Effects of Equatorial Ocean Current Bias on Simulated El Niño Pattern in CMIP6 Models

• Published in: Geophysical research letters Vol. 50; no. 8
• Main Authors: Lin, Yu‐Shen, Wang, Li‐Chiao, Li, Jui‐Lin F.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28.04.2023; Wiley
• Subjects: Anomalies; Bias; Climate; Climate models; CMIP6; El Nino; El Nino phenomena; El Nino-Southern Oscillation event; El Niño; Equatorial currents; Evolution; Feedback; Interannual variability; Intercomparison; Modelling; ocean current bias; Ocean currents; Oceans; Sea surface; Sea surface temperature; Sea surface temperature anomalies; Simulation; Southern Oscillation; Surface temperature; Temperature anomalies; zonal advection; United States > US; China
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2023GL102890

This study utilized the Coupled Model Intercomparison Project Phase 6 (CMIP6) models to examine the simulations of equatorial ocean currents and explore their substantial influences on the systematic bias of westward‐extended sea surface temperature anomalies (SSTA) pattern during El Niño. The results show that models simulate an excessive westward ocean current field over the equatorial central Pacific in the mean state. It tends to suppress the equatorial eastward ocean current anomalies with their maximum centering over the equatorial western Pacific in the El Niño developing phase. As a consequence, an overestimated zonal advective feedback toward the maritime continent exists, subsequently inducing the biased westward extension of SSTA pattern. Our results show that the mean‐state performance of equatorial ocean currents plays a key role on simulations of El Niño evolution in CMIP6 models. Plain Language Summary El Niño is the warm phase of El Niño–Southern Oscillation, known as a coupled air–sea phenomenon with considerable interannual variability in the tropics. In recent decades, many climate models have been developed to help us better understand the potential dynamics of El Niño. This study emphasizes the role of dynamical processes related to ocean currents in affecting the behavior of El Niño patterns in a series of the latest released CMIP6 climate models. We find that models have a relatively large bias in simulating the equatorial ocean currents in the Pacific. With an extremely strong equatorial zonal current in mean‐state field, the maximum of zonal current anomalies tends to shift toward the equatorial western Pacific and enhances the corresponding oceanic feedback mechanism, which substantially contributes to the overestimated sea surface temperature anomalies during El Niño evolution. Key Points The Coupled Model Intercomparison Project Phase 6 (CMIP6) models simulate an excessive westward ocean current field over the equatorial central Pacific in the mean state Overestimated zonal advective feedback in the warm pool region is the dominant factor for the westward extension of El Niño pattern Mean‐state performance of equatorial ocean current field plays a key role on the simulations of El Niño evolution in CMIP6 models