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The latitude of the westerly jet stream is influenced by a variety of climate forcings, but their effects on the jet latitude often manifest as a tug of war between tropical forcing (e.g., tropical upper-tropospheric warming) and polar forcing (e.g., Antarctic stratospheric cooling or Arctic amplification). Here we present a unified forcing-feedback framework relating different climate forcings to their forced jet changes, in which the interactions between the westerly jet and synoptic eddies are synthesized by a zonal advection feedback, analogous to the feedback framework for assessing climate sensitivity. This framework is supported by a prototype feedback analysis in the atmospheric dynamical core of a climate model with diverse thermal and mechanical forcings. Our analysis indicates that the latitude of a westerly jet is most sensitive to the climate change-induced jet speed changes near the tropopause. The equatorward jet shift also displays a larger deviation from linearity than the poleward counterpart.

Plain Language Summary The westerly jet stream is perceived as the bellwether of midlatitude storminess, surface temperature extremes, and precipitation. The effects of different climate forcings, such as greenhouse gas warming and Antarctic ozone hole, on the westerly jet often result in large cancelations. Here we show the competing effects can be quantified by a unified forcing-feedback framework. Our analysis demonstrates the critical role in jet shift of the zonal wind changes near the tropopause, which are associated with changes in the equator-to-pole temperature gradient under climate change. We also found that the equatorward jet shift is larger than the linear feedback prediction, but this nonlinear effect is small for a poleward jet shift.