Bias correction methods for decadal sea-surface temperature forecasts

Two traditional bias correction techniques: (1) systematic mean correction (SMC) and (2) systematic least-squares correction (SLC) are extended and applied on sea-surface temperature (SST) decadal forecasts in the North Pacific produced by Climate Forecast System version 2 (CFSv2) to reduce large systematic biases. The bias-corrected forecast anomalies exhibit reduced root-mean-square errors and also significantly improve the anomaly correlations with observations. The spatial pattern of the SST anomalies associated with the Pacific area average (PAA) index (spatial average of SST anomalies over 20°–60°N and 120°E–100°W) is improved after employing the bias correction methods, particularly SMC. Reliability diagrams show that the bias-corrected forecasts better reproduce the cold and warm events well beyond the 5-yr lead-times over the 10 forecasted years. The comparison between both correction methods indicates that: (1) prediction skill of SST anomalies associated with the PAA index is improved by SMC with respect to SLC and (2) SMC-derived forecasts have a slightly higher reliability than those corrected by SLC.