1 Introduction

In the global climate system the atmosphere has an important role in connecting climates of different regions, a phenomenon called atmospheric teleconnection, in response to a range of surface boundary conditions. Thus, in investigations of intraseasonal to seasonal climate links between the Arctic and the midlatitudes, it is essential to ask if and how an observed Arctic sea ice loss, by affecting atmospheric circulation aloft, is able to influence weather and climate in remote regions [Deser et al., 2010]. Both observations and numerical simulations have shown that a reduction in the Arctic summer‐to‐fall sea ice extent, particularly over the Barents‐Kara Sea, modulates atmospheric circulation in the subsequent fall‐to‐winter so as to strengthen the Siberia High, which often brings severe winters to eastern Eurasia [Honda et al., 2009; Overland et al., 2011; Hopsch et al., 2012; Orsolini et al., 2012; Mori et al., 2014]. In addition, when the sea ice cover is low, Northern Hemisphere jets tend to meander, and this meandering often brings anomalously cold weather to the midlatitudes, especially in the Euro‐Atlantic sector although there is a debate on this notion especially in terms of the choice of a metric [Francis and Vavrus, 2012; Barnes, 2013; Screen and Simmonds, 2014]. Anomalously, cold winters and meandering jets occur more frequently during the negative phase of the Arctic Oscillation (AO) [Thompson and Wallace, 2001; Barriopedro and Garcia‐Herrera, 2006; Vavrus et al., 2006], which is the predominant variability pattern of the Northern Hemisphere winter climate [Thompson and Wallace, 1998]. Dynamically, the negative AO phase represents the atmospheric state in which a larger air mass resides over the polar region and is associated with weak westerlies, anomalously meandering jets in the upper troposphere, and anomalous surface weather patterns.

Recent observational studies have reported that following a summer with a low Arctic sea ice cover, upward propagation of planetary‐scale waves is enhanced in late fall and early winter, which leads to a weakened stratospheric polar vortex and subsequent surface signals [Jaiser et al., 2012; King et al., 2015]. On the other hand, modeling studies have also provided supporting evidence for this dynamical process in the stratosphere and troposphere as responses to changes in both sea ice [Orsolini et al., 2012; Kim et al., 2014; Nakamura et al., 2015] and snow boundary conditions [Fletcher et al., 2007; Peings et al., 2012]. Other modeling studies have contradicting results on the AO phase as an Arctic sea ice response [Cai et al., 2012].

At present the exact role of the stratospheric processes in the Arctic‐midlatitude climate linkage under the present climatic conditions, especially that associated with an observed rapid sea ice loss, remains unclear. Observationally, it is very difficult to assess the impact of sea ice or snow alone because they might covary [Liu et al., 2012; Wegmann et al., 2015]. Although in principle modeling studies can isolate the impacts of sea ice and snow, few studies to date have used a fully stratosphere‐resolving (i.e., high‐top) model and explicitly examined the role of the stratosphere in the Arctic‐midlatitude climate linkage [e.g., Fletcher et al., 2009]. A recent study based on a high‐top model by Sun et al. [2015] found that reduced sea ice in the Arctic would lead to significant modulation of the AO behavior and consequential impacts on the surface climate through stratospheric wave mean flow interactions. However, their focus was on a projected sea ice response in a centennial time scale, and there has been no modeling study examining impacts of an observed rapid Arctic sea ice loss with an attention on stratospheric processes using a high‐top model. Nor is there a model study directly investigating the role of stratospheric wave mean flow interactions in the context of the sea ice impacts on midlatitudes climate.

Here we show that based on numerical experiments using a high‐top atmospheric general circulation model [Nakamura et al., 2015] that has already shown sea ice impacts on the stratosphere highly consistent with observations, midlatitude surface signals as a response to the Arctic sea ice reduction disappear when artificially suppressing stratospheric wave mean flow interaction. The results confirm the active role of the stratosphere in the Arctic midlatitude climate linkage. Then, from a posteriori analysis we argue that an observed reduction in sea ice alone can sufficiently affect atmospheric circulation to influence surface climate via the stratospheric pathway.