Abstract
Atmospheric rivers cause extreme precipitation and sustain water resources in the western United States. Their occurrence has often been attributed to extratropical cyclones. Here, we apply a recently proposed multiscale index to atmospheric rivers identified from reanalysis data and show that their landfalls in this region are not merely synoptic-scale phenomena but are also driven by large-scale circulation independent of extratropical cyclones. Specifically, quasi-stationary waves with centers of action along the Eurasian and North American coasts form a circum-North Pacific pattern. This large-scale teleconnection pattern channels subtropical moisture toward the U.S. West Coast on intraseasonal timescales, enabling its constructive interference with extratropical cyclone-induced moisture transport. The resulting “intermediate” atmospheric rivers account for up to twice as much winter precipitation as purely synoptic atmospheric rivers and exhibit a stronger correspondence with high-category events. Recognizing this multiscale process will be critical for the improved understanding of their predictability, variability and projected changes.
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Data availability
The ERA5 data are accessible at https://cds.climate.copernicus.eu/datasets/reanalysis-era5-pressure-levels?tab=overview. The CPC precipitation data can be downloaded from https://psl.noaa.gov/data/gridded/data.cpc.globalprecip.html. The Niño 3.4 index can be accessed at https://psl.noaa.gov/data/timeseries/month/DS/Nino34/. The authors-produced AR catalogs, labeled with MI, are available upon request from CP (parkcha@bc.edu, cpark15@alaska.edu). The ARTMIP AR catalogs are available from the Climate Data Gateway of the ARTMIP. The data used for producing figures are available at Zenodo (https://zenodo.org/records/18349404).
Code availability
All the codes used to produce the results of the present study are available upon request from CP (parkcha@bc.edu, cpark15@alaska.edu).
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Acknowledgements
This study was funded by the U.S. NOAA through Grant NA23OAR4310132. Chanil Park was also supported by Basic Science Research Program through the NRF of Korea funded by the Ministry of Education (RS-2024-00406720).
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C.P. conceptualized the study and performed the initial analysis. The manuscript was written by C.P. and revised by Y.M. Both authors contributed to the interpretation and discussion of the results.
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Communications Earth and Environment thanks Tim Higgins and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary Handling Editors: Min-Hui Lo and Alice Drinkwater. [A peer review file is available].
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Park, C., Ming, Y. Large-scale circulation drives atmospheric river landfall in the western United States. Commun Earth Environ (2026). https://doi.org/10.1038/s43247-026-03281-w
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DOI: https://doi.org/10.1038/s43247-026-03281-w
