Critical role of extreme midlatitude-storms in Arctic amplification

Abstract

Here we show that Atlantic windstorms of extreme category in northern winter tend to follow a well-defined route toward the Atlantic sector of Arctic, and that heat and moisture transported by these extreme storms significantly warm the Arctic. A positive North Atlantic Oscillation condition and the associated intensified upper-level Atlantic jet provide favorable conditions for those extreme storm developments through enhanced vertical wind shear. These extreme windstorms lead to two discernible impacts on the Arctic: 1) enhanced poleward energy transport by moisture intrusion to the Arctic, which accompanies increased longwave downward radiation and 2) the occurrence of blocking-like patterns after the storm break-up. During these periods, significant Arctic warming was observed of a 10-fold increase versus normal and weak storms. The poleward deflections of extreme storms, and the Arctic warming driven by such storms, are well simulated in numerical experiments with ocean-atmosphere coupled models.