Meridional dipole in eddy activity along Peruvian coast during El Niño events

Resumen: Mesoscale oceanic eddies (O(100)km) play a key role in regulating climate by affecting the transport of heat and water mass properties. However, most climate models struggle to simulate these eddies due to coarse horizontal resolution. Using a 120-year ultra-high-resolution simulation with 1/10° horizontal ocean resolution, conducted with the Community Earth System Model (UHR-CESM), this study examines how eddy activity off Peru changes during strong eastern Pacific El Niño events. The model shows a meridional dipole in eddy activity during El Niño, with increased (decreased) energy north (south) of ~14°S, matching satellite data except for the extreme 1997/98 El Niño. This pattern is caused by baroclinic instabilities linked to El Niño-driven changes in the equatorial undercurrent. The study also finds a nonlinear relationship between the strength of the dipole pattern and El Niño-related equatorial influences, providing new insights into the dynamics of the El Niño-Southern Oscillation.