Hemispheric Impact of North Atlantic SSTs in Subseasonal Forecasts

Coupled Earth system models of the type used for weather and climate predictions suffer from sea-surface temperature (SST) biases associated with errors in the location and structure of the Gulf Stream. Here, we show that such SST biases can have a significant impact on initialized forecasts at the subseasonal time range. In the European Center for Medium-Range Weather Forecasts (ECMWF) subseasonal forecast system, correcting these errors with an online SST bias-correction scheme improves the mean state of the North Atlantic region and has a significant positive impact on forecasts of atmospheric circulation anomalies. Improvements to forecast skill extend beyond the North Atlantic into Europe and along the northern hemisphere subtropical waveguide. These impacts provide important evidence for the potential benefits to initialized coupled forecast systems of higher-resolution ocean models that can better resolve the position of the Gulf Stream.

Automated summary

Coupled Earth system models used for weather and climate predictions are impacted by sea-surface temperature biases related to errors in the Gulf Stream. Correcting these biases in subseasonal forecasts can significantly improve forecast accuracy in the North Atlantic region and atmospheric circulation anomalies, extending improvements into Europe and the northern hemisphere subtropical waveguide. This highlights the potential benefits of higher-resolution ocean models in enhancing forecast skill in initialized coupled forecast systems.