Teleconnection Pattern Influence on Sea-Wave Climate in the Bay of Biscay

The potential modification of hydrodynamic factors, such as waves, is a source of concern for many coastal communities because of its potential effect on shoreline evolution. In the northern Atlantic, swell is created by storm winds that cross the Atlantic following west-east tracks. These tracks are shifted more southward or northward depending on the season and on recurring large-scale atmospheric pressure anomalies, also called teleconnection patterns. This study investigates the trends of sea-wave patterns in the Bay of Biscay and relates their interannual variability to teleconnection patterns. Sea-wave parameter time series from the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) show a satisfying correlation with an in situ buoy of Meteo-France during the period they overlap. Using a k-means algorithm, data from this 44-yr-long time series were clustered into a few sea-state modes, each of them corresponding to an observable sea state associated with an averaged value for wave height, period, and direction. This analysis shows that most of the increase in annual mean sea-wave height since the 1970s has occurred because the relative frequency of occurrence of persistent observable sea states is evolving over time: from 1970 to 2001, the data indicate that energetic northwest swell becomes more frequent than low-energy intermediate sea states. Moreover, anomalies of the relative frequency of occurrence of observable sea states are related to large-scale recurring pressure anomalies: principally, the Northern Atlantic Oscillation (NAO) but also (during winters) the east Atlantic (EA) pattern, as well other teleconnection patterns of the Northern Hemisphere (NOAA data).