Record-breaking emergence of upstream-downstream zonal-consistent variation in the Eurasian jet axis.

Eurasian weather/climate extremes are often considerably linked to the meandering and/or latitudinal shifts of upper-level westerly jet, but the variation and impact of the upstream-downstream zonal consistency (UDZC) in the Eurasian jet axis are less known. Here we report a record-breaking emergence of an enhanced UDZC during the past two-to-three decades. In particular, the upstream-downstream covariance has increased from <10% to >60%, with the Eurasian upper-tropospheric westerly wind anomalies dominated by the Eurasian jet intensity change mode, which prompts a large-scale interplay between Asian and Pacific subtropical highs and thereby induces mega-shifts in the distribution patterns of circulation and climate anomalies across Eurasia. Such large-range circulation adjustments are also accompanied by a circumglobal Silk Road teleconnection, a Rossby wavetrain with zonal wavenumber 6, which originates from the Northeast Atlantic and connects Asian climate with western Europe and North America heatwave and drought conditions. Climate model simulations suggest that the UDZC would further intensify as the northern mid-latitude warming becomes more pronounced. Our results highlight that the emergence of enhancing UDZC in the Eurasian jet axis is capable of triggering planetary-scale climate extremes even across the whole Northern Hemisphere, imposing more serious climate threats.