Coupled air-sea interaction drove and sustained the 2013–2016 North Pacific Marine Heatwave

The 2013–2016 marine heatwave (MHW) in the Northeastern Pacific ranks among the most intense extratropical ocean warming events on record. Its complex evolution has complicated efforts to understand underlying dynamics, which are crucial for predicting future MHWs. Therefore, we track the MHW using a novel Lagrangian heat budget method that allows us to quantify processes driving the MHW evolution. Three dimensional particle trajectories separate the MHW into northern and southern components. The northern half was sustained by weakened Ekman heat transport across the North Pacific Current and reduced wintertime surface heat loss. The southern half was driven by weakened Ekman upwelling caused by reduced alongshore winds over the California Current. A persistent low sea level pressure (SLP) over the central Pacific altered wind patterns, moving heat and moisture poleward, and ultimately caused the MHW. Elevated surface temperature, in turn, boosted the SLP anomaly, completing a positive feedback loop.