Characterizing blocking mobility and its role in Northern Hemisphere cold extremes

Abstract Atmospheric blocking events, commonly studied as quasi-stationary regional phenomena, are often observed with zonal movement influenced by the background flow, retrograding Rossby waves, and sea ice cover. However, the effects of these movements on cold extremes remain understudied. This study classifies the movements of atmospheric blocking into westward-moving, eastward-moving, and quasi-stationary across different regions during winters from 1979/80–2020/21 and investigates their respective impacts on surface air temperature. We found that, in the western North Pacific, westward-moving blocking events exhibited the highest frequency, while other regions showed quasi-stationary blocking occurring most frequently. These results reveal the regional difference in the frequency of blocking movement types, but the blocking persistence showed a common characteristic across all regions, with westward-moving blocking events persisting longer compared to other types. Interestingly, these long-lasting and westward-moving blockings were associated with notable cold temperature anomalies in downstream areas during blocking dissipation phase. This arises from the enhanced advection of high-latitude mean cold temperature by blocking-induced wind anomalies at low levels, despite their relatively low occurrences. These characteristics were successfully reproduced in Community Earth System Model version 1 Large Ensemble (CESM1-LENS) simulations, suggesting that better understanding of blocking mobility can improve our ability to predict extreme cold winters.