Atmospheric and Climate Drivers of Extreme Swells Along the Peruvian Coast

Extreme swell events along the Peruvian coast pose recurrent risks to coastal communities, infrastructure, and maritime activities. These events originate far offshore, with their sources varying seasonally: during the austral winter they primarily develop in the South Pacific, while in summer they are typically generated in the western North Pacific. This study investigates the atmospheric circulation patterns associated with extreme wave events along the Peruvian coast generated in both hemispheres, with particular emphasis on the characteristics of the upper-level jet. Furthermore, the potential influence of climate change on the intensity of these events is assessed using an analogue-based methodology.

Events classified by the Peruvian Directorate of Hydrography and Navigation as very strong were selected for those originating in the Southern Hemisphere (SH), whereas strong events were selected for those originating in the Northern Hemisphere (NH). This difference is because events originating further away experience greater dissipation and therefore tend to be weaker. Using ERA5 reanalysis data, a composite analysis of atmospheric circulation revealed characteristic patterns in each hemisphere. SH events were associated with a dipolar cyclonic–anticyclonic pattern, producing strong pressure gradients, intense southwesterly surface winds, and an almost barotropic vertical structure. In contrast, events originating in the western North Pacific were linked to a deep cyclonic system, also exhibiting a barotropic structure. Complementing these results, analysis of the upper-level jet across multiple parameters indicates a more intense and latitudinally confined jet, generally exhibiting a positive tilt in both hemispheres. However, a key hemispheric difference emerges: in the SH, these features correspond to the polar front jet, whereas in the NH they reflect a strengthening of the subtropical jet.

Finally, to assess the anthropogenic influence on 10-m wind intensity between past and present periods, a flow-analogue approach was applied. In the SH, atmospheric circulation similar to those observed during the events is associated with stronger winds in the recent period. This intensification appears to be partly driven by the positive trend in the Southern Annular Mode, linked to anthropogenic ozone depletion and greenhouse gas forcing. In contrast, for events originating in the NH, the anthropogenic signal is less evident due to the pronounced interannual and interdecadal variability of the North Pacific, resulting in analogue-based reconstructions that show wind intensification in some events and weakening in others. Overall, these results highlight the distinct atmospheric dynamics governing swell generation in each hemisphere and provide insights that may inform early-warning systems, coastal risk assessments, and long-term adaptation strategies for Peru.

Acknowledgments: This work was supported by the SAFETE project, which has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No 847635 (UNA4CAREER).