Equatorial Submesoscale Eddies Contribute to the Asymmetry in ENSO Amplitude

Abstract

El Niño/Southern Oscillation (ENSO) exhibits evident amplitude asymmetry with stronger El Niño than La Niña events. Equatorial submesoscale eddies act as an important damper of ENSO via their induced upward heat flux ((Formula presented.)) from the subsurface to the surface ocean. Yet their effect on ENSO amplitude asymmetry remains unexplored. Using a high-resolution global climate simulation, we found that strengthening of (Formula presented.) in the Niño3.4 region during La Niña is more evident than weakening of (Formula presented.) during El Niño, resulting in stronger damping of La Niña than El Niño events. This asymmetric response of (Formula presented.) to ENSO is primarily ascribed to that of the temperature fronts associated with larger-scale processes. Using a recharge oscillator model modified to include the effects of (Formula presented.), we show that the asymmetric damping of ENSO by (Formula presented.) contributes importantly to the ENSO amplitude asymmetry.