Fig. 2: Skilful predictions of the DJF-mean North Atlantic Oscillation (NAO).
From: Skilful global seasonal predictions from a machine learning weather model trained on reanalysis data
a DJF-mean NAO index, standardised to unit variance, from ERA5 (black), GloSea (red) and ACE2 (blue). b ensemble mean RMSE (solid) and spread (dashed) for the NAO (hPa) as a function of lead time during November each year, averaged over all years. c Relationship between NAO correlation score and ensemble size (solid lines) and skill in predicting individual withheld ensemble members (dashed lines) based on 1000 random samples with no replacement. The dashed lines are thickened when significantly below the corresponding solid line (outside 95% sampling range). The horizontal dashed grey line indicates the 95% significance level for a sample size of 23 years.
