Asymmetric impact of ENSO on the late winter Warm Arctic-Cold Eurasian pattern

The Arctic warming around the Barents and Kara Sea frequently coincides with the Eurasian cooling winters, which is referred to as the warm Arctic-cold Eurasia (WACE) pattern. We here show that the WACE pattern during late winter (January-March) is closely associated with the tropical El Niño-Southern Oscillation but with a striking asymmetric linkage. In general, La Niña events are accompanied with an anomalous high-pressure system over Eurasia, facilitating the formation of the positive WACE pattern. However, a weak connection is detected between the El Niño and WACE pattern. This asymmetric influence of El Niño-Southern Oscillation (ENSO) on Eurasian circulation and surface air temperature can be attributed to the nonlinearity in its modulation on planetary waves and the spatial structure of stratospheric polar vortex during the warm and cold phases. During La Niña winters, the height anomalies over Eurasia tend to prevail in the troposphere due to an enhancement in the wave-1 planetary wave in the middle and low layers, in contrast to El Niño years with height anomalies more confined to the upper stratosphere. The identified linkage between La Niña and the WACE pattern provides a potential predictability source of cold winters over Eurasia on seasonal-to-interannual timescales.