Uncovering missing Eurasian blocking events and their robust role in East Asian winter extremes: a region-dependent detection approach

Abstract

Despite the profound influence of Eurasian blocking on the East Asian winter monsoon, its objective detection remains challenging 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 neglects the lower geopotential-height variability over the Eurasian continent, filtering out meteorologically significant events prematurely. Here, we propose the regional hybrid method (RHYB), incorporating anomaly thresholds tailored to local geopotential height variance. RHYB captures “reversal-dominated” systems—clear flow disruption but modest amplitude—previously obscured. These newly identified events robustly drive severe East Asian winter cold surges, showing their prior omission led to significant risk underestimation. These results underscore that RHYB is an essential tool for accurately diagnosing midlatitude extremes and their evolving dynamics in a warming world.