Datensatz

Zusammenfassung

Eurasia and North America experienced a robust subseasonal swing of surface air temperature(SAT) extremes in 2020/21 winter, featuring severe cold (warm) extremes over Eurasia before(after) 15 January and conversely over North America. This sharp subseasonal swing ofintercontinental cold and warm extremes exerted considerable severe impacts on human activitiesand the global economy. Here we examined the initiation and physical process based on dataanalyses. Our results show annual cycle (AC) anomalies of SAT caused this subseasonal alternatingof temperature extremes in two regions. The AC anomalies of SAT are regulated by the phasetransition of the North-Pacific-Oscillation-like (NPO-like) circumglobal Rossby wave (CRW)train. Unprecedented warming sea surface temperature over midlatitude Northwest Atlantic inearly winter initiated a positive phase of the NPO-like CRW train, via eddy-mediated physicalprocesses and the resultant feedback of sea ice loss over the Barents-Kara Seas. While, thesubsequent downward feedback of stratospheric processes resulted in the negative phase of theNPO-like CRW pattern in late winter. This work advances the understanding of the subseasonalpredictability of SAT extremes from impacts of AC anomalies and intercontinental seesawing.