The amplified wintertime Arctic warming has accelerated in recent decades. However, whether and how the warming can cause Eurasian cooling remains debated. By identifying daily Arctic warming events, we find direct observational evidence that the Arctic warming tends to cause substantial Eurasian cooling and an increase in occurrence frequency of Eurasian cooling events with a roughly 2-day lag. We propose a mechanism explaining the causality. We find that the Arctic warming causes a large suppression in activities of daily weather disturbances (referred to as synoptic eddies) over high-latitude Eurasia. This produces a meridional dipole in geopotential height anomalies characterized by an equivalent-barotropic anomalous low (high) and a lower-level cooling (warming) over mid-latitude Eurasia (the Arctic) via a nonlinear eddy–to–mean flow feedback. The feedback induces near-surface northeasterly anomalies that enlarge the Eurasian cooling via cold advection. Thus, we conclude that the warm Arctic versus cold Eurasia is essentially an intrinsic dipole determined by synoptic eddy–mean flow interaction.

North Atlantic Oscillation (NAO) has a significant impact on surrounding winter weather and climate. However, the causes of its occasional reversal between early and late winter remain unclear. This study proposes a mechanism for the mid‐winter reversal of NAO from the perspective of local midlatitude air‐sea interaction. Strong sea surface temperature (SST) tripole events, which are defined by empirical orthogonal function of winter‐mean interannual North Atlantic SST anomalies, are primarily induced by NAO in early winter and peak in January. In late winter, the persistent SST tripole exerts active feedback on atmosphere through diabatic heat and transient eddy forcing. The resulting atmospheric circulation anomalies exhibit an almost reversed NAO pattern in February, which forms a wavetrain originating above the Gulf Stream and propagating to the Middle East and weakens the former SST tripole. Consequently, significant reversals of air temperature anomalies occur in Europe and the Caspian Sea area between February and December.

Sea surface temperature anomaly (SSTA) modes are considered as primary sources of climate variabilities on various timescales. The North Pacific Mode (NPM), an El Niño‐Southern Oscillation‐independent, principal interannual SSTA mode in the midlatitude North Pacific during wintertime, can have a significant climate impact over the adjacent areas. However, the air‐sea coupling processes associated with NPM remain unclear, which are identified in this study. The NPM‐related SSTA develops in early winter, matures in midwinter, but decays in late winter, while the associated atmospheric anomalies exhibit a dramatic midwinter reversal. The SSTA development is forced by the atmosphere in early winter and then feedbacks upon the atmosphere through diabatic heating and transient eddy forcing, inducing a midwinter reversal of whole‐layer atmospheric anomalies. Therefore, the NPM is an atmosphere‐forced, air‐sea coupled damping mode through which, however, the ocean provides a memory mechanism responsible for how the preceding atmospheric anomaly can have a cross‐season, subsequent impact.

The stochastic sea surface temperature (SST) anomalies are always present because of the internal oceanic variability due to small‐scale SST variability and based on a set of ensemble experiments forced by Pacific Decadal Oscillation‐related midlatitude North Pacific SST anomalies with and without oceanic stochastic forcing, their influences on atmospheric variability in coarse‐resolution models are investigated in this study. Comparisons of experiment results show that oceanic stochastic forcing can improve the simulated atmospheric response by generating more organized atmospheric transient eddies through the increases of both thermal activity and atmospheric baroclinicity, similar to the high‐resolution observations and simulations. Dynamic diagnostics further reveal the dominant contributions of corresponding transient eddy vorticity forcing to the significantly enhanced westerly wind with equivalent barotropic structure. It suggests that the oceanic stochastic forcing is important and nonnegligible for the understanding and theory of oceanic feedback to the atmosphere in the midlatitudes.

Prior research extensively investigates the delayed influence of El Niño‐Southern Oscillation (ENSO) events on subsequent summer climates, with persistent sea surface temperature anomalies (SSTAs) in remote tropical oceans serving as crucial pathways. This study unveils a previously overlooked midlatitude pathway. During the developing winter, El Niño events induce basin‐scale cold SSTAs in the central North Pacific, which can persist into the following summer. These anomalies significantly influence early‐summer atmospheric circulation by enhancing atmospheric baroclinicity and transient eddy activities. Primarily driven by transient eddy vorticity forcing, an equivalent barotropic geopotential low anomaly emerges over the North Pacific. Enhanced by the southwesterly winds of the atmospheric low, tropical moisture is transported farther northeastward in the early summer, resulting in increased rainfall in the Pacific Northwest region. By elucidating this meridional pathway, our study advances the understanding of ENSO's delayed impacts and associated dynamical processes, in which the midlatitude oceanic feedbacks are emphasized.