Changes in the North Pacific Jet Stream in Recent Decades

Changes in the path and intensity of jet streams have major impacts on regional weather and climate patterns. We investigated changes in the intensity, meridional position, and altitude of the North Pacific jet in different seasons during the period 1979–2020 using the European Centre for Medium-Range Weather Forecasts (ECMWF) fifth-generation reanalysis (ERA5) dataset. Our analysis indicates that the intensity and the meridional position of the North Pacific jet exhibit a pronounced seasonal cycle, with the most intense core of the jet in winter and its equatorward shift from 32.75 ∘ N in winter to around 40.75 ∘ N in summer. The jet also has a relatively large latitudinal spread in spring compared to the other seasons. The North Pacific jet has only weakened over the Yellow Sea in summer during the period 1979–2020. Maximum upper-tropospheric wind speeds have intensified over the Sea of Japan in winter in response to the poleward shift of the jet but weakened in spring due to the equatorward shift of the jet. Indeed, the jet has shifted poleward over the far western (125–140 ∘ E) and central (180 ∘ -150 ∘ W) North Pacific in winter, but the poleward shift of the jet is smaller over the far western North Pacific where the jet is stronger. This suggests that there might be a link between the speed of the North Pacific jet and the magnitude of its longitudinal poleward shifting variability. The jet has also shifted poleward over the central-eastern North Pacific (135–155 ∘ W) in summer, while changes in the altitude of the North Pacific jet have been insignificant during the period 1979–2020. The identified changes in the characteristics of the North Pacific jet have important implications for the understanding of weather patterns and the frequency of extreme events in the North Pacific and nearby regions.