Changes in Wind Extremes Shaped the Summertime Weakening of the Eurasian Subtropical Westerly Jet

Abstract The Eurasian subtropical westerly jet (ESWJ), a key feature of the upper‐tropospheric circulation, plays a crucial role in regulating regional weather and climate. Observations reveal a significant summertime weakening of the ESWJ in recent decades. However, whether this weakening reflects a uniform shift in the wind‐speed distribution remains unclear. Here, we quantify the contributions of winds with different intensities from an occurrence‐based perspective. Our analysis shows that while both an increased frequency of lower‐tail winds and a reduced frequency of upper‐tail winds contribute to the area‐averaged weakening trend, their spatial manifestations are markedly different, indicating that although the area‐mean trend appears as a uniform shift, the spatial patterns exhibit a heterogeneous structural reorganization. Crucially, the reduction of strong winds (above the 80th percentile) specifically shapes the structural weakening of the jet core, whereas changes in the lower tail exhibit a distinct geographical footprint that diverges from the overall trend. Further insights from moist thermal wind decomposition indicate that anthropogenic aerosols drive the weakening primarily by suppressing the dry thermodynamic component, accounting for ∼76% of the total weakening. In contrast, greenhouse gas forcing triggers a “tug‐of‐war” between dry and moist processes, resulting in comparable contributions from both to the net change. These results highlight that changes in wind extremes exert a controlling influence on the mean jet behavior. Given the substantial impacts of jet‐related regional climate phenomena such as aviation turbulence and weather extremes, our findings underscore the importance of explicitly considering circulation extremes, particularly the upper tail, in future climate risk assessments.