Reduced future North Atlantic eddy-driven jet variability in high-resolution, fully coupled global climate models

Abstract The westerly jet streams are a key component of North Atlantic climate, particularly during winter. Projections of European surface climate change depend largely on models’ ability to capture jet behaviour, which requires sufficient resolution in both the atmosphere and ocean. We evaluated the impact of model resolution on the winter climatological zonal wind and on eddy-driven jet position and speed simulated under historical (1950–2014) and future (2015–2050) climate conditions in an ensemble of fully coupled global climate models, with resolution spanning ~100 to ~25 km in the atmosphere and 1 to 1/12° in the ocean. We find that increasing resolution improves the North Atlantic climatological zonal wind field at mid-to-high latitudes, but biases remain around the low-latitude, equatorward flank of the upper-level subtropical jet. By 2050, low-resolution models simulate a small equatorward shift in the mid-latitude jet, reducing the meridional separation of the subtropical and mid-latitude jets, but high-resolution models project a strengthening of the jets and a small poleward shift of the mid-latitude jet. Analysis of the large-scale meridional temperature gradient over the North Atlantic suggests that tropical amplification influences the future zonal-wind response, and there is some sensitivity of lower-level temperature gradient trends to ocean resolution. At low resolution, the eddy-driven jet shows little mean meridional shift, but increasing resolution reduces the jet’s latitudinal variance. These results help clarify the role of model resolution in near-term North Atlantic climate projections and suggest further increases in atmosphere and ocean resolution may advance understanding of future jet behaviour and its downstream impacts on surface climate over Europe.