Multi-year persistence of the 2014/15 North Pacific marine heatwave

Between the winters of 2013/14 and 2014/15 during the strong North American drought, the northeast Pacific experienced the largest marine heatwave ever recorded. Here we combine observations with an ensemble of climate model simulations to show that teleconnections between the North Pacific and the weak 2014/2015 El Nino linked the atmospheric forcing patterns of this event. These teleconnection dynamics from the extratropics to the tropics during winter 2013/14, and then back to the extratropics during winter 2014/15, are a key source of multi-year persistence of the North Pacific atmosphere. The corresponding ocean anomalies map onto known patterns of North Pacific decadal variability, specifically the North Pacific Gyre Oscillation (NPGO) in 2014 and the Pacific Decadal Oscillation (PDO) in 2015. A large ensemble of climate model simulations predicts that the winter variance of the NPGO- and PDO-like patterns increases under greenhouse forcing, consistent with other studies suggesting an increase in the atmospheric extremes that lead to drought over North America. In 2014–2015 the northeast Pacific Ocean experienced a strong marine heatwave. This study shows teleconnections to the tropical Pacific and the weak El Nino were key sources in the atmospheric forcing and persistence of the event.