Cause of biases in Ola’s La Niña simulation and the role of missing ocean currents

Ascertain the causal origin of the biases observed in the Ola model’s La Niña simulation, including its weakened amplitude and central-Pacific displacement at a six-month lead time, and evaluate whether the exclusion of ocean current variables from the SFNO-based ocean state vector is responsible for these biases.

Background

In the July 2020 case paper, the Ola model predicted a weaker La Niña than observed and placed the strongest anomaly more toward the central Pacific. The authors explicitly state uncertainty about the cause of these biases and suggest that the lack of explicit ocean currents in the data-driven ocean component could be a contributing factor, noting that currents are critical for ENSO development.