A new nudging scheme for the current operational climate prediction system of the National Marine Environmental Forecasting Center of China

A new nudging scheme is proposed for the operational prediction system of the National Marine Environmental Forecasting Center (NMEFC) of China, mainly aimed at improving El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) predictions. Compared with the origin nudging scheme of NMEFC, the new scheme adds a nudge assimilation for wind components, and increases the nudging weight at the subsurface. Increasing the nudging weight at the subsurface directly improved the simulation performance of the ocean component, while assimilating low-level wind components not only affected the atmospheric component but also benefited the oceanic simulation. Hindcast experiments showed that the new scheme remarkably improved both ENSO and IOD prediction skills. The skillful prediction lead time of ENSO was up to 11 months, 1 month longer than a hindcast using the original nudging scheme. Skillful prediction of IOD could be made 4–5 months ahead by the new scheme, with a 0.2 higher correlation at a 3-month lead time. These prediction skills approach the level of some of the best state-of-the-art coupled general circulation models. Improved ENSO and IOD predictions occurred across all seasons, but mainly for target months in the boreal spring for the ENSO and the boreal spring and summer for the IOD.