Uncovering Missing Eurasian Blocking Events and Their Robust Role in East Asian Winter Extremes

Despite the profound influence of Eurasian blocking on the East Asian winter monsoon, its objective detection remains a challenge due to a systematic under-detection in standard algorithms. The widely adopted Hybrid method (HYB) applies a hemispheric constant threshold for anomaly detection prior to the flow reversal criterion. This constrained design neglects the lower geopotential height variability characteristic of the Eurasian continent, resulting in the premature filtering of meteorologically significant events. Here, we propose the Regional Hybrid method (RHYB), a refined framework that incorporates anomaly thresholds tailored to local geopotential height variance. By reconciling detection criteria with regional physical characteristics, RHYB explicitly captures "reversal-dominated" systems—events with clear flow disruption but modest amplitude—that were previously obscured. Using ERA5 reanalysis, we demonstrate that these newly identified events are robust drivers of severe wintertime cold surges over East Asia, indicating that their prior omission has led to a significant underestimation of regional climate risks. These results underscore that RHYB is an essential tool for accurately diagnosing midlatitude extremes and their evolving dynamics in a warming world.