Effect of Increased Ocean Resolution on Model Errors in ENSO and Its Teleconnections

Despite the complexity of the underlying processes, coupled climate models simulate fairly realistic El Niño-Southern Oscillation (ENSO) dynamics and teleconnections. However, there are many long-standing errors which remain. We use the HighResMIP suite of models to assess how ENSO and its late-winter teleconnection to the North Pacific changes when ocean resolution is quadrupled from 1° to 0.25°. We find that increased resolution eliminates large errors in the western extent of El Niño and La Niña sea surface temperature (SST) anomalies, and that there is some improvement in the asymmetry between El Niño and La Niña. In low resolution models, the teleconnections from El Niño and La Niña to the North Pacific are both underestimated and are centred too far west. With increased resolution, the position of the teleconnection is highly accurate during El Niño, but there is less improvement during La Niña. We find no significant improvements in teleconnection strength for either phase. Tropical mean state SSTs are found to be too cold by around 1 °C throughout the central/eastern Pacific in low resolution models, but this bias is not present in high resolution models. Despite this, a large discrepancy between observed and modelled mean state tropical rainfall persists in high resolution models, which may limit improvements in the simulation of the La Niña teleconnection.