Subsurface Mixing Promotes Central Pacific–like ENSO in an Intermediate Coupled Model

Abstract El Niño–Southern Oscillation (ENSO) is experiencing changes, including an increasing occurrence of central Pacific (CP)-type ENSO and weakening of intensity, with mechanisms still under debate. Previous studies of subsurface turbulent mixing ( κ υ ) revealed close correlations between its interannual variability ( ) and ENSO evolution and its importance on CP-type ENSO. However, how to adequately represent in climate models and how it modulates ENSO variability remain unclear. Here, a model is first established by the singular value decomposition (SVD) method using outputs from a 40-yr simulation of high vertical resolution. We then incorporate it into an improved intermediate coupled model (ICM) of ENSO simulation and prediction. When is incorporated into the ICM, the standard deviation of the Niño-3.4 index is reduced by ∼0.5°C compared with the original ICM with constant κ υ ; the center of maximum in the interannual sea surface temperature anomaly (SSTA) shifts westward by ∼20° longitude, favoring the emergence of CP-like ENSO. SSTA budget analysis revealed that the advection reduction determines the ENSO amplitude weakening and that vertical diffusion, which is intensified in the CP while suppressed in the eastern Pacific (EP), dominates the westward shift of ENSO pattern. These findings improve our understanding of the impact of on ENSO variability, which may further help improve ENSO simulation by identifying as a potential cause for the long-standing underestimation of CP-like ENSO and overestimation of ENSO amplitude in climate models.