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This paper revealed a physical connection between the antiphase variation in the preceding autumn Tibetan Plateau (TP) and Lake Baikal snow cover anomalies (TBSA) and the following winter North Atlantic Oscillation (NAO) on interannual time scales during 1979–2021. The antiphase variation in TBSA, accounting for 44% of the total years, has a dipole structure in autumn, which prolonged into the following winter. The persistent antiphase TBSA associated diabatic forcing, disturbances and transient eddies favor a double wave train structure spanning the TP (east of Baikal) and North Atlantic from autumn to winter. Amid the wave train, the circulation anomalies over the North Atlantic extract more energy from the basic flow due to the seasonal increase in the westerly jet, which further evolves into the winter NAO pattern. Our results provide new insights into the formation and projection of winter NAO from the perspective of subtropical and extratropical Eurasia snow. Plain Language Summary: A robust link exists in the preceding autumn antiphase Tibetan Plateau (TP) and Lake Baikal snow cover anomalies (TBSA) and the winter North Atlantic Oscillation (NAO) during 1979–2021. There are 44% years of antiphase variation in TBSA in autumn, which shows a dipole structure with one positive center over the TP and another negative center over the Baikal. Larger (smaller) snow cover over the TP (Baikal) stimulates a local low (high) pressure system via diabatic cooling (heating). Due to the jet waveguide effect, the antiphase TBSA associated diabatic forcing and perturbation along the subtropical westerly jet favor the atmospheric wave train spanning the TP and North Atlantic. The antiphase TBSA associated transient eddies along the extratropical belt contribute to the atmospheric wave train lying between the eastern Baikal and the North Atlantic owing to the eddy‐flow interaction. Along with the seasonal increase in the subtropical westerly jet from autumn to winter, the geopotential height anomalies in the double wave train associated with the antiphase TBSA gradually develop into the winter large‐scale NAO circulation through more energy extraction from the stronger basic flow. Key Points: A robust link of winter North Atlantic Oscillation (NAO) to the preceding fall antiphase Tibetan Plateau‐Baikal snow cover anomalies (TBSA)The antiphase TBSA associated diabatic forcing, disturbances and transient eddies favor a double wave train structure around 30°N and 60°NMore energy extracts over the North Atlantic due to the seasonal increase in the westerly jet, favoring the development of the winter NAO [ABSTRACT FROM AUTHOR]

This paper compares surface signatures of the zonally symmetric and asymmetric modes of stratospheric variability, which describe the strength of the polar vortex and a planetary wave‐1 pattern, respectively. Unlike a weak polar vortex followed by negative Arctic Oscillation–like anomalies, strong stratospheric wave activity features a polar vortex displacement with a deep planetary wave‐1 structure, resulting in positive North Atlantic Oscillation–like North American cooling in about 10 days. Moreover, the linkage between the stratosphere and surface is examined in two reanalyzes and four models of different configurations, which show more robust North American cooling following the displacement of the polar vortex due to strong stratospheric wave activity than the zonally symmetric weakening of the polar vortex. This suggests strong stratospheric wave activity acts as a better predictor for cold spells in the northern U.S. and Canada compared with a weak polar vortex. Plain Language Summary: A weak polar vortex in the winter stratosphere is likely associated with cold spells at the surface, yet there are large uncertainties in predicting surface cold events based on stratospheric signals. This study introduces a new method to separate stratospheric variability into the leading modes of zonally symmetric and asymmetric circulations. The zonally symmetric mode describes the strength of the polar vortex. A weak polar vortex is followed by cooling over northern Eurasia and midlatitude North America. In contrast, the zonally asymmetric mode characterizes a displacement of the polar vortex or a planetary wave‐1 pattern, with the positive phase featuring a high anomaly over North America and a low anomaly over Eurasia. This stratospheric wave pattern extends down to the surface, resulting in North American cooling and Eurasian warming in about 10 days. While both stratospheric modes are associated with surface cooling over North America, the linkage is more robust for the displacement than the zonally symmetric weakening of the polar vortex, based on analyses of several reanalyzes and models. This indicates that strong stratospheric wave activity serves as a better predictor for cold air outbreaks in the northern U.S. and Canada than the commonly used weak polar vortex events. Key Points: Distinct North American cooling signatures follow zonally symmetric and asymmetric modes of the stratosphereStrong stratospheric wave activity precedes positive North Atlantic Oscillation like North American coolingThe linkage between the stratospheric wave activity and the surface is robust in reanalyzes and models [ABSTRACT FROM AUTHOR]

This study investigates how El Niño‐Southern Oscillation (ENSO) modulates winter cold anomalies over central Eurasia (CE) using reanalysis data during 1950–2019. It is found that ENSO can significantly influence winter air temperature over CE mainly through modulating the strength and location of the cyclonic anomaly of Ural blocking (UB) or long‐lived UB events. A strong (weak) cyclonic anomaly of UB on the southeastern (eastern) side of the Ural Mountains tends to occur over midlatitude (high‐latitude) Eurasia during La Niña (El Niño) winters. Such anomalous circulation leads to a strong (weak) cold anomaly over CE, especially over East Asia, due to enhanced (weakened) cold air advection toward the CE during La Niña (El Niño). The UB‐related cyclonic anomaly in the midlatitude (high latitude) side of Eurasia is shown to be related to weakened (enhanced) eastward extension of strong westerly winds over midlatitude Eurasia during La Niña (El Niño) winters. Plain Language Summary: Observations show that in recent decades a strong cold anomaly appears over Eurasia, especially over central Eurasia (CE). This cold anomaly shows notable variations on interannual, decadal and interdecadal timescales. However, what factors lead to its interannual variations is not well understood. Here we show that El Niño‐Southern Oscillation (ENSO) events can influence Eurasian winter air temperature by modulating the strength and location of the cyclonic anomaly of Ural blocking (UB) or the frequency of long‐lived UB events. A La Niña (El Niño) favors a strong (weak) cyclonic anomaly circulation located in the southeastern (eastern) side of the Ural Mountains in the midlatitudes (high latitudes), which leads to a strong (weak) cold anomaly over CE especially in the low latitude Eurasia (i.e., East Asia) through enhanced (weakened) cold air advection. These new results help us understand the physical cause of the interannual variability of the Eurasian cold anomaly modulated by ENSO. Key Points: This paper examines the causal relationship between the Ural blocking (UB) and Eurasian cold anomaly during the La Niña phase in winterEl Niño‐Southern Oscillation plays an important role in the interannual variability of winter cold anomaly over the EurasiaThe UB leads to stronger cold anomaly over the Eurasian during the La Niña than El Niño [ABSTRACT FROM AUTHOR]