Tropical and Subtropical Pacific Sources of the Asymmetric El Nino-La Nina Decay and Their Future Changes

El Ninos (EN) are known to decay more rapidly, while La Ninas (LN) tend to decay more slowly. Observational analyses and coupled model experiments are conducted to show that sea surface temperature (SST) anomalies over the subtropical northeastern Pacific (SNEP) and equatorial western Pacific (EWP) are key factors to determine the decay pace of the EN and LN and their asymmetry. In the present climate the LN produces larger cold SST anomalies over the regions than the warm SST anomalies produced by the EN. The magnitude difference over the SNEP and EWP helps to slow down the LN decay via subtropical footprinting and tropical thermocline variation mechanisms, respectively. Coupled Model Intercomparison Project Phase 6 models project the magnitude differences of SNEP SST anomalies between EN and LN to reduce in the future warming world, causing the asymmetric EN-LN decay to weaken.