Equatorial Submesoscale Eddies Contribute to the Asymmetry in ENSO Amplitude

Abstract

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 (Qeddy,vsub) 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 Qeddy,vsub in the Niño3.4 region during La Niña is more evident than weakening of Qeddy,vsub during El Niño, resulting in stronger damping of La Niña than El Niño events. This asymmetric response of Qeddy,vsub 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 Qeddy,vsub, we show that the asymmetric damping of ENSO by Qeddy,vsub contributes importantly to the ENSO amplitude asymmetry.

Keywords

• ENSO asymmetry
• submesoscale eddy
• vertical heat flux