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1. The Hydrologic Cycle and Atmospheric Rivers in CESM2 Simulations of the Last Glacial Maximum

   https://doi.org/10.1029/2023GL104805  

   Lora, J. M. ; Skinner, C. B. ; Rush, W. D. ; Baek, S. H. ( September 2023 , Geophysical Research Letters)

   Proxy reconstructions and model simulations of precipitation during Earth's glacial periods suggest that the locations and mechanisms of atmospheric moisture transport have changed considerably during Earth's past. We investigate the hydroclimate of the Last Glacial Maximum (LGM) using simulations with the Community Earth System Model, with a focus on the extratropics and the influence of atmospheric rivers (ARs), a key driver of modern‐day moisture transport globally. Mean and extreme precipitation increase significantly over southwestern Patagonia, Iberia, and southwestern North America—mid‐latitude regions affected by ARs in the modern climate—despite overall decreases elsewhere. In each, the associated moisture transport changes are different, with increased transport and AR activity mainly occurring in the North Atlantic. The overall LGM response is dominated by the response to ice sheets, with other forcings causing additional cooling and drying over the extratropics and a strong decrease of moisture transport over the subpolar North Atlantic.

    

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2. Assessing the climate-scale variability of atmospheric rivers affecting western North America: Atmospheric River Climate-Scale Behavior

   https://doi.org/10.1002/2017GL074175  

   Gershunov, Alexander ; Shulgina, Tamara ; Ralph, F. Martin ; Lavers, David A. ; Rutz, Jonathan J. ( August 2017 , Geophysical Research Letters)
3. Atmospheric Blocking and Other Large‐Scale Precursor Patterns of Landfalling Atmospheric Rivers in the North Pacific: A CESM2 Study

   https://doi.org/10.1029/2019JD030790  

   Benedict, James J. ; Clement, Amy C. ; Medeiros, Brian ( November 2019 , Journal of Geophysical Research: Atmospheres)

   Atmospheric rivers (ARs) manifest as transient filaments of intense water vapor transport that contribute to synoptic‐scale extremes and interannual variability of precipitation. Despite these influences, the synoptic‐ to planetary‐scale processes that lead to ARs remain inadequately understood. In this study, North Pacific ARs within the November–April season are objectively identified in both reanalysis data and the Community Earth System Model Version 2, and atmospheric patterns preceding AR landfalls beyond 1 week in advance are examined. Latitudinal dependence of the AR processes is investigated by sampling events near the Oregon (45°N, 230°E) and southern California (35°N, 230°E) coasts. Oregon ARs exhibit a pronounced anticyclone emerging over Alaska 1–2 weeks before AR landfall that migrates westward into Siberia, dual midlatitude cyclones developing over southeast coastal Asia and the northeast Pacific, and a zonally elongated band of enhanced water vapor transport spanning the entire North Pacific basin that guides anomalous moisture toward the North American west coast. The precursor high‐latitude anticyclone corresponds to a significant increase in atmospheric blocking probability, suppressed synoptic eddy activity, and an equatorward‐shifted storm track. Southern California ARs also exhibit high‐latitude blocking but have an earlier‐developing and more intense northeast Pacific cyclone. Compared to reanalysis, Community Earth System Model Version 2 underestimates Northeast Pacific AR frequencies by 5–20% but generally captures AR precursor patterns well, particularly for Oregon ARs. Collectively, these results indicate that the identified precursor patterns represent physical processes that are central to ARs and are not simply an artifact of statistical analysis.

    

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4. Glacial reduction of the North American Monsoon via surface cooling and atmospheric ventilation: GLACIAL NAM

   https://doi.org/10.1002/2017GL073632  

   Bhattacharya, Tripti ; Tierney, Jessica E. ; DiNezio, Pedro ( May 2017 , Geophysical Research Letters)
5. North Atlantic meltwater during Heinrich Stadial 1 drives wetter climate with more atmospheric rivers in western North America

   https://doi.org/10.1126/sciadv.adj2225  

   Oster, Jessica L. ; Macarewich, Sophia ; Lofverstrom, Marcus ; de Wet, Cameron ; Montañez, Isabel ; Lora, Juan M. ; Skinner, Christopher ; Tabor, Clay ( November 2023 , Science Advances)

   Atmospheric rivers (ARs) bring concentrated rainfall and flooding to the western United States (US) and are hypothesized to have supported sustained hydroclimatic changes in the past. However, their ephemeral nature makes it challenging to document ARs in climate models and estimate their contribution to hydroclimate changes recorded by time-averaged paleoclimate archives. We present new climate model simulations of Heinrich Stadial 1 (HS1; 16,000 years before the present), an interval characterized by widespread wetness in the western US, that demonstrate increased AR frequency and winter precipitation sourced from the southeastern North Pacific. These changes are amplified with freshwater fluxes into the North Atlantic, indicating that North Atlantic cooling associated with weakened Atlantic Meridional Overturning Circulation (AMOC) is a key driver of HS1 climate in this region. As recent observations suggest potential weakening of AMOC, our identified connection between North Atlantic climate and northeast Pacific AR activity has implications for future western US hydroclimate.

    

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