A pathway for Northeast Pacific marine heatwaves to influence temperatures in western Europe during early winter

Abstract In recent decades, the northeast Pacific (NEP) has experienced multiple long-lasting and intense marine heatwaves (MHWs), which have significantly impacted both local ecosystems and climate in nearby regions. This study investigates the remote effects of NEP MHWs during early winter on downstream regions, particularly the North Atlantic and western Europe. First, we identify 14 MHWs in the NEP from 1981 to 2023, with peak day (i.e., the day when MHWs reach maximum intensity) occurring between November and December. Our results show that after the peak day, the ocean transfers heat to the atmosphere via surface heat fluxes, accompanied by positive diabatic heating anomalies in the lower troposphere. The diabatic heating anomalies induce a reversal in the low-level atmospheric circulation, transforming from high-pressure anomalies before the peak of the MHWs to large-scale low-pressure anomalies thereafter. Moreover, the low-pressure anomalies are also present in the upper troposphere after the peak. Accordingly, precipitation along the west coast of North America increases, which is associated with the intensification and northeastward extension of atmospheric rivers. Then, atmospheric Rossby waves are stimulated, due to increased precipitation and related circulation anomalies, and travel across the Atlantic to arrive in western Europe. The development of high-pressure anomalies in southern Europe and low-pressure anomalies in the central North Atlantic results in anomalous warm advection, which largely contributes to the warmer-than-normal temperatures in western Europe. Finally, we employ an atmospheric linear baroclinic model and the Community Atmosphere Model version 5.0 to evaluate the aforementioned teleconnection mechanisms. Overall, this study provides valuable insights into the linkage between NEP MHWs and temperatures in western Europe, providing an example of the remote climatic impacts that can be modulated by MHWs.