Tropical Forcing of Barents‐Kara Sea Ice During Autumn.

The causality of the link between Autumn Barents‐Kara (BK) sea ice and the winter North Atlantic Oscillation (NAO) is uncertain, given teleconnections stemming from the tropics may influence both the extra‐tropics and the Arctic. We explore the relationship between tropical rainfall and BK sea ice in autumn, by nudging the tropics to follow observed variability in otherwise free running ensemble simulations. Tropical forcing alone can skillfully reproduce a significant fraction of observed interannual NAO variability in late autumn. We also show that interannual variability in the NAO is strongly related to simulated BK sea ice. As a result, we are able to reproduce some of the observed link between tropical rainfall and autumn BK sea ice. However, only during the strong 1997 El Niño are clear tropical influences at high latitudes found. Large ensembles and strong tropical forcing are required to detect tropical forced variability in models at high latitudes. Plain Language Summary: Regional variations in Arctic sea ice during autumn have been linked to large scale weather patterns over the Atlantic, which impact on European weather. Commonly, this can be attributed to the North Atlantic Oscillation (NAO). Whether the relationship with sea ice and the NAO is physical, or coincidental, is unclear, given that remote tropical weather can impact on both Arctic sea‐ice and the NAO. In this study, we explore how the tropics could impact sea ice in the Barents‐Kara (BK) seas during autumn, by constructing controlled experiments where we specify the state of the tropical atmosphere. We repeat this many times, to determine how much variability there is in this relationship. We find that there is a link between tropical weather and large‐scale weather patterns in the Atlantic, with a weak link found between tropical weather and BK sea‐ice. However, during years when tropical convection is particularly active in the east Pacific, we can see a much stronger impact on the Arctic during autumn. Our results indicate that the link between the tropics and Arctic may be too weak in models and is only detectable during years where the tropical variability is particularly strong. Key Points: Tropical nudging experiments reproduce some of the observed interannual variability in autumn Barents‐Kara sea iceTropical nudging reproduces a significant fraction of observed autumn North Atlantic Oscillation (NAO) variability, and the anticorrelation of NAO with sea iceOnly during the strong El Niño of 1997 is the model able to reproduce the strong observed teleconnection from the tropics to sea ice [ABSTRACT FROM AUTHOR]