1. Introduction 2. The model and experimental design 3. Space-time structure of systematic error 4. Space-time structure of forecast error 5. Error growth and predictability (Lorenz curves) 6. Summary and conclusion Predictability of NCEP Coupled Forecast System (CFS)

Fig. 1. Systematic error of ensemble mean forecasts of monthly SST with respect to the lead time over the period From top to bottom, December, March, June, and September forecast cases, respectively.

Fig months averaging systematic error of monthly ensemble mean SST over the period with respect to the lead time.

Fig months averaging systematic error of monthly ensemble mean SST over the period with respect to the 12 calendar months.

Fig. 4. Same as Fig. 1 except root-mean-square error after removing systematic error.

Fig. 5. RMS error of ensemble mean forecasts of the monthly mean NINO3, NINO4, NINO3.4 and NINO1.2 SST over the period , as a function of target month and lead month. Nino3 is defined as the spatial mean SST over 5 o S-5 o N and 170 o W-120 o W, Nino4 over 5 o S-5 o N and 90 o W-150 o W, Nino3.4 over 5 o S-5 o N and 160 o E-150 o W, and Nino1.2 over 10 o S-equator and 80 o W-90 o W, respectively.

Fig. 6. Time series of Nino 3 SST anomalies during with respect to lead time. January, April, July, October SST anomalies, respectively.

Fig months forecast error of Nino3 SST anomalies with initial conditions of all 12 calendar months. Thick solid lines denote ensemble mean and thin dashed lines denote each ensemble member.

Forecast error Each member Lorenz curve Each member Dec IC Jun IC Fig. 8. Forecast error and Lorenz curve of Nino 3.4 and Nino 1.2 SST anomalies over period. Upper panels for December initial condition case and lower for June initial conditions, respectively. Thick black line for ensemble mean forecast error and dashed grey lined for each ensemble member, and thick red line for ensemble mean Lorenz curve and dashed orange lined for ensemble members.

Fig. 9. Forecast error and Lorenz curve of Nino 3.4 and Nino 1.2 SST anomalies following to 3 segments of initial conditions over period for December initial condition. Blue denotes first segment form 9th to 13th of the month, green for second covering 19th to 23th of the month, and red for last set including the second-to-last day of the month, the last day of the month, and 1st, 2nd and 3rd days of the next month. Solid line for forecast error and dashed line for Lorenz curve, respectively.

Fig. 10. Error growth rate. NINO3.4 NINO1.2

Ensemble skill of anomalous monthly NINO indices

Forecast error and Lorenz curves: Dec IC forecast, anomalous SST anomalies