Deciphering the variations and mechanisms of the westerly jets across the Northern Hemisphere during the Last Interglacial based on PMIP4 models.

Understanding the variations of the westerly jets (WJs) during the Last Interglacial (~ 127 ka; LIG) aids in deciphering the reconstructed hydrological conditions and dust activities at that time. Here, we investigated variations of the WJs over the Northern Hemisphere during the LIG based on the Paleoclimate Modelling Intercomparison Project 4. We demonstrated that WJs exhibited divergent responses across regions and seasons during the LIG. In summer, WJs over the African–Asian–Pacific regions moved poleward by ~ 5° and weakened by 19% during the LIG, whereas there was only a slight change (+ 1°/− 2%) over the North American–Atlantic regions. In contrast, the winter WJs over the North American–Atlantic regions shifted poleward by ~ 2° and weakened by 7%, but with no obvious responses (− 0.2°/− 0.8%) over the African–Asian–Pacific regions. The WJs variations were linked to changes in meridional temperature gradients and maximum eddy growth rates. Furthermore, the poleward shift and weakening of the WJs over the East Asian–Pacific regions in summer resulted from the anomalous anticyclone triggered by the deep warm center over East Siberia and the anomalous cyclone linked with diabatic cooling over the western tropical Pacific. For the poleward-displaced and depressed WJs over the North American–Atlantic regions in winter, the propagation of Rossby waves from the eastern Pacific played a more important role, compared with the effect of tropical heating. Our work highlights divergent responses of the WJs to orbital forcing during the LIG, which helps to decipher the reconstructed westerlies-related processes and hence to obtain a better understanding of the climate change during this orbitally induced warm period. [ABSTRACT FROM AUTHOR]