Decadal Evolution of Mid-latitude Jet Stream Dynamics: Spatio-temporal Trends and Seasonal Oscillations over North America and the North Pacific Ocean

The response of upper-tropospheric jet streams to warming effects is a pivotal uncertainty in current climate projections. This study provides a rigorous diagnostic analysis of the spatio-temporal variability and seasonal evolution of jet stream characteristics over North America (NA) and the North Pacific Ocean (NPO) during the four-decade period of 1984-2023. Utilizing high-resolution ERA5 and NCEP/NCAR reanalysis datasets, we analyzed the three-dimensional structure of jet cores and their interaction with localized baroclinic environments.

Our diagnostics reveal two distinct centers of action where jet dynamics are significantly perturbed: the North Pacific Ocean (NPO) and the Eastern portion of North America (EPNA). A systematic poleward migration of the jet axes approximately 10 degrees in latitude is identified across all seasons except summer, concurrent with a persistent altitudinal ascent. Seasonal analysis indicates that trajectory instability reaches its maximum during summer in the NPO, whereas the most pronounced variability in EPNA occurs during the autumn months. Notably, our results establish a significant positive trend in zonal wind speeds, ranging from 0.5 to 1.5 m/s per decade, which is closely coupled with enhanced meridional temperature gradients in the mid-to-upper troposphere.

Furthermore, wavelet power spectrum analysis across multiple pressure levels (100-400 hPa) uncovers dominant multi-annual periodicities of 5, 7, and 10 years, suggesting robust modulation by large-scale climatic oscillations. A critical finding is the divergent altitudinal behavior between the two regions: while NPO jet streams exhibit an upward trend with stabilized flow, winter and autumn jet streams over EPNA demonstrate a significant downward intrusion into the lower troposphere. This vertical shift facilitates intensified moisture advection from the Gulf of Mexico, potentially exacerbating the frequency and magnitude of extreme hydrological events, such as atmospheric rivers, in northeastern Canada. These findings underscore the non-uniform regional response of the global circulation to a warming atmosphere and provide a framework for improving regional climate predictability.