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Three-dimensional variability of the winter westerly jet stream in the Northern Hemisphere
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DOI：10.1016/j.accre.2026.06.010.png)
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Abstract
En 中文
As a precursor signal, the westerly jet stream (WJS) plays an important role in abnormal atmospheric circulation. However, its three-dimensional structure and vertical coupling remain poorly characterised, hindering a clear understanding of its climate impacts. Using ERA5 reanalysis data and CMIP6 simulations, we statistically examined the spatiotemporal evolution of the winter WJS during the hindcast (1940–2024) and projection (2025–2100) periods, with statistical diagnostics applied to quantify changes in jet intensity, axis stability, meridional and zonal shifts and vertical structure. The ERA5 reveals that the mean 200 hPa WJS intensity over 15°–45°N increased by 0.59 m/s during winter from 1940 to 2024, accompanied by a 4.4 °C decrease in 200 hPa air temperature over the midlatitudes (45°–60°N). A significant statistical association exists between WJS intensity and the stability of its main axis (r = −0.75, p < 0.05), with stronger (weaker) WJS corresponding to more stable (oscillatory) conditions, highlighting a robust coupling between WJS intensity and axis stability. Meridionally, the main axis of the westerly jet stream (MAWJS) shifts northward by 0.34° in winter from 1940 to 2024. Changes in the MAWJS position are accompanied by variations in the maximum wind speed of the WJS ( = 0.42, p < 0.05), with the WJS intensifying during northward shifts and weakening during southward shifts, indicating coherent meridional coupling. Zonally, the MAWJS shifts eastward by 1.5°. Vertically, on the basis of pronounced features in the meridional–vertical diagnostics of the WJS structure, the Atlantic–northern Africa sector (60°W–30°E, 1000–100 hPa) exhibits a weakening of 0.24 m/s in the WJS during 1940–2024, with the vertical jet axis shifting westward over the Atlantic and eastward over northern Africa. Under the SSP5-8.5 scenario, CMIP6 simulations project sustained increases in mean and maximum 200 hPa WJS intensities (at rates of 0.3 and 0.36 m/s per decade, respectively), accompanied by a continuous northward shift of the MAWJS (0.03 per decade). These results provide a clearer understanding of the long-term structural evolution of the WJS, with implications for improving projections of large-scale circulation and associated climate extremes.
Keywords:
Westerly jet stream
Main axis of the westerly jet stream
Three-dimensional morphology
CMIP6
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