Linking upstream cold, continental air to the intensity of marine cold air outbreaks along the western boundary currents of the North Pacific and North Atlantic: A Lagrangian analysis

Abstract Marine cold air outbreaks (CAOs) occurring at the entrance of the Northern Hemisphere storm tracks induce vigorous air-sea interaction and may alter storm track activity downstream. However, a mechanistic understanding of the processes governing the intensity of marine CAOs is lacking. A reanalysis-based climatology of marine CAOs occurring in the winters of 1979–2023 along the Gulf Stream and the Kuroshio Current highlights that such phenomena involve the advection of dry, cold air from the upstream continents, where surface radiative cooling occurs during the winter months over Canada and Siberia. We refer to these extremely cold regions as boreal cold air reservoirs (BCARs). Leveraging the Lagrangian perspective to diagnose the origins of air involved in CAOs, we identify distinct air streams contributing to CAOs, among which are those originating from BCARs and the dry intrusion (DI). The two air streams modulate the intensity of sensible and latent heat fluxes within the CAOs, respectively. The strongest CAOs feature a large contribution of BCAR trajectories and are preceded by the development of a strong surface anticyclone over the upstream continent 6–8 days prior to the CAOs. Our findings suggest that the interaction of a thermal high with an upper-level ridge is a crucial precursor to the strongest CAOs. Thus, our study offers insights into the adiabatic and non-adiabatic processes governing the intensity of CAOs, which determine the climatological hot spots of global air-sea interaction near the western boundary currents.