Since the 1980s, anthropogenic aerosols have been rapidly and concurrently decreasing over Europe (EU) and North America (NA). Yet it remains poorly constrained whether this coordinated mitigation induces consistent regional adjustments in large-scale circulation and, in turn, coherent changes in landfalling atmospheric rivers (ARs) along the west coasts of NA and EU. Here we use CESM2 large ensemble simulations together with a single forcing aerosol experiment to quantify anthropogenic aerosol impacts on winter (November-March) landfalling AR frequency over the west coasts of NA and EU from 1980 to 2014, and to diagnose the associated mechanisms. We find that anthropogenic aerosols significantly reduce winter landfalling AR frequency over both NA and EU, but the contributions strongly depend on circulation patterns and the regional responses are not uniform. Using k-means clustering of the 500-hPa geopotential height field, we identify six large-scale circulation patterns closely associated with landfalling ARs over NA and EU. In both regions, the changes in AR frequency are dominated by two key patterns, but the operative pathways differ. Over NA, anthropogenic aerosols suppress landfalling ARs primarily by reducing the occurrence of a cluster characterized by an intensified Aleutian low and a strengthened zonal jet. The other cluster features a suppressed Aleutian low. In this cluster, anthropogenic aerosols reduce landfalling ARs mainly by decreasing the landfall efficiency, with thermodynamic contributions dominating. In contrast, EU exhibits a pronounced dipole response. Anthropogenic aerosols significantly suppress landfalling ARs under a Scandinavian blocking pattern, while enhancing them under a positive North Atlantic Oscillation pattern and a strong westerly trough pattern, indicating strong regional sensitivity of aerosol-induced North Atlantic circulation reorganization and storm track configurations. These results suggest that, under ongoing climate change, future anthropogenic aerosol emission pathways may not uniformly reshape landfalling AR risks through changes in circulation pattern occurrence and landfall efficiency.

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