Interannual variability of ocean surface waves in the Southeast Pacific

Ocean surface (wind-driven) waves continuously shape the coastal environment and play a relevant role in ocean-atmosphere interaction processes. They are also important in operational aspects of ports and have significant energy potential. This research is focused on the interannual variability of the wind waves in the Southeast Pacific, particularly its relationship with the Southern Annular Mode (SAM) and El Niño Southern Oscillation (ENSO). We used a 38-year wave simulation (1979-2016) performed using the Wavewatch III model forced with surface winds and ice concentration from the ERA-Interim reanalysis. Additionally, a cyclone tracking software was used to analyze the trajectories of the extratropical storms which generate the wind waves that reach the coast of western South America. Time series statistics, such as correlation and composites analysis, have been applied to both wave parameters (such as significant wave height and mean period) and directional spectra. Results show a significant and positive correlation between the SAM and the significant wave height and the mean period of the wind waves. However, local storms in central Chile, which are the most damaging extreme wave events for coastal infrastructure, are less frequent during the positive phase of the SAM. Furthermore, a trend analysis shows an increase of the significant wave height during the last decades, which is consistent with the trend toward the positive phase experienced by the SAM. On the other hand, the wave energy of remote origin that travels from the North Pacific toward the Southeast Pacific, which is maximum during the austral summer, shows a significant relationship with the extreme El Niño events. These energetic swells events that reach the coast of western South America during the austral summer are more intense and frequent during the warm phase of ENSO.