Intraseasonal contributions of Arctic sea-ice loss and Pacific decadal oscillation to a century cold event during early 2020/21 winter

An unprecedented cold event occurred in Central and eastern Eurasia during the 2020/21 winter, including five episodes of consecutive cold spells (EP1-5). Through analysis of both observational and simulations, we show that the concurrent Arctic sea-ice loss and extratropical Pacific decadal oscillation (EPDO) warming are potential drivers for the cold event. Their relative contributions to the intraseasonal evolutions of atmospheric circulation and concomitant cold surges are thoroughly investigated. The circulation anomalies highlight the gradual development of the negative Arctic oscillation, accompanied by strengthened Siberian high and deepened Aleutian low. Stratospheric pathways were integrally involved in the dynamical response and the timing of episodes. Our results suggest that the sea-ice, irrespective of seasonality, and autumn EPDO experiments can generally capture the spatial patterns of atmospheric circulation and temperature in observation, albeit weaker in magnitude. Autumn (winter) sea-ice loss led to the EP1-3 (EP2-3) cold spells, and autumn EPDO led to the EP1-3 cold surges; whereas the EP4-5 cold spells induced by autumn SIC and PDO were not statistically robust. The Eurasian cooling response to winter PDO is weak due to the extensive warming over southern China and Eurasian highlatitudes that offsets the midlatitude cooling. The largest coolings were found in SIC and EPDO combined experiments, suggesting their synergic importance in driving such cold events. Our results have implications for the potential predictability of winter extreme events over Eurasia in the context of ongoing sea-ice decline and a recent shift to the positive PDO phase.

Automated summary

An unprecedented cold event occurred in Central and eastern Eurasia during the 2020/21 winter, with potential drivers being the concurrent Arctic sea-ice loss and extratropical Pacific decadal oscillation (EPDO) warming. Simulation experiments suggest that sea-ice and autumn EPDO play important roles in driving cold events, with their combined effects showing the largest cooling response.