The Impact of Arctic Amplification on Midlatitude Winter Weather: Assessing the Stratospheric Pathway in a Warming Climate

Abstract The Arctic midlatitude linkage (AML) suggests a connection between Arctic amplification (AA) and cold midlatitude winter weather. This study explores the role of the stratospheric pathway of the AML in a warming climate, assessing its detectability alongside other factors related to climate change. We investigate tropospheric and stratospheric climate change signals using the chemistry–climate model ECHAM/Modular Earth Submodel System (MESSy) Atmospheric Chemistry (EMAC) and three time slice experiments, representing preindustrial (1850), present (2020), and future (2100) climates. Both climate change simulations reveal increasing wave propagation and wave breaking in the stratosphere, accompanied by an increased frequency of sudden stratospheric warmings (SSWs). The intensified wave activity enters the stratosphere, particularly from the North Pacific and the Atlantic–European region. An evaluation of subseasonal wave activity episodes reveals more frequent tropopause-level wave events during winter. Further analysis of tropospheric baroclinicity reveals that AA suppresses baroclinic wave formation by weakening horizontal temperature gradients in the lower troposphere. In contrast, the enhanced wave generation in the midlatitude upper troposphere could be attributed to temperature changes outside the Arctic, specifically, tropical warming and lower-stratospheric cooling. Additionally, a jet stream analysis shows no pronounced weakening or increased waviness in the polar jet. Thus, the hypothesis that weaker temperature gradients slow down jet streams was not supported in our real-world climate scenarios. Finally, the more frequent SSWs in our model reveal no cooling influence on midlatitude winter weather. Instead, AA appears to diminish the downward influence of SSWs, a previously overlooked effect that stands in contrast to the expectations of the AML hypothesis. Significance Statement The discussion continues on how Arctic warming might influence winter weather in midlatitudes through a stratospheric pathway. This study examines whether indicators for this hypothesis appear in climate model simulations of a warmer world. Although Arctic warming is assumed to increase wave activity, our model shows a reduction near the surface. We find enhanced upper-tropospheric wave activity, but this seems driven by temperature variations in other regions, not by Arctic processes. Jet streams exhibit no general weakening, a fact that does not support the simple assumption of extending the thermal wind balance from the surface to the tropopause. Our results also indicate that Arctic warming weakens the influence of stratospheric events on surface weather, leading to milder cold air outbreaks.