Characteristics and mechanisms of summer long-lived heatwaves in Western North America: Perspective from Rossby wave train

Atmospheric heatwave events have substantial socioeconomic impacts, which have been widely studied under global climate change. This study investigates the characteristics and differences between long-lived and short-lived heatwave events (LHWs and SHWs). First, we identify heatwave events over the Western North America (WNA) over 1981–2022 and categorize them based on the 90th percentile of their duration parameter. Then, we reveal that the LHWs exhibit stronger surface warming with a stronger and thicker warm layer. Circulation anomalies show an anomalous ridge above the WNA, which is more persistent with a greater central value of positive geopotential height anomalies for LHWs. Furthermore, we reveal the important role of mid-to-high-latitude teleconnection in maintaining the LHWs. We find that the diabatic heating released by increased precipitation near Japan can excite Rossby wave trains crossing the Pacific Ocean, and then reach North America, which contributes to maintaining the anomalous ridge of LHWs. Moreover, positive diabatic heating anomalies, related to land-atmosphere interaction, in Central Siberia are also favorable for the generation or persistence of the anomalous ridge and thus the LHWs. Finally, we validate the above teleconnection mechanisms by using the linear baroclinic model and Community Atmosphere Model 5.0 model. By comparison, there is negligible cross-Pacific propagation of Rossby wave energy before the peak of SHWs. This study presents evidence of climate linkages of East Asia and Central Siberia with WNA, which may provide potential predictability for LHWs over the WNA.