LAUSR

The leading modes of the North Pacific Jet (NPJ) variability include intensity changes and meridional shifts in jet position on the low frequency timescales. These leading modes of NPJ variability are closely associated with weather and climate conditions spanning from Asia to the United States (US). In this study, we investigated changes in the NPJ’s role as a conduit for US surface air temperature (SAT) anomalies during the boreal winter across the late 1990s. We found that the leading mode of NPJ variability changed from the NPJ intensity changes to meridional shifts in NPJ position across the late 1990s. It leads to the change in the role of NPJ as a conduit for US SAT anomalies. Before the late 1990s, the variability of NPJ’s intensity significantly impacted western US SAT anomalies related to the anomalous surface cyclonic circulation over the North Pacific. After the late 1990s, however, the variability of NPJ’s meridional shift significantly influenced on the eastern US SAT anomalies in association with the anomalous surface cyclonic circulation over the northern North Pacific. Further analysis and model experiments revealed that the western to central North Pacific Ocean has been warming since the late 1990s and modulates atmospheric baroclinicity. This phenomenon mainly leads to a northward NPJ shift and implies that the eddy driven mechanism on the NPJ’s formation, which acts to enhance the meridional variability of NPJ position, becomes dominant. We conclude that this northward shift of NPJ could have contributed to enhancing the NPJ’s meridional shift variability, significantly influencing the eastern US SAT anomalies since the late 1990s.