Effect of increased ocean resolution on model errors in El Ni?o-Southern Oscillation and its teleconnections

Despite the complexity of the underlying processes, coupled climate models simulate fairly realistic El Nino-Southern Oscillation dynamics and teleconnections. However, there are many long-standing errors that remain. We use the High Resolution Model Intercomparison Project suite of models to assess how El Nino-Southern Oscillation and its late-winter teleconnection to the North Pacific changes when ocean resolution is quadrupled from 1 degrees to 0.25 degrees. We find that increased resolution eliminates large errors in the western extent of El Nino and La Nina sea-surface temperature anomalies, and that there is some improvement in the asymmetry between El Nino and La Nina. In low-resolution models, the teleconnections from El Nino and La Nina 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 Nino, but there is less improvement during La Nina. We find no significant improvements in teleconnection strength for either phase. Tropical mean-state sea-surface temperatures are found to be too cold by around 1 degrees 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 Nina teleconnection. Pacific sea-surface temperature anomalies during El Nino and La Nina in observations and models. A long-standing bias in the westward extent of these anomalies is present in low-resolution ocean High Resolution Model Intercomparison Project models, but it is eliminated in high-resolution ocean models. This is shown to have an impact on simulated teleconnections to the North Pacific. image