Increased Turbulence in the Eurasian Upper-Level Jet Stream in Winter: Past and Future

Anthropogenic activities have been increasingly strengthening the meridional temperature gradient in the upper atmosphere, which has a profound impact on the wind shear and turbulence in mid-latitudes. Here we examined the trends of the wintertime jet stream and clear-air turbulence at 250 hPa over the Eurasian. The zonal wind speed showed a significantly increasing trend in the region between 40 degrees N and 60 degrees N where the meridional temperature gradient between the equator and the pole were increasing sharply in the past 4 decades (1980-2019). In addition, there existed a clear trend toward stronger vertical shear at 250 hPa in the latitudinal zone between 30 degrees N and 40 degrees N where the zonal wind increased, while a declining trend was shown to the south of 30 degrees N, according to three different reanalysis datasets, including ERA5, JRA55, and NCAR/NCEP, which may be related to the poleward shift of the subtropical jet stream. The turbulence, closely related to the occurrence of vertical wind shear, was found to become stronger in the latitudinal zone between 30 degrees N and 40 degrees N consequently. The projections based on Phase 6 of Coupled Model Intercomparison Project models show that the zonal wind speed in the mid-latitudes will increase significantly for the period 2015-2100, especially between the latitudinal zone between 40 degrees N and 60 degrees N, and the corresponding vertical wind shear in this area tend to dramatically increase. The findings not only help us better understanding of turbulence occurrence in the past 40 years, but also have profound implications for the projection of turbulence occurrence under global warming over mid-latitude regions of North Hemisphere.