Intraseasonal shift in the wintertime North Atlantic jet structure projected by CMIP6 models

The projected changes of the wintertime North Atlantic eddy-driven jet (EDJ) under climate change conditions have been extensively studied in recent years. Although most previous studies agree on a squeezing and elongation of the EDJ over Europe, there are still large uncertainties related to the intensity and latitude. In particular, some studies detect an intensification of the jet core region. However, there is no consensus as some studies find it insignificant or do not detect it. Similarly, the EDJ latitude in winter present a strong inter-model spread, spanning from poleward to equatorward responses. Here, we use a novel multiparametric description of the EDJ to scrutinize the EDJ projections of a CMIP6 multi-model ensemble. Further, we analyze separately these projections in early and late winter. Our results show a non-stationary response of the EDJ latitude through the winter, presenting a poleward migration in early winter and equator shift in late winter. This intra-seasonal shift is related to the climate change response of the different drivers. In particular, thermodynamic processes, involving the change in the 200hPa meridional temperature gradient and the North Atlantic sea surface temperature warming hole are found to influence the early winter change of the EDJ latitude. As for late winter, dynamical process related to the stratospheric vortex response to climate change plays a major role on the EDJ projections. Model biases also have an effect in the EDJ latitudinal projections. Relatedly, the well-established future squeezing of the winter EDJ is no longer found, suggesting it is an artefact from mixing intra-seasonal responses.