Seasonal and Regional Variations of Long-Term Changes in Upper-Tropospheric Jets from Reanalyses

AbstractLong-term changes in upper tropospheric jet latitude, altitude, and strength are assessed using five modern reanalyses, MERRA and MERRA-2, ERA-Interim, JRA-55, and NCEP-CFSR. Changes are computed from jet locations evaluated daily at each longitude to analyze regional and seasonal variations. The changes in subtropical and polar (eddy-driven) jets are evaluated separately. Good agreement among the reanalyses in many regions and seasons provides confidence in the robustness of the diagnosed trends. Jet shifts show strong regional and seasonal variations, resulting in changes that are not robust in zonal or annual means. Robust changes in the subtropical jet indicate tropical widening over Africa except during northern hemisphere (NH) spring, and tropical narrowing over the eastern Pacific in NH winter. The Southern Hemisphere (SH) polar jet shows a robust poleward shift, while the NH polar jet shifts equatorward in most regions/seasons. Both subtropical and polar jet altitudes typically increase; t...