-2010. The analysis was conducted using the Barnett-Preisendorfer approach to canonical correlation analysis (CCA) of reanalysis surface winds and HF radar-derived surface currents. The CCA yields two canonical patterns: the first wind-current interaction pattern corresponds to the classical Ekman drift at the sea surface, whilst the second describes an anticyclonic/cyclonic surface circulation. The results obtained demonstrate that local winds play an important role in driving the upper water circulation. The wind-current interaction timescales are mainly related to diurnal breezes and synoptic variability. In particular, the breezes force diurnal currents in waters of the continental shelf and slope of the south-eastern Bay. It is concluded that the breezes may force diurnal currents over considerably wider areas than that covered by the HF radar, considering that the northern and southern continental shelves of the Bay exhibit stronger diurnal than annual wind amplitudes.The authors thank two anonymous reviewers and, particularly, the editor Mike Kosro for their very constructive comments, which have led to an improved version of the manuscript. The authors thank the Directorate of Emergency Attention and Meteorology of the Basque Government for establishing the operational data acquisition system. The authors acknowledge financial support from the ETORTEK Strategic Research Programme (Department of Industry, Trade and Tourism and Department of Transport and Civil Works of the Basque Government) through the ITSASEUS II project. The Basque Government (Department of Agriculture, Fisheries and Food) has funded the project "VARIACIONES". We thank Qualitas Remos for the work performed on HF radar data processing and also L. Solabarrieta for her enthusiasm and interest in the HF radar measurements. Jon Saenz is grateful for financial support from projects CGL2008-03321 (Spanish National R+D+I Programme) and CTP10-03 PYNATEO (Basque Government). He also acknowledges funding provided by the University of the Basque Country (UFI 11/55, GIU 11/01 and PPM12/01). The wind data for this study are from the Research Data Archive (RDA), which is maintained by the Computational and Information Systems Laboratory (CISL) at the National Center for Atmospheric Research (NCAR). NCAR is sponsored by the National Science Foundation (NSF). The original data are available from the RDA (http://dss.ucar.edu) in dataset number ds093.1. G. Esnaola is supported by a research grant from the Fundacion Centros Tecnologicos, Inaki Goenaga. This is contribution number 618, of the Marine Research Division of AZTI-Tecnalia