“Warm Arctic-Cold Siberia” as an Internal Mode Instigated by North Atlantic Warming

Eurasia has experienced more frequent bitter winters over the past two decades, which concurred with a prominent “Warm Arctic-Cold Siberia” (WACS) pattern that is unexpected from global warming. Here we show, by analysis of 117-year observations and climate model's millennial simulations, that the WACS is an internal mode of winter temperature variability, which cannot be excited by greenhouse gases and solar forcing. Observational and simulated results suggest that frequent occurrences of that WACS pattern are instigated by warm phases of Atlantic Multidecadal Oscillation (AMO). North Atlantic warming may activate the WACS by generating a background Atlantic-Eurasian wave train characterized by enhanced Ural Mountain ridge and East Asian trough, which is conducive to recurrent WACS pattern. The wave train-induced the Barents Sea ice melting can act as an amplifier, reinforcing the WACS. Although increased greenhouse gases favor a uniform warming pattern, they may contribute to WACS formation by affecting AMO.